JP4112248B2 - Light emitting device, electronic equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a technology of a light emitting device and a display device. Furthermore, the present invention relates to an electronic device equipped with the light emitting device or the display device. The light-emitting device in this specification refers to a device that uses light emitted from a self-luminous element. Examples of the self-light emitting element include an organic light emitting diode (OLED) element, an inorganic material light emitting diode element, and a field emission light emitting element (FED element). The display device in this specification refers to a device that arranges a plurality of pixels in a matrix and visually transmits image information, a so-called display.
[0002]
[Prior art]
In recent years, the importance of display devices that display images has increased. As a display device, a liquid crystal display device that displays an image using a liquid crystal element is widely used as a display device for various applications including a mobile phone and a personal computer, taking advantage of high image quality, thinness, and light weight. It has been.
[0003]
On the other hand, development of display devices and light-emitting devices using self-luminous elements is also underway. There are various types of self-luminous elements such as organic materials, inorganic materials, thin film materials, bulk materials, and dispersion materials.
[0004]
Among the above self-luminous elements, organic light emitting diode (OLED) elements are promising in the future for display devices. OLED display devices that use OLED elements as self-luminous elements have features such as high response speed, high viewing angle, and low voltage drive suitable for video display, in addition to features that are thinner and lighter than existing liquid crystal display devices. Therefore, a wide range of applications such as mobile phones and personal digital assistants (PDAs), televisions and monitors are expected. As a result, OLED display devices are attracting attention as next-generation displays.
[0005]
In particular, an active matrix (hereinafter referred to as AM) type OLED display device is capable of high-definition and large-screen display, which is difficult with a passive matrix (hereinafter referred to as PM) type. Expectations for practical use are very strong because of its low power consumption and high reliability.
[0006]
The OLED element has a structure having an anode, a cathode, and an organic compound layer sandwiched between the anode and the cathode. The amount of current flowing through the OLED element and the light emission luminance of the OLED element are generally proportional. In a pixel included in an AM type OLED display device, a driving transistor for controlling the light emission luminance of the OLED element of the pixel is often connected in series to the OLED element.
[0007]
By the way, driving methods for displaying an image in an AM type OLED display device are roughly classified into a voltage input method and a current input method. In the former voltage input method, a video signal of voltage value format data is input as a video signal input to a pixel. In the latter current input method, a video signal of current value format data is input as a video signal input to the pixel.
[0008]
In the voltage input method, the voltage of the video signal is directly applied to the gate electrode of the driving transistor of the normal pixel. Therefore, when the OLED element emits light at a constant current, if the electric characteristics of the driving transistor are not uniform among the pixels, the OLED element driving current of each pixel varies. The variation in the OLED element driving current is a variation in the light emission luminance of the OLED element. That is, the variation in the light emission luminance of the OLED element is a sandstorm-like or carpet-like unevenness on the entire screen, and degrades the quality of the display image.
[0009]
Therefore, there is a current input method as one of effective means for suppressing variations in the OLED element driving current in the voltage input method. In the current input method, a data current value of a normal video signal is stored, and a current that is the same as the stored current value or several times (a positive real number including less than 1) is supplied as an OLED element driving current.
[0010]
A typical example of a pixel circuit of a current input type AM-type OLED display device is shown in FIG. 10A (see A. Yumoto et al., Proc. Asia Display / IDW '01 pp1395-1398 (2001), etc.) ). In FIG. 10A, reference numeral 516 denotes an OLED element. The pixel circuit illustrated in FIG. 10A includes a current mirror circuit. Therefore, as long as the two transistors constituting the current mirror circuit have the same electrical characteristics, the data current value of the video signal can be stored accurately. Even if the electrical characteristics of the driving transistors of different pixels vary, if the two transistors in the same pixel have the same electrical characteristics, the emission luminance of the OLED element varies. Will be suppressed.
[0011]
Next, FIG. 10B shows an example of a pixel circuit of an AM type OLED display device of a current input system different from that in FIG. 10A (IM Hunter et al., Proc. AM-LCD 2000 pp249-252 (2000 ) Etc.). In FIG. 10B, reference numeral 611 denotes an OLED element. In the pixel circuit illustrated in FIG. 10B, when a voltage corresponding to a video signal is written to the gate electrode of the driving transistor, the drain electrode and the gate electrode of the driving transistor are short-circuited. In this state, a data current of the video signal is supplied, and then the gate electrode is electrically insulated. At this time, if the driving transistor is operated in the saturation region when the OLED element emits light, the driving transistor supplies the OLED element with a current having the same value as the data current at the time of writing. Therefore, even if there is a variation in the electrical characteristics of the driving transistor of each pixel, the variation in the light emission luminance of the OLED element is suppressed.
[0012]
[Problems to be solved by the invention]
The pixels shown in FIGS. 10A and 10B should be able to store the data current value accurately as described above, but have the following serious problems.
[0013]
First, the problem with the pixel circuit of FIG. 10A is that it is a precondition that the two transistors constituting the current mirror have the same electrical characteristics. If a device is devised at the time of designing the pixel circuit, both transistors can be manufactured next to each other on the substrate, so that variations can be reduced to some extent. However, a transistor made of polysilicon still has a variation exceeding the allowable limit in the electrical characteristics such as the threshold voltage of the TFT and the field effect mobility due to defects at the grain boundaries. End up.
[0014]
Here, a case where a 64 gradation image is displayed will be described as an example. When displaying an image with 64 gradations, it is necessary to suppress the variation in luminance of the self-luminous element to about 1% or less. However, in the pixel circuit of FIG. 10A, it is difficult to store the data current value with an accuracy of 1% in the polysilicon that is normally used at present. That is, only by using the pixel circuit of FIG. 10A, there is no unevenness on the entire screen, and a sufficiently uniform high-quality display image cannot be obtained.
[0015]
Next, the problem in the pixel circuit of FIG. 10B is that the video signal data current written to the pixel and the OLED element driving current when the OLED element emits light have the same value. When an AM type OLED display device is manufactured, the fact that both currents must have the same value is a practically severe restriction.
[0016]
This is because in the AM type OLED display device, a large amount of parasitic capacitance and parasitic resistance are attached to signal lines and the like. If a large amount of parasitic capacitance and parasitic resistance are attached, it is often necessary to take measures to make the video signal data current larger than the OLED element driving current. In particular, when the video signal data current is expressed in grayscale with an analog value, it becomes very difficult to write the video signal data current in the dark part.
[0017]
The present invention has been made in view of the above problems. First, the present invention differs from the pixel circuit of FIG. 10B in that the ratio of the video signal data current written to the pixel and the OLED element driving current when the OLED element emits light is not fixed to “1”. It is an object to provide an OLED display device. Next, unlike the pixel circuit of FIG. 10A, the present invention is based on the premise that some variation in electrical characteristics still remains between adjacent transistors in the same pixel. In addition, the present invention provides an AM type OLED display device in which variation in OLED element driving current is sufficiently suppressed as compared with a pixel circuit using a current mirror as shown in FIG. Is an issue.
[0018]
In addition, the self-luminous element has a problem of low reliability and the like caused by deterioration of the organic compound layer. Therefore, an object of the present invention is to provide a display device and a light-emitting device in which the problem of reliability of the self-light-emitting element is improved.
[0019]
[Means for Solving the Problems]
In order to solve the above problems, according to the present invention, in an AM display device or a light emitting device, a driving element installed in each pixel is configured by a plurality of transistors, and when the data current is read into the pixel, the plurality of transistors are arranged. When the self-light-emitting elements are caused to emit light in parallel connection, the plurality of transistors are connected in series.
[0020]
Note that even in the case of a display device or a light-emitting device using an element other than an OLED element, the configuration of the present invention can be used when a current-driven element is used.
[0021]
In order to solve the above problems, the present invention is characterized in that a drive voltage (reverse bias voltage) having a polarity opposite to that during light emission is applied to the light emitting element at regular intervals. This utilizes the fact that, when a drive voltage having a reverse polarity is applied to a light emitting element, the variation in current-voltage characteristics of the light emitting element is improved.
[0022]
The present invention includes a self-luminous element having first and second electrodes;
A light-emitting device provided with a pixel provided with driving means having n transistors (n is a natural number of 2 or more) to which each gate electrode is connected in common,
Corresponding to the synchronization timing of the video signal input to the pixel, the sources and drains of the n transistors are connected in series, and the current I _W In response to the video signal, the sources and drains of the n transistors are connected in parallel, and a current I is supplied to the self-luminous element. _E Setting means to flow,
Supply means for supplying a reverse bias voltage to the self-luminous element by changing the potential of the first or second electrode for a predetermined period of a unit frame period corresponding to the synchronization timing of the video signal It is characterized by having.
[0023]
The present invention includes a self-luminous element having first and second electrodes;
A light-emitting device provided with a pixel provided with driving means having n transistors (n is a natural number of 2 or more) to which each gate electrode is connected in common,
Corresponding to the synchronization timing of the video signal input to the pixel, the current I is connected between the sources and drains of the n transistors in series. _W In response to the video signal, the sources and drains of the n transistors are connected in parallel, and a current I is supplied to the self-luminous element. _E Setting means to flow,
Erasing that stops the light emission of each of the self light emitting elements when the light emission period of each of the self light emitting elements reaches a predetermined light emission period with respect to a predetermined period of a unit frame period corresponding to the synchronization timing of the video signal Means,
Supply means for supplying a reverse bias voltage to the self-luminous element by changing the potential of the first or second electrode with respect to a predetermined period of the frame period.
