JP5041673B2 - Display device, display module, and electronic device - Google Patents

Description

  The present invention relates to a light-emitting device that forms a display color using light emitted from a light-emitting element and a driving method thereof.

  A light-emitting device using light emission from an electroluminescence element (light-emitting element) has a wide viewing angle and low power consumption. In recent years, in the field of light-emitting device development, research and development of light-emitting devices that can provide high-quality images has been active in order to obtain a market as a display device applied to various information processing devices such as television receivers and car navigation systems. Has been done.

  Incidentally, the luminance of the light emitting element gradually decreases as the light emission time accumulates. Further, the decrease in luminance accompanying the accumulation of the light emission time is more remarkable when light is emitted at a high luminance. Such a decrease in luminance causes a change in display color particularly in a light emitting device that functions as a display device, leading to deterioration in image quality.

  Therefore, development of a long-life light-emitting element in which a decrease in light emission luminance accompanying the accumulation of light emission time is being promoted is underway. For example, Patent Document 1 discloses a method for driving a light emitting element that can achieve a long lifetime by applying a recovery voltage. Extending the lifetime of such a light emitting element is important in obtaining a light emitting device capable of displaying a high quality image.

JP-A-10-55154

  It is an object of the present invention to provide a light emitting device that can reduce a decrease in light emission luminance associated with accumulation of light emission time or high luminance light emission. The present invention also relates to a driving method that can reduce a decrease in light emission luminance associated with accumulation of light emission time or high luminance light emission.

  One of the light-emitting devices of the present invention is a device that can obtain a plurality of display colors having different brightness and chromaticity by visually mixing light emitted from a plurality of light-emitting elements having different emission colors. And when forming the visually mixed display color, it is characterized by exhibiting white light emission.

  One light-emitting device of the present invention includes a plurality of first light-emitting elements that emit different colors and a second light-emitting element that emits white light. When the light emitting device of the present invention is driven, a video signal is input to the second transistor provided for controlling the supply of current to the first light emitting element through the common first transistor. Is done. By this video signal, the second transistor is turned on or off. And a light emitting element will be in a light emission state or a non-light-emission state at a respectively different timing. Here, the method further includes the step of causing the second light emitting element that emits white light to emit light when at least one of the first light emitting elements emits light.

  One light-emitting device of the present invention includes a plurality of light-emitting elements that exhibit different emission colors. When the light-emitting device of the present invention is driven, a video signal is input to the second transistor provided for controlling the supply of current to the light-emitting element through the common first transistor. By this video signal, the second transistor is turned on or off. And a light emitting element will be in a light emission state or a non-light-emission state at a respectively different timing. Here, when at least one light emitting element emits light, the method further includes a step of causing the at least two light emitting elements to emit light simultaneously so as to exhibit white.

  A light-emitting device of the present invention includes a gate signal line, a source signal line, n (n is a natural number, 2 ≦ n) current supply lines, a power source, and a first transistor that controls input of a video signal And n second transistors for controlling the supply of current from the current supply line, and n first light emitting elements having different emission colors. In the first transistor, the gate electrode is electrically connected to the gate signal line, and the first electrode is electrically connected to the source signal line. Further, the second electrode of the first transistor is electrically connected to the gate electrode of the second transistor. Here, in the m (m is a natural number, 2 ≦ m ≦ n−1) th light emitting element, the first electrode is electrically connected to the mth current supply line through the mth second transistor. The second electrode is electrically connected to the (m + 1) th current supply line via the (m + 1) th second transistor. In the nth light-emitting element, the first electrode is electrically connected to the nth current supply line via the nth second transistor, and the second electrode is electrically connected to the power source. Yes.

  One light-emitting device of the present invention includes a layer in which electrodes of a light-emitting element and light-emitting layers are alternately stacked. The light emitting device of the present invention further includes a driving transistor and a current supply line. Here, the electrodes of the light emitting element are electrically connected to different current supply lines through different driving transistors.

  According to the present invention, a light-emitting device that emits white light can be obtained. Further, the luminance of the display color can be increased by emitting white light. Moreover, the contrast of an image can be improved by emitting white light. Therefore, for example, when a display color is formed by combining light emission from red, green, and blue light emitting elements, the burden on each light emitting element can be reduced, and the life of the light emitting element is extended.

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

(Embodiment 1)
A circuit included in the pixel portion of the light-emitting device of the present invention will be described with reference to FIG.

FIG. 1 is a diagram illustrating a circuit configuration of a pixel 320 included in the light emitting device of the present invention.
Each of the switching transistor 301 and the driving transistors 302a, 302b, 302c, and 302d is a three-terminal element including a gate electrode, a drain region, and a source region, and a channel region is formed between the drain region and the source region. Have. Here, since it is difficult to limit which of the source region and the drain region is a source region or a drain region depending on a transistor structure, operation conditions, or the like, one is a first electrode and the other is a first electrode. It describes as 2 electrodes. Here, the switching transistor is a transistor that controls input of a video signal to the driving transistor. The driving transistor is a transistor that controls the supply of current from the current supply line based on the input video signal and determines whether the light emitting element emits light or not. Note that there is no particular limitation on each of the switching transistor 301 and the driving transistors 302a, 302b, 302c, and 302d, and an organic thin film transistor including a semiconductor layer made of an organic compound can be used in addition to a MOS transistor. The switching transistor 301 may be either an N channel type or a P channel type. Further, the driving transistors 302a, 302b, 302c, and 302d may be either N-channel type or P-channel type, but are controlled by a common video signal according to the example shown in FIG. It is preferable that

  Each of the light emitting elements 303a, 303b, 303c, and 303d is a two-terminal element. Each of the light-emitting elements 303a, 303b, 303c, and 303d has a light-emitting layer between the first electrode and the second electrode, and current flows due to a potential difference between the first electrode and the second electrode. It emits light when it hits. Note that when the driving transistors 302a, 302b, 302c, and 302d are p-channel transistors, in the light-emitting elements 303a, 303b, 303c, and 303d, the first electrode functions as an anode and the second electrode functions as a cathode. . On the other hand, when the driving transistors 302a, 302b, 302c, and 302d are n-channel transistors, in the light-emitting elements 303a, 303b, 303c, and 303d, the first electrode functions as a cathode and the second electrode functions as an anode. . There is no particular limitation on the light emission color of the light emitting elements 303a, 303b, 303c, and 303d, but it is preferable that the light emission colors are different. In addition, it is particularly preferable that any one of the light-emitting elements exhibits white light or emits white light by combining light emission from at least two light-emitting elements. The light emitting element 303a exhibits a red light emission color when emitted light is extracted outside the light emitting device, and the light emitting element 303b exhibits a green light emitted color when emitted light is extracted outside the light emitting device. 303c exhibits a blue emission color when emitted light is extracted outside the light emitting device, and the light emitting element 303d exhibits a white emission color when emitted light is extracted outside the light emitting device. Here, the red emission color means a color having coordinates in a region where x is 0.6 or more and y is 0.35 or less in the chromaticity diagram when expressed in the CIE-XYZ color system. The green emission color is a color having coordinates in a region where x in the chromaticity diagram is 0.3 or less and y is 0.6 or more when expressed in the CIE-XYZ color system. The blue emission color means a color having coordinates in a region where x is 0.15 or less and y is 0.2 or less in the chromaticity diagram when expressed in the CIE-XYZ color system. The white emission color is a region where x in the chromaticity diagram is 0.25 or more and 0.35 or less and y is 0.25 or more and 0.35 or less when expressed in the CIE-XYZ color system. Means a color having coordinates in a region where x is 0.28 to 0.32 and y is 0.28 to 0.32 in the chromaticity diagram. The CIE-XYZ color system is a color system based on tristimulus values X, Y, and Z. The chromaticity diagram represents colors in x, y coordinate space based on tristimulus values X, Y, Z. Note that chromaticity is a quantitative definition of the type of light color excluding lightness.

