JP2002221938A - Light-emitting device and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To propose a light-emitting device which facilitates the recognition of a physical object even when an image itself which a video signal inputted into the light-emitting device has as information is dark or indistinct as a whole. SOLUTION: In at least one display period within a single-frame period, the absolute value of the EL driving voltage applied between the pixel electrode and the counter electrode is made temporarily larger to increase the brightness of an EL device. That is, the difference between the power source electrical potential and the opposite electrical potential in all display periods is not always kept constant, but the absolute value of the difference between the power source electrical potential and the opposite electrical potential in a certain fixed period within at least one display period (strong emission period) is made larger than the difference of the potential of other periods to make the brightness of the EL element higher. In this configuration, the actually displayed image becomes brighter even if the image itself which the video signal inputted into the light- emitting device has as information is dark on the whole, and hence recognition of the physical object is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an EL panel in which an EL element formed on a substrate is sealed between the substrate and a cover material. In addition, E in which an IC is mounted on the EL panel
Regarding the L module. In this specification, the EL panel and the EL module are collectively referred to as a light emitting device. The invention further relates to an electronic device using a light-emitting device that performs display by the driving method.

[0002]

2. Description of the Related Art An EL element emits light by itself and thus has high visibility, does not require a backlight necessary for a liquid crystal display (LCD), is optimal for thinning, and has no restriction on a viewing angle. Therefore, in recent years, light emitting devices using EL
It is attracting attention as a display device replacing T and LCD.

An EL element has a layer containing an organic compound capable of obtaining luminescence (Electro Luminescence) generated by applying an electric field (hereinafter, referred to as an EL layer), an anode layer, and a cathode layer. The luminescence of the organic compound includes light emission (fluorescence) when returning from the singlet excited state to the ground state and light emission (phosphorescence) when returning from the triplet excited state to the ground state. In the light emitting device of the present invention, Either light emission may be used.

[0004] In this specification, all layers formed between an anode and a cathode are defined as EL layers. Specifically, the EL layer includes a light emitting layer, a hole injection layer, an electron injection layer, a hole transport layer,
An electron transport layer and the like are included. Basically, the EL element has an anode /
It has a structure in which a light emitting layer / cathode is laminated in order. In addition to this structure, an anode / hole injection layer / light emitting layer / cathode or anode / hole injection layer / light emitting layer / electron transport layer / cathode Etc. in some cases.

[0005] In this specification, a light emitting element formed by an anode, an EL layer and a cathode is called an EL element. In this specification, emission of an EL element is referred to as driving of the EL element.

The pixel portion of the light emitting device includes source signal lines S1 to Sx, gate signal lines G1 to Gy, and a power supply line V
1 to Vx and a plurality of pixels are provided. FIG.
FIG. 2A is a circuit diagram of a pixel 9004 of a general light-emitting device. The pixel 9004 includes a source signal line Si (S1 to Sx
, A power supply line Vi (any one of V1 to Vx), and a gate signal line Gj (any one of G1 to Gy).

The pixel 9004 is a switching TFT.
9008 and an EL driving TFT 9009.
The gate electrode of the switching TFT 9008 is connected to the gate signal line Gj. Switching TFT 9
One of the source region and the drain region 008 is connected to the source signal line Si, and the other is connected to the gate electrode of the EL driving TFT 9009.

The source region of the EL driving TFT 9009 is connected to the power supply line Vi, and the drain region is the EL region.
Connected to element 9011.

The EL element 9011 includes an anode and a cathode, and an EL layer provided between the anode and the cathode. The anode is EL
When connected to the drain region of the driving TFT 9009, the anode serves as a pixel electrode and the cathode serves as a counter electrode. Conversely, when the cathode is connected to the drain region of the EL driving TFT 9009, the cathode serves as a pixel electrode and the anode serves as a counter electrode.

A power supply potential is applied to all power supply lines V1 to Vx. Also, the EL element 9 of all the pixels
The counter electrode 011 is provided with a counter potential. The power supply potential and the counter potential are provided by a power supply 9005 provided in an external IC of the display device.

Next, the operation of the pixel shown in FIG. In the case of performing the time-division gray scale display, the operation of the light-emitting device can be separately described in a writing period and a display period.

In the writing period, the gate signal line Gj
Switching TFT by the selection signal input to
9008 is turned on, and a digital signal (hereinafter, referred to as a digital video signal) having image information input to the source signal line Si is input to the gate electrode of the EL driving TFT 9009 via the switching TFT 9008. Note that in this specification, a digital video signal is transmitted through a switching TFT 9008 to an EL driving TFT 9.
Inputting to the gate electrode of 009 is referred to as inputting a digital video signal to the pixel.

The switching of the EL driving TFT 9009 is controlled by information of 1 or 0 included in the digital video signal input to the gate electrode of the EL driving TFT 9009.

When the EL driving TFT 9009 is turned off, the potential of the power supply line Vi is not applied to the pixel electrode of the EL element 9011. In addition, the EL driving TFT 90
When 09 is turned on, the potential of the power supply line Vi is applied to the pixel electrode of the EL element 9011.

Until the digital video signal is input to all the pixels, the changeover switch is off, and the opposing potential is at the same level as the power supply potential.

When the digital video signal is input to all the pixels, the writing period ends, and the display period starts. In the display period, the changeover switch is turned on, and the power supply 9005 causes the counter potential to have a height having a potential difference from the power supply potential. When the EL driving TFT 9009 is on, this potential difference is applied between the pixel electrode and the counter electrode of the EL element 9011, and the EL element 9011 emits light.
Note that the potential difference between the opposing potential and the power supply potential at this time needs to be large enough for the EL element to emit light.

Conversely, when the EL driving TFT 9009 is off, the pixel electrode of the EL element 9009 is kept at the same height as the counter potential, so that the EL element 9011 does not emit light. Note that in this specification, a potential difference between a pixel electrode and a counter electrode of the EL element 9011 is referred to as an EL drive voltage.

The writing period and the display period are collectively called a sub-frame period. In one frame period, a plurality of sub-frame periods corresponding to each bit of the digital video signal are provided.

FIG. 14B shows a sub-frame period (SF1 to SF5) corresponding to a 5-bit digital video signal.
Shows the timing at which. The horizontal axis indicates time, and the vertical axis indicates EL driving voltage. Note that for simplicity of description, FIG. 14B shows a case where the EL driving TFT 9009 is always on by a digital video signal of each bit.

In the writing period in each sub-frame period, the EL element 9011 does not emit light because the EL driving voltage is 0. In the display period of each sub-frame period,
The absolute value of the EL drive voltage becomes larger than 0, and the EL element 9011 emits light.

In this case, the EL driving voltage is always constant. EL when changeover switch 9006 is on
The drive voltage is always kept the same.

By controlling the length of the period during which the EL element 9011 emits light, a desired gray scale can be displayed.

[0023]

By the way, an image of an unknown object, for example, an image of a surveillance camera provided for detecting a crime prevention or an illegal intruder into a restricted area, and an individual for collation. When recognizing an object by displaying an image of a captured face or fingerprint, in the medical field, an image of an organ in a living body obtained by radiation, charged particles, electromagnetic waves, or the like on a light emitting device, a clearer image is displayed. Display is required.

However, no matter how much the performance of the light emitting device is improved and a clearer image can be displayed,
If an image itself as information of a video signal input to the light emitting device is entirely dark or unclear, a clear image cannot be displayed, and it becomes difficult to recognize a target.

In view of the above problems, the present invention makes it easy to recognize an object even if an image itself as information contained in a video signal input to a light emitting device is entirely dark or unclear. It is an object to devise a light emitting device that can be used.

[0026]

According to the present invention, the absolute value of an EL drive voltage applied between a pixel electrode and a counter electrode in at least one display period within one frame period is calculated as follows.
The brightness was temporarily increased to increase the luminance of the EL element. That is, the potential difference between the power supply potential and the opposing potential in all display periods is not always kept constant, but the absolute difference between the power supply potential and the opposing potential in at least one certain period (strong light emission period) in one display period. The value was made larger than in other periods, so that the luminance of the EL element was increased.

With the above arrangement, even if the image itself as information contained in the video signal input to the light emitting device is entirely dark, the actually displayed image becomes bright, so that the object can be easily recognized. it can.

Further, when the gradation displayed by a certain pixel is brighter than a certain gradation, the absolute value of the EL drive voltage applied to the EL element of the pixel is increased to increase the luminance of the EL element. May be. According to the above configuration, the pixel displaying a bright gradation becomes brighter, the contrast of the image is increased, the image is sharpened, and the object can be easily recognized.

Further, by identifying, from the digital video signal input to each pixel, a pixel whose gradation is greatly different from that of an adjacent pixel, the contour of the object is detected, and the pixel at the contour portion of the image is detected. Only the contrast may be increased. According to the above configuration, the outline of the image is extracted, the image is sharpened, and the object can be easily recognized.

The configuration of the present invention will be described below.

According to the present invention, there is provided a light emitting device provided with a plurality of pixels each having an EL element, wherein the luminance of the EL element in a predetermined period of the period in which the EL element emits light in one frame period However, there is provided a light emitting device characterized in that the luminance of the plurality of EL elements is higher than the luminance of the plurality of EL elements in a period other than a predetermined period of the period in which the EL elements emit light.

According to the present invention, there is provided a light emitting device provided with a plurality of pixels having EL elements, wherein a plurality of subframe periods are provided in one frame period, and at least one of the plurality of subframe periods is provided. In the frame period, the luminance of the EL element in a predetermined period of the period in which the EL element emits light is the luminance of the plurality of ELs in a period other than the predetermined period of the period in which the EL element emits light. There is provided a light emitting device characterized by having a higher luminance than an element.

According to the present invention, there is provided a light emitting device provided with a plurality of pixels having EL elements, wherein the EL elements are a pixel electrode, a counter electrode, and an EL provided between the pixel electrode and the counter electrode. And the potential applied to the pixel electrode when the EL element emits light is always constant. The height of the potential applied to the counter electrode when the EL element emits light is In other words, in one frame period, the luminance of the EL element in a predetermined period is changed to a value corresponding to the plurality of EL elements in a period other than the predetermined period.
There is provided a light emitting device characterized in that the luminance is higher than the luminance of the element.

According to the present invention, there is provided a light emitting device provided with a plurality of pixels having an EL element, wherein a plurality of sub-frame periods are provided in one frame period, and the EL element includes a pixel electrode, a counter electrode, And an EL layer provided between the pixel electrode and the counter electrode. When the EL element emits light, the potential applied to the pixel electrode is always constant, and the EL element emits light. By changing the level of the potential applied to the counter electrode during the operation, the luminance of the EL element during a predetermined period in at least one of the plurality of sub-frame periods is different from the luminance during the period other than the predetermined period. The plurality of E in the period of
There is provided a light emitting device characterized in that the luminance is higher than the luminance of the L element.

According to the present invention, there is provided a light emitting device provided with a plurality of pixels having EL elements, wherein the EL elements are a pixel electrode, a counter electrode, and an EL provided between the pixel electrode and the counter electrode. And the potential applied to the counter electrode when the EL element emits light is always constant. The height of the potential applied to the pixel electrode when the EL element emits light is In other words, in one frame period, the luminance of the EL element in a predetermined period is changed to a value corresponding to the plurality of EL elements in a period other than the predetermined period.
There is provided a light emitting device characterized in that the luminance is higher than the luminance of the element.

According to the present invention, there is provided a light emitting device provided with a plurality of pixels having an EL element, wherein a plurality of sub-frame periods are provided in one frame period, and the EL element includes a pixel electrode, a counter electrode, An EL layer provided between the pixel electrode and the counter electrode, the potential applied to the counter electrode when the EL element emits light is always constant, and the EL element emits light. By changing the level of the potential applied to the pixel electrode during the operation, the luminance of the EL element in a predetermined period in at least one of the plurality of sub-frame periods is different from the luminance in the predetermined period. The plurality of E in the period of
There is provided a light emitting device characterized in that the luminance is higher than the luminance of the L element.

According to the present invention, there is provided a light emitting device provided with a plurality of pixels having an EL element, a first EL driving TFT, and a second EL driving TFT, a first power supply, and a second power supply. The EL element has a pixel electrode, a counter electrode, and an EL layer provided between the pixel electrode and the counter electrode. When the EL element emits light, the potential applied to the counter electrode is always When the EL element is emitting light, a potential is applied to the pixel electrode from the first power supply via the first EL driving TFT, or the potential is applied to the pixel electrode via the second EL driving TFT. By selecting whether to apply a potential to the pixel electrode from the second power source and changing the level of the potential applied to the pixel electrode, the luminance of the EL element in a predetermined period in the one frame period can be adjusted to the predetermined level. Period of Said plurality of EL in the period of the external
There is provided a light emitting device characterized in that the luminance is higher than the luminance of the element.

According to the present invention, there is provided a light emitting device provided with a plurality of pixels having an EL element, a first EL driving TFT, and a second EL driving TFT, a first power supply, and a second power supply. A plurality of sub-frame periods are provided in a frame period, and the EL element includes a pixel electrode, a counter electrode, and an EL element provided between the pixel electrode and the counter electrode.
And the potential applied to the counter electrode when the EL element emits light is always constant. When the EL element emits light, the potential is applied to the counter electrode via the first EL driving TFT. By selecting whether to apply a potential to the pixel electrode from a first power supply or to apply a potential to the pixel electrode from the second power supply via the second EL driving TFT, the potential of the potential applied to the pixel electrode is selected. By changing the height, in at least one of the plurality of sub-frame periods, the luminance of the EL element during a predetermined period is reduced by the EL elements during a period other than the predetermined period.
There is provided a light emitting device characterized in that the luminance is higher than the luminance of the element.