[0024]
The setting means corresponds to a transistor that controls input of a video signal to a pixel, and more specifically corresponds to the first switch 12 and the second switch 13 in FIG. The setting means corresponds to a signal line driving circuit, a scanning line driving circuit, or a control circuit for driving the pixels.
Further, the driving means corresponds to a driving transistor in the pixel. The driving transistor has a role of driving the self-luminous element, and in many cases, refers to a transistor directly connected to the self-luminous element.
Finally, the erasing means has a function of stopping the light emission of the self-luminous element, and specifically corresponds to the fourth switch 18 in FIG.
[0025]
Here, an outline of a pixel structure of the display device or the light-emitting device of the present invention will be described with reference to FIGS. FIG. 1A illustrates a pixel 11 arranged in the jth row and the ith column in a pixel portion having a plurality of pixels. The pixel 11 includes a signal line (Si), a power supply line (Vi), a first scanning line (Gaj), a first switch 12 to a third switch 14 having a switching function, a driving element 15, a capacitive element 16, and a self-luminous element. 17. Note that the capacitor 16 is not necessarily provided when the parasitic capacitance of the node where the capacitor 16 is installed in FIGS. 1A and 1B is large.
[0026]
The first or second electrode of the self-light-emitting element 17 is connected to a counter power source 19a that is a common power source. In the present invention, the reverse bias voltage is applied to the self-light-emitting element 17 by changing the potential of the counter power source 19a.
[0027]
Since the self-emitting element typically corresponds to an OLED element, a diode symbol is used as a symbol representing the self-emitting element in this specification. However, the diode characteristics are not essential for the self-luminous elements, and the present invention is not limited to the self-luminous elements having the diode characteristics. Further, the self-light-emitting element in this specification may be a current-driven display element, and does not need to bear a display function by self-light emission. For example, an element that serves as an optical shutter, such as liquid crystal, and is controlled by a current value instead of a voltage value is also included in the self-luminous element in this specification.
[0028]
For the first switch 12 to the third switch 14, one or more semiconductor elements having a switching function such as a transistor can be used. Similarly, a plurality of semiconductor elements such as transistors can be used for the driving element 15. The first switch 12 and the second switch 13 are determined to be turned on or off by a signal given from the first scanning line (Gaj). Since the 1st switch 12 and the 2nd switch 13 should just function as a switch, there is no limitation in particular in the conductivity type of the semiconductor element used.
[0029]
The first switch 12 is disposed between the signal line (Si) and the driving element 15 and plays a role of controlling signal writing to the pixel 11. The second switch 13 is installed between the power supply line (Vi) and the driving element 15 and controls the supply of current from the power supply line to the pixel 11.
[0030]
FIG. 1B shows a case where a fourth switch 18 and a second scanning line (Gbj) are additionally provided in the pixel 11 shown in FIG. For the fourth switch 18, one or more semiconductor elements having a switching function such as a transistor can be used. The fourth switch 18 is turned on or off by a signal given from the second scanning line (Gbj). Since the 1st switch 12 and the 2nd switch 13 should just function as a switch, there is no limitation in particular in the conductivity type of the semiconductor element used.
[0031]
The fourth switch 18 plays a role as an element for initializing the pixel 11. When the fourth switch 18 is turned on, the charge held in the capacitive element 16 is released, the driving element 15 is turned off, and the light emission of the self-light emitting element 17 is finished.
[0032]
In the present invention, the driving element 15 is composed of a plurality of transistors, and when the data current of the video signal is written into the pixel 11 and when the current is caused to flow through the self-light-emitting element 17 to emit light. It is characterized in that the connection is switched between parallel and series. In FIGS. 1A and 1B, the first switch 12 and the second switch 13 are controlled to be turned on / off by a signal from the first scanning line (Gaj). These transistors serve as means for switching between a parallel connection state and a series connection state.
[0033]
As an example, the pixel 11 in the case where the driving element 15 includes four transistors 20a to 20d is shown in FIGS. 1C and 1D, and the operation of the pixel 11 will be described below.
[0034]
FIG. 1C shows a case where a data current is written to the pixel 11, and FIG. 1D shows a case where a self-luminous element emits light. 1C and 1D, the first switch 12, the second switch 13, the driving element 15, the self-light emitting element 17, the elements other than the signal line (Si) and the power supply line (Vi), and the wiring are illustrated. Omitted.
[0035]
First, a case where a data current is written to the pixel 11 will be described. In FIG. 1C, the first switch 12 and the second switch 13 are turned on by a signal given from the first scanning line (Gaj). Then, in the driving element 15, each transistor is in a diode connection state and in a parallel connection state with each other. The current path is a path that reaches the signal line (Si) from the power supply line (Vi) through the second switch 13, the driving element 15, and the first switch 12. Current value I at this time _W Is a data current value of the video signal, which is a predetermined current value output from the signal line drive circuit (not shown) to the signal line (Si).
[0036]
Next, a case where the self light emitting element 17 emits light will be described. In FIG. 1D, the first switch 12 and the second switch 13 are turned off by a signal given from the first scanning line (Gaj). Then, in the driving element 15, the transistors are connected in series with each other. The current path is a path that reaches the self-luminous element 17 from the power supply line (Vi) through the transistors 20a, 20b, 20c, and 20d. Current value I at this time _E Thus, the light emission luminance of the self light emitting element 17 is determined.
[0037]
Finally, a case where a reverse bias is applied to the self-light-emitting element 17 will be described.
[0038]
In FIG. 1E, a reverse bias can be applied to the light-emitting element 17 by making the potential of the counter power source (cathode) 19a higher than the potential of the anode. In FIG. 1E, an arrow is shown in the direction from the counter power source 19a to the switch 14. Actually, when a reverse bias is applied to the self-light-emitting element 17, no current flows, but FIG. 1 (E) shows it for easy understanding.
[0039]
As described above, according to the present invention, when writing a data current to a pixel, the transistors 20a to 20d constituting the driving element 15 are used in parallel (FIG. 1C). On the other hand, when a current is passed through the self-light-emitting element 17 of the pixel 11, that is, when the self-light-emitting element is driven, the transistors 20a to 20d constituting the driving element 15 are used in series (FIG. 1D). . Accordingly, assuming that the electrical characteristics of the transistors 20a to 20d are the same, the current value I at the time of writing is _W Is the current value I when driving the self-luminous element _E 16 times (= 4 ² Times). More generally, considering the case where the number of transistors constituting the driving element 15 is n, under the condition that all of the transistors have the same electrical characteristics, the current value at the time of video signal writing I _W And the current value I when driving the self-luminous element _E The relationship of the following formula (1) is established between
[0040]
[Expression 1]
I _W = N ² × I _E ... (1)
[0041]
In order for Expression (1) to be strictly established, it is a condition that all the transistors constituting the driving element 15 have the same electrical characteristics. However, even if the electrical characteristics of the transistor are slightly different from each other, it is practically possible to treat that the expression (1) is approximately established.
[0042]
Therefore, in the present invention, the driving element 15 is composed of a plurality of transistors, and when the video signal current is written to the pixel 11 and the self-light emitting element emits light, the connection of the plurality of transistors is connected in parallel and in series. By switching to, current value I at the time of writing _W And the current value I when driving the self-luminous element _E And can be set arbitrarily.
[0043]
As another feature of the present invention, even if the electrical characteristics of the transistors constituting the driving element 15 are slightly different from each other, the influence of the self-luminous element driving current I _E There is a point that can greatly reduce the reflection. This will be described in Embodiment 5 with a specific example.
[0044]
Further, in the pixel circuit using the current mirror as shown in FIG. 10A, there is a problem that it is required to have the same electrical characteristics as far as two transistors in the pixel are concerned. However, in the present invention, it is already premised that even the transistors in the same pixel have slightly different electrical characteristics. That is, the present invention is superior to a pixel circuit using a current input type current mirror in terms of tolerance to variations in transistor characteristics. As a result, the present invention provides a self-luminous element driving current I even if there is a variation in the electrical characteristics of the polysilicon TFT due to defects at the crystal grain boundaries. _E Can be made uniform to a practical level.
[0045]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
The outline of the pixel of the display device and the light emitting device of the present invention has been described with reference to FIG. In Embodiment Mode 1, specific examples of pixels of the display device and the light-emitting device of the present invention will be described with reference to FIGS. For simplicity, an example in which the number n of transistors constituting the driving element 15 is 2 to 4 will be given.
[0046]
A first example will be described with reference to FIG.
[0047]
FIG. 2A shows the pixel 11 arranged in the j-th row and the i-th column. The pixel 11 includes a signal line (Si), a power supply line (Vi), a scanning line (Gaj), transistors 21 to 26, a capacitor element 27, and a self-light emitting element 28. A pixel 11 illustrated in FIG. 2A specifically illustrates the pixel 11 illustrated in FIG. 1A as a transistor, and the p-channel transistors 21 and 22 correspond to the first switch 12. The p-channel transistor 23 corresponds to the second switch 13, and the n-channel transistor 24 corresponds to the third switch 14. The p-channel transistors 25 and 26 correspond to the driving element 15.
