JP2008134625A - Semiconductor device, display device and electronic apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress variations of a current value caused by variations in the threshold voltage of a transistor, and to provide a display device with little deviation from luminance specified by a video signal. <P>SOLUTION: The device has a pixel having a transistor which controls a current value to be supplied to a load, a first storage capacitor, a second storage capacitor, and first to fourth switches. After the threshold voltage of the transistor is held in the second storage capacitor, a potential corresponding to the video signal is input to the pixel. Voltage obtained by adding a potential in which the potential corresponding to the video signal and the first storage capacitor are capacitively divided to the threshold voltage in this manner, so that variations of a current value caused by variations in the threshold voltage of the transistor can be suppressed. Thus, a desired current can be supplied to the load such as a light emitting element. Moreover, a display device with little deviation from the luminance specified by the video signal can be provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a semiconductor device provided with a function of controlling a current supplied to a load with a transistor, and includes a pixel formed of a display element whose luminance changes according to a signal, a signal line driving circuit for driving the pixel, and a scanning line driving. The present invention relates to a display device including a circuit. Further, the present invention relates to the driving method. Furthermore, the present invention relates to an electronic device having the display device in a display portion.

  2. Description of the Related Art In recent years, a self-luminous display device using a light emitting element such as an electroluminescence (EL) pixel, that is, a so-called light emitting device has attracted attention. Organic light emitting diodes (OLEDs) and EL elements are attracting attention as light emitting elements used in such self-luminous display devices, and have been used for EL displays and the like. Yes. Since these light emitting elements emit light by themselves, the visibility of pixels is higher than that of a liquid crystal display, and a backlight is unnecessary. In addition, there are advantages such as a high response speed. Note that the luminance of the light emitting element is often controlled by the value of current flowing therethrough.

  In addition, an active matrix display device in which a transistor for controlling light emission of a light emitting element is provided for each pixel is being developed. Active matrix display devices not only enable high-definition display and large-screen display, which are difficult with passive matrix display devices, but also operate with lower power consumption than passive matrix display devices. Yes.

  FIG. 62 shows a pixel configuration of a conventional active matrix display device (Patent Document 1). The pixel shown in FIG. 62 includes a thin film transistor (TFT) 11, a TFT 12, a capacitor element 13, and a light emitting element 14, and is connected to a signal line 15 and a scanning line 16. Note that a power supply potential Vdd is supplied to one of the source electrode or the drain electrode of the TFT 12 and one electrode of the capacitor 13, and a ground potential is supplied to the counter electrode of the light emitting element 14.

  At this time, when amorphous silicon is used for the TFT 12 that controls the current value supplied to the light emitting element, that is, the semiconductor layer of the driving TFT, the threshold voltage (Vth) varies due to deterioration or the like. In this case, even though the same potential is applied to the different pixels from the signal line 15, the current flowing through the light emitting element 14 is different for each pixel, and the displayed luminance is nonuniform among the pixels. Note that even when polysilicon is used for the semiconductor layer of the driving TFT, the characteristics of the transistor deteriorate or vary.

  In order to improve this problem, Patent Document 2 proposes an operation method using the pixel of FIG. The pixel shown in FIG. 63 includes a transistor 21, a driving transistor 22 that controls a current value supplied to the light emitting element 24, a capacitor 23, and a light emitting element 24. The pixel is connected to the signal line 25 and the scanning line 26. ing. Note that the driving transistor 22 is an NMOS transistor, and a ground potential is supplied to either the source electrode or the drain electrode of the driving transistor 22, and Vca is supplied to the counter electrode of the light emitting element 24.

  A timing chart in the operation of this pixel is shown in FIG. In FIG. 64, one frame period is divided into an initialization period 31, a threshold voltage (Vth) writing period 32, a data writing period 33, and a light emitting period 34. Note that one frame period corresponds to a period during which an image for one screen is displayed, and the initialization period, the threshold voltage (Vth) writing period, and the data writing period are collectively referred to as an address period.

  First, in the threshold voltage writing period 32, the threshold voltage of the driving transistor 22 is written into the capacitor. Thereafter, in the data writing period 33, a data voltage (Vdata) indicating the luminance of the pixel is written into the capacitor, and Vdata + Vth is accumulated in the capacitor. In the light emission period, the driving transistor 22 is turned on, and the light emitting element 24 emits light with the luminance specified by the data voltage by changing Vca. By such an operation, variation in luminance due to variation in threshold voltage of the driving transistor is reduced.

  Also in Patent Document 3, the voltage obtained by adding the data potential to the threshold voltage of the driving TFT becomes the gate-source voltage, and the flowing current does not change even when the threshold voltage of the TFT fluctuates. It is disclosed.

As described above, the display device is required to suppress the variation in the current value caused by the variation in the threshold voltage of the driving TFT.
JP-A-8-234683 JP 2004-295131 A JP 2004-280059 A

  In any case, the operation methods described in Patent Documents 2 and 3 perform the above-described initialization, threshold voltage writing, and light emission by changing the potential of Vca to several degrees per frame period. It was. In these pixels, one electrode of the light emitting element to which Vca is supplied, that is, the counter electrode is formed in the entire pixel region. Therefore, in addition to initialization and threshold voltage writing, data writing operation is performed. If even one pixel is present, the light emitting element cannot emit light. Therefore, as shown in FIG. 65, the ratio of the light emission period in one frame period (that is, the duty ratio) becomes small.

  When the duty ratio is low, it is necessary to increase a current value flowing through the light emitting element and the driving transistor, so that a voltage applied to the light emitting element increases and power consumption increases. In addition, since the light emitting element and the driving transistor are likely to be deteriorated, screen burn-in occurs, and more electric power is required to obtain the same luminance as that before deterioration.

  In addition, since the counter electrode is connected to all pixels, the light-emitting element functions as an element having a large capacitance. Therefore, high power consumption is required to change the potential of the counter electrode.

  In view of the above problems, an object of the present invention is to provide a bright display device with low power consumption. It is another object of the present invention to obtain a pixel structure, a semiconductor device, and a display device with little deviation from the luminance specified by the data potential. Note that the present invention is not limited to a display device including a light-emitting element, and an object of the present invention is to suppress variation in current value caused by variation in threshold voltage of a transistor.

  One embodiment of the present invention includes a pixel including a transistor that controls a current value supplied to a load, a first storage capacitor, a second storage capacitor, and first to fourth switches, After the threshold voltage of the transistor is held in the second storage capacitor, a potential corresponding to the video signal is input to the pixel. In this manner, the second holding capacitor holds the voltage obtained by adding the first holding capacitor and the divided potential among the potentials corresponding to the video signal to the threshold voltage. Thus, variation in current value due to variation in threshold voltage of the transistor is suppressed. Therefore, a desired current can be supplied to a load such as a light emitting element. In addition, it is possible to provide a display device with little deviation from the luminance specified by the video signal.

  One embodiment of the present invention includes a transistor, a storage capacitor, a first switch, a second switch, a third switch, and a fourth switch, and one of a source electrode and a drain electrode of the transistor Is electrically connected to the pixel electrode, the other of the source electrode and the drain electrode of the transistor is electrically connected to the first wiring through the second switch, and the other of the source electrode and the drain electrode of the transistor Is electrically connected to the gate electrode of the transistor through the third switch, and the gate electrode of the transistor is electrically connected to the second wiring through the storage capacitor and the fourth switch. The gate electrode of the transistor is a semiconductor device electrically connected to a third wiring through the storage capacitor and the first switch.

  One of the present invention includes a transistor, a first storage capacitor, a second storage capacitor, a first switch, a second switch, a third switch, and a fourth switch, One of the source electrode and the drain electrode of the transistor is electrically connected to the pixel electrode, and one of the source electrode and the drain electrode of the transistor is electrically connected to the gate electrode of the transistor through the second storage capacitor The other of the source electrode and the drain electrode of the transistor is electrically connected to the first wiring via the second switch, and the other of the source electrode and the drain electrode of the transistor is connected to the third switch. Electrically connected to the gate electrode of the transistor, and the gate electrode of the transistor is connected to the first storage capacitor and the fourth switch through the fourth switch. A wiring electrically connected, the gate electrode of the transistor is the third wiring and the semiconductor device are electrically connected via the first storage capacitor and the first switch.

  According to one aspect of the present invention, a transistor, a first storage capacitor, a second storage capacitor, a first switch, a second switch, a third switch, a fourth switch, One of the source electrode and the drain electrode of the transistor is electrically connected to the pixel electrode, and one of the source electrode and the drain electrode of the transistor is connected to the gate of the transistor through the second storage capacitor. Electrically connected to an electrode, one of a source electrode and a drain electrode of the transistor is electrically connected to a fourth wiring through a fifth switch, and the other of the source electrode and the drain electrode of the transistor is connected to the first electrode And the other of the source electrode and the drain electrode of the transistor is connected to the transistor via the third switch. The transistor gate electrode is electrically connected to the second wiring through the first storage capacitor and the fourth switch, and the transistor gate electrode is electrically connected to the gate electrode of the transistor. , A semiconductor device electrically connected to a third wiring through the first storage capacitor and the first switch.

  In the above structure, the second wiring may be the same as the wiring that controls the first switch. Further, the second wiring may be any one of scanning lines for controlling the first switch to the fourth switch in the previous row or the next row.

  One of the present invention includes a transistor, a first storage capacitor, a second storage capacitor, a first switch, a second switch, a third switch, and a fourth switch, One of the source electrode and the drain electrode of the transistor is electrically connected to the pixel electrode, and one of the source electrode and the drain electrode of the transistor is electrically connected to the gate electrode of the transistor through the second storage capacitor The other of the source electrode and the drain electrode of the transistor is electrically connected to the first wiring via the second switch, and the other of the source electrode and the drain electrode of the transistor is connected to the third switch. Electrically connected to the gate electrode of the transistor, and the gate electrode of the transistor is connected to the front via the first storage capacitor and the fourth switch. A first wiring electrically connected, the gate electrode of the transistor is the third wiring and the semiconductor device are electrically connected via the first storage capacitor and the first switch.

  One embodiment of the present invention includes a transistor, a first storage capacitor, a second storage capacitor, a first switch, a second switch, a third switch, and a rectifier element, and the transistor One of the source electrode and the drain electrode is electrically connected to the pixel electrode, and one of the source electrode and the drain electrode of the transistor is electrically connected to the gate electrode of the transistor through the second storage capacitor, The other of the source electrode and the drain electrode of the transistor is electrically connected to the first wiring through the second switch, and the other of the source electrode and the drain electrode of the transistor is connected to the first wiring through the third switch. A gate electrode of the transistor is electrically connected to the second wiring through the first storage capacitor and the rectifier element. Is connected, the gate electrode of the transistor is a semiconductor device which is electrically connected to the third wiring through the first storage capacitor and the first switch.

  One of the present invention includes a transistor, a first storage capacitor, a second storage capacitor, a first switch, a second switch, a third switch, and a fourth switch, One of the source electrode and the drain electrode of the transistor is electrically connected to the pixel electrode, and one of the source electrode and the drain electrode of the transistor is electrically connected to the gate electrode of the transistor through the second storage capacitor The other of the source electrode and the drain electrode of the transistor is electrically connected to the first wiring via the second switch, and the other of the source electrode and the drain electrode of the transistor is connected to the third switch. Electrically connected to the gate electrode of the transistor, and the gate electrode of the transistor is connected to the first storage capacitor and the first switch through the first switch. The fourth switch is electrically connected in parallel with the first storage capacitor, and is electrically connected to the third wiring via the first switch. It is a semiconductor device.

  The transistor may be an N-channel transistor. The semiconductor layer of the transistor may be formed of an amorphous semiconductor film. Furthermore, the semiconductor layer of the transistor may be made of amorphous silicon.

  The semiconductor layer of the transistor may be formed of a crystalline semiconductor film.

  In the above invention, the potential of the first wiring may be higher than a value obtained by adding the threshold voltage of the transistor to the potential of the pixel electrode.

  The transistor may be a P-channel transistor. In that case, in the above invention, the potential of the first wiring may be lower than a value obtained by subtracting the threshold voltage of the transistor from the potential of the pixel electrode.

  According to one embodiment of the present invention, a first storage capacitor, one of a source electrode and a drain electrode is electrically connected to a load, the other of the source electrode and the drain electrode is electrically connected to a first wiring, and a gate electrode Includes a transistor electrically connected to a second wiring through the first storage capacitor, a second storage capacitor that holds a gate-source voltage of the transistor, and a first storage capacitor Means for holding the second voltage in the second storage capacitor, means for discharging the second voltage of the second storage capacitor to the threshold voltage of the transistor, And a means for supplying a current set to the transistor to the load by inputting a potential corresponding to a video signal from a wiring to the first storage capacitor.

  The transistor may be an N-channel transistor. The semiconductor layer of the transistor may be formed of an amorphous semiconductor film. Furthermore, the semiconductor layer of the transistor may be made of amorphous silicon.

  The semiconductor layer of the transistor may be formed of a crystalline semiconductor film.

  The transistor may be a P-channel transistor.

  Another embodiment of the present invention is a display device including the above-described semiconductor device. Further, the electronic apparatus includes the display device.

  Note that a variety of switches can be used as a switch shown in the specification. Examples include electrical switches and mechanical switches. That is, it is only necessary to be able to control the current flow, and is not limited to a specific one. For example, as a switch, a transistor (for example, bipolar transistor, MOS transistor, etc.), a diode (for example, PN diode, PIN diode, Schottky diode, MIM (Metal Insulator Metal) diode, MIS (Metal Insulator Semiconductor) diode, diode-connected Transistor), a thyristor, or the like can be used. It is also possible to use a logic circuit combining these as a switch.

  In the case where a transistor is used as a switch, the transistor operates as a mere switch, and thus the polarity (conductivity type) of the transistor is not particularly limited. However, it is desirable to use a transistor having a polarity with a smaller off-state current. As a transistor with low off-state current, a transistor having an LDD region, a transistor having a multi-gate structure, and the like can be given. In addition, when the transistor operates as a switch with the source electrode potential close to a low potential power source (Vss, GND, 0 V, etc.), the N channel type is used, and conversely, the source electrode potential is a high potential power source. When operating in a state close to (Vdd or the like), it is desirable to use a P-channel transistor. By operating in this way, the absolute value of the gate-source voltage can be increased, so that the operation as a switch becomes easier. In addition, since the source follower operation is rarely performed, it is possible to prevent the output voltage from becoming small.

  Note that a CMOS switch may be used as a switch by using both an N-channel transistor and a P-channel transistor. When a CMOS type switch is used, the output voltage can be easily controlled with respect to various input voltages, so that an appropriate operation can be performed. Furthermore, since the voltage amplitude value of the signal for turning on / off the switch can be reduced, power consumption can be reduced.

  Note that in the case where a transistor is used as the switch, one of the source electrode and the drain electrode functions as an input terminal of the switch, the other of the source electrode and the drain electrode functions as an output terminal, and the gate electrode functions as a terminal that controls conduction of the switch. On the other hand, when a diode is used as the switch, the switch may not have a terminal for controlling conduction. Therefore, when a diode is used as a switch rather than a transistor, a wiring for controlling the terminal is unnecessary, and the number of wirings can be reduced.

  In the present invention, being connected is synonymous with being electrically connected. Therefore, in the configuration disclosed by the present invention, in addition to a predetermined connection relationship, for example, the connection relationship shown in the figure or text, other elements that enable electrical connection therebetween (for example, a switch, a transistor, or a capacitor element) Or an inductor, a resistance element, a diode, or the like) may be disposed. Of course, it may be arranged without interposing other elements in between, and being electrically connected includes the case of being directly connected.

Note that the load is not limited to a light-emitting element typified by an electroluminescent element, and a display medium whose brightness, color tone, polarization, and the like change with the passage of current can be used. In addition, since it is sufficient that a desired current can be supplied to the load, the load includes, for example, an electron-emitting device, a liquid crystal device, electronic ink, an electrophoretic device, a grating light valve (GLV), a plasma display (PDP), and a digital micromirror. A display medium whose contrast is changed by a magnetic action such as a device (DMD) can also be applied. It is also possible to use carbon nanotubes for the electron-emitting device. Note that a display device using an EL element is an EL display, and a display device using an electron-emitting device is a field emission display (FED), an SED type flat display (SED: Surface-conduction Electro-emitter Display), or the like. It is done. A display device using a liquid crystal element includes a liquid crystal display, a transmissive liquid crystal display, a transflective liquid crystal display, and a reflective liquid crystal display, and a display device using electronic ink includes electronic paper.

  Note that a transistor is an element having at least three terminals including a gate electrode, a drain region, and a source region, and has a channel formation region between the drain region and the source region. Here, since the source region and the drain region vary depending on the structure and operating conditions of the transistor, it is difficult to accurately limit the range of the source region or the drain region. Therefore, in describing the connection relationship of the transistors, for the two terminals of the drain region and the source region, one of the electrodes connected to these regions is referred to as a first electrode and the other is referred to as a second electrode. Used for.

  Note that the transistor may be an element having at least three terminals including a base, an emitter, and a collector, and one of the emitter and the collector corresponds to the first electrode and the other corresponds to the second electrode.

  In the present invention, various types of transistors can be applied to the transistor, and the type is not particularly limited. For example, a thin film transistor (TFT) including a non-single-crystal semiconductor film typified by amorphous silicon, polycrystalline silicon, microcrystalline (also referred to as semi-amorphous) silicon, or the like can be used. When using TFT, there are various advantages. For example, since manufacturing can be performed at a lower temperature than that of single crystal silicon, manufacturing cost can be reduced and a manufacturing apparatus can be increased in size. Since the manufacturing apparatus can be increased in size, it can be manufactured on a large substrate, and a large number of display devices can be manufactured at the same time. Therefore, it becomes possible to manufacture at a lower cost. Further, since the manufacturing temperature is low, a substrate with low heat resistance can be used, and a transistor can be manufactured over a light-transmitting substrate such as a glass substrate.

  Note that in the case of manufacturing polycrystalline silicon, the use of a catalyst (such as nickel) can further improve crystallinity and manufacture a transistor with good electrical characteristics. As a result, a gate driver circuit (scanning line driving circuit), a source driver circuit (signal line driving circuit), and a signal processing circuit (signal generation circuit, gamma correction circuit, DA conversion circuit, etc.) can be integrally formed on the substrate. It becomes. It is not always necessary to use a catalyst.

  Even when microcrystalline silicon is used, a part of a gate driver circuit (scanning line driver circuit) or a source driver circuit (such as an analog switch) can be formed over the substrate.

  In addition, a transistor can be formed using a semiconductor substrate, an SOI substrate, or the like. In that case, a MOS transistor, a junction transistor, a bipolar transistor, or the like can be used as the transistor. Accordingly, a transistor with little variation in characteristics, size, shape, and the like and high current supply capability can be manufactured. Thus, low power consumption of the circuit, high integration of the circuit, and the like can be achieved.

  In addition, a transistor having a compound semiconductor or oxide semiconductor such as ZnO, a-InGaZnO, SiGe, GaAs, IZO, ITO, or SnO, or a thin film transistor in which these compound semiconductor or oxide semiconductor is thinned can be used. . Thus, the manufacturing temperature can be lowered, and for example, the transistor can be manufactured at room temperature. As a result, the transistor can be formed directly on a substrate having low heat resistance, such as a plastic substrate or a film substrate. Note that these compound semiconductors or oxide semiconductors can be used not only for a channel portion of a transistor but also for other purposes. For example, these compound semiconductors or oxide semiconductors can be used as resistance elements, pixel electrodes, and transparent electrodes. Further, since these can be formed or formed simultaneously with the transistor, cost can be reduced.

  In addition, a transistor formed using an inkjet method or a printing method can also be used. Thus, it can be manufactured at room temperature, manufactured at a low vacuum, or manufactured on a large substrate. Further, since the transistor can be manufactured without using a mask (reticle), the layout of the transistor can be easily changed. Furthermore, since it is not necessary to use a resist, the number of steps can be reduced, and the manufacturing cost can be reduced. In addition, since the film is formed only on a necessary portion, the material is not wasted compared to a case where etching is performed after the film is formed on the entire surface, and it can be manufactured at a low cost.

  In addition, a transistor including an organic semiconductor or a carbon nanotube can be used. Since such a transistor can be provided over a flexible substrate, it has excellent impact resistance. In addition to these, various other transistors can be used.

  Note that various types of substrates over which transistors are formed can be used and are not limited to specific types. As a substrate on which a transistor is formed, for example, a single crystal substrate, an SOI substrate, a glass substrate, a quartz substrate, a plastic substrate, a paper substrate, a cellophane substrate, a stone substrate, a wood substrate, a cloth substrate (natural fiber (silk, cotton, hemp) ), Synthetic fibers (including nylon, polyurethane, polyester) or recycled fibers (including acetate, cupra, rayon, recycled polyester), rubber substrates, stainless steel substrates, substrates with stainless steel foil, etc. it can. Alternatively, a transistor may be formed over a certain substrate, and then the transistor may be transferred to another substrate, and the transistor may be disposed over another substrate. The substrate to which the transistor is transferred is a single crystal substrate, SOI substrate, glass substrate, quartz substrate, plastic substrate, paper substrate, cellophane substrate, stone substrate, wood substrate, cloth substrate (natural fiber (silk, cotton, hemp) , Using synthetic fibers (nylon, polyurethane, polyester) or recycled fibers (including acetate, cupra, rayon, recycled polyester), leather substrates, rubber substrates, stainless steel substrates, substrates with stainless steel foil, etc. be able to. By using these substrates, formation of transistors with higher characteristics, improvement in heat resistance, and weight reduction can be achieved.

  Note that the structure of the transistor can take a variety of forms and is not limited to a specific structure. For example, a multi-gate structure having two or more gate electrodes may be used. When the multi-gate structure is employed, the channel regions are connected in series, so that a plurality of transistors are connected in series. With such a multi-gate structure, the reliability of the transistor can be further improved by reducing off-state current and improving the withstand voltage of the transistor. In addition, when operating in a saturation region, the multi-gate structure can obtain a voltage-current characteristic with a flat slope because the drain-source current does not change much even if the drain-source voltage changes. By using voltage-current characteristics with a flat slope, an ideal current source circuit and an active load having a very high resistance value can be realized. As a result, a differential circuit or a current mirror circuit with good characteristics can be realized. Alternatively, a structure in which gate electrodes are arranged above and below the channel region may be employed. By disposing the gate electrodes above and below the channel region, the effective channel region increases, so that it is possible to reduce the S value by increasing the amount of current and easily forming a depletion layer. Note that in the case where gate electrodes are provided above and below the channel region, a structure in which a plurality of transistors are connected in parallel is provided.

  Further, a structure in which a gate electrode is disposed over a channel region may be employed, or a structure in which a gate electrode is disposed under a channel region may be employed. Alternatively, a normal stagger structure or a reverse stagger structure may be used. Further, the channel region may be divided into a plurality of regions, or the channel regions may be connected in parallel or in series. Further, a source electrode or a drain electrode may overlap with the channel region (or a part thereof). In this manner, with the structure where the source electrode and the drain electrode overlap with the channel region (or part of it), it is possible to prevent electric charges from being accumulated in part of the channel region and unstable operation. Further, an LDD region may be provided. By providing the LDD region, the reliability of the transistor can be further improved by reducing off-state current and improving the withstand voltage of the transistor. Alternatively, by providing the LDD region, even when the drain-source voltage changes, the drain-source current does not change so much and the voltage-current characteristic with a flat slope can be obtained when operating in the saturation region. .

  Note that as described above, various types of transistors can be used as the transistor in the present invention, and the transistor can be formed over various substrates. Therefore, all of the circuits necessary for realizing a predetermined function may be formed on the same substrate. For example, all the circuits necessary for realizing a predetermined function may be formed over a glass substrate, a plastic substrate, a single crystal substrate, or an SOI substrate. By forming all the circuits necessary for realizing a predetermined function on the same substrate in this way, the cost can be reduced by reducing the number of components and the reliability can be improved by reducing the number of connection points with circuit components. be able to. On the other hand, a part of a circuit necessary for realizing a predetermined function may be formed on one substrate, and another part of a circuit necessary for realizing the predetermined function may be formed on another substrate. That is, it is not necessary to form all the circuits necessary for realizing a predetermined function on the same substrate.

  For example, a part of a circuit necessary for realizing a predetermined function is formed on a glass substrate and another part is formed on a single crystal substrate, and thus an IC chip constituted by transistors on the single crystal substrate. May be connected to the glass substrate by COG (Chip On Glass) and placed on the glass substrate. Alternatively, the IC chip may be connected to the glass substrate using TAB (Tape Automated Bonding) or a printed board. As described above, since a part of the circuit is formed on the same substrate, the cost can be reduced by reducing the number of components and the reliability can be improved by reducing the number of connection points with circuit components. In addition, since a circuit in a portion where the drive voltage is high or a portion where the drive frequency is high consumes a large amount of power, such a portion of the circuit is not formed on the same substrate as other circuits. For example, an IC chip formed on a single crystal substrate By using, increase in power consumption can be prevented.

Note that in this specification, one pixel represents one element whose brightness can be controlled. As an example, one pixel represents one color element, and brightness is expressed by one color element. Therefore, at that time, in the case of a color display device composed of R (red), G (green), and B (blue) color elements, the minimum unit of an image is an R pixel, a G pixel, and a B pixel. It is assumed to be composed of three pixels. Note that the color elements are not limited to three colors, and three or more colors may be used, or colors other than RGB may be used. For example, there are RGBW (W is white) or RGB in which one or more colors such as yellow, cyan, magenta, emerald green, vermilion are added. Further, a color similar to at least one of RGB may be added to RGB. For example, R, G, B1, and B2 may be used. B1 and B2 are both blue, but have slightly different frequencies. Similarly, R1, R2, G, B or R, G1, G2, B may be used. By using such color elements, it is possible to perform display closer to the real thing. Further, by using such color elements, power consumption can be reduced. As another example, when brightness is controlled using a plurality of areas for one color element, one area may be used as one pixel. As an example, there are a case where area gradation is performed or a case where sub-pixels (sub-pixels) are provided. In such a case, there are a plurality of areas for controlling the brightness for one color element, and the gradation is expressed as a whole, but one area for controlling the brightness may be one pixel, In this case, one color element is composed of a plurality of pixels. Further, even when there are a plurality of areas for controlling the brightness in one color element, they may be combined into one pixel. In that case, one color element constitutes one pixel. Further, when brightness is controlled using a plurality of areas for one color element, the size of the area contributing to display may be different depending on pixels. In addition, in a plurality of brightness control areas for one color element, a signal supplied to each may be slightly different to widen the viewing angle. That is, by changing the potentials of the pixel electrodes in a plurality of regions for one color element, the voltage applied to the liquid crystal molecules can be varied, and the viewing angle can be improved.