  In the switching transistor 301, the gate electrode is electrically connected to the gate signal line 311, and the first electrode is electrically connected to the source signal line 312. The light emitting elements 303a, 303b, 303c, and 303d are connected in series. In the driving transistor 302a, the first electrode is electrically connected to the current supply line 313a, and the second electrode is electrically connected to the first electrode of the light-emitting element 303a. In the driving transistor 302b, the first electrode is electrically connected to the current supply line 313b, and the second electrode is electrically connected to the first electrode of the light-emitting element 303b. In the driving transistor 302c, the first electrode is electrically connected to the current supply line 313c, and the second electrode is electrically connected to the first electrode of the light-emitting element 303c. In the driving transistor 302d, the first electrode is electrically connected to the current supply line 313d, and the second electrode is electrically connected to the first electrode of the light-emitting element 303d. Note that the second electrode of the light-emitting element 303d is electrically connected to the power source 316. The gate electrodes of the driving transistors 302a, 302b, 302c, and 302d are electrically connected to each other. Further, a capacitor 304 is provided between the gate electrodes of the driving transistors 302a, 302b, 302c, and 302d and the capacitor line 315, and the gate electrodes of the driving transistors 302a, 302b, 302c, and 302d are provided. Each potential can be held. The second electrode of the switching transistor 301 is electrically connected to the gate electrode of each of the driving transistors 302a, 302b, 302c, and 302d.

  Note that although a structure including four light-emitting elements is described in this embodiment mode, the number of light-emitting elements is not limited to this. However, it is preferable that at least two light emitting elements are included. Further, the number of driving transistors is not particularly limited. There is no particular limitation on the number of current supply lines. Note that when including n (n is preferably 2 or more) light emitting elements, it is preferable to include n current supply lines and n driving transistors. In the m (2 ≦ m ≦ n) th light emitting element, the first electrode is electrically connected to the mth current supply line, and the second electrode is electrically connected to the m + 1th current supply line or the power source. It is preferable to connect to.

  Next, a method for driving the circuit shown in FIG. 1 will be described. When the gate signal line 311 is selected, the switching transistor 301 is turned on, and a video signal is input from the source signal line 312 to the gate electrodes of the driving transistors 302a, 302b, 302c, and 302d via the switching transistor 301. Is done. Here, when the switching transistor 301 is an N-channel transistor and the driving transistors 302a, 302b, 302c, and 302d are P-channel transistors, if the potential of the video signal is Low Level, the driving transistors 302a and 302b , 302c and 302d are turned on, and if the video signal is High Level, the driving transistors 302a, 302b, 302c and 302d are turned off. Further, when the current supply line 313a and the current supply line 313b have different potentials, a potential difference is generated between the first electrode and the second electrode in the light-emitting element 303a. Accordingly, a current flows through the light emitting element 303a, and the light emitting element 303a emits light. Further, when the current supply line 313b and the current supply line 313c have different potentials, a potential difference is generated between the first electrode and the second electrode in the light-emitting element 303b. Accordingly, current flows through the light emitting element 303b, and the light emitting element 303b emits light. Further, when the current supply line 313c and the current supply line 313d have different potentials, a potential difference is generated between the first electrode and the second electrode in the light-emitting element 303c. Accordingly, a current flows through the light emitting element 303c, and the light emitting element 303c emits light. Further, when the current supply line 313d and the power source 316 have different potentials, a potential difference is generated between the first electrode and the second electrode in the light-emitting element 303d. Accordingly, a current flows through the light emitting element 303d, and the light emitting element 303d emits light.

  As described above, the light emitting elements 303a, 303b, 303c, and 303d can emit light. Note that the light emitting elements 303a, 303b, 303c, and 303d are independently controlled to emit light and not emit light. Therefore, for example, the current supply line 313a and the current supply line 313b may be set to different potentials, and the current supply lines 313b, 313c, and 313d and the power supply 316 may be set to the same potential so that only the light emitting element 303a emits light. . Further, the current supply line 313a and the current supply line 313b are set to different potentials, the current supply lines 313b and 313c, the current supply lines 313c and 313d, the current supply line 313d and the power supply 316 are set to different potentials, and the light emitting element 303a. , 303b, 303c, and 303d may all emit light.

  The circuit described above can drive the light emitting element so as to emit white light.

(Embodiment 2)
In this embodiment mode, a light-emitting device of the present invention including a pixel having the circuit configuration described in Embodiment Mode 1 and a driving method thereof will be described.

  FIG. 2 is a schematic view of a light emitting device to which the present invention is applied as viewed from above. In FIG. 2, 6510 indicated by a dotted line is a driver circuit portion (source side driver circuit), 6511 is a pixel portion, and 6512 is a driver circuit portion (gate side driver circuit). The pixel portion 6511 is provided with the light-emitting element of the present invention. The driver circuit portions 6510 and 6512 are connected to an FPC 6503 that is an external input terminal through a wiring group formed on the substrate 6500. When a video signal, a clock signal, a start signal, a reset signal, or the like is received from an FPC (flexible printed circuit) 6503, signals are input to the driver circuit portion 6510 and the driver circuit portion 6512. A printed wiring board (PWB) 6513 is attached to the FPC 6503. The driver circuit portion 6510 is provided with a shift register 6515, a switch 6516, and memories (latch) 6517 and 6518, and the driver circuit portion 6512 is provided with a shift register 6519 and a buffer 6520.

  Note that the driver circuit portion is not necessarily provided over the same substrate as the pixel portion 6511 as described above. For example, an IC chip mounted on an FPC on which a wiring pattern is formed (TCP) or the like is used. It may be used and provided outside the substrate. Further, the circuit configurations of the driver circuit portions 6510 and 6512 are not limited to those described above, and a configuration in which a circuit having a function different from the above is further provided may be used.

  As shown in FIG. 3, in the pixel portion 6511, a plurality of source signal lines 412 extending in the column direction are arranged side by side in the row direction. In addition, a current supply line 413 including a set of current supply lines 413a, 413b, 413c, and 413d is arranged side by side in the row direction. A plurality of gate signal lines 411 extending in the row direction are arranged side by side in the column direction. The pixel portion 6511 includes a circuit 420 having a structure similar to that described in Embodiment 1. A circuit 420 including a gate signal line 411, a source signal line 412, a current supply line 413, a power supply 416, a switching transistor 401, driving transistors 402a, 402b, 402c, and 402d, and light emitting elements 403a, 403b, 403c, and 403d. A plurality are arranged in the vertical and horizontal directions. Note that the circuit 420 may further include a capacitor 404. In the circuit 420, the gate signal line 411 corresponds to the gate signal line 311 in Embodiment 1, the source signal line 412 corresponds to the source signal line 312 in Embodiment 1, and the current supply lines 413a, 413b, 413c, and 413d. Respectively correspond to the current supply lines 313a, 313b, 313c, and 313d in Embodiment 1, the power source 416 corresponds to the power source 316 in Embodiment 1, and the capacitor line 415 corresponds to the capacitor line 315 in Embodiment 1. Equivalent to. The switching transistor 401 corresponds to the switching transistor 301 in the first embodiment, and the driving transistors 402a, 402b, 402c, and 402d are the driving transistors 302a, 302b, 302c, and 302d in the first embodiment, respectively. The capacitor 404 corresponds to the capacitor 304 in Embodiment 1. The light emitting elements 403a, 403b, 403c, and 403d correspond to the light emitting elements 303a, 303b, 303c, and 303d in Embodiment 1, respectively.

  There is no particular limitation on the emission color of each of the light emitting elements 403a, 403b, 403c, and 403d, but any one of the light emitting elements preferably exhibits a white emission color. Note that in this embodiment, the light-emitting element 403a exhibits a red light emission color when light emission is extracted outside the light-emitting device, and the light-emitting element 403b exhibits a green light emission color when light emission is extracted outside the light-emitting device. The light emitting element 403c exhibits a blue emission color when emitted light is extracted outside the light emitting device, and the light emitting element 403d exhibits a white emission color when emitted light is extracted outside the light emitting device. . Note that red, green, blue, and white are the same as those described in the first embodiment.

  Next, a driving method will be described. FIG. 4 is a diagram for explaining the operation of a frame over time. In FIG. 4, the horizontal direction represents the passage of time, and the vertical direction represents the number of scanning stages of the gate signal line.

  When image display is performed using the light emitting device of the present invention, the screen rewriting operation and the display operation are repeatedly performed during the display period. The number of rewrites is not particularly limited, but is preferably at least about 60 times per second so that a person viewing the image does not feel flicker. Here, a period during which one screen (one frame) is rewritten and displayed is referred to as one frame period.