[0048]
Each gate electrode of the transistors 21 to 24 is connected to a scanning line (Gaj). The capacitor element 27 plays a role of holding a gate-source voltage of the transistor 25. Note that the capacitor 27 is not necessarily provided when the gate capacitance of the transistors 25 and 26 is large or when the parasitic capacitance of the node is large.
[0049]
When a video signal data current is written to the pixel 11 shown in FIG. 2A, a low potential signal is sent to the scanning line (Gaj), the transistors 21 to 23 are turned on, and the transistor 24 is turned off. At this time, the transistors 25 and 26 are connected in parallel with each other on the current path. On the other hand, when a current is passed through the self-light emitting element 28, a high potential signal is sent to the scanning line (Gaj), the transistors 21 to 23 are turned off, and the transistor 24 is turned on. At this time, the transistors 25 and 26 are connected in series with each other on the current path.
[0050]
In the example of FIG. 2A, switching of the connection relationship of the transistors 25 and 26 of the driving element 15 is controlled only by the first scanning line (Gaj). Further, the first switch is composed of a minimum number of transistors, that is, two first switches and the second switch is composed of only one transistor. As described above, the example in FIG. 2A is a preferable structure when importance is placed on securing the aperture ratio and improving the yield because the number of scanning lines and the number of transistors are reduced.
[0051]
Next, an example different from FIG. 2A will be described with reference to FIG.
[0052]
FIG. 2B shows the pixel 11 arranged in the j-th row and the i-th column. The pixel 11 includes a signal line (Si), a power supply line (Vi), a first scanning line (Gaj), a second scanning line (Gbj), transistors 31 to 39 and 42, a capacitor element 40, and a self-light emitting element 41. . A pixel 11 illustrated in FIG. 2B specifically illustrates the pixel 11 illustrated in FIG. 1B as a transistor, and the p-channel transistors 31 to 34 correspond to the first switch 12. The p-channel transistors 35 and 36 correspond to the second switch 13, and the n-channel transistor 37 corresponds to the third switch 14. The p-channel transistors 38 and 39 correspond to the driving element 15. The n-channel transistor 42 corresponds to the fourth switch 18.
[0053]
Each gate electrode of the transistors 31 to 34 is connected to the first scanning line (Gaj). The gate electrodes of the transistors 35 to 37 and 42 are connected to the second scanning line (Gbj). The capacitive element 40 plays a role of holding a gate-source voltage of the transistor 38. Note that the capacitor 40 is not necessarily provided when the gate capacitance of the transistors 38 and 39 is large or when the parasitic capacitance of the node is large.
[0054]
When a video signal data current is written to the pixel 11 shown in FIG. 2B, a low potential signal is sent to the first scanning line (Gaj) and the second scanning line (Gbj), and the transistors 31 to 36 are turned on. 37 and 42 are turned off. At this time, the transistors 38 and 39 are in parallel connection with each other on the current path. On the other hand, when a current is passed through the self-luminous element 41, a high potential signal is sent to the scanning line (Gaj), the transistors 31 to 36 are turned off, and the transistors 37 and 42 are turned on. At this time, the transistors 38 and 39 are connected in series with each other on the current path.
[0055]
In the example of FIG. 2B, switching of the connection relationship of the transistors 38 and 39 of the driving element 15 is controlled using the first scanning line (Gaj) and the second scanning line (Gbj). However, none of the transistors controlled by the second scanning line (Gbj) is connected to the signal line (Si). In addition, whether or not the self-light emitting element 41 is caused to emit light by being supplied with current has a feature that can be controlled only by the potential of the second scanning line (Gbj) regardless of the potential of the first scanning line (Gaj). Therefore, the light emission time of the self-light emitting element 41 can be arbitrarily controlled by sending a signal independent of the first scanning line (Gaj) to the second scanning line (Gbj) except when the data current is written.
[0056]
This is a very important feature when the intermediate gradation expression is expressed by the time gradation method. When the time gray scale method is applied to an AM type OLED display device having a drive circuit formed of a polysilicon TFT, a sufficient number can be obtained without means for stopping light emission of the self-light emitting element during the column scanning period. This is because gradation display is difficult. In addition, even when halftone expression is expressed by using analog video signal data current, it is useful for applications such as impulse-type light emission to prevent moving picture blurring peculiar to the hold type display. (Refer to, for example, T. Kurita, Proc. AM-LCD 2000 pp1-4 (2000) etc. for moving image blur peculiar to the hold type display).
[0057]
Another feature of the example of FIG. 2B is that the video signal data current can be stored more accurately. In the example of FIG. 2A, the transistor 25 is directly connected to the power supply line (Vi) while the data current is written, whereas the transistor 26 is connected via the transistor 23. Therefore, the data current is written inaccurately by the voltage drop caused by the transistor 23. However, in the example of FIG. 2B, the transistor 38 is connected to the power supply line (Vi) via the transistor 35, and the transistor 39 is connected to the power supply line (Vi) via the transistor 36. If the voltage drops caused by the transistors 35 and 36 are approximately the same, the video signal data current can be stored more accurately.
[0058]
Next, a third example will be described with reference to FIG.
[0059]
FIG. 3A shows the pixel 11 arranged in the j-th row and the i-th column. The pixel 11 includes a signal line (Si), a power supply line (Vi), a first scanning line (Gaj), a second scanning line (Gbj), transistors 51 to 57 and 60, a capacitor element 58, and a self-light emitting element 59. . A pixel 11 illustrated in FIG. 3A specifically illustrates the pixel 11 illustrated in FIG. 1B as a transistor, and the n-channel transistors 51 to 53 correspond to the first switch 12. The n-channel transistor 54 corresponds to the second switch 13, and the p-channel transistor 55 corresponds to the third switch 14. The p-channel transistors 56 and 57 correspond to the driving element 15. The n-channel transistor 60 corresponds to the fourth switch 18.
[0060]
Each gate electrode of the transistors 51 to 55 is connected to the first scanning line (Gaj). The gate electrode of the transistor 60 is connected to the second scanning line (Gbj). The capacitor 58 plays a role of holding a gate-source voltage of the transistor 56. Note that the capacitor 58 is not necessarily provided when the gate capacitance of the transistors 56 and 57 is large, or when the parasitic capacitance of the node is large.
[0061]
When a video signal data current is written to the pixel 11 shown in FIG. 3A, a high potential signal is sent to the first scanning line (Gaj), the transistors 51 to 54 are turned on, and the transistor 55 is turned off. At this time, the transistors 56 and 57 are connected in parallel with each other on the current path. On the other hand, when a current is passed through the self-luminous element 59, a low potential signal is sent to the scanning line (Gaj), the transistors 51 to 54 are turned off, and the transistor 55 is turned on. At this time, the transistors 56 and 57 are connected in series with each other on the current path.
[0062]
During the above period, a low potential signal is sent to the second scanning line (Gbj), and the transistor 60 is turned off.
[0063]
In the pixel 11 shown in FIG. 3A as well, as in the case of the example of FIG. 2B, the light emission time of the self-luminous element 59 can be arbitrarily controlled by a signal sent to the second scanning line (Gbj). That is, while the self light emitting element 59 emits light, a high potential signal is sent to the second scanning line (Gbj), and when the transistor 60 is turned on, the transistor 56 is turned off and the self light emitting element 59 is extinguished. However, once the self-luminous element 59 is extinguished, the self-luminous element 59 cannot emit light unless the video signal data current is written again. This point is different from the example of FIG.
[0064]
In the pixel 11 shown in FIG. 3A, the feature that the light emission time of the self-luminous element 59 can be arbitrarily controlled is the same as that in the example of FIG. That is, first, it is possible to express the intermediate gradation expression by the time gradation method. Even if the halftone representation is expressed by using an analog video signal data current, it is useful for applications such as impulse-type light emission in order to prevent the motion blur inherent to the hold-type display. is there.
[0065]
In the pixel 11 shown in FIG. Switch 12 or Second switch 13 The transistors 51 to 54 and the transistor 60 of the fourth switch 18 are n-channel type, and the transistor 55 of the third switch 14 is p-channel type. This is different from the example of FIGS. 2 (A) and 2 (B). However, this is merely an example that there is no particular limitation on the channel type of the transistor of the switch.
[0066]
Next, a fourth example will be described with reference to FIG.
[0067]
FIG. 3B shows the pixel 11 arranged in the j-th row and the i-th column. The pixel 11 includes a signal line (Si), a power supply line (Vi), a first scanning line (Gaj), a second scanning line (Gbj), transistors 71 to 82, 85, a capacitor element 83, and a self-light emitting element 84. . A pixel 11 illustrated in FIG. 3B specifically illustrates the pixel 11 illustrated in FIG. 1B as a transistor, and p-channel transistors 71 to 75 correspond to the first switch 12. The p-channel transistors 76 to 78 correspond to the second switch 13, and the n-channel transistor 79 corresponds to the third switch 14. The p-channel transistors 80 to 82 correspond to the driving element 15. The n-channel transistor 85 corresponds to the fourth switch 18.
[0068]
The gate electrodes of the transistors 71 to 75 and 85 are connected to the first scanning line (Gaj). The gate electrodes of the transistors 76 to 79 are connected to the second scanning line (Gbj). The capacitor 83 plays a role of holding the gate-source voltage of the transistor 80. Note that the capacitor 83 is not necessarily provided when the gate capacitance of the transistors 80 to 82 is large, or when the parasitic capacitance of the node is large.
