JP5099974B2 - Light emitting device - Google Patents

Description

  The present invention relates to a light emitting device having a light emitting element and means for supplying current to the light emitting element in each of a plurality of pixels.

  Since the light emitting element emits light by itself, the visibility is high, a backlight necessary for a liquid crystal display (LCD) is not necessary, and it is optimal for thinning, and the viewing angle is not limited. For this reason, a light emitting device using a light emitting element has attracted attention as a display device that replaces a CRT or LCD, and in recent years, it has been put into practical use, such as being mounted on an electronic device such as a mobile phone or a digital still camera. The configuration of the pixel of the active matrix light-emitting device that has been specifically proposed differs depending on the manufacturer. Usually, at least the light-emitting element, a TFT (switching TFT) that controls input of a video signal to the pixel, and the light-emitting element Each pixel is provided with a TFT (driving TFT) for controlling a current value supplied to the pixel.

  By the way, a TFT (thin film transistor) using a polycrystalline semiconductor film has a mobility two or more digits higher than that of a TFT using an amorphous semiconductor film, and the pixel portion of the light emitting device and its peripheral drive circuit are formed on the same substrate. It has the advantage that it can be integrally formed. The polycrystalline semiconductor film can be formed on an inexpensive glass substrate by using a laser annealing method. However, the energy of the laser beam output from the oscillator has a fluctuation of at least several percent due to various factors, and this fluctuation prevents uniform crystallization of the semiconductor film. If the crystallization is not performed uniformly and the crystallinity of the polycrystalline semiconductor film varies, characteristics of TFTs using the polycrystalline semiconductor film as an active layer, such as on-current, mobility, threshold value, etc., vary. . Therefore, when a driving TFT is formed using a polycrystalline semiconductor film formed by a laser annealing method, the luminance of the light emitting element varies due to variations in characteristics of the driving TFT.

  By forming a circuit for correcting variation in characteristics of the driving TFT in each pixel, variation in luminance of the light-emitting element due to variation in characteristics can be suppressed. However, this method is not preferable because the number of TFTs in the pixel increases, which prevents high definition.

  In addition, there is a problem in that the luminance of the light emitting element is reduced as the electroluminescent material used for the light emitting element is deteriorated. By making the current supplied to the light emitting element constant, a decrease in luminance of the light emitting element can be suppressed as compared to making the voltage supplied to the light emitting element constant. However, even if the current supplied to the light emitting element is constant, the luminance is lowered due to deterioration of the electroluminescent material. The degree of deterioration depends on the time during which the light emitting element is lit and the amount of current flowing through the light emitting element. Therefore, if the gradation for each pixel differs depending on the image to be displayed, a difference occurs in the deterioration of the light emitting element of each pixel, resulting in variations in luminance.

  Note that, by operating the driving TFT in the saturation region, it is possible to suppress a decrease in luminance due to deterioration of the electroluminescent material to some extent. However, the value of the drain current of the TFT operating in the saturation region is easily affected by a slight change in the gate-source voltage (hereinafter referred to as the gate voltage) Vgs, and the luminance of the light emitting element is likely to change. Therefore, when the driving TFT is operated in the saturation region, care must be taken so that the gate voltage Vgs of the driving TFT does not fluctuate during the period in which the light emitting element emits light. However, when the off-state current of the switching TFT is large, the gate voltage Vgs of the driving TFT is likely to fluctuate with a change in the potential of the video signal input to another pixel. In order to prevent the fluctuation of the gate voltage Vgs, it is necessary to increase the capacitance of the capacitive element for holding the gate voltage Vgs of the TFT or to suppress the off current of the switching TFT. However, in order to optimize the TFT manufacturing process so as to satisfy both of keeping the off-current of the switching TFT low and increasing the on-current in order to charge a large capacity within a predetermined time. Costly, time consuming and difficult task. Also, increasing the area occupied by the capacitive element is not desirable because it increases the probability of leakage between the electrodes due to dust and the like, thus leading to a decrease in yield. Further, there is a problem that the gate voltage Vgs of the driving TFT is likely to fluctuate due to the parasitic capacitance attached to the gate electrode due to the switching of other TFTs, the fluctuation of the potential of the signal line and the scanning line, and the like.

  In view of the above-described problems, the present invention is caused by a difference in characteristics of a driving TFT and a variation in a gate voltage Vgs of the driving TFT while using a TFT manufactured by an existing process while suppressing the area of the capacitive element. It is an object of the present invention to provide a light-emitting device that can suppress variations in luminance of light-emitting elements and can suppress a decrease in luminance or uneven luminance due to deterioration of an electroluminescent material.

  In the present invention, a transistor (current control transistor) functioning as a switching element is connected in series with a transistor (driving transistor) that determines the value of the current supplied to the light emitting element. Then, by applying a potential at which the driving transistor is turned on to the gate of the driving transistor, a state in which a current can always flow through the driving transistor is created. Further, the current control transistor is operated in a linear region, and the gate potential is controlled by a video signal input to the pixel. The driving transistor is preferably operated in a saturation region, and the luminance of the light-emitting element is controlled by the drain current of the driving transistor.

  By operating the current control transistor in the linear region, the source-drain voltage (drain voltage) Vds becomes very small with respect to the voltage Vel applied to the light emitting element, and a slight variation in the gate voltage Vgs is caused by the light emitting element. It becomes difficult to influence the current flowing through the. Therefore, without increasing the capacitance of the capacitive element provided between the gate and the source of the current control transistor or suppressing the off-current of the switching transistor that controls the input of the video signal to the pixel, The current flowing through the light emitting element is less likely to fluctuate. Further, the current flowing through the light emitting element is not affected by the parasitic capacitance attached to the gate of the current control transistor. The current control transistor only selects whether or not current is supplied to the light emitting element, and the value of the current flowing through the light emitting element is determined by the driving transistor operating in the saturation region.

  In the present invention, the potential of the gate of the driving transistor operated in the saturation region is not controlled by the video signal and is maintained at such a height that the driving transistor is turned on. In the driving transistor operating in the saturation region, the drain current is easily influenced by a slight fluctuation in the gate voltage Vgs. However, in the present invention, since the gate potential of the driving transistor can be fixed, the gate voltage Vgs fluctuates. do not do. For this reason, irrespective of the switching of the switching transistor, the drain current of the driving transistor can be easily kept constant, and the image quality can be greatly improved. In addition, since it is not necessary to optimize the process in order to reduce the off-state current of the transistor that controls the input of the video signal to the pixel, the transistor manufacturing process can be simplified, which greatly contributes to cost reduction and yield improvement. be able to.

  In addition, by operating the driving transistor in a saturation region, the drain current does not change with the drain-source voltage (hereinafter referred to as drain voltage) Vds, but is determined only by Vgs, which causes deterioration of the light emitting element. Accordingly, even if Vds decreases instead of Vel increasing, the value of the drain current is kept relatively constant. Therefore, it is possible to suppress a decrease in luminance or luminance unevenness due to deterioration of the electroluminescent material.

  Furthermore, in the present invention, the potential applied to the gate of the driving transistor is corrected in accordance with the characteristics of the correcting transistor. Specifically, a correction transistor having a gate and drain connected (hereinafter referred to as a correction transistor) is used, and a potential obtained by adding a threshold voltage of the correction transistor to the power supply potential is applied to the gate of the drive transistor. give. By correcting the potential applied to the gate of the driving transistor in accordance with the threshold voltage, it is possible to suppress variation in luminance depending on variation in threshold voltage. In particular, when the driving transistor is operated in the saturation region, the ratio of | Vgs | to | Vth | is small, so that the current flowing through the light-emitting element is easily influenced by variations in the threshold voltage Vth. Since the potential applied to the gate of the driving transistor can be corrected, variation in luminance can be suppressed even when the saturation region is used.

  Alternatively, the gate voltage Vgs of the correction transistor is determined so that the drain current of the correction transistor becomes a desired value, instead of applying a potential obtained by simply adding the threshold voltage of the correction transistor to the power supply potential. The potential applied to the gate of the driving transistor may be corrected and applied to the gate of the driving transistor. In this case, the potential applied to the gate of the driving transistor is corrected by taking into account not only the variation in threshold voltage of the driving transistor but also other characteristics that affect the magnitude of the drain current, such as mobility. be able to.

  Note that when the characteristics of the correcting transistor are closer to the characteristics of the driving transistor, the potential can be corrected more accurately. Therefore, in the present invention, when a semiconductor film used for a transistor is crystallized with laser light, a region serving as an active layer of a driving transistor and a region serving as an active layer of a correction transistor corresponding to the driving transistor are provided. It is desirable to be within the same beam spot. Note that in the case where a plurality of pulses of laser light are irradiated to one place, at least one pulse is set so that the two regions are within the same beam spot. With the above structure, variation in crystallinity can be reduced between the active layer of the driving transistor and the active layer of the correcting transistor corresponding to the driving transistor even if the output of the laser light varies between pulses. Therefore, the characteristics of these two transistors can be made uniform, and the potential can be corrected more accurately.

  In the present invention, a wiring for applying a potential to the gate of the driving transistor is shared by a plurality of pixels. Therefore, it is not necessary to form a correction transistor for each pixel, and the correction transistor may be formed so as to correspond to a wiring for applying a potential to the gate of the driving transistor.

  Further, in order to make the characteristics of the driving transistor and the correcting transistor corresponding to the driving transistor uniform, the ratio of the channel length to the channel width may be made substantially equal in these two transistors.

  The drive transistor L may be longer than W, and the current control transistor L may be equal to or shorter than W. More preferably, the ratio of L to W of the driving transistor is 5 or more. By making L of the driving transistor longer than W, the linearity of the drain current in the saturation region is further increased, and variation in luminance of the light-emitting element between pixels due to a difference in characteristics of the driving transistor can be further suppressed. it can. Further, when the channel length of the driving transistor is L1, the channel width is W1, the channel length of the current control transistor is L2, and the channel width is W2, X is 5 when L1 / W1: L2 / W2 = X: 1. It is desirable to set it to 6000 or more. Examples include L1 / W1 = 500 μm / 3 μm and L2 / W2 = 3 μm / 100 μm.

  In this specification, a light-emitting element includes, in its category, an element whose luminance is controlled by current or voltage. Specifically, the light-emitting element is used in an OLED (Organic Light Emitting Diode) or an FED (Field Emission Display). MIM type electron source elements (electron emitting elements) and the like are included.

  An OLED (Organic Light Emitting Diode), which is one of the light emitting elements, includes a layer (hereinafter referred to as an electroluminescent layer) containing an electroluminescent material from which luminescence generated by applying an electric field is obtained, an anode, And a cathode. The electroluminescent layer is provided between the anode and the cathode, and is composed of a single layer or a plurality of layers. In some cases, these layers contain an inorganic compound. Luminescence in the electroluminescent layer includes light emission (fluorescence) when returning from the singlet excited state to the ground state and light emission (phosphorescence) when returning from the triplet excited state to the ground state.

  In this specification, of the two electrodes of the anode and the cathode, one electrode whose potential can be controlled by the driving transistor is a first electrode, and the other electrode is a second electrode.

  The light-emitting device includes a panel in which the light-emitting element is sealed, and a module in which an IC including a controller or the like is mounted on the panel. Furthermore, the present invention relates to an element substrate corresponding to one mode before the light emitting element is completed in the process of manufacturing the light emitting device, and the element substrate includes a unit for supplying current to the light emitting element. Prepare for.