  One frame includes four subframes 501, 502, 503, and 504 including a writing period 501a and a holding period 501b, a writing period 502a and a holding period 502b, a writing period 503a and a holding period 503b, and a writing period 504a and a holding period 504b. It is time divided.

  First, in the subframe 501, the write operation is performed in order from the first row to the last row. Therefore, the start time of the writing period 501a differs depending on the row. After the writing period 501a ends, the holding period 501b is started. In the light-emitting element connected to the driving transistor to which a signal for light emission is applied in the writing period 501a, different potentials are applied between the first electrode and the second electrode with the light-emitting layer interposed in the holding period 501b. It emits light when In this embodiment mode, different potentials are applied to the first electrode and the second electrode included in the light-emitting element 403a in the subframe 501, and the light-emitting element 403a emits light. At this time, a potential is applied so that the first electrode and the second electrode included in each of the other light emitting elements 403b, 403c, and 403d are equipotential. After the holding period 501b ends, the process proceeds to the next subframe 502, and writing operations are performed in order from the first line to the last line as in the case of the subframe 501. Then, the light-emitting element 403b emits light during the holding period 502b. After the holding period 502b ends in the subframe 502, the process proceeds to the subframe 503. In the subframe 503, the light emitting element 403c emits light. After the holding period 503b ends in the subframe 503, the process proceeds to the subframe 504. In the subframe 504, the light emitting element 403d emits light. The operation as described above is repeated until the holding period 504b of the subframe 504 ends. When the operation in the subframe 504 is completed, the process proceeds to the next frame. Note that in this embodiment mode, light is emitted in the order of the light emitting elements 403a, 403b, 403c, and 403d. However, the order of light emission is not particularly limited, and the light emission may be performed by appropriately changing the order.

  Next, driving of the pixel in the writing period is described. In the writing period, the gate signal line 411 in the n-th row (n is a natural number) is selected, and the switching transistor 401 connected to the gate signal line 411 is turned on. At this time, video signals are simultaneously input to the source signal lines from the first column to the last column. Note that the video signals input from the source signal lines 412 in each column are independent from each other. The video signal input from the source signal line 412 is input to the gate electrodes of the driving transistors 402a, 402b, 402c, and 402d through the switching transistor 401 connected to each source signal line. At this time, in accordance with a signal input to the driving transistors 402a, 402b, 402c, and 402d and a potential difference between the first electrode and the second electrode included in each of the light emitting elements 403a, 403b, 403c, and 403d. Light emission / non-light emission of the light emitting elements 403a, 403b, 403c, and 403d is determined. For example, when the driving transistor is a P-channel transistor, any of the light-emitting elements 403a, 403b, 403c, and 403d emits light when a Low Level signal is input. On the other hand, when the driving transistor is an N-channel transistor, any of the light-emitting elements 403a, 403b, 403c, and 403d emits light when a High Level signal is input.

  As writing to the source signal line ends, the writing period in the n-th row (n is a natural number) ends and the holding period starts. Next, the (n + 1) th row is a writing period, and a writing operation similar to the above is performed. The writing operation is performed from the first row to the last row by repeating the above operation.

  As described above, the light emitting elements 403a, 403b, and 403c sequentially emit light, and the light emission colors from the respective light emitting elements are visually mixed by the afterimage effect, whereby various display colors can be obtained. Note that light emission whose luminance is adjusted by changing the voltage applied to each of the light emitting elements 403a, 403b, and 403c can be appropriately combined to obtain a desired display color. Further, when the light emitting element 403d exhibiting white emits light, the luminance of the display color is visually recognized as if it has been increased. Accordingly, the voltage applied to the light emitting elements 403a, 403b, and 403c is applied to the light emitting elements 403a, 403b, and 403c, as compared with the case where the luminance of the display color is increased by using the method of increasing the luminance of each light emitting color by increasing the voltage applied to the light emitting elements 403a, 403b, and 403c. The burden can be reduced. As a result, the lifetime of the light emitting elements 403a, 403b, and 403c can be extended. In addition, when the light-emitting element 403d exhibiting white light emits light, the light-emitting device described above can display an image with high contrast.

  Note that in this embodiment mode, all the light emitting elements 403a, 403b, and 403c emit light. However, the present invention is not limited to this. For example, the light emitting element 403a and the light emitting element 403b emit light and the light emitting element 403c does not emit light. A desired display color may be obtained, or a desired display color may be obtained by emitting any one of the light emitting elements 403a, 403b, and 403c. Further, when it is desired to obtain a display color with low luminance, it is not always necessary to cause the light emitting element 403d exhibiting white to emit light, and the timing, luminance, and the like for causing the light emitting element 403d exhibiting white to emit light in a series of display operations may be adjusted as appropriate. Good.

(Embodiment 3)
In this embodiment mode, a driving method of the light emitting device of the present invention, which is different from the driving method of the light emitting device of the present invention described in Embodiment Mode 2, will be described. Note that the circuit configuration of the pixel portion can be the same as that shown in Embodiment Mode 2, and therefore, in this embodiment mode, the description in FIG.

  Hereinafter, the operation of the light-emitting device of this embodiment will be described with reference to FIGS. FIGS. 5A and 5B are diagrams for explaining the operation of a frame over time. FIG. 5B is a diagram for explaining the operation of a frame over time in one first subframe among a plurality of subframes included in one frame. In FIG. 5B, the horizontal direction represents the passage of time, and the vertical direction represents the number of stages of the gate signal lines.

In the light-emitting device of this embodiment, one frame is time-divided into four first sub-frames 601, 602, 603, and 604 as shown in FIG. The first subframe 601 is further time-divided into second subframes 611, 612, 613, and 614 (FIG. 5B). The first subframe 602 is further time-divided into second subframes 621, 622, 623, and 624 (FIG. 5C). The second subframes 621, 622, 623, and 624 each include a writing period and a holding period. In addition, the first subframe 603 is further time-divided into second subframes 631, 632, 633, and 634 (FIG. 11A). Each of the second subframes 631, 632, 633, and 634 includes a writing period and a holding period. In addition, the first subframe 604 is further time-divided into second subframes 641, 642, 643, and 644 (FIG. 11B). The second subframes 641, 642, 643, and 644 each include a writing period and a holding period. A light emitting element to which a signal for emitting light is given is in a light emitting state in the holding period. The ratio of the retention period lengths in each of the second subframes 611, 612, 613, and 614 is as follows: second subframe 611b: second subframe 612b: second subframe 613b: second subframe 614b = 2 ³ : 2 ² : 2 ¹ : 2 ⁰ = 8: 4: 2: 1. The ratio of the retention period lengths in each of the second subframes 621, 622, 623, and 624 is as follows: second subframe 621b: second subframe 622b: second subframe 623b: second subframe 624b = 2 ³ : 2 ² : 2 ¹ : 2 ⁰ = 8: 4: 2: 1. The ratio of the retention period lengths in each of the second subframes 631, 632, 633, and 634 is as follows: second subframe 631b: second subframe 632b: second subframe 633b: second subframe 634b = 2 ³ : 2 ² : 2 ¹ : 2 ⁰ = 8: 4: 2: 1. The ratio of the retention period lengths in each of the second subframes 641, 642, 643, and 644 is as follows: second subframe 641b: second subframe 642b: second subframe 643b: second subframe 644b = 2 ³ : 2 ² : 2 ¹ : 2 ⁰ = 8: 4: 2: 1. As a result, 4-bit gradation can be expressed. However, the number of bits and the number of gradations are not limited to those described here. For example, eight second subframes may be provided so that 8-bit gradation can be performed, or four or more 4-bit gradations may be provided. May be represented by the second subframe.