  Note that in this specification, a semiconductor device refers to a device having a circuit including a semiconductor element (such as a transistor or a diode). In addition, any device that can function by utilizing semiconductor characteristics may be used. The display device is not only a display panel body in which a plurality of pixels including a load and a peripheral drive circuit for driving these pixels are formed on a substrate, but also a flexible printed circuit (FPC) and a printed wiring board (PWB). ) Is also included.

  In addition, in this invention, it is formed on a certain thing, or is formed on the top. It is not limited to being in direct contact. This includes cases where they are not in direct contact, that is, when another object is sandwiched between them. Therefore, for example, when the layer B is formed on the layer A (or on the layer A), the case where the layer B is formed in direct contact with the layer A is different from the case where the layer B is formed on the layer A. And the case where the layer B is formed on the layer (for example, the layer C or the layer D). The same applies to the description of “above”, and it is not limited to being in direct contact with a certain object, and includes a case where another object is sandwiched therebetween. Therefore, for example, when the layer B is formed above the layer A, when the layer B is formed directly on the layer A, another layer (for example, the layer C) is formed on the layer A. And the layer D) are formed, and the layer B is formed thereon. In addition, the case where it is described below or below-includes the case where it is directly in contact and the case where it is not in contact.

  According to the present invention, variation in current value due to variation in threshold voltage of transistors can be suppressed. Therefore, a desired current can be supplied to a load such as a light emitting element. In particular, when a light-emitting element is used as a load, a display device in which luminance variation is small and the ratio of the light-emitting period in one frame period is high can be provided.

  Hereinafter, one embodiment of the present invention will be described. However, the present invention can be implemented in many different modes, and those skilled in the art can easily understand that the modes and details can be variously changed without departing from the spirit and scope of the present invention. Is done. Therefore, the present invention is not construed as being limited to the description of the embodiment. Note that in the structures of the present invention described below, the same reference numerals are used in common in different drawings.

(Embodiment 1)
The basic configuration of the pixel of the present invention will be described with reference to FIG. 1 includes a transistor 110, a first switch 111, a second switch 112, a third switch 113, a fourth switch 114, a first capacitor 115, a second capacitor 116, and a light-emitting element. 117. Note that the pixel is connected to the signal line 118, the first scanning line 119, the second scanning line 120, the third scanning line 121, the power supply line 122, and the potential supply line 123. In this embodiment, the transistor 110 is an N-channel transistor and is turned on when its gate-source voltage (Vgs) exceeds a threshold voltage (Vth). In addition, the pixel electrode of the light emitting element 117 functions as an anode, and the counter electrode 124 functions as a cathode. Note that the gate-source voltage of the transistor is Vgs, the drain-source voltage is Vds, the threshold voltage is Vth, and the voltages accumulated in the first capacitor element 115 and the second capacitor element 116 are Vc1 and Vc2, respectively. The power supply line 122, the potential supply line 123, and the signal line 118 are also referred to as a first wiring, a second wiring, and a third wiring, respectively. In addition, the first scanning line 119, the second scanning line 120, and the third scanning line 121 may be referred to as a fourth wiring, a fifth wiring, and a sixth wiring, respectively.

  The first electrode (one of the source electrode and the drain electrode) of the transistor 110 is connected to the pixel electrode of the light-emitting element 117, and the second electrode (the other of the source electrode and the drain electrode) is connected via the second switch 112. The gate electrode is connected to the power supply line 122 through the third switch 113 and the second switch 112. Note that the third switch 113 is connected between the gate electrode of the transistor 110 and the second switch 112.

  Further, when a connection portion between the gate electrode of the transistor 110 and the third switch 113 is a node 130, the node 130 is connected to the signal line 118 through the first capacitor 115 and the first switch 111. That is, the first electrode of the first capacitor 115 is connected to the signal line 118 through the first switch 111, and the second electrode is connected to the gate electrode of the transistor 110. The first electrode of the first capacitor 115 is also connected to the potential supply line 123 through the fourth switch 114. The node 130 is further connected to the first electrode of the transistor 110 through the second capacitor 116. That is, the first electrode of the second capacitor 116 is connected to the gate electrode of the transistor 110, and the second electrode is connected to the first electrode of the transistor 110. These capacitor elements may be formed by sandwiching an insulating film between wirings, semiconductor layers, and electrodes. In some cases, the second capacitor element 116 is omitted by using the gate capacitor of the transistor 110 as shown in FIG. It is also possible to do. A means for holding these voltages is called a holding capacitor. Further, a connection portion between the node 130 and a wiring connecting the second electrode of the first capacitor 115 and the first electrode of the second capacitor 116 is the node 131, and the first of the transistor 110 is connected. The node 132, the second electrode of the transistor 110, and the second switch are connected to the electrode and the wiring to which the second electrode of the second capacitor 116 and the pixel electrode of the light emitting element 117 are connected. A connection point between the line 112 and the wiring to which the third switch 113 is connected is a node 133.

  Note that by inputting a signal to the first scan line 119, the second scan line 120, and the third scan line 121, the first switch 111, the second switch 112, the third switch 113, and the third scan line 121, respectively. The on / off state of the fourth switch 114 is controlled.

  A signal according to the gradation of a pixel corresponding to a video signal, that is, a potential corresponding to luminance data is input to the signal line 118.

  Next, the operation of the pixel shown in FIG. 1 will be described with reference to the timing chart of FIG. 2 and FIG. In FIG. 2, one frame period corresponding to a period for displaying an image for one screen is divided into an initialization period, a threshold voltage writing period, a data writing period, and a light emission period. The initialization period, threshold voltage writing period, and data writing period are collectively referred to as an address period. There is no particular limitation on the period of one frame, but it is preferable to set it to at least 1/60 second or less so that a person viewing the image does not feel flicker.

Note that a potential V1 (V1: any number) is input to the counter electrode 124 of the light-emitting element 117. Further, if at least a potential difference necessary for the light emitting element 117 to emit light is V _EL , a potential of V1 + V _EL + Vth + α (α: an arbitrary positive number) is input to the power supply line 122. That is, the power supply line 122 may have a potential equal to or higher than V1 + V _EL + Vth + α. The potential of the potential supply line 123 is not particularly limited, but is preferably within the range of the potential input to the panel in which the pixels are formed. This eliminates the need for a separate power source. Note that here, the potential of the potential supply line 123 is V2.

First, as shown in FIGS. 2A and 3A, in the initialization period, the first switch 111 is turned off, and the second switch 112, the third switch 113, and the fourth switch 114 are turned on. And At this time, the transistor 110 is in a conductive state, V1 + V _EL + Vth + α−V2 is held in the first capacitor 115, and Vth + α is held in the second capacitor 116. Note that in the initialization period, the first capacitor 115 may hold a predetermined voltage, and the second capacitor 116 may hold at least a voltage higher than Vth.

  In the threshold voltage writing period shown in FIGS. 2B and 3B, the second switch 112 is turned off. Therefore, the potential of the first electrode or the source electrode of the transistor 110 gradually increases, and the transistor 110 is turned off when the gate-source voltage Vgs of the transistor 110 reaches the threshold voltage (Vth). Therefore, the voltage Vc2 held in the second capacitor element 116 is approximately Vth.

In the subsequent data writing period shown in FIGS. 2C and 3C, after the third switch 113 and the fourth switch 114 are turned off, the first switch 111 is turned on and the signal line 118 is turned on. A potential (V2 + Vdata) corresponding to the luminance data is input. At this time, the voltage Vc2 held in the second capacitor 116 is C3> when the capacitances of the first capacitor 115, the second capacitor 116, and the light emitting element 117 are C1, C2, and C3, respectively. > From C1 and C2, it can be expressed as in formula (1).

  Note that C1 and C2 are necessary when determining the potential supplied from the signal line 118, but their relationship is not particularly limited. Note that in the case of C1> C2, the power consumption can be reduced because the amplitude of Vdata accompanying the change in luminance can be reduced. On the other hand, when C2> C1, it is possible to suppress changes in Vc2 due to on / off of surrounding switches and off-current. From these contradictory effects, it is preferable that C1 and C2 are equal, and the first capacitor element 115 and the second capacitor element 116 have the same size.

  Note that if the light emitting element 117 does not emit light in the next light emission period, a potential of Vdata ≦ 0 may be input.

  Next, in the light emission period illustrated in FIGS. 2D and 3D, after the first switch 111 is turned off, the second switch 112 is turned on. At this time, the gate-source voltage of the transistor 110 is Vgs = Vth + Vdata × (C1 / (C1 + C2)), a current corresponding to the luminance data flows to the transistor 110 and the light-emitting element 117, and the light-emitting element 117 emits light. Of course, the potential corresponding to the luminance data input from the signal line 118 is determined in consideration of the fact that the gate-source voltage of the transistor 110 is Vgs = Vth + Vdata × (C1 / (C1 + C2)).

Note that the current I flowing through the light-emitting element 117 is expressed by Expression (2) when the transistor 110 is operated in the saturation region.

Further, when the transistor 110 is operated in a linear region, the current I flowing through the light emitting element 117 is expressed by Expression (3).

  Here, W is the channel width of the transistor 110, L is the channel length, μ is the mobility, and Cox is the storage capacitance.

  From equations (2) and (3), the current flowing through the light-emitting element 117 does not depend on the threshold voltage (Vth) of the transistor 110 when the operation region of the transistor 110 is either the saturation region or the linear region. . Accordingly, variation in current value due to variation in threshold voltage of the transistor 110 can be suppressed, and current corresponding to luminance data can be supplied to the light-emitting element 117.

  From the above, variation in luminance due to variation in threshold voltage of the transistor 110 can be suppressed. In addition, since the counter electrode is operated at a constant potential, power consumption can be reduced.

Further, when the transistor 110 is operated in a saturation region, luminance variation due to deterioration of the light-emitting element 117 can be suppressed. Note that the deterioration of the light emitting element is not limited to the case where the current-voltage characteristics are shifted in parallel as compared to before the deterioration. For example, when the slope or characteristic of a characteristic is represented by a curve, the differential value is different from that before deterioration. When the light-emitting element 117 is deteriorated, V _{EL of the} light-emitting element 117 is increased, and the potential of the first electrode of the transistor 110, that is, the source electrode is increased. At this time, the source electrode of the transistor 110 is connected to the second electrode of the second capacitor 116, the gate electrode of the transistor 110 is connected to the first electrode of the second capacitor 116, and the gate electrode side is It is floating. Therefore, as the source potential increases, the gate potential of the transistor 110 also increases by the same potential. Therefore, since Vgs of the transistor 110 does not change, even if the light emitting element is deteriorated, the current flowing through the transistor 110 and the light emitting element 117 is not affected. Note that also in Equation (2), the current I flowing through the light-emitting element does not depend on the source potential or the drain potential.

  Thus, when the transistor 110 is operated in the saturation region, variation in threshold voltage of the transistor 110 and variation in current flowing in the transistor 110 due to deterioration of the light-emitting element 117 can be suppressed.

  Note that when the transistor 110 is operated in the saturation region, as the channel length L is shorter, a large amount of current tends to flow when the drain voltage is significantly increased by a breakdown phenomenon.

  When the drain voltage is increased above the pinch-off voltage, the pinch-off point moves to the source side, and the effective channel length that functions as a substantial channel decreases. As a result, the current value increases. This phenomenon is called channel length modulation. Note that the pinch-off point is a boundary where the channel disappears and the channel thickness becomes 0 under the gate, and the pinch-off voltage indicates a voltage when the pinch-off point becomes the drain end. This phenomenon is more likely to occur as the channel length L is shorter. For example, a model diagram of voltage-current characteristics by channel length modulation is shown in FIG. In FIG. 4, the channel length L of the transistor is (a)> (b)> (c).

  From the above, when the transistor 110 is operated in the saturation region, the current I with respect to the drain-source voltage Vds is preferably closer to a constant value. Therefore, the channel length L of the transistor 110 is preferably longer. For example, the channel length L of the transistor is preferably larger than the channel width W. The channel length L is preferably 10 μm or more and 50 μm or less, more preferably 15 μm or more and 40 μm or less. However, the channel length L and the channel width W are not limited to this.

  As described above, since variation in current value due to variation in threshold voltage of a transistor can be suppressed, the supply destination of current controlled by the transistor is not particularly limited in the present invention. Therefore, as the light-emitting element 117 illustrated in FIG. 1, an EL element (an organic EL element, an inorganic EL element, or an EL element including an organic substance and an inorganic substance) can be typically used. Further, instead of the light-emitting element 117, an electron-emitting element, a liquid crystal element, electronic ink, or the like can be used. FIG. 5 illustrates an example in which the EL element 517 is used as the light-emitting element 117. FIG. 5 shows a state in which current flows from the pixel electrode 511 to the counter electrode 124.

  In addition, the transistor 110 only needs to have a function of controlling current supplied to the light-emitting element 117; therefore, there are no particular limitations on the type of transistor, and a variety of transistors can be used. For example, a thin film transistor (TFT) using a crystalline semiconductor film, a thin film transistor using a non-single crystal semiconductor film typified by amorphous silicon or polycrystalline silicon, a transistor formed using a semiconductor substrate or an SOI substrate, MOS A transistor using a type transistor, a junction type transistor, a bipolar transistor, a transistor using a compound semiconductor such as ZnO or a-InGaZnO, a transistor using an organic semiconductor or a carbon nanotube, or another transistor can be applied to the transistor 110.

  The first switch 111 selects a potential corresponding to luminance data, that is, a timing at which a video signal is input to the pixel from the signal line 118, and mainly the voltage held in the first capacitor 115 and the second capacitor The voltage held at 116, that is, the gate-source voltage of the transistor 110 is changed. The second switch 112 selects the timing for supplying a predetermined potential to the second electrode of the transistor 110. Note that in some cases, the predetermined potential is also supplied to the second electrode of the first capacitor 115 and the first electrode of the second capacitor 116. The third switch 113 controls the connection between the gate electrode and the second electrode of the transistor 110, and the fourth switch 114 holds a predetermined voltage in the first capacitor 115 every frame period. The timing at which the first capacitor element 115 is selected and whether or not a predetermined potential is supplied to the first electrode of the first capacitor 115 is controlled. Therefore, the first switch 111, the second switch 112, the third switch 113, and the fourth switch 114 are not particularly limited as long as they have the above functions. For example, a transistor or a diode may be used, or a logic circuit combining them may be used. Note that the first switch 111, the second switch 112, and the fourth switch 114 are not particularly required as long as a signal or a potential can be supplied to the pixel at the above timing. The third switch 113 is not particularly required as long as the above function can be realized.

For example, a predetermined voltage can be held in the first capacitor 115 in the initialization period and the threshold voltage writing period, and a signal in accordance with the gradation of the pixel can be input to the pixel in the data writing period. If possible, the first switch 111 and the fourth switch 114 are not necessarily provided in the pixel. Further, as long as V1 + V _EL + Vth + α (α> 0) can be supplied to the pixel in the initial period and the light emission period, the second switch 112 is not necessarily provided as illustrated in FIG. The pixel illustrated in FIG. 43 includes a transistor 110, a first capacitor 115, a third switch 113, and a pixel electrode 4300. A first electrode (one of a source electrode and a drain electrode) of the transistor 110 is connected to the pixel electrode 4300, and a gate electrode is connected to the second electrode of the transistor 110 through the third switch 113. The gate electrode of the transistor 110 is also connected to the second electrode of the first capacitor 115. Note that the first electrode of the first capacitor 115 has a signal in accordance with the gradation, that is, a potential corresponding to the luminance data (that is, V2 + Vdata) and the first capacitor 115 for holding a predetermined voltage. An arbitrary potential (that is, V2) is supplied for a predetermined period. Note that since the gate capacitor 4310 of the transistor 110 is used as a storage capacitor, the second capacitor 116 in FIG. 1 is not particularly necessary. In such a pixel as well, by supplying a desired potential to each electrode as in the timing chart shown in FIG. 2, variation in current value due to variation in threshold voltage of the transistor 110 can be suppressed. it can. Accordingly, a desired current can be supplied to the pixel electrode 4300. Needless to say, the gate capacitor of the transistor 110 can also be used for the second capacitor 116 in FIG. 1 and can be omitted.

  Next, FIG. 6 illustrates the case where N-channel transistors are used for the first switch 111, the second switch 112, the third switch 113, and the fourth switch 114. Note that portions common to the configuration in FIG. 1 are denoted by common reference numerals and description thereof is omitted.

  The first switching transistor 611 corresponds to the first switch 111 in FIG. 1, the second switching transistor 612 corresponds to the second switch 112, and the third switching transistor 613 corresponds to the third switch 113. The fourth switching transistor 614 corresponds to the fourth switch 114. Note that the channel length of the transistor 110 is preferably longer than the channel length of any of the first switching transistor 611, the second switching transistor 612, the third switching transistor 613, and the fourth switching transistor 614.

  The first switching transistor 611 has a gate electrode connected to the first scanning line 119, a first electrode connected to the signal line 118, and a second electrode connected to the first electrode of the first capacitor 115.

  The second switching transistor 612 has a gate electrode connected to the second scanning line 120, a first electrode connected to the node 133, and a second electrode connected to the power supply line 122.

  The third switching transistor 613 has a gate electrode connected to the third scanning line 121, a first electrode connected to the node 130, and a second electrode connected to the node 133.

  The fourth switching transistor 614 has a gate electrode connected to the third scanning line 121, a first electrode connected to the first electrode of the first capacitor 115, and a second electrode connected to the potential supply line. 123.

  Each switching transistor is turned on when the signal input to each scanning line is at the H level, and is turned off when the input signal is at the L level.

  One mode of the pixel layout shown in FIG. 6 is shown in FIG. 44 using a top view. Note that the structure of a transistor, a capacitor, a light-emitting element, and the like will be described in an embodiment described later, and thus only the layout will be described here. As the transistor 110 and the first switching transistor 611 to the fourth switching transistor 614 illustrated in FIG. 44, bottom-gate transistors in which a gate electrode is located below a semiconductor layer are used.

  A conductive layer 4410 illustrated in FIG. 44 includes a portion which functions as the first scan line 119 and the gate electrode of the first switching transistor 611, and the conductive layer 4411 includes the signal line 118 and the first switching transistor 611. A portion that functions as an electrode is included. The conductive layer 4412 includes a portion functioning as the second electrode of the first switching transistor 611, the first electrode of the first capacitor 115, and the first electrode of the fourth switching transistor 614. . The conductive layer 4413 includes a second electrode of the first capacitor 115, a first electrode of the second capacitor 116, and a portion functioning as the gate electrode of the transistor 110. Note that this conductive layer 4413 is connected to a conductive layer 4415 including a portion functioning as the first electrode of the third switching transistor 613 through a wiring 4414. The conductive layer 4416 includes a second electrode of the second capacitor 116 and a portion functioning as the first electrode of the transistor 110, and is connected to the pixel electrode 4455 of the light-emitting element through a contact. The conductive layer 4417 includes a portion functioning as the second electrode of the transistor 110, the second electrode of the third switching transistor 613, and the first electrode of the second switching transistor 612, and the conductive layer 4418. Includes a power source line 122 and a portion functioning as a second electrode of the second switching transistor 612. The conductive layer 4419 includes the second scan line 120 and a portion functioning as the gate electrode of the second switching transistor 612. The conductive layer 4420 includes a portion functioning as the gate electrode of the third switching transistor 613 and the gate electrode of the fourth switching transistor 614, and is connected to the third scan line 121 through the wiring 4421. In addition, the conductive layer 4422 including a portion functioning as the second electrode of the fourth switching transistor 614 is connected to the potential supply line 123 through the wiring 4423.

  Note that portions of the conductive layers that function as the gate electrode, the first electrode, and the second electrode of the first switching transistor 611 are formed so that the conductive layer including each of them overlaps with the semiconductor layer 4431. The portion which functions as the gate electrode, the first electrode, and the second electrode of the second switching transistor 612 is a portion where the conductive layer including each of them and the semiconductor layer 4432 are overlapped. In addition, a portion of each conductive layer that functions as the gate electrode, the first electrode, and the second electrode of the third switching transistor 613 is formed so as to overlap with the conductive layer including the semiconductor layer 4433. The portions functioning as the gate electrode, the first electrode, and the second electrode of the fourth switching transistor 614 are portions where a conductive layer including each overlaps with the semiconductor layer 4434. Similarly, in the transistor 110, the portions functioning as the gate electrode, the first electrode, and the second electrode are conductive layer portions formed so as to overlap with the conductive layer including each of them and the semiconductor layer 4430. Note that the first capacitor 115 is formed in a portion where the conductive layer 4412 and the conductive layer 4413 overlap, and the second capacitor 116 is formed in a portion where the conductive layer 4413 and the conductive layer 4416 overlap. .

  Note that the conductive layer 4410, the conductive layer 4413, the conductive layer 4419, the conductive layer 4420, the third scan line 121, and the potential supply line 123 can be formed using the same material and the same layer. The semiconductor layer 4430, the semiconductor layer 4431, the semiconductor layer 4432, the semiconductor layer 4433, and the semiconductor layer 4434, the conductive layer 4411, the conductive layer 4412, the conductive layer 4415, the conductive layer 4416, the conductive layer 4417, the conductive layer 4418, and the conductive layer 4422 are Each can be manufactured using the same material and the same layer. The wiring 4414, the wiring 4421, and the wiring 4423 can be manufactured using the same material and the same layer as the pixel electrode 4455.

  As shown in FIG. 44, the channel width can be increased by employing a structure in which one of the source electrode and the drain electrode surrounds the other electrode in each transistor except the first switching transistor 611. Therefore, it is particularly effective when an amorphous semiconductor layer having lower mobility than the crystalline semiconductor layer is used for the semiconductor layer of the transistor included in the pixel. Needless to say, the first switching transistor 611 may have a structure in which one of the source electrode and the drain electrode surrounds the other electrode.

  Next, one form of a layout different from that of FIG. 44 of the pixel shown in FIG. 6 is shown in FIG. 45 using a top view. Note that as the transistor 110 and the first switching transistor 611 to the fourth switching transistor 614 illustrated in FIG. 45, a top-gate transistor such as a forward stagger type in which a gate electrode is located over a semiconductor layer is used.

  In FIG. 45, the conductive layer 4510 includes a portion functioning as the gate electrode of the first scan line 119 and the first switching transistor 611, and the conductive layer 4511 includes the signal line 118 and the first switching transistor 611. A portion that functions as an electrode is included. The semiconductor film 4520 includes a portion functioning as the semiconductor layer and the second electrode of the first switching transistor 611, a portion functioning as the first electrode and the semiconductor layer of the fourth switching transistor 614, and the first capacitor element 115. A portion functioning as the first electrode is included. Note that the semiconductor film 4520 is connected to the potential supply line 123 through a wiring 4512, and the wiring 4512 functions as a second electrode of the fourth switching transistor 614. The conductive layer 4513 includes a portion functioning as the second electrode of the first capacitor 115, the first electrode of the second capacitor 116, and the gate electrode of the transistor 110. Note that the conductive layer 4513 is connected to the semiconductor film 4521 through a wiring 4514 functioning as the first electrode of the third switching transistor 613. The semiconductor film 4521 includes a portion that functions as the semiconductor layer and the second electrode of the third switching transistor 613, a portion that functions as the first electrode and the semiconductor layer of the second switching transistor 612, and the first portion of the transistor 110. A portion that functions as an electrode, a semiconductor, and a second electrode, and a portion that functions as a second electrode of the second capacitor 116 are included. The conductive layer 4515 includes a portion functioning as the second scan line 120 and the gate electrode of the second switching transistor 612. The conductive layer 4516 includes a power source line 122 and a portion functioning as the second electrode of the second switching transistor 612. The conductive layer 4517 includes a portion functioning as the gate electrode of the third switching transistor 613 and a portion functioning as the gate electrode of the fourth switching transistor 614, and is connected to the third scan line 121 through the wiring 4518. ing. Note that the pixel electrode 4545 of the light-emitting element is connected to the semiconductor film 4521 through a wiring 4519.

  Note that the first capacitor 115 is formed in a portion where the semiconductor film 4520 and the conductive layer 4513 overlap, and the second capacitor 116 is formed in a portion where the semiconductor film 4521 and the conductive layer 4513 overlap. .

  The conductive layer 4510, the conductive layer 4513, the conductive layer 4515, the conductive layer 4517, the third scan line 121, and the potential supply line 123 can be formed using the same material and the same layer. The semiconductor film 4520 and the semiconductor film 4521 can be formed using the same material and the same layer. The wiring 4512, the wiring 4514, the conductive layer 4516, and the wiring 4518 can be manufactured using the same material and the same layer as the conductive layer 4511.

  Note that the pixel layout is not limited to the above.

  Also in the pixel configuration in FIG. 6, variation in current value due to variation in threshold voltage of the transistor 110 can be suppressed by the same operation method as in FIG. Therefore, a current corresponding to the luminance data can be supplied to the light emitting element 117, and variation in luminance can be suppressed. In addition, when the transistor 110 is operated in the saturation region, variation in luminance due to deterioration of the light-emitting element 117 can be suppressed.

  In addition, since a pixel can be formed using only N-channel transistors, the manufacturing process can be simplified. In addition, an amorphous semiconductor, a semi-amorphous semiconductor, or the like can be used for a semiconductor layer of a transistor included in the pixel. For example, amorphous silicon (a-Si: H) can be given as an amorphous semiconductor. By using these semiconductors, the manufacturing process can be further simplified. Therefore, the manufacturing cost can be reduced and the yield can be improved.

  Note that the first switching transistor 611, the second switching transistor 612, the third switching transistor 613, and the fourth switching transistor 614 are operated as simple switches; therefore, the polarity (conductivity type) of the transistors is not particularly limited. However, it is preferable to use a transistor with low off-state current. As a transistor with low off-state current, there are a transistor provided with an LDD region and a transistor having a multi-gate structure. Further, a CMOS switch may be used by using both an N channel type and a P channel type.

  In addition, as long as the operation similar to that in FIG. 1 is performed, connection of the switches can take various configurations, and is not limited to FIG. As can be seen from FIG. 3 describing the operation of the pixel configuration of FIG. 1, in the present invention, the initialization period, the threshold voltage writing period, the data writing period, and the light emitting period are shown in FIGS. 53A to 53D, respectively. What is necessary is just to have conduction as shown by the solid line. Therefore, any configuration may be used as long as a switch or the like can be arranged and operated so as to satisfy this.