  Note that the element substrate corresponds to one mode before the light-emitting element is completed in the process of manufacturing the light-emitting device of the present invention. Specifically, only the first electrode of the light-emitting element may be formed, or after the conductive film to be the first electrode is formed, the first electrode is patterned by patterning. The state before forming may be used, and all forms are applicable.

  Note that as a transistor used in the light-emitting device of the present invention, a polycrystalline semiconductor, a microcrystalline semiconductor (including a semi-amorphous semiconductor), or a thin film transistor using an amorphous semiconductor can be used. It is not limited to a thin film transistor. A transistor formed using single crystal silicon or a transistor using SOI may be used. Further, a transistor using an organic semiconductor or a transistor using carbon nanotubes may be used. In addition, the transistor provided in the pixel of the light-emitting device of the present invention may have a single gate structure, a double gate structure, or a multi-gate structure having more gate electrodes.

A semi-amorphous semiconductor is a film containing a semiconductor having an intermediate structure between amorphous and crystalline structures (including single crystal and polycrystal). This semi-amorphous semiconductor is a semiconductor having a third state which is stable in terms of free energy, and is a crystalline one having a short-range order and having a lattice strain, and having a grain size of 0.5 to 20 nm. It can be dispersed in a single crystal semiconductor. The semi-amorphous semiconductor has its Raman spectrum shifted to a lower wavenumber than 520 cm ⁻¹ , and diffraction peaks of (111) and (220), which are considered to be derived from the Si crystal lattice in X-ray diffraction, are observed. . Further, hydrogen or halogen is contained at least 1 atomic% or more as a neutralizing agent for dangling bonds. Here, for convenience, such a semiconductor is referred to as a semi-amorphous semiconductor (SAS). Further, by adding a rare gas element such as helium, argon, krypton, or neon to further promote lattice distortion, stability is improved and a good semi-amorphous semiconductor can be obtained.

  In the present invention, light emission can be achieved without increasing the capacitance of the capacitive element provided between the gate and source of the current control transistor or suppressing the off-current of the transistor that controls the input of the video signal to the pixel. The current flowing through the element is less likely to fluctuate. Further, the current flowing through the light emitting element is not affected by the parasitic capacitance attached to the gate of the current control transistor. The current control transistor only selects whether or not current is supplied to the light emitting element, and the value of the current flowing through the light emitting element is determined by the driving transistor. For this reason, variation factors can be reduced and the image quality can be greatly improved. In addition, since it is not necessary to optimize the process in order to reduce the off-state current of the transistor that controls the input of the video signal to the pixel, the transistor manufacturing process can be simplified, which greatly contributes to cost reduction and yield improvement. be able to.

  Further, in the present invention, even when the driving transistor is operated in the saturation region, the gate potential of the driving transistor can be fixed, and thus the gate voltage Vgs is not easily changed. By operating the driving transistor in the saturation region, the drain current is not changed by the drain voltage Vds, but is determined only by Vgs. Therefore, Vds is reduced instead of increasing Vel as the light emitting element is deteriorated. However, the drain current value is kept constant. Therefore, it is possible to suppress a decrease in luminance or luminance unevenness due to deterioration of the electroluminescent material.

  Further, by correcting the potential applied to the gate of the driving transistor in accordance with the threshold voltage, it is possible to suppress variation in luminance depending on variation in threshold voltage. In particular, when the driving transistor is operated in the saturation region, the ratio of | Vgs | to | Vth | is small, so that the current flowing through the light-emitting element is easily influenced by variations in the threshold voltage Vth. Since the potential applied to the gate of the driving transistor can be corrected, variation in luminance can be suppressed even when the saturation region is used.

  Furthermore, in the present invention, the correction transistor may be formed so as to correspond to the wiring for applying a potential to the gate of the driving transistor, and it is not necessary to form the correction transistor for each pixel. Therefore, an increase in the number of transistors in the pixel can be suppressed, and high definition can be easily promoted.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 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 this embodiment mode.

  FIG. 1A illustrates one mode of a pixel included in the light-emitting device of the present invention. The pixel shown in FIG. 1 controls a light emitting element 101, a transistor (switching transistor) 102 used as a switching element for controlling input of a video signal to the pixel, and a value of a current supplied to the light emitting element 101. A driving transistor 103 and a current control transistor 104 for selecting whether or not to supply current to the light emitting element 101 are provided. Further, although not shown in FIG. 1A, a capacitor for holding the potential of the video signal may be formed in the pixel.

  The driving transistor 103 and the current control transistor 104 may have the same polarity or different polarities. The driving transistor 103 is operated in the saturation region, and the current control transistor 104 is operated in the linear region. Note that the driving transistor 103 is desirably operated in a saturation region; however, the present invention is not necessarily limited to this configuration, and the driving transistor 103 may be operated in a linear region. The switching transistor 102 is operated in a linear region. The driving transistor 103 may be an enhancement type transistor or a depletion type transistor. The switching transistor 102 may be either n-type or p-type.

  The light emitting element 101 includes an anode, a cathode, and an electroluminescent layer provided between the anode and the cathode. One of the anode and the cathode is used as the first electrode, and the other is used as the second electrode.

  As shown in FIG. 1A, in the case where the driving transistor 103 is a p-type, it is preferable to use the anode of the light-emitting element 101 as a first electrode and the cathode as a second electrode. On the other hand, when the driving transistor 103 is n-type, it is preferable to use the cathode of the light-emitting element 101 as the first electrode and the anode as the second electrode.

  The gate of the switching transistor 102 is connected to the scanning line Gj (j = 1 to y). One of the source and the drain of the switching transistor 102 is connected to the signal line Si (i = 1 to x), and the other is connected to the gate of the current control transistor 104. The gate of the driving transistor 103 is connected to the second power supply line Vbi (i = 1 to x). In the driving transistor 103 and the current control transistor 104, the current supplied from the first power supply line Vai (i = 1 to x) is used as the drain current of the driving transistor 103 and the current control transistor 104. Is connected to the first power supply line Vai (i = 1 to x) and the light emitting element 101. In this embodiment mode, the source of the driving transistor 103 is connected to the first power supply line Vai (i = 1 to x), and current control is performed between the driving transistor 103 and the first electrode of the light-emitting element 101. A transistor 104 is provided.

  In the case of forming a capacitor, one of the two electrodes of the capacitor is connected to the first power supply line Vai (i = 1 to x), and the other is connected to the gate of the current control transistor 104. Like that. The capacitor element is provided to hold the gate potential of the current control transistor 104.

  Note that the structure of the pixel illustrated in FIG. 1A is only one embodiment of the present invention, and the light-emitting device of the present invention is not limited to FIG. For example, as shown in FIG. 1B, the drain of the driving transistor 103 is connected to the first electrode of the light-emitting element 101, and between the driving transistor 103 and the first power supply line Vai (i = 1 to x). Alternatively, the current control transistor 104 may be formed. Note that in FIG. 1B, the same reference numerals are given to those already shown in FIG.

  Further, a transistor (erase transistor) for erasing the potential of the written video signal may be formed in each pixel. FIG. 1C illustrates an example in which an erasing transistor is formed in the pixel illustrated in FIG. Note that in FIG. 1C, the same reference numerals are given to those already shown in FIG. In the pixel shown in FIG. 1C, in addition to the scanning line connected to the gate of the switching transistor 102, a scanning line connected to the gate of the erasing transistor 105 is formed. In order to distinguish these two scanning lines, in FIG. 1C, the former is the first scanning line Gaj (j = 1 to y), and the latter is the second scanning line Gbj (j = 1 to y). Show. One of the source and drain of the erasing TFT 105 is connected to the first power supply line Vai (i = 1 to x), and the other is connected to the gate of the current control TFT 104.

  Note that as illustrated in FIG. 1D, in the pixel illustrated in FIG. 1C, the drain of the driving transistor 103 is connected to the first electrode of the light-emitting element 101, and the driving transistor 103 and the first power supply line are connected. The current control transistor 104 may be formed between Vai (i = 1 to x). Note that in FIG. 1D, the same reference numerals are given to those already shown in FIG.

  Next, a circuit for correcting the potential of the second power supply line Vbi (i = 1 to x) connected to the gate of the driving transistor 103 (hereinafter referred to as a correction circuit) will be described. FIG. 2 shows an example of the structure of the pixel portion and the correction circuit of the light emitting device of the present invention. In FIG. 2, the same reference numerals are given to those already shown in FIG.

  As shown in FIG. 2, a plurality of pixels 202 are formed in the pixel portion 201. Note that FIG. 2 illustrates the pixel 202 having the structure illustrated in FIG. 1A; however, the structure of the pixel 202 included in the pixel portion 201 is not limited thereto.

  The second power supply lines Vb1 to Vb3 are connected to the correction circuit 203, respectively. 2 illustrates an example in which the first power supply lines Va1 to Va3, the second power supply lines Vb1 to Vb3, and the scanning lines G1 to G3 are formed in the pixel portion 201. The first scan line and the second scan line may be formed in the pixel portion 201 as in the pixel illustrated in FIGS. 1C and 1D.

  The correction circuit 203 includes a correction transistor 204 having a gate and a drain connected to each of the second power supply lines Vb1 to Vb3, a drain and a gate of the correction transistor 204, and a third power supply line 205. And a transistor 206 for controlling the connection therebetween. The source of the correction transistor 204 is connected to the fourth power supply line 207. The drain and gate of the correction transistor 204 are connected to the second power supply lines Vb1 to Vb3.

  The correction transistor 204 has the same polarity as the driving transistor 103 included in the pixel 202. Further, it is desirable that the correction transistor 204 and the driving transistor 103 have the same characteristics such as a threshold voltage. Specifically, it is desirable to make the ratio between the channel length and the channel width substantially the same.

  When the driving transistor 103 and the correction transistor 204 are p-type, the potential of the fourth power supply line 207 is set lower than the potentials of the first power supply lines Va1 to Va3. The potential of the third power supply line 205 is set to be lower than the potential obtained by subtracting the threshold voltage Vth of the correcting transistor from the potential of the fourth power supply line. Then, the potentials of the first power supply lines Va1 to Va3 are set to be higher than the potential of the second electrode included in the light emitting element 101. Specifically, the potential difference between the first power supply lines Va1 to Va3 and the second electrode of the light-emitting element 101 is such that a forward bias is applied to the light-emitting element 101 when both the driving transistor 103 and the current control transistor 104 are on. It is assumed that the current is supplied.

  Conversely, when the driving transistor 103 and the correction transistor 204 are n-type, the potential of the fourth power supply line 207 is set higher than the potentials of the first power supply lines Va1 to Va3. Further, the potential of the third power supply line 205 is set to be higher than the potential obtained by adding the threshold voltage Vth of the correcting transistor to the potential of the fourth power supply line. Then, the potentials of the first power supply lines Va1 to Va3 are set to be higher than the potential of the second electrode included in the light emitting element 101. Specifically, the potential difference between the first power supply lines Va1 to Va3 and the second electrode of the light-emitting element 101 is such that a forward bias is applied to the light-emitting element 101 when both the driving transistor 103 and the current control transistor 104 are on. It is assumed that the current is supplied.

  Note that the transistor 206 may be either n-type or p-type.

  Next, taking the pixel shown in FIG. 1A as an example, a driving method of the light-emitting device of the present invention shown in FIG. 2 will be described. The operation of the pixel illustrated in FIG. 1A can be described by being divided into a writing period and a holding period. FIG. 3A shows an operation when the current control transistor 104 is on in the writing period, and FIG. 3B shows an operation when the current control transistor 104 is off in the writing period. FIG. 3C shows an operation when the current control transistor 104 is on in the holding period, and FIG. 3D shows an operation when the current control transistor 104 is off in the holding period. 3A to 3D, the switching transistor 102 and the current control transistor 104 are simply shown as switches for easy understanding of the operation.