  First, the operation in the first subframe 601 will be described. Note that in the first subframe 601, the second subframe 611 includes a writing period 611a and a holding period 611b, and the second subframe 612 includes a writing period 612a and a holding period 612b. The second subframe 613 includes a writing period 613a and a holding period 613b, and the second subframe 614 includes a writing period 614a and a holding period 614b. First, in the second subframe 611, a write operation is performed in order from the first row to the last row. Therefore, the start time of the writing period differs depending on the row. After the writing period 611a ends, the holding period 611b is started. In the holding period, the light-emitting element to which a signal for emitting light is given is in a light-emitting state. In addition, after the holding period 611b ends, the process proceeds to the next second subframe 612, and in the same manner as in the second subframe 611, the writing operation is performed sequentially from the first row to the last row, and then in the holding period. Move. The above operation is repeated, and the operation ends until the holding period of the second subframe 614. When the first subframe 601 is completed as described above, the process proceeds to the next first subframe 602. In the first subframe 602 as well as the first subframe 601, the writing period and the holding period are repeated from the second subframe 621 to the second subframe 624. Note that as shown in FIG. 5C, in the first subframe 602, the second subframe 621 includes a writing period 621a and a holding period 621b, and the second subframe 622 includes a writing period. 622a and a holding period 622b, the second subframe 623 includes a writing period 623a and a holding period 613b, and the second subframe 624 includes a writing period 624a and a holding period 624b. Yes. In addition, as illustrated in FIG. 11A, in the first subframe 603, the second subframe 631 includes a writing period 631a and a holding period 631b, and the second subframe 632 includes a writing period. 632a and a holding period 632b, the second subframe 633 includes a writing period 633a and a holding period 633b, and the second subframe 634 includes a writing period 634a and a holding period 634b. Yes. In addition, as illustrated in FIG. 11B, in the first subframe 604, the second subframe 641 includes a writing period 641a and a holding period 641b, and the second subframe 642 includes a writing period. 642a and a holding period 642b, the second subframe 643 includes a writing period 643a and a holding period 643b, and the second subframe 644 includes a writing period 644a and a holding period 644b. Yes. In the first subframe 603 as well as the first subframe 601, the writing period and the holding period are repeated from the second subframe 631 to the second subframe 634. In the first subframe 604 as well as the first subframe 601, the writing period and the holding period are repeated from the second subframe 641 to the second subframe 644. Thus, the accumulated time of the light emission times in each of the first subframes 601, 602, 603, and 604 is the light emission time of each light emitting element in one frame. Note that in this embodiment, the light-emitting element 403a that emits red light in the first subframe 601 emits light, and the light-emitting element 403b that emits green light in the first subframe 602 emits light. In the frame 603, the light emitting element 403c that emits blue light is emitted, and in the first subframe 604, the light emitting element 403d that emits white light is emitted. The luminance of each light emitting element is determined by the accumulated time during which light is emitted in each of the first subframes 601, 602, 603, and 604.

  Note that in this embodiment, the holding period is started after the writing period of all the rows is ended. However, the present invention is not limited to this, and the holding period may be sequentially started from the row in which the writing period is ended. Further, in this embodiment, the writing period of the next second subframe is started after the holding period of all the rows is ended, but the writing period of the next second subframe is sequentially started from the row after the holding period is ended. You may move. In that case, in a subframe having a holding period longer than the writing period including the writing period from the writing period of the first row to the last row, an erasing period is provided after the holding period to forcibly emit no light. You may control as follows. Accordingly, it is possible to prevent the writing period of the second subframe from overlapping with the writing period of the next second subframe.

  In the present embodiment, the second subframes 611 to 614, 621 to 624, 631 to 634, and 641 to 644 are arranged in order from the one having the long retention period. There is no need, and for example, it may be arranged in order from the shortest holding period, or long and short holding periods may be arranged at random.

  Next, driving of the pixel in the writing period is described. In the writing period, the gate signal line 411 in the n-th row (n is a natural number) is selected, and the switching transistor 401 connected to the gate signal line 411 is turned on. At this time, video signals are simultaneously input to the source signal lines from the first column to the last column. Note that the video signals input from the source signal lines 412 in each column are independent from each other. The video signal input from the source signal line 412 is input to the gate electrodes of the driving transistors 402a, 402b, 402c, and 402d through the switching transistor 401 connected to each source signal line. At this time, in accordance with a signal input to the driving transistors 402a, 402b, 402c, and 402d and a potential difference between the first electrode and the second electrode included in each of the light emitting elements 403a, 403b, 403c, and 403d. Light emission / non-light emission of the light emitting elements 403a, 403b, 403c, and 403d is determined. For example, when the driving transistor is a P-channel transistor, any of the light-emitting elements 403a, 403b, 403c, and 403d emits light when a Low Level signal is input. On the other hand, when the driving transistor is an N-channel transistor, any of the light-emitting elements 403a, 403b, 403c, and 403d emits light when a High Level signal is input.

  As writing to the source signal line ends, the writing period in the n-th row (n is a natural number) ends and the holding period starts. Next, the (n + 1) th row is a writing period, and a writing operation similar to the above is performed. The writing operation is performed from the first row to the last row by repeating the above operation.

  As described above, the light emitting elements 403a, 403b, and 403c sequentially emit light, and the light emission colors from the respective light emitting elements are visually mixed by the afterimage effect, whereby various display colors can be obtained. Note that light emission whose luminance is adjusted by changing the light emission time of each of the light emitting elements 403a, 403b, and 403c can be appropriately combined to obtain a desired display color. Further, when the light emitting element 403d exhibiting white emits light, the luminance of the display color is visually recognized as if it has been increased. Therefore, the light emitting elements 403a, 403b, and 403c are subjected to light emitting elements 403a, 403b, and 403c, as compared with the case where the luminance of the display color is increased by using the method of increasing the luminance of each light emitting color by increasing the light emission time of the light emitting elements 403a, 403b, and 403c. The burden can be reduced. As a result, the lifetime of the light emitting elements 403a, 403b, and 403c can be extended. In addition, when the light-emitting element 403d exhibiting white light emits light, the light-emitting device described above can display an image with high contrast.

  Note that in this embodiment mode, all the light emitting elements 403a, 403b, and 403c emit light. However, the present invention is not limited to this. For example, the light emitting element 403a and the light emitting element 403b emit light and the light emitting element 403c does not emit light. A desired display color may be obtained, or a desired display color may be obtained by emitting any one of the light emitting elements 403a, 403b, and 403c. Further, when it is desired to obtain a display color with low luminance, it is not always necessary to cause the light emitting element 403d exhibiting white to emit light, and the timing, time, and the like for causing the light emitting element 403d exhibiting white to emit light in a series of display operations may be appropriately adjusted. Good.

(Embodiment 4)
In this embodiment mode, a light-emitting device of the present invention and a driving method thereof which are different from those described in Embodiment Mode 2 will be described.

FIG. 6 is a diagram illustrating a circuit configuration of the pixel 720 included in the light emitting device of the present invention.
Each of the switching transistor 701 and the driving transistors 702a, 702b, and 702c is a three-terminal element including a gate electrode, a drain region, and a source region, and has a channel region between the drain region and the source region. Here, since it is difficult to limit which of the source region and the drain region is a source region or a drain region depending on a transistor structure, operation conditions, or the like, one is a first electrode and the other is a first electrode. It describes as 2 electrodes. Here, the switching transistor is a transistor that controls input of a video signal to the driving transistor. The driving transistor is a transistor that controls supply of current from the current supply line depending on an input video signal and determines light emission / non-light emission of the light emitting element. Note that there is no particular limitation on each of the switching transistor 701 and the driving transistors 702a, 702b, and 702c, and an organic thin film transistor including a semiconductor layer made of an organic compound can be used in addition to a MOS transistor. The switching transistor 701 may be either an N-channel type or a P-channel type. Further, the driving transistors 702a, 702b, and 702c may be either N-channel type or P-channel type, but according to the example shown in FIG. 6, they are controlled by a common video signal, and therefore have the same polarity. Is preferred.
.