According to the present invention, there is provided a light emitting device provided with a plurality of pixels each having an EL element, which operates in a first mode or a second mode. During the light emitting period, the E
The luminance of the L element is always kept constant, and in the second mode, the luminance of the EL element during a predetermined period of the period during which the EL element emits light is such that the EL element emits light. The luminance of the plurality of EL elements is higher than the luminance of the plurality of EL elements in a period other than a predetermined period in the period.

According to the present invention, there is provided a light emitting device provided with a plurality of pixels each having an EL element, operating in a first mode or a second mode, wherein the EL element is in the first mode. During the light emitting period, the E
The luminance of the L element is always kept constant, and in the second mode, the luminance of the EL element during a predetermined period of the period during which the EL element emits light is such that the EL element emits light. Of the plurality of EL elements in a period other than a predetermined period of the predetermined period, and among the plurality of pixels, a pixel whose displayed gray scale is darker than a certain gray scale is the first. A light-emitting device that operates in a second mode and operates in a second mode among pixels of which a gray level to be displayed is brighter than a certain gray level.

According to the present invention, there is provided a light emitting device provided with a plurality of pixels each having an EL element, operating in a first mode or a second mode, wherein the EL element is in the first mode. During the light emitting period, the E
The luminance of the L element is always kept constant, and in the second mode, the luminance of the EL element during a predetermined period of the period during which the EL element emits light is such that the EL element emits light. Brightness of the plurality of EL elements in a period other than a predetermined period of the predetermined period, and a gray scale to be displayed is equal to or more than a certain value as compared with an adjacent pixel among the plurality of pixels. Only the bright pixels operate in the second mode, and, of the plurality of pixels, the pixels other than the pixels whose display gradation is brighter than a certain value or more than the adjacent pixels operate in the first mode. Is provided.

According to the present invention, there is provided a driving method of a light emitting device provided with a plurality of pixels having an EL element, wherein the EL element emits light in a predetermined period of a period during which the EL element emits light in one frame period. A method for driving a light emitting device is provided, wherein the luminance of the element is higher than the luminance of the plurality of EL elements in a period other than a predetermined period of the period in which the EL element emits light.

According to the present invention, there is provided a method of driving a light emitting device provided with a plurality of pixels having EL elements, wherein a plurality of sub-frame periods are provided in one frame period.
In at least one sub-frame period of the plurality of sub-frame periods, the luminance of the EL element in a predetermined period of the period in which the EL element emits light is the luminance of the period in which the EL element emits light. There is provided a method for driving a light-emitting device, wherein the luminance is higher than the luminance of the plurality of EL elements in a period other than a predetermined period.

According to the present invention, there is provided a method of driving a light emitting device provided with a plurality of pixels having EL elements,
The L element has a pixel electrode, a counter electrode, and an EL layer provided between the pixel electrode and the counter electrode. When the EL element emits light, the potential applied to the pixel electrode is always By changing the height of the potential applied to the counter electrode when the EL element is emitting light,
In one frame period, the EL in a predetermined period
A method for driving a light emitting device is provided, wherein the luminance of the element is higher than the luminance of the plurality of EL elements in a period other than the predetermined period.

According to the present invention, there is provided a method of driving a light emitting device provided with a plurality of pixels having EL elements, wherein a plurality of sub-frame periods are provided in one frame period.
The EL element has a pixel electrode, a counter electrode, and an EL layer provided between the pixel electrode and the counter electrode. When the EL element emits light, a potential given to the pixel electrode is By constantly changing the level of the potential applied to the counter electrode when the EL element emits light, at least one of the plurality of sub-frame periods, E
There is provided a driving method of a light emitting device, wherein the luminance of the L element is higher than the luminance of the plurality of EL elements in a period other than the predetermined period.

According to the present invention, there is provided a method for driving a light emitting device provided with a plurality of pixels having EL elements,
The L element has a pixel electrode, a counter electrode, and an EL layer provided between the pixel electrode and the counter electrode. When the EL element emits light, the potential applied to the counter electrode is always By changing the height of the potential applied to the pixel electrode while the EL element is emitting light,
In one frame period, the EL in a predetermined period
A method for driving a light emitting device is provided, wherein the luminance of the element is higher than the luminance of the plurality of EL elements in a period other than the predetermined period.

According to the present invention, there is provided a method of driving a light emitting device provided with a plurality of pixels having EL elements, wherein a plurality of sub-frame periods are provided in one frame period.
The EL element has a pixel electrode, a counter electrode, and an EL layer provided between the pixel electrode and the counter electrode. When the EL element emits light, a potential given to the counter electrode is By constantly changing the level of the potential applied to the pixel electrode when the EL element is emitting light, at least one of the plurality of subframe periods, E
There is provided a driving method of a light emitting device, wherein the luminance of the L element is higher than the luminance of the plurality of EL elements in a period other than the predetermined period.

According to the present invention, there is provided a driving method of a light emitting device provided with a plurality of pixels having an EL element, a first EL driving TFT, and a second EL driving TFT, a first power supply, and a second power supply. The EL element has a pixel electrode, a counter electrode, and an EL layer provided between the pixel electrode and the counter electrode, and is provided to the counter electrode when the EL element emits light. The potential is always constant.
When the L element emits light, the first EL driving TF
Selecting whether to apply a potential to the pixel electrode from the first power supply via T or applying a potential to the pixel electrode from the second power supply via the second EL driving TFT; By changing the level of the potential applied to
In a frame period, a driving method of a light-emitting device is provided, in which luminance of the EL element in a predetermined period is higher than luminance of the plurality of EL elements in a period other than the predetermined period.

According to the present invention, there is provided a method for driving a light emitting device provided with a plurality of pixels having an EL element, a first EL driving TFT and a second EL driving TFT, a first power supply, and a second power supply. A plurality of sub-frame periods provided in one frame period, wherein the EL element has a pixel electrode, a counter electrode, and an EL layer provided between the pixel electrode and the counter electrode; The potential applied to the counter electrode when the EL element emits light is always constant, and when the EL element emits light, the first EL
Selecting whether to apply a potential to the pixel electrode from the first power supply via a driving TFT or applying a potential to the pixel electrode from the second power supply via the second EL driving TFT; By changing the height of the potential applied to the pixel electrode, the luminance of the EL element in a predetermined period in at least one of the plurality of sub-frame periods is reduced in a period other than the predetermined period. And a method for driving the light emitting device, wherein the luminance is higher than the luminance of the EL element.

According to the present invention, there is provided a method for driving a light emitting device provided with a plurality of pixels having EL elements, wherein the method is operated in a first mode or a second mode. In the period in which the EL element emits light, the luminance of the EL element is always kept constant. In the second mode, the EL element emits light in a predetermined period of the period in which the EL element emits light. Wherein the luminance of the plurality of EL elements is higher than the luminance of the plurality of EL elements during a period other than a predetermined period of the period in which the EL elements emit light. You.

According to the present invention, there is provided a method for driving a light emitting device provided with a plurality of pixels having EL elements, wherein the method operates in a first mode or a second mode. In the period in which the EL element emits light, the luminance of the EL element is always kept constant. In the second mode, the EL element emits light in a predetermined period of the period in which the EL element emits light. Is higher than the luminance of the plurality of EL elements in a period other than a predetermined period of the period in which the EL element emits light. A light emitting device characterized by operating in a first mode for a pixel darker than a certain gray level, and operating in a second mode for a pixel of a plurality of pixels whose displayed gray level is brighter than a certain gray level. Drive method It is subjected.

According to the present invention, there is provided a method of driving a light emitting device provided with a plurality of pixels having EL elements, wherein the method operates in a first mode or a second mode. In the period in which the EL element emits light, the luminance of the EL element is always kept constant. In the second mode, the EL element emits light in a predetermined period of the period in which the EL element emits light. Is higher than the luminance of the plurality of EL elements in a period other than a predetermined period in the period in which the EL element emits light, and is higher than the luminance of an adjacent pixel among the plurality of pixels. Therefore, only pixels whose gradation to be displayed is brighter than a certain value
Wherein the pixels other than the pixels whose display gradation is brighter than a certain value by a certain value or more than the adjacent pixels among the plurality of pixels operate in the first mode. A driving method is provided.

[0053]

(Embodiment 1) The configuration of the present invention will be described below. FIG. 1 shows a block diagram of a light emitting device of the present embodiment.

The EL panel 100 includes a pixel portion 101, a source signal line driving circuit 102, and a gate signal line driving circuit 1
03. The pixel portion 101 has a source signal line S
1 to Sx, gate signal lines G1 to Gy, and power supply line V
1 to Vx and opposing power supply lines Ve1 to Vey. Note that the number of opposing power supply lines is not always the same as the number of gate signal lines, and the number of power supply lines is not necessarily the same as the number of source signal lines.

At least one of the source signal lines S1 to Sx, at least one of the gate signal lines G1 to Gy, at least one of the power supply lines V1 to Vx, and the opposite power line Ve
A region having at least one of 1 to Vey is a pixel 10
Equivalent to 4. Therefore, a plurality of pixels 1
04 is provided on the matrix.

A power supply circuit 105 is provided with two power supplies, a power supply A (first power supply) 106 and a power supply B (second power supply) 107. The power supply lines V1 to Vx are always kept at a constant potential (power supply potential) by the power supply A106 and the power supply B107.

The power supply circuit 105 includes a selection switch A10.
8, selection switch B109, and changeover switch 11
0. The changeover switch 110 is a switch for selecting whether or not to apply a potential to the opposing power supply lines Ve1 to Vey by the power supply A106 or the power supply B107.

When one of the selection switch A 108 and the selection switch B 109 is on, the other is off. When the changeover switch 110 is on and the selection switch A108 is on, a potential (non-emphasized potential) is applied from the power supply A106 to the opposing power supply lines Ve1 to Vey via the selection switch A108 and the changeover switch 110. Conversely, when the changeover switch 110 is on and the selection switch B109 is on, the potential (emphasis potential) is supplied from the power supply B107 via the selection switch B109 and the changeover switch 110 to the opposite power supply line Ve1.
Vey.

In this embodiment mode, the source signal line driving circuit 102, the gate signal line driving circuit 103, and the pixel portion 101 are formed on the same substrate, and the power supply circuit 105
Although formed on a C chip and connected to each other via a connector such as an FPC, the present invention is not limited to this configuration. The source signal line driver circuit 102 and the gate signal line driver circuit 103 are not necessarily formed over the same substrate as the pixel portion 101, and may be formed over the same substrate as the power supply circuit 105. Further, the selection switch A 108, the selection switch B 109, and the changeover switch 110 included in the power supply circuit 105 are not necessarily formed on an IC chip, and may be formed on the same substrate as the pixel portion 101.

FIG. 2A shows a detailed configuration of the pixel 104. The pixel 104 includes a source signal line Si (one of S1 to Sx), a power supply line Vi (one of V1 to Vx), and a gate signal line Gj (one of G1 to Gy). And an opposing power supply line Vej (any one of Ve1 to Vey).

The pixel 104 is a switching TFT 1
11 and an EL driving TFT 112. The gate electrode of the switching TFT 111 is connected to the gate signal line G.
j. One of a source region and a drain region of the switching TFT 111 has a source signal line Si.
The other is connected to the gate electrode of the EL driving TFT 112.

One of a source region and a drain region of the EL driving TFT 112 is connected to the power supply line Vi, and the other is connected to the EL element 113.

The EL element 113 includes an anode and a cathode, and an EL layer provided between the anode and the cathode. When the anode is connected to the source region or the drain region of the EL driving TFT 112, the anode serves as a pixel electrode and the cathode serves as a counter electrode. Conversely, when the cathode is connected to the source region or the drain region of the EL driving TFT 112, the cathode serves as a pixel electrode and the anode serves as a counter electrode.

All power supply lines V1 to Vx have power supply A
A constant power supply potential is given by the power supply 106 and the power supply B 107. In addition, a counter electrode of the EL element 113 included in all pixels is connected to one of the counter power supply lines Ve1 to Vey. When the changeover switch 110 and the selection switch A108 are on, all the opposing power supply lines Ve1 to Ve1
Vey is supplied with the non-emphasized potential by the power supply A106, and the changeover switch 110 and the selection switch B109
Are on, all the opposite power supply lines Ve1 to Vey
The emphasis potential is supplied by the power supply B107.

Next, the operation of the light emitting device of the present invention shown in FIGS. 1 and 2A will be described. When performing time-division gray scale display, the operation of the light-emitting device of the present invention can be described separately in a writing period and a display period.

In the writing period, the gate signal line G1
To Gy are sequentially selected by the selection signal, and the digital video signals input to the source signal lines S1 to Sx are input to each pixel. In this specification, a signal line is selected when all the TFTs whose gate electrodes are connected to the signal line are selected.
Is turned on. In this specification, the input of a digital video signal to a pixel means that the digital video signal is a switching TF of the pixel.
This means that the signal is input to the gate electrode of the EL driving TFT via T.

The detailed operation of the pixel will now be described with reference to FIG.
A description will be given by taking the pixel shown in FIG.

The switching TFT 111 is turned on by the selection signal input to the gate signal line Gj, and a digital signal (hereinafter, referred to as a digital video signal) having image information input to the source signal line Si is used for switching. The signal is input to the gate electrode of the EL driving TFT 112 via the TFT 111.

The switching of the EL driving TFT 112 is controlled by 1 or 0 information included in the digital video signal input to the gate electrode of the EL driving TFT 112.