Further, in the initialization period, the first capacitor 115 needs to hold a predetermined voltage and the second capacitor 116 needs to hold at least a voltage higher than the threshold voltage Vth of the transistor 110. As shown, the node 132 may be connected to the potential supply line 5401 through the fifth switch 5405. The fifth switch 5405 is turned on only during the initialization period. In FIG. 54, a scanning line for controlling on / off of the fifth switch 5405 is not shown. The potential of the potential supply line 5401 may be any lower than V1 _{+ V EL} potential. More preferably, the potential is equal to or lower than V1, and by setting such a potential, a reverse bias voltage can be applied to the light emitting element 117, so that a short-circuit portion in the light emitting element is insulated or deterioration of the light emitting element is suppressed. be able to. Therefore, the lifetime of the light emitting element can be extended.

  Next, a display device having the above-described pixel of the present invention will be described with reference to FIG.

  The display device includes a signal line driver circuit 711, a scan line driver circuit 712, and a pixel portion 713. The pixel portion 713 extends from the signal line driver circuit 711 in the column direction and is arranged in a plurality of signal lines S1 to Sm. And a plurality of first scanning lines G1_1 to Gn_1, second scanning lines G1_2 to Gn_2, and third scanning lines G1_3 to Gn_3 arranged extending in the row direction from the scanning line driving circuit 712. And a plurality of pixels 714 arranged in a matrix corresponding to the potential supply lines P1_2 to Pn_2 and the signal lines S1 to Sm. Each pixel 714 includes a signal line Sj (any one of the signal lines S1 to Sm), a power supply line Pj_1, a first scanning line Gi_1 (any one of the scanning lines G1_1 to Gn_1), a second scanning. The line Gi_2, the third scanning line Gi_3, and the potential supply line Pi_2 are connected.

  Note that the signal line Sj, the power supply line Pj_1, the first scanning line Gi_1, the second scanning line Gi_2, the third scanning line Gi_3, and the potential supply line Pi_2 are the signal line 118, the power supply line 122, and the first scanning line in FIG. This corresponds to one scanning line 119, second scanning line 120, third scanning line 121, and potential supply line 123.

  A row of pixels to be operated is selected by a signal output from the scan line driver circuit 712, and the operation shown in FIG. 2 is simultaneously performed on each pixel belonging to the same row. Note that in the data writing period in FIG. 2, the video signal output from the signal line driver circuit 711 is written to the pixel in the selected row. At this time, a potential corresponding to the luminance data of each pixel is input to each of the signal lines S1 to Sm.

  As shown in FIG. 8, for example, when the data writing period of the i-th row is completed, the signal is written to the pixel belonging to the i + 1-th row. In FIG. 8, the operation of the first switch 111 in FIG. 2 that can faithfully represent the data writing period in each row is extracted and described. Then, the pixel that has completed the data writing period in the i-th row moves to the light emission period, and emits light according to the signal written to the pixel.

  Therefore, if even the data writing period in each row does not overlap, the initialization start time can be set freely for each row. In addition, since each pixel can emit light except its own address period, the ratio of the light emission period in one frame period (that is, the duty ratio) can be very large, and can be almost 100%. . Therefore, a display device with a small luminance variation and a high duty ratio can be obtained.

  Further, since the threshold voltage writing period can be set long, the threshold voltage of the transistor can be written to the capacitor more accurately. Therefore, reliability as a display device can be improved.

  Note that the configuration of the display device illustrated in FIG. 7 is an example, and the present invention is not limited to this. For example, the potential supply lines P1_2 to Pn_2 do not have to be arranged in parallel with the first scanning lines G1_1 to Gn_1, and may be arranged in parallel to the signal lines S1 to Sm. Further, the power supply lines P1_1 to Pm_1 do not need to be arranged in parallel with the signal lines S1 to Sm, and may be arranged in parallel to the first scanning lines G1_1 to Gn_1.

  In the present embodiment, the case where the third switch 113 and the fourth switch 114 are controlled to be turned on and off using the same scanning line, that is, the third scanning line 121 is described. However, different scanning lines are used. Each switch may be controlled according to the timing chart of FIG.

  Note that the variation in threshold voltage includes a change in threshold voltage over time when attention is paid to one transistor in addition to a difference in threshold voltage of each transistor between pixels. Further, the difference in threshold voltage of each transistor includes a difference in transistor characteristics at the time of manufacturing the transistor. Note that the transistor here refers to a transistor having a function of supplying current to a load such as a light emitting element.

(Embodiment 2)
In this embodiment mode, a pixel having a different structure from that in Embodiment Mode 1 is shown in FIG. Note that components similar to those in Embodiment 1 are denoted by common reference numerals, and detailed description of the same portions or portions having similar functions is omitted.

  The pixel illustrated in FIG. 9A includes a transistor 110, a first switch 111, a second switch 112, a third switch 113, a rectifier element 914, a first capacitor element 115, a second capacitor element 116, and light emission. An element 117 is included. Note that the pixel is connected to the signal line 118, the first scan line 119, the second scan line 120, the third scan line 921, the fourth scan line 922, and the power supply line 122. The pixel illustrated in FIG. 9A has a structure in which the rectifier element 914 is used for the fourth switch 114 in FIG. 1, and the first electrode of the first capacitor 115 is interposed through the rectifier element 914. Are connected to the fourth scanning line 922. That is, the rectifier element 914 is connected so that current flows from the first electrode of the first capacitor 115 to the fourth scanning line 922. Needless to say, as described in Embodiment 1, the first switch 111, the second switch 112, and the fourth switch 114 may be transistors. For the rectifier element 914, a diode-connected transistor 954, 955, or the like can be used in addition to the Schottky barrier type 951, the PIN type 952, and the PN type 953 shown in FIG. 9B. . Note that the polarity of the transistors 954 and 955 needs to be selected as appropriate depending on the direction in which current flows.

  In the rectifying element 914, no current flows when an H level signal is input to the fourth scanning line 922, and an electric current flows in the rectifying element 914 when an L level signal is input. Therefore, when the pixel in FIG. 9 is operated in the same manner as the pixel illustrated in FIG. 1, an L level signal is input to the fourth scanning line 922 in the initialization period and the threshold voltage writing period. During this period, an H level signal is input. The L level signal is not only a current that flows through the rectifier element 914, but, similarly to the first embodiment, if the potential corresponding to the luminance data input to the pixel is (V2 + Vdata), the first capacitance of the second capacitor element 116. Since the potential of the electrode needs to be lowered to V2, it is assumed that the potential is obtained by subtracting the threshold voltage in the forward direction of the rectifying element 914 from V2. However, V2 is an arbitrary value, and when it is desired to make the light emitting element 117 not emit light during the light emission period, a potential of Vdata = 0 may be input. Further, since the H level signal does not have to flow through the rectifying element 914 as described above, it should be larger than the value obtained by subtracting the threshold voltage in the forward direction of the rectifying element 914 from V2.

  In consideration of the above matters, the pixel configuration in FIG. 9 can also be operated in the same manner as in FIG. 1, whereby variation in current value due to variation in threshold voltage of the transistor 110 can be suppressed. Therefore, a current corresponding to the luminance data can be supplied to the light emitting element 117, and variation in luminance can be suppressed. In addition, when the transistor 110 is operated in the saturation region, variation in luminance due to deterioration of the light-emitting element 117 can be suppressed.

  Further, the pixel shown in this embodiment mode can be applied to the display device in FIG. As in the first embodiment, the initialization start time can be set freely for each row as long as even the data writing periods in each row do not overlap. Further, since each pixel can emit light except its own address period, the ratio of the light emission period in one frame period (that is, the duty ratio) can be very large, and can be almost 100%. Therefore, a display device with a small luminance variation and a high duty ratio can be obtained.

  Further, since the threshold voltage writing period can be set long, the threshold voltage of the transistor that controls the value of the current flowing through the light-emitting element can be written into the capacitor more accurately. Therefore, the reliability as a display device is improved.

  This embodiment mode can be freely combined with the pixel structures shown in the other embodiment modes in addition to the above-described FIG. That is, the rectifying element 914 can be applied to the pixels described in other embodiments.

(Embodiment 3)
In this embodiment, a pixel having a different structure from those in Embodiments 1 and 2 is shown in FIGS. Specifically, a pixel having a structure in which the potential supply line 123 illustrated in FIG. 1 is replaced with another wiring will be described. Note that this structure can be obtained because an arbitrary potential may be supplied to the first electrode of the first capacitor 115. Components similar to those in Embodiment 1 are denoted by common reference numerals, and detailed description of the same portions or portions having similar functions is omitted.

  A pixel illustrated in FIG. 10A includes a transistor 110, a first switch 111, a second switch 112, a third switch 113, a fourth switch 114, a first capacitor 115, a second capacitor 116, A light emitting element 117 is included. Note that the pixel is connected to the signal line 118, the first scanning line 119, the second scanning line 120, the third scanning line 121, and the power supply line 122.

  In the pixel in FIG. 1 described in Embodiment 1, the first electrode of the first capacitor 115 is connected to the potential supply line 123 through the fourth switch 114, whereas FIG. Then, it can be connected to the power line 122. This is because the potential is not limited to the potential supply line 123, as long as a potential can be supplied to the first electrode so that a predetermined voltage is held in the first capacitor 115 in the initialization period and the threshold voltage writing period. is there. Therefore, the power supply line 122 can be used instead of the potential supply line. In this manner, the number of wirings can be reduced by replacing the power supply line 122 with a wiring that supplies a potential to the first electrode of the first capacitor 115, and the aperture ratio can be improved.

  Alternatively, the fourth switch 114 may be connected in parallel with the first capacitor 115 as illustrated in FIG. That is, the first electrode of the first capacitor 115 may be connected to the node 131 through the fourth switch 114. Even in such a structure, a potential can be supplied to the first electrode so that a predetermined voltage is held in the first capacitor 115 in the initialization period and the threshold voltage writing period.

  Further, as shown in the pixel of FIG. 11, the fourth switch 114 is connected to the first electrode of the first capacitor element 115 as the counter electrode 124 of the light emitting element 117 or the wiring supplying a predetermined potential to the counter electrode 124. You may connect via. That is, a predetermined potential supplied to the counter electrode 124 may be used instead of the potential supplied from the potential supply line 123 in FIG. As described above, the number of wirings can be reduced, and the aperture ratio can be improved.

  In addition, the wiring connecting the first electrode of the first capacitor 115 and the counter electrode 124 of the light emitting element 117 is not only connected to the counter electrode 124 but also extends in parallel with the counter electrode 124. You may use as auxiliary wiring in a counter electrode. Of course, the auxiliary wiring is not limited to one pixel, but may extend to adjacent pixels or the entire pixel region. The resistance of the counter electrode 124 can be reduced by such an auxiliary wiring. Therefore, when the counter electrode is thinned, an increase in resistance value can be prevented. This is particularly effective when a transparent electrode is used as the counter electrode. In addition, when the resistance value of the counter electrode increases, variation in luminance of the light-emitting element 117 caused by non-uniform in-plane potential distribution of the counter electrode due to voltage drop can be suppressed. Therefore, reliability can be further improved.

  10 and 11 also, by performing the same operation as that in Embodiment 1, variation in current value due to variation in threshold voltage of the transistor 110 can be suppressed. . Therefore, a current corresponding to the luminance data can be supplied to the light emitting element 117, and variation in luminance can be suppressed. In addition, since the counter electrode is operated at a constant potential, power consumption can be reduced. Note that there is no particular limitation on the operation region of the transistor 110, but when the transistor 110 is operated in the saturation region, variation in current flowing in the transistor 110 due to deterioration of the light-emitting element 117 can be suppressed.

  Note that the potential supply line in FIG. 1 supplies an arbitrary potential to the first electrode of the first capacitor 115 in the initialization period and the threshold voltage writing period, so that a predetermined voltage is applied to the first capacitor 115. Should be retained. Therefore, the wiring that substitutes the potential supply line is not limited to the above, and any wiring that does not change its potential in the initialization period and the threshold voltage writing period may be used. For example, a first scanning line 119 or a third scanning line 121 can be used as shown in FIG. However, in the case where the third scanning line 121 is used, it is necessary to select a switch type in consideration of the fact that the fourth switch 114 may function as the rectifying element described in Embodiment 2.

  Further, the pixel shown in this embodiment mode can be applied to the display device in FIG. As in the first embodiment, the initialization start time can be set freely for each row as long as even the data writing periods in each row do not overlap. Further, since each pixel can emit light except its own address period, the ratio of the light emission period in one frame period (that is, the duty ratio) can be very large, and can be almost 100%. Therefore, a display device with a small luminance variation and a high duty ratio can be obtained.

  Further, since the threshold voltage writing period can be set long, the threshold voltage of the transistor that controls the value of the current flowing through the light-emitting element can be written into the capacitor more accurately. Therefore, the reliability as a display device is improved.

  In addition to the above, this embodiment mode can be freely combined with the pixel structures shown in other embodiment modes.

(Embodiment 4)
In this embodiment mode, pixels having different structures from those in Embodiment Modes 1 to 3 are shown in FIGS. Note that in the third embodiment, attention is paid to one pixel, but the number of wirings can be reduced by sharing the wirings connected to each pixel among the pixels. In this case, various wirings can be shared if they operate normally. For example, it is possible to share a wiring with an adjacent pixel, and an example of the method will be described in this embodiment. Note that components similar to those in Embodiment 1 are denoted by common reference numerals, and detailed description of the same portions or portions having similar functions is omitted.

  A pixel 1300 illustrated in FIG. 13 includes a transistor 110, a first switch 111, a second switch 112, a third switch 113, a fourth switch 114, a first capacitor 115, a second capacitor 116, and a light-emitting element. 117. Note that the pixel is connected to the signal line 118, the first scanning line 119, the second scanning line 120, the third scanning line 121, and the power supply line 1322 in the previous column.

  In the pixel in FIG. 1 described in Embodiment Mode 1, the first electrode of the first capacitor 115 is connected to the potential supply line 123 through the fourth switch 114, whereas in FIG. A power supply line 1322 can be connected. This is not limited to the potential supply line 123 but is applied to the first electrode of the first capacitor 115 so that a predetermined voltage is held in the first capacitor 115 in the initialization period and the threshold voltage writing period. This is because it is sufficient if a potential can be supplied. Therefore, the power supply line 1322 in the previous row can be used instead of the potential supply line. As described above, the pixel 1300 can reduce the number of wirings by sharing the wiring with the pixels in the previous column, and can improve the aperture ratio.

  Note that also in the pixel structure illustrated in FIG. 13, by performing the same operation as that in Embodiment 1, variation in current value due to variation in threshold voltage of the transistor 110 can be suppressed. Therefore, a current corresponding to the luminance data can be supplied to the light emitting element 117, and variation in luminance can be suppressed. In addition, since the counter electrode is operated at a constant potential, power consumption can be reduced. Note that there is no particular limitation on the operation region of the transistor 110, but when the transistor 110 is operated in the saturation region, variation in current flowing in the transistor 110 due to deterioration of the light-emitting element 117 can be suppressed.

  Further, as shown in the pixel 1400 in FIG. 14, the potential supply line 123 in FIG. 1 may be shared with the first scanning line 1419 in the next row. The pixel 1400 can also perform the same operation as that in Embodiment 1. However, it is necessary to operate so that the initialization period and the threshold voltage writing period of the row to which the pixel 1400 belongs do not overlap with the data writing period of the row sharing the wiring.

  Further, as shown in the pixel 1500 in FIG. 15, the potential supply line 123 in FIG. 1 may be shared with the second scanning line 1520 in the next row. The pixel 1500 can also operate in the same manner as in the first embodiment. However, the initialization period and the threshold voltage writing period of the row to which the pixel 1500 belongs are operated so as to overlap with the threshold voltage writing period and the data writing period of the row sharing the wiring, or not at all. Need to work. In other words, one of signals for turning on or off the second switch 112 is used as the potential supplied to the first electrode of the first capacitor 115.

  In addition to the above, the potential supply line 123 in FIG. 1 may be shared with the third scanning line 1621 in the previous row as shown in FIG. However, it is necessary to operate so that the initialization period and the threshold voltage writing period of the row to which the pixel 1600 belongs do not overlap with the threshold voltage writing period and the data writing period of the row sharing the wiring.

  Note that although the case where the potential supply line 123 in FIG. 1 is shared with the power supply line of the previous column or the scanning line of the next row or the previous row has been described in this embodiment mode, Any wiring that can supply a potential to the first electrode so that a predetermined voltage is held in the capacitor 115 may be used.

  Further, the pixel shown in this embodiment mode can be applied to the display device in FIG. Note that in the display device, the initialization start time can be freely set for each row within a range where the operation restrictions for each pixel described in FIGS. 13 to 16 and the data writing period in each row do not overlap. In addition, since each pixel can emit light except its own address period, the ratio of the light emission period in one frame period (that is, the duty ratio) can be very large, and can be almost 100%. . Therefore, a display device with a small luminance variation and a high duty ratio can be obtained.

  Further, since the threshold voltage writing period can be set long, the threshold voltage of the transistor that controls the value of the current flowing through the light-emitting element can be written into the capacitor more accurately. Therefore, the reliability as a display device is improved.

  In addition to the above, this embodiment mode can be freely combined with the pixel structures shown in other embodiment modes.

(Embodiment 5)
In this embodiment mode, a pixel having a structure different from that in Embodiment Mode 1 is shown in FIG. Note that components similar to those in Embodiment 1 are denoted by common reference numerals, and detailed description of the same portions or portions having similar functions is omitted.

  29 includes a transistor 2910, a first switch 111, a second switch 112, a third switch 113, a fourth switch 114, a first capacitor 115, a second capacitor 116, and a light-emitting element. 117. Note that the pixel is connected to the signal line 118, the first scan line 119, the second scan line 120, the third scan line 121, the power supply line 122, and the potential supply line 123.

  The transistor 2910 in this embodiment is a multi-gate transistor in which two transistors are connected in series, and is provided at the same position as the transistor 110 in Embodiment 1. However, the number of transistors connected in series is not particularly limited.

  By operating the pixel shown in FIG. 29 similarly to the pixel in FIG. 1, variation in current value due to variation in threshold voltage of the transistor 2910 can be suppressed. Therefore, a current corresponding to the luminance data can be supplied to the light emitting element 117, and variation in luminance can be suppressed. In addition, since the counter electrode is operated at a constant potential, power consumption can be reduced. Note that the operation region of the transistor 2910 is not particularly limited; however, when the transistor 2910 is operated in the saturation region, variation in current flowing in the transistor 2910 due to deterioration of the light-emitting element 117 can be suppressed.

  In this embodiment, the channel length L of the transistor 2910 acts as the sum of the channel lengths of the transistors when the channel widths of two transistors connected in series are equal. Therefore, it is easy to obtain a current value closer to a constant value regardless of the drain-source voltage Vds in the saturation region. In particular, the transistor 2910 is effective when it is difficult to manufacture a transistor having a long channel length L. Note that the connection portion of the two transistors functions as a resistor.

  Note that the transistor 2910 only needs to have a function of controlling a current value supplied to the light-emitting element 117, and the type of the transistor is not particularly limited. Therefore, a thin film transistor (TFT) using a crystalline semiconductor film, a thin film transistor using a non-single crystal semiconductor film typified by amorphous silicon or polycrystalline silicon, a transistor formed using a semiconductor substrate or an SOI substrate, MOS Type transistors, junction transistors, bipolar transistors, transistors using compound semiconductors such as ZnO and a-InGaZnO, transistors using organic semiconductors and carbon nanotubes, and other transistors can be used.

  29, similarly to the pixel shown in FIG. 1, the first switch 111, the second switch 112, the third switch 113, and the fourth switch 114 can use transistors or the like. .

  Further, the pixel shown in this embodiment mode can be applied to the display device in FIG. As in the first embodiment, the initialization start time can be set freely for each row as long as even the data writing periods in each row do not overlap. In addition, since each pixel can emit light except its own address period, the ratio of the light emission period in one frame period (that is, the duty ratio) can be very large, and can be almost 100%. . Therefore, a display device with a small luminance variation and a high duty ratio can be obtained.

  Further, since the threshold voltage writing period can be set long, the threshold voltage of the transistor that controls the value of the current flowing through the light-emitting element can be written into the capacitor more accurately. Therefore, the reliability as a display device is improved.

  Note that the transistor 2910 is not limited to a transistor connected in series, and may have a structure in which transistors are connected in parallel as illustrated in a transistor 3010 in FIG. A larger current can be supplied to the light-emitting element 117 by the transistor 3010. Further, since the transistor characteristics are averaged by the two transistors connected in parallel, the original characteristic variation of the transistors constituting the transistor 3010 can be further reduced. Therefore, if the variation is small, it is possible to more easily suppress the variation in the current value caused by the variation in the threshold voltage of the transistor.

  Further, each of the transistors connected in parallel shown in the transistor 3010 may be further connected in series like a transistor 2910 shown in FIG.

  In addition to the above, this embodiment mode can be freely combined with the pixel structures shown in other embodiment modes. That is, the transistor 2910 or the transistor 3010 can be applied to the pixel structures described in other embodiments.

(Embodiment 6)
In this embodiment mode, a pixel configuration in which deterioration over time of a transistor is averaged by switching a transistor for controlling a current value supplied to a light emitting element for each period in the pixel of the present invention will be described with reference to FIG.

  31 includes a first transistor 3101, a second transistor 3102, a first switch 3111, a second switch 3112, a third switch 3113, a fourth switch 3114, a fifth switch 3103, 6 switch 3104, first capacitor element 3115, second capacitor element 3116, and light emitting element 3117. Note that the pixel is connected to a signal line 3118, a first scan line 3119, a second scan line 3120, a third scan line 3121, a power supply line 3122, and a potential supply line 3123. Further, although not shown in FIG. 31, the fifth switch 3103 and the sixth switch 3104 are also connected to fourth and fifth scanning lines for controlling on / off of the fifth switch 3103 and the sixth switch 3104. In this embodiment, the first transistor 3101 and the second transistor 3102 are N-channel transistors, and each transistor becomes conductive when the gate-source voltage (Vgs) exceeds the threshold voltage. And The pixel electrode of the light-emitting element 3117 is an anode, and the counter electrode 3124 is a cathode. Note that a gate-source voltage of the transistor is denoted as Vgs, and voltages stored in the first capacitor element 3115 and the second capacitor element 3116 are denoted as Vc1 and Vc2, respectively. The threshold voltage of the first transistor 3101 is denoted as Vth1, the threshold voltage of the second transistor 3102 is denoted as Vth2, and the power supply line 3122, the potential supply line 3123, and the signal line 3118 are connected to the first wiring, It is also called a second wiring or a third wiring.

  A first electrode (one of a source electrode and a drain electrode) of the first transistor 3101 is connected to a pixel electrode of the light-emitting element 3117 through a fifth switch 3103, and a second electrode (a source electrode and a drain electrode) The other is connected to the power supply line 3122 via the second switch 3112. The gate electrode of the first transistor 3101 is also connected to the power supply line 3122 through the third switch 3113 and the second switch 3112. Note that the third switch 3113 is connected between the gate electrode of the first transistor 3101 and the second switch 3112, and the second electrode of the first transistor 3101, the second switch 3112, A connection point with the wiring to which the third switch 3113 is connected is a node 3133.

  The first electrode (one of the source electrode and the drain electrode) of the second transistor 3102 is connected to the pixel electrode of the light-emitting element 3117 through the sixth switch 3104, and the second electrode (the source electrode and the drain electrode) The other is connected to the second electrode of the first transistor 3101. Note that when a connection portion between the second electrode of the first transistor 3101 and the second electrode of the second transistor 3102 is a node 3132, the node 3132 is connected to the node 3133. The gate electrode of the second transistor 3102 is connected to the node 3133 through the third switch 3113. Note that the gate electrode of the first transistor 3101 and the gate electrode of the second transistor 3102 are connected.

  Further, when a connection position between the gate electrodes of the first transistor 3101 and the second transistor 3102 and the third switch 3113 is a node 3130, the node 3130 is connected to the first capacitor 3115 and the first switch 3111. Are connected to the signal line 3118. In other words, the first electrode of the first capacitor 3115 is connected to the signal line 3118 via the first switch 3111 and the second electrode is connected to the gate electrodes of the first transistor 3101 and the second transistor 3102. Yes. The first electrode of the first capacitor 3115 is also connected to the potential supply line 3123 through the fourth switch 3114. The node 3130 is further connected to the pixel electrode of the light emitting element 3117 through the second capacitor 3116. That is, the first electrode of the second capacitor 3116 is the gate electrode of the first transistor 3101 and the second transistor 3102, and the second electrode is the fifth switch 3103 or the sixth switch 3104 through the sixth switch 3104. The first transistor 3101 and the second transistor 3102 are connected to first electrodes. These capacitor elements may be formed by sandwiching an insulating film between wirings, semiconductor layers, and electrodes. In some cases, the second capacitor element may be formed using the gate capacitors of the first transistor 3101 and the second transistor 3102. It is also possible to omit 3116.

  Note that by inputting a signal to the first scan line 3119, the second scan line 3120, and the third scan line 3121, the first switch 3111, the second switch 3112, the third switch 3113, and the third scan line 3121, respectively. The on / off state of the fourth switch 3114 is controlled. As described above, in FIG. 31, the scanning lines for controlling on / off of the fifth switch 3103 and the sixth switch 3104 are omitted.

  A signal in accordance with the gradation of a pixel corresponding to a video signal, that is, a potential corresponding to luminance data is input to the signal line 3118.

  Next, the operation of the pixel shown in FIG. 31 will be described with reference to the timing chart of FIG. In FIG. 32, one frame period corresponding to a period for displaying an image for one screen is divided into an initialization period, a threshold voltage writing period, a data writing period, and a light emission period.

Note that a potential V1 (V1: any number) is input to the counter electrode 3124 of the light-emitting element 3117. Further, if at least a potential difference necessary for the light emitting element 3117 to emit light is V _EL , a potential of V1 + V _EL + Vth + α (α: an arbitrary positive number) is input to the power supply line 3122. That is, the power supply line 3122 may have a potential equal to or higher than V1 + V _EL + Vth + α. Note that Vth is the larger value of Vth1 or Vth2. The potential of the potential supply line 3123 is not particularly limited, but is preferably within the range of potentials input to the panel in which the pixels are formed. This eliminates the need for a separate power source. Note that here, the potential of the potential supply line 3123 is set to V2.

First, as illustrated in FIG. 32A, in the initialization period, the first switch 3111 and the sixth switch 3104 are turned off, and the second switch 3112, the third switch 3113, the fourth switch 3114, 5 switch 3103 is turned on. At this time, the first transistor 3101 is in a conductive state, and the first capacitor 3115 holds V1 + V _EL + Vth + α−V2 and the second capacitor 3116 holds Vth + α. Note that in this initialization period, the first capacitor 3115 may hold a predetermined voltage, and the second capacitor 3116 may hold at least a voltage higher than Vth1.