[0069]
When a video signal data current is written to the pixel 11 shown in FIG. 3B, a low potential signal is sent to the first scanning line (Gaj) and the second scanning line (Gbj), and the transistors 71 to 78 are turned on. 79 and 85 are turned off. At this time, the transistors 80 to 82 are connected in parallel with each other on the current path. On the other hand, when a current is passed through the self-luminous element 84, a high potential signal is sent to the scanning line (Gaj), the transistors 71 to 78 are turned off, and the transistors 79 and 85 are turned on. At this time, the transistors 80 to 82 are connected in series with each other on the current path.
[0070]
In the example of FIG. 3B, switching of the connection relationship of the transistors 80 to 82 of the driving element 15 is controlled using the first scanning line (Gaj) and the second scanning line (Gbj). However, none of the transistors controlled by the second scanning line (Gbj) is connected to the signal line (Si). Whether or not the self-light emitting element 84 is caused to emit light by being supplied with current has a feature that can be controlled only by the potential of the second scanning line (Gbj) regardless of the potential of the first scanning line (Gaj). Therefore, the light emission time of the self-light emitting element 84 can be arbitrarily controlled by sending a signal independent of the first scanning line (Gaj) to the second scanning line (Gbj) except when the data current is written. This is the same as the example of FIG.
[0071]
Therefore, the pixel 11 shown in FIG. 3B also has the following features resulting from the fact that the light emission time of the self-light emitting element 84 can be arbitrarily controlled. That is, it is possible to express the intermediate gradation expression by the time gradation method. Even if the halftone representation is expressed by using an analog video signal data current, it is useful for applications such as impulse-type light emission in order to prevent the motion blur inherent to the hold-type display. That is.
[0072]
A fifth example will be described with reference to FIG.
[0073]
FIG. 4A shows the pixel 11 arranged in the j-th row and the i-th column. The pixel 11 includes a signal line (Si), a power supply line (Vi), a first scanning line (Gaj), a second scanning line (Gbj), transistors 91 to 103 and 106, a capacitor element 104, and a self-light emitting element 105. . A pixel 11 illustrated in FIG. 4A specifically illustrates the pixel 11 illustrated in FIG. 1B as a transistor, and the p-channel transistors 91 to 94 correspond to the first switch 12. The p-channel transistors 95 to 98 correspond to the second switch 13, and the n-channel transistor 99 corresponds to the third switch 14. The p-channel transistors 100 to 103 correspond to the driving element 15. n-channel transistor 10 6 Corresponds to the fourth switch 18.
[0074]
Each gate electrode of the transistors 91 to 94 is connected to the first scanning line (Gaj). The gate electrodes of the transistors 95 to 99 and 106 are connected to the second scanning line (Gbj). The capacitor 104 plays a role of holding a gate-source voltage of the transistor 100. Note that the capacitor 104 is not necessarily provided when the gate capacitance of the transistors 100 to 103 is large or the parasitic capacitance of the node is large.
[0075]
When a video signal data current is written to the pixel 11 shown in FIG. 4A, a low potential signal is sent to the first scanning line (Gaj) and the second scanning line (Gbj), and the transistors 91 to 98 are turned on. 99 and 106 are turned off. At this time, the transistors 100 to 103 are connected in parallel to each other on the current path. On the other hand, when a current is passed through the self-luminous element 105, a high potential signal is sent to the scanning line (Gaj), the transistors 91 to 98 are turned off, and the transistors 99 and 106 are turned on. At this time, the transistors 100 to 103 are connected in series with each other on the current path.
[0076]
In the example of FIG. 4A, switching of the connection relationship of the transistors 100 to 103 of the driving element 15 is controlled using the first scanning line (Gaj) and the second scanning line (Gbj). However, none of the transistors controlled by the second scanning line (Gbj) is connected to the signal line (Si). Whether or not the self-light-emitting element 105 is caused to emit light by being supplied with current has a feature that can be controlled only by the potential of the second scanning line (Gbj) regardless of the potential of the first scanning line (Gaj). Therefore, the light emission time of the self-light emitting element 84 can be arbitrarily controlled by sending a signal independent of the first scanning line (Gaj) to the second scanning line (Gbj) except when the data current is written. This is the same as the example of FIG.
[0077]
Therefore, the pixel 11 shown in FIG. 4A also has the following features resulting from the fact that the light emission time of the self light emitting element 84 can be arbitrarily controlled. That is, first, it becomes possible to express the intermediate gradation expression by the time gradation method. Even if the halftone representation is expressed by using an analog video signal data current, it is useful for applications such as impulse-type light emission in order to prevent the motion blur inherent to the hold-type display. That is.
[0078]
A sixth example will be described with reference to FIG.
[0079]
FIG. 4B shows the pixel 11 arranged in the j-th row and the i-th column. The pixel 11 includes a signal line (Si), a power supply line (Vi), a first scanning line (Gaj), a second scanning line (Gbj), transistors 111 to 120, 122, a capacitor element 123, and a self-light emitting element 121. . A pixel 11 illustrated in FIG. 4B specifically illustrates the pixel 11 illustrated in FIG. 1B as a transistor, and the p-channel transistors 111 to 113 correspond to the first switch 12. The p-channel transistors 114 and 115 correspond to the second switch 13, and the n-channel transistor 116 corresponds to the third switch 14. The p-channel transistors 117 to 120 correspond to the driving element 15. The p-channel transistor 122 corresponds to the fourth switch 18.
[0080]
Each gate electrode of the transistors 111 to 116 is connected to the first scanning line (Gaj). The gate electrode of the transistor 122 is connected to the second scanning line (Gbj). The capacitor 123 plays a role of holding a gate-source voltage of the transistor 117. Note that the capacitor 123 is not necessarily provided when the gate capacitance of the transistors 117 to 120 is large or the parasitic capacitance of the node is large.
[0081]
When a video signal data current is written to the pixel 11 shown in FIG. 4B, a high potential signal is sent to the first scanning line (Gaj), the transistors 111 to 115 are turned on, and the transistor 116 is turned off. At this time, the transistors 117 to 120 are connected in parallel to each other on the current path. On the other hand, when a current is passed through the self-luminous element 121, a low potential signal is sent to the first scanning line (Gaj), the transistors 111 to 115 are turned off, and the transistor 116 is turned on. At this time, the transistors 117 to 120 are connected in series with each other on the current path.
[0082]
During the above period, a low potential signal is sent to the second scanning line (Gbj), and the transistor 122 is turned off.
[0083]
In the pixel 11 shown in FIG. 4B as well, as in the case of the example of FIG. 2B, the light emission time of the self-light emitting element 121 can be arbitrarily controlled by a signal sent to the second scanning line (Gbj). That is, when the self light emitting element 121 emits light, a high potential signal is sent to the second scanning line (Gbj) and the transistor 122 is turned on, so that the transistor 117 is turned off and the self light emitting element 121 is extinguished. However, once the self-light-emitting element 121 is extinguished, the self-light-emitting element 121 cannot be made to emit light unless the video signal data current is written again. This point is different from the example of FIG.
[0084]
In the pixel 11 shown in FIG. 4B, the feature that the light emission time of the self-light-emitting element 121 can be arbitrarily controlled is the same as that in the example of FIG. That is, first, it is possible to express the intermediate gradation expression by the time gradation method. Even if the halftone representation is expressed by using an analog video signal data current, it is useful for applications such as impulse-type light emission in order to prevent the motion blur inherent to the hold-type display. is there.
[0085]
As described above, as an example of the pixel 11 of the display device and the light emitting device of the present invention, the six types of pixels 11 having different configurations have been described with reference to FIGS. However, the pixel configuration of the display device and the light emitting device of the present invention is not limited to these six types.
[0086]
(Embodiment 2)
In this embodiment, a method for driving the pixel 11 will be described. The case of the pixel 11 shown in FIG. 4B will be described as an example with reference to FIG.
[0087]
First, the video signal writing operation and the light emitting operation will be described.
[0088]
First, the first scanning line (Gaj) in the j-th row is selected by a signal output from a scanning line driving circuit (not shown) provided around the pixel 11. That is, a low potential (L level) signal is output to the first scanning line (Gaj), and the gate electrodes of the transistors 111 to 116 are set to a low potential (L level). At this time, the p-channel transistors 111 to 115 are turned on, and the n-channel transistor 116 is turned off. Then, a video signal data current I is supplied from the signal line driving circuit (not shown) provided around the pixel 11 to the pixel 11 via the i-th signal line (Si). _W Is entered.
[0089]
When the transistors 111 to 113 are turned on, the transistors 117 to 120 are in a diode connection state in which the drain and the gate are short-circuited. That is, the pixel 11 is equivalent in circuit to four diodes in parallel. In this state, the current I between the power line (Vi) and the signal line (Si) of the pixel 11 _W (See FIG. 5A).
[0090]
Current I flowing through four diodes in parallel _W Is in a steady state, the first scanning line (Gaj) is set to a high potential (H level). Then, the transistors 111 to 113 are turned off, and the video signal data current I _W Is stored in the pixel.
[0091]
Subsequently, when the first scanning line (Gaj) becomes a high potential (H level), the p-channel transistors 111 to 115 are turned off and the n-channel transistor 116 is turned on. The transistors 117 to 120 are reconnected in series. At this time, if a voltage condition is set in advance so that the transistor 120 operates in a saturation region, the driving element supplies a constant current I to the self-luminous element. _E Supply.