When the EL driving TFT 112 is turned off, the power supply potential of the power supply line Vi is not applied to the pixel electrode of the EL element 113. In addition, EL driving TFT
When 112 is turned on, the power supply potential of the power supply line Vi is given to the pixel electrode of the EL element 113.

The switch is turned off until the digital video signal is input to all the pixels.
The pixel electrode and the counter electrode of the EL element 113 are kept at the same potential.

When the digital video signal is input to all the pixels, the writing period ends, and the display period starts. During the display period, the changeover switch 110 is turned on.

Then, the emphasis potential or the non-emphasis potential is applied to all the opposing power supply lines Ve1 to Vey via the changeover switch 110 and the selection switch A108 or the selection switch B109.

The power supply potential and the emphasis potential have a potential difference, and the power supply potential and the non-emphasis potential have a potential difference.

When the EL driving TFT 112 is on, this potential difference is applied between the pixel electrode and the counter electrode of the EL element 113, and the EL element 113 emits light. In this embodiment, the potential difference between the pixel electrode and the counter electrode of the EL element 113 when the potential at the time of emphasis is applied to the counter electrode is emphasized at the time of emphasis.
This is referred to as an L drive voltage Va. Further, in the present embodiment, when the non-emphasized potential is applied to the counter electrode, the EL element 11
The potential difference between the third pixel electrode and the counter electrode is referred to as the non-emphasized EL drive voltage Vb. In this specification, the emphasized EL drive voltage and the non-emphasized EL drive voltage are collectively referred to as an EL drive voltage.

The EL element 11 is driven by the EL driving voltage during emphasis.
The luminance when the EL element 113 emits light by the non-emphasized EL driving voltage and the luminance when the EL element 113 emits light are higher in the former. In the following, in this specification, the emphasis EL
When the EL element emits light by the drive voltage, it is called that the EL element emits strong light.
The light emission of the L element is referred to as the normal light emission of the EL element.

On the other hand, when the EL driving TFT 112 is off, the pixel electrode of the EL element 113 is kept at the same height as the potential of the counter electrode, so that the EL element 113 does not emit light.

The writing period and the display period are collectively called a sub-frame period SF. In one frame period, a plurality of sub-frame periods corresponding to each bit of the digital video signal are provided.

FIG. 2B shows the timing at which the sub-frame periods (SF1 to SF5) appear when the light emitting device of the present invention is driven by a 5-bit digital video signal. The horizontal axis indicates time, and the vertical axis indicates EL driving voltage. For the sake of simplicity, FIG.
In (B), E is determined by the digital video signal of each bit.
The case where the L driving TFT 112 is always on is shown. Although FIG. 2B illustrates the case where the digital video signal is driven by a 5-bit digital video signal, the present invention is not limited to this number of bits.

Since the EL drive voltage is 0 during the writing period of each of the subframe periods SF1 to SF5,
The L element 113 does not emit light. In the display period of each of the subframes SF1 to SF5, the absolute value of the EL drive voltage becomes larger than 0, and the EL element 113 emits light.

In this embodiment, the selection switch A108 is turned on only during a part of the display period of the sub-frame period SF5 corresponding to the digital video signal of the fifth bit.
The selection switch B109 is turned off, and the emphasis potential is applied to the opposite power supply lines Ve1 to Vey by the power supply A106. When the potential at the time of emphasis is applied to the opposite power supply lines Ve1 to Vey, the potential at the time of emphasis is applied to the pixel electrode via the ON EL driving TFT 112. As a result, the EL element 113
At the time of emphasis, the EL element 113 emits strong light. Note that a period during which the EL element emits light is called a strong light emission period.

In the display period of the sub-frame period SF5, in the periods other than the strong light emission period and in all the display periods of the other sub-frame periods SF1 to SF4, the selection switch A108 is turned off, and the selection switch B10 is turned off.
9 is turned on, and the non-emphasized potential is applied to the opposite power supply lines Ve1 to Vey by the power supply B107. When the non-emphasized potential is applied to the opposite power supply lines Ve1 to Vey, the ON EL
A non-emphasized potential is applied to the pixel electrode via the driving TFT 112. As a result, the non-emphasized EL element 113
A driving voltage is applied, and the EL element 113 normally emits light.

The strong light emission period does not necessarily need to be provided within the subframe period corresponding to the most significant bit, as described in this embodiment. The strong light emission period can be provided in any subframe period. In this embodiment mode, a strong light emission period is provided only in one subframe period in one frame period; however, the present invention is not limited to this structure. During one frame period, a strong light emission period may be provided in each of a plurality of subframe periods.

The length of the intense light emission period can be arbitrarily set by the designer, but is preferably equal to or shorter than the shortest display period.

In the light emitting device of the present invention, a normal mode in which an image is displayed in a frame period in which no strong light emission period is provided, and a strong light emission mode in which an image is displayed in a frame period in which a strong light emission period is provided. And can be freely selected. For example, the strong light emission mode may be selected only when selected by the user or automatically selected by an electronic device having a light emitting device.

According to the present invention, when display is performed using an n-bit (n is an arbitrary natural number) digital video signal,
In order from the display period length ratio of the display period, corresponding to the least significant bit of the digital video signal, 2 ^0: 2 ^1: 2 ^2: ...:
2 ^(n-2) : It is necessary to make 2 ^(n-1) .
A desired gradation display out of 2 ⁿ gradations can be performed by the combination of the display periods. The order in which the subframe periods appear is not limited to the order shown in this embodiment. The sub-frame periods SF1 to SFn may appear in any order.

In the present invention, by providing a strong light emission period within one frame period, even if an image itself as information of a video signal input to the light emitting device is entirely dark,
Since the actually displayed image becomes brighter, it is possible to easily recognize the object.

(Embodiment Mode 2) In this embodiment mode, a structure in which a strong light emission period is provided only for a specific pixel included in a pixel portion will be described. FIG. 3 shows a block diagram of the light emitting device of the present embodiment.

The EL panel 200 has a pixel portion 201, a first source signal line driving circuit 202a, a second source signal line driving circuit 202b, and a gate signal line driving circuit 203. The pixel unit 201 has a first source signal line Sa1
To Sax, the second source signal lines Sb1 to Sbx, the gate signal lines G1 to Gy, and the first power supply lines Va1 to Vax.
, Second power supply lines Vb1 to Vbx, and opposing power supply line Ve
1 to Vey. Note that the number of opposing power supply lines is not necessarily the same as the number of gate signal lines, and the number of first or second power supply lines is not necessarily the same as the number of first or second source signal lines. Not necessarily.

At least one of the first source signal lines Sa1 to Sax, at least one of the second source signal lines Sb1 to Sbx, at least one of the gate signal lines G1 to Gy, and at least one of the first power supply lines Va1 to Vax One region, at least one of the second power supply lines Vb1 to Vbx, and at least one of the opposing power lines Ve1 to Vey correspond to the pixel 204. Therefore, the pixel portion 20
In one, a plurality of pixels 204 are provided on a matrix.

A power supply circuit 205 is provided with two power supplies, a power supply A 206 and a power supply B 207. Power supply A2
06, a constant potential (power supply potential at the time of emphasis) is applied to the first power supply lines Va1 to Vax. The power supply B207 applies a constant potential (non-emphasized power supply potential) to the second power supply lines Vb1 to Vbx.

The power supply circuit 205 is provided with a switch 2
It has ten. The changeover switch 210 is a switch for selecting whether or not to apply a potential to the opposing power supply lines Ve1 to Vey by the power supply A206 and the power supply B207.

When the changeover switch 210 is turned on,
Through the changeover switch 210, the power supply A 206 and the power supply B 207 generate a constant opposing potential to the opposing power supply line Ve.
1 to Vey.

In this embodiment, the first source signal line driving circuit 202a and the second source signal line driving circuit 20a
2b, the gate signal line driving circuit 203, and the pixel portion 201
Are formed on the same substrate and the power supply circuit 205 is formed on an IC chip and connected to each other via a connector such as an FPC, but the present invention is not limited to this configuration.
The first source signal line driver circuit 202a, the second source signal line driver circuit 202b, and the gate signal line driver circuit 203 do not need to be formed over the same substrate as the pixel portion 201; It may be formed on top. Further, the changeover switch 210 included in the power supply circuit 205 is not necessarily formed on an IC chip, and may be formed on the same substrate as the pixel portion 201.

FIG. 4A shows a detailed configuration of the pixel 204. The pixel 204 includes a first source signal line Sai (Sa1 to Sa1).
Sax) and the second source signal line Sbi.
(One of Sb1 to Sbx), first power supply line Vai (one of Va1 to Vax), second power supply line Vbi (one of Vb1 to Vbx), and gate signal It has a line Gj (any one of G1 to Gy) and a counter power supply line Vej (any one of Ve1 to Vey).

The pixel 204 has a first switching T
FT211a and second switching TFT211b
And a first EL driving TFT 212a and a second EL driving TFT 212b. T for first switching
FT211a and second switching TFT211b
Have the same polarity as each other. Also, the first EL driving T
The FT 212a and the second EL driving TFT 212b have the same polarity.

First and second switching TFT 211
Gate electrodes a and 211b are connected to a gate signal line Gj. One of the source region and the drain region of the first switching TFT 211a is the first source signal line Sa.
The other is connected to the gate electrode of the first EL driving TFT 212a. The source region and the drain region of the second switching TFT 211b are
One is on the second source signal line Sbi and the other is on the second EL
It is connected to the gate electrode of the driving TFT 212b.

One of the source region and the drain region of the first EL driving TFT 212a is the first power supply line Va.
i and the other is connected to the EL element 213. One of a source region and a drain region of the second EL driving TFT 212b is connected to the second power supply line Vbi, and the other is connected to the EL element 213.

The EL element 213 includes an anode and a cathode, and an EL layer provided between the anode and the cathode. The anode is 1E
When connected to the source or drain region of the L driving TFT 212a, or when the anode is connected to the source or drain region of the second EL driving TFT 212b, the anode becomes a pixel electrode and the cathode becomes a counter electrode. . Conversely, when the cathode is connected to the source or drain region of the first EL driving TFT 212a, or when the cathode is connected to the source or drain region of the second EL driving TFT 212b, the cathode is a pixel electrode or an anode. Becomes the counter electrode.

A fixed emphasis power supply potential is applied to all the first power supply lines Va1 to Vax by the power supply A206. Also, all the second power supply lines Vb1 to Vb
x is given a constant non-emphasized power supply potential by the power supply B 207.

The opposing electrode of the EL element 213 of all the pixels is connected to one of the opposing power supply lines Ve1 to Vey. When the changeover switch 210 is turned on, a counter potential is applied to all the counter power lines Ve1 to Vey by the power source A206 and the power source B207.

Next, the operation of the light emitting device of the present invention shown in FIGS. 3 and 4A will be described. When performing time-division gray scale display, the operation of the light-emitting device of the present invention can be described separately in a writing period and a display period.

In the writing period, the gate signal line G1
Gy are sequentially selected by a selection signal, and a digital video signal is input to each pixel.

The detailed operation of the pixel will now be described with reference to FIG.
A description will be given by taking the pixel shown in FIG.

In the writing period, the gate signal line Gj
, The first and second switching TFTs 211a and 211b are turned on.

In the present embodiment, the first digital video signal is input to the first source signal lines Sa1 to Sax, and the second digital video signal is input to the second source signal lines Sb1 to Sbx.

The first signal input to the first source signal line Sai is
The digital video signal is transmitted to the first switching TFT 21.
The signal is input to the gate electrode of the first EL driving TFT 212a via 1a. At the same time, the second digital video signal input to the second source signal line Sbi is transmitted to the first EL driving TFT 212 via the second switching TFT 211b.
a is input to the gate electrode a.

In the present embodiment, the input of the digital video signal to the pixel means that the first digital video signal corresponds to the first switching TFT of the pixel.
And the second digital video signal is input to the gate electrode of the second EL driving TFT via the second switching TFT of the pixel. Means

First and second EL driving TFTs 212a,
Switching of 12b is controlled by 1 or 0 information included in the first and second digital video signals input to the gate electrode.

The first EL driving TFT 212a and the second EL
One of the driving TFTs 212b is on and the other is off, or both are off.

The first and second EL driving TFTs 212a,
When both 212b are turned off, the first power supply line V
The emphasis power supply potential of ai and the non-emphasis power supply potential of the second power supply line Vbi are not applied to the pixel electrode of the EL element 213.

The first or second EL driving TFT 2
When one of 12a and 212b is turned on, the emphasized power supply potential of the first power supply line Vai or the non-emphasized power supply potential of the second power supply line Vbi is supplied to the pixel electrode of the EL element 213.

The changeover switch is turned off until the digital video signal is input to all the pixels.
The pixel electrode and the counter electrode of the EL element 213 are kept at the same potential.

When the digital video signal is input to all the pixels, the writing period ends, and the display period starts. During the display period, the changeover switch 210 is turned on.

Then, the opposing potential is applied to all the opposing power supply lines Ve1 to Vey by the power supply A206 and the power supply B207 via the changeover switch 210.

The power supply potential at the time of emphasis and the opposing potential, and the power supply potential at the time of non-emphasis and the opposing potential have potential differences, respectively.

When the first EL driving TFT 212a is on and the second EL driving TFT 212b is off, the potential difference between the emphasis power supply potential and the counter potential is applied between the pixel electrode and the counter electrode of the EL element 213, and the EL element 213 emits light. I do. In the present embodiment, the emphasis power supply potential is set to the first EL driving TF.
EL when applied to the pixel electrode via T212a
The potential difference between the pixel electrode and the counter electrode of the element 213 is referred to as an emphasis EL drive voltage Va.