  In the threshold voltage writing period illustrated in FIG. 32B, the second switch 3112 is turned off. Therefore, the potential of the first electrode, that is, the source electrode of the first transistor 3101 gradually increases, and when the gate-source voltage Vgs of the first transistor 3101 reaches the threshold voltage (Vth1), the first transistor 3101 becomes non-conductive. Therefore, the voltage Vc2 held in the second capacitor element 3116 is approximately Vth1.

  In the subsequent data writing period shown in FIG. 32C, the third switch 3113 and the fourth switch 3114 are turned off, the first switch 3111 is turned on, and luminance data is obtained from the signal line 3118. A potential (V2 + Vdata) is input. At this time, the voltage Vc2 held in the second capacitor element 3116 is C3> when the capacitances of the first capacitor element 3115, the second capacitor element 3116, and the light emitting element 3117 are C1, C2, and C3, respectively. > From C1 and C2, Vth1 + Vdata × (C1 / (C1 + C2)).

  Note that C1 and C2 are necessary when determining the potential supplied from the signal line 3118, but their relationship is not particularly limited. Note that in the case of C1> C2, the power consumption can be reduced because the amplitude of Vdata accompanying the change in luminance can be reduced. On the other hand, when C2> C1, it is possible to suppress changes in Vc2 due to on / off of surrounding switches and off-current. From these contradictory effects, it is preferable that C1 and C2 are equal and the first capacitor element 3115 and the second capacitor element 3116 have the same size.

  Note that in the case where the light emitting element 3117 does not emit light in the next light emission period, a potential of Vdata ≦ 0 may be input.

  Next, in the light emission period shown in FIG. 32D, the first switch 3111 is turned off and then the second switch 3112 is turned on. At this time, the gate-source voltage Vgs of the first transistor 3101 is Vth1 + Vdata × (C1 / (C1 + C2)), and current corresponding to the luminance data flows to the first transistor 3101 and the light-emitting element 3117. Emits light.

  With such an operation, the current flowing through the light-emitting element 3117 depends on the threshold voltage (Vth1) of the first transistor 3101 regardless of whether the operation region of the first transistor 3101 is the saturation region or the linear region. do not do.

Further, in the initialization period in the next one frame period illustrated in FIG. 32E, the fifth switch 3103 is turned off, and the third switch 3113, the fourth switch 3114, and the sixth switch 3104 are turned on. . The second transistor 3102 is turned on, and V1 + V _EL + Vth + α−V2 is held in the first capacitor 3115, and Vth + α is held in the second capacitor 3116. Note that in this initialization period, the first capacitor 3115 may hold a predetermined voltage, and the second capacitor 3116 may hold at least a voltage higher than Vth2.

  Next, in the threshold voltage writing period illustrated in FIG. 32F, the second switch 3112 is turned off. Therefore, the potential of the first electrode, that is, the source electrode of the second transistor 3102 gradually increases, and the second transistor 3102 when the gate-source voltage Vgs of the second transistor 3102 reaches the threshold voltage (Vth2). 3102 becomes non-conductive. Therefore, the voltage Vc2 held in the second capacitor element 3116 is approximately Vth2.

  In the subsequent data writing period shown in FIG. 32G, the third switch 3113 and the fourth switch 3114 are turned off, the first switch 3111 is turned on, and luminance data is supplied from the signal line 3118. A potential (V2 + Vdata) is input. At this time, the voltage Vc2 held in the second capacitor 116 is Vth2 + Vdata × (C1 / (C1 + C2)).

  Next, in the light emission period illustrated in FIG. 32H, the first switch 3111 is turned off and then the second switch 3112 is turned on. At this time, the gate-source voltage Vgs of the second transistor 3102 is Vth2 + Vdata × (C1 / (C1 + C2)), and a current corresponding to the luminance data flows to the second transistor 3102 and the light-emitting element 3117. Emits light.

  In addition, in the case where the operation region of the second transistor 3102 is either the saturation region or the linear region, the current flowing through the light-emitting element 3117 does not depend on the threshold voltage (Vth2).

  Therefore, even when the current supplied to the light-emitting element is controlled using any of the first transistor 3101 and the second transistor 3102, variation in current value due to variation in threshold voltage of the transistor is suppressed, A current value corresponding to the luminance data can be supplied to the light emitting element 3117. Note that when the first transistor 3101 and the second transistor 3102 are switched and used, a change in threshold voltage of the transistor with time can be reduced by reducing a load applied to one transistor.

  From the above, variation in luminance due to the threshold voltages of the first transistor 3101 and the second transistor 3102 can be suppressed. In addition, since the potential of the counter electrode is kept constant, power consumption can be reduced.

  Further, in the case where the first transistor 3101 and the second transistor 3102 are operated in a saturation region, variation in current flowing through each transistor due to deterioration of the light-emitting element 3117 can be suppressed.

  Note that in the case where the first transistor 3101 and the second transistor 3102 are operated in the saturation region, it is preferable that the channel length L of these transistors be long.

  Further, in the present invention, variation in current value caused by variation in threshold voltage of a transistor can be suppressed, and therefore, a supply destination of current controlled by the transistor is not particularly limited. Therefore, as the light-emitting element 3117 illustrated in FIG. 31, an EL element (an organic EL element, an inorganic EL element, or an EL element including an organic substance and an inorganic substance) can be typically used. Further, instead of the light-emitting element 3117, an electron-emitting element, a liquid crystal element, electronic ink, or the like can be used.

  The first transistor 3101 and the second transistor 3102 are only required to have a function of controlling a current value supplied to the light-emitting element 3117; Therefore, a thin film transistor (TFT) using a crystalline semiconductor film, a thin film transistor using a non-single crystal semiconductor film typified by amorphous silicon or polycrystalline silicon, a transistor formed using a semiconductor substrate or an SOI substrate, MOS Type transistors, junction transistors, bipolar transistors, transistors using compound semiconductors such as ZnO and a-InGaZnO, transistors using organic semiconductors and carbon nanotubes, and other transistors can be used.

  The first switch 3111 selects a potential corresponding to luminance data, that is, a timing at which a signal is input to the pixel from the signal line 3118, and mainly includes a voltage held in the first capacitor 3115 and a second capacitor 3116. , That is, the voltage between the gate and source of the first transistor 3101 or the second transistor 3102 is changed. The second switch 3112 selects timing for supplying a predetermined potential to the first transistor 3101 or the second electrode of the second transistor 3102. Note that the predetermined potential is also supplied to the second electrode of the first capacitor 3115 and the first electrode of the second capacitor 3116 depending on circumstances. The third switch 3113 controls connection between the gate electrode of the first transistor 3101 or the second transistor 3102 and the second electrode of each transistor, and the fourth switch 3114 is set for each frame period. The timing at which the first capacitor element 3115 holds a predetermined voltage is selected and whether or not a predetermined potential is supplied to the first electrode of the first capacitor element 3115 is controlled. Therefore, the first switch 3111, the second switch 3112, the third switch 3113, and the fourth switch 3114 are not particularly limited as long as they have the above functions. For example, a transistor or a diode may be used, or a logic circuit combining them may be used. Note that the first switch 3111, the second switch 3112, and the fourth switch 3114 are not particularly required as long as a signal or a potential can be supplied to the pixel at the above timing. The third switch 3113 is not particularly required as long as the above function can be realized.

  For example, in the case where N-channel transistors are used for the first switch 3111, the second switch 3112, the third switch 3113, the fourth switch 3114, the fifth switch 3103, and the sixth switch 3104, the pixel Since the transistor can be formed using only N-channel transistors, the manufacturing process can be simplified. In addition, an amorphous semiconductor, a semi-amorphous semiconductor, or the like can be used for a semiconductor layer of a transistor included in the pixel. For example, amorphous silicon (a-Si: H) can be given as an amorphous semiconductor. By using these semiconductors, the manufacturing process can be further simplified. Therefore, the manufacturing cost can be reduced and the yield can be improved.

  Note that when transistors are used for the first switch 3111, the second switch 3112, the third switch 3113, the fourth switch 3114, the fifth switch 3103, and the sixth switch 3104, the polarity of the transistor (conductivity type) ) Is not particularly limited. However, it is preferable to use a transistor with low off-state current.

  In addition, the first transistor 3101 and the fifth switch 3103 and the second transistor 3102 and the sixth switch 3104 may be interchanged as shown in FIG. In other words, the first electrodes of the first transistor 3101 and the second transistor 3102 are connected to the gate electrodes of the first transistor 3101 and the second transistor 3102 through the second capacitor 3116. The second electrode of the first transistor 3101 is connected to the node 3132 through the fifth switch 3103, and the second electrode of the second transistor 3102 is connected to the node 3132 through the sixth switch 3104. Has been.

  In FIGS. 31 and 37, when the number of parallels is 2 with a set of transistors and switches, that is, the first transistor 3101 and the fifth switch 3103, and the second transistor 3102 and the sixth switch 3104 as a set. However, the number arranged in parallel is not particularly limited.

  In addition, by applying the pixels shown in this embodiment to the display device in FIG. 7, the initialization start time can be set freely in each row as long as the data writing period in each row does not overlap as in the first embodiment. Can do. Further, since each pixel can emit light except its own address period, the ratio of the light emission period in one frame period (that is, the duty ratio) can be very large, and can be almost 100%. Therefore, a display device with a small luminance variation and a high duty ratio can be obtained.

  Further, since the threshold voltage writing period can be set long, the threshold voltage of the transistor that controls the value of the current flowing through the light-emitting element can be written into the capacitor more accurately. Therefore, the reliability as a display device is improved.

  Note that also in this embodiment mode, the potential supply line 3123 may be substituted with a wiring in the same pixel as shown in Embodiment Mode 3, or may be shared with wiring in other rows as in Embodiment Mode 4. . Alternatively, each of the first transistor 3101 and the second transistor 3102 may be a multi-gate transistor in which transistors are connected in series or a transistor arranged in parallel. The present embodiment is not limited to this, and can be applied to the pixel structures described in Embodiments 1 to 5.

(Embodiment 7)
In this embodiment, a pixel having a structure different from that in Embodiment 1 is shown. Components similar to those in Embodiment 1 are denoted by common reference numerals, and detailed description of the same portions or portions having similar functions is omitted. These operations are the same as in the first embodiment.

  In the present embodiment, a pixel configuration in which current is not forced to flow through the light emitting element 117 will be described. That is, it is an object of the present invention to obtain a display device that is difficult to see an afterimage and has excellent moving image characteristics by forcibly creating a non-light emitting state.

  One such pixel configuration is shown in FIG. 38 includes a transistor 110, a first switch 111, a second switch 112, a third switch 113, a fourth switch 114, a first capacitor 115, a second capacitor 116, and a light-emitting element. In addition to 117, a fifth switch 3801 is provided. Note that the pixel includes the signal line 118, the first scanning line 119, the second scanning line 120, the third scanning line 121, the power supply line 122, the potential supply line 123, and the fourth scanning line 3802. It is connected.

  In FIG. 38, the fifth switch 3801 is connected in parallel with the second capacitor 116. Therefore, when the fifth switch 3801 is turned on, the gate electrode and the first electrode of the transistor 110 are short-circuited. Accordingly, the gate-source voltage of the transistor 110 held in the second capacitor 116 can be 0 V, so that the transistor 110 is turned off and the light-emitting element 117 can emit no light. Note that on / off control of the fifth switch 3801 is performed by scanning each pixel row by a signal input to the fourth scan line 3802.

  By such an operation, the signal written in the pixel is erased. Therefore, it is possible to provide an erasing period in which light emission is forcibly stopped until the next initialization period. That is, a black display is inserted. Therefore, it is difficult to see the afterimage, and the moving image characteristics can be improved.

  Incidentally, there are an analog gray scale method and a digital gray scale method as drive methods for expressing the gray scale of the display device. The analog gradation method includes a method of analog control of the light emission intensity of the light emitting element and a method of analog control of the light emission time of the light emitting element. In the analog gradation method, a method of analog control of the light emission intensity of the light emitting element is often used. On the other hand, in the digital gradation method, gradation is expressed by turning on and off the light emitting element by digital control. In the digital gradation method, since it can be processed with a digital signal, there is a merit of being resistant to noise. However, since there are only two states of light emission and non-light emission, only two gradations can be expressed as it is. In view of this, multi-gradation is being achieved by combining different methods. As a method for multi-gradation, there are an area gradation method in which gradation display is performed by weighting the light emitting area of the pixel and selection is performed, and a time in which gradation display is performed by weighting the light emission time and selected. There is a gradation method.

When the digital gradation method and the time gradation method are combined, one frame period is divided into a plurality of subframe periods (SFn) as shown in FIG. Each subframe period includes an address period (Ta) having an initialization period, a threshold voltage writing period, and a data writing period, and a light emission period (Ts). Note that a number corresponding to the number n of display bits is provided in one frame period in the subframe period. In addition, the ratio of the lengths of the light emitting periods in each subframe period is set to 2 ^(n-1) : 2 ^(n-2) :...: 2: 1, and the light emitting element emits light or does not emit light in each light emitting period. Is selected, and gradation expression is performed using a difference in total time during one frame period in which the light emitting element emits light. In one frame period, the luminance is high if the total emission time is long, and the luminance is low if it is short. Note that FIG. 39 shows an example of 4-bit gradation, and one frame period is divided into four subframe periods, and 2 ⁴ = 16 gradations can be expressed by a combination of light emission periods. Note that gradation expression is possible even if the ratio of the lengths of the light emission periods is not particularly a power-of-two ratio. Further, a certain subframe period may be further divided.

  Note that when multi-gradation is performed using the time gray scale method as described above, since the light emission period of the lower bits is short, the data writing operation for the next subframe period starts immediately after the light emission period ends. Attempting to do so overlaps the data write operation in the previous subframe period, and normal operation cannot be performed. Therefore, by providing such an erasing period in the subframe period, light emission shorter than the data writing period required for all rows can be expressed. That is, the light emission period can be set freely.

  The present invention is not only particularly effective in the analog gradation method, but also in the method combining the digital gradation method and the time gradation method, the light emission period can be freely set, so an erasing period is provided. It is effective.

  Further, an erasing period may be provided by cutting off a current path from the power supply line 122 to the pixel electrode of the light emitting element 117 through the transistor 110. For example, a new switch is provided in the current path from the power supply line 122 to the pixel electrode of the light emitting element 117 via the transistor 110, and the erase period is provided by scanning the pixels row by row and turning off the switch. Can do.

  One such configuration is shown in FIG. In the configuration in FIG. 40, in addition to the pixel configuration in FIG. 1, a fifth switch 4001 is connected between the first electrode of the transistor 110 and the node 132. Then, on / off of the fifth switch 4001 is controlled by a signal input to the fourth scan line 4002. By turning off the fifth switch 4001, an erasing period can be provided.

  Alternatively, an erasing period may be provided by connecting a fifth switch between the second electrode of the transistor 110 and the node 133 or between the pixel electrode of the light-emitting element 117 and the node 132 as illustrated in FIG. good.

  Needless to say, the second switch 112 is turned off in the pixel in FIG. 1 and the current path from the power supply line 122 to the light-emitting element 117 is cut, so that an erasing period may be provided without providing a new switch.

  Further, an erasing period can be forcibly provided by changing the potential of the gate electrode of the transistor 110.

  One such configuration is shown in FIG. The structure in FIG. 42 includes a rectifier element 4201 in addition to the pixel structure in FIG. 1, and the gate electrode of the transistor 110 and the fourth scanning line 4202 are connected through the rectifier element 4201. Note that when the transistor 110 is an N-channel transistor, the rectifier element 4201 is connected so that current flows from the gate electrode of the transistor 110 to the fourth scan line 4202. The fourth scanning line 4202 receives an L level signal only when the transistor 110 is forcibly turned off, and receives an H level signal otherwise. When the fourth scanning line 4202 is at the H level, no current flows through the rectifier element 4201. When the fourth scanning line 4202 is at the L level, a current flows from the gate electrode of the transistor 110 to the fourth scanning line 4202. In this manner, by passing a current through the fourth scan line 4202, the gate-source voltage of the transistor 110 is reduced to a threshold voltage (Vth) or less, and the transistor 110 is forcibly turned off. Note that the L-level potential must be determined in consideration of the fact that the potential of the gate electrode of the transistor 110 does not become lower than the potential obtained by adding the threshold voltage in the forward direction of the rectifying element 4201 to the L-level potential.

  Note that as the rectifying element 4201, a diode-connected transistor or the like can be used in addition to the Schottky barrier type, PIN type, or PN type diode shown in FIG. 9B.

  Note that the pixel configuration is not particularly limited to the above configuration because it can make an afterimage difficult to see by insertion of black display as long as it has means for forcibly turning off light emission.

  The switch or the like for providing an erasing period shown in this embodiment mode can be applied not only to the pixel configuration in FIG. 1 described above but also to the pixel configurations shown in other embodiments.

  Further, by setting a long initialization period without providing such a switch, the initialization period can also serve as an erasing period. Therefore, when the pixels described in Embodiments 1 to 6 are operated, the moving image characteristics can be improved by setting the period of black display in order to make the afterimage difficult to see, as the length of the initialization period. . Note that an erasing period can be provided by turning off the second switch as described above. Further, black display may be inserted by making the potential of the power supply line 122 the same as the potential of the counter electrode 124 in the light emission period.

  Note that the pixel described in this embodiment can be applied to the display device described in Embodiment 1. From the above, it is possible to obtain a display device with little variation in luminance and excellent moving image characteristics.

(Embodiment 8)
In this embodiment, the case where a P-channel transistor is applied to a transistor for controlling a current value supplied to a light emitting element will be described with reference to FIG.

  46 includes a transistor 4610, a first switch 4611, a second switch 4612, a third switch 4613, a fourth switch 4614, a first capacitor element 4615, a second capacitor element 4616, and a light-emitting element. 4617. The pixel is connected to a signal line 4618, a first scan line 4619, a second scan line 4620, a third scan line 4621, a power supply line 4622, and a potential supply line 4623. In this embodiment, the transistor 4610 is a P-channel transistor, and the absolute value (| Vgs |) of the gate-source voltage exceeds the threshold voltage (| Vth |) (that is, Vgs exceeds Vth). When it falls below). In addition, the pixel electrode of the light-emitting element 4617 functions as a cathode, and the counter electrode 4624 functions as an anode. Note that the absolute value of the gate-source voltage of the transistor is | Vgs |, the absolute value of the threshold voltage is | Vth |, and the voltages accumulated in the first capacitor element 4615 and the second capacitor element 4616 are Vc1. , Vc2. The power supply line 4622, the potential supply line 4623, and the signal line 4618 are also referred to as a first wiring, a second wiring, and a third wiring, respectively. Further, the first scan line 4619, the second scan line 4620, and the third scan line 4621 may be referred to as a fourth wiring, a fifth wiring, and a sixth wiring, respectively.

  A first electrode (one of a source electrode and a drain electrode) of the transistor 4610 is connected to the pixel electrode of the light-emitting element 4617, and a second electrode (the other of the source electrode and the drain electrode) is connected to the pixel 4617 through a second switch 4612. The gate electrode is connected to the power supply line 4622 through the third switch 4613 and the second switch 4612. Note that the third switch 4613 is connected between the gate electrode of the transistor 4610 and the second switch 4612.

  Further, when a connection position between the gate electrode of the transistor 4610 and the third switch 4613 is a node 4630, the node 4630 is connected to the signal line 4618 through the first capacitor element 4615 and the first switch 4611. In other words, the first electrode of the first capacitor 4615 is connected to the signal line 4618 through the first switch 4611, and the second electrode is connected to the gate electrode of the transistor 4610. The first electrode of the first capacitor element 4615 is also connected to the potential supply line 4623 through the fourth switch 4614. The node 4630 is further connected to the first electrode of the transistor 4610 through the second capacitor 4616. In other words, the first electrode of the second capacitor 4616 is connected to the gate electrode of the transistor 4610 and the second electrode is connected to the first electrode of the transistor 4610. These capacitor elements may be formed by sandwiching an insulating film with a wiring, a semiconductor layer, or an electrode. In some cases, the gate capacitor of the transistor 4610 may be used and the second capacitor element 4616 may be omitted. .

  Note that by inputting a signal to the first scan line 4619, the second scan line 4620, and the third scan line 4621, the first switch 4611, the second switch 4612, the third switch 4613, and the third scan line 4621, respectively. The on / off state of the fourth switch 4614 is controlled.

  A signal in accordance with the gradation of a pixel corresponding to a video signal, that is, a potential corresponding to luminance data is input to the signal line 4618.

  Next, the operation of the pixel shown in FIG. 46 will be described with reference to the timing chart of FIG. 47 and FIG. In FIG. 47, one frame period corresponding to a period for displaying an image for one screen is divided into an initialization period, a threshold voltage writing period, a data writing period, and a light emission period. The initialization period, threshold voltage writing period, and data writing period are collectively referred to as an address period. There is no particular limitation on the period of one frame, but it is preferable to set it to at least 1/60 second or less so that a person viewing the image does not feel flicker.

Note that a potential V1 (V1: any number) is input to the counter electrode 4624 of the light-emitting element 4617. Further, when a potential difference at least necessary for the light-emitting element 4617 to emit light is V _EL , a potential of V1−V _EL − | Vth | −α (α: any positive number) is input to the power supply line 4622. The In other words, the power supply line 4622 may have a potential equal to or lower than V1−V _EL − | Vth | −α. There is no particular limitation on the potential of the potential supply line 4623, but it is preferably within the range of potentials input to the panel in which the pixels are formed. This eliminates the need for a separate power source. Note that here, the potential of the potential supply line 4623 is set to V2.

First, as shown in FIGS. 47A and 48A, in the initialization period, the first switch 4611 is turned off, and the second switch 4612, the third switch 4613, and the fourth switch 4614 are turned on. And At this time, the transistor 4610 is in a conductive state, and V1-V _EL − | Vth | −α−V2 is held in the first capacitor element 4615, and | Vth | + α is held in the second capacitor element 4616. Note that in the initialization period, the first capacitor element 4615 may hold a predetermined voltage, and the second capacitor element 4616 may hold a voltage having an absolute value higher than at least | Vth |.

  In the threshold voltage writing period shown in FIGS. 47B and 48B, the second switch 4612 is turned off. Therefore, the gate electrode of the transistor 4610 gradually rises, and the transistor 4610 is turned off when the gate-source voltage Vgs of the transistor 4610 reaches the threshold voltage | Vth |. Therefore, the voltage Vc2 held in the second capacitor element 4616 is approximately | Vth |.

In the subsequent data writing period shown in FIGS. 2C and 3C, after the third switch 4613 and the fourth switch 4614 are turned off, the first switch 4611 is turned on and the signal line 4618 is turned on. A potential (V2-Vdata) corresponding to the luminance data is input. At this time, the voltage Vc2 held in the second capacitor element 4616 is C3> when the capacitances of the first capacitor element 4615, the second capacitor element 4616, and the light emitting element 4617 are C1, C2, and C3, respectively. > From C1 and C2, it can be expressed as in equation (4).

  Note that C1 and C2 are necessary when determining the potential supplied from the signal line 4618, but their relationship is not particularly limited. Note that in the case of C1> C2, the power consumption can be reduced because the amplitude of Vdata accompanying the change in luminance can be reduced. On the other hand, when C2> C1, it is possible to suppress changes in Vc2 due to on / off of surrounding switches and off-current. From these contradictory effects, it is preferable that C1 and C2 are equal, and the first capacitor element 4615 and the second capacitor element 4616 have the same size.

  Note that when the light-emitting element 4617 does not emit light in the next light-emitting period, a potential of Vdata ≦ 0 may be input.

  Next, in the light emission period shown in FIGS. 47D and 48D, the first switch 4611 is turned off and then the second switch 4612 is turned on. At this time, the gate-source voltage of the transistor 4610 is Vgs = − | Vth | −Vdata × (C1 / (C1 + C2)), and a current corresponding to the luminance data flows to the transistor 4610 and the light-emitting element 4617. Emits light. Of course, the potential corresponding to the luminance data input from the signal line 4618 is Vdata considering that the gate-source voltage of the transistor 4610 is Vgs = − | Vth | −Vdata × (C1 / (C1 + C2)). Need to be determined.

Note that the current I flowing through the light-emitting element 4617 is expressed by Expression (5) when the transistor 4610 is operated in the saturation region.

Since the transistor 4610 is a P-channel transistor, Vth <0. Therefore, equation (5) can be transformed into equation (6).

In addition, when the transistor 4610 is operated in a linear region, a current I that flows through the light-emitting element is represented by Expression (7).

From Vth <0, equation (7) can be transformed into equation (8).

  Here, W is the channel width of the transistor 4610, L is the channel length, μ is the mobility, and Cox is the storage capacitance.

  From the equations (6) and (8), the current flowing through the light-emitting element 4617 does not depend on the threshold voltage (Vth) of the transistor 4610 when the operation region of the transistor 4610 is either the saturation region or the linear region. Accordingly, variation in current value due to variation in threshold voltage of the transistor 4610 can be suppressed, and current corresponding to luminance data can be supplied to the light-emitting element 4617.

  From the above, variation in luminance due to variation in threshold voltage of the transistor 4610 can be suppressed. In addition, since the counter electrode is operated at a constant potential, power consumption can be reduced.

Further, when the transistor 4610 is operated in the saturation region, variation in luminance due to deterioration of the light-emitting element 4617 can be suppressed. When the light-emitting element 4617 deteriorates, V _{EL of the} light-emitting element 4617 increases, and the potential of the first electrode of the transistor 4610, that is, the source electrode decreases. At this time, the source electrode of the transistor 4610 is connected to the second electrode of the second capacitor element 4616, the gate electrode of the transistor 4610 is connected to the first electrode of the second capacitor element 4616, and the gate electrode side is It is floating. Therefore, as the source potential decreases, the gate potential of the transistor 4610 also decreases by the same potential. Accordingly, since Vgs of the transistor 4610 does not change, even if the light-emitting element is deteriorated, current flowing in the transistor 4610 and the light-emitting element 4617 is not affected. Note that also in Equation (6), the current I flowing through the light-emitting element does not depend on the source potential or the drain potential.

  Thus, when the transistor 4610 is operated in the saturation region, variation in threshold voltage of the transistor 4610 and variation in current flowing to the transistor 4610 due to deterioration of the light-emitting element 4617 can be suppressed.

  Note that in the case where the transistor 4610 is operated in the saturation region, it is preferable that the channel length L of the transistor 4610 be long in order to suppress increase in current amount due to breakdown phenomenon or channel length modulation.

  As described above, since variation in current value due to variation in threshold voltage of a transistor can be suppressed, the supply destination of current controlled by the transistor is not particularly limited in the present invention. Therefore, as the light-emitting element 4617 illustrated in FIG. 46, an EL element (an organic EL element, an inorganic EL element, or an EL element including an organic substance and an inorganic substance) can be typically used. Further, instead of the light-emitting element 4617, an electron-emitting element, a liquid crystal element, electronic ink, or the like can be used. FIG. 49 shows an example in which an EL element 4917 is used as the light-emitting element 4617. FIG. 49 shows a state in which current flows from the counter electrode 4624 to the pixel electrode 4911.