  First, in the writing period, the scanning lines Gj (j = 1 to y) are sequentially selected. When the scanning line Gj is selected, the switching transistor 102 whose gate is connected to the scanning line Gj is turned on. Then, the video signal input to the signal line Si (i = 1 to x) is input to the gate of the current control transistor 104 when the switching transistor 102 is turned on.

  Note that when the current control transistor 104 is turned on in accordance with the potential of the video signal as shown in FIG. 3A, a current is supplied to the light-emitting element 101 through the first power supply line Vai (i = 1 to x). Supplied. The current flowing through the light emitting element 101 is determined by the drain current of the driving transistor 103 and the voltage-current characteristics of the light emitting element 101. Then, the light emitting element 101 emits light with a luminance with a height corresponding to the supplied current. On the other hand, when the current control transistor 104 is turned off in accordance with the potential of the video signal as shown in FIG. 3B, the supply of current to the light-emitting element 101 is stopped, and the light-emitting element 101 enters a non-light-emitting state.

  Next, in the holding period, selection of the scanning line Gj (j = 1 to y) is completed, and the switching transistor 102 is turned off. The potential of the video signal input to the pixel in the writing period is held by a capacitor or the like in the holding period. Therefore, when the current control transistor 104 is on as shown in FIG. 3A during the writing period, the current control transistor 104 remains on even during the holding period as shown in FIG. 3C. . Therefore, the light emitting element 101 maintains a light emitting state. On the other hand, when the current control transistor 104 is off in the writing period as shown in FIG. 3B, the current control transistor 104 remains off in the holding period as shown in FIG. 3D. is there. Therefore, the light emitting element 101 maintains a non-light emitting state.

  With the above operation, an image can be displayed. Note that gradation can be displayed by repeating the above operation within one frame period. The number of gradations can be determined by controlling the total time of the writing period and the holding period during which the light emitting element emits light within one frame period.

  Note that in the above operation, light emission of the light-emitting element 101 is controlled in accordance with the video signal in the writing period; however, the present invention is not limited to this structure. For example, the supply of current to the light-emitting elements 101 may be stopped during the writing period without depending on the video signal so that all the light-emitting elements 101 are in a non-light-emitting state. Specifically, the potential difference between the second electrode of the light-emitting element 101 and the first power supply line Vai (i = 1 to x) may be filled only during the writing period. Alternatively, when the light-emitting element is regarded as a diode only during the writing period, a reverse bias voltage is applied between the pair of electrodes included in the light-emitting element 101 and the first power supply line Vai (i = 1 to x) may be set. Alternatively, the path of the current flowing through the light emitting element may be blocked by a switch or the like.

  In the case of a pixel having the erasing transistor 105 as shown in FIGS. 1C and 1D, the second scanning line Gbj (j = 1 to y) is selected and the erasing TFT 105 is turned on. Then, the potentials of the first power supply lines Va1 to Vax can be applied to the gate of the current control TFT 104. Accordingly, since the current control TFT 104 is turned off, a state where no current is forcibly supplied to the light emitting element 101 can be created.

  Next, the operation of the correction circuit 203 shown in FIG. 2 will be described with reference to FIG. FIG. 4A shows the operation of the correction circuit 203 when correcting the potential of the second power supply line Vbi. FIG. 4B illustrates the operation of the correction circuit 203 during a period in which the corrected potential is maintained. Note that in FIGS. 4A and 4B, the transistor 206 is simply illustrated as a switch for easy understanding of the operation.

  First, as shown in FIG. 4A, the transistor 206 is turned on, so that the potential of the third power supply line 205 is supplied to the gate and the drain of the correction transistor 204. Further, the potential of the fourth power supply line 207 is applied to the source of the correction transistor 204. As described above, when the correction transistor 204 is p-type, the potential of the third power supply line 205 is lower than the potential obtained by subtracting the threshold voltage Vth of the correction transistor 204 from the potential of the fourth power supply line. It is set as follows. Accordingly, the correction transistor 204 is turned on, and a current corresponding to the potential difference between the third power supply line 205 and the fourth power supply line 207 flows between the source and drain of the correction transistor 204.

  Next, as shown in FIG. 4B, the transistor 206 is turned off. Then, the path of the current flowing between the source and drain of the correction transistor 204 is cut off. Therefore, until the gate voltage Vgs of the correction transistor 204 becomes equal to the threshold voltage Vth, current continues to flow to some extent between the source and drain of the correction transistor 204, and finally the gate voltage Vgs becomes equal to the threshold voltage Vth. The correction transistor 204 is turned off. Therefore, when the correction transistor 204 is turned off, the potential obtained by subtracting the threshold voltage Vth from the potential of the fourth power supply line 207 is applied to the second power supply line Vbi connected to the gate and drain of the correction transistor 204. Will be.

  Note that as described above, when the correction transistor 204 is p-type, the potential of the fourth power supply line 207 is set lower than the potential of the first power supply line Vai. Therefore, when the current control transistor 104 is on, assuming that the threshold voltages of the driving transistor 103 and the correction transistor 204 are the same, the gate voltage of the driving transistor 103 is lower than the threshold voltage, so that the transistor is turned on. A current is supplied to the element 101. With the above structure, even if the threshold voltage of the driving transistor 103 varies, the gate voltage Vgs of the driving transistor 103 can be corrected in accordance with the variation, so that variation in current supplied to the light emitting element 101 can be suppressed. Can do.

  Note that the correction circuit 203 illustrated in FIG. 2 can operate in parallel with the operation of the pixel 202.

  2 and 4 show examples in which the drain and gate of the correction transistor 204 are directly connected to the second power supply lines Vb1 to Vb3, the present invention is not limited to this configuration. A switch for controlling the connection between the drain and gate of the correction transistor 204 and the second power supply lines Vb1 to Vb3 may be provided. In this case, as shown in FIG. 4A, when the transistor 206 is turned on and the potential of the third power supply line 205 is applied to the gate and drain of the correction transistor 204, the switch is turned on. Then, as shown in FIG. 4B, by turning off the transistor 206, the correction transistor 204 is turned off, and then the second power supply line Vbi connected to the gate and the drain is connected to the fourth power supply line 207. The switch may be turned off when the potential obtained by subtracting the threshold voltage Vth from the potential is applied. By providing the switch, fluctuations in the potential of the second power supply line Vbi after correction can be further suppressed.

  The correction circuit 203 may be provided with an impedance converter on the output side. FIG. 17A illustrates an example in which a voltage follower 220 is provided between the second power supply line Vbi and the drain and gate of the correction transistor 204. The voltage follower 220 is provided such that the non-inverting input terminal is connected to the drain and gate of the correction transistor 204 and the output terminal is connected to the second power supply line Vbi. With the above structure, a potential drop due to the wiring resistance of the second power supply line Vbi can be suppressed.

  Next, a correction circuit having a configuration different from that in FIG. 2 will be described. FIG. 5 shows an example of the structure of the pixel portion and the correction circuit of the light emitting device of the present invention. In FIG. 5, the same reference numerals are given to those already shown in FIG.

  As shown in FIG. 5, a plurality of pixels 502 are formed in the pixel portion 501. Note that FIG. 5 illustrates the pixel 502 having the structure illustrated in FIG. 1A; however, the structure of the pixel 502 included in the pixel portion 501 is not limited thereto.

  The second power supply lines Vb1 to Vb3 are connected to the correction circuit 503, respectively. Note that FIG. 5 shows an example in which the first power supply lines Va1 to Va3, the second power supply lines Vb1 to Vb3, and the scanning lines G1 to G3 are formed in the pixel portion 501, but the number of wirings is as follows. The first scan line and the second scan line may be formed in the pixel portion 501 as in the pixel illustrated in FIGS. 1C and 1D.

  The correction circuit 503 includes a correction transistor 504 having a gate and a drain connected to each of the second power supply lines Vb1 to Vb3, a drain and a gate of the correction transistor 504, and a third power supply line 505. A transistor 506 for controlling the connection between them, and a transistor 508 for controlling the connection between the drain and gate of the correcting transistor 504 and the second power supply lines Vb1 to Vb3. The source of the correction transistor 504 is connected to the fourth power supply line 507.

  Note that the transistor 508 only needs to be able to control the current flowing between the fourth power supply line 507 and the second power supply line Vbi. Therefore, as shown in FIG. It is not necessary to form between the two power supply lines Vb1 to Vb3. For example, the transistor 508 may be formed between the fourth power supply line 507 and the source of the correction transistor 504. Alternatively, the transistor 508 may be formed between the node between the drain and gate of the correction transistor 504 and the drain of the correction transistor 504.

  The correction transistor 504 has the same polarity as the driving transistor 103 included in the pixel 502. Further, it is desirable that the correction transistor 504 and the driving transistor 103 have the same characteristics such as a threshold voltage. Specifically, it is desirable to make the ratio between the channel length and the channel width substantially the same.

  The potential of the fourth power supply line 507 is most preferably set to be about the same as the potential of the first power supply lines Va1 to Va3. If the potential of the fourth power supply line 507 and the potential of the first power supply lines Va1 to Va3 are the same, the variation in the threshold voltage of the driving transistor 103 is accurately reflected in the correction of the potential of the second power supply line Vbi. It is because it can be made. However, the potential of the fourth power supply line 507 and the potential of the first power supply lines Va1 to Va3 are not necessarily the same. The degree of the same may be set as appropriate by the designer within the allowable range of accuracy required for correction.

  However, when the driving transistor 103 and the correction transistor 504 are p-type, the potential of the fourth power supply line 507 is set to be equal to or higher than the potentials of the first power supply lines Va1 to Va3. Then, the potentials of the first power supply lines Va1 to Va3 are set to be higher than the potential of the second electrode of the light emitting element 101. Specifically, the potential difference between the first power supply lines Va1 to Va3 and the second electrode of the light-emitting element 101 is such that a forward bias is applied to the light-emitting element 101 when both the driving transistor 103 and the current control transistor 104 are on. It is assumed that the current is supplied.

  On the other hand, when the driving transistor 103 and the correction transistor 504 are n-type, the potential of the fourth power supply line 507 is set to be the same as or lower than the potential of the first power supply lines Va1 to Va3. Then, the potentials of the first power supply lines Va1 to Va3 are set to be higher than the potential of the second electrode of the light emitting element 101. Specifically, the potential difference between the first power supply lines Va1 to Va3 and the second electrode of the light-emitting element 101 is such that a forward bias is applied to the light-emitting element 101 when both the driving transistor 103 and the current control transistor 104 are on. It is assumed that the current is supplied.

  Note that the transistor 506 and the transistor 508 may be either n-type or p-type.

  Next, the operation of the correction circuit 503 shown in FIG. 5 will be described with reference to FIG. FIG. 6A shows the operation of the correction circuit 503 when correcting the potential of the second power supply line Vbi. FIG. 6B illustrates the operation of the correction circuit 503 during a period in which the corrected potential is maintained. Note that in FIGS. 6A and 6B, the transistor 506 and the transistor 508 are simply illustrated as switches for easy understanding of the operation.