When the first EL driving TFT 212a is off and the second EL driving TFT 212b is on, the potential difference between the non-emphasized power supply potential and the opposing potential is applied between the pixel electrode and the opposing electrode of the EL element 213. 213 emits light. In this embodiment, the non-emphasized potential is the EL driving T
EL when applied to the pixel electrode via FT212
The potential difference between the pixel electrode and the counter electrode of the element 213 is referred to as a non-emphasized EL drive voltage Vb.

In this specification, the emphasized EL drive voltage Va and the non-emphasized EL drive voltage Vb are collectively referred to as an EL drive voltage.

The EL element 21 is driven by the EL drive voltage during emphasis.
The luminance of the EL element 213 due to the non-emphasized EL driving voltage and the luminance of the EL element 213 when the EL element 213 emits light is higher in the former case.

On the other hand, the first and second EL driving TFTs 21
When both 2a and 212b are off, the potential of the pixel electrode of the EL element 213 and the potential of the counter electrode are maintained at the same level.
The L element 213 does not emit light.

The writing period and the display period are collectively called a sub-frame period SF. In one frame period, a plurality of sub-frame periods corresponding to each bit of the digital video signal are provided.

FIG. 4B shows the timings at which the sub-frame periods (SF1 to SF5) appear when the light emitting device of the present invention is driven by a 5-bit digital video signal. The horizontal axis indicates time, and the vertical axis indicates EL driving voltage. For the sake of simplicity, FIG.
In (B), the first EL driving TFT 212a and the second EL driving TFT 2
12B shows a case where one of the switches 12b is turned on. FIG. 2B illustrates a case where the digital video signal is driven by a 5-bit digital video signal.
The present invention is not limited to this number of bits.

Since the EL drive voltage is 0 in the writing period of each of the sub-frame periods SF1 to SF5, E
The L element 213 does not emit light. In the display period of each sub-frame period of SF1 to SF5, the absolute value of the EL drive voltage becomes larger than 0, and the EL element 213 emits light.

In the present embodiment, the first EL driving TFT 212a is provided only in a part of the display period of the subframe period SF5 corresponding to the digital video signal of the fifth bit.
Is turned on, the second EL driving TFT 212b is turned off,
The power supply potential at the time of emphasis is given to the pixel electrode of the EL element 213. As a result, the emphasis EL driving voltage is applied to the EL element 213, and the EL element 213 emits strong light. Note that a period during which the EL element emits light is called a strong light emission period.

In the display period of the sub-frame period SF5, in the periods other than the strong light emission period and in all the display periods of the other sub-frame periods SF1 to SF4, the first EL driving TFT 212a is turned off and the second EL The driving TFT 212b is turned on, and the power supply potential at the time of non-emphasis is given to the pixel electrode of the EL element 213. As a result, E
The non-emphasized EL drive voltage is applied to the L element 213,
The element 213 normally emits light.

Note that the strong light emission period does not necessarily need to be provided in the subframe period corresponding to the most significant bit, as described in this embodiment. The strong light emission period can be provided in any subframe period. In this embodiment mode, a strong light emission period is provided only in one subframe period in one frame period; however, the present invention is not limited to this structure. During one frame period, a strong light emission period may be provided in each of a plurality of subframe periods.

The length of the intense light emission period can be arbitrarily set by a designer, but is preferably equal to or shorter than the shortest display period.

In the light emitting device of the present invention, a normal mode in which an image is displayed in a frame period in which no strong light emission period is provided, and a strong light emission mode in which an image is displayed in a frame period in which a strong light emission period is provided. And can be freely selected. For example, the strong light emission mode may be selected only when selected by the user or automatically selected by an electronic device having a light emitting device.

In the present invention, when display is performed using an n-bit digital video signal, the length ratio of the display period is as follows:
In order from the display period corresponding to the least significant bit of the digital video ^{signal, 2 0: 2 1: 2} 2: ...: 2 (n-2): it is necessary to be a 2 ^(n-1). A desired gradation display out of 2 ⁿ gradations can be performed by the combination of the display periods. The order in which the subframe periods appear is not limited to the order shown in this embodiment. Subframe period S
F1 to SFn may appear in any order.

According to the present invention, by providing a strong light emission period within one frame period, even if an image itself as information of a video signal input to the light emitting device is entirely dark,
Since the actually displayed image becomes brighter, it is possible to easily recognize the object.

Further, when the gradation displayed by a certain pixel is brighter than a certain gradation, the absolute value of the EL drive voltage applied to the EL element of the pixel is increased to increase the luminance of the EL element. May be. According to the above configuration, the pixel displaying a bright gradation becomes brighter, the contrast of the image is increased, the image is sharpened, and the object can be easily recognized.

Further, by identifying a pixel having a gradation greatly different from that of an adjacent pixel from a digital video signal inputted to each pixel, an outline of the object is detected, and a pixel at an outline portion of the image is detected. Only the contrast may be increased. According to the above configuration, the outline of the image is extracted, the image is sharpened, and the object can be easily recognized.

(Embodiment 3) In Embodiments 1 and 2, the configuration provided with the changeover switch has been described, but the present invention is not limited to this configuration. It is not always necessary to provide a changeover switch.

However, in this case, at the same time as the digital video signal (including the first and second digital video signals) is input to the pixel during the writing period, the EL element emits or does not emit light, and the pixel is displayed. I do.

In the present embodiment, when display is performed using an n-bit digital video signal, the length ratio of the sub-frame period is set to 20 ^{0 in} order from the sub-frame period corresponding to the least significant bit of the digital video signal. : 2 ¹ : 2 ² : ...: 2
^(n-2) : 2 ^(n-1) . A desired gray scale display out of 2 ⁿ gray scales can be performed by the combination of the sub-frame periods.

The order in which the sub-frame periods appear is as follows:
It is not limited to the order shown in the present embodiment. The sub-frame periods SF1 to SFn may appear in any order.

[0138]

Embodiments of the present invention will be described below.

(Embodiment 1) In this embodiment, an example will be described in which the timing at which the strong light emission period appears in the strong light emission mode is different from those in the first and second embodiments.

FIG. 5 shows the appearance timings of the sub-frame periods (SF1 to SF5) when the light emitting device of the present invention is driven by a 5-bit digital video signal.
The timing at which the strong light emission period appears is shown. The horizontal axis indicates time, and the vertical axis indicates EL driving voltage. Note that for simplicity of description, FIG. 5 illustrates a case where the EL element emits strong light or normal light in all display periods. Although FIG. 5 shows an example in which the digital video signal is driven by a 5-bit digital video signal, the present invention is not limited to this number of bits.

In FIG. 5A, five subframe periods corresponding to each bit of the 5-bit digital video signal appear in the order of SF3, SF2, SF5, SF4, and SF1. As described above, in one sub-frame period, the intermediate gradation is displayed by causing another sub-frame period to appear before and after the sub-frame period (SF5 in this embodiment) having the longest display period. When this is done, it is possible to prevent the generation of a moving image false contour.

In FIG. 5A, the strong light emission period is provided in the sub-frame period SF5.

In FIG. 5B, five subframe periods corresponding to each bit of the 5-bit digital video signal appear in the order of SF1, SF2, SF5, SF3, and SF4.

In FIG. 5A, a strong light emission period is provided in the subframe period SF1, and the strong light emission period and the display period of the subframe period SF1 completely overlap. That is, in the display period of the sub-frame period SF1, the EL element always emits strong light.

The length of the intense light emission period can be arbitrarily set by a designer, but is preferably equal to or shorter than the shortest display period.

(Embodiment 2) In the second embodiment, when the gradation displayed by a pixel is brighter than a certain gradation, the absolute value of the EL drive voltage applied to the EL element of the pixel is increased. The case where the luminance of the EL element is increased will be described in detail with reference to FIG.

A digital video signal for displaying a normal mode is supplied to the switching circuit 220 and the level comparing circuit 2.
23. In the level comparison circuit 223,
It is determined whether or not the gradation of a pixel to be displayed is brighter than a predetermined gradation based on the input digital video signal.

Data serving as the criterion (reference data)
Are stored in the nonvolatile memory 221, read by the volatile memory 222, and input to the level comparison circuit 223.

In the level comparison circuit 223, the reference data and the digital video signal are compared, and when it is determined that the gradation of the pixel to be displayed by the digital video signal is darker than the predetermined gradation, the switching circuit 220 normally supplies Signal to operate in the mode. Conversely, when it is determined that the gradation of the pixel to be displayed by the digital video signal is brighter than the predetermined gradation, a signal is sent to the switching circuit 220 so as to operate in the strong light emission mode.

When the switching circuit 220 is operating in the normal mode, the first digital video signal for displaying the normal mode and the second digital video signal for displaying the normal mode are input from the input digital video signals. Are generated and input to the first source signal line driving circuit 202a and the second source signal line driving circuit 202b, respectively. As a result, the EL element of the pixel emits normal light.

Conversely, when the switching circuit 220 is operating in the intense light emission mode, the first digital video signal for displaying the intense light emission mode and the second digital video signal are displayed from the input digital video signal. Generate a video signal and
The signals are input to the first source signal line driving circuit 202a and the second source signal line driving circuit 202b, respectively. As a result, the EL element included in the pixel emits strong light.

According to the above configuration, the pixels displaying a bright gradation become brighter, the contrast of the image is increased, the image becomes clear, and the object can be easily recognized.

This embodiment can be implemented by freely combining with the structure shown in the first embodiment.

(Embodiment 3) In the second embodiment, the contour of an object is detected by specifying a pixel whose gradation is greatly different from that of an adjacent pixel from a digital video signal input to each pixel. The case where the contrast is increased only in the pixels at the outline of the image will be described in detail with reference to FIG.

A digital video signal for displaying a normal mode is input to a selection time correction circuit 230 and a digital signal processor (DSP) 232.

The digital video signal input to the DSP 232 is input to the differential filter 233. In the differential filter 233, for all the pixels included in the pixel portion, the gradation difference between adjacent pixels is digitized from the input digital video signal, and is sent to the comparison circuit 234 as data.

When the digitized data is larger than the reference value (reference digitized data),
It is determined that an outline is formed by adjacent pixels. The reference digitized data is stored in the reference value memory 235 and read by the comparison circuit 234.

When the level comparison circuit 234 determines that an outline is formed in adjacent pixels,
A signal is sent to the switching circuit 231 so as to operate in the normal mode. Conversely, when it is determined that no contour is formed in the adjacent pixel, a signal is sent to the switching circuit 231 so as to operate in the strong light emission mode.

On the other hand, the digital video signal input to the selection time correction circuit 230 is input to the switching circuit 231 in synchronization with the input of the mode selection signal to the switching circuit 231.

When the switching circuit 231 is operating in the normal mode, the first digital video signal for displaying the normal mode and the second digital video signal for displaying the normal mode are input from the input digital video signal. Are generated and input to the first source signal line driving circuit 202a and the second source signal line driving circuit 202b, respectively. As a result, the EL elements of two adjacent pixels each emit normal light.

Conversely, when the switching circuit 231 is operating in the intense light emission mode, the first digital video signal for displaying the intense light emission mode and the second digital video signal are displayed from the input digital video signal. Generate a video signal and
The signals are input to the first source signal line driving circuit 202a and the second source signal line driving circuit 202b, respectively. As a result, of the two adjacent pixels, the EL element included in the pixel displaying a bright gradation emits strong light.

According to the above configuration, the outline of the image is extracted, the image becomes clear, and the object can be easily recognized.

This embodiment can be implemented by freely combining with the structure shown in the first embodiment. Embodiment 4 In this embodiment, a source signal line driver circuit (including a first source signal line driver circuit and a second source signal line driver circuit) used for driving a pixel portion of a light emitting device of the present invention, A detailed configuration of the gate signal line driving circuit will be described.

FIG. 8 is a block diagram of a driving circuit of the light emitting device of this embodiment. FIG. 8A shows the source signal line driving circuit 6.
01, the shift register 602, the latch (A) 60
3. It has a latch (B) 604.

In the source signal line driver circuit 601, a clock signal (CLK) and a start pulse (SP) are input to the shift register 602. Shift register 6
02 sequentially generates a timing signal based on the clock signal (CLK) and the start pulse (SP), and sequentially inputs the timing signal to a subsequent circuit through a buffer or the like (not shown).

The timing signal from the shift register 602 is buffer-amplified by a buffer or the like. The wiring to which the timing signal is input has a large load capacitance (parasitic capacitance) because many circuits or elements are connected.
This buffer is provided to prevent "dulling" of the rise or fall of the timing signal caused by the large load capacitance. It is not always necessary to provide a buffer.

The timing signal buffer-amplified by the buffer is input to the latch (A) 603. The latch (A) 603 is an n-bit digital video signal (first
(Including a digital video signal or a digital video signal).
When the timing signal is input, the latch (A) 603 sequentially captures and holds an n-bit digital video signal input from outside the source signal line driving circuit 601.

When the digital video signal is taken into the latch (A) 603, the digital video signal may be sequentially input to the latches of a plurality of stages of the latch (A) 603. However, the present invention is not limited to this configuration. The latches of a plurality of stages included in the latch (A) 603 may be divided into several groups, and a so-called divided drive in which digital video signals are input simultaneously in parallel for each group may be performed. The number of groups at this time is called a division number. For example, when the latch is divided into groups for every four stages, it is referred to as divided drive in four divisions.

The time until the writing of the digital video signal to the latches of all the stages of the latch (A) 603 is completed is called a line period. Actually, the line period may include a period obtained by adding the horizontal retrace period to the line period.