[0092]
In the present embodiment, since the driving element is composed of four transistors, the constant current I _E Is the video signal data current I _W It is about 1/16 of the size. More generally, when the driving element is composed of n transistors, the current I _E Is the video signal data current I _W About n ² It becomes the size of 1 /.
[0093]
In the present embodiment, the write data current I _W Drive current I of the self-luminous element _E The value can be about 16 times as large as. Therefore, the self-luminous element drive current I _E Even if it is difficult to directly write such a minute current directly to the pixel, the video signal data current I _W Can be written to the pixel.
[0094]
In the present embodiment, an analog video system or a digital video system may be employed as a method for expressing halftones. In the case of the analog video system, the data current I that changes in an analog manner is used as the video signal data current. _W Is used. In the case of the digital video system, one data current I _W Unit luminance is prepared using only the on-current as a reference. Then, it is convenient to use a time gray scale method in which unit luminance is expressed by adding time in terms of time (also referred to as digital time gray scale method). Alternatively, the digital video system can also be performed by an area gradation method in which unit luminance is expressed by adding area in terms of area, or a method in which a time gradation method and an area gradation method are combined.
[0095]
In this embodiment, the video signal data current I can be obtained regardless of whether the analog video system or the digital video system is adopted. _W May be required to be 0. However, the video signal data current I _W When 0 is set to 0, it means that the light emission luminance of the self-luminous element is set to 0. _W Does not need to be accurately written and stored in the pixel. Therefore, in such a case, a gate voltage that turns off the transistors 117 to 120 of the driving element may be directly output to the signal line (Si). That is, the video signal may be output as a voltage value instead of a current value as an exception.
[0096]
Next, the light emission stop operation will be described.
[0097]
First, the second scanning line (Gbj) in the j-th row is selected by a signal output from another scanning line driving circuit (not shown) provided around the pixel 11. That is, a low potential (L level) signal is output to the second scanning line (Gbj). The p-channel transistor 122 is turned on because the gate electrode has a low potential (L level).
[0098]
Then, the source and gate of the transistor 117 are short-circuited and turned off. As a result, the current supply to the self-light-emitting element 121 is cut off, and light emission stops.
[0099]
By using such a light emission stop operation, it is possible to arbitrarily control the light emission time of the self light emitting element 121 without being restricted by the one-row scanning time. This is advantageous in that it is easy to express the intermediate gradation expression by the time gradation method. In addition, even in the case where halftone expression is expressed by using an analog video signal data current, there is an advantage in performing impulse-type light emission, etc. in order to prevent moving image blur peculiar to the hold-type display. .
[0100]
Finally, an operation for applying a reverse bias to the self-light-emitting element 121 will be described.
[0101]
When applying a reverse bias to the self-light emitting element 121, the potential of the counter power source (cathode) 124 is set higher than the potential of the anode. Note that the operation for applying the reverse bias may be performed in a period in which the light-emitting element 121 does not emit light. For example, the operation for applying the reverse bias and the light emission stopping operation can be performed simultaneously. The timing for applying the reverse bias is not particularly limited, and can be arbitrarily set, for example, every time a video signal is input or every one frame period.
[0102]
This embodiment mode can be arbitrarily combined with Embodiment Mode 1.
[0103]
(Embodiment 3)
In the present embodiment, a case where a new semiconductor element is disposed in order to apply a reverse bias voltage to the self-light-emitting element 17 will be described with reference to FIG.
[0104]
A pixel 11 illustrated in FIG. 11A has a structure in which a switch 19b, a power supply line (Vai), and a second scanning line (Gbj) are provided in the pixel 11 illustrated in FIG. A pixel 11 illustrated in FIG. 11B has a structure in which a switch 19b, a power supply line (Vai), and a third scanning line (Gcj) are arranged in the pixel 11 illustrated in FIG. The description of the structure of the pixel 11 illustrated in FIGS. 11A and 11B is similar to the description of the structure of the pixel 11 illustrated in FIGS.
[0105]
An operation when a reverse bias is applied to the pixel 11 shown in FIGS. 11A and 11B will be described with reference to FIG. Switch 19 via the third scanning line (Gcj) b Is input to the switch 19 b Is turned on, a reverse bias is applied to the self-light-emitting element 17. That is, switch 19 b When is turned on, the power line (Vai) and the self-luminous element 17 are electrically connected. At this time, by setting the potential of the power supply line (Vai) lower than the potential of the counter power supply 19a of the light emitting element 17, the switch 19 b As a result, the reverse bias is applied to the light-emitting element 17 at the same time.
[0106]
Switch 19 b 11D includes a transistor illustrated in FIG. 11D, a diode illustrated in FIG. 11E, an n-channel transistor in which the gate electrode and the drain electrode illustrated in FIG. 11F are connected, and FIG. A p-channel transistor in which a gate electrode and a drain electrode are connected is used. The switch 19 b When a three-terminal element such as a transistor is used, the second scanning line (Gbj) is arranged in the pixel 11 shown in FIG. 11A, and the third scanning line (Gcj) is arranged in the pixel 11 shown in FIG. However, when a two-terminal element such as a diode shown in FIG. 11E or a transistor in which a gate electrode and a drain electrode are connected is used, it is not necessary to arrange the wiring as described above.
[0107]
Next, the case where the structure of this embodiment is applied to the pixel 11 illustrated in FIGS. 4 and 5 will be described with reference to FIGS.
[0108]
In the pixel 11 illustrated in FIG. 12, a transistor 125, a power supply line (Vai), and a third scanning line (Gcj) are newly provided in the pixel 11 illustrated in FIGS. A detailed description of the configuration of the pixel 11 illustrated in FIG. 12 is the same as the description of the configuration of the pixel 11 illustrated in FIGS.
[0109]
Then, the operation of the pixel 11 shown in FIG. 12 will be described. Since the video signal writing operation, the light emission operation, and the light emission stop operation are in accordance with the second embodiment described above, description thereof is omitted in this embodiment. In this embodiment, only the operation of applying a reverse bias will be described.
[0110]
In the operation of applying the reverse bias, first, when the transistor 125 is turned on by a signal input through the third scanning line (Gcj), the self-light emitting element 121 and the power supply line (Vai) are electrically connected. It becomes a state. At this time, the potential of the power supply line (Vai) is set lower than the potential of the self-light-emitting element 121, whereby the transistor 125 becomes conductive and at the same time the self-light-emitting element 12 1 A reverse bias can be applied.
[0111]
Note that the operation for applying the reverse bias may be performed in a period in which the light-emitting element 121 does not emit light. For example, the operation for applying the reverse bias and the light emission stop operation can be performed simultaneously. The timing for applying the reverse bias is not particularly limited and may be set arbitrarily. For example, it can be arbitrarily set every time a video signal is inputted or every frame period.
[0112]
This embodiment can be arbitrarily combined with Embodiments 1 and 2.
[0113]
(Embodiment 4)
In this embodiment, an example of a planar layout (top view) of pixels in a display device and a light-emitting device of the present invention is presented. As the pixel circuit of this embodiment, the pixel circuit illustrated in FIG. 3B is described as an example.
[0114]
FIG. 6 shows the pixel 11 in the j-th row and the i-th column. In FIG. 6, a region surrounded by a two-dot broken line corresponds to the pixel 11. The dotted pattern region is a polysilicon film. The upper right diagonal line and the right downward double diagonal line are conductor films (metal films, etc.) in different layers. A cross mark indicates a contact point between layers. The check pattern area 86 is a self-luminous element. 8 4 corresponds to the anode.
[0115]
Transistors 71 to 75 and 85 are formed under the first scanning line (Gaj). Transistors 76 to 79 are formed under the second scanning line (Gbj). A capacitive element 83 is formed under the power line (Vi).
[0116]
The three transistors 80 to 82 constituting the driving element are formed in the same size and adjacent to each other. By forming the transistor in this way, the variation between the transistors 80 to 82 in the same pixel can be prevented from increasing from the stage of manufacturing the transistor. “Parallel write serial drive”, which is a configuration of the present invention, is a method of further reducing the influence of variations that originally exist between a plurality of transistors constituting a drive element. Therefore, it is preferable to use a plurality of transistors, in which variation is suppressed from the beginning, as driving elements because the effects of the present invention can be utilized to a great extent. And the variation in the light emission luminance of the self-light-emitting element is further reduced.
[0117]
For a process for manufacturing the display device and the light-emitting device of the present invention, for example, JP-A-2001-343933 can be referred to. The plurality of transistors constituting the driving element are preferably symmetrical with respect to the source and drain. However, it is not essential that the sources and drains of the plurality of transistors be symmetric.
[0118]
This embodiment can be arbitrarily combined with Embodiments 1 to 3.
[0119]
(Embodiment 5)
In this embodiment, structural examples of the display device and the light-emitting device of the present invention will be described with reference to FIGS. An example of the overall configuration of the apparatus, not within the pixel, will be described.
[0120]
The display device and the light-emitting device of the present invention each include a pixel portion 1802 in which a plurality of pixels are arranged in a matrix on a substrate 1801. In the periphery of the pixel portion 1802, a signal line driver circuit 1803, a first scan line driver circuit 1804, and a second scan line driver circuit 1805 are provided. Power and signals are supplied to the signal line driver circuit 1803, the first scan line driver circuit 1804, and the second scan line driver circuit 1805 from the outside through the FPC 1806.