First, as illustrated in FIG. 6A, the transistors 506 and 508 are turned on. Then, a constant current I flows between the third power supply line 505 and the fourth power supply line 507. This constant current I corresponds to the drain current of the correction transistor 504. Note that since the correcting transistor 504 operates in the saturation region, the drain current of the correcting transistor 504 follows Equation 1 shown in Equation 1 below. In Equation 1, β = μC ₀ W / L, μ is the mobility, C ₀ is the gate capacitance per unit area, and W / L is the ratio of the channel width W to the channel length L in the channel formation region.

From Equation 1, it can be seen that the gate voltage Vgs of the correction transistor 504 is determined by the current I flowing between the third power supply line 505 and the fourth power supply line 507. At this time, since the transistor 508 is on, when the potential of the fourth power supply line 507 and the potential of the first power supply line Vai are the same, the correction transistor 504 and the driving transistor 103 have the gate voltage Vgs. Are the same. Therefore, as the characteristics of the correcting transistor 504 and the driving transistor 103, specifically, μC ₀ W / L and the threshold voltage Vth are the same, the driving transistor 103 has the same characteristics when the current controlling transistor 104 is on. The drain current is the same as the drain current I of the correction transistor 504. Therefore, variation in luminance of the light-emitting element 101 can be suppressed even when the characteristics of the driving transistor 103 vary in the pixel portion.

  Next, as shown in FIG. 6B, the transistors 506 and 508 are turned off. It is more preferable to turn off the transistor 508 first than the transistor 506, because a change in the potential of the second power supply line Vbi can be suppressed. By turning off the transistors 506 and 508, the gate voltage Vgs of the driving transistor 103 is maintained.

  Note that the correction circuit 503 illustrated in FIG. 5 can operate in parallel with the operation of the pixel 502.

  The correction circuit 503 may be provided with an impedance converter on the output side. FIG. 17B illustrates an example in which a voltage follower 520 and a capacitor 521 are provided between the second power supply line Vbi and the source or drain of the transistor 508. The voltage follower 520 is provided so that the non-inverting input terminal is connected to the source or drain of the transistor 508 and the output terminal is connected to the second power supply line Vbi. The capacitor 521 has one electrode connected to the non-inverting input terminal of the voltage follower 520 and the other electrode connected to the ground. With the above structure, a potential drop due to the wiring resistance of the second power supply line Vbi can be suppressed.

  In the present invention, when a plurality of pixels share the second power supply line Vbi, it is desirable that the characteristics of the driving transistor included in each of the plurality of pixels be aligned with the characteristics of the corresponding one correction transistor. . The characteristics of the TFT can be made more uniform by aligning the channel length, channel width, materials such as the active layer, insulating film, and gate electrode, and the film thickness. In addition, in the case of a TFT using a semi-amorphous semiconductor or a polycrystalline semiconductor as an active layer, in addition to aligning the outline and material of the TFT in this way, it is also very easy to align the crystallinity of the semiconductor film used as the active layer. is important. For example, in the case of crystallizing a semiconductor film by using a laser annealing method, a region serving as an active layer of a plurality of driving transistors sharing the second power supply line Vbi and a correction corresponding to the driving transistor The region to be the active layer of the transistor is set within the same beam spot. Note that when a plurality of pulses of laser light are irradiated to one place, at least one pulse is set so that all the above-described regions are within the same beam spot.

  Note that the crystallization of the semiconductor film may be combined with a crystallization method using a catalytic element instead of a laser crystallization method.

A known pulse oscillation gas laser or solid-state laser can be used as the laser. For example, YAG laser doped with Cr, Nd, Er, Ho, Ce, Co, Ti or Tm, YVO ₄ laser, YLF laser, YAlO ₃ laser, glass laser, ruby laser, alexandrite laser, Ti: sapphire laser, fol Stellite laser (Mg ₂ SiO ₄ ). Although the fundamental wave of the laser differs depending on the material to be doped, laser light having a fundamental wave of around 1 μm can be obtained. The second harmonic, the third harmonic, and the fourth harmonic with respect to the fundamental wave can be obtained by using a nonlinear optical element.

  The structure of the light-emitting device of the present invention formed using a laser annealing method will be described with reference to FIGS. In FIG. 7, the same reference numerals are given to those already shown in FIG.

  FIG. 7A illustrates a top view of the pixel 202 illustrated in FIG. 2 as an example. Note that FIG. 7A illustrates only the first electrode 701 of the light-emitting element 101 and the region 702 where the first electrode 701 actually overlaps the electroluminescent layer and the second electrode. In FIG. 7A, the switching transistor 102 has an active layer 703, and the driving transistor 103 and the current control transistor 104 share the active layer 704.

  FIG. 7B illustrates an example of a top view of the correction circuit 203 illustrated in FIG. In FIG. 7B, the correction transistor 204 and the transistor 206 share the active layer 705.

  Next, FIG. 8 shows a state in which a semiconductor film used as an active layer is crystallized by a laser annealing method. In FIG. 8, the laser beam is scanned as indicated by the white arrow. The regions indicated by reference numerals 703a to 703c correspond to regions used later as the active layer 703 of the switching transistor 102 illustrated in FIG. A region indicated by reference numerals 704a to 704c corresponds to a region to be used later as the active layer 704 of the driving transistor 103 and the current control transistor 104 shown in FIG. The regions indicated by reference numerals 705a to 705c correspond to regions used later as the active layers 705 of the correction transistor 204 and the transistor 206 shown in FIG.

  A region indicated by 704a corresponds to the plurality of pixels 202 sharing the second power supply line Vb1, and a region indicated by 705a is used for correction for correcting the potential of the second power supply line Vb1. This corresponds to the transistor 204. In the present invention, laser annealing is performed so that the region indicated by 704a and the region indicated by 705a are within the beam spot 710 of the laser beam. Note that when a plurality of pulses of laser light are irradiated to one place, the region indicated by 704a and the region indicated by 705a are accommodated in the same beam spot 710 in at least one pulse.

  Similarly, the region indicated by 704b corresponds to the plurality of pixels 202 sharing the second power supply line Vb2, and the region indicated by 705b is used for correcting the potential of the second power supply line Vb2. This corresponds to the correction transistor 204. In the present invention, laser annealing is performed so that the region indicated by 704b and the region indicated by 705b fall within the laser beam spot 710. Note that when a plurality of pulses of laser light are irradiated to one place, the region indicated by 704b and the region indicated by 705b are accommodated in the same beam spot 710 in at least one pulse.

  Similarly, a region indicated by 704c corresponds to the plurality of pixels 202 sharing the second power supply line Vb3, and a region indicated by 705c is for correcting the potential of the second power supply line Vb3. This corresponds to the correction transistor 204. In the present invention, laser annealing is performed so that the region indicated by 704c and the region indicated by 705c fall within the laser beam spot 710. Note that when a plurality of pulses of laser light are irradiated to one place, the region indicated by 704c and the region indicated by 705c are accommodated in the same beam spot 710 in at least one pulse.

  The regions 704a, 704b, and 704c that serve as the active layer of the driving transistor and the regions 705a, 705b, and 705c that serve as the active layer of the correction transistor have substantially the same carrier moving direction and path when used as the active layer. It is desirable to lay out so that it becomes.

  In FIG. 8, since it is assumed that the signal line and the second power supply line are formed in parallel, the major axis direction of the beam spot 710 and the direction in which the signal line extends are arranged in parallel. However, the present invention is not limited to this configuration. When the scanning line and the second power supply line are formed in parallel, the major axis direction of the beam spot 710 and the direction in which the scanning line extends are arranged in parallel.

  With the above structure, variation in crystallinity can be reduced between the active layer of the driving transistor and the active layer of the correcting transistor corresponding to the driving transistor even if the output of the laser light varies between pulses. Therefore, the characteristics of the driving transistor included in each of the plurality of pixels sharing the second power supply line Vbi can be aligned with the characteristics of the corresponding one correcting transistor, and the threshold voltage can be corrected more accurately. it can.

  In this embodiment, a structure of a pixel in which a TFT (AC transistor) for applying a reverse bias voltage to the light emitting element 101 is formed in the pixel shown in FIG. FIG. 9 illustrates a structure of a pixel in which an AC transistor 106 is formed in the pixel illustrated in FIG. In FIG. 9, the same reference numerals are given to those already shown in FIG.

  One of the source and the drain of the AC transistor 106 is connected to the first electrode of the light-emitting element 101 and the other is connected to the first power supply line Vai. In FIG. 9, either the source or the drain is connected to the first power supply line Vai, but the present invention is not limited to this configuration. Either one may be connected to the second power supply line Vbi, or may be connected to another wiring prepared separately.

  The AC transistor 106 has a gate electrode connected to the first power supply line Vai. In FIG. 9, the gate electrode of the AC transistor 106 is connected to the first power supply line Vai, but the present invention is not limited to this configuration. The gate electrode of the AC transistor 106 may be connected to the second power supply line Vbi or may be connected to another wiring prepared separately. Note that the AC transistor 106 is configured such that the potential of the gate electrode is the same as or lower than the potential of the source when a forward bias voltage is applied. The AC transistor 106 may be either n-type or p-type.

  By forming the AC transistor 106, a reverse bias voltage can be reliably applied to the light emitting element 101 regardless of the operation of the driving TFT 103 and the current control TFT 104. Further, by applying a reverse bias voltage to the light-emitting element 101, the reliability of the light-emitting element 101 can be improved. In addition, since dust or the like that causes a short circuit can be burned out between the first electrode and the second electrode, the yield can be increased.

  Note that although an example in which an AC transistor is formed in the pixel illustrated in FIG. 1A has been described in this embodiment, the present invention is not limited to this structure. For example, an AC transistor may be formed in the pixel illustrated in FIGS. 1B to 1D.

  In this embodiment, a driver circuit used in the light emitting device of the present invention will be described. FIG. 10 shows a block diagram of the light emitting device of this embodiment. The light-emitting device illustrated in FIG. 10 includes a pixel portion 1111 having a plurality of pixels each including a light-emitting element, a scanning line driver circuit 1112 that selects each pixel, and a signal line driver that controls input of a video signal to the selected pixel. A circuit 1113 and a correction circuit 1117 for correcting the potential of the second power supply line Vbi are provided.

  In FIG. 10, the signal line driver circuit 1113 includes a shift register 1114, a latch A 1115, and a latch B 1116. A clock signal (CLK), a start pulse signal (SP), and a switching signal (L / R) are input to the shift register 1114. When the clock signal (CLK) and the start pulse signal (SP) are input, a timing signal is generated in the shift register 1114. Further, the order of appearance of the pulses of the timing signal is switched by the switching signal (L / R). The generated timing signals are sequentially input to the first-stage latch A1115. When a timing signal is input to the latch A 1115, video signals are sequentially written and held in the latch A 1115 in synchronization with the pulse of the timing signal. In this embodiment, video signals are sequentially written in the latch A 1115, but the present invention is not limited to this configuration. A plurality of stages of latches A1115 may be divided into several groups, and so-called divided driving may be performed in which video signals are input in parallel for each group. Note that the number of groups at this time is called the number of divisions. For example, when the latches are divided into groups for every four stages, it is said that the driving is divided into four.

  The time until video signal writing to all the latches of the latch A 1115 is completed is called a line period. Actually, the line period may include a period in which a horizontal blanking period is added to the line period.

  When one line period ends, a latch signal (Latch Signal) is supplied to the second-stage latch B 1116, and the video signal held in the latch A 1115 is simultaneously written to the latch B 1116 in synchronization with the latch signal, Retained. In the latch A 1115 that has finished sending the video signal to the latch B 1116, the next video signal is sequentially written again in synchronization with the timing signal from the shift register 1114. During the second line 1-line period, a video signal written and held in the latch B 1116 is input to the pixel portion 1111.