  In addition, each of the light emitting elements 703a, 703b, and 703c is a two-terminal element. Each of the light-emitting elements 703a, 703b, and 703c has a light-emitting layer between the first electrode and the second electrode, and current flows due to a potential difference between the first electrode and the second electrode Flashes on. Note that when the driving transistors 702a, 702b, and 702c are p-channel transistors, in the light-emitting elements 703a, 703b, and 703c, the first electrode functions as an anode and the second electrode functions as a cathode. On the other hand, when the driving transistors 702a, 702b, and 702c are N-channel transistors, in the light-emitting elements 703a, 703b, and 703c, the first electrode functions as a cathode and the second electrode functions as an anode. There is no particular limitation on the emission color of the light-emitting elements 703a, 703b, and 703c, but it is preferable that the emission colors are different from each other. In addition, it is particularly preferable that any one of the light-emitting elements exhibits white color or can emit white light by combining light emission from at least two light-emitting elements. The light-emitting element 713a exhibits a red light emission color when light emission is extracted outside the light-emitting device, the light-emitting element 713b exhibits a green light emission color when light emission is extracted outside the light-emitting device, and the light-emitting element 713c When the emitted light is taken out of the light emitting device, it exhibits a blue emission color. Here, the red emission color means a color having coordinates in a region where x is 0.6 or more and y is 0.35 or less in the chromaticity diagram when expressed in the CIE-XYZ color system. The green emission color is a color having coordinates in a region where x in the chromaticity diagram is 0.3 or less and y is 0.6 or more when expressed in the CIE-XYZ color system. The blue emission color means a color having coordinates in a region where x is 0.15 or less and y is 0.2 or less in the chromaticity diagram when expressed in the CIE-XYZ color system. The CIE-XYZ color system is a color system based on tristimulus values X, Y, and Z. The chromaticity diagram represents colors in x, y coordinate space based on tristimulus values X, Y, Z. Note that chromaticity is a quantitative definition of the type of light color excluding lightness.

  In the switching transistor 701, the gate electrode is electrically connected to the gate signal line 711, and the first electrode is electrically connected to the source signal line 712. The light emitting elements 703a, 703b, and 703c are connected in series. In the driving transistor 702a, the first electrode is electrically connected to the current supply line 713a, and the second electrode is electrically connected to the first electrode of the light-emitting element 703a. In the driving transistor 702b, the first electrode is electrically connected to the current supply line 713b, and the second electrode is electrically connected to the first electrode of the light-emitting element 703b. In the driving transistor 702c, the first electrode is electrically connected to the current supply line 713c, and the second electrode is electrically connected to the first electrode of the light-emitting element 703c. Note that the second electrode of the light-emitting element 703c is electrically connected to the power source 716. The gate electrodes of the driving transistors 702a, 702b, and 702c are electrically connected to each other. Further, a capacitor 704 is provided between the gate electrode of each of the driving transistors 702a, 702b, and 702c and the capacitor line 715, and holds the potential of the gate electrode of each of the driving transistors 702a, 702b, and 702c. It can be done. The second electrode of the switching transistor 701 is electrically connected to the gate electrodes of the driving transistors 702a, 702b, and 702c.

  A method for driving the above circuit will be described.

  When the gate signal line 711 is selected, the switching transistor 701 is turned on, and a video signal is input from the source signal line 712 to the gate electrodes of the driving transistors 702a, 702b, and 702c via the switching transistor 701. . Here, when the switching transistor 701 is an N-channel transistor and the driving transistors 702a, 702b, and 702c are P-channel transistors, the driving transistors 702a, 702b, and 702c are provided if the video signal potential is Low Level. Is in the ON state, and if the video signal is High Level, the driving transistors 702a, 702b, and 702c are in the OFF state. Further, when the current supply line 713a and the current supply line 713b are set to different potentials, a potential difference is generated between the first electrode and the second electrode in the light-emitting element 703a. Accordingly, a current flows through the light emitting element 703a, and the light emitting element 703a emits light. Further, when the current supply line 713b and the current supply line 713c have different potentials, a potential difference is generated between the first electrode and the second electrode in the light-emitting element 703b. Accordingly, a current flows through the light emitting element 703b, and the light emitting element 703b emits light. In addition, when the current supply line 713c and the power source 716 have different potentials, a potential difference is generated between the first electrode and the second electrode in the light-emitting element 703c. Accordingly, current flows through the light emitting element 703c, and the light emitting element 703c emits light. In addition, the current supply line 713a and the current supply line 713b, the current supply line 713b and the current supply line 713c, the current supply line 713c and the power source 716 are simultaneously set to different potentials, and the light emitting elements 703a, 703b, and 703c When a potential difference is generated between the first electrode and the second electrode, the light emitting elements 703a, 703b, and 703c emit light simultaneously. As described above, the light-emitting elements 703a, 703b, and 703c can emit light. Note that white light emission can be obtained by the light emitting elements 703a, 703b, and 703c emitting light simultaneously. Here, the white emission color is a region where x in the chromaticity diagram is 0.25 or more and 0.35 or less, and y is 0.25 or more and 0.35 or less when expressed in the CIE-XYZ color system. Preferably, a color having coordinates in a region where x is 0.28 or more and 0.32 or less and y is 0.28 or more and 0.32 or less in the chromaticity diagram.

Next, a driving method of the light emitting device using the circuit having the above-described configuration will be described.
Also in this embodiment, the light emitting device has a configuration as shown in the schematic diagram of FIG.
In the pixel portion 6511, a plurality of source signal lines 712 extending in the column direction are arranged side by side in the row direction. In addition, a current supply line 713 including a set of current supply lines 713a, 713b, and 713c is arranged side by side in the row direction. A plurality of gate signal lines 711 extending in the row direction are arranged side by side in the column direction. The pixel portion 6511 includes a circuit having a structure similar to that described with reference to FIG. 6 includes a gate signal line 711, a source signal line 712, a current supply line 713, a power supply 716, a switching transistor 701, driving transistors 702a, 702b, 702c, light emitting elements 703a, 703b, 703c, and a capacitor 704. A plurality of circuits are arranged in the vertical direction and the horizontal direction.

  There is no particular limitation on the emission color of each of the light emitting elements 703a, 703b, and 703c. Note that in this embodiment, the light-emitting element 703a exhibits a red light emission color, the light-emitting element 703b exhibits a green light emission color, and the light-emitting element 703c exhibits a blue light emission color. Note that red, green, and blue are the same as those described in the first embodiment.

  Next, a driving method will be described. FIG. 7 is a diagram for explaining the operation of a frame over time. In FIG. 7, the horizontal direction represents time, and the vertical direction represents the number of scanning stages of the gate signal line.

  When image display is performed using the light emitting device of the present invention, the screen rewriting operation and the display operation are repeatedly performed during the display period. The number of times of rewriting is not particularly limited, but it is preferably 60 times per second so that a person viewing the image does not feel flicker. Here, a period during which one screen (one frame) is rewritten and displayed is referred to as one frame period.

  One frame includes four subframes 801, 802, 803, and 804 including a writing period 801a and a holding period 801b, a writing period 802a and a holding period 802b, a writing period 803a and a holding period 803b, and a writing period 804a and a holding period 804b. It is time divided.

  First, in the subframe 801, write operations are performed in order from the first row to the last row. Therefore, the start time of the writing period 801a differs depending on the row. After the writing period 801a ends, the holding period 801b is started. In the light-emitting element connected to the driving transistor to which a signal for light emission is applied in the writing period 801a, different potentials are applied between the first electrode and the second electrode sandwiching the light-emitting layer in the holding period 801b. It emits light when In this embodiment mode, different potentials are applied to the first electrode and the second electrode included in the light-emitting element 703a in the subframe 801, so that the light-emitting element 703a emits light. At this time, a potential is applied so that the first electrode and the second electrode included in each of the other light emitting elements 703b and 703c are equipotential. After the holding period 801b ends, the process proceeds to the next subframe 802, and the writing operation is performed in order from the first line to the last line as in the case of the subframe 801. Then, the light-emitting element 703b emits light during the holding period 802b. After the holding period 802b ends in the subframe 802, the process proceeds to the subframe 803. In the subframe 803, the light emitting element 703c emits light. After the holding period 803b ends in the subframe 803, the process proceeds to the subframe 804. In the subframe 804, the light emitting elements 703a, 703b, and 703c emit light so as to have the same intensity at the same time. The above operation is repeated until the subframe 804 is held until the holding period 804b. When the operation in the subframe 804 is completed, the process proceeds to the next frame. Note that in this embodiment mode, light is emitted in the order of the light-emitting elements 703a, 703b, and 703c. However, the order of light emission is not particularly limited, and light emission may be performed by appropriately changing the order.