When one line period ends, the latch (B)
A latch signal (Latch Signal) is input to 604. At this moment, the digital video signal written and held in the latch (A) 603 is simultaneously sent to the latch (B) 604, and written and held in the latches of all the stages of the latch (B) 604.

The digital video signal is latched (B) 604
The digital video signal is sequentially written into the latch (A) 603 which has been transmitted to the latch 603 based on the timing signal from the shift register 602.

During the second one line period, the digital video signal written and held in the latch (B) 604 is supplied to the source signal line (the first source signal line or the second source signal line).
(Including source signal lines).

FIG. 8B is a block diagram showing the structure of the gate signal line driving circuit.

The gate signal line driving circuit 605 has a shift register 606 and a buffer 607, respectively.
In some cases, a level shift may be provided.

In the gate signal line driving circuit 605, the timing signal from the shift register 606 is
07 and input to the corresponding gate signal line.
The gate electrodes of the first switching TFT and the second switching TFT of one line of pixels are connected to the gate signal line. Since the first switching TFT and the second switching TFT of the pixels for one line must be turned on at the same time, a buffer capable of flowing a large current is used.

This embodiment can be implemented by freely combining with Embodiments 1 to 3.

Embodiment 5 An example of a method for manufacturing a light emitting device of the present invention will be described with reference to FIGS. Here, a method for simultaneously manufacturing a switching TFT and an EL driving TFT in a pixel portion of the light-emitting device described in Embodiment 1 and a TFT in a driving portion provided around the pixel portion will be described in detail according to steps. . Note that although the method for manufacturing the light-emitting device described in Embodiment 1 is described in this embodiment, the present embodiment can be applied to a method for manufacturing a light-emitting device having the structure described in Embodiment 2. .

First, in this embodiment, Corning # 70
A substrate 900 made of glass such as barium borosilicate glass typified by 59 glass or # 1737 glass or aluminoborosilicate glass is used. Note that the substrate 900 is not limited as long as it is a light-transmitting substrate, and a quartz substrate may be used. Further, a plastic substrate having heat resistance enough to withstand the processing temperature of this embodiment may be used.

Next, as shown in FIG.
A base film 901 made of an insulating film such as a silicon oxide film, a silicon nitride film, or a silicon oxynitride film is formed over the substrate. Although a two-layer structure is used as the base film 901 in this embodiment, a single-layer film of the insulating film or a structure in which two or more layers are stacked may be used. The first layer of the base film 901 is formed by plasma CVD.
The silicon oxynitride film 901a formed by using SiH ₄ , NH ₃ , and N ₂ O as reaction gases is
m (preferably 50 to 100 nm). In this embodiment, a 50-nm-thick silicon oxynitride film 901a (composition ratio: Si = 32%, O = 27%, N = 24%, H = 17%)
Was formed. Next, as the second layer of the base film 901,
Using a plasma CVD method, a silicon oxynitride film 901b formed by using SiH ₄ and N ₂ O as reaction gases is reduced to 50 to 2
The layer is formed to a thickness of 00 nm (preferably 100 to 150 nm). In this embodiment, a 100 nm-thick silicon oxynitride film 901b (composition ratio Si = 32%, O = 59%, N
= 7%, H = 2%).

Next, a semiconductor layer 902 is formed on the underlayer 901.
To 905 are formed. The semiconductor layers 902 to 905 are formed by forming a semiconductor film having an amorphous structure by a known means (sputtering method, L
After forming a film by a PCVD method or a plasma CVD method, a known crystallization treatment (a laser crystallization method, a thermal crystallization method, or a thermal crystallization method using a catalyst such as nickel).
Is performed and the crystalline semiconductor film obtained is patterned into a desired shape. The thickness of the semiconductor layers 902 to 905 is 25 to 80 nm (preferably 30 to 60 nm). Although there is no limitation on the material of the crystalline semiconductor film,
Preferably silicon (silicon) or silicon germanium _{(Si X Ge 1-X (} X = 0.0001~0.02)) may be formed such as an alloy. In this embodiment, the plasma CV
After a 55-nm amorphous silicon film was formed by method D, a solution containing nickel was held on the amorphous silicon film. After dehydrogenation (500 ° C., 1 hour) of this amorphous silicon film, thermal crystallization (550 ° C., 4 hours) is performed, and further, a laser annealing process for improving crystallization is performed. Thus, a crystalline silicon film was formed. Then, the crystalline silicon film is patterned by a photolithography method,
Semiconductor layers 902 to 905 were formed.

After the formation of the semiconductor layers 902 to 905, the semiconductor layer 90 is controlled to control the threshold value of the TFT.
2 to 905 may be doped with a trace amount of an impurity element (boron or phosphorus).

When a crystalline semiconductor film is formed by a laser crystallization method, a pulse oscillation type or continuous emission type excimer laser, a YAG laser, or a YVO ₄ laser can be used. In the case of using these lasers, it is preferable to use a method in which laser light emitted from a laser oscillator is linearly condensed by an optical system and irradiated on a semiconductor film. The crystallization conditions are appropriately selected by the practitioner. When an excimer laser is used, the pulse oscillation frequency is set to 300 Hz, and the laser energy density is set to 100 to 4.
00 mJ / cm ² (typically 200 to 300 mJ / cm
² ). When a YAG laser is used, its second harmonic is used and a pulse oscillation frequency of 30 to 300 kHz is used.
And a laser energy density of 300 to 600 mJ /
cm ² (typically 350 to 500 mJ / cm ² ). And a width of 100 to 1000 μm, for example 400 μ
The laser light condensed linearly at m may be irradiated over the entire surface of the substrate, and the superposition rate (overlap rate) of the linear laser light at this time may be set to 50 to 90%.

Next, a gate insulating film 906 covering the semiconductor layers 902 to 905 is formed. The gate insulating film 906 is formed by a plasma CVD method or a sputtering method and has a thickness of 40 to
The insulating film containing silicon is formed to have a thickness of 150 nm. In this embodiment, a silicon oxynitride film (composition ratio: Si = 32%, O = 59%, N =
7%, H = 2%). Needless to say, the gate insulating film is not limited to the silicon oxynitride film, and another insulating film containing silicon may be used as a single layer or a stacked structure.

When a silicon oxide film is used, TEOS (Tetraethyl Orthosilicat
e) and O ₂ were mixed, the reaction pressure was 40 Pa, and the substrate temperature was 30.
It can be formed by discharging at a high-frequency (13.56 MHz) power density of 0.5 to 0.8 W / cm ² at 0 to 400 ° C. The silicon oxide film thus manufactured can obtain favorable characteristics as a gate insulating film by subsequent thermal annealing at 400 to 500 ° C.

Then, a heat-resistant conductive layer 907 for forming a gate electrode on the gate insulating film 906 is
It is formed with a thickness of 0 nm (preferably 250 to 350 nm). The heat-resistant conductive layer 907 may be formed as a single layer,
If necessary, a laminated structure including a plurality of layers such as two layers or three layers may be employed. Ta, T for the heat-resistant conductive layer
It includes an element selected from i and W, an alloy containing the above element, or an alloy film combining the above elements. These heat-resistant conductive layers are formed by a sputtering method or a CVD method, and it is preferable to reduce the impurity concentration to reduce the resistance, and it is particularly preferable that the oxygen concentration be 30 ppm or less. In this embodiment, the W film is 3
It is formed with a thickness of 00 nm. The W film may be formed by a sputtering method using W as a target, or may be formed by a thermal CVD method using tungsten hexafluoride (WF ₆ ). In any case, it is necessary to lower the resistance in order to use it as a gate electrode, and the resistivity of the W film is 20 μΩc.
m or less. The resistivity of the W film can be reduced by enlarging the crystal grains. However, when there are many impurity elements such as oxygen in W, crystallization is inhibited and the resistance is increased. Thus, in the case of using the sputtering method, a W target having a purity of 99.9999% is used, and further, the W film is formed with sufficient care so as not to mix impurities from the gas phase during film formation. 9 to 20 μΩcm can be realized.

On the other hand, when a Ta film is used for the heat-resistant conductive layer 907, it can be similarly formed by a sputtering method. The Ta film uses Ar as a sputtering gas. Also, if an appropriate amount of Xe or Kr is added to the gas during sputtering,
The internal stress of the film to be formed can be relaxed to prevent the film from peeling. The resistivity of the α-phase Ta film is about 20 μΩcm and can be used for the gate electrode.
The resistivity of the a-film was about 180 μΩcm, and was not suitable for use as a gate electrode. Since the TaN film has a crystal structure close to the α phase, if the TaN film is formed under the Ta film,
A phase Ta film is easily obtained. Although not shown, it is effective to form a silicon film doped with phosphorus (P) with a thickness of about 2 to 20 nm under the heat-resistant conductive layer 907. Thereby, the adhesion of the conductive film formed thereon is improved and oxidation is prevented, and at the same time, the heat-resistant conductive layer 90 is formed.
It is possible to prevent a small amount of an alkali metal element contained in 7 from diffusing into the gate insulating film 906 in the first shape. In any case, the heat-resistant conductive layer 907 has a resistivity of 10 to 5
It is preferable to set it in the range of 0 μΩcm.

Next, a resist mask 908 is formed by using a photolithography technique. And
A first etching process is performed. In this embodiment, an ICP etching apparatus is used, Cl ₂ and CF ₄ are used as etching gases, and RF (13.5) of 3.2 W / cm ² at a pressure of 1 Pa.
(6 MHz) power is supplied to form plasma. 224 mW / cm ² RF on substrate side (sample stage)
(13.56 MHz) power is applied, thereby applying a substantially negative self-bias voltage. Under these conditions, the etching rate of the W film is about 100 nm / min. First
In the etching process, the time for just etching the W film was estimated based on the etching rate, and the time obtained by increasing the etching time by 20% was set as the etching time.

By the first etching process, conductive layers 909 to 912 having a first tapered shape are formed. The angle of the tapered portion of the conductive layers 909 to 912 is 15 to 30 °
It is formed so that In order to perform etching without leaving a residue, over-etching is performed to increase the etching time at a rate of about 10 to 20%. Silicon oxynitride film (gate insulating film 9) for W film
06) is 2-4 (typically 3),
By the overetching treatment, the exposed surface of the silicon oxynitride film is etched by about 20 to 50 nm.
(FIG. 9 (B))

Then, a first doping process is performed to
An electric impurity element is added to the semiconductor layer. Here, n
A step of adding an impurity element for giving a mold is performed. First shape
The mask 908 having the conductive layer formed thereon is left as it is,
Conductive layers 909 to 912 having a tapered shape are masked
As an impurity element that imparts n-type in a self-aligned manner
It is added by a doping method. The impurity element imparting n-type
And the gate insulating film 906 at the end of the gate electrode
Through to reach the underlying semiconductor layer
Dosage is 1 × 10 to add¹³~ 5 × 10¹⁴at
oms / cm^Two And the acceleration voltage is 80 to 160 keV.
Do it. belongs to Group 15 as an impurity element imparting n-type
Element, typically phosphorus (P) or arsenic (As)
In this case, phosphorus (P) was used. Such a
In the first impurity regions 914 to 917 by the on-doping method
Is 1 × 10²⁰~ 1 × 10^{twenty one}atomic / cm^ThreeConcentration range
, An impurity element imparting n-type is added. (FIG. 9
(C))

In this step, depending on the doping conditions, the impurities flow under the first shape conductive layers 909 to 912, and the first impurity regions 914 to 917 are removed from the first shape.
May overlap with the conductive layers 909 to 912 having the shape shown in FIG.

Next, a second etching process is performed as shown in FIG. The etching process is also performed by an ICP etching apparatus, and CF ₄ and Cl ₂ are used as etching gases.
RF power of 3.2 W / cm ² (13.5
6 MHz), bias power 45 mW / cm ² (13.56 M
(Hz) at a pressure of 1.0 Pa. Conductive layers 918 to 921 having the second shape formed under these conditions
Is formed. A tapered portion is formed at the end, and the tapered shape gradually increases inward from the end. As compared with the first etching process, the ratio of isotropic etching is increased by the amount of the lower bias power applied to the substrate side, and the angle of the tapered portion is 30 to 60 °. The mask 908 is etched and its edge is shaved, and becomes a mask 922. In the step of FIG. 9D, the surface of the gate insulating film 906 is etched by about 40 nm.

Then, an impurity element for imparting n-type is doped under a condition of a higher acceleration voltage with a lower dose than in the first doping process. For example, when the accelerating voltage is 70 to 120
keV, a dose of 1 × 10 ¹³ / cm ² , and the first impurity regions 924 to 92 having an increased impurity concentration.
7 and second impurity regions 928 to 931 in contact with the first impurity regions 924 to 927 are formed. In this step, depending on the doping conditions, the impurity
The second impurity regions 928 to 931 extend below the conductive layers 918 to 921 of the second shape.
921 may also occur. The impurity concentration in the second impurity region is 1 × 10 ¹⁶ to 1 × 10 ^{18 at.}
ms / cm ³ . (FIG. 10A)

Then, as shown in FIG. 10 (B),
Semiconductor layers 902 and 905 forming a p-channel TFT
The impurity region 933 having a conductivity type opposite to the one conductivity type (933)
a, 933b) and 934 (934a, 934b). Also in this case, the second shape conductive layers 918 and 921 are used.
Is used as a mask to add an impurity element imparting a p-type, and an impurity region is formed in a self-aligned manner. At this time, a resist mask 932 is formed on the semiconductor layers 903 and 904 forming the n-channel TFT, and the entire surface is covered. The impurity regions 933 and 934 formed here are formed of diborane (B
It is formed by an ion doping method using ₂ H ₆ ). The concentration of the impurity element imparting p-type in the impurity regions 933 and 934 is
The density is set to 2 × 10 ^{20 to} 2 × 10 ²¹ atoms / cm ³ .