  Further, since the transistor 4610 only needs to have a function of controlling a current value supplied to the light-emitting element 4617, the type thereof is not particularly limited, and various types can be used. For example, a thin film transistor (TFT) using a crystalline semiconductor film, a thin film transistor using a non-single crystal semiconductor film typified by amorphous silicon or polycrystalline silicon, a transistor formed using a semiconductor substrate or an SOI substrate, MOS The transistor 4610 can be a type transistor, a junction transistor, a bipolar transistor, a transistor using a compound semiconductor such as ZnO or a-InGaZnO, a transistor using an organic semiconductor or a carbon nanotube, or the like.

  The first switch 4611 selects a potential corresponding to luminance data, that is, a timing at which a signal is input to the pixel from the signal line 4618, and mainly includes a voltage held in the first capacitor 4615 and a second capacitor 4616. , That is, the voltage between the gate and the source of the transistor 4610 is changed. The second switch 4612 selects timing for supplying a predetermined potential to the second electrode of the transistor 4610. Note that in some cases, the predetermined potential is supplied to the second electrode of the first capacitor element 4615 and the first electrode of the second capacitor element 4616. The third switch 4613 controls connection between the gate electrode and the second electrode of the transistor 4610. The fourth switch 4614 causes the first capacitor element 4615 to hold a predetermined voltage every frame period. The timing is selected and whether or not a predetermined potential is supplied to the first electrode of the first capacitor element 4615 is controlled. Therefore, the first switch 4611, the second switch 4612, the third switch 4613, and the fourth switch 4614 are not particularly limited as long as they have the above functions. For example, a transistor or a diode may be used, or a logic circuit combining them may be used. Note that the first switch 4611, the second switch 4612, and the fourth switch 4614 are not particularly required as long as a signal or a potential can be supplied to the pixel at the above timing. Further, the third switch 4613 is not particularly required as long as the above function can be realized.

  Note that when a transistor is used, the polarity (conductivity type) of the transistor is not particularly limited. However, it is preferable to use a transistor with low off-state current. As a transistor with low off-state current, there are a transistor provided with an LDD region and a transistor having a multi-gate structure. Further, a CMOS switch may be used by using both an N channel type and a P channel type.

  For example, when a p-channel transistor is used for the first switch 4611, the second switch 4612, the third switch 4613, and the fourth switch 4614, the scan line that controls on / off of each switch is turned on. An L level signal is input when desired, and an H level signal is input when desired. In this case, since a pixel can be formed using only P-channel transistors, the manufacturing process can be simplified.

  Further, the pixels shown in this embodiment can be applied to the display device of FIG. 7, and, as in the first embodiment, if the data writing period in each row does not overlap, the initialization start time can be freely set in each row. Can do. Further, since each pixel can emit light except its own address period, the ratio of the light emission period in one frame period (that is, the duty ratio) can be very large, and can be almost 100%. Therefore, a display device with a small luminance variation and a high duty ratio can be obtained.

  Further, since the threshold voltage writing period can be set long, the threshold voltage of the transistor that controls the value of the current flowing through the light-emitting element can be written into the capacitor more accurately. Therefore, the reliability as a display device is improved.

  Note that this embodiment mode can be freely combined with the pixel structures shown in the other embodiment modes. For example, a rectifier element may be used for the fourth switch 4614 as in the second embodiment, or the potential supply line 4623 may be replaced with another wiring as in the third and fourth embodiments. The transistor 4610 can have the structure of the transistor described in any of Embodiments 5 and 6. In addition, the configuration and operation described in Embodiment 7 can be applied. The transistor 4610 described in this embodiment is not limited to these, and can be applied to the pixels described in the other embodiments.

  However, the direction of the current flowing through the rectifying element needs to be varied depending on the polarity of the transistor that controls the current flowing through the light emitting element. For example, the case where a rectifying element is used to provide an erasing period will be described with reference to FIG.

  In the case where the transistor 4610 is a P-channel transistor, the rectifier element 5001 is connected so that current flows from the fourth scan line 5002 to the node 4630. The fourth scanning line 5002 receives an H level signal only when the transistor 4610 is forcibly turned off, and receives an L level signal otherwise. When the fourth scan line 5002 is at the L level, no current flows through the rectifier element 5001, and when it is at the H level, a current flows from the fourth scan line 5002 to the node 4630. In this manner, the current flows to the node 4630, whereby the gate potential of the transistor 4610 is increased, the gate-source voltage of the transistor 4610 is set to be equal to or lower than the threshold voltage (| Vth |), and the transistor 4610 is forcibly turned off. . By such an operation, a black display is inserted and an afterimage becomes difficult to see, and the moving image characteristics can be improved.

(Embodiment 9)
In this embodiment, one embodiment of a partial cross-sectional view of a pixel of the present invention is described with reference to FIG. Note that the transistor illustrated in the partial cross-sectional view in this embodiment is a transistor having a function of controlling a current value supplied to the light-emitting element.

  First, the base film 1712 is formed over the substrate 1711 having an insulating surface. As the substrate 1711 having an insulating surface, a glass substrate, a quartz substrate, a plastic substrate (polyimide, acrylic, polyethylene terephthalate, polycarbonate, polyarylate, polyethersulfone, etc.), an insulating substrate such as a ceramic substrate, a metal substrate (tantalum) In addition, an insulating film formed on the surface of a semiconductor substrate or the like can also be used. However, it is necessary to use a substrate that can withstand at least the heat generated during the process.

As the base film 1712, an insulating film such as a silicon oxide film, a silicon nitride film, or a silicon oxynitride film (SiO _x N _y ) is used, and these insulating films are formed as a single layer or two or more layers. Note that the base film 1712 may be formed by a sputtering method, a CVD method, or the like. In this embodiment, the base film 1712 is a single layer, but of course, two or more layers may be used.

  Next, a transistor 1713 is formed over the base film 1712. The transistor 1713 includes at least a semiconductor layer 1714, a gate insulating film 1715 formed over the semiconductor layer 1714, and a gate electrode 1716 formed over the semiconductor layer 1714 with the gate insulating film 1715 interposed therebetween. 1714 has a source region and a drain region.

  The semiconductor layer 1714 includes an amorphous semiconductor (a-Si: H), an amorphous semiconductor mainly containing silicon, silicon germanium (SiGe), or the like, and a semi-amorphous semiconductor in which an amorphous state and a crystalline state are mixed. A microcrystalline semiconductor capable of observing crystal grains of 0.5 nm to 20 nm in an amorphous semiconductor or a crystalline semiconductor film such as polysilicon (p-Si: H) can be used. Note that a microcrystalline state in which crystal grains of 0.5 nm to 20 nm can be observed is called a so-called microcrystal. For example, when an amorphous semiconductor film is used for the semiconductor layer 1714, it may be formed by sputtering, CVD, or the like. When a crystalline semiconductor film is used, for example, an amorphous semiconductor film is formed. Further crystallization may be performed later. If necessary, a small amount of impurity elements (phosphorus, arsenic, boron, etc.) may be included in addition to the main component in order to control the threshold voltage of the transistor.

  Next, a gate insulating film 1715 is formed so as to cover the semiconductor layer 1714. The gate insulating film 1715 is formed by stacking a single layer or a plurality of films using, for example, silicon oxide, silicon nitride, silicon nitride oxide, or the like. Note that a CVD method, a sputtering method, or the like can be used as a film formation method.

  Subsequently, a gate electrode 1716 is formed over the semiconductor layer 1714 with a gate insulating film 1715 interposed therebetween. The gate electrode 1716 may be formed as a single layer or a stack of a plurality of metal films. The gate electrode was selected from tantalum (Ta), tungsten (W), titanium (Ti), molybdenum (Mo), aluminum (Al), copper (Cu), chromium (Cr), niobium (Nb), and the like. It can be formed of an element or an alloy material or a compound material containing these elements as main components. For example, tantalum nitride may be used as the first conductive layer and tungsten (W) may be used as the second conductive layer, and the gate electrode may be formed of a first conductive film and a second conductive film.

  Next, an impurity imparting n-type or p-type conductivity is selectively added to the semiconductor layer 1714 using the gate electrode 1716 or a resist formed in a desired shape as a mask. In this manner, a channel formation region and an impurity region (including a source region, a drain region, a GOLD region, and an LDD region) are formed in the semiconductor layer 1714. In addition, an n-channel transistor or a p-channel transistor can be distinguished from each other depending on the conductivity type of the added impurity element.

  In FIG. 17, in order to manufacture the LDD region 1720 in a self-aligned manner, a silicon compound such as a silicon oxide film, a silicon nitride film, or a silicon oxynitride film is formed so as to cover the gate electrode 1716, and then etched back. Thus, a sidewall 1717 is formed. After that, an impurity imparting conductivity is added to the semiconductor layer 1714, whereby the source region 1718, the drain region 1719, and the LDD region 1720 can be formed. Therefore, the LDD region 1720 is located below the sidewall 1717. Note that the sidewall 1717 is provided in order to form the LDD region 1720 in a self-aligning manner, and is not necessarily provided. Note that phosphorus, arsenic, boron, or the like is used as the impurity imparting conductivity.

Next, a first insulating film 1721 and a second insulating film 1722 are stacked and formed as the first interlayer insulating film 1730 so as to cover the gate electrode 1716. As the first insulating film 1721 and the second insulating film 1722, an inorganic insulating film such as a silicon oxide film, a silicon nitride film, or a silicon oxynitride film (SiO _x N _y ), or an organic resin film having a low dielectric constant (photosensitive) Or non-photosensitive organic resin film) can be used. Alternatively, a film containing siloxane may be used. Note that siloxane is a material having a skeleton structure formed of a bond of silicon (Si) and oxygen (O), and an organic group (for example, an alkyl group or aromatic hydrocarbon) is used as a substituent. Further, the substituent may contain a fluoro group.

  Note that an insulating film of the same material may be used for the first insulating film 1721 and the second insulating film 1722. In this embodiment, the first interlayer insulating film 1730 has a two-layer structure, but may have a single layer structure or a three-layer structure or more.

  Note that the first insulating film 1721 and the second insulating film 1722 may be formed by a sputtering method, a CVD method, a spin coating method, or the like. When an organic resin film or a film containing siloxane is used, a coating method is used. What is necessary is just to form using.

  Thereafter, a source electrode and a drain electrode 1723 are formed over the first interlayer insulating film 1730. Note that the source electrode and the drain electrode 1723 are connected to a source region 1718 and a drain region 1719 through contact holes, respectively.

  Note that the source and drain electrodes 1723 are formed of silver (Ag), gold (Au), copper (Cu), nickel (Ni), platinum (Pt), palladium (Pd), iridium (Ir), rhodium (Rh), Tungsten (W), aluminum (Al), tantalum (Ta), molybdenum (Mo), cadmium (Cd), zinc (Zn), iron (Fe), titanium (Ti), silicon (Si), germanium (Ge), A metal such as zirconium (Zr), barium (Ba), neodymium (Nd) or an alloy thereof, a metal nitride thereof, or a stacked film thereof can be used.

  Next, a second interlayer insulating film 1731 is formed so as to cover the source and drain electrodes 1723. As the second interlayer insulating film 1731, an inorganic insulating film, a resin film, or a stacked layer thereof can be used. As the inorganic insulating film, a silicon nitride film, a silicon oxide film, a silicon oxynitride film, or a film in which these are stacked can be used. As the resin film, polyimide, polyamide, acrylic, polyimide amide, epoxy, or the like can be used.

  A pixel electrode 1724 is formed over the second interlayer insulating film 1731. Next, an insulator 1725 is formed so as to cover an end portion of the pixel electrode 1724. The insulator 1725 is preferably formed so that the upper end portion or the lower end portion of the insulator 1725 has a curved surface in order to improve the formation of the layer 1726 containing a light-emitting substance to be formed later. For example, in the case where positive photosensitive acrylic is used as a material for the insulator 1725, it is preferable that only the upper end portion of the insulator 1725 has a curved surface with a curvature radius (0.2 μm to 3 μm). As the insulator 1725, either a negative type that becomes insoluble in an etchant by photosensitive light or a positive type that becomes soluble in an etchant by light can be used. Furthermore, the material of the insulator 1725 is not limited to an organic material, and an inorganic material such as silicon oxide or silicon oxynitride can also be used.

  Next, a layer 1726 containing a light-emitting substance and a counter electrode 1727 are formed over the pixel electrode 1724 and the insulator 1725.

  Note that a light-emitting element 1728 is formed in a region where the layer 1726 containing a light-emitting substance is sandwiched between the pixel electrode 1724 and the counter electrode 1727.

  Next, details of the light-emitting element 1728 will be described with reference to FIGS. Note that the pixel electrode 1724 and the counter electrode 1727 in FIG. 17 correspond to the pixel electrode 1801 and the counter electrode 1802 in FIG. 18, respectively. In FIG. 18A, the pixel electrode is an anode and the counter electrode is a cathode.

  As shown in FIG. 18A, between the pixel electrode 1801 and the counter electrode 1802, in addition to the light emitting layer 1813, a hole injection layer 1811, a hole transport layer 1812, an electron transport layer 1814, and an electron injection layer 1815. Etc. are also provided. In these layers, holes are injected from the pixel electrode 1801 side and electrons are injected from the counter electrode 1802 side when a voltage is applied so that the potential of the pixel electrode 1801 is higher than the potential of the counter electrode 1802. Are stacked.

  In such a light-emitting element, holes injected from the pixel electrode 1801 and electrons injected from the counter electrode 1802 are recombined in the light-emitting layer 1813 so that the light-emitting substance is excited. Then, light is emitted when the excited light-emitting substance returns to the ground state. Note that the light-emitting substance may be any substance that can obtain luminescence (electroluminescence).

  There is no particular limitation on the substance forming the light-emitting layer 1813, and a layer formed using only the light-emitting substance may be used. However, when concentration quenching occurs, a substance having an energy gap larger than that of the light-emitting substance ( A layer in which a light emitting substance is dispersed in a layer made of a host is preferable. Thereby, concentration quenching of the luminescent material can be prevented. Note that the energy gap is an energy difference between the lowest unoccupied molecular orbital (LUMO) level and the highest occupied molecular orbital (HOMO) level.

  There is no particular limitation on the light-emitting substance, and a substance that can emit light with a desired emission wavelength may be used. For example, to obtain red light emission, 4-dicyanomethylene-2-isopropyl-6- [2- (1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] -4H-pyran ( Abbreviation: DCJTI), 4-dicyanomethylene-2-methyl-6- [2- (1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] -4H-pyran (abbreviation: DCJT), 4 -Dicyanomethylene-2-tert-butyl-6- [2- (1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] -4H-pyran (abbreviation: DCJTB), periflanthene, 2,5 -Dicyano-1,4-bis [2- (10-methoxy-1,1,7,7-tetramethyljulolidin-9-yl) ethenyl] benzene, etc., emission spectrum from 600 nm to 680 nm It can be used and a substance which exhibits emission with a peak. When green light emission is desired, N, N′-dimethylquinacridone (abbreviation: DMQd), coumarin 6 or coumarin 545T, tris (8-quinolinolato) aluminum (abbreviation: Alq), N, N′-diphenyl A substance exhibiting light emission having a peak of an emission spectrum from 500 nm to 550 nm, such as quinacridone (abbreviation: DPQd), can be used. When blue light emission is desired, 9,10-bis (2-naphthyl) -tert-butylanthracene (abbreviation: t-BuDNA), 9,9′-bianthryl, 9,10-diphenylanthracene (abbreviation) : DPA), 9,10-bis (2-naphthyl) anthracene (abbreviation: DNA), bis (2-methyl-8-quinolinolato) -4-phenylphenolato-gallium (BGaq), bis (2-methyl-8) -Quinolinolato) -4-phenylphenolato-aluminum (BAlq) or the like can be used a substance that emits light having an emission spectrum peak from 420 nm to 500 nm.

There is no particular limitation on a substance used for dispersing the light-emitting substance, for example, an anthracene derivative such as 9,10-di (2-naphthyl) -2-tert-butylanthracene (abbreviation: t-BuDNA), or In addition to carbazole derivatives such as 4,4′-bis (N-carbazolyl) biphenyl (abbreviation: CBP), bis [2- (2-hydroxyphenyl) pyridinato] zinc (abbreviation: Znpp ₂ ), bis [2- (2 Metal complexes such as -hydroxyphenyl) benzoxazolate] zinc (abbreviation: ZnBOX) can be used.

  The anode material for forming the pixel electrode 1801 is not particularly limited, but it is preferable to use a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like having a high work function (work function of 4.0 eV or more). Specific examples of such an anode material include indium tin oxide (abbreviation: ITO), ITO containing silicon oxide (abbreviation: ITSO), and indium oxide 2 to 20 wt% as an oxide of a metal material. In addition to indium zinc oxide (abbreviation: IZO) formed using a target mixed with zinc oxide (ZnO), gold (Au), platinum (Pt), nickel (Ni), tungsten (W), chromium ( Examples thereof include Cr), molybdenum (Mo), iron (Fe), cobalt (Co), copper (Cu), palladium (Pd), or a nitride of a metal material (for example, titanium nitride).

  On the other hand, as a material for forming the counter electrode 1802, a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like having a low work function (work function of 3.8 eV or less) can be used. Specific examples of such a cathode material include elements belonging to Group 1 or Group 2 of the periodic table, that is, alkali metals such as lithium (Li) and cesium (Cs), magnesium (Mg), calcium (Ca), strontium ( Alkaline earth metals such as Sr) and alloys containing them (Mg: Ag, Al: Li). In addition, by providing a layer having excellent electron-injecting properties between the counter electrode 1802 and the light-emitting layer 1813 so as to be stacked with the counter electrode, Al, Ag, ITO, or silicon oxide can be used regardless of the work function. Various conductive materials including the materials mentioned as the material of the pixel electrode 1801 such as ITO can be used as the counter electrode 1802. Further, the same effect can be obtained by using a material having an excellent function of injecting electrons for the electron injection layer 1815 described later.

  Note that in order to extract emitted light to the outside, one or both of the pixel electrode 1801 and the counter electrode 1802 are formed with a transparent electrode such as ITO, or with a thickness of several to several tens of nm so that visible light can be transmitted. It is preferable that the electrode is made.

  A hole transport layer 1812 is provided between the pixel electrode 1801 and the light emitting layer 1813 as shown in FIG. The hole transport layer is a layer having a function of transporting holes injected from the pixel electrode 1801 to the light emitting layer 1813. In this manner, by providing the hole transport layer 1812 and separating the pixel electrode 1801 and the light-emitting layer 1813, it is possible to prevent the light emission from being quenched due to the metal.

Note that the hole-transport layer 1812 is preferably formed using a substance having a high hole-transport property, and particularly, a substance having a hole mobility of 1 × 10 ⁻⁶ cm ² / Vs or higher. It is preferable. Note that a substance having a high hole-transport property refers to a substance having a higher hole mobility than electrons. Specific examples of a substance that can be used for forming the hole-transport layer 1812 include 4,4′-bis [N- (1-naphthyl) -N-phenylamino] biphenyl (abbreviation: NPB), 4, 4′-bis [N- (3-methylphenyl) -N-phenylamino] biphenyl (abbreviation: TPD), 4,4 ′, 4 ″ -tris (N, N-diphenylamino) triphenylamine (abbreviation: TDATA), 4,4 ′, 4 ″ -tris [N- (3-methylphenyl) -N-phenylamino] triphenylamine (abbreviation: MTDATA), 4,4′-bis {N- [4- ( N, N-di-m-tolylamino) phenyl] -N-phenylamino} biphenyl (abbreviation: DNTPD), 1,3,5-tris [N, N-di (m-tolyl) amino] benzene (abbreviation: m -MTDAB), 4, 4 ', 4 " Tris (N- carbazolyl) triphenylamine (abbreviation: TCTA), phthalocyanine _{(abbreviation:} H 2 Pc), copper phthalocyanine (abbreviation: CuPc), or vanadyl phthalocyanine (abbreviation: VOPc), and the like. Further, the hole transport layer 1812 may be a layer having a multilayer structure formed by combining two or more layers made of the above-described substances.

  Further, an electron transport layer 1814 may be provided between the counter electrode 1802 and the light emitting layer 1813 as shown in FIG. Here, the electron transporting layer is a layer having a function of transporting electrons injected from the counter electrode 1802 to the light emitting layer 1813. In this manner, by providing the electron transport layer 1814 and separating the counter electrode 1802 and the light emitting layer 1813, it is possible to prevent light emission from being quenched due to the metal of the electrode material.

The electron-transport layer 1814 is not particularly limited, and tris (8-quinolinolato) aluminum (abbreviation: Alq), tris (4-methyl-8-quinolinolato) aluminum (abbreviation: Almq ₃ ), bis (10-hydroxybenzo [h] -Quinolinato) beryllium (abbreviation: BeBq ₂ ), bis (2-methyl-8-quinolinolato) -4-phenylphenolato-aluminum (abbreviation: BAlq), and the like, formed by a metal complex having a quinoline skeleton or a benzoquinoline skeleton Can be used. In addition, bis [2- (2-hydroxyphenyl) -benzoxazolate] zinc (abbreviation: Zn (BOX) ₂ ), bis [2- (2-hydroxyphenyl) -benzothiazolate] zinc (abbreviation: Zn (BTZ) ) ₂ ) and the like may be formed by a metal complex having an oxazole-based or thiazole-based ligand. In addition, 2- (4-biphenylyl) -5- (4-tert-butylphenyl) -1,3,4-oxadiazole (abbreviation: PBD), 1,3-bis [5- (p-tert- Butylphenyl) -1,3,4-oxadiazol-2-yl] benzene (abbreviation: OXD-7), 3- (4-tert-butylphenyl) -4-phenyl-5- (4-biphenylyl)- 1,2,4-triazole (abbreviation: TAZ), 3- (4-tert-butylphenyl) -4- (4-ethylphenyl) -5- (4-biphenylyl) -1,2,4-triazole (abbreviation) : P-EtTAZ), bathophenanthroline (abbreviation: BPhen), bathocuproin (abbreviation: BCP), or the like. The electron transport layer 1814 is preferably formed using a substance having higher electron mobility than the hole mobility described above. The electron transport layer 1814 is more preferably formed using a substance having an electron mobility of 10 ⁻⁶ cm ² / Vs or higher. Note that the electron-transport layer 1814 may have a multilayer structure formed by combining two or more layers formed of the substances described above.

  Further, a hole injection layer 1811 may be provided between the pixel electrode 1801 and the hole transport layer 1812 as shown in FIG. Here, the hole injection layer is a layer having a function of promoting injection of holes from the electrode functioning as an anode into the hole transport layer 1812.

There is no particular limitation on the hole-injecting layer 1811, and a layer formed of a metal oxide such as molybdenum oxide, vanadium oxide, ruthenium oxide, tungsten oxide, or manganese oxide can be used. In addition, phthalocyanine compounds such as phthalocyanine (abbreviation: H ₂ Pc) and copper phthalocyanine (CuPc), 4,4-bis (N- (4- (N, N-di-m-tolylamino) phenyl) -N -Hole injection by aromatic amine compounds such as phenylamino) biphenyl (abbreviation: DNTPD) or polymers such as poly (ethylenedioxythiophene) / poly (styrenesulfonic acid) aqueous solution (PEDOT / PSS) A layer 1811 can be formed.

  In addition, a mixture of the metal oxide and a substance having a high hole-transport property may be provided between the pixel electrode 1801 and the hole-transport layer 1812. Such a layer does not increase the driving voltage even when it is thickened, so that the optical design utilizing the microcavity effect and the light interference effect can be performed by adjusting the film thickness of the layer. Therefore, a high-quality light-emitting element with excellent color purity and a small color change depending on the viewing angle can be manufactured. In addition, a film thickness that prevents the pixel electrode 1801 and the counter electrode 1802 from being short-circuited by the influence of unevenness generated during the film formation on the surface of the pixel electrode 1801 or a minute residue remaining on the electrode surface can be selected.

  Further, an electron injection layer 1815 may be provided between the counter electrode 1802 and the electron transport layer 1814 as shown in FIG. Here, the electron injection layer is a layer having a function of promoting injection of electrons from the electrode functioning as a cathode into the electron transport layer 1814. Note that in the case where the electron transport layer is not particularly provided, an electron injection layer may be provided between the electrode functioning as a cathode and the light emitting layer to assist the injection of electrons into the light emitting layer.

The electron injection layer 1815 is not particularly limited, and is formed using an alkali metal or alkaline earth metal compound such as lithium fluoride (LiF), cesium fluoride (CsF), calcium fluoride (CaF ₂ ), or the like. Things can be used. In addition, a substance having a high electron transport property such as Alq or 4,4-bis (5-methylbenzoxazol-2-yl) stilbene (BzOs), and an alkali metal or alkaline earth such as magnesium or lithium. A material mixed with a similar metal can also be used as the electron injection layer 1815.

  Note that the hole injection layer 1811, the hole transport layer 1812, the light-emitting layer 1813, the electron transport layer 1814, and the electron injection layer 1815 can be formed by any method such as an evaporation method, an inkjet method, or a coating method, respectively. I do not care. Further, the pixel electrode 1801 or the counter electrode 1802 may be formed by any method such as a sputtering method or an evaporation method.

  In addition, the layer structure of the light-emitting element is not limited to that illustrated in FIG. 18A, and may be sequentially formed from an electrode functioning as a cathode as illustrated in FIG. In other words, the pixel electrode 1801 is used as a cathode, and an electron injection layer 1815, an electron transport layer 1814, a light emitting layer 1813, a hole transport layer 1812, a hole injection layer 1811, and a counter electrode 1802 are stacked in this order on the pixel electrode 1801. good. Note that the counter electrode 1802 functions as an anode.

  Note that although the light-emitting element has a single light-emitting layer, it may have a plurality of light-emitting layers. White light can be obtained by providing a plurality of light emitting layers and mixing light emitted from the respective light emitting layers. For example, in the case of a light-emitting element having two light-emitting layers, an interval layer, a layer that generates holes, and a layer that generates electrons may be provided between the first light-emitting layer and the second light-emitting layer. preferable. With such a configuration, each light emitted to the outside is visually mixed and visually recognized as white light. Therefore, white light can be obtained.

  Light emission is extracted to the outside through one or both of the pixel electrode 1724 and the counter electrode 1727 in FIG. Accordingly, one or both of the pixel electrode 1724 and the counter electrode 1727 are formed using a light-transmitting substance.