[0121]
In the example of FIG. 7A, the signal line driver circuit 1803 and the scanning line driver circuits 1804 and 1805 are integrated, but the present invention is not limited to this. For example, the second scan line driver circuit 1805 may be missing. Alternatively, the signal line driver circuit 1803 and the scan line driver circuits 1804 and 1805 may be omitted.
[0122]
Examples of the first scan line driver circuit 1804 and the second scan line driver circuit 1805 are described with reference to FIG. Scan line driver circuits 1804 and 1805 illustrated in FIG. 7B each include a shift register 1821 and a buffer circuit 1822.
[0123]
The operation of the circuit in FIG. 7B will be briefly described. The shift register 1821 sequentially outputs pulses based on the clock signal (G-CLK), the clock inversion signal (G-CLKb), and the start pulse signal (G-SP). The pulse is amplified by the buffer circuit 1822 and then input to the scan line. Thus, the scanning lines are sequentially selected row by row.
[0124]
Note that in this specification, the synchronization timing refers to a pulse output based on a clock signal (G-CLK), a clock inversion signal (G-CLKb), and a start pulse signal (G-SP).
[0125]
Note that a level shifter may be provided in the buffer circuit 1822 as necessary. The voltage amplitude can be changed by the level shifter.
[0126]
Next, an example of the signal line driver circuit 1803 is described with reference to FIG. A signal line driver circuit 1803 illustrated in FIG. 7C includes a shift register 1831, a first latch circuit 1832, a second latch circuit 1833, Pressure Electric Flow A conversion circuit 1834 is included.
[0127]
The operation of the circuit in FIG. 7C will be briefly described. The circuit in FIG. 7C is a circuit in the case where a digital time gray scale method is adopted as an intermediate gray scale display method.
[0128]
The shift register 1831 sequentially outputs sampling pulses to the first latch circuit 1832 based on the clock signal (S-CLK), the clock inversion signal (S-CLKb), and the start pulse signal (S-SP). The first latch circuit 1832 in each column sequentially reads the digital video signal in accordance with the timing of the pulse. When the first latch circuit 1832 completes reading of the video signal up to the last column, a latch pulse is input to the second latch circuit 1833. The video signals read into the first latch circuit 1832 in each column are transferred to the second latch circuit 1833 in each column all at once by the latch pulse. The video signal transferred to the second latch circuit 1833 is appropriately subjected to format conversion processing in the voltage / current conversion circuit 1834 and transferred to the pixel. Of the video signal, the on data is converted into a current format, and the off data is current amplified in the voltage format. After the latch pulse, the shift register 1831 and the first latch circuit 1832 repeat the above operation as the video signal reading operation for the next row.
[0129]
The structure of the signal line driver circuit 1803 in FIG. 7C is merely an example, and when the analog gray scale method is employed, another structure is employed. Even when the digital time gray scale method is adopted, other configurations can be used.
[0130]
This embodiment can be arbitrarily combined with Embodiments 1 to 4.
[0131]
(Embodiment 6)
In this embodiment mode, effects of the present invention are described with reference to a characteristic curve of a transistor (FIG. 8). In order to simplify the description, a case where the number of transistors constituting the driving element is two will be described as an example. The configuration of the pixel circuit is as shown in FIG. Further, the characteristic curve of the transistor used here is ideal, and is slightly different from the actual characteristic curve of the transistor. For example, in FIG. 8, the channel length modulation of the transistor is zero.
[0132]
The gate potential is set to V with reference to the transistor source potential. _g , Drain potential to V _d Current flowing between source and drain is I _d And However, when the transistor is a p-channel transistor, the positive / negative direction is appropriately set, for example, by switching the positive / negative. For example, in FIGS. 8A and 8B, curves 801 to 804 indicate a certain gate potential V. _g I below _d -V _d It is a characteristic curve. A one-dot chain thick curve 805 is obtained by short-circuiting the gate and the drain of one of the two transistors constituting the driving element. _g And V _d I under the same condition _d -V _d It shows a change. In other words, the one-dot chain thick curve 805 reflects electrical characteristics (field-effect mobility, threshold voltage value) unique to the transistor. Similarly, a two-dot chain thick curve 806 is obtained by short-circuiting the gate and the drain of the other transistor constituting the driving element. _g And V _d I under the same condition _d -V _d It shows a change.
[0133]
FIGS. 8A and 8B show that when the two transistors constituting the driving element have different electrical characteristics, the self-light emitting element driving is performed by the “parallel writing serial driving” which is the configuration of the present invention. This is a study of what happens to the current. FIG. 8A illustrates an example in which the difference in field-effect mobility is particularly large between two transistors. FIG. 8B shows an example in which the difference in threshold voltage value is particularly large between two transistors. 8A and 8B, as a conclusion, the self-luminous element driving current in each case is as indicated by the length of the triangular arrow 807. FIG. The reason for this will be briefly described below.
[0134]
First, let us consider a case where the characteristics of the transistors 38 and 39 have the same characteristics, and the one-dot chain curve 805 corresponds to the characteristic curves of the transistors 38 and 39.
[0135]
When data current is written, the transistors 31 to 36 in FIG. 2B are turned on. Since the transistors 31 to 34 are turned on, the gates and drains of the two transistors 38 and 39 constituting the driving element are short-circuited. Therefore, the operating point of the transistors 38 and 39 is a point on the one-dot chain curve 805, and the data current value I _W It is a certain point determined by. Assume that the operating point is an intersection of 805 and 801. That is, the vertical axis value I at the intersection of 805 and 801 _d Is twice the data current value I _W Let's say that.
[0136]
When the light emitting element emits light, the transistors 31 to 36 in FIG. 2B are turned off and the transistors 37 and 42 are turned on. Since the transistors 31 to 34 are turned off, the gate potentials of the transistors 38 and 39 are held as they are when the data current is written. When the light emitting element emits light, the transistor 39 operates in the saturation region, and the transistor 38 operates in the non-saturation region. I of the transistor 38 when the light emitting element emits light. _d -V _d The curve is represented by 801 and I of transistor 39 _d -V _d The curve is represented by 803.
[0137]
In the graph shown in FIG. 8A, each one-dot chain line arrow has the same length and the same vertical axis coordinate. The operating point of the transistor 38 at the time of light emission of the self-light emitting element is a contact point between the right end of the left one-dot chain line arrow and 801. And the driving current I of the self-luminous element to be obtained _E Is the vertical axis coordinate of the dash-dot line arrow, that is, the length of the solid triangle arrow 807. The same applies to the graph shown in FIG. 8B, and the self-luminous element driving current I to be obtained is to be obtained. _E Is the length of 807 solid triangle arrow. When the characteristic curve of the transistor 38 and the characteristic curve of the transistor 39 are both equal, the self-luminous element driving current I to be obtained is consequently obtained. _E Is the data current value I _W It becomes the size of 1/4.
[0138]
Next, consider a case where a two-dot chain thick curve 806 corresponds to the characteristic curve of the transistor 38 and a one-dot chain thick curve 805 corresponds to the characteristic curve of the transistor 39. Data current value I _W Is the same as the case where 805 corresponds to the characteristic curves of the transistors 38 and 39 described above.
[0139]
At the time of writing data current, the gate and the drain are short-circuited in the two transistors 38 and 39 constituting the driving element of FIG. Therefore, the operating point of the transistor 38 is a point on the two-dot chain curve 806, and the operating point of the transistor 39 is a point on the one-dot chain curve 805. The sum of the vertical coordinate of the operating point of the transistor 38 and the vertical coordinate of the operating point of the transistor 39 is the data current value I _W It is. Therefore, the operating point of the transistor 38 is the intersection of 806 and 802. The operating point of the transistor 39 is a point on the curve 805 whose horizontal axis coordinate is the same as that of the transistor 38.
[0140]
When the light emitting element emits light, the transistors 31 to 34 in FIG. 2B are turned off, so that the gate potentials of the transistors 38 and 39 are maintained as they are when the data current is written. When the light emitting element emits light, the transistor 39 operates in the saturation region, and the transistor 38 operates in the non-saturation region. I of transistor 38 at the time of self-luminous element light emission _d -V _d The curve is represented by 802.
[0141]
In the graph shown in FIG. 8A, the two-dot chain arrows on the same vertical axis coordinate value have the same length. A pair of two-dot chain arrows positioned at the top in FIG. 8A corresponds to the two-dot chain thick curve 806 as the characteristic curve of the transistor 38, and the one-dot chain thick curve 805 corresponds to the characteristic curve of the transistor 39. It is a case. The operating point of the transistor 38 at the time of light emission of the self light emitting element is a contact point between the right end of the two-dot chain line arrow located on the left side and 802 in the graph shown in FIG. And the self-luminous element driving current I to be obtained _E Is the vertical axis coordinate of the two-dot chain arrow, that is, the length of the long dotted triangle arrow (left side) 807. Note that the same situation is established in FIG. 8B, and the self-luminous element driving current I to be obtained is to be obtained. _E Is the length of 807 long dotted triangle arrow (left side).