However, these impurity regions 933, 9
34 specifically contains an impurity element imparting n-type.
It can be divided into two areas. The third impurity regions 933a and 934a have a size of 1 × 10 ²⁰ to 1 × 10 ²¹ atoms.
an impurity element imparting n-type at a concentration of s / cm ³ ,
The fourth impurity regions 933b and 934b are 1 × 10 ¹⁷ to 1
Contains an impurity element imparting n-type at a concentration of × 10 ²⁰ atoms / cm ³ . However, these impurity regions 9
The concentration of the p-type imparting impurity element of 33b and 934b is set to 1 × 10 ¹⁹ atoms / cm ³ or more, and the concentration of the p-type imparting impurity element is set to n in the third impurity regions 933a and 934a. By making the concentration of the impurity element giving the mold 1.5 to 3 times,
Since the third impurity region functions as a source region and a drain region of the p-channel TFT, no problem occurs.

Thereafter, as shown in FIG.
A first interlayer insulating film 937 is formed over the conductive layers 918 to 921 having the above-mentioned shape and the gate insulating film 906. First
The interlayer insulating film 937 may be formed using a silicon oxide film, a silicon oxynitride film, a silicon nitride film, or a stacked film in which these are combined. In any case, the first interlayer insulating film 937 is formed from an inorganic insulating material. The thickness of the first interlayer insulating film 937 is 100 to 200 nm. In the case where a silicon oxide film is used as the first interlayer insulating film 937, TEOS and O ₂ are mixed by plasma CVD, the reaction pressure is 40 Pa, the substrate temperature is 300 to 400 ° C., and the high-frequency (13.56 MHz) power density is used. It can be formed by discharging at 0.5 to 0.8 W / cm ² . In the case where a silicon oxynitride film is used as the first interlayer insulating film 937,
The insulating film may be formed using a silicon oxynitride film formed from SiH ₄ , N ₂ O, and NH ₃ by a plasma CVD method, or a silicon oxynitride film formed from SiH ₄ and N ₂ O. The manufacturing conditions in this case are a reaction pressure of 20 to 200 Pa, a substrate temperature of 3
00 to 400 ° C. and a high frequency (60 MHz) power density of 0.
It can be formed at 1 to 1.0 W / cm ² . Also, the first
As the interlayer insulating film 937, a silicon oxynitride hydride film formed from SiH ₄ , N ₂ O, and H ₂ may be used.
Similarly, the silicon nitride film is made of SiH ₄ ,
It can be made from NH ₃ .

Then, a step of activating the impurity elements imparting n-type or p-type added at the respective concentrations is performed. This step is performed by a thermal annealing method using a furnace annealing furnace. In addition, a laser annealing method or a rapid thermal annealing method (RTA method) can be applied. In the thermal annealing method, the oxygen concentration is 1 ppm or less,
Preferably in a nitrogen atmosphere of 0.1 ppm or less 400 ~
The heat treatment is performed at 700 ° C., typically 500 to 600 ° C. In this embodiment, the heat treatment is performed at 550 ° C. for 4 hours.
When a plastic substrate having a low heat-resistant temperature is used as the substrate 501, a laser annealing method is preferably used.

After the activation step, the atmosphere gas is changed.
And in an atmosphere containing 3 to 100% hydrogen,
A heat treatment is performed at 450 ° C. for 1 to 12 hours, and the semiconductor layer is
Perform a quenching step. This process involves thermally excited hydrogen
10 in the semiconductor layer¹⁶ -10¹⁸/cm^ThreeDanglin
This is the step of terminating the bonding. As another means of hydrogenation
Plasma hydrogenation (hydrogen excited by plasma
Use). In any case, the semiconductor layer 9
The defect density in 02 to 905 was 10¹⁶/cm^ThreeThe following
Is desirable, for which hydrogen is added at 0.01 to 0.1 atomic
% May be provided.

Then, a second interlayer insulating film 939 made of an organic insulating material is formed with an average thickness of 1.0 to 2.0 μm. As organic resin materials, polyimide, acrylic,
Polyamide, polyimide amide, BCB (benzocyclobutene) and the like can be used. For example, in the case of using a polyimide of a type that is thermally polymerized after being applied to a substrate, it is formed by firing at 300 ° C. in a clean oven.
In the case of using acrylic, a two-component type is used, and after mixing the main material and the curing agent, the whole surface is applied using a spinner and then pre-heated at 80 ° C. for 60 seconds on a hot plate. Then, it can be formed by firing in a clean oven at 250 ° C. for 60 minutes.

As described above, by forming the second interlayer insulating film 939 with an organic insulating material, the surface can be satisfactorily planarized. In addition, since organic resin materials generally have a low dielectric constant, parasitic capacitance can be reduced. However, since it is hygroscopic and not suitable as a protective film, it is preferable to use it in combination with a silicon oxide film, a silicon oxynitride film, a silicon nitride film, or the like formed as the first interlayer insulating film 937 as in this embodiment. .

Thereafter, a resist mask having a predetermined pattern is formed, and a contact hole formed in each semiconductor layer and reaching an impurity region serving as a source region or a drain region is formed. The contact hole is formed by a dry etching method. In this case, CF ₄ ,
A _second material made of an organic resin material using a mixed gas of O ₂ and He
The first interlayer insulating film 939 is etched first, and then the first interlayer insulating film 937 is etched using CF ₄ and O ₂ as etching gases. Further, in order to increase the selectivity with respect to the semiconductor layer, a contact hole can be formed by switching the etching gas to CHF ₃ and etching the third shape gate insulating film 570.

Then, a conductive metal film is formed by a sputtering method or a vacuum evaporation method, patterned by a mask, and then etched to form source wirings 940 to 943 and drain wirings 944 to 946. Although not shown, in this embodiment, this wiring is formed of a laminated film of a 50 nm-thick Ti film and a 500 nm-thick alloy film (an alloy film of Al and Ti).

Next, a transparent conductive film is formed on the
The pixel electrode 947 is formed by patterning with a thickness of 0 nm and patterning (FIG. 11A). In this embodiment, indium tin oxide (I
A transparent conductive film in which 2 to 20% of zinc oxide (ZnO) is mixed with a TO) film or indium oxide is used.

The pixel electrode 947 is connected to the drain wiring 9
The EL driving T
An electrical connection is formed with the drain region of the FT.

Next, as shown in FIG. 11B, a third interlayer insulating film 949 having an opening at a position corresponding to the pixel electrode 947 is formed. The third interlayer insulating film 949 has insulating properties, functions as a bank, and has a role of separating an EL layer of an adjacent pixel. In this embodiment, a third interlayer insulating film 949 is formed using a resist.

In this embodiment, the thickness of the third interlayer insulating film 949 is set to about 1 μm, and the opening is formed so as to become wider as it approaches the pixel electrode 947, that is, to form a so-called reverse taper. This is formed by forming a resist, covering a portion other than a portion where an opening is to be formed with a mask, irradiating with UV light, and removing the exposed portion with a developing solution.

As in the present embodiment, the third interlayer insulating film 94
9 is formed into an inversely tapered shape, so that EL
When the layer is formed, the EL layer is divided between adjacent pixels. Therefore, even if the EL layer and the third interlayer insulating film 949 have different coefficients of thermal expansion, the EL layer may be cracked or peeled off. Can be suppressed.

In this embodiment, a resist film is used as the third interlayer insulating film. However, depending on the case, polyimide, polyamide, acrylic, BCB may be used.
(Benzocyclobutene), a silicon oxide film, or the like can also be used. The third interlayer insulating film 949 may be an organic substance or an inorganic substance as long as the substance has an insulating property.

Next, an EL layer 950 is formed by an evaporation method, and a cathode (MgAg electrode) 951 and a protection electrode 952 are formed by an evaporation method. At this time, it is preferable that a heat treatment be performed on the pixel electrode 947 before the EL layer 950 and the cathode 951 are formed to completely remove moisture. In this embodiment, Mg is used as the cathode of the EL element.
Although an Ag electrode is used, other known materials may be used.

[0209] As the EL layer 950, a known material can be used. In this embodiment, the hole transport layer (Hole
transporting layer) and emitting layer (Emitting layer)
The EL layer has a two-layer structure of, but any of a hole injection layer, an electron injection layer, and an electron transport layer may be provided. As described above, various examples of the combination have already been reported, and any of the configurations may be used.

In this embodiment, polyphenylene vinylene is formed as a hole transport layer by a vapor deposition method. The light emitting layer is formed by vapor deposition of a 30% to 40% molecular dispersion of PBD of a 1,3,4-oxadiazole derivative in polyvinyl carbazole, and about 1% of coumarin 6 is used as a green light emitting center. Has been added.

Although the protection layer 952 can protect the EL layer 950 from moisture and oxygen, a protection film 953 is more preferably provided. In this embodiment, a 300-nm-thick silicon nitride film is provided as the protective film 953.
This protective film may be formed continuously without opening to the atmosphere after the protective electrode 952.

The protective electrode 952 is provided to prevent the deterioration of the cathode 951, and is typically a metal film containing aluminum as a main component. Of course, other materials may be used. Also,
Since the EL layer 950 and the cathode 951 are very weak to moisture, the protection electrode 952 is formed continuously without opening to the atmosphere,
It is desirable to protect the EL layer from outside air.

The thickness of the EL layer 950 is 10 to 400.
[nm] (typically 60 to 150 [nm]), cathode 951
Has a thickness of 80 to 200 [nm] (typically 100 to 15 nm).
0 [nm]).

Thus, a light emitting device having a structure as shown in FIG. 11B is completed. Note that the pixel electrode 947 and the EL layer 9
The overlapping portion 954 of the cathode 50 and the cathode 951 corresponds to the EL element.

A p-channel TFT 960 and an n-channel TFT 961 are TFTs included in a driving circuit,
OS is formed. The switching TFT 962 and the EL driving TFT 963 are TFTs included in the pixel portion, and the driver circuit TFT and the pixel portion TFT can be formed over the same substrate.

In the case of a light emitting device using an EL element,
The voltage of the power supply of the drive circuit is about 5-6V, and the maximum is 10V
Since the degree is sufficient, deterioration due to hot electrons in the TFT does not cause much problem. Since the driving circuit needs to operate at high speed, it is preferable that the gate capacitance of the TFT is small. Therefore, as in this embodiment, E
In a driver circuit of a light-emitting device using an L element, a second impurity region 929 and a fourth impurity region 933b included in a semiconductor layer of a TFT are formed with gate electrodes 918 and 919, respectively.
It is preferable to adopt a configuration that does not overlap with.

[0217] The method for manufacturing the light emitting device of the present invention is not limited to the manufacturing method described in this embodiment. The light emitting device of the present invention can be manufactured using a known method.

This embodiment can be implemented by freely combining with Embodiments 1 to 4.

[Embodiment 6] In this embodiment, a method for manufacturing a light emitting device which is different from that of Embodiment 5 will be described.

The steps up to the formation of the second interlayer insulating film 939 are the same as in the fifth embodiment. As shown in FIG. 12A, after forming a second interlayer insulating film 939, the passivation film 9 is in contact with the second interlayer insulating film 939.
Form 39.

The passivation film 939 is effective for preventing moisture contained in the second interlayer insulating film 939 from entering the EL layer 950 via the pixel electrode 947 and the third interlayer insulating film 982. is there. When the second interlayer insulating film 939 includes an organic resin material, the provision of the passivation film 939 is particularly effective because the organic resin material contains a large amount of moisture.

In this embodiment, the passivation film 939 is used.
A silicon nitride film was used.

Thereafter, a resist mask having a predetermined pattern is formed, and a contact hole formed in each semiconductor layer and reaching an impurity region serving as a source region or a drain region is formed. The contact hole is formed by a dry etching method. In this case, CF ₄ ,
A _second material made of an organic resin material using a mixed gas of O ₂ and He
The first interlayer insulating film 939 is etched first, and then the first interlayer insulating film 937 is etched using CF ₄ and O ₂ as etching gases. Further, in order to increase the selectivity with respect to the semiconductor layer, a contact hole can be formed by switching the etching gas to CHF ₃ and etching the third shape gate insulating film 570.

Then, a conductive metal film is formed by a sputtering method or a vacuum evaporation method, patterned by a mask, and then etched to form source wirings 940 to 943 and drain wirings 944 to 946. Although not shown, in this embodiment, this wiring is formed of a laminated film of a 50 nm-thick Ti film and a 500 nm-thick alloy film (an alloy film of Al and Ti).

Next, a transparent conductive film is formed on the
A pixel electrode 947 is formed by patterning with a thickness of 0 nm and patterning (FIG. 12A). In this embodiment, indium tin oxide (I
A transparent conductive film in which 2 to 20% of zinc oxide (ZnO) is mixed with a TO) film or indium oxide is used.

The pixel electrode 947 is connected to the drain wiring 9
The EL driving T
An electrical connection is formed with the drain region of the FT.

Next, as shown in FIG. 12B, a third interlayer insulating film 982 having an opening at a position corresponding to the pixel electrode 947 is formed. In this embodiment, when the opening is formed, the side wall is tapered by using a wet etching method. Unlike the case shown in the fifth embodiment, the third
Since the EL layer formed on the interlayer insulating film 982 is not divided, if the side wall of the opening is not sufficiently smooth, the deterioration of the EL layer due to the step becomes a remarkable problem. .

Although a film made of silicon oxide is used as the third interlayer insulating film 982 in this embodiment, depending on the case, polyimide, polyamide, acryl, B
An organic resin film such as CB (benzocyclobutene) can also be used.