  Next, the configuration of the scan line driver circuit 1112 is described. The scan line driver circuit 1112 includes a shift register 1119 and a buffer 1118. In some cases, a level shifter may be provided. In the scan line driver circuit 1112, when the clock CLK and the start pulse signal SP are input to the shift register 1119, a selection signal is generated. The generated selection signal is buffered and amplified in the buffer 1118 and supplied to the corresponding scanning line. The gate of the transistor of the pixel for one line is connected to the scanning line. Since the transistors of the pixels for one line must be turned on all at once, a buffer 1118 that can flow a large current is used.

  Instead of the shift registers 1114 and 1119, another circuit capable of selecting a signal line such as a decoder circuit may be used.

  FIG. 10 illustrates an example in which the correction circuit 1117 is laid out on the opposite side of the signal line driver circuit 1113 with the pixel portion 1111 interposed therebetween, but the present invention is not limited to this structure. A correction circuit 1117 may be laid out between the signal line driver circuit 1113 and the pixel portion 1111. Alternatively, the correction circuit 1117 may be laid out both between the signal line driver circuit 1113 and the pixel portion 1111 and on the opposite side of the signal line driver circuit 1113 with the pixel portion 1111 interposed therebetween. By laying out the correction circuit 1117 in both, the period required to correct the potential of the second power supply line can be shortened, and the potential drop of the second power supply line due to the wiring resistance can be suppressed. be able to.

  Note that in the case where an amorphous semiconductor is used for the semiconductor element formed in the pixel portion 1111, the scan line driver circuit 1112 and the signal line driver circuit 1113 are formed over a substrate different from the substrate over which the pixel portion 1111 is formed. However, it may be mounted on a substrate on which the pixel portion 1111 is formed.

  In the case where a semiconductor element formed in the pixel portion 1111 uses a microcrystalline semiconductor, the scan line driver circuit 1112 is formed over the same substrate as the pixel portion 1111 and the signal line driver circuit 1113 is formed in the pixel portion 1111. You may form on the board | substrate different from the substrate which is different. The signal line driver circuit 1113 may be mounted on the substrate over which the pixel portion 1111 and the scan line driver circuit 1112 are formed.

  In this embodiment, a cross-sectional structure of a pixel when a driving transistor is a p-type is described with reference to FIGS. Note that FIG. 11 illustrates the case where the first electrode is an anode and the second electrode is a cathode; however, the first electrode may be a cathode and the second electrode may be an anode.

  FIG. 11A is a cross-sectional view of a pixel in the case where the driving transistor 6001 and the current control transistor 6002 are p-type and light emitted from the light-emitting element 6003 is extracted from the first electrode 6004 side. In FIG. 11A, the first electrode 6004 of the light-emitting element 6003 and the current control transistor 6002 are electrically connected to each other, but as in the pixels illustrated in FIGS. 1B and 1D. The first electrode 6004 of the light-emitting element 6003 and the driving transistor 6001 may be electrically connected.

  The driving transistor 6001 and the current control transistor 6002 are covered with an interlayer insulating film 6007, and a partition wall 6008 having an opening is formed over the interlayer insulating film 6007. A part of the first electrode 6004 is exposed in the opening of the partition wall 6008, and the first electrode 6004, the electroluminescent layer 6005, and the second electrode 6006 are sequentially stacked in the opening.

  The interlayer insulating film 6007 is formed using an organic resin film, an inorganic insulating film, or an insulating film including a Si—O—Si bond (hereinafter referred to as a siloxane-based insulating film) formed using a siloxane-based material as a starting material. Can do. The siloxane insulating film may have at least one of fluorine, an alkyl group, and aromatic hydrocarbon in addition to hydrogen as a substituent. A material called a low dielectric constant material (low-k material) may be used for the interlayer insulating film 6007.

  The partition wall 6008 can be formed using an organic resin film, an inorganic insulating film, or a siloxane-based insulating film. For example, acrylic resin, polyimide, polyamide, or the like can be used for the organic resin film, and silicon oxide, silicon nitride oxide, or the like can be used for the inorganic insulating film. In particular, a photosensitive organic resin film is used for the partition wall 6008, an opening is formed on the first electrode 6004, and the side wall of the opening is formed to have an inclined surface formed with a continuous curvature. Thus, the connection between the first electrode 6004 and the second electrode 6006 can be prevented.

  The first electrode 6004 is formed using a light-transmitting material or film thickness, and is formed using a material suitable for use as an anode. For example, another light-transmitting oxide conductive material such as indium tin oxide (ITO), zinc oxide (ZnO), indium zinc oxide (IZO), or zinc oxide added with gallium (GZO) is used for the first electrode 6004. Is possible. In addition, indium tin oxide containing ITO and silicon oxide (hereinafter referred to as ITSO), or indium oxide containing silicon oxide mixed with 2 to 20% zinc oxide (ZnO) is used as the first electrode 6004. It may be used. In addition to the light-transmitting oxide conductive material, for example, a single layer film made of one or more of TiN, ZrN, Ti, W, Ni, Pt, Cr, Ag, Al, etc., titanium nitride and aluminum are used. The first electrode 6004 can be formed using a stack including a main component film, a three-layer structure including a titanium nitride film, an aluminum main component film, and a titanium nitride film. Note that in the case where a material other than the light-transmitting oxide conductive material is used, the first electrode 6004 is formed with a thickness enough to transmit light (preferably, about 5 nm to 30 nm).

The second electrode 6006 can be formed using a material and a film thickness that reflect or shield light, and can be formed using a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like with a low work function. Specifically, alkali metals such as Li and Cs, and alkaline earth metals such as Mg, Ca, and Sr, alloys containing these (Mg: Ag, Al: Li, Mg: In, etc.), and compounds thereof ( In addition to CaF ₂ and CaN, rare earth metals such as Yb and Er can be used. When an electron injection layer is provided, other conductive layers such as Al can be used.

  The electroluminescent layer 6005 is composed of one or more layers. When composed of a plurality of layers, these layers can be classified into a hole injection layer, a hole transport layer, a light emitting layer, an electron transport layer, an electron injection layer, and the like from the viewpoint of carrier transport characteristics. In the case where the electroluminescent layer 6005 includes any of a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer in addition to the light emitting layer, the first electrode 6004 to the positive hole injection layer, A hole transport layer, a light emitting layer, an electron transport layer, and an electron injection layer are laminated in this order. Note that the boundaries between the layers are not necessarily clear, and there are cases where the materials constituting the layers are partially mixed and the interface is unclear. For each layer, an organic material or an inorganic material can be used. As the organic material, any of a high molecular weight material, a medium molecular weight material, and a low molecular weight material can be used. The medium molecular weight material corresponds to a low polymer having a number of repeating structural units (degree of polymerization) of about 2 to 20. The distinction between a hole injection layer and a hole transport layer is not necessarily strict, and these are the same in the sense that hole transportability (hole mobility) is a particularly important characteristic. For convenience, the hole injection layer is a layer in contact with the anode, and the layer in contact with the hole injection layer is referred to as a hole transport layer to be distinguished. The same applies to the electron transport layer and the electron injection layer. The layer in contact with the cathode is called an electron injection layer, and the layer in contact with the electron injection layer is called an electron transport layer. The light emitting layer may also serve as an electron transport layer, and is also referred to as a light emitting electron transport layer.

  In the case of the pixel shown in FIG. 11A, light emitted from the light-emitting element 6003 can be extracted from the first electrode 6004 side as shown by a hollow arrow.

  Next, FIG. 11B is a cross-sectional view of a pixel in the case where the driving transistor 6011 and the current control transistor 6012 are p-type and light emitted from the light-emitting element 6013 is extracted from the second electrode 6016 side. In FIG. 11B, the first electrode 6014 of the light-emitting element 6013 and the current control transistor 6012 are electrically connected to each other, as in the pixels illustrated in FIGS. 1B and 1D. The first electrode 6014 of the light-emitting element 6013 and the driving transistor 6011 may be electrically connected. In addition, an electroluminescent layer 6015 and a second electrode 6016 are sequentially stacked over the first electrode 6014.

  The first electrode 6014 is formed using a material and a film thickness that reflect or shield light, and is formed using a material that is suitable for use as an anode. For example, in addition to a single layer film made of one or more of TiN, ZrN, Ti, W, Ni, Pt, Cr, Ag, Al, etc., a laminate of titanium nitride and a film mainly composed of aluminum, a titanium nitride film A three-layer structure of a film mainly containing aluminum and aluminum and a titanium nitride film can be used for the first electrode 6014.

The second electrode 6016 can be formed using a light-transmitting material or film thickness, and can be formed using a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like with a low work function. Specifically, alkali metals such as Li and Cs, and alkaline earth metals such as Mg, Ca, and Sr, alloys containing these (Mg: Ag, Al: Li, Mg: In, etc.), and compounds thereof ( In addition to CaF ₂ and CaN, rare earth metals such as Yb and Er can be used. When an electron injection layer is provided, other conductive layers such as Al can be used. Then, the second electrode 6016 is formed with a thickness enough to transmit light (preferably, about 5 nm to 30 nm). Note that other light-transmitting oxide conductive materials such as indium tin oxide (ITO), zinc oxide (ZnO), indium zinc oxide (IZO), and zinc oxide to which gallium is added (GZO) can also be used. Alternatively, indium tin oxide containing ITO and silicon oxide (hereinafter referred to as ITSO) or indium oxide containing silicon oxide mixed with 2 to 20% zinc oxide (ZnO) may be used. In the case of using a light-transmitting oxide conductive material, it is preferable to provide an electron injection layer in the electroluminescent layer 6015.

  The electroluminescent layer 6015 can be formed in a manner similar to that of the electroluminescent layer 6005 in FIG.

  In the case of the pixel shown in FIG. 11B, light emitted from the light-emitting element 6013 can be extracted from the second electrode 6016 side as shown by a hollow arrow.

  Next, FIG. 11C illustrates the case where the driving transistor 6021 and the current control transistor 6022 are p-type, and light emitted from the light-emitting element 6023 is extracted from the first electrode 6024 side and the second electrode 6026 side. A cross-sectional view of a pixel is shown. In FIG. 11C, the first electrode 6024 of the light-emitting element 6023 and the current control transistor 6022 are electrically connected to each other, as in the pixels illustrated in FIGS. 1B and 1D. The first electrode 6024 of the light-emitting element 6023 and the driving transistor 6021 may be electrically connected. Further, an electroluminescent layer 6025 and a second electrode 6026 are sequentially stacked over the first electrode 6024.

  The first electrode 6024 can be formed in a manner similar to that of the first electrode 6004 in FIG. The second electrode 6026 can be formed in a manner similar to that of the second electrode 6016 in FIG. The electroluminescent layer 6025 can be formed in a manner similar to that of the electroluminescent layer 6005 in FIG.

  In the case of the pixel shown in FIG. 11C, light emitted from the light-emitting element 6023 can be extracted from the first electrode 6024 side and the second electrode 6026 side as indicated by white arrows.

  In this embodiment, a cross-sectional structure of a pixel in the case where an n-type driving transistor is described with reference to FIG. Note that FIG. 12 illustrates the case where the first electrode is a cathode and the second electrode is an anode, but the first electrode may be an anode and the second electrode may be a cathode.