  When only the counter electrode 1727 is made of a light-transmitting substance, light emission is extracted from the opposite side of the substrate through the counter electrode 1727 as shown in FIG. In the case where only the pixel electrode 1724 is made of a light-transmitting substance, light emission is extracted from the substrate side through the pixel electrode 1724 as shown in FIG. In the case where both the pixel electrode 1724 and the counter electrode 1727 are made of a light-transmitting substance, light emission passes through the pixel electrode 1724 and the counter electrode 1727 as shown in FIG. Taken from both sides.

  The wiring and electrodes are not limited to the materials described above, but are aluminum (Al), tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten (W), neodymium (Nd), chromium (Cr), nickel (Ni ), Platinum (Pt), gold (Au), silver (Ag), copper (Cu), magnesium (Mg), scandium (Sc), cobalt (Co), zinc (Zn), niobium (Nb), silicon (Si) ), Phosphorus (P), boron (B), arsenic (As), gallium (Ga), indium (In), tin (Sn) or the like, or selected from the above group Compound or alloy material containing one or more elements as components (for example, indium tin oxide (ITO), indium zinc oxide (IZO), ITO containing silicon oxide (ITSO), zinc oxide (Zn ), Aluminum neodymium (Al-Nd), magnesium silver (Mg-Ag), etc.), or it can be formed using a combination material such these compounds. Alternatively, a compound of these elements and silicon (silicide) (eg, aluminum silicon, molybdenum silicon, nickel silicide, or the like) or a compound of nitrogen (eg, titanium nitride, tantalum nitride, molybdenum nitride, or the like) may be used. . Note that silicon (Si) may contain a large amount of n-type impurities (such as phosphorus) and p-type impurities (such as boron). By containing these impurities, the conductivity is improved, and it becomes easy to use as a wiring or an electrode. Note that any of single crystal, polycrystalline (polysilicon), and amorphous (amorphous silicon) may be used for silicon. When single crystal silicon or polycrystalline silicon is used, the resistance can be reduced, and amorphous silicon can be manufactured by a simple manufacturing process.

  When aluminum or silver is used, signal delay can be reduced because of high conductivity. Further, since etching is easy, patterning is easy and fine processing can be performed. Also in copper, since the conductivity is high, signal delay can be reduced. Molybdenum can be produced without causing problems such as material defects even when it comes into contact with an oxide semiconductor such as ITO or IZO or silicon. Further, it is desirable because it is easy to perform patterning and etching and has excellent heat resistance. Titanium is also desirable because it can be manufactured without causing problems such as defective materials even when it comes into contact with oxide semiconductors such as ITO and IZO and silicon, and has excellent heat resistance. Tungsten and neodymium are desirable because they have excellent heat resistance. When neodymium is alloyed with aluminum, the heat resistance is improved and hillocks of aluminum can be suppressed. Silicon can be formed at the same time as a semiconductor layer included in a transistor and has high heat resistance. Indium tin oxide (ITO), indium zinc oxide (IZO), ITO containing silicon oxide (ITSO), zinc oxide (ZnO), and silicon (Si) are light-transmitting and thus transmit light. It is particularly desirable when used in such a portion, and these can be used as, for example, a pixel electrode or a common electrode.

  Note that the wirings and the electrodes are not limited to a single layer structure formed using the above materials, and may have a multilayer structure. For example, in the case of forming with a single layer structure, the manufacturing process can be simplified and the cost can be reduced. In the multilayer structure, the merit of each material can be utilized and the demerit can be reduced, so that wiring and electrodes having excellent performance can be formed. For example, the resistance of the wiring can be reduced by using a structure in which a material having low resistance (such as aluminum) is included in a part of the multilayer structure. Moreover, if it is configured to include a material having high heat resistance (for example, a laminated structure in which a material having low merit but having other merits is sandwiched between materials having high heat resistance), it has high heat resistance, In addition, it is possible to take advantage of the benefits that were not possible with a single layer. Therefore, for example, it is desirable to use a wiring or an electrode having a structure in which a layer containing aluminum is sandwiched between layers containing molybdenum or titanium.

  In addition, when there is a portion where the wiring or electrode is in direct contact with the wiring or electrode of another material, it may adversely affect each other. For example, one material may be mixed into the other material, changing the properties of each material, making it impossible to achieve its original purpose, or causing problems in manufacturing, and making it impossible to manufacture normally. . In such a case, it can be solved by sandwiching or covering a certain layer with another layer. For example, when it is desired to contact indium tin oxide (ITO) and aluminum, it is desirable to interpose titanium or molybdenum between them. Similarly, when it is desired to bring silicon and aluminum into contact, it is desirable to interpose titanium or molybdenum therebetween.

  Next, a transistor with a forward stagger structure in which an amorphous semiconductor film is used for the transistor 1713 as a semiconductor layer is described. A partial cross-sectional view of the pixel is shown in FIG. Note that in FIG. 20, a forward staggered transistor is shown, and a capacitor included in the pixel is also described.

  As illustrated in FIG. 20, a base film 2012 is formed over a substrate 2011. Further, a pixel electrode 2013 is formed on the base film 2012. A first electrode 2014 made of the same material is formed in the same layer as the pixel electrode 2013.

  Further, a wiring 2015 and a wiring 2016 are formed over the base film 2012, and an end portion of the pixel electrode 2013 is covered with the wiring 2015. Over the wiring 2015 and the wiring 2016, an N-type semiconductor layer 2017 and an N-type semiconductor layer 2018 having an N-type conductivity are formed. A semiconductor layer 2019 is formed over the base film 2012 between the wiring 2015 and the wiring 2016. A part of the semiconductor layer 2019 extends to the N-type semiconductor layer 2017 and the N-type semiconductor layer 2018. This semiconductor layer is formed of an amorphous semiconductor such as amorphous silicon (a-Si: H). Note that not only an amorphous semiconductor but also a semi-amorphous semiconductor, a microcrystalline semiconductor, or the like may be used. A gate insulating film 2020 is formed over the semiconductor layer 2019. An insulating film 2021 made of the same material and in the same layer as the gate insulating film 2020 is also formed over the first electrode 2014.

  Further, a gate electrode 2022 is formed over the gate insulating film 2020, and a transistor 2025 is formed. A second electrode 2023 made of the same material and in the same layer as the gate electrode 2022 is formed over the first electrode 2014 with an insulating film 2021 interposed therebetween, and the insulating film 2021 is formed of the first electrode 2014 and the second electrode 2023. A capacitor element 2024 having a structure sandwiched between and is formed. An interlayer insulating film 2026 is formed so as to cover the end portion of the pixel electrode 2013, the transistor 2025, and the capacitor 2024.

  A region 2027 containing a light emitting substance and a counter electrode 2028 are formed over the interlayer insulating film 2026 and the pixel electrode 2013 located in the opening, and the layer 2027 containing the light emitting substance is sandwiched between the pixel electrode 2013 and the counter electrode 2028. Thus, a light emitting element 2029 is formed.

  20A. The first electrode 2014 shown in FIG. 20A is formed of the same material in the same layer as the wirings 2015 and 2016 as shown in FIG. 20B, and the insulating film 2021 is formed with the first electrode 2030 and the second electrode. The capacitor 2031 may be sandwiched between the electrodes 2023. In FIG. 20, an N-channel transistor is used as the transistor 2025; however, a P-channel transistor may be used.

  The materials used for the substrate 2011, the base film 2012, the pixel electrode 2013, the gate insulating film 2020, the gate electrode 2022, the interlayer insulating film 2026, the light-emitting substance layer 2027, and the counter electrode 2028 are the same as those of the substrate 1711 described in FIG. The same materials as the base film 1712, the pixel electrode 1724, the gate insulating film 1715, the gate electrode 1716, the interlayer insulating films 1730 and 1731, the layer 1726 containing a light-emitting substance, and the counter electrode 1727 can be used, respectively. The wiring 2015 and the wiring 2016 may be formed using a material similar to that of the source and drain electrodes 1723 in FIG.

  Next, as another structure of a transistor using an amorphous semiconductor film as a semiconductor layer, a structure in which a gate electrode is sandwiched between a substrate and a semiconductor layer, that is, a bottom gate type in which the gate electrode is located under the semiconductor layer FIG. 21 is a partial cross-sectional view of a pixel having the above transistor.

  A base film 2112 is formed over the substrate 2111. Further, a gate electrode 2113 is formed over the base film 2112. A first electrode 2114 made of the same material is formed in the same layer as the gate electrode 2113. The material of the gate electrode 2113 may be polycrystalline silicon to which phosphorus is added or silicide which is a compound of metal and silicon, in addition to the material used for the gate electrode 1716 in FIG.

  A gate insulating film 2115 is formed so as to cover the gate electrode 2113 and the first electrode 2114.

  A semiconductor layer 2116 is formed over the gate insulating film 2115. In addition, a semiconductor layer 2117 made of the same material as the semiconductor layer 2116 is formed over the first electrode 2114. This semiconductor layer is formed of an amorphous semiconductor such as amorphous silicon (a-Si: H). Further, the present invention is not limited thereto, and a semi-amorphous semiconductor, a microcrystalline semiconductor, or the like may be used.

  An N-type semiconductor layer 2118 and an N-type semiconductor layer 2119 having an N-type conductivity are formed over the semiconductor layer 2116, and an N-type semiconductor layer 2120 is formed over the semiconductor layer 2117.

  A wiring 2121 and a wiring 2122 are formed over the N-type semiconductor layer 2118 and the N-type semiconductor layer 2119, respectively, and a transistor 2129 is formed. A conductive layer 2123 made of the same material as the wiring 2121 and the wiring 2122 is formed over the N-type semiconductor layer 2120, and the conductive layer 2123, the N-type semiconductor layer 2120, and the semiconductor layer 2117 are second layers. The electrode is comprised. Note that a capacitor 2130 having a structure in which the gate insulating film 2115 is sandwiched between the second electrode and the first electrode 2114 is formed.

  One end of the wiring 2121 extends, and a pixel electrode 2124 is formed in contact with the upper part of the extended wiring 2121.

  An insulator 2125 is formed so as to cover an end portion of the pixel electrode 2124, the transistor 2129, and the capacitor 2130.

  A layer 2126 containing a light-emitting substance and a counter electrode 2127 are formed over the pixel electrode 2124 and the insulator 2125, and a light-emitting element 2128 is formed in a region where the layer 2126 containing a light-emitting substance is sandwiched between the pixel electrode 2124 and the counter electrode 2127. Has been.

  The semiconductor layer 2117 and the N-type semiconductor layer 2120 which are part of the second electrode of the capacitor 2130 are not necessarily provided. That is, the capacitor may have a structure in which the second electrode is the conductive layer 2123 and the gate insulating film 2115 is sandwiched between the first electrode 2114 and the conductive layer 2123.

  Further, although an N-channel transistor is used as the transistor 2129, a P-channel transistor may be used.

  Note that in FIG. 21A, the pixel electrode 2124 is formed before the wiring 2121 is formed, so that the second electrode 2131 made of the same material as that of the pixel electrode 2124 as shown in FIG. A capacitor 2132 having a structure in which the gate insulating film 2115 is sandwiched between the first electrode 2114 and the first electrode 2114 may be formed.

  Although an inverted staggered channel etch transistor has been described, a channel protection transistor may of course be used. Next, the case of a transistor having a channel protective structure will be described with reference to FIGS. Note that in FIG. 22, the same components as those in FIG. 21 are denoted by common reference numerals.

  The transistor 2201 having a channel protection structure shown in FIG. 22A is different from the transistor 2129 having a channel etch structure shown in FIG. 21A in that an insulator serving as an etching mask over a region where a channel is formed in the semiconductor layer 2116. The difference is that 2202 is provided.

  Similarly, the transistor 2201 having a channel protection structure illustrated in FIG. 22B is different from the transistor 2129 having a channel etching structure illustrated in FIG. 21B in an etching mask over a region where a channel is formed in the semiconductor layer 2116. This is different in that an insulator 2202 is provided.

  By using an amorphous semiconductor film for a semiconductor layer of a transistor included in the pixel of the present invention, manufacturing cost can be reduced. In addition, what was demonstrated in FIG. 17 can be used for each material.

  Further, the structure of the transistor and the structure of the capacitor are not limited to those described above, and transistors and capacitors having various structures or configurations can be used.

  In addition, the semiconductor layer of the transistor includes an amorphous semiconductor such as amorphous silicon (a-Si: H), a semi-amorphous semiconductor, a semiconductor film made of a microcrystalline semiconductor, and a crystal such as polysilicon (p-Si: H). A conductive semiconductor film may be used.

  FIG. 23 is a partial cross-sectional view of a pixel including a transistor using a crystalline semiconductor film as a semiconductor layer, which will be described below. Note that the transistor 2318 illustrated in FIG. 23 is the multi-gate transistor illustrated in FIG.

  As shown in FIG. 23, a base film 2302 is formed on a substrate 2301, and a semiconductor layer 2303 is formed thereon. Note that the semiconductor layer 2303 is formed by patterning a crystalline semiconductor film into a desired shape.

  An example of a method for manufacturing a crystalline semiconductor film is described below. First, an amorphous silicon film is formed over the substrate 2301 by a sputtering method, a CVD method, or the like. Then, the amorphous silicon film thus formed is crystallized using a thermal crystallization method, a laser crystallization method, a thermal crystallization method using a catalyst element such as nickel, or the like to obtain a crystalline semiconductor film. In addition, you may crystallize combining these crystallization methods.

  The film to be crystallized is not necessarily limited to an amorphous semiconductor film such as an amorphous silicon film, and may be a semiconductor film such as a semi-amorphous semiconductor or a microcrystalline semiconductor. Alternatively, a compound semiconductor film including an amorphous structure such as an amorphous silicon germanium film may be used.

  In the case of forming a crystalline semiconductor film by a thermal crystallization method, a heating furnace, laser irradiation, RTA (Rapid Thermal Annealing), or a combination thereof can be used.

In the case of forming a crystalline semiconductor film by a laser crystallization method, a continuous wave laser beam (CW laser beam) or a pulsed laser beam (pulse laser beam) can be used. The laser beam that can be used here is a gas laser such as an Ar laser, a Kr laser, or an excimer laser, single crystal YAG, YVO ₄ , forsterite (Mg ₂ SiO ₄ ), YAlO ₃ , GdVO ₄ , or polycrystalline ( (Ceramics) YAG, Y ₂ O ₃ , YVO ₄ , YAlO ₃ , GdVO ₄ with one or more of Nd, Yb, Cr, Ti, Ho, Er, Tm, Ta added as dopants A laser oscillated from one or more of laser, glass laser, ruby laser, alexandrite laser, Ti: sapphire laser, copper vapor laser, or gold vapor laser as a medium can be used. By irradiating the fundamental wave of such a laser beam and the second to fourth harmonic laser beams of these fundamental waves, a crystal having a large grain size can be obtained. For example, a second harmonic (532 nm) or a third harmonic (355 nm) of an Nd: YVO ₄ laser (fundamental wave 1064 nm) can be used. Energy density of the laser is about 0.01 to 100 MW / cm ² (preferably 0.1 to 10 MW / cm ²⁾ is required. Then, irradiation is performed at a scanning speed of about 10 to 2000 cm / sec.

Note that single crystal YAG, YVO ₄ , forsterite (Mg ₂ SiO ₄ ), YAlO ₃ , GdVO ₄ , or polycrystalline (ceramic) YAG, Y ₂ O ₃ , YVO ₄ , YAlO ₃ , GdVO ₄ , dopants Nd, Yb, Cr, Ti, Ho, Er, Tm, and Ta, a laser using a medium added with one or more, an Ar ion laser, or a Ti: sapphire laser should be continuously oscillated. It is also possible to perform pulse oscillation at an oscillation frequency of 10 MHz or more by performing Q switch operation or mode synchronization. When the laser beam is oscillated at an oscillation frequency of 10 MHz or more, the semiconductor film is irradiated with the next pulse during the period from when the semiconductor film is melted by the laser to solidification. Therefore, unlike the case of using a pulse laser having a low oscillation frequency, the solid-liquid interface can be continuously moved in the semiconductor film, so that crystal grains continuously grown in the scanning direction can be obtained.

  In the case where a crystalline semiconductor film is formed by a thermal crystallization method using a catalyst element such as nickel, it is preferable to perform a gettering process for removing the catalyst element such as nickel after crystallization.

  By the above crystallization, a partially crystallized region is formed in the amorphous semiconductor film. This partially crystallized crystalline semiconductor film is patterned into a desired shape to form an island-shaped semiconductor film. This semiconductor film is used for the semiconductor layer 2303 of the transistor.

  The crystalline semiconductor layer is used for the channel formation region 2304 of the transistor 2318 and the impurity region 2305 to be a source region or a drain region, and also to the semiconductor layer 2306 and the impurity region 2308 to be a lower electrode of the capacitor 2319. . Note that the impurity region 2308 is not necessarily provided. In addition, channel doping may be performed on the channel formation region 2304 and the semiconductor layer 2306.

  Next, a gate insulating film 2309 is formed over the semiconductor layer 2303 and the lower electrode of the capacitor 2319. Further, a gate electrode 2310 is formed over the semiconductor layer 2303 through a gate insulating film 2309, and an upper electrode made of the same material as the gate electrode 2310 is formed over the semiconductor layer 2306 of the capacitor 2319 through the gate insulating film 2309. 2311 is formed. In this manner, the transistor 2318 and the capacitor 2319 are manufactured.

  Next, an interlayer insulating film 2312 is formed so as to cover the transistor 2318 and the capacitor 2319, and a wiring 2313 in contact with the impurity region 2305 is formed over the interlayer insulating film 2312 through a contact hole. A pixel electrode 2314 is formed on the interlayer insulating film 2312 so as to be in contact with the wiring 2313, and an insulator 2315 is formed so as to cover an end portion of the pixel electrode 2314 and the wiring 2313. Further, a layer 2316 containing a light-emitting substance and a counter electrode 2317 are formed over the pixel electrode 2314, and a light-emitting element 2320 is formed in a region where the layer 2316 containing a light-emitting substance is sandwiched between the pixel electrode 2314 and the counter electrode 2317. .

  FIG. 24 shows a partial cross section of a pixel having a bottom-gate transistor using a crystalline semiconductor film such as polysilicon (p-Si: H) as a semiconductor layer.

  A base film 2402 is formed over a substrate 2401, and a gate electrode 2403 is formed thereon. The first electrode 2404 of the capacitor 2423 made of the same material is formed in the same layer as the gate electrode 2403.

  Note that a gate insulating film 2405 is formed so as to cover the gate electrode 2403 and the first electrode 2404.

  A semiconductor layer is formed over the gate insulating film 2405. Note that the semiconductor film is formed using a thermal crystallization method, a laser crystallization method, or a thermal crystallization method using a catalytic element such as nickel. Crystallization and patterning into a desired shape form a semiconductor layer.

  With such a semiconductor layer, a channel formation region 2406, an LDD region 2407, and an impurity region 2408 that serves as a source region or a drain region of the transistor 2422, a region 2409 that serves as a second electrode of the capacitor 2423, an impurity region 2410, and an impurity Region 2411 is formed. Note that the impurity region 2410 and the impurity region 2411 are not necessarily provided. Further, an impurity may be added to the channel formation region 2406 and the region 2409.

  Note that the capacitor 2423 has a structure in which the gate insulating film 2405 is sandwiched between the first electrode 2404, the second electrode including the region 2409 formed of the semiconductor layer, and the like.

  Next, a first interlayer insulating film 2412 is formed to cover the semiconductor layer, and a wiring 2413 that is in contact with the impurity region 2408 through a contact hole is formed over the first interlayer insulating film 2412.

  An opening 2415 is formed in the first interlayer insulating film 2412. A second interlayer insulating film 2416 is formed so as to cover the transistor 2422, the capacitor 2423, and the opening 2415. A pixel electrode 2417 connected to the wiring 2413 through a contact hole is formed over the second interlayer insulating film 2416. Is formed. In addition, an insulator 2418 is formed to cover an end portion of the pixel electrode 2417. A layer 2419 containing a light-emitting substance and a counter electrode 2420 are formed over the pixel electrode 2417, and a light-emitting element 2421 is formed in a region where the layer 2419 containing a light-emitting substance is sandwiched between the pixel electrode 2417 and the counter electrode 2420. . Note that an opening 2415 is located below the light emitting element 2421. In other words, when light emitted from the light-emitting element 2421 is extracted from the substrate side, the transmittance can be increased because the opening 2415 is provided in the first interlayer insulating film 2412.

  By using a crystalline semiconductor film for a semiconductor layer of a transistor included in the pixel of the present invention, for example, the scan line driver circuit 712 and the signal line driver circuit 711 in FIG. 7 can be easily formed integrally with the pixel portion 713. .

  Note that the structure of a transistor including a crystalline semiconductor film as a semiconductor layer is not limited to the above structure, and various structures can be employed. The same applies to the capacitive element. Moreover, in this embodiment, the material in FIG. 17 can be used suitably unless there is particular notice.

  The transistor described in this embodiment can be used as a transistor for controlling a current value supplied to a light-emitting element in the pixel described in any of Embodiments 1 to 8. Therefore, by operating a pixel as described in Embodiments 1 to 8, variation in current value due to variation in threshold voltage of a transistor can be suppressed. Therefore, a current corresponding to the luminance data can be supplied to the light emitting element, and variations in luminance can be suppressed. In addition, since the counter electrode is operated at a constant potential, power consumption can be reduced.

  Further, by applying such a pixel to the display device of FIG. 7, each pixel can emit light except its own address period, and therefore the ratio of the light emission period in one frame period (that is, the duty ratio). Can be made very large and can be made to be almost 100%. Therefore, a display device with a small luminance variation and a high duty ratio can be obtained.

  Further, since the threshold voltage writing period can be set long, the threshold voltage of the transistor that controls the value of the current flowing through the light-emitting element can be written into the capacitor more accurately. Therefore, the reliability as a display device is improved.

(Embodiment 10)
In this embodiment, an element having a structure different from that of the light-emitting element described in Embodiment 9 will be described.

  A light-emitting element using electroluminescence is distinguished depending on whether a light-emitting material is an organic compound or an inorganic compound. Generally, the former is called an organic EL element and the latter is called an inorganic EL element.

  Inorganic EL elements are classified into a dispersion-type inorganic EL element and a thin-film inorganic EL element depending on the element structure. The former has a light-emitting layer in which particles of a light-emitting material are dispersed in a binder, and the latter has a light-emitting layer made of a thin film of the light-emitting material. It is common in the point that requires. Note that the obtained light emission mechanism includes donor-acceptor recombination light emission using a donor level and an acceptor level, and localized light emission using inner-shell electron transition of a metal ion. In general, the dispersion-type inorganic EL element often has donor-acceptor recombination light emission, and the thin-film inorganic EL element often has localized light emission.

  The light-emitting material used in this embodiment includes at least a base material and an impurity element (also referred to as a light-emitting substance) serving as a light emission center. By changing the impurity element to be contained, light emission of various colors can be obtained. As a method for manufacturing the light-emitting material, various methods such as a solid phase method and a liquid phase method (coprecipitation method) can be used. Also, spray pyrolysis method, metathesis method, precursor thermal decomposition method, reverse micelle method, method combining these methods with high temperature firing, liquid phase method such as freeze-drying method, etc. can be used.

  The solid phase method is a method in which a base material and an impurity element or a compound containing the impurity element are weighed, mixed in a mortar, heated and fired in an electric furnace, reacted, and the base material contains the impurity element. The firing temperature is preferably 700 to 1500 ° C. This is because the solid phase reaction does not proceed when the temperature is too low, and the base material is decomposed when the temperature is too high. In addition, although baking may be performed in a powder state, it is preferable to perform baking in a pellet state. Although firing at a relatively high temperature is required, it is a simple method, so it has high productivity and is suitable for mass production.

  The liquid phase method (coprecipitation method) is a method in which a base material or a compound containing the base material and an impurity element or a compound containing the impurity element are reacted in a solution, dried, and then fired. The particles of the luminescent material are uniformly distributed, and the reaction can proceed even at a low firing temperature with a small particle size.

As a base material used for the light-emitting material, sulfide, oxide, or nitride can be used. Examples of the sulfide include zinc sulfide (ZnS), cadmium sulfide (CdS), calcium sulfide (CaS), yttrium sulfide (Y ₂ S ₃ ), gallium sulfide (Ga ₂ S ₃ ), strontium sulfide (SrS), sulfide. Barium (BaS) or the like can be used. As the oxide, for example, zinc oxide (ZnO), yttrium oxide (Y ₂ O ₃ ), or the like can be used. As the nitride, for example, aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), or the like can be used. Furthermore, zinc selenide (ZnSe), zinc telluride (ZnTe), and the like can also be used, and calcium sulfide-gallium sulfide (CaGa ₂ S ₄ ), strontium sulfide-gallium sulfide (SrGa ₂ S ₄ ), barium sulfide-gallium (BaGa). _It may be a ternary mixed crystal such as ₂ S ₄ ).

  As emission centers of localized emission, manganese (Mn), copper (Cu), samarium (Sm), terbium (Tb), erbium (Er), thulium (Tm), europium (Eu), cerium (Ce), praseodymium (Pr) or the like can be used. Note that a halogen element such as fluorine (F) or chlorine (Cl) may be added as charge compensation.

  On the other hand, a light-emitting material containing a first impurity element that forms a donor level and a second impurity element that forms an acceptor level can be used as the emission center of donor-acceptor recombination light emission. As the first impurity element, for example, fluorine (F), chlorine (Cl), aluminum (Al), or the like can be used. For example, copper (Cu), silver (Ag), or the like can be used as the second impurity element.

In the case where a light-emitting material for donor-acceptor recombination light emission is synthesized using a solid-phase method, a base material, a first impurity element or a compound containing the first impurity element, a second impurity element, or a second impurity element Each compound containing an impurity element is weighed and mixed in a mortar, and then heated and fired in an electric furnace. As the base material, the above-described base material can be used, and examples of the first impurity element or the compound containing the first impurity element include fluorine (F), chlorine (Cl), and aluminum sulfide (Al ₂ S). ₃ ) or the like, and examples of the second impurity element or the compound containing the second impurity element include copper (Cu), silver (Ag), copper sulfide (Cu ₂ S), and silver sulfide (Ag). ₂ S) or the like can be used. The firing temperature is preferably 700 to 1500 ° C. This is because the solid phase reaction does not proceed when the temperature is too low, and the base material is decomposed when the temperature is too high. In addition, although baking may be performed in a powder state, it is preferable to perform baking in a pellet state.

  In addition, as an impurity element in the case of using a solid phase reaction, a compound including a first impurity element and a second impurity element may be used in combination. In this case, since the impurity element is easily diffused and the solid-phase reaction easily proceeds, a uniform light emitting material can be obtained. Further, since no extra impurity element is contained, a light-emitting material with high purity can be obtained. As the compound including the first impurity element and the second impurity element, for example, copper chloride (CuCl), silver chloride (AgCl), or the like can be used.