  Next, driving of the pixel in the writing period is described. In the writing period, the gate signal line 711 in the n-th row (n is a natural number) is selected, and the switching transistor 701 connected to the gate signal line 711 is turned on. At this time, video signals are simultaneously input to the source signal lines from the first column to the last column. Note that the video signals input from the source signal lines 712 in each column are independent from each other. The video signal input from the source signal line 712 is input to the gate electrodes of the driving transistors 702a, 702b, and 702c through the switching transistor 701 connected to each source signal line. At this time, the light-emitting element 703a corresponds to a signal input to the driving transistors 702a, 702b, and 702c and a potential difference between the first electrode and the second electrode included in each of the light-emitting elements 703a, 703b, and 703c. , 703b, and 703c are determined to emit or not emit light. For example, in the case where the driving transistor is a P-channel transistor, any of the light emitting elements 703a, 703b, and 703c emits light when a Low Level signal is input. On the other hand, when the driving transistor is an N-channel transistor, at least one of the light-emitting elements 703a, 703b, and 703c emits light when a high level signal is input.

  As writing to the source signal line ends, the writing period in the n-th row (n is a natural number) ends and the holding period starts. Next, the (n + 1) th row is a writing period, and a writing operation similar to the above is performed. The writing operation is performed from the first row to the last row by repeating the above operation.

  As described above, the light emitting elements 703a, 703b, and 703c sequentially emit light, and the light emission colors from the respective light emitting elements are visually mixed by the afterimage effect, whereby various display colors can be obtained. Note that light emission whose luminance is adjusted by changing the voltage applied to each of the light emitting elements 703a, 703b, and 703c can be appropriately combined to obtain a desired display color. Further, when the light emitting elements 703a, 703b, and 703c simultaneously emit light with the same intensity to emit white light, the luminance of the display color is visually recognized as if it has increased. Therefore, the voltage applied to the light emitting elements 703a, 703b, and 703c is applied to the light emitting elements 703a, 703b, and 703c more than the case where the luminance of the display color is increased by using the method of increasing the luminance of each light emitting color by increasing the voltage applied to the light emitting elements 703a, 703b, and 703c. The burden can be reduced. As a result, the lifetime of the light emitting elements 703a, 703b, and 703c can be extended. Moreover, by exhibiting white, the light emitting device described above can display an image with high contrast.

  Note that in this embodiment mode, all the light emitting elements 703a, 703b, and 703c emit light. However, the present invention is not limited to this. For example, the light emitting element 703a and the light emitting element 703b emit light and the light emitting element 703c does not emit light. A desired display color may be obtained, or a desired display color may be obtained by emitting any one of the light emitting elements 703a, 703b, and 703c. In addition, when it is desired to obtain a display color with low luminance, it is not always necessary to emit white light by using the light emitting elements 703a, 703b, and 703c. Good.

(Embodiment 5)
FIG. 8 is a top view of a pixel having the structure described in Embodiment Mode 1, and FIG. 9 is a cross-sectional view of a portion represented by a broken line aa ′ in FIG.

In FIG. 8, reference numerals 301, 302a, 302b, 302c, 302d, 304, 311, 312, 313a, 313b, 313c, 313d, and 315 are the same as those shown in FIG.
The switching transistor 301 and the gate electrodes of the driving transistors 302a, 302b, 302c, and 302d are connected to each other through a wiring formed in the same layer as the source signal line 312.

  As shown in FIG. 9, the driving transistor 302a is formed by stacking a semiconductor layer 903a, a gate insulating layer 904, and a gate electrode 905. In addition, as illustrated in FIG. 9, the driving transistor 302b is formed by stacking a semiconductor layer 903b, a gate insulating layer 904, and a gate electrode 905.

  As shown in FIG. 8, a capacitor line 315 is provided so as to overlap with the gate electrode 905. As shown in FIG. 9, an insulating layer 906 is provided between the gate electrode 905 and the capacitor line 315, and the capacitor 304 is formed.

  The semiconductor layer 903a and the current supply line 313a are connected through a connection portion that penetrates the insulating layer 906. The electrode 908 of the light-emitting element is provided in the same layer as the current supply line 313a and the like, and is connected to the semiconductor layer 903a through a connection portion 907a penetrating the insulating layer 906. With such a structure, the driving transistor 302a is electrically connected to each of the current supply line 313a and the electrode 908 of the light emitting element.

  The semiconductor layer 903b and the current supply line 313b are connected through a connection portion that penetrates the insulating layer 906. Further, the electrode 909 of the light-emitting element is connected to the semiconductor layer 903b through a connection portion 907b that penetrates the insulating layer 906. With such a structure, the driving transistor 302b is electrically connected to each of the current supply line 313b and the electrode 909 of the light emitting element. Note that the electrode 909 of the light-emitting element covers the current supply line 313a and the like and is provided over the insulating layer 917 having an opening.

  A light emitting layer 913 is provided between the electrode 908 of the light emitting element and the electrode 909 of the light emitting element. Further, a light-emitting layer 914, a light-emitting element electrode 910, a light-emitting layer 915, a light-emitting element electrode 911, a light-emitting layer 916, and a light-emitting element electrode 912 are sequentially stacked over the electrode 909 of the light-emitting element. Then, a first light emitting element including the electrode 908 of the light emitting element, the light emitting layer 913, and the electrode 909 of the light emitting element, and a second light emitting element including the electrode 909 of the light emitting element, the light emitting layer 914, and the electrode 910 of the light emitting element. A third light emitting element comprising a light emitting element electrode 910, a light emitting layer 915 and a light emitting element electrode 911, and a fourth light emitting element comprising a light emitting element electrode 911, a light emitting layer 916 and a light emitting element electrode 912. Each is composed. Note that the electrodes 908, 909, 910, 911, and 912 of the light-emitting element are provided in different layers with insulating layers 918, 919, and 920 having openings therebetween, respectively. The first light-emitting element, the second light-emitting element, the third light-emitting element, and the fourth light-emitting element are provided in the openings of the insulating layers 917, 918, 919, and 920, respectively.

  Here, the electrodes 909, 910, and 911 of the light-emitting element serve as both the first electrode and the second electrode in the light-emitting element described in Embodiment 1. For example, the electrode 909 of the light-emitting element functions as a second electrode for the first light-emitting element and functions as the first electrode for the second light-emitting element. Further, the electrode 912 of the light-emitting element has the function as the second electrode for the fourth light-emitting element and the function as the power supply 316 described in Embodiment 1. In FIG. 8, the electrodes 908, 909, 910, and 911 of the light-emitting element have different sizes and are drawn so as to decrease in order. This indicates that the electrodes are provided in different layers. For convenience of illustration, the size of the electrodes 908, 909, 910, and 911 of the light emitting element is not limited.

Note that there is no particular limitation on the structure of the switching transistor 301 and the driving transistors 302a, 302b, 302c, and 302d, and either a top gate type or a bottom gate type may be used. Further, a single drain structure or an LDD (Lightly Doped Drain) structure may be used. Further, a single gate structure or a multi-gate structure may be used. Further, there is no particular limitation on the crystallinity of the semiconductor layer included in each of the switching transistor 301 and the driving transistors 302a, 302b, 302c, and 302d, and it is amorphous or crystalline, or crystalline and amorphous. Both of them may be used, or they may be semi-amorphous. Here, the semi-amorphous semiconductor is as follows. A semiconductor having an intermediate structure between amorphous and crystalline (including single crystal and polycrystal) and having a third state that is stable in terms of free energy, has a short-range order, and has a lattice distortion. It contains a crystalline region. Further, at least a partial region in the film contains crystal grains of 0.5 to 20 nm. The Raman spectrum is shifted to the lower wavenumber side than 520 cm ⁻¹ . In X-ray diffraction, diffraction peaks of (111) and (220) that are derived from the Si crystal lattice are observed. At least 1 atomic% or more of hydrogen or halogen is contained as a neutralizing agent for dangling bonds. It is also called a so-called microcrystalline semiconductor (microcrystal semiconductor). A silicide gas is formed by glow discharge decomposition (plasma CVD). As the silicide gas, SiH ₄ , Si ₂ H ₆ , SiH ₂ Cl ₂ , SiHCl ₃ , SiCl ₄ , SiF ₄ or the like can be used. This silicide gas may be diluted with H ₂ , or H ₂ and one or more kinds of rare gas elements selected from He, Ar, Kr, and Ne. The dilution rate is in the range of 2 to 1000 times. The pressure is generally in the range of 0.1 Pa to 133 Pa, and the power supply frequency is 1 MHz to 120 MHz, preferably 13 MHz to 60 MHz. The substrate heating temperature may be 300 ° C. or less, preferably 100 to 250 ° C. As an impurity element in the film, impurities of atmospheric components such as oxygen, nitrogen, and carbon are desirably 1 × 10 ²⁰ / cm ³ or less, and in particular, the oxygen concentration is 5 × 10 ¹⁹ / cm ³ or less, preferably 1 × 10 ¹⁹ / cm ³ or less Note that the mobility of a TFT (thin film transistor) using a semi-amorphous semiconductor is approximately 1 to 10 m ² / Vsec.