  FIG. 12A is a cross-sectional view of a pixel in the case where the driving transistor 6031 and the current control transistor 6032 are n-type and light emitted from the light-emitting element 6033 is extracted from the first electrode 6034 side. In FIG. 12A, the first electrode 6034 of the light-emitting element 6033 and the current control transistor 6032 are electrically connected to each other, as in the pixels illustrated in FIGS. 1B and 1D. The first electrode 6034 of the light-emitting element 6033 and the driving transistor 6031 may be electrically connected. Further, an electroluminescent layer 6035 and a second electrode 6036 are sequentially stacked over the first electrode 6034.

The first electrode 6034 can be formed using a light-transmitting material or film thickness, and can be formed using a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like with a low work function. Specifically, alkali metals such as Li and Cs, and alkaline earth metals such as Mg, Ca, and Sr, alloys containing these (Mg: Ag, Al: Li, Mg: In, etc.), and compounds thereof ( In addition to CaF ₂ and CaN, rare earth metals such as Yb and Er can be used. When an electron injection layer is provided, other conductive layers such as Al can be used. Then, the first electrode 6034 is formed with a thickness enough to transmit light (preferably, about 5 nm to 30 nm). Further, a light-transmitting conductive layer is formed using a light-transmitting oxide conductive material so as to be in contact with or under the conductive layer having a thickness enough to transmit light, and the first electrode 6034 is formed. The sheet resistance may be suppressed. Note that only conductive layers using other light-transmitting oxide conductive materials such as indium tin oxide (ITO), zinc oxide (ZnO), indium zinc oxide (IZO), and zinc oxide to which gallium is added (GZO) should be used. Is also possible. Alternatively, indium tin oxide containing ITO and silicon oxide (hereinafter referred to as ITSO) or indium oxide containing silicon oxide mixed with 2 to 20% zinc oxide (ZnO) may be used. In the case of using a light-transmitting oxide conductive material, it is preferable to provide an electron injection layer in the electroluminescent layer 6035.

  The second electrode 6036 is formed of a material and a film thickness that reflect or shield light, and is formed using a material that is suitable for use as an anode. For example, in addition to a single layer film made of one or more of TiN, ZrN, Ti, W, Ni, Pt, Cr, Ag, Al, etc., a laminate of titanium nitride and a film mainly composed of aluminum, a titanium nitride film A three-layer structure of a film containing aluminum and aluminum as main components and a titanium nitride film can be used for the second electrode 6036.

  The electroluminescent layer 6035 can be formed in a manner similar to that of the electroluminescent layer 6005 in FIG. However, in the case where the electroluminescent layer 6035 includes any one of a hole injection layer, a hole transport layer, an electron transport layer, and an electron injection layer in addition to the light emitting layer, the first electrode 6034 to the electron injection layer The electron transport layer, the light emitting layer, the hole transport layer, and the hole injection layer are laminated in this order.

  In the case of the pixel shown in FIG. 12A, light emitted from the light-emitting element 6033 can be extracted from the first electrode 6034 side as shown by a hollow arrow.

  Next, FIG. 12B is a cross-sectional view of a pixel in the case where the driving transistor 6041 and the current control transistor 6042 are n-type and light emitted from the light-emitting element 6043 is extracted from the second electrode 6046 side. In FIG. 12B, the first electrode 6044 of the light-emitting element 6043 and the current control transistor 6042 are electrically connected to each other, as in the pixels illustrated in FIGS. 1B and 1D. The first electrode 6044 of the light-emitting element 6043 and the driving transistor 6041 may be electrically connected. Further, an electroluminescent layer 6045 and a second electrode 6046 are sequentially stacked over the first electrode 6044.

The first electrode 6044 can be formed using a material and a film thickness that reflect or shield light, and can be formed using a metal, an alloy, an electrically conductive compound, a mixture thereof, or the like with a low work function. Specifically, alkali metals such as Li and Cs, and alkaline earth metals such as Mg, Ca, and Sr, alloys containing these (Mg: Ag, Al: Li, Mg: In, etc.), and compounds thereof ( In addition to CaF ₂ and CaN, rare earth metals such as Yb and Er can be used. When an electron injection layer is provided, other conductive layers such as Al can be used.

  The second electrode 6046 is formed using a light-transmitting material or film thickness, and is formed using a material suitable for use as an anode. For example, another light-transmitting oxide conductive material such as indium tin oxide (ITO), zinc oxide (ZnO), indium zinc oxide (IZO), or zinc oxide added with gallium (GZO) is used for the second electrode 6046. Is possible. In addition, indium tin oxide containing ITO and silicon oxide (hereinafter referred to as ITSO), indium oxide containing silicon oxide, and further mixed with 2 to 20% zinc oxide (ZnO) are used as the second electrode 6046. It may be used. In addition to the light-transmitting oxide conductive material, for example, a single layer film made of one or more of TiN, ZrN, Ti, W, Ni, Pt, Cr, Ag, Al, etc., titanium nitride and aluminum are used. The second electrode 6046 can be formed using a stack of a main component film, a three-layer structure including a titanium nitride film, an aluminum main component film, and a titanium nitride film. Note that in the case where a material other than the light-transmitting oxide conductive material is used, the second electrode 6046 is formed with a thickness enough to transmit light (preferably, about 5 nm to 30 nm).

  The electroluminescent layer 6045 can be formed in a manner similar to that of the electroluminescent layer 6035 in FIG.

  In the case of the pixel shown in FIG. 12B, light emitted from the light-emitting element 6043 can be extracted from the second electrode 6046 side as shown by a hollow arrow.

  Next, FIG. 12C illustrates the case where the driving transistor 6051 and the current control transistor 6052 are n-type, and light emitted from the light-emitting element 6053 is extracted from the first electrode 6054 side and the second electrode 6056 side. A cross-sectional view of a pixel is shown. In FIG. 12C, the first electrode 6054 of the light-emitting element 6053 and the current control transistor 6052 are electrically connected to each other, as in the pixels illustrated in FIGS. 1B and 1D. The first electrode 6054 of the light-emitting element 6053 and the driving transistor 6051 may be electrically connected. Further, an electroluminescent layer 6055 and a second electrode 6056 are stacked over the first electrode 6054 in this order.

  The first electrode 6054 can be formed in a manner similar to that of the first electrode 6034 in FIG. The second electrode 6056 can be formed in a manner similar to that of the second electrode 6046 in FIG. The electroluminescent layer 6055 can be formed in a manner similar to that of the electroluminescent layer 6035 in FIG.

  In the case of the pixel shown in FIG. 12C, light emitted from the light-emitting element 6053 can be extracted from the first electrode 6054 side and the second electrode 6056 side as indicated by white arrows.

  The light-emitting device of the present invention can be formed by a screen printing method, a printing method typified by an offset printing method, or a droplet discharge method. The droplet discharge method means a method of forming a predetermined pattern by discharging droplets containing a predetermined composition from the pores, and includes an ink jet method and the like in its category. By using the above printing method and droplet discharge method, signal lines, scanning lines, first power supply lines, various wirings typified by second power supply lines, and TFT gate electrodes can be used without using an exposure mask. It becomes possible to form electrodes of light emitting elements. However, it is not necessary to use a printing method or a droplet discharge method for all the steps of forming a pattern. Therefore, for example, a printing method or a droplet discharge method is used in at least a part of the process, for example, a printing method or a droplet discharge method is used for forming a wiring and a gate electrode, and a lithography method is used for patterning a semiconductor film. What is necessary is just to use, and the lithography method may be used together. A mask used for patterning may be formed by a printing method or a droplet discharge method.

  FIG. 13 shows, as an example, a cross-sectional view of a light-emitting device of the present invention formed using a droplet discharge method. In FIG. 13, 1301 is a current control transistor, 1302 is a driving transistor, 1303 is a switching transistor, and 1304 is a light emitting element. Note that in FIG. 13, the current control transistor 1301 is electrically connected to the first electrode of the light-emitting element 1304; however, the present invention is not limited to this structure. The driving transistor 1302 may be electrically connected to the first electrode 1330 of the light-emitting element 1304. The driving transistor 1302 is preferably n-type. In this case, the first electrode 1330 is preferably a cathode, and the second electrode 1331 is preferably an anode.

  The switching transistor 1303 includes a gate electrode 1310, a first semiconductor film 1311 including a channel formation region, a gate insulating film 1317 formed between the gate electrode 1310 and the first semiconductor film 1311, a source region or a drain The semiconductor device includes second semiconductor films 1312 and 1313 functioning as regions, a wiring 1314 connected to the second semiconductor film 1312, and a wiring 1315 connected to the second semiconductor film 1313.

  The current control transistor 1301 includes a gate electrode 1320, a first semiconductor film 1321 including a channel formation region, a gate insulating film 1317 formed between the gate electrode 1320 and the first semiconductor film 1321, a source region or The semiconductor device includes second semiconductor films 1322 and 1323 functioning as drain regions, a wiring 1324 connected to the second semiconductor film 1322, and a wiring 1325 connected to the second semiconductor film 1323.

  The driving transistor 1302 includes a gate electrode 1330, a first semiconductor film 1321 including a channel formation region, a gate insulating film 1317 formed between the gate electrode 1330 and the first semiconductor film 1321, a source region or a drain The semiconductor device includes second semiconductor films 1323 and 1333 that function as regions, a wiring 1325 connected to the second semiconductor film 1323, and a wiring 1335 connected to the second semiconductor film 1333.

  The wiring 1314 corresponds to a signal line, and the wiring 1315 is electrically connected to the gate electrode 1320 of the current control transistor 1301. The wiring 1335 corresponds to the first power supply line, and the gate electrode 1330 is connected to the second power supply line (not shown).

  By forming a pattern using a droplet discharge method or a printing method, a series of steps such as photoresist film formation, exposure, development, etching, and peeling performed by a lithography method can be simplified. Further, unlike the lithography method, the droplet discharge method and the printing method do not waste material that is removed by etching. Further, it is not necessary to use an expensive exposure mask, so that the cost for manufacturing the light-emitting device can be suppressed.

  Further, unlike the lithography method, it is not necessary to perform etching to form the wiring. Therefore, the time spent for the process of forming the wiring can be significantly shortened compared to the case of the lithography method. In particular, when the wiring thickness is 0.5 μm or more, and more desirably 2 μm or more, the wiring resistance can be suppressed. Therefore, the wiring accompanying the increase in the size of the light-emitting device while suppressing the time spent in the wiring manufacturing process. An increase in resistance can be suppressed.

  Note that the first semiconductor films 1311 and 1321 may be either an amorphous semiconductor or a semi-amorphous semiconductor (SAS).

An amorphous semiconductor can be obtained by glow discharge decomposition of a silicide gas. Typical silicide gases include SiH ₄ and Si ₂ H ₆ . This silicide gas may be diluted with hydrogen, hydrogen and helium.

SAS can also be obtained by glow discharge decomposition of silicide gas. A typical silicide gas is SiH ₄ , and in addition, Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , SiF _{4 and the} like can be used. In addition, it is easy to form a SAS by diluting and using this silicide gas with hydrogen or a gas obtained by adding one or more kinds of rare gas elements selected from helium, argon, krypton, and neon to hydrogen. It can be. It is preferable to dilute the silicide gas at a dilution rate in the range of 2 to 1000 times. Furthermore, a carbide gas such as CH ₄ or C ₂ H ₆ , a germanium gas such as GeH ₄ or GeF ₄ , F ₂ or the like is mixed in the silicide gas, so that the energy bandwidth is 1.5-2. You may adjust to 4 eV or 0.9-1.1 eV. A TFT using SAS as the first semiconductor film can obtain a mobility of 1 to 10 cm ² / Vsec or more.