[0142]
In another case, the same can be done in the case where the one-dot chain thick curve 805 corresponds to the characteristic curve of the transistor 38 and the two-dot chain thick curve 806 corresponds to the characteristic curve of the transistor 39. Although a detailed description is omitted in this embodiment mode, the self-luminous element driving current I to be obtained in both FIGS. _E Is the length of 807 long dotted triangle arrow (right side).
[0143]
As another case, the case where the two-dot chain thick curve 805 corresponds to the characteristic curves of the transistors 38 and 39 can be similarly performed. Although a detailed description is omitted in this embodiment mode, the self-luminous element driving current I to be obtained in both FIGS. _E Is the length of the 807 short dotted triangle arrow.
[0144]
8A and 8B, the characteristic variation of the transistors 38 and 39 constituting the driving element is determined from the length of the triangular arrow 807 in FIGS. 8A and 8B. _E An overview of how it is reflected in
[0145]
For comparison, FIGS. 8A and 8B also show a narrow-angle arrow 808 and a wide-angle arrow 809. A narrow-angle arrow 808 is a result of the same examination as described above in the case of a pixel circuit using a current mirror type with a current input method. That is, when there is a characteristic variation similar to the above between the two transistors of the current mirror, the drive current I of the self-luminous element is _E Shows what happens. A wide-angle arrow 809 is the result of the same examination in the case of a voltage input type pixel circuit. That is, when there is a characteristic variation similar to the above between the self-light emitting element driving transistors of different pixels, the self-light emitting element driving current I _E Shows what happens.
[0146]
8A and 8B can be understood by comparing the triangular arrow 807, the narrow-angle arrow 808, and the wide-angle arrow 809 shown in FIGS.
[0147]
First, with the triangular arrow 807 and the narrow-angle arrow 808, the self-luminous element is driven even if the characteristic curve of the transistor is 805 or 806, as long as there is no characteristic variation even between two transistors in the same pixel. Current I _E Is constant. That is, it is not necessary for the pixel circuit using the current mirror type in the current input method or the pixel circuit of the “parallel writing serial driving” of the present invention to have the transistor characteristics uniform over the entire substrate. It is sufficient to suppress even the characteristic variation between them. This is very advantageous over the voltage input type pixel circuit.
[0148]
However, if there is a characteristic variation between two transistors in the same pixel, the narrow-angle arrow 808 indicates the self-luminous element driving current I. _E The variation of. That is, in the pixel circuit using the current mirror type in the current input method, the influence of the characteristic variation between the two transistors in the same pixel appears greatly. In an extreme case, the self-luminous element driving current I is higher than the voltage input type pixel circuit. _E The variation in the size may increase. From this point of view, in the “parallel writing serial drive” pixel circuit of the present invention, the influence of characteristic variation between two transistors in the same pixel is greatly suppressed. In actual display devices and light-emitting devices, transistor characteristic variations are more serious over the entire substrate than in the same pixel. Therefore, if the characteristic variation between two transistors in the same pixel is suppressed as in the “parallel writing serial driving” pixel circuit of the present invention, there is almost no problem in practical use.
[0149]
In the present embodiment, the effect of the present invention has been described by taking as an example the case where the number of transistors constituting the driving element is two. However, the same situation holds when the number of transistors constituting the driving element is three or more.
[0150]
This embodiment can be arbitrarily combined with Embodiments 1 to 5.
[0151]
(Embodiment 7)
In this embodiment, in a self-luminous element in which a polymer compound is applied as an organic compound layer and a buffer layer made of a conductive polymer compound is provided between the anode and the light emitting layer, direct current driving (always in the forward direction) A description will be given of the results of measurement of luminance degradation when bias is applied) and AC drive (forward bias and reverse bias are alternately applied at a constant period).
[0152]
FIGS. 13A and 13B show the results of a reliability test when AC driving is performed at a forward bias of 3.7 V, a reverse bias of 1.7 V, a duty of 50%, and an AC frequency of 60 Hz. . Initial brightness is about 400cd / cm ² Met. For comparison, the results of a reliability test when DC driving (forward bias: 3.65 V) was performed are also shown. As a result, in the direct current drive, the luminance was reduced by half in about 400 hours, whereas in the alternating current drive, after about 700 hours, the brightness was not reduced to half.
[0153]
FIGS. 13C and 13D show the results of a reliability test when AC driving is performed at a forward bias of 3.8 V, a reverse bias of 1.7 V, a duty of 50%, and an AC frequency of 600 Hz. . Initial brightness is about 300cd / cm ² Met. For comparison, the results of a reliability test when DC driving (forward bias: 3.65 V) was performed are also shown. As a result, in the direct current drive, the luminance was reduced by half in about 500 hours, whereas in the alternating current drive, about 60% of the initial luminance was maintained even after about 700 hours had elapsed.
[0154]
From the above results, it can be seen that the self-luminous element driven by alternating current is more reliable than the self-luminous element driven by direct current.
[0155]
(Embodiment 8)
In this embodiment mode, a cross-sectional structure of the light-emitting device of the present invention will be briefly described with reference to FIGS. For the sake of simplicity, FIG. 14 shows only the cross-sectional structure of the driving TFT 507 and the light emitting element.
[0156]
In FIG. 14, reference numeral 500 denotes a substrate having an insulating surface. A driving TFT 507 is provided over the substrate 500. A wiring is provided so as to be connected to an impurity region provided in an active layer included in the driving TFT 507, and a pixel electrode 509 is provided so as to be connected to the wiring. An organic conductor film 522 is provided on the pixel electrode 509, and an organic thin film (light emitting layer) 523 is provided on the organic conductor film 522. On the organic thin film (light emitting layer) 523, a counter electrode 524 is provided.
[0157]
A stacked body of the pixel electrode 509, the organic conductor film 522, the organic thin film (light emitting layer) 523, and the counter electrode 524 corresponds to a light emitting element. Light emitted from the light emitting element may be emitted toward the substrate 500 or may be emitted in a direction opposite to the substrate 500. The former is called bottom emission, and the latter is called top emission. In the case of bottom emission, the pixel electrode 509 corresponds to the anode and the counter electrode 524 corresponds to the cathode. In the case of top emission, the pixel electrode 509 corresponds to the cathode and the counter electrode 524 corresponds to the anode.
[0158]
Note that a material that emits light such as red, blue, green, and white can be used as appropriate for the organic thin film (light-emitting layer) 523. When the organic thin film (light emitting layer) 523 is formed using a material that emits white light, the pixel electrode 509 or the counter electrode 524 is formed of a transparent conductive film, and a color filter coloring layer is disposed on the surface facing the pixel electrode 509. Good. Then, a color display can be realized even if a white material is used.
[0159]
(Embodiment 9)
In this embodiment, several electronic devices and the like mounted with the display device and the light-emitting device of the present invention are illustrated.
[0160]
Electronic devices equipped with the display device and light-emitting device of the present invention include monitors, video cameras, digital cameras, goggle-type displays (head-mounted displays), navigation systems, sound playback devices (audio components, car audio, etc.), notebook-type personal computers Computers, game machines, portable information terminals (mobile computers, mobile phones, portable game machines, electronic books, etc.), image playback devices equipped with recording media (specifically, playback media such as Digital Versatile Disc (DVD)) And an apparatus provided with a display capable of displaying the image). In particular, for an electronic device that often has an opportunity to see the screen from an oblique direction, it is desirable to use a light-emitting device because a wide viewing angle is important. Specific examples of these electronic devices are shown in FIGS.
[0161]
FIG. 9A shows a monitor. A monitor illustrated in FIG. 9A includes a housing 2001, a support base 2002, a display portion 2003, a speaker portion 2004, a video input terminal 2005, and the like. The display device and the light-emitting device of the present invention can be used for the display portion 2003. The monitor includes all information display devices such as a personal computer, a TV broadcast receiver, and an advertisement display.
[0162]
FIG. 9B shows a digital still camera. A digital still camera shown in FIG. 9B includes a main body 2101, a display portion 2102, an image receiving portion 2103, operation keys 2104, an external connection port 2105, a shutter 2106, and the like. The display device and the light-emitting device of the present invention can be used for the display portion 2102.
[0163]
FIG. 9C illustrates a laptop personal computer. A laptop personal computer illustrated in FIG. 9C includes a main body 2201, a housing 2202, a display portion 2203, a keyboard 2204, an external connection port 2205, a pointing mouse 2206, and the like. The display device and the light-emitting device of the present invention can be used for the display portion 2203.
[0164]
FIG. 9D illustrates a mobile computer. A mobile computer shown in FIG. 9D includes a main body 2301, a display portion 2302, a switch 2303, operation keys 2304, an infrared port 2305, and the like. The display device and the light-emitting device of the present invention can be used for the display portion 2302.
[0165]
FIG. 9E shows a portable image reproducing apparatus (specifically, a DVD reproducing apparatus) provided with a recording medium. A DVD reproducing device shown in FIG. 9E includes a main body 2401, a housing 2402, a display portion A2403, a display portion B2404, a recording medium (DVD or the like) reading portion 2405, operation keys 2406, a speaker portion 2407, and the like. The display device and the light-emitting device of the present invention can be used for the display portion A 2403 and the display portion B 2404. Note that an image reproducing device provided with a recording medium includes a home game machine and the like.
[0166]
FIG. 9F shows a goggle type display (head mounted display). A display shown in FIG. 9F includes a main body 2501, a display portion 2502, an arm portion 2503, and the like. The display device and the light-emitting device of the present invention can be used for the display portion 2502.