Then, the EL is formed on the third interlayer insulating film 982.
Before the layer 950 is formed, it is preferable that the surface of the third interlayer insulating film 982 be subjected to plasma treatment using argon to make the surface of the third interlayer insulating film 982 dense. With the above structure, the third interlayer insulating film 982 to the EL layer 9
It is possible to prevent moisture from entering the 50.

Next, an EL layer 950 is formed by an evaporation method, and a cathode (MgAg electrode) 951 and a protection electrode 952 are formed by an evaporation method. At this time, it is preferable that a heat treatment be performed on the pixel electrode 947 before the EL layer 950 and the cathode 951 are formed to completely remove moisture. In this embodiment, Mg is used as the cathode of the EL element.
Although an Ag electrode is used, other known materials may be used.

Note that a known material can be used for the EL layer 950. In this embodiment, the hole transport layer (Hole
transporting layer) and emitting layer (Emitting layer)
The EL layer has a two-layer structure of, but any of a hole injection layer, an electron injection layer, and an electron transport layer may be provided. As described above, various examples of the combination have already been reported, and any of the configurations may be used.

In this embodiment, polyphenylene vinylene is formed as a hole transport layer by an evaporation method. The light emitting layer is formed by vapor deposition of a 30% to 40% molecular dispersion of PBD of a 1,3,4-oxadiazole derivative in polyvinyl carbazole, and about 1% of coumarin 6 is used as a green light emitting center. Has been added.

Although the protection layer 952 can protect the EL layer 950 from moisture and oxygen, it is more preferable to provide a protection film 953. In this embodiment, a 300-nm-thick silicon nitride film is provided as the protective film 953.
This protective film may be formed continuously without opening to the atmosphere after the protective electrode 952.

The protection electrode 952 is provided to prevent the deterioration of the cathode 951, and is typically a metal film containing aluminum as a main component. Of course, other materials may be used. Also,
Since the EL layer 950 and the cathode 951 are very weak to moisture, the protection electrode 952 is formed continuously without opening to the atmosphere,
It is desirable to protect the EL layer from outside air.

The thickness of the EL layer 950 is 10 to 400.
[nm] (typically 60 to 150 [nm]), cathode 951
Has a thickness of 80 to 200 [nm] (typically 100 to 15 nm).
0 [nm]).

Thus, a light emitting device having a structure as shown in FIG. 12B is completed. Note that the pixel electrode 947 and the EL layer 9
The overlapping portion 954 of the cathode 50 and the cathode 951 corresponds to the EL element.

A p-channel TFT 960 and an n-channel TFT 961 are TFTs included in a driving circuit, and include a CM
OS is formed. The switching TFT 962 and the EL driving TFT 963 are TFTs included in the pixel portion, and the driver circuit TFT and the pixel portion TFT can be formed over the same substrate.

[0238] The method for manufacturing the light emitting device of the present invention is not limited to the manufacturing method described in this embodiment. The light emitting device of the present invention can be manufactured using a known method.

This embodiment can be implemented by freely combining with Embodiments 1 to 4.

(Embodiment 8) In this embodiment, the first embodiment will be described.
The structure of the light emitting device of the present invention shown in FIG. 1 will be described with reference to FIG.

FIG. 13A is a top view of an EL panel included in the light emitting device of the present invention, and FIG.
FIG. 13C is a cross-sectional view taken along line AA ′ of FIG.
It is sectional drawing in BB 'of 3 (A).

A pixel portion 400 provided over a substrate 4001
2, the source signal line driving circuit 4003, and the first and second
A sealing material 4009 is provided so as to surround the gate signal line driving circuits 4004a and 4004b. A sealing material 4008 is provided over the pixel portion 4002, the source signal line driver circuit 4003, and the first and second gate signal line driver circuits 4004a and 4004b. Therefore, the pixel portion 4002, the source signal line driver circuit 4003, and the first and second gate signal line driver circuits 4004a and 4004b are each composed of a substrate 4001, a sealant 4009, and a sealant 4008.
, And is sealed with the filler 4210.

The pixel portion 4 provided on the substrate 4001
002, the source signal line driver circuit 4003, and the first and second gate signal line driver circuits 4004a and 4004b have a plurality of TFTs. In FIG. 13B, typically, the source signal line driving circuit 4 formed on the base film 4010 is formed.
The drive TFT 4201 included in 003 (here, an n-channel TFT and a p-channel TFT are illustrated)
And an EL driving TFT (EL included in the pixel portion 4002)
(TFT) 4202 for controlling the current to the device.

In this embodiment, a p-channel TFT or an n-channel TFT manufactured by a known method is used as the driving TFT 4201, and a p-channel TFT manufactured by a known method is used as the EL driving TFT 4202. Used. The pixel portion 4002 includes an EL driving TFT 42.
A storage capacitor (not shown) connected to the gate 02 is provided.

Driving TFT 4201 and EL Driving TFT
An interlayer insulating film (flattening film) 4301 is formed over the surface 4202, and a pixel electrode (anode) 4203 electrically connected to the drain of the EL driving TFT 4202 is formed thereon. As the pixel electrode 4203, a transparent conductive film having a large work function is used. As the transparent conductive film, a compound of indium oxide and tin oxide, a compound of indium oxide and zinc oxide, zinc oxide, tin oxide, or indium oxide can be used. Further, a material obtained by adding gallium to the transparent conductive film may be used.

[0246] An insulating film 4302 is formed on the pixel electrode 4203, and the insulating film 4302 is formed on the pixel electrode 4203.
An opening is formed on 3. In this opening, an EL (electroluminescence) layer 4204 is formed on the pixel electrode 4203. For the EL layer 4204, a known organic EL material or inorganic EL material can be used. As the organic EL material, there are a low-molecular (monomer) material and a high-molecular (polymer) material, and either may be used.

[0247] As a method for forming the EL layer 4204, a known vapor deposition technique or coating technique may be used. The EL layer may have a stacked structure or a single-layer structure by freely combining a hole injection layer, a hole transport layer, a light-emitting layer, an electron transport layer, or an electron injection layer.

On the EL layer 4204, a cathode 4205 made of a light-shielding conductive film (typically, a conductive film containing aluminum, copper, or silver as a main component or a laminated film of these and another conductive film) is provided. It is formed. In addition, the cathode 4205
It is desirable that moisture and oxygen existing at the interface between the EL layer and the EL layer 4204 be eliminated as much as possible. Therefore, it is necessary to devise a method in which the EL layer 4204 is formed in a nitrogen or rare gas atmosphere and the cathode 4205 is formed without being exposed to oxygen or moisture. In this embodiment, the above-described film formation is made possible by using a multi-chamber type (cluster tool type) film formation apparatus. The cathode 4205 is given a predetermined voltage.

As described above, the pixel electrode (anode) 42
03, an EL element 4303 comprising an EL layer 4204 and a cathode 4205 is formed. Then, a protective film 4303 is formed over the insulating film 4302 so as to cover the EL element 4303. The protective film 4303 is effective in preventing oxygen, moisture, and the like from entering the EL element 4303.

A wiring 4005a is connected to a power supply line or a counter power supply line.
202 is electrically connected to the source region. The lead wiring 4005a passes between the sealing material 4009 and the substrate 4001 and passes through the FP through the anisotropic conductive film 4300.
The wiring is electrically connected to the FPC wiring 4301 included in the C4006. The power supply line or the opposing power supply line is connected to a power supply circuit provided outside the EL panel through the lead wiring 4005a and the FPC 4006.

As the sealing material 4008, a glass material, a metal material (typically, a stainless steel material), a ceramic material, and a plastic material (including a plastic film) can be used. FRP as plastic material
(Fiberglass-Reinforced Pl
aics) plate, PVF (polyvinyl fluoride)
A film, a mylar film, a polyester film, or an acrylic resin film can be used. Further, a sheet having a structure in which an aluminum foil is sandwiched between PVF films or mylar films can also be used.

However, when the direction of light emission from the EL element is directed toward the cover material, the cover material must be transparent. In that case, a transparent material such as a glass plate, a plastic plate, a polyester film or an acrylic film is used.

As the filler 4103, besides an inert gas such as nitrogen or argon, an ultraviolet curable resin or a thermosetting resin can be used, such as PVC (polyvinyl chloride), acrylic, polyimide, epoxy resin, or silicone. Resin, PVB (polyvinyl butyral) or E
VA (ethylene vinyl acetate) can be used. In this embodiment, nitrogen was used as the filler.

In order to expose the filler 4103 to a hygroscopic substance (preferably barium oxide) or a substance capable of adsorbing oxygen, the substrate 400
A concave portion 4007 is provided on the one surface, and a hygroscopic substance or a substance 4207 capable of adsorbing oxygen is arranged. Then, the hygroscopic substance or the substance 4207 capable of adsorbing oxygen is held in the concave part 4007 by the concave part cover material 4208 so that the hygroscopic substance or the substance 4207 capable of adsorbing oxygen is not scattered. Note that the concave portion cover member 4208 has a fine mesh shape and is configured to allow air and moisture to pass therethrough and not allow a hygroscopic substance or a substance 4207 capable of adsorbing oxygen to pass therethrough. By providing the hygroscopic substance or the substance 4207 which can adsorb oxygen, deterioration of the EL element 4303 can be suppressed.

As shown in FIG. 13C, the pixel electrode 42
Simultaneously with the formation of 03, a conductive film 4203a is formed so as to be in contact with the lead wiring 4005a.

The anisotropic conductive film 4300 has a conductive filler 4300a. Substrate 4001 and F
By thermocompression bonding with the PC 4006, the conductive film 4203a on the substrate 4001 and the FPC wiring 4301 on the FPC 4006 are electrically connected by the conductive filler 4300a.

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

(Embodiment 9) In the present invention, by using an EL material capable of utilizing phosphorescence from triplet excitons for emission, external light emission quantum efficiency can be remarkably improved. As a result, the power consumption and the life of the EL element can be reduced,
And weight reduction becomes possible.

Here, a report is shown in which triplet excitons are used to improve the external emission quantum efficiency. (T.Tsutsui, C.Adac
hi, S. Saito, Photochemical Processes in Organized
Molecular Systems, ed.K. Honda, (Elsevier Sci. Pub.,
Tokyo, 1991) p.437.)

The molecular formula of the EL material (coumarin dye) reported in the above article is shown below.

[0261]

Embedded image

(MABaldo, DFO'Brien, Y. You, A. Shou
stikov, S. Sibley, METhompson, SRForrest, Nature
395 (1998) p.151.)

The EL materials (P
The molecular formula of (t complex) is shown below.

[0264]

Embedded image

(MABaldo, S. Lamansky, PEBurrrows,
METhompson, SRForrest, Appl.Phys.Lett., 75 (199
9) p.4.) (T.Tsutsui, M.-J.Yang, M.Yahiro, K.Nakamu
ra, T.Watanabe, T.tsuji, Y.Fukuda, T.Wakimoto, S.Ma
yaguchi, Jpn.Appl.Phys., 38 (12B) (1999) L1502.)

The EL materials (I
The molecular formula of (r complex) is shown below.

[0267]

Embedded image

As described above, if the phosphorescence emission from the triplet exciton can be used, an external emission quantum efficiency three to four times higher than the case of using the fluorescence emission from the singlet exciton can be realized in principle. .

The structure of this embodiment can be implemented by freely combining with any structure of Embodiments 1 to 8.

Embodiment 10 Since a light emitting device using an EL element is of a self-luminous type, it has better visibility in a bright place and a wider viewing angle than a liquid crystal display device. Therefore, it can be used for display portions of various electronic devices.

Electronic equipment using the light emitting device of the present invention include a video camera, a digital camera, a goggle type display (head mounted display), a navigation system, a sound reproducing device (car audio, audio component, etc.), a notebook personal computer, Game devices, portable information terminals (mobile computers, mobile phones, portable game machines, electronic books, etc.), and image reproducing devices provided with recording media (specifically, DVD: Digital Versat)
device that reproduces a recording medium such as an ile Disc and displays the image of the recording medium). In particular,
It is desirable to use a light-emitting device for a portable information terminal that frequently views a screen from an oblique direction, since a wide viewing angle is regarded as important. FIG. 15 shows specific examples of these electronic devices.

FIG. 15A shows an EL display device which 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 light emitting device of the present invention can be used for the display portion 2003.
Since the light-emitting device is a self-luminous type, it does not require a backlight and can have a thinner display portion than a liquid crystal display device. Note that the EL display device includes all information display devices for personal computers, TV broadcast reception, advertisement display, and the like.

FIG. 15B shows a digital still camera, which includes a main body 2101, a display portion 2102, an image receiving portion 2103,
An operation key 2104, an external connection port 2105, a shutter 2106, and the like are included. The light emitting device of the present invention has a display portion 210
2 can be used.

[0274] FIG. 15C illustrates a notebook personal computer, which includes a main body 2201, a housing 2202, and a display portion 2.
203, keyboard 2204, external connection port 220
5, including a pointing mouse 2206 and the like. The light emitting device of the present invention can be used for the display portion 2203.

FIG. 15D shows a mobile computer, which includes a main body 2301, a display portion 2302, and a switch 230.
3, an operation key 2304, an infrared port 2305, and the like. The light emitting device of the present invention can be used for the display portion 2302.

FIG. 15E shows a portable image reproducing apparatus (specifically, a DVD reproducing apparatus) provided with a recording medium, and includes a main body 2401, a housing 2402, a display portion A 2403, a display portion B 2404, and a recording medium ( DVD, etc.) reading unit 240
5, operation keys 2406, a speaker unit 2407, and the like. The display portion A 2403 mainly displays image information, and the display portion B 2404 mainly displays character information.
Can be used. Note that the image reproducing device provided with the recording medium includes a home game machine and the like.