  Further, the light emitting layers 913, 914, 915, and 916 are not particularly limited, and may be either a single layer or a multilayer. Moreover, there is no limitation in particular also about the substance which comprises a light emitting layer. In this embodiment mode, the light emitting layer 913 emits red light, the light emitting layer 914 emits green light, the light emitting layer 915 emits blue light, and the light emitting layer 916 emits white light. The emission color is not limited to this.

  In order to form the light emitting layer 913 that emits red light, for example, 4-dicyanomethylene-2-methyl-6- [2- (1,1,7,7-tetramethyl-9-julolidylethenyl)] is used. -4H-pyran (abbreviation: DCJT), 4-dicyanomethylene-2-t-butyl-6- [2- (1,1,7,7-tetramethyljulolidin-9-ylethenyl)] -4H-pyran ( Abbreviation: DCJTB), perifuranthene, 2,5-dicyano-1,4-bis [2- (10-methoxy-1,1,7,7-tetramethyljulolidin-9-ylethenyl)] benzene and the like And it is sufficient. In addition, a substance capable of obtaining light emission from an excited triplet state such as a metal complex may be used.

  In order to form the light-emitting layer 914 that emits green light, light emission including N, N′-dimethylquinacridone (abbreviation: DMQd), coumarin 6 or coumarin 545T, tris (8-quinolinolato) aluminum (abbreviation: Alq), or the like. A layer may be used. In addition, a substance capable of obtaining light emission from an excited triplet state such as a metal complex may be used.

  In order to form the light-emitting layer 915 that emits blue light, 9,9′-bianthryl, 9,10-diphenylanthracene (abbreviation: DPA) and 9,10-bis (2-naphthyl) anthracene (abbreviation: DNA) Or the like. In addition, a substance capable of obtaining light emission from an excited triplet state such as a metal complex may be used.

Note that a layer formed of a substance having a high carrier (electron / hole) transporting property may be provided in part of the light-emitting layers 913, 914, 915, and 916. This can prevent quenching that may occur due to the proximity of the light emitting portion to the electrode.
Examples of the substance having a high electron transporting property include tris (8-quinolinolato) aluminum (abbreviation: Alq ₃ ), tris (5-methyl-8-quinolinolato) aluminum (abbreviation: Almq ₃ ), and bis (10-hydroxybenzo). [H] -quinolinato) beryllium (abbreviation: BeBq ₂ ), bis (2-methyl-8-quinolinolato) -4-phenylphenolato-aluminum (abbreviation: BAlq), metal complexes having a quinoline skeleton or a benzoquinoline skeleton, etc. Is mentioned. As a substance having a high hole-transport property, for example, 4,4′-bis [N- (1-naphthyl) -N-phenyl-amino] -biphenyl (abbreviation: α-NPD), 4,4′-bis [ N- (3-methylphenyl) -N-phenyl-amino] -biphenyl (abbreviation: TPD) or 4,4 ′, 4 ″ -tris (N, N-diphenyl-amino) -triphenylamine (abbreviation: TDATA) ), 4,4 ′, 4 ″ -tris [N- (3-methylphenyl) -N-phenyl-amino] -triphenylamine (abbreviation: MTDATA) (ie, benzene ring-nitrogen) And a compound having a bond of

  In addition, a part of the light emitting layers 913, 914, 915, and 916 may be provided with a layer for assisting injection of electrons or holes from the electrode of the light emitting element to the light emitting layers 913, 914, 915, and 916. .

Examples of substances that can assist electron injection include alkali metal or alkaline earth metal compounds such as lithium fluoride (LiF), cesium fluoride (CsF), and calcium fluoride (CaF ₂ ). In addition, a mixture of a substance having a high electron transport property such as Alq ₃ and an alkaline earth metal such as magnesium (Mg) may be used. Examples of substances that can assist hole injection include molybdenum oxide (MoOx), vanadium oxide (VOx), ruthenium oxide (RuOx), tungsten oxide (WOx), and manganese oxide (MnOx). These metal oxides can be mentioned. In addition, phthalocyanine compounds such as phthalocyanine (abbreviation: H ₂ Pc) and copper phthalocyanine (CuPC) can be given. Alternatively, a polymer material obtained by mixing polystyrene sulfonic acid (PSS) and polyethylenedioxythiophene (PEDOT), which are substances having a high hole injecting property and a high hole transporting property, may be used.

  The high molecular weight organic light emitting material has higher physical strength than the low molecular weight material, and the durability of the device is high. In addition, since the film can be formed by coating, the device can be manufactured relatively easily.

To form the light emitting layer 916 that emits white light, for example, Alq _3, partially Alq doped with Nile Red _{3, Alq 3, p-EtTAZ} , TPD are sequentially stacked by a vapor deposition method (aromatic diamine) Can give a white color. Moreover, when forming a light emitting layer by the apply | coating method using spin coating, after apply | coating, it is preferable to bake by vacuum heating. For example, a poly (ethylenedioxythiophene) / poly (styrenesulfonic acid) aqueous solution (PEDOT / PSS) is applied to the entire surface and fired, and then a dye (1,1,4,4-tetraphenyl-1,3-butadiene (TPB), 4-dicyanomethylene-2-methyl-6- (p-dimethylamino-styryl) -4H-pyran (DCM1), Nile Red, Coumarin 6 etc.) doped polyvinylcarbazole (PVK) solution over the entire surface What is necessary is just to apply | coat and bake.

  Note that when the driving transistors 302a, 302b, 302c, and 302d are p-channel transistors, the light-emitting layers 913, 914, 915, and 916 each have an electrode of the light-emitting element with the light-emitting region as a center. It is preferable that a layer that easily transports holes on the 908 side and a layer that easily transports electrons on the electrode 912 side of the light-emitting element are provided. In addition, when the driving transistors 302a, 302b, 302c, and 302d are N-channel type, the light emitting layers 913, 914, 915, and 916 each have an electrode of the light emitting element with the light emitting region as the center. It is preferable that a layer that easily transports electrons is provided on the side 908 and a layer that easily transports holes is provided on the electrode 912 side of the light-emitting element.

The electrodes 909, 910, and 911 of the light-emitting element are preferably formed using a substance that can transmit visible light. Examples of such substances include indium tin oxide, indium tin oxide containing silicon oxide, indium zinc oxide obtained by mixing indium oxide with 2 to 20% zinc oxide (ZnO), and zinc oxide several Examples include zinc gallium oxide formed by mixing [%] gallium oxide (Ga ₂ O ₃ ), but a different material may be used.

  In addition, at least one of the electrodes 908 and 912 of the light-emitting element is preferably formed using a material that can transmit visible light as described above. When one electrode is made of a material that can transmit visible light, the other electrode is preferably formed of a material having a small work function such as aluminum in the case of functioning as a cathode, and in the case of functioning as an anode. Is preferably formed of a material having a high work function such as silver.

  The light emitting device of the present invention having the above configuration can emit white light. In addition, when a display color is formed by light emission from at least one of the first light-emitting element, the second light-emitting element, and the third light-emitting element, the fourth light-emitting element exhibiting white is used for light emission. Thus, the brightness of the display color can be increased.

(Embodiment 6)
One embodiment of an electronic device mounted with a light emitting device to which the present invention is applied is shown in FIG.

  FIG. 10A illustrates a computer manufactured by applying the present invention, which includes a main body 5521, a housing 5522, a display portion 5523, a keyboard 5524, and the like. A computer can be completed by incorporating the light emitting device of the present invention as a display portion. In addition, there is no limitation in particular about the aspect of a computer, A laptop type other than a desktop type may be sufficient.