[0167]
FIG. 9G illustrates a video camera. A video camera shown in FIG. 9G includes a main body 2601, a display portion 2602, a housing 2603, an external connection port 2604, a remote control receiving portion 2605, an image receiving portion 2606, a battery 2607, an audio input portion 2608, operation keys 2609, and the like. It is out. The display device and the light-emitting device of the present invention can be used for the display portion 2602.
[0168]
FIG. 9H illustrates a mobile phone. A cellular phone shown in FIG. 9H includes a main body 2701, a housing 2702, a display portion 2703, an audio input portion 2704, an audio output portion 2705, operation keys 2706, an external connection port 2707, an antenna 2708, and the like. The display device and the light-emitting device of the present invention can be used for the display portion 2703. Note that the display portion 2703 can suppress power consumption of the mobile phone by displaying white characters on a black background.
[0169]
If it becomes possible to stably increase the light emission luminance of the self-light emitting element in the future, light including image information output from the display device and the light emitting device of the present invention is enlarged and projected by a lens or the like, and the front type or rear type is projected. It can also be used for a type of projector.
[0170]
As described above, the application range of the present invention is extremely wide and can be used for electronic devices and the like in various fields.
[0171]
【The invention's effect】
According to the present invention, in the AM display device and the light emitting device, a driving element provided in each pixel is constituted by a plurality of transistors. In addition, the plurality of transistors are connected in parallel when the data current is read into the pixel, and the plurality of transistors are connected in series when the light-emitting element emits light. As described above, the connection state of the plurality of transistors constituting the driving element is appropriately switched between parallel and series. As a result, the following effects occur.
[0172]
First, if even a plurality of transistors constituting a driving element in the same pixel are not varied, it is possible to avoid a serious defect in display quality such that unevenness in emission luminance appears on the entire display screen. That is, the electrical characteristics of the transistors installed in each pixel have considerable variations when observed over the entire substrate. This variation is the drive current I of the self-luminous element. _E Therefore, it is possible to prevent the light emission luminance from being uneven over the entire display screen. However, even in the case of a pixel circuit using a current mirror as shown in FIG. 10A, if even the two transistors of the current mirror in the same pixel are not varied, the emission luminance may be uneven across the entire display screen. Can be prevented. In this respect, the present invention has the same effect as the pixel circuit using the current mirror as shown in FIG.
[0173]
However, in the case of a pixel circuit using a current mirror as shown in FIG. 10A, if there is a variation between the two transistors of the current mirror in the same pixel, the emission luminance will eventually differ between the pixels. Can not be prevented. In that respect, in the case of the present invention, even if there is a variation between a plurality of transistors constituting the driving element in the same pixel, the influence is suppressed to a small extent, so that the light emission luminance between the pixels becomes a problem in practice. Can be prevented from falling apart.
[0174]
Further, in the case of the pixel circuit as illustrated in FIG. 10B, it is possible to prevent the emission luminance from varying between the pixels. However, in the case of the pixel circuit of FIG. 10B, the data current I to be written to the pixel. _W And the drive current I of the self light emitting element when the self light emitting element emits light _E And the ratio must be the same. This is a very severe limitation in practical use. In the case of the present invention, the data current I written to the pixel is divided in order to divide the transistor constituting the driving element into a plurality of transistors. _W Self-luminous element drive current I _E It is possible to make it larger.
[0175]
Since the present invention has the advantages as described above, it is an important technique in manufacturing practical AM type display devices and light emitting devices.
[0176]
From the measurement results of FIG. 13, it can be seen that the self-luminous element driven by alternating current has higher reliability than the self-luminous element driven by direct current. Therefore, the present invention provides a display device and a light-emitting device in which the reliability of the self-light-emitting element is improved by performing AC driving in a predetermined period of the frame period.
[Brief description of the drawings]
FIG. 1 shows a pixel of a display device and a light-emitting device of the present invention.
FIG. 2 is a diagram showing a pixel of a display device and a light-emitting device of the present invention.
FIG. 3 is a diagram showing a pixel of a display device or a light-emitting device of the present invention.
FIG. 4 is a diagram showing a pixel of a display device and a light emitting device of the present invention.
FIG. 5 is a diagram showing a current path in a pixel of a display device and a light-emitting device of the present invention.
FIG. 6 is a diagram showing a planar layout of a pixel of a display device and a light-emitting device of the present invention.
FIGS. 7A and 7B illustrate a display device and a light-emitting device of the present invention. FIGS.
FIG. 8 is a graph showing characteristics of a transistor constituting a driving element.
9 is a diagram showing an electronic device to which the display device and the light-emitting device of the present invention are applied. FIG.
FIG. 10 is a diagram showing a pixel of a known display device or light-emitting device.
11 is a diagram showing a pixel of a display device and a light-emitting device of the present invention. FIG.
12 is a diagram showing a pixel of a display device or a light-emitting device of the present invention. FIG.
FIG. 13 is a diagram showing a relationship between luminance and time of a self-luminous element.
14 is a cross-sectional view of a display device and a light-emitting device of the present invention.

Claims (17)

A first switch, a second switch, a third switch, a fourth switch, a driving element including a plurality of transistors connected in series between a first power supply line and the third switch, and self-luminous A pixel including an element is provided;
Gate electrodes of the plurality of transistors are connected to each other;
The first switch controls conduction between the plurality of transistors and a signal line;
The second switch controls the conduction of the said plurality of transistors the first power supply line,
The third switch controls conduction between the plurality of transistors and the light-emitting element;
The fourth switch controls conduction between the self-luminous element and the second power line,
When the first switch, the second switch, and the plurality of transistors are on, a first current based on an input of a video signal to the pixel flows through each of the plurality of transistors,
When the first switch and the second switch are off, and when the third switch and the plurality of transistors are on, each of the plurality of transistors and the self-light-emitting element has a first signal based on the video signal. 2 current flows,
A light-emitting device, wherein a reverse bias voltage is applied to the self-light-emitting element when the third switch is off and the fourth switch is on. Drive including a first switch, a second switch, a third switch, a fourth switch, a fifth switch, and a plurality of transistors connected in series between the first power supply line and the third switch A pixel including a light emitting device and a self-luminous device is provided,
Gate electrodes of the plurality of transistors are connected to each other;
The first switch controls conduction between the plurality of transistors and a signal line;
Wherein the second switch 5 switches, respectively, to control the conduction of the said plurality of transistors the first power supply line,
The third switch controls conduction between the plurality of transistors and the light-emitting element;
The fourth switch controls conduction between the self-luminous element and the second power line,
When the first switch, the second switch, and the plurality of transistors are on, a first current based on an input of a video signal to the pixel flows through each of the plurality of transistors,
When the first switch and the second switch are off, and when the third switch and the plurality of transistors are on, each of the plurality of transistors and the self-light-emitting element has a first signal based on the video signal. 2 current flows,
When the fifth switch is on, the self-luminous element does not emit light ,
A light-emitting device, wherein a reverse bias voltage is applied to the self-light-emitting element when the third switch is off and the fourth switch is on. Oite to claim 1 or claim 2,
The light emitting device, wherein the first switch includes at least two transistors. Oite to claim 1 or claim 2,
The light emitting device, wherein the second switch includes at least one transistor. Oite to claim 1 or claim 2,
The light emitting device, wherein the third switch includes at least one transistor. Oite to claim 1 or claim 2,
The light emitting device according to claim 4, wherein the fourth switch is a transistor. Oite to claim 1 or claim 2,
The light emitting device is characterized in that the fourth switch is a transistor or a diode in which a gate and a drain are connected. Oite to claim 2,
The light emitting device, wherein the fifth switch includes at least one transistor. Oite to claim 1 or claim 2,
The light-emitting device is characterized in that the first current I _W , the second current I _E , and the number n (n is a natural number) of the plurality of transistors satisfy I _W = n ² × _IE . In any one of Claims 1 thru | or 9 ,
The pixel is provided with a capacitive element,
The light-emitting device, wherein the capacitor element holds a potential of a gate electrode of the plurality of transistors. In any one of Claims 1 thru | or 9 ,
A drive circuit is provided,
The light emitting device is characterized in that the pixel and the driving circuit are provided over the same substrate. In any one of Claims 1 thru | or 9 ,
A drive circuit is provided,
The pixel and the driving circuit are provided on the same substrate,
The light-emitting device, wherein the driving circuit includes a scanning line driving circuit. In any one of Claims 1 thru | or 9 ,
A drive circuit is provided,
The pixel and the driving circuit are provided on the same substrate,
The driving circuit includes a signal line driving circuit. In any one of Claims 1 thru | or 9 ,
A drive circuit is provided,
The pixel and the driving circuit are provided on the same substrate,
The light-emitting device, wherein the driving circuit includes a signal line driving circuit and a scanning line driving circuit. According to claim 1 3 or claim 1 4,
The light-emitting device, wherein the signal line driver circuit includes a voltage-current conversion circuit that performs an operation of converting a voltage-format video signal into a current-format video signal or an operation of amplifying a voltage-format video signal. In any one of Claim 1 thru | or Claim 15 ,
The self-luminous element is an organic light-emitting diode. Electronic devices using the light emitting device according to any one of claims 1 to 16.

Images