  Note that the concentration of these impurity elements may be 0.01 to 10 atom% with respect to the base material, and is preferably in the range of 0.05 to 5 atom%.

  In the case of a thin film type inorganic EL element, the light emitting layer is a layer containing the above light emitting material, and a physical vapor deposition method such as a vacuum evaporation method such as a resistance heating vapor deposition method or an electron beam vapor deposition (EB vapor deposition) method, or a sputtering method ( PVD), metal organic chemical vapor deposition (CVD), chemical vapor deposition (CVD) such as hydride transport low pressure CVD, atomic layer epitaxy (ALE), or the like.

  FIGS. 51A to 51C illustrate an example of a thin film inorganic EL element that can be used as a light-emitting element. 51A to 51C, the light-emitting element includes a first electrode 5101, a light-emitting layer 5102, and a second electrode 5103.

  A light-emitting element illustrated in FIGS. 51B and 51C has a structure in which an insulating layer is provided between an electrode and a light-emitting layer in the light-emitting element in FIG. A light-emitting element illustrated in FIG. 51B includes an insulating layer 5104 between the first electrode 5101 and the light-emitting layer 5102, and the light-emitting element illustrated in FIG. 51C includes the first electrode 5101 and the light-emitting layer. An insulating layer 5104 a is provided between the second electrode 5103 and the light emitting layer 5102, and an insulating layer 5104 b is provided between the second electrode 5103 and the light emitting layer 5102. Thus, the insulating layer may be provided only between one of the pair of electrodes that sandwich the light emitting layer and the light emitting layer, or may be provided between both. Further, the insulating layer may be a single layer or a stacked layer including a plurality of layers.

  In FIG. 51B, the insulating layer 5104 is provided in contact with the first electrode 5101; however, the insulating layer and the light-emitting layer are reversed in order, and the insulating layer is in contact with the second electrode 5103. 5104 may be provided.

  In the case of a dispersion-type inorganic EL element, a particulate light emitting material is dispersed in a binder to form a film light emitting layer. When particles having a desired size cannot be obtained sufficiently by the method for manufacturing a light emitting material, the particles may be processed into particles by pulverization or the like in a mortar or the like. A binder is a substance for fixing a granular light emitting material in a dispersed state and maintaining the shape as a light emitting layer. The light emitting material is uniformly dispersed and fixed in the light emitting layer by the binder.

  In the case of a dispersion-type inorganic EL element, a light emitting layer can be formed by a droplet discharge method capable of selectively forming a light emitting layer, a printing method (screen printing, offset printing, etc.), a coating method such as a spin coating method, or a dipping method. A dispenser method or the like can also be used. The film thickness is not particularly limited, but is preferably in the range of 10 to 1000 nm. In the light-emitting layer including the light-emitting material and the binder, the ratio of the light-emitting material may be 50 wt% or more and 80 wt% or less.

  52A to 52C illustrate an example of a dispersion-type inorganic EL element that can be used as a light-emitting element. A light-emitting element in FIG. 52A has a stacked structure of a first electrode 5101, a light-emitting layer 5202, and a second electrode 5103, and includes a light-emitting material 5201 held in a light-emitting layer 5202 by a binder.

As a binder that can be used in this embodiment mode, an insulating organic material or an inorganic material can be used. Note that a mixed material of an organic material and an inorganic material may be used. As the organic insulating material, a polymer having a relatively high dielectric constant such as a cyanoethyl cellulose resin, or a resin such as polyethylene, polypropylene, polystyrene resin, silicone resin, epoxy resin, or vinylidene fluoride can be used. Alternatively, a heat-resistant polymer such as aromatic polyamide, polybenzimidazole, or siloxane resin may be used. Note that a siloxane resin corresponds to a resin including a Si—O—Si bond. Siloxane has a skeleton structure formed of a bond of silicon (Si) and oxygen (O). As a substituent, an organic group containing at least hydrogen (for example, an alkyl group or an aryl group) is used. In addition, a fluoro group may be used as a substituent. Alternatively, an organic group containing at least hydrogen and a fluoro group may be used as a substituent. In addition to the above, the organic material may be a resin material such as a vinyl resin such as polyvinyl alcohol or polyvinyl butyral, a phenol resin, a novolac resin, an acrylic resin, a melamine resin, a urethane resin, or an oxazole resin (polybenzoxazole). . The dielectric constant can also be adjusted by appropriately mixing fine particles having a high dielectric constant such as barium titanate (BaTiO ₃ ) and strontium titanate (SrTiO ₃ ) with these resins.

As the inorganic insulating material contained in the binder, silicon oxide (SiO _x ), silicon nitride (SiN _x ), silicon containing oxygen and nitrogen, aluminum nitride (AlN), aluminum containing oxygen and nitrogen, or aluminum oxide (Al ₂ O ₃ ), titanium oxide (TiO ₂ ), BaTiO ₃ , SrTiO ₃ , lead titanate (PbTiO ₃ ), potassium niobate (KNbO ₃ ), lead niobate (PbNbO ₃ ), tantalum oxide (Ta ₂ O ₅ ) , Barium tantalate (BaTa ₂ O ₆ ), lithium tantalate (LiTaO ₃ ), yttrium oxide (Y ₂ O ₃ ), zirconium oxide (ZrO ₂ ), zinc sulfide (ZnS), and other inorganic materials It can be formed of a material. By including an inorganic material having a high dielectric constant in the organic material (by addition or the like), the dielectric constant of the light emitting layer made of the light emitting material and the binder can be further controlled, and the dielectric constant can be further increased.

  In the manufacturing process, the light-emitting material is dispersed in a solution containing a binder, but as a solvent of the solution containing the binder that can be used in this embodiment mode, a method of forming a light-emitting layer by dissolving the binder material (various wet types A solvent capable of producing a solution having a viscosity suitable for the process) and a desired film thickness may be appropriately selected. For example, when a siloxane resin is used as a binder, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate (also referred to as PGMEA), 3-methoxy-3-methyl-1-butanol (also referred to as MMB) can be used. Etc. can be used.

  The light-emitting element illustrated in FIGS. 52B and 52C has a structure in which an insulating layer is provided between the electrode and the light-emitting layer in the light-emitting element in FIG. The light-emitting element illustrated in FIG. 52B includes an insulating layer 5104 between the first electrode 5101 and the light-emitting layer 5202, and the light-emitting element illustrated in FIG. 52C includes the first electrode 5101 and the light-emitting layer. An insulating layer 5104 a is provided between the second electrode 5103 and the light emitting layer 5202, and an insulating layer 5104 b is provided between the second electrode 5103 and the light emitting layer 5202. Thus, the insulating layer may be provided only between one of the pair of electrodes that sandwich the light emitting layer and the light emitting layer, or may be provided between both. Further, the insulating layer may be a single layer or a stacked layer including a plurality of layers.

  In FIG. 52B, the insulating layer 5104 is provided in contact with the first electrode 5101; however, the insulating layer and the light emitting layer are reversed in order, and the insulating layer is in contact with the second electrode 5103. 5104 may be provided.

The insulating layers 5104, 5104a, and 5104b in FIGS. 51 and 52 are not particularly limited, but have high insulation resistance, preferably have a dense film quality, and preferably have a high dielectric constant. For example, silicon oxide (SiO ₂ ), yttrium oxide (Y ₂ O ₃ ), titanium oxide (TiO ₂ ), aluminum oxide (Al ₂ O ₃ ), hafnium oxide (HfO ₂ ), tantalum oxide (Ta ₂ O ₅ ), Barium titanate (BaTiO ₃ ), strontium titanate (SrTiO ₃ ), lead titanate (PbTiO ₃ ), silicon nitride (Si ₃ N ₄ ), zirconium oxide (ZrO ₂ ), etc., a mixed film thereof, or two or more kinds thereof A laminated film can be used. These insulating films can be formed by sputtering, vapor deposition, CVD, or the like. The insulating layer may be formed by dispersing particles of these insulating materials in a binder. The binder material may be formed using the same material and method as the binder contained in the light emitting layer. The film thickness is not particularly limited, but is preferably in the range of 10 to 1000 nm.

  Note that for the first electrode 5101 and the second electrode 5103, a metal, an alloy, a conductive compound, a mixture thereof, or the like can be used. For example, the materials used for the pixel electrode 1801 and the counter electrode 1802 described in Embodiment 9 can be selected as appropriate.

  Note that the light-emitting element described in this embodiment can emit light by applying voltage between a pair of electrodes that sandwich the light-emitting layer, that is, the first electrode 5101 and the second electrode 5103.

  The inorganic EL element obtained as described above can be used as the light-emitting element in Embodiment 9, and can be freely combined with other embodiments.

(Embodiment 11)
In this embodiment, one embodiment of a display device of the present invention will be described with reference to FIGS.

  FIG. 25A is a top view showing the display device, and FIG. 25B is a cross-sectional view taken along the line A-A ′ in FIG. 25A (a cross-sectional view cut along A-A ′). The display device includes a signal line driver circuit 2501, a pixel portion 2502, a first scan line driver circuit 2503, and a second scan line driver circuit 2506 which are indicated by dotted lines in the drawing over a substrate 2510. These are sealed using a sealing substrate 2504 and a sealing material 2505.

  Note that reference numeral 2508 denotes wiring for transmitting signals input to the first scan line driver circuit 2503, the second scan line driver circuit 2506, and the signal line driver circuit 2501, and is an FPC (flexible printer) serving as an external input terminal. Tide circuit) 2509 receives a video signal, a clock signal, a start signal, and the like. IC chips (semiconductor chips on which a memory circuit, a buffer circuit, and the like are formed) 2518 and 2519 are mounted on a connection portion between the FPC 2509 and the display device using COG (Chip On Glass) or the like. Although only the FPC is shown here, a printed wiring board (PWB) may be attached to the FPC. The display device of the present invention includes not only the display device main body but also a state in which an FPC or PWB is attached. In addition, an IC chip or the like mounted is also included.

  A cross-sectional structure will be described with reference to FIG. A pixel portion 2502 and its peripheral driver circuits (a first scan line driver circuit 2503, a second scan line driver circuit 2506, and a signal line driver circuit 2501) are formed over the substrate 2510. Here, the signal line driver is used. A circuit 2501 and a pixel portion 2502 are shown.

  Note that the signal line driver circuit 2501 includes transistors of the same conductivity type, such as N-channel transistors 2520 and 2521. Of course, a CMOS circuit may be formed using not only a P-channel transistor or a transistor of the same conductivity type but also a P-channel transistor. In this embodiment, a display panel in which a peripheral drive circuit is integrally formed on a substrate is shown. However, this is not always necessary, and all or a part of the peripheral drive circuit is formed on an IC chip or the like, and COG or the like is used. May be implemented.

  The pixel described in Embodiment Modes 1 to 8 is used for the pixel portion 2502. Note that FIG. 25B illustrates a transistor 2511 that functions as a switch, a transistor 2512 that controls a current value supplied to the light-emitting element, and a light-emitting element 2528. Note that the first electrode of the transistor 2512 is connected to the pixel electrode 2513 of the light-emitting element 2528. In addition, an insulator 2514 is formed so as to cover an end portion of the pixel electrode 2513. Here, the insulator 2514 is formed using a positive photosensitive acrylic resin film.

  In order to improve the coverage, a curved surface in which the upper end portion or the lower end portion of the insulator 2514 has a curvature in a cross section is formed. For example, in the case where positive photosensitive acrylic is used as a material for the insulator 2514, it is preferable that only the upper end portion of the insulator 2514 has a curved surface with a curvature radius (0.2 μm to 3 μm). As the insulator 2514, either a negative type that becomes insoluble in an etchant by photosensitive light or a positive type that becomes soluble in an etchant by light can be used. Further, the material of the insulator 2514 is not limited to an organic material, and an inorganic material such as silicon oxide or silicon oxynitride can also be used.

  In addition, over the pixel electrode 2513, a layer 2516 containing a light-emitting substance and a counter electrode 2517 are formed. The layer 2516 containing a light-emitting substance is not particularly limited and can be appropriately selected as long as at least a light-emitting layer is provided.

  Further, the sealing substrate 2504 and the substrate 2510 are attached to each other using the sealing material 2505, whereby the light emitting element 2528 is provided in the space 2507 surrounded by the substrate 2510, the sealing substrate 2504, and the sealing material 2505. ing. Note that the space 2507 includes a structure filled with a sealant 2505 in addition to a case where the space 2507 is filled with an inert gas (nitrogen, argon, or the like).

  Note that an epoxy-based resin is preferably used for the sealant 2505. Moreover, it is desirable that these materials are materials that do not transmit moisture and oxygen as much as possible. As a material used for the sealing substrate 2504, a glass substrate or a quartz substrate, or a plastic substrate made of FRP (Fiberglass-Reinforced Plastics), PVF (polyvinyl fluoride), polyester, acrylic, or the like can be used.

  Note that when the pixel portion 2502 is operated using the pixel described in any of Embodiments 1 to 8, luminance variation with time can be suppressed between pixels or between pixels, and a high-quality display with a high duty ratio can be achieved. A device can be obtained. Further, in the present invention, the power consumption can be reduced because the potential of the counter electrode is kept constant.

  As shown in FIG. 25, the signal line driver circuit 2501, the pixel portion 2502, the first scan line driver circuit 2503, and the second scan line driver circuit 2506 are integrally formed, so that the cost of the display device can be reduced. Can do. Further, when transistors used for the signal line driver circuit 2501, the pixel portion 2502, the first scan line driver circuit 2503, and the second scan line driver circuit 2506 are of the same conductivity type, the manufacturing process can be simplified. Therefore, further cost reduction can be achieved.

  As described above, the display device of the present invention can be obtained. The configuration described above is an example, and the configuration of the display device of the present invention is not limited to this.

  As a configuration of the display device, a signal line driver circuit 2601 may be formed over an IC chip as shown in FIG. 26A and mounted on the display device by COG or the like. Note that the substrate 2600, the pixel portion 2602, the first scan line driver circuit 2603, the second scan line driver circuit 2604, the FPC 2605, the IC chip 2606, the IC chip 2607, the sealing substrate 2608, and the sealing material in FIG. Reference numeral 2609 denotes a substrate 2510, a pixel portion 2502, a first scan line driver circuit 2503, a second scan line driver circuit 2506, an FPC 2509, an IC chip 2518, an IC chip 2519, a sealing substrate 2504, and a seal in FIG. It corresponds to the material 2505.

  That is, only the signal line driver circuit that requires high-speed operation of the driver circuit is formed on the IC chip using a CMOS or the like to reduce power consumption. Further, by using a semiconductor chip such as a silicon wafer as the IC chip, it is possible to achieve higher speed operation and lower power consumption.

  Note that cost reduction can be achieved by forming the first scan line driver circuit 2603 and the second scan line driver circuit 2604 integrally with the pixel portion 2602. Further, the first scan line driver circuit 2603, the second scan line driver circuit 2604, and the pixel portion 2602 are formed using transistors of the same conductivity type, so that cost can be further reduced. At this time, the use of a boot trap circuit for the first scan line driver circuit 2603 and the second scan line driver circuit 2604 can prevent the output potential from being lowered. In addition, when amorphous silicon is used for the semiconductor layers of the transistors included in the first scan line driver circuit 2603 and the second scan line driver circuit 2604, the threshold voltage fluctuates due to deterioration. It is preferable to have.

  Note that by operating the pixel portion 2602 using the pixels described in Embodiment Modes 1 to 8, luminance variation with time can be suppressed between pixels or between pixels, and the duty ratio is high and high quality. A display device can be obtained. Further, in the present invention, the power consumption can be reduced because the potential of the counter electrode is kept constant. Further, by mounting an IC chip on which a functional circuit (memory or buffer) is formed at a connection portion between the FPC 2605 and the substrate 2600, the substrate area can be effectively used.

  In addition, the signal line driver circuit 2611, the first scan line driver circuit 2613, and the first scan line driver circuit 2613 corresponding to the signal line driver circuit 2501, the first scan line driver circuit 2503, and the second scan line driver circuit 2506 in FIG. Two scanning line driving circuits 2614 may be formed on an IC chip as shown in FIG. 26B and mounted on a display panel by COG or the like. Note that the substrate 2610, the pixel portion 2612, the FPC 2615, the IC chip 2616, the IC chip 2617, the sealing substrate 2618, and the sealant 2619 in FIG. 26B are the substrate 2510, the pixel portion 2502, the FPC 2509, and the like in FIG. It corresponds to an IC chip 2518, an IC chip 2519, a sealing substrate 2504, and a sealing material 2505.

  Further, by using an amorphous semiconductor such as amorphous silicon (a-Si: H) for the semiconductor layer of the transistor in the pixel portion 2612, cost reduction can be achieved. Further, a large display panel can be manufactured.

  Further, the signal line driver circuit, the first scan line driver circuit, and the second scan line driver circuit may not be provided in the row direction and the column direction of the pixel, respectively. For example, as shown in FIG. 27A, the peripheral driving circuit 2701 formed on the IC chip is replaced with the first scanning line driving circuit 2613, the second scanning line driving circuit 2614, and the signal line shown in FIG. The driver circuit 2611 may have a function. Note that the substrate 2700, the pixel portion 2702, the FPC 2704, the IC chip 2705, the IC chip 2706, the sealing substrate 2707, and the sealant 2708 in FIG. 27A are respectively the substrate 2510, the pixel portion 2502, the FPC 2509, and the like. It corresponds to an IC chip 2518, an IC chip 2519, a sealing substrate 2504, and a sealing material 2505.

  FIG. 27B is a schematic diagram for explaining the wiring connection of the display device of FIG. Note that FIG. 27B illustrates a substrate 2710, a peripheral driver circuit 2711, a pixel portion 2712, an FPC 2713, and an FPC 2714.

  The FPC 2713 and the FPC 2714 input an external signal and a power supply potential to the peripheral driver circuit 2711. An output from the peripheral driver circuit 2711 is input to a wiring in a row direction and a column direction connected to the pixel included in the pixel portion 2712.

  In the case where a white light emitting element is used as the light emitting element, full color display can be realized by providing a color filter on the sealing substrate. The present invention can also be applied to such a display device. FIG. 28 shows an example of a partial cross-sectional view of the pixel portion.

  As shown in FIG. 28, a base film 2802 is formed over a substrate 2800, a transistor 2801 for controlling a current value supplied to the light-emitting element is formed over the substrate 2800, and a pixel electrode 2803 is in contact with the first electrode of the transistor 2801. A layer 2804 containing a light-emitting substance and a counter electrode 2805 are formed thereover.

  Note that a light-emitting element is obtained by sandwiching a layer 2804 containing a light-emitting substance between the pixel electrode 2803 and the counter electrode 2805. In FIG. 28, white light is emitted. A red color filter 2806R, a green color filter 2806G, and a blue color filter 2806B are provided above the light-emitting element, so that full color display can be performed. A black matrix (also referred to as BM) 2807 is provided to isolate these color filters.

  The display device of this embodiment can be combined with not only Embodiments 1 to 8 but also the structure described in Embodiment 9 or 10 as appropriate. The configuration of the display device is not limited to the above, and the present invention can be applied to display devices having other configurations.

(Embodiment 12)
The display device of the present invention can be applied to various electronic devices. Specifically, it can be applied to a display portion of an electronic device. As electronic devices, cameras such as video cameras and digital cameras, goggle type displays, navigation systems, sound playback devices (car audio, audio components, etc.), computers, game devices, portable information terminals (mobile computers, mobile phones, mobile phones) Type game machines, electronic books, etc.), image playback devices equipped with recording media (specifically, devices equipped with a display capable of playing back recording media such as Digital Versatile Disc (DVD) and displaying the images), etc. Can be mentioned.

  FIG. 33A shows a display which includes a housing 3301, a support base 3302, a display portion 3303, a speaker portion 3304, a video input terminal 3305, and the like.

  Note that the pixel described in any of Embodiments 1 to 8 is used for the display portion 3303. According to the present invention, variation in luminance with time can be suppressed between pixels or between pixels, and a display having a high-quality display unit with a high duty ratio can be obtained. Further, in the present invention, the power consumption can be reduced because the potential of the counter electrode is kept constant. The display includes all display devices for displaying information such as for personal computers, for receiving television broadcasts, and for displaying advertisements.

  In recent years, as the need for an increase in the size of a display has become stronger, an increase in price has become a problem as the size of the display increases. Therefore, the issue is how to reduce manufacturing costs and keep high-quality products as low as possible.

  Since the pixel of the present invention can be manufactured using transistors of the same conductivity type, the number of steps can be reduced and manufacturing cost can be reduced. In addition, by using an amorphous semiconductor such as amorphous silicon (a-Si: H) for the semiconductor layer of the transistor included in the pixel, the process can be simplified and the cost can be further reduced. In this case, a driver circuit around the pixel portion is preferably formed over an IC chip and mounted on the display panel by COG (Chip On Glass) or the like. Note that the signal line driver circuit having a high operation speed may be formed over an IC chip, and the scan line driver circuit having a relatively low operation speed may be integrally formed with a circuit formed of transistors of the same conductivity type together with the pixel portion.

  FIG. 33B shows a camera, which includes a main body 3311, a display portion 3312, an image receiving portion 3313, operation keys 3314, an external connection port 3315, a shutter button 3316, and the like.

  Note that the pixel described in any of Embodiments 1 to 8 is used for the display portion 3312. According to the present invention, it is possible to suppress a luminance variation with time between pixels or between pixels, and it is possible to obtain a camera having a high-quality display unit with a high duty ratio. Note that in the present invention, since the potential of the counter electrode is kept constant, the power consumption can be reduced.

  In recent years, production competition has intensified along with the improvement in performance of digital cameras and the like. And how to keep high-performance products at low prices is important.

  Since the pixel of the present invention can be manufactured using transistors of the same conductivity type, the number of steps can be reduced and manufacturing cost can be reduced. In addition, by using an amorphous semiconductor such as amorphous silicon (a-Si: H) for the semiconductor layer of the transistor included in the pixel, the process can be simplified and the cost can be further reduced. In this case, a driver circuit around the pixel portion is preferably formed over an IC chip and mounted on the display panel by COG or the like. Note that the signal line driver circuit having a high operation speed may be formed over an IC chip, and the scan line driver circuit having a relatively low operation speed may be integrally formed with a circuit formed of transistors of the same conductivity type together with the pixel portion.

  FIG. 33C illustrates a computer, which includes a main body 3321, a housing 3322, a display portion 3323, a keyboard 3324, an external connection port 3325, a pointing device 3326, and the like. Note that the pixel described in any of Embodiments 1 to 8 is used for the display portion 3323. According to the present invention, a luminance variation with time can be suppressed between pixels or between pixels, and a computer having a high-quality display portion with a high duty ratio can be obtained. Note that in the present invention, since the potential of the counter electrode is kept constant, the power consumption can be reduced. In addition, the cost can be reduced by using a transistor having the same conductivity type as a transistor included in the pixel portion or an amorphous semiconductor film as a semiconductor layer of the transistor.

  FIG. 33D illustrates a mobile computer, which includes a main body 3331, a display portion 3332, a switch 3333, operation keys 3334, an infrared port 3335, and the like. Note that the pixel described in any of Embodiments 1 to 8 is used for the display portion 3332. According to the present invention, variation in luminance with time can be suppressed between pixels or between pixels, and a mobile computer having a high-quality display unit with a high duty ratio can be obtained. Note that in the present invention, since the potential of the counter electrode is kept constant, the power consumption can be reduced. In addition, cost reduction can be achieved by using a transistor having the same conductivity type or a semiconductor layer amorphous semiconductor film of a transistor as a transistor included in the pixel portion.

  FIG. 33E shows a portable image reproducing device (specifically, a DVD reproducing device) provided with a recording medium, which includes a main body 3341, a housing 3342, a display portion A 3343, a display portion B 3344, a recording medium (DVD, etc.). A reading unit 3345, operation keys 3346, a speaker unit 3347, and the like are included. The display portion A 3343 can mainly display image information, and the display portion B 3344 can mainly display character information. Note that the pixel described in any of Embodiments 1 to 8 is used for the display portion A 3343 and the display portion B 3344. According to the present invention, it is possible to suppress a variation in luminance with time between pixels or between pixels, and to obtain an image reproducing device having a high-quality display unit with a high duty ratio. Note that in the present invention, since the potential of the counter electrode is kept constant, the power consumption can be reduced. In addition, the cost can be reduced by using a transistor having the same conductivity type as a transistor included in the pixel portion or an amorphous semiconductor film as a semiconductor layer of the transistor.

  FIG. 33F illustrates a goggle type display which includes a main body 3351, a display portion 3352, and an arm portion 3353. Note that the pixel described in any of Embodiments 1 to 8 is used for the display portion 3352. According to the present invention, a variation in luminance with time can be suppressed between pixels or between pixels, and a goggle type display having a high-quality display unit with a high duty ratio can be obtained. Note that in the present invention, since the potential of the counter electrode is kept constant, the power consumption can be reduced. In addition, the cost can be reduced by using a transistor having the same conductivity type as a transistor included in the pixel portion or an amorphous semiconductor film as a semiconductor layer of the transistor.

  FIG. 33G illustrates a video camera, which includes a main body 3361, a display portion 3362, a housing 3363, an external connection port 3364, a remote control reception portion 3365, an image receiving portion 3366, a battery 3367, an audio input portion 3368, operation keys 3369, and an eyepiece. Part 3360 and the like. Note that the pixel described in any of Embodiments 1 to 8 is used for the display portion 3362. According to the present invention, it is possible to suppress a variation in luminance over time between pixels or between pixels, and to obtain a video camera having a high-quality display unit with a high duty ratio. In the present invention, the power consumption can be reduced because the counter electrode is operated at a constant potential. In addition, the cost can be reduced by using a transistor having the same conductivity type as a transistor included in the pixel portion or an amorphous semiconductor film as a semiconductor layer of the transistor.

  FIG. 33H illustrates a cellular phone, which includes a main body 3371, a housing 3372, a display portion 3373, an audio input portion 3374, an audio output portion 3375, operation keys 3376, an external connection port 3377, an antenna 3378, and the like. Note that the pixel described in any of Embodiments 1 to 8 is used for the display portion 3373. According to the present invention, a variation in luminance with time can be suppressed between pixels or between pixels, and a mobile phone having a high-quality display portion with a high duty ratio can be obtained. Further, in the present invention, the power consumption can be reduced because the potential of the counter electrode is kept constant. In addition, the cost can be reduced by using a transistor having the same conductivity type as a transistor included in the pixel portion or an amorphous semiconductor film as a semiconductor layer of the transistor.

  Thus, the present invention can be applied to all electronic devices.

(Embodiment 13)
In this embodiment mode, a structural example of a mobile phone including the display device of the present invention in a display portion will be described with reference to FIG.