  The first semiconductor films 1311 and 1321 may be formed using a semiconductor obtained by laser crystallization of an amorphous semiconductor or a semi-amorphous semiconductor (SAS).

  Next, a correction circuit having a configuration different from those in FIGS. 2 and 5 will be described.

  FIG. 15A shows the configuration of the correction circuit of this embodiment. The correction circuit of this embodiment includes a first correction transistor 401 having a gate and a drain connected to correspond to the second power supply line Vbi (i = 1 to x), and a first correction transistor 401. A second correction transistor 402 having a polarity opposite to that of the first correction transistor 401, a transistor 403 that controls connection between the drain and gate of the first correction transistor 401 and the drain of the second correction transistor 402, and Transistor 405 for controlling the connection between the drain of the second correction transistor 402 and the third power supply line 404, and the connection between the drain and gate of the first correction transistor 401 and the second power supply line Vbi. Transistor 406 for controlling the transistor and transistor 4 for controlling the connection between the gate of the second correction transistor 402 and the third power supply line 404 7, and a capacitor element 408 for retaining a gate voltage of the second correcting transistor 402. The source of the first correction transistor 401 is connected to the fourth power supply line 409, and the source of the second correction transistor 402 is connected to the fifth power supply line 410.

  Note that the transistor 406 only needs to be able to control the current flowing between the fourth power supply line 409 and the second power supply line Vbi. Therefore, as illustrated in FIG. It is not necessary to form it between the drain of the second power supply line Vbi. For example, the transistor 406 may be formed between the fourth power supply line 409 and the source of the first correction transistor 401.

  The first correction transistor 401 has the same polarity as the driving transistor included in the pixel. Further, it is desirable that the first correction transistor 401 and the driving transistor have the same characteristics such as a threshold voltage. Specifically, it is desirable to make the ratio between the channel length and the channel width substantially the same.

  The potential of the fourth power supply line 409 is most preferably set to be approximately the same as the potential of the first power supply line for controlling the source potential of the driving transistor. If the potential of the fourth power supply line 409 and the potential of the first power supply line are the same, variations in characteristics of the driving transistor can be accurately reflected in the correction of the potential of the second power supply line Vbi. It is. However, the potential of the fourth power supply line 409 and the potential of the first power supply line are not necessarily the same. The degree of the same may be set as appropriate by the designer within the allowable range of accuracy required for correction.

  However, in the case where the driving transistor and the first correction transistor 401 are p-type, the potential of the fourth power supply line 409 is set to be the same as or higher than the potential of the first power supply line. Then, the potential of the first power supply line is set to be higher than the potential of the second electrode of the light emitting element. Specifically, the potential difference between the first power supply line and the second electrode of the light emitting element is such that forward bias current is supplied to the light emitting element when both the driving transistor and the current control transistor are on. And

  On the other hand, when the driving transistor and the first correction transistor 401 are n-type, the potential of the fourth power supply line 409 is set to be the same as or lower than the potential of the first power supply line. Then, the potential of the first power supply line is set to be higher than the potential of the second electrode of the light emitting element. Specifically, the potential difference between the first power supply line and the second electrode of the light emitting element is such that forward bias current is supplied to the light emitting element when both the driving transistor and the current control transistor are on. And

  In the case where the second correction transistor 402 is n-type, the potential of the fifth power supply line 410 is set lower than the potential of the fourth power supply line 409. On the other hand, when the second correction transistor 402 is p-type, the potential of the fifth power supply line 410 is set higher than the potential of the fourth power supply line 409.

  The current flowing through the third power supply line 404 is controlled by the constant current source 411.

  Note that the transistor 403, the transistor 405, the transistor 406, and the transistor 407 may be either n-type or p-type.

  Next, operation of the correction circuit illustrated in FIG. Note that in FIGS. 15B and 15C, the transistor 403, the transistor 405, the transistor 406, and the transistor 407 are simply illustrated as switches for easy understanding of the operation.

  First, as illustrated in FIG. 15B, the transistors 405 and 407 are turned on, and the transistors 403 and 406 are turned off. A constant current source 411 is used to pass a constant current I between the fifth power supply line 410 and the third power supply line 404. This constant current I corresponds to the drain current of the second correction transistor 402. Note that since the transistor 405 and the transistor 407 are on, the gate and the drain of the second correction transistor 402 are connected and operate in the saturation region. Therefore, the second correction transistor 402 operates in accordance with Equation 1 shown in Equation 1 above. From Equation 1, it can be seen that the gate voltage Vgs of the second correction transistor 402 is determined by the current I. The gate voltage Vgs of the second correction transistor 402 is held by the capacitor 408.

  Next, as illustrated in FIG. 15C, the transistors 405 and 407 are turned off, and the transistors 403 and 406 are turned on. It is more preferable to turn off the transistor 407 before the transistor 405 because a change in voltage held in the capacitor 408 can be suppressed.

  When the transistors 405 and 407 are turned off and the transistors 403 and 406 are turned on, the fourth power supply line 409 and the fifth power supply line 409 are connected to the fifth power supply line 409 and the fifth A current flows between the power supply lines 410. The current flowing between the fourth power supply line 409 and the fifth power supply line 410 is determined by the gate voltage of the first correction transistor 401 held in the capacitor 408. That is, in FIG. 15B, a current having the same magnitude as the drain current I of the second correction transistor 402 controlled by the constant current source 411 is the fourth power line 409 in FIG. And the fifth power supply line 410.

  The first correction transistor 401 operates in the saturation region because the gate and the drain are connected. Accordingly, the gate voltage of the first correction transistor 401 is set to a value corresponding to the current I flowing between the fourth power supply line 409 and the fifth power supply line 410. Further, since the transistor 406 is on, when the potential of the fourth power supply line 409 and the potential of the first power supply line are the same, the first correction transistor 401 and the driving transistor have the gate voltage Vgs. Are the same. Accordingly, the gate voltage Vgs of the first correction transistor 401 determined by the current I is the same as the gate voltage Vgs of the driving transistor.

Therefore, as the characteristics of the first correction transistor 401 and the drive transistor, specifically, μC ₀ W / L and the threshold voltage Vth are the same, the drive transistor when the current control transistor is turned on The drain current is the same as the drain current I of the first correction transistor 401. Accordingly, variation in luminance of the light-emitting element can be suppressed even when the characteristics of the driving transistor vary in the pixel portion.

  Note that the correction circuit illustrated in FIG. 15A can operate in parallel with the operation of the pixel.

  In the case of the correction circuit shown in this embodiment, unlike the correction circuit shown in FIGS. 2 and 5, the potential of the second power supply line can always be corrected, so that it is driven by switching the current control transistor, for example. Even if the potential of the source and drain of the transistor for use varies, the potential of the second power supply line Vbi can be suppressed from varying.

  Next, a correction circuit having a configuration different from those shown in FIGS. 2, 5, and 15 will be described.

  FIG. 18A shows the configuration of the correction circuit of this embodiment. The correction circuit of this embodiment includes a first correction transistor 421 having a gate and a drain connected to correspond to the second power supply line Vbi (i = 1 to x), and a first correction transistor 421. The second correction transistor 422 and the third correction transistor 423 having the opposite polarity to each other, and the connection between the gate of the second correction transistor 422 and the gate and drain of the third correction transistor 423 , A transistor 426 for controlling connection between the gate and drain of the third correction transistor 423 and the third power supply line 425, and a gate voltage of the third correction transistor 423 are held. And a capacitor 427 for this purpose. The source of the first correction transistor 421 is connected to the fourth power supply line 428, and the source of the second correction transistor 422 is connected to the fifth power supply line 429. The third correction transistor 423 has its gate and drain connected.

  The current flowing through the third power supply line 425 is controlled by the constant current source 430.

  The first correction transistor 421 has the same polarity as the driving transistor included in the pixel. Further, it is desirable that the first correction transistor 421 and the driving transistor have the same characteristics such as a threshold voltage. Specifically, it is desirable to make the ratio between the channel length and the channel width substantially the same. The second correction transistor 422 and the third correction transistor 423 preferably have the same characteristics such as threshold voltage. Specifically, it is desirable to make the ratio between the channel length and the channel width substantially the same.

  The potential of the fourth power supply line 428 is most preferably set to be the same as the potential of the first power supply line for controlling the source potential of the driving transistor. If the potential of the fourth power supply line 428 and the potential of the first power supply line are the same, variations in characteristics of the driving transistor can be accurately reflected in the correction of the potential of the second power supply line Vbi. It is. However, the potential of the fourth power supply line 428 and the potential of the first power supply line are not necessarily the same. The degree of the same may be set as appropriate by the designer within the allowable range of accuracy required for correction.

  However, in the case where the driving transistor and the first correction transistor 421 are p-type, the potential of the fourth power supply line 428 is set to be the same as or higher than the potential of the first power supply line. Then, the potential of the first power supply line is set to be higher than the potential of the second electrode of the light emitting element. Specifically, the potential difference between the first power supply line and the second electrode of the light emitting element is such that forward bias current is supplied to the light emitting element when both the driving transistor and the current control transistor are on. And

  On the other hand, when the driving transistor and the first correction transistor 421 are n-type, the potential of the fourth power supply line 428 is set to be the same as or lower than the potential of the first power supply line. Then, the potential of the first power supply line is set to be lower than the potential of the second electrode of the light emitting element. Specifically, the potential difference between the first power supply line and the second electrode of the light emitting element is such that forward bias current is supplied to the light emitting element when both the driving transistor and the current control transistor are on. And

  In the case where the second correction transistor 422 and the third correction transistor 423 are n-type, the potential of the fifth power supply line 429 is set lower than the potential of the fourth power supply line 428. On the other hand, when the second correction transistor 422 and the third correction transistor 423 are p-type, the potential of the fifth power supply line 429 is set higher than the potential of the fourth power supply line 428. In any case, the potential difference between the fourth power supply line 428 and the fifth power supply line 429 is set to such a size that the second correction transistor 422 operates in the saturation region.

  Note that the transistor 424 and the transistor 426 may be either n-type or p-type.

  Next, an operation of the correction circuit illustrated in FIG. Note that in FIGS. 18B and 18C, the transistor 424 and the transistor 426 are simply illustrated as switches for easy understanding of the operation.

  First, as shown in FIG. 18B, the transistors 424 and 426 are turned on. Then, a constant current source 430 is used to pass a constant current I between the fifth power supply line 429 and the third power supply line 425. This constant current I corresponds to the drain current of the third correction transistor 423. Note that the third correction transistor 423 operates in the saturation region because the gate and the drain are connected. Therefore, the third correction transistor 423 operates in accordance with Equation 1 shown in Equation 1 above. From Equation 1, it can be seen that the gate voltage Vgs of the third correction transistor 423 is determined by the current I. The gate voltage Vgs of the third correction transistor 423 is held by the capacitor 427.

  On the other hand, since the gates and sources of the second correction transistor 422 and the third correction transistor 423 are connected to each other, the gate voltage of the second correction transistor 422 is the third correction transistor 423. Is equal to the gate voltage. Therefore, as the characteristics of the second correction transistor 422 and the third correction transistor 423 are closer, the drain current of the second correction transistor 422 becomes equal to the drain current of the third correction transistor 423. .

  The drain current of the second correction transistor 422 flows between the fourth power supply line 428 and the fifth power supply line 429. Therefore, the drain current of the first correction transistor 421 also has the same magnitude as the drain current of the second correction transistor 422. That is, the drain current I of the third correction transistor 423 controlled by the constant current source 430 and the drain current of the first correction transistor 421 have the same magnitude.