  FIG. 10B illustrates a mobile phone manufactured by applying the present invention, which includes a main body 5552 which includes a display portion 5551, an audio output portion 5554, an audio input portion 5555, operation switches 5556 and 5557, an antenna 5553, and the like. Has been. A mobile phone can be completed by incorporating the light emitting device of the present invention as a display portion.

  FIG. 10C illustrates a television set manufactured by applying the present invention, which includes a display portion 5531, a housing 5532, a speaker 5533, and the like. A television receiver can be completed by incorporating the light-emitting device of the present invention as a display portion.

  As described above, the light-emitting device of the present invention is very suitable for use as a display portion of various electronic devices.

  Note that although this embodiment describes a computer, the light-emitting device of the present invention may be mounted on a mobile phone, a car navigation system, a lighting device, or the like.

  The electronic apparatus to which the present invention is applied can obtain a good display image with little deterioration over a long period of time by using the light emitting device of the present invention as a display portion.

FIG. 6 is a diagram of a driving circuit used in the light emitting device of the present invention. 1 is a schematic view of a light emitting device of the present invention. FIG. 6 is a diagram of a driving circuit used in the light emitting device of the present invention. 4A and 4B illustrate a driving method of a light-emitting device of the present invention. 4A and 4B illustrate a driving method of a light-emitting device of the present invention. FIG. 6 is a diagram of a driving circuit used in the light emitting device of the present invention. 4A and 4B illustrate a driving method of a light-emitting device of the present invention. FIG. 6 is a top view of a pixel portion of a light emitting device of the present invention. FIG. 6 is a cross-sectional view of a pixel portion of a light emitting device of the present invention. 6A and 6B illustrate electronic devices to which the present invention is applied. 4A and 4B illustrate a driving method of a light-emitting device of the present invention.

Explanation of symbols

301 switching transistor 302a driving transistor 302b driving transistor 302c driving transistor 302d driving transistor 303a light emitting element 303b light emitting element 303c light emitting element 303d light emitting element 304 capacitor element 311 gate signal line 312 source signal line 313a current supply line 313b current supply Line 313c Current supply line 313d Current supply line 315 Capacitance line 316 Power supply

Claims (6)

First to fifth wirings;
First to fourth transistors;
First to third display elements,
A gate of the first transistor is electrically connected to the first wiring;
One of a source and a drain of the first transistor is electrically connected to the second wiring;
The other of the source and the drain of the first transistor is electrically connected to the gate of the second transistor;
A gate of the second transistor is electrically connected to a gate of the third transistor;
One of a source and a drain of the second transistor is electrically connected to a first electrode of the first display element;
The other of the source and the drain of the second transistor is electrically connected to the third wiring;
A gate of the third transistor is electrically connected to a gate of the fourth transistor;
One of a source and a drain of the third transistor is electrically connected to the first electrode of the second display element;
The other of the source and the drain of the third transistor is electrically connected to the fourth wiring;
One of a source and a drain of the fourth transistor is electrically connected to the first electrode of the third display element;
The other of the source and the drain of the fourth transistor is electrically connected to the fifth wiring;
The first display element, the second display element, and the third display element are connected in series,
The first wiring has a function of supplying a selection signal to a gate of the first transistor;
The second wiring has a function of supplying a video signal to one of a source and a drain of the first transistor;
The third wiring has a function of supplying a current flowing through the second transistor;
The fourth wiring has a function of supplying a current flowing through the third transistor;
The display device, wherein the fifth wiring has a function of supplying a current flowing through the fourth transistor. First to sixth wirings;
First to fourth transistors;
First to third display elements;
A capacitive element;
A gate of the first transistor is electrically connected to the first wiring;
One of a source and a drain of the first transistor is electrically connected to the second wiring;
The other of the source and the drain of the first transistor is electrically connected to the gate of the second transistor, and is electrically connected to the sixth wiring through the capacitor.
A gate of the second transistor is electrically connected to a gate of the third transistor;
One of a source and a drain of the second transistor is electrically connected to a first electrode of the first display element;
The other of the source and the drain of the second transistor is electrically connected to the third wiring;
A gate of the third transistor is electrically connected to a gate of the fourth transistor;
One of a source and a drain of the third transistor is electrically connected to the first electrode of the second display element;
The other of the source and the drain of the third transistor is electrically connected to the fourth wiring;
One of a source and a drain of the fourth transistor is electrically connected to the first electrode of the third display element;
The other of the source and the drain of the fourth transistor is electrically connected to the fifth wiring;
The first display element, the second display element, and the third display element are connected in series,
The first wiring has a function of supplying a selection signal to a gate of the first transistor;
The second wiring has a function of supplying a video signal to one of a source and a drain of the first transistor;
The third wiring has a function of supplying a current flowing through the second transistor;
The fourth wiring has a function of supplying a current flowing through the third transistor;
The fifth wiring has a function of supplying a current flowing through the fourth transistor;
The display device, wherein the sixth wiring has a function of supplying a potential to the capacitor. First to fifth wirings;
First to fourth transistors;
First to third display elements,
A gate of the first transistor is electrically connected to the first wiring;
One of a source and a drain of the first transistor is electrically connected to the second wiring;
The other of the source and the drain of the first transistor is electrically connected to the gate of the second transistor;
A gate of the second transistor is electrically connected to a gate of the third transistor;
One of a source and a drain of the second transistor is electrically connected to a first electrode of the first display element;
The other of the source and the drain of the second transistor is electrically connected to the third wiring;
A gate of the third transistor is electrically connected to a gate of the fourth transistor;
One of a source and a drain of the third transistor is electrically connected to the first electrode of the second display element;
The other of the source and the drain of the third transistor is electrically connected to the fourth wiring;
One of a source and a drain of the fourth transistor is electrically connected to the first electrode of the third display element;
The other of the source and the drain of the fourth transistor is electrically connected to the fifth wiring;
The first display element, the second display element, and the third display element are connected in series,
The first wiring has a function of supplying a selection signal to a gate of the first transistor;
The second wiring has a function of supplying a video signal to one of a source and a drain of the first transistor;
The third wiring has a function of supplying a current flowing through the second transistor;
The fourth wiring has a function of supplying a current flowing through the third transistor;
The fifth wiring has a function of supplying a current flowing through the fourth transistor;
A first electrode layer capable of functioning as a second electrode of the first display element and a first electrode of the second display element is provided over the first electrode of the first display element. And
A second electrode layer capable of functioning as a second electrode of the second display element and a first electrode of the third display element is provided on the first electrode layer. A display device. First to sixth wirings;
First to fourth transistors;
First to third display elements;
A capacitive element;
A gate of the first transistor is electrically connected to the first wiring;
One of a source and a drain of the first transistor is electrically connected to the second wiring;
The other of the source and the drain of the first transistor is electrically connected to the gate of the second transistor, and is electrically connected to the sixth wiring through the capacitor.
A gate of the second transistor is electrically connected to a gate of the third transistor;
One of a source and a drain of the second transistor is electrically connected to a first electrode of the first display element;
The other of the source and the drain of the second transistor is electrically connected to the third wiring;
A gate of the third transistor is electrically connected to a gate of the fourth transistor;
One of a source and a drain of the third transistor is electrically connected to the first electrode of the second display element;
The other of the source and the drain of the third transistor is electrically connected to the fourth wiring;
One of a source and a drain of the fourth transistor is electrically connected to the first electrode of the third display element;
The other of the source and the drain of the fourth transistor is electrically connected to the fifth wiring;
The first display element, the second display element, and the third display element are connected in series,
The first wiring has a function of supplying a selection signal to a gate of the first transistor;
The second wiring has a function of supplying a video signal to one of a source and a drain of the first transistor;
The third wiring has a function of supplying a current flowing through the second transistor;
The fourth wiring has a function of supplying a current flowing through the third transistor;
The fifth wiring has a function of supplying a current flowing through the fourth transistor;
The sixth wiring has a function of supplying a potential to the capacitor;
A first electrode layer capable of functioning as a second electrode of the first display element and a first electrode of the second display element is provided over the first electrode of the first display element. And
A second electrode layer capable of functioning as a second electrode of the second display element and a first electrode of the third display element is provided on the first electrode layer. Display device. A display module comprising: the display device according to claim 1; and an FPC. An electronic apparatus comprising: the display module according to claim 5, a speaker, and the operation switch, the.

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