  A display panel 3410 is incorporated in a housing 3400 so as to be detachable. The shape and dimensions of the housing 3400 can be changed as appropriate in accordance with the size of the display panel 3410. A housing 3400 to which the display panel 3410 is fixed is fitted into a printed board 3401 and assembled as a module.

  The display panel 3410 is connected to the printed board 3401 through the FPC 3411. A signal processing circuit 3405 including a speaker 3402, a microphone 3403, a transmission / reception circuit 3404, a CPU, a controller, and the like is formed over the printed board 3401. Such a module is combined with the input means 3406 and the battery 3407 and housed in the housing 3409 and the housing 3412. Note that the pixel portion of the display panel 3410 is arranged so as to be visible from an opening window formed in the housing 3412.

  In the display panel 3410, a pixel portion and some peripheral driver circuits (a driver circuit having a low operating frequency among a plurality of driver circuits) are formed over a substrate using transistors, and another peripheral driver circuit (a plurality of driver circuits) is formed. A driving circuit having a high operating frequency may be formed on an IC chip, and the IC chip may be mounted on the display panel 3410 by COG (Chip On Glass). Alternatively, the IC chip may be connected to the glass substrate using TAB (Tape Automated Bonding) or a printed board. Alternatively, all peripheral drive circuits may be formed on an IC chip, and the IC chip may be mounted on the display panel using COG or the like.

  Note that the pixel described in any of Embodiments 1 to 8 is used for the pixel portion. According to the present invention, variation in luminance with time can be suppressed between pixels or between pixels, and a display panel 3410 having a high-quality display portion with a high duty ratio can be obtained. In the present invention, the power consumption can be reduced because the counter electrode is operated at a constant potential. In addition, the cost can be reduced by using a transistor having the same conductivity type as a transistor included in the pixel portion or an amorphous semiconductor film as a semiconductor layer of the transistor.

  The configuration shown in this embodiment is an example of a mobile phone, and is not limited to the mobile phone having such a configuration, and can be applied to mobile phones having various configurations.

(Embodiment 14)
In this embodiment, an EL module in which a display panel and a circuit board are combined will be described with reference to FIGS.

  As shown in FIG. 35, the display panel 3501 includes a pixel portion 3503, a scanning line driver circuit 3504, and a signal line driver circuit 3505. For example, a control circuit 3506, a signal dividing circuit 3507, and the like are formed on the circuit board 3502. Note that the display panel 3501 and the circuit board 3502 are connected by a connection wiring 3508. An FPC or the like can be used for the connection wiring 3508.

  In the display panel 3501, a pixel portion and some peripheral driver circuits (a driver circuit having a low operating frequency among a plurality of driver circuits) are formed over a substrate using transistors, and other peripheral driver circuits (a plurality of driver circuits) are formed. A driving circuit with a high operating frequency may be formed on an IC chip, and the IC chip may be mounted on the display panel 3501 by COG (Chip On Glass). Alternatively, the IC chip may be connected to the glass substrate using TAB (Tape Automated Bonding) or a printed board. Alternatively, all peripheral drive circuits may be formed on an IC chip, and the IC chip may be mounted on the display panel using COG or the like.

  Note that the pixel described in any of Embodiments 1 to 8 is used for the pixel portion. According to the present invention, variation in luminance with time can be suppressed between pixels or between pixels, and a high-quality display panel 3501 with a high duty ratio can be obtained. In the present invention, the power consumption can be reduced because the counter electrode is operated at a constant potential. In addition, the cost can be reduced by using a transistor having the same conductivity type as a transistor included in the pixel portion or an amorphous semiconductor film as a semiconductor layer of the transistor.

  With such an EL module, an EL television receiver can be completed. FIG. 36 is a block diagram illustrating a main configuration of an EL television receiver. A tuner 3601 receives a video signal and an audio signal. The video signal includes a video signal amplification circuit 3602, a video signal processing circuit 3603 that converts a signal output from the signal to a color signal corresponding to each color of red, green, and blue, and uses the video signal as input specifications of the drive circuit. Processed by a control circuit 3506 for conversion. The control circuit 3506 outputs a signal to each of the scanning line side and the signal line side. In the case of digital driving, a signal dividing circuit 3507 may be provided on the signal line side so that an input digital signal is divided into m pieces and supplied.

  Of the signals received by the tuner 3601, the audio signal is sent to the audio signal amplification circuit 3604, and the output is supplied to the speaker 3606 via the audio signal processing circuit 3605. The control circuit 3607 receives control information on the receiving station (reception frequency) and volume from the input unit 3608 and sends a signal to the tuner 3601 and the audio signal processing circuit 3605.

  For example, the television set can be completed by incorporating the EL module in FIG. 35 into the housing 3301 in FIG. 33A described in Embodiment 12.

  Of course, the present invention is not limited to a television receiver, and is applied to various uses, particularly as a display medium with a large area, such as a personal computer monitor, an information display board in a railway station or airport, and an advertisement display board in a street. can do.

(Embodiment 15)
In this embodiment, an application example of the display device according to the present invention will be described.

  FIG. 56 shows an example in which the display device according to the present invention is provided integrally with a building. FIG. 56 illustrates a building including a housing 5600, a display panel 5601, a speaker portion 5602, and the like. Note that reference numeral 5603 denotes a remote control device for operating the display panel 5601.

  The display panel 5601 uses the pixel described in any of Embodiments 1 to 8. According to the present invention, it is possible to suppress luminance variation over time between pixels or between pixels, and to obtain a high-quality display panel having a high duty ratio. Note that in the present invention, since the potential of the counter electrode is kept constant, the power consumption can be reduced. In addition, the cost can be reduced by using a transistor having the same conductivity type as a transistor included in the pixel portion or an amorphous semiconductor film as a semiconductor layer of the transistor.

  The display device illustrated in FIG. 56 is provided so as to be integrated with a structure, and thus can be installed without requiring a wide space.

  FIG. 57 shows another example in which the display device according to the present invention is provided integrally with a building. The display panel 5701 is attached to the unit bath 5702 so that the bather can view the display panel 5701 while taking a bath. Information can be displayed on the display panel 5701 by operation of the bather. Therefore, it has a function that can be used as an advertisement or entertainment means.

  The display panel 5701 uses the pixel described in any of Embodiments 1 to 8. According to the present invention, it is possible to suppress luminance variation over time between pixels or between pixels, and to obtain a high-quality display panel having a high duty ratio. Note that in the present invention, since the potential of the counter electrode is kept constant, the power consumption can be reduced. In addition, the cost can be reduced by using a transistor having the same conductivity type as a transistor included in the pixel portion or an amorphous semiconductor film as a semiconductor layer of the transistor.

  Note that the display device according to the present invention can be provided not only on the side wall of the unit bus 5702 shown in FIG. 57 but also in various places. For example, it may be provided integrally with a part of the mirror surface or the bathtub itself. Moreover, the shape of the display device may be adapted to the shape of the mirror surface or the bathtub.

  FIG. 58 shows another example in which the display device according to the present invention is provided integrally with a building. In FIG. 58, the display panel 5802 is curved in accordance with the curved surface of the columnar body 5801. Here, the columnar body 5801 is described as a utility pole.

  The display panel 5802 shown in FIG. 58 is provided at a position higher than the human viewpoint. By installing the display panel 5802 on a building that is repeatedly forested outdoors such as a utility pole, information can be provided to the unspecified number of viewers via the display panel 5802. Therefore, it is suitable to use the display panel as an advertisement. Further, the display panel 5802 can easily display the same image by external control, and can easily switch the image instantly. Therefore, extremely efficient information display and advertisement effect can be expected. Further, it can be said that providing a self-luminous display element in the display panel 5802 is useful as a display medium with high visibility even at night. Further, by providing the display panel 5802 on a power pole, it is easy to secure a power supply unit for the display panel 5802. Further, in the event of an emergency such as the occurrence of a disaster, it can also be a means for quickly and accurately transmitting information to the victims.

  A pixel described in any of Embodiments 1 to 8 is used for the display panel 5802. According to the present invention, it is possible to suppress luminance variation over time between pixels or between pixels, and to obtain a high-quality display panel having a high duty ratio. Note that in the present invention, since the potential of the counter electrode is kept constant, the power consumption can be reduced. In addition, the cost can be reduced by using a transistor having the same conductivity type as a transistor included in the pixel portion or an amorphous semiconductor film as a semiconductor layer of the transistor. Further, an organic transistor provided on a film-like substrate may be used.

  In this embodiment, a wall, a unit bath, and a columnar body are illustrated as a building integrated with the display device of the present invention, but it can be provided in various other buildings.

  Next, an example in which the display device according to the present invention is provided integrally with a moving object will be described.

  FIG. 59 is a diagram showing an example in which the display device according to the present invention is provided integrally with an automobile. The display panel 5902 is provided integrally with the vehicle body 5901 of the automobile, and can display the operation of the vehicle body and information input from inside and outside the vehicle body on demand. Further, the display panel 5902 may have a navigation function.

  A pixel described in any of Embodiments 1 to 8 is used for the display panel 5902. According to the present invention, it is possible to suppress luminance variation over time between pixels or between pixels, and to obtain a high-quality display panel having a high duty ratio. Note that in the present invention, since the potential of the counter electrode is kept constant, the power consumption can be reduced. In addition, the cost can be reduced by using a transistor having the same conductivity type as a transistor included in the pixel portion or an amorphous semiconductor film as a semiconductor layer of the transistor.

  Note that the display device according to the present invention can be provided not only in the vehicle body 5901 shown in FIG. 59 but also in various places. For example, you may provide integrally with a glass window, a door, a handle | steering-wheel, a shift lever, a seat, a room mirror, etc. At this time, the shape of the display panel 5902 may be adapted to the shape of what is to be installed.

  FIG. 60 is a diagram showing an example in which the display device according to the present invention is provided integrally with a train car.

  FIG. 60A shows an example in which a display panel 6002 is provided on the glass of a door 6001 of a train car. Compared to conventional paper advertisements, there is an advantage that labor costs required for advertisement switching are not incurred. In addition, since the display panel 6002 can instantaneously switch the image displayed on the display unit in response to an external signal, for example, the display panel image is displayed for each time zone when the customer class of passengers on the train changes. Can be switched. Thus, more effective advertising effect can be expected by switching images instantly.

  FIG. 60B is a diagram showing an example in which a display panel 6002 is provided on a glass window 6003 and a ceiling 6004 in addition to the glass of the door 6001 of the train car. As described above, since the display device according to the present invention can be easily provided in a place where it has been difficult to install conventionally, an effective advertising effect can be obtained. In addition, the display device according to the present invention can instantaneously switch the image displayed on the display unit by an external signal, thereby reducing the cost and time that have occurred at the time of advertisement switching, and more flexible. Advertisement operation and information transmission.

  Note that the pixel described in any of Embodiments 1 to 8 is used for the display panel 6002 illustrated in FIG. According to the present invention, it is possible to suppress luminance variation over time between pixels or between pixels, and to obtain a high-quality display panel having a high duty ratio. Note that in the present invention, since the potential of the counter electrode is kept constant, the power consumption can be reduced. In addition, the cost can be reduced by using a transistor having the same conductivity type as a transistor included in the pixel portion or an amorphous semiconductor film as a semiconductor layer of the transistor.

  The display device according to the present invention is not limited to the above, and can be provided in various places. For example, the display device according to the present invention may be provided integrally with a strap, a seat, a rail, a floor, and the like. At this time, the shape of the display panel 6002 may be adapted to the shape of what is to be installed.

  FIG. 61 is a diagram showing an example in which the display device according to the present invention is provided integrally with a passenger airplane.

  FIG. 61 (a) is a diagram showing a shape in use when the display panel 6102 is provided on the ceiling 6101 above the seat of the passenger airplane. The display panel 6102 is provided integrally with the ceiling 6101 through the hinge portion 6103, and the passenger can view the display panel 6102 at a desired position by the expansion and contraction of the hinge portion 6103. The display panel 6102 can display information when operated by a passenger. Therefore, it has a function that can be used as an advertisement or entertainment means. In addition, as shown in FIG. 61 (b), safety at the time of takeoff and landing can be considered by folding the hinge part and storing it in the ceiling 6101. Note that the display panel 6102 can be used as an information transmission unit and a guide light by lighting the display element of the display panel 6102 in an emergency.

  Note that the pixel described in any of Embodiments 1 to 8 is used for the display panel 6102 shown in FIG. According to the present invention, it is possible to suppress luminance variation over time between pixels or between pixels, and to obtain a high-quality display panel having a high duty ratio. Note that in the present invention, since the potential of the counter electrode is kept constant, the power consumption can be reduced. In addition, the cost can be reduced by using a transistor having the same conductivity type as a transistor included in the pixel portion or an amorphous semiconductor film as a semiconductor layer of the transistor.

  Note that the display device according to the present invention can be provided not only in the ceiling 6101 shown in FIG. 61 but also in various places. For example, you may provide integrally with a seat sheet, a seat table, an armrest, a window, etc. In addition, a large display panel that can be viewed simultaneously by a large number of people may be installed on the wall of the aircraft. At this time, the shape of the display panel 6102 may be adapted to the shape of what is to be installed.

  In the present embodiment, the train car main body, the automobile body, and the airplane body are illustrated as the moving body, but the present invention is not limited to these. A motorcycle, an automobile (including an automobile, a bus, etc.), a train (monorail, railway) Etc.), various things such as ships can be applied. Since the display device according to the present invention can instantaneously switch the display of the display panel in the moving body by a signal from the outside, the moving body can be prevented by installing the display device according to the present invention on the moving body. It can be used for applications such as advertisement display boards targeting a large number of specific customers and information display boards in the event of a disaster.

  The display device of this embodiment can be combined with not only Embodiments 1 to 8 but also the structure described in Embodiment 9 or 10 as appropriate. Note that the configuration of the display device is not limited to that described above.

3A and 3B illustrate a pixel structure described in Embodiment 1; 2 is a timing chart illustrating the operation of the pixel illustrated in FIG. 1. 2A and 2B illustrate an operation of the pixel illustrated in FIG. 1. The model figure of the voltage-current characteristic by channel length modulation. 3A and 3B illustrate a pixel structure described in Embodiment 1; 3A and 3B illustrate a pixel structure described in Embodiment 1; 3A and 3B each illustrate a display device described in Embodiment 1; 3A and 3B illustrate a writing operation of the display device described in Embodiment 1. FIG. 5 illustrates a pixel structure shown in Embodiment Mode 2; FIG. 6 illustrates a pixel structure described in Embodiment 3; FIG. 6 illustrates a pixel structure described in Embodiment 3; FIG. 6 illustrates a pixel structure described in Embodiment 3; FIG. 5 illustrates a pixel structure described in Embodiment 4; FIG. 5 illustrates a pixel structure described in Embodiment 4; FIG. 5 illustrates a pixel structure described in Embodiment 4; FIG. 5 illustrates a pixel structure described in Embodiment 4; FIG. 10 is a partial cross-sectional view of a pixel described in Embodiment 9; FIG. 10 illustrates a light-emitting element described in Embodiment 9. FIG. 10 illustrates a light extraction direction shown in Embodiment Mode 9; FIG. 10 is a partial cross-sectional view of a pixel described in Embodiment 9; FIG. 10 is a partial cross-sectional view of a pixel described in Embodiment 9; FIG. 10 is a partial cross-sectional view of a pixel described in Embodiment 9; FIG. 10 is a partial cross-sectional view of a pixel described in Embodiment 9; FIG. 10 is a partial cross-sectional view of a pixel described in Embodiment 9; FIG. 10 illustrates a display device shown in Embodiment 11; FIG. 10 illustrates a display device shown in Embodiment 11; FIG. 10 illustrates a display device shown in Embodiment 11; FIG. 21 is a partial cross-sectional view of a pixel shown in Embodiment Mode 11; FIG. 7 illustrates a pixel structure described in Embodiment 5; FIG. 7 illustrates a pixel structure described in Embodiment 5; FIG. 7 illustrates a pixel structure described in Embodiment 6; FIG. 32 is a timing chart illustrating operation of the pixel illustrated in FIG. 31. FIG. 8A and 8B illustrate electronic devices to which the present invention can be applied. The figure which shows the structural example of a mobile telephone. The figure which shows the example of EL module. The block diagram which shows the main structures of EL television receiver. FIG. 7 illustrates a pixel structure described in Embodiment 6; FIG. 9 illustrates a pixel configuration described in Embodiment 7; The figure explaining the drive system which combined the digital gradation system and the time gradation system. FIG. 9 illustrates a pixel configuration described in Embodiment 7; FIG. 9 illustrates a pixel configuration described in Embodiment 7; FIG. 9 illustrates a pixel configuration described in Embodiment 7; 3A and 3B illustrate a pixel structure described in Embodiment 1; FIG. 7 is a top view illustrating the layout of the pixel illustrated in FIG. 6. FIG. 7 is a top view illustrating the layout of the pixel illustrated in FIG. 6. FIG. 10 illustrates a pixel structure described in Embodiment 8; 47 is a timing chart illustrating operation of the pixel illustrated in FIG. FIG. 47 is a diagram for explaining the operation of the pixel shown in FIG. 46. FIG. 10 illustrates a pixel structure described in Embodiment 8; FIG. 10 illustrates a pixel structure described in Embodiment 8; FIG. 10 illustrates a light-emitting element described in Embodiment 10. FIG. 10 illustrates a light-emitting element described in Embodiment 10. 3A and 3B illustrate operation of the pixel described in Embodiment 1; 3A and 3B illustrate a pixel structure described in Embodiment 1; 3A and 3B illustrate a pixel structure described in Embodiment 1; FIG. 10 illustrates an application example of a display device according to the present invention. FIG. 10 illustrates an application example of a display device according to the present invention. FIG. 10 illustrates an application example of a display device according to the present invention. FIG. 10 illustrates an application example of a display device according to the present invention. FIG. 10 illustrates an application example of a display device according to the present invention. FIG. 10 illustrates an application example of a display device according to the present invention. FIG. 6 is a diagram illustrating a pixel configuration of a conventional technique. FIG. 6 is a diagram illustrating a pixel configuration of a conventional technique. 6 is a timing chart for operating pixels shown in the related art. The figure explaining the ratio of the light emission period in 1 frame period at the time of using a prior art.

Explanation of symbols

110 Transistor 111 First switch 112 Second switch 113 Third switch 114 Fourth switch 115 First capacitor element 116 Second capacitor element 117 Light emitting element 118 Signal line 119 First scanning line 120 Second Scanning line 121 Third scanning line 122 Power supply line 123 Potential supply line 124 Counter electrode 611 First switching transistor 612 Second switching transistor 613 Third switching transistor 614 Fourth switching transistor 2910 Transistor 3010 Transistor 3101 First Transistor 3102 second transistor 3103 fifth switch 3104 sixth switch 3111 first switch 3112 second switch 3113 third switch 3114 fourth switch 3115 first capacitor Child 3116 Second capacitor element 3117 Light emitting element 3118 Signal line 3119 First scanning line 3120 Second scanning line 3121 Third scanning line 3122 Power supply line 3123 Potential supply line 3124 Counter electrode 3801 Fifth switch 3802 Fourth Scan line 4001 Fifth switch 4002 Fourth scan line 4201 Rectifier element 4202 Fourth scan line 4610 Transistor 4611 First switch 4612 Second switch 4613 Third switch 4614 Fourth switch 4615 First capacitor 4616 2nd capacitor element 4617 Light emitting element 4618 Signal line 4619 1st scanning line 4620 2nd scanning line 4621 3rd scanning line 4622 Power supply line 4623 Potential supply line 4624 Counter electrode 5001 Rectifier element 5002 4th scanning line

Claims (26)

A transistor, a storage capacitor, a first switch, a second switch, a third switch, and a fourth switch;
One of a source electrode and a drain electrode of the transistor is electrically connected to the pixel electrode;
The other of the source electrode and the drain electrode of the transistor is electrically connected to the first wiring through the second switch,
The other of the source electrode and the drain electrode of the transistor is electrically connected to the gate electrode of the transistor through the third switch,
A gate electrode of the transistor is electrically connected to a second wiring through the storage capacitor and the fourth switch;
The semiconductor device is characterized in that the gate electrode of the transistor is electrically connected to a third wiring through the storage capacitor and the first switch. A transistor, a first storage capacitor, a second storage capacitor, a first switch, a second switch, a third switch, and a fourth switch;
One of a source electrode and a drain electrode of the transistor is electrically connected to the pixel electrode;
One of the source electrode and the drain electrode of the transistor is electrically connected to the gate electrode of the transistor through the second storage capacitor,
The other of the source electrode and the drain electrode of the transistor is electrically connected to the first wiring through the second switch,
The other of the source electrode and the drain electrode of the transistor is electrically connected to the gate electrode of the transistor through the third switch,
A gate electrode of the transistor is electrically connected to a second wiring through the first storage capacitor and the fourth switch;
The gate electrode of the transistor is electrically connected to a third wiring through the first storage capacitor and the first switch. A transistor, a first storage capacitor, a second storage capacitor, a first switch, a second switch, a third switch, a fourth switch, and a fifth switch;
One of a source electrode and a drain electrode of the transistor is electrically connected to the pixel electrode;
One of the source electrode and the drain electrode of the transistor is electrically connected to the gate electrode of the transistor through the second storage capacitor,
One of a source electrode and a drain electrode of the transistor is electrically connected to a fourth wiring through a fifth switch;
The other of the source electrode and the drain electrode of the transistor is electrically connected to the first wiring through the second switch,
The other of the source electrode and the drain electrode of the transistor is electrically connected to the gate electrode of the transistor through the third switch,
A gate electrode of the transistor is electrically connected to a second wiring through the first storage capacitor and the fourth switch;
The semiconductor device is characterized in that a gate electrode of the transistor is electrically connected to a third wiring through the first storage capacitor and the first switch. In any one of Claims 1 thru | or 3,
The semiconductor device according to claim 1, wherein the second wiring is the same as the wiring for controlling the first switch. In any one of Claims 1 thru | or 3,
2. The semiconductor device according to claim 1, wherein the second wiring is any one of scanning lines for controlling the first switch to the fourth switch of the previous row or the next row. A transistor, a first storage capacitor, a second storage capacitor, a first switch, a second switch, a third switch, and a fourth switch;
One of a source electrode and a drain electrode of the transistor is electrically connected to the pixel electrode;
One of the source electrode and the drain electrode of the transistor is electrically connected to the gate electrode of the transistor through the second storage capacitor,
The other of the source electrode and the drain electrode of the transistor is electrically connected to the first wiring through the second switch,
The other of the source electrode and the drain electrode of the transistor is electrically connected to the gate electrode of the transistor through the third switch,
A gate electrode of the transistor is electrically connected to the first wiring through the first storage capacitor and the fourth switch;
The gate electrode of the transistor is electrically connected to a third wiring through the first storage capacitor and the first switch. A transistor, a first storage capacitor, a second storage capacitor, a first switch, a second switch, a third switch, and a rectifying element;
One of a source electrode and a drain electrode of the transistor is electrically connected to the pixel electrode;
One of the source electrode and the drain electrode of the transistor is electrically connected to the gate electrode of the transistor through the second storage capacitor,
The other of the source electrode and the drain electrode of the transistor is electrically connected to the first wiring through the second switch,
The other of the source electrode and the drain electrode of the transistor is electrically connected to the gate electrode of the transistor through the third switch,
A gate electrode of the transistor is electrically connected to a second wiring through the first storage capacitor and the rectifier;
The semiconductor device is characterized in that a gate electrode of the transistor is electrically connected to a third wiring through the first storage capacitor and the first switch. A transistor, a first storage capacitor, a second storage capacitor, a first switch, a second switch, a third switch, and a fourth switch;
One of a source electrode and a drain electrode of the transistor is electrically connected to the pixel electrode;
One of the source electrode and the drain electrode of the transistor is electrically connected to the gate electrode of the transistor through the second storage capacitor,
The other of the source electrode and the drain electrode of the transistor is electrically connected to the first wiring through the second switch,
The other of the source electrode and the drain electrode of the transistor is electrically connected to the gate electrode of the transistor through the third switch,
A gate electrode of the transistor is electrically connected to a third wiring through the first storage capacitor and the first switch;
The semiconductor device is characterized in that the fourth switch is electrically connected in parallel with the first storage capacitor and is electrically connected to the third wiring via the first switch. . In any one of Claims 1 thru | or 8,
The semiconductor device is a thin film transistor. In any one of Claims 1 thru | or 9,
The semiconductor device is an N-channel transistor. In any one of Claims 1 to 10,
A semiconductor device, wherein the semiconductor layer of the transistor is made of an amorphous semiconductor film. In any one of Claims 1 to 11,
A semiconductor device, wherein the semiconductor layer of the transistor is made of amorphous silicon. In any one of Claims 1 thru | or 9,
A semiconductor device, wherein the semiconductor layer of the transistor is made of a crystalline semiconductor film. In any one of Claims 1 to 13,
The semiconductor device is characterized in that the potential of the first wiring is higher than a value obtained by adding the threshold voltage of the transistor to the potential of the pixel electrode. In any one of Claims 1 thru | or 9,
The semiconductor device is a P-channel transistor. In any one of Claim 1 thru | or Claim 9, and Claim 15,
The semiconductor device according to claim 1, wherein the potential of the first wiring is lower than a value obtained by subtracting a threshold voltage of the transistor from the potential of the pixel electrode. In any one of Claims 1 thru | or 16,
The semiconductor device, wherein the first to fourth switches are transistors. A first holding capacity;
One of the source electrode and the drain electrode is electrically connected to the load, the other of the source electrode and the drain electrode is electrically connected to the first wiring, and the gate electrode is connected to the second via the first storage capacitor. A transistor electrically connected to the wiring;
A second holding capacitor for holding a gate-source voltage of the transistor;
Means for holding the first voltage in the first holding capacitor and holding the second voltage in the second holding capacitor;
Means for discharging a second voltage of the second storage capacitor to a threshold voltage of the transistor;
And a means for supplying a current set to the transistor to the load by inputting a potential corresponding to a video signal from the second wiring to the first storage capacitor. In claim 18,
The semiconductor device is a thin film transistor. In claim 18 or claim 19,
The semiconductor device is an N-channel transistor. In any one of claims 18 to 20,
A semiconductor device, wherein the semiconductor layer of the transistor is made of an amorphous semiconductor film. In any one of Claims 18 to 21,
A semiconductor device, wherein the semiconductor layer of the transistor is made of amorphous silicon. In any one of claims 18 to 20,
A semiconductor device, wherein the semiconductor layer of the transistor is made of a crystalline semiconductor film. In claim 18 or claim 19,
The semiconductor device is a P-channel transistor. A display device comprising the semiconductor device according to any one of claims 1 to 24. An electronic apparatus comprising the display device according to claim 25 in a display portion.

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