  The first correction transistor 421 operates in the saturation region because the gate and the drain are connected. Therefore, the gate voltage of the first correction transistor 421 is set to a value corresponding to the drain current I. When the potential of the fourth power supply line 428 and the potential of the first power supply line are the same, the first correction transistor 421 and the driving transistor have the same gate voltage Vgs. Therefore, the gate voltage Vgs of the first correction transistor 421 determined by the current I is the same as the gate voltage Vgs of the driving transistor.

  Next, as illustrated in FIG. 18C, the transistor 424 and the transistor 426 are turned off. It is more preferable to turn off the transistor 424 first than the transistor 426 because fluctuation in the voltage held in the capacitor 427 can be suppressed. Even when the transistor 424 and the transistor 426 are turned off, the gate voltage of the second correction transistor is held, so that the potential of the second power supply line Vbi can be held.

  Note that the correction circuit illustrated in FIG. 18A can operate in parallel with the operation of the pixel.

In the correction circuit of this embodiment, as the characteristics of the first correction transistor 421 and the driving transistor, specifically, μC ₀ W / L and the threshold voltage Vth are the same, the current control transistor is turned on. The drain current of the driving transistor at that time is the same as the drain current I of the first correction transistor 421. Accordingly, variation in luminance of the light-emitting element can be suppressed even when the characteristics of the driving transistor vary in the pixel portion.

  In the case of the correction circuit shown in this embodiment, unlike the correction circuit shown in FIGS. 2 and 5, the potential of the second power supply line can always be corrected, so that it is driven by switching the current control transistor, for example. Even if the potential of the source and drain of the transistor for use varies, the potential of the second power supply line Vbi can be suppressed from varying.

  In this example, the appearance of a panel corresponding to one embodiment of the light-emitting device of the present invention will be described with reference to FIG. 14 is a top view of a panel in which a transistor and a light-emitting element formed over the first substrate are sealed with a sealant between the second substrate and FIG. 14B. This corresponds to a cross-sectional view taken along line AA ′ in FIG.

  A sealant 4005 is provided so as to surround the pixel portion 4002, the signal line driver circuit 4003, the scan line driver circuit 4004, and the correction circuit 4020 provided over the first substrate 4001. A second substrate 4006 is provided over the pixel portion 4002, the signal line driver circuit 4003, the scan line driver circuit 4004, and the correction circuit 4020. Therefore, the pixel portion 4002, the signal line driver circuit 4003, the scanning line driver circuit 4004, and the correction circuit 4020 are sealed together with the filler 4007 by the first substrate 4001, the sealant 4005, and the second substrate 4006. ing.

  In addition, the pixel portion 4002, the signal line driver circuit 4003, the scan line driver circuit 4004, and the correction circuit 4020 provided over the first substrate 4001 each include a plurality of transistors. In FIG. The transistor 4008 included in the signal line driver circuit 4003, the current control transistor 4010 and the driving transistor 4009 included in the pixel portion 4002, and the correction transistor 4030 included in the correction circuit 4020 are illustrated.

  Reference numeral 4011 corresponds to a light-emitting element, and the first electrode of the light-emitting element 4011 is electrically connected to the drain of the driving transistor 4009 through a wiring 4017. In this embodiment, the second electrode of the light emitting element 4011 and the transparent conductive film 4012 are electrically connected. Note that the structure of the light-emitting element 4011 is not limited to the structure described in this embodiment. The structure of the light-emitting element 4011 can be changed as appropriate depending on the direction of light extracted from the light-emitting element 4011, the polarity of the driving transistor 4009, or the like.

  Note that in this example, the current control transistor 4010 is connected to the first electrode of the light emitting element 4011; however, the driving transistor 4009 is connected to the first electrode of the light emitting element 4011. Also good.

  Further, various signals and potentials applied to the signal line driver circuit 4003, the scan line driver circuit 4004, or the pixel portion 4002 are not shown in the cross-sectional view in FIG. 14B, but are routed through lead wirings 4014 and 4015. It is supplied from the connection terminal 4016.

  In this embodiment, the connection terminal 4016 is formed using the same conductive film as the first electrode included in the light-emitting element 4011. Further, the lead wiring 4014 is formed of the same conductive film as the wiring 4017. The lead wiring 4015 is formed using the same conductive film as the gate electrodes of the driving transistor 4009 and the transistor 4008.

  The connection terminal 4016 is electrically connected to a terminal included in the FPC 4018 through an anisotropic conductive film 4019.

  Note that as the first substrate 4001 and the second substrate 4006, glass, metal (typically stainless steel), ceramics, or plastic can be used. As the plastic, an FRP (Fiberglass-Reinforced Plastics) plate, a PVF (polyvinyl fluoride) film, a mylar film, a polyester film, or an acrylic resin film can be used. Alternatively, a sheet having a structure in which aluminum is sandwiched between PVF films or mylar films can be used.

  Note that the second substrate 4006 must have a light-transmitting property with respect to the substrate positioned in the light extraction direction from the light-emitting element 4011. In that case, a light-transmitting material such as a glass plate, a plastic plate, a polyester film, or an acrylic film is used.

  As the filler 4007, in addition to an inert gas such as nitrogen or argon, an ultraviolet curable resin or a thermosetting resin can be used. PVC (polyvinyl chloride), acrylic, polyimide, epoxy resin, silicon resin, PVB (Polyvinyl butyral) or EVA (ethylene vinyl acetate) can be used. In this example, nitrogen was used as the filler.

  This embodiment can be implemented by freely combining with Embodiments 1 to 7.

  Since the light-emitting device of the present invention can suppress variations in luminance between pixels, the light-emitting device is optimal for an electronic device having a display unit for viewing images such as a display device and a goggle type display.

  Other electronic devices that can use the light emitting device of the present invention include a video camera, a digital camera, a goggle type display (head mounted display), a navigation system, a sound reproduction device (car audio, audio component, etc.), and a notebook type personal computer. A game machine, a portable information terminal (mobile computer, mobile phone, portable game machine, electronic book or the like), an image playback device equipped with a recording medium (typically a DVD: Digital Versatile Disc or the like, And a device having a display capable of displaying the image). Specific examples of these electronic devices are shown in FIGS.

  FIG. 16A illustrates a personal digital assistant (PDA), which includes a main body 2101, a display portion 2102, operation keys 2103, a speaker portion 2104, and the like. The light emitting device of the present invention can be used for the display portion 2102.

  FIG. 16B illustrates a goggle type display device, which includes a main body 2201, a display portion 2202, earphones 2203, and a support portion 2204. The light emitting device of the present invention can be used for the display portion 2202. The support unit 2204 may be a type that fixes the goggle type display device to the head itself, or may be a type that fixes the goggle type display device to a portion other than the head of the user's body.

  FIG. 16C illustrates a display device, which includes a housing 2401, a display portion 2402, a speaker portion 2403, and the like. The light emitting device of the present invention can be used for the display portion 2402. Since the light-emitting device is a self-luminous type, a backlight is not necessary and a display portion thinner than a liquid crystal display can be obtained. The display devices include all information display devices for personal computers, TV broadcast reception, advertisement display, and the like. Note that in the case where a light-emitting device is used for the display device, a polarizing plate is provided in order to prevent external light from being reflected by the first electrode or the second electrode included in the light-emitting element to cause an image to be projected like a mirror surface. You can keep it.

  As described above, the applicable range of the present invention is so wide that it can be used for electronic devices in various fields. In addition, the electronic device of this embodiment may use the light emitting device having any structure shown in Embodiments 1 to 8.

FIG. 6 illustrates a structure of a pixel included in a light-emitting device of the present invention. FIG. 6 illustrates a structure of a pixel portion and a correction circuit included in a light-emitting device of the present invention. 4A and 4B illustrate operation of a pixel included in a light-emitting device of the present invention. FIG. 9 shows operation of a correction circuit included in the light-emitting device of the present invention. FIG. 6 illustrates a structure of a pixel portion and a correction circuit included in a light-emitting device of the present invention. FIG. 9 shows operation of a correction circuit included in the light-emitting device of the present invention. The top view of a pixel and the top view of a correction circuit. The figure which shows the layout of the area | region in which a beam spot and an active layer are formed. FIG. 6 illustrates a structure of a pixel included in a light-emitting device of the present invention. 1 is a block diagram illustrating a configuration of a light emitting device of the present invention. 4 is a cross-sectional view of a pixel included in a light-emitting device of the present invention. FIG. 4 is a cross-sectional view of a pixel included in a light-emitting device of the present invention. FIG. 4 is a cross-sectional view of a pixel included in a light-emitting device of the present invention. FIG. 2A and 2B are a top view and a cross-sectional view of a light-emitting device of the present invention. FIG. 6 illustrates a structure of a pixel portion and a correction circuit included in a light-emitting device of the present invention. FIG. 14 is a diagram of an electronic device using the light-emitting device of the present invention. FIG. 6 illustrates a configuration of a correction circuit included in a light-emitting device of the present invention. FIG. 6 illustrates a configuration of a correction circuit included in a light-emitting device of the present invention.

Claims (4)

A pixel having a light emitting element, a first transistor, and a second transistor;
The first transistor and the second transistor are electrically connected in series between the light emitting element and a wiring having a function of supplying a power supply potential,
A potential that determines a current flowing through the light emitting element is supplied to a gate of the first transistor,
Data for selecting light emission or non-light emission of the light emitting element is supplied to the gate of the second transistor,
The potential applied to the gate of the first transistor is corrected according to the threshold voltage ,
The correction, the light emitting device according to claim Rukoto performed by the correction circuit provided outside the pixel. A pixel having a light emitting element, a first transistor, and a second transistor;
The first transistor and the second transistor are electrically connected in series between the light emitting element and a wiring having a function of supplying a power supply potential,
A potential that determines a current flowing through the light emitting element is supplied to a gate of the first transistor,
Data for selecting light emission or non-light emission of the light emitting element is supplied to the gate of the second transistor,
The potential applied to the gate of the first transistor is corrected according to the threshold voltage,
The correction is performed by a correction circuit provided outside the pixel,
The light-emitting device, wherein the first transistor operates in a saturation region and the second transistor operates in a linear region. A pixel having a light emitting element, a first transistor, and a second transistor;
The first transistor and the second transistor are electrically connected in series between the light emitting element and a wiring having a function of supplying a power supply potential,
A potential that determines a current flowing through the light emitting element is supplied to a gate of the first transistor,
Data for selecting light emission or non-light emission of the light emitting element is supplied to the gate of the second transistor,
The potential applied to the gate of the first transistor is corrected according to the threshold voltage,
The correction is performed by a correction circuit provided outside the pixel,
The light-emitting device is characterized in that the first transistor has a channel length longer than a channel width. A pixel having a light emitting element, a first transistor, and a second transistor;
The first transistor and the second transistor are electrically connected in series between the light emitting element and a wiring having a function of supplying a power supply potential,
A potential that determines a current flowing through the light emitting element is supplied to a gate of the first transistor,
Data for selecting light emission or non-light emission of the light emitting element is supplied to the gate of the second transistor,
The potential applied to the gate of the first transistor is corrected according to the threshold voltage,
The correction is performed by a correction circuit provided outside the pixel,
The first transistor has a channel length longer than a channel width,
The light-emitting device is characterized in that the second transistor has a channel length equal to or smaller than a channel width.