FIG. 15F shows a goggle-type display (head-mounted display).
1, including a display unit 2502 and an arm unit 2503. The light emitting device of the present invention can be used for the display portion 2502.

FIG. 15G shows a video camera, which includes a main body 2601, a display portion 2602, a housing 2603, an external connection port 2604, a remote control receiving portion 2605, and an image receiving portion 260.
6, a battery 2607, a voice input unit 2608, operation keys 2609, and the like. The light emitting device of the present invention has a display portion 260
2 can be used.

[0279] Here, FIG. 15H illustrates a mobile phone, which includes a main body 2701, a housing 2702, a display portion 2703, a voice input portion 2704, a voice output portion 2705, operation keys 2706,
An external connection port 2707, an antenna 2708, and the like are included.
The light emitting device of the present invention can be used for the display portion 2703. Note that the display portion 2703 displays white characters on a black background, so that power consumption of the mobile phone can be suppressed.

If the emission luminance of the EL material becomes higher in the future, it becomes possible to use the front or rear projector by enlarging and projecting the light containing the output image information with a lens or the like.

Also, the above electronic equipment can be connected to the Internet or C
Information distributed through an electronic communication line such as an ATV (cable television) is frequently displayed, and in particular, opportunities to display moving image information are increasing. Since the response speed of the EL material is extremely high, the light-emitting device is preferable for displaying moving images.

[0282] Since the light emitting device consumes power in a light emitting portion, it is desirable to display information so that the light emitting portion is reduced as much as possible. Therefore, when a light emitting device is used for a portable information terminal, particularly a display portion mainly for text information such as a mobile phone or a sound reproducing device, the light emitting portion is driven to form the text information with a non-light emitting portion as a background. It is desirable to do.

As described above, the applicable range of the present invention is extremely wide, and the present invention can be used for electronic devices in various fields. Further, the electronic apparatus of this embodiment may use the light emitting device having any of the structures shown in Embodiments 1 to 9.

[0284]

As described above, according to the present invention, even if an image itself as information contained in a video signal input to a light emitting device is entirely dark, an actually displayed image becomes bright. Can be easier.

When the gradation displayed by a certain pixel is brighter than a certain gradation, the absolute value of the EL drive voltage applied to the EL element of the pixel is increased to increase the luminance of the EL element. May be. According to the above configuration, the pixel displaying a bright gradation becomes brighter, the contrast of the image is increased, the image is sharpened, and the object can be easily recognized.

[0286] Further, by specifying, from the digital video signal input to each pixel, a pixel whose gradation is significantly different from that of an adjacent pixel, the contour of the object is detected, and the pixel of the contour portion of the image is detected. Only the contrast may be increased. According to the above configuration, the outline of the image is extracted, the image is sharpened, and the object can be easily recognized.

[Brief description of the drawings]

FIG. 1 is a block diagram of a light emitting device of the present invention.

FIG. 2 is a circuit diagram of a pixel of a light emitting device of the present invention and a timing chart.

FIG. 3 is a block diagram of a light emitting device of the present invention.

FIG. 4 is a circuit diagram and a timing chart of a pixel of the light emitting device of the present invention.

FIG. 5 is a timing chart of the light emitting device of the present invention.

FIG. 6 is a circuit group for generating first and second digital video signals.

FIG. 7 is a circuit group for generating first and second digital video signals.

FIG. 8 illustrates a structure of a driving circuit.

FIG. 9 illustrates a method for manufacturing a light-emitting device of the present invention.

FIG. 10 illustrates a method for manufacturing a light-emitting device of the present invention.

FIG. 11 illustrates a method for manufacturing a light-emitting device of the present invention.

FIG. 12 illustrates a method for manufacturing a light-emitting device of the present invention.

13A and 13B are a top view and a cross-sectional view of an EL panel included in a light-emitting device of the present invention.

14A and 14B are a circuit diagram and a timing chart of a pixel of a general light-emitting device.

FIG. 15 illustrates an electronic device using the light-emitting device of the present invention.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H05B 33/14 H05B 33/14 A

Claims (22)

[Claims] 1. A light-emitting device provided with a plurality of pixels each having an EL element, wherein a luminance of the EL element in a predetermined period of a period during which the EL element emits light in one frame period is: A light-emitting device, wherein the luminance of the plurality of EL elements is higher than the luminance of the plurality of EL elements in a period other than a predetermined period in the period in which the EL element emits light. 2. A light-emitting device provided with a plurality of pixels having EL elements, wherein a plurality of sub-frame periods are provided in one frame period, and at least one of the plurality of sub-frame periods is provided. The luminance of the EL element in a predetermined period of the period in which the EL element emits light, the luminance of the plurality of EL elements in a period other than the predetermined period of the period in which the EL element emits light; A light-emitting device characterized by being higher in luminance. 3. A light emitting device provided with a plurality of pixels having an EL element, wherein the EL element includes a pixel electrode, a counter electrode, and an EL layer provided between the pixel electrode and the counter electrode. The potential given to the pixel electrode when the EL element emits light is always constant; and changing the level of the potential given to the counter electrode when the EL element emits light. A light-emitting device wherein, in one frame period, the luminance of the EL element in a predetermined period is higher than the luminance of the plurality of EL elements in a period other than the predetermined period. 4. A light emitting device provided with a plurality of pixels having an EL element, wherein a plurality of subframe periods are provided in one frame period, wherein the EL element has a pixel electrode, a counter electrode, and An EL layer provided between the pixel electrode and the counter electrode; a potential applied to the pixel electrode is always constant when the EL element emits light; and the EL element emits light. Sometimes, by changing the level of the potential applied to the counter electrode, in at least one of the plurality of sub-frame periods, the luminance of the EL element in a predetermined period is increased during a period other than the predetermined period. Wherein the luminance of the plurality of EL elements is higher than the luminance of the plurality of EL elements. 5. A light-emitting device provided with a plurality of pixels having an EL element, wherein the EL element includes a pixel electrode, a counter electrode, and an EL layer provided between the pixel electrode and the counter electrode. The potential applied to the counter electrode when the EL element emits light is always constant, and the height of the potential applied to the pixel electrode when the EL element emits light is changed. A light-emitting device wherein, in one frame period, the luminance of the EL element in a predetermined period is higher than the luminance of the plurality of EL elements in a period other than the predetermined period. 6. A light emitting device provided with a plurality of pixels having an EL element, wherein a plurality of subframe periods are provided in one frame period, wherein the EL element has a pixel electrode, a counter electrode, and An EL layer provided between the pixel electrode and the counter electrode; a potential applied to the counter electrode when the EL element emits light is always constant; and the EL element emits light. Sometimes, by changing the level of the potential applied to the pixel electrode, in at least one of the plurality of sub-frame periods, the luminance of the EL element in a predetermined period becomes longer than a period other than the predetermined period. Wherein the luminance of the plurality of EL elements is higher than the luminance of the plurality of EL elements. 7. An EL device, a first EL driving TFT and a second EL driving TFT.
A light-emitting device provided with a plurality of pixels each having an EL driving TFT, a first power supply, and a second power supply, wherein the EL element includes a pixel electrode, a counter electrode, and the counter electrode. An EL layer provided between the electrodes, wherein the potential applied to the counter electrode when the EL element emits light is always constant, and when the EL element emits light, Selecting whether to apply a potential to the pixel electrode from the first power supply via a 1EL driving TFT or applying a potential to the pixel electrode from the second power supply via the second EL driving TFT; By changing the level of the potential applied to the pixel electrode, the luminance of the EL element in a predetermined period in one frame period is higher than the luminance of the plurality of EL elements in a period other than the predetermined period. To do A light-emitting device and butterflies. 8. An EL device, a first EL driving TFT and a second EL driving TFT.
A light emitting device provided with a plurality of pixels having an EL driving TFT, a first power supply, and a second power supply, wherein a plurality of subframe periods are provided in one frame period, and the EL element Has a pixel electrode, a counter electrode, and an EL layer provided between the pixel electrode and the counter electrode. When the EL element emits light, the potential applied to the counter electrode is always constant. When the EL element emits light, a potential is applied to the pixel electrode from the first power supply via the first EL driving TFT, or the second potential is supplied to the pixel electrode via the second EL driving TFT. By selecting whether to apply a potential to the pixel electrode from a power supply and changing the level of the potential applied to the pixel electrode, at least one of the plurality of sub-frame periods is a predetermined period in a predetermined period. The EL
A light-emitting device, wherein the luminance of the element is higher than the luminance of the plurality of EL elements in a period other than the predetermined period. 9. A light emitting device provided with a plurality of pixels having an EL element, operating in a first mode or a second mode, wherein the EL element emits light in the first mode. In the second mode, the luminance of the EL element is always kept constant. In the second mode, the luminance of the EL element in a predetermined period of the period in which the EL element emits light is:
A light-emitting device, wherein the luminance of the plurality of EL elements is higher than the luminance of the plurality of EL elements in a period other than a predetermined period in a period in which the EL element emits light. 10. A light-emitting device provided with a plurality of pixels having an EL element, operating in a first mode or a second mode, wherein in the first mode, the EL element emits light. In the second mode, the luminance of the EL element is always kept constant. In the second mode, the luminance of the EL element in a predetermined period of the period in which the EL element emits light is:
The luminance of the plurality of EL elements is higher than the luminance of the plurality of EL elements in a period other than a predetermined period of the period in which the EL element emits light, and a gradation to be displayed is constant among the plurality of pixels. A light-emitting device which operates in a first mode for darker pixels, and operates in a second mode for pixels of the plurality of pixels whose display gradations are brighter than a certain gradation. 11. A light-emitting device provided with a plurality of pixels each having an EL element, operating in a first mode or a second mode, wherein in the first mode, the EL element emits light. In the second mode, the luminance of the EL element is always kept constant. In the second mode, the luminance of the EL element in a predetermined period of the period in which the EL element emits light is:
The luminance of the plurality of EL elements is higher than the luminance of the plurality of EL elements in a period other than a predetermined period of the period in which the EL element emits light, and display is performed in comparison with an adjacent pixel among the plurality of pixels. Only the pixels whose gradations are brighter than a certain value operate in the second mode, and among the plurality of pixels, the pixels other than the pixels whose gradations to be displayed are brighter than a certain value are compared with the first pixels. A light-emitting device which operates in a mode. 12. A method for driving a light emitting device provided with a plurality of pixels having an EL element, wherein the EL element emits light in a predetermined period of a period during which the EL element emits light in one frame period. A driving method of a light-emitting device, wherein luminance is higher than luminance of the plurality of EL elements in a period other than a predetermined period of a period during which the EL element emits light. 13. A driving method of a light-emitting device provided with a plurality of pixels having EL elements, wherein a plurality of sub-frame periods are provided in one frame period, and at least one of the plurality of sub-frame periods is provided. In the sub-frame period, the luminance of the EL element in a predetermined period of the period in which the EL element emits light is the luminance of the plurality of EL elements in a period other than the predetermined period of the period in which the EL element emits light. A method for driving a light-emitting device, which is higher in luminance than an EL element. 14. A driving method of a light emitting device provided with a plurality of pixels having an EL element, wherein the EL element is provided between a pixel electrode, a counter electrode, and the pixel electrode and the counter electrode. An EL layer, wherein the potential applied to the pixel electrode when the EL element emits light is always constant; and the height of the potential applied to the counter electrode when the EL element emits light. The driving of the light emitting device is characterized in that, in one frame period, the luminance of the EL element in a predetermined period is higher than the luminance of the plurality of EL elements in a period other than the predetermined period in one frame period. Method. 15. A driving method of a light emitting device provided with a plurality of pixels having an EL element, wherein a plurality of sub-frame periods are provided in one frame period, wherein the EL element includes a pixel electrode and a counter electrode. And an EL layer provided between the pixel electrode and the counter electrode. When the EL element emits light, the potential applied to the pixel electrode is always constant, and the EL element emits light. By changing the level of the potential applied to the counter electrode during the operation, the luminance of the EL element in a predetermined period in at least one of the plurality of subframe periods is reduced by the predetermined period. A method of driving the light emitting device, wherein the luminance of the plurality of EL elements is set higher than periods other than the period. 16. A driving method of a light emitting device provided with a plurality of pixels having an EL element, wherein the EL element is provided between a pixel electrode, a counter electrode, and the pixel electrode and the counter electrode. An EL layer, wherein the potential applied to the counter electrode when the EL element emits light is always constant; and the height of the potential applied to the pixel electrode when the EL element emits light. The driving of the light emitting device is characterized in that, in one frame period, the luminance of the EL element in a predetermined period is higher than the luminance of the plurality of EL elements in a period other than the predetermined period in one frame period. Method. 17. A driving method of a light-emitting device provided with a plurality of pixels having an EL element, wherein a plurality of sub-frame periods are provided in one frame period, wherein the EL element includes a pixel electrode and a counter electrode. And an EL layer provided between the pixel electrode and the counter electrode. When the EL element emits light, the potential applied to the counter electrode is always constant, and the EL element emits light. By changing the level of the potential applied to the pixel electrode during the operation, the luminance of the EL element in a predetermined period in at least one of the plurality of sub-frame periods is reduced by the predetermined period. A method of driving the light emitting device, wherein the luminance of the plurality of EL elements is set higher than periods other than the period. 18. A method for driving a light-emitting device provided with an EL element, a plurality of pixels having a first EL driving TFT and a second EL driving TFT, a first power supply, and a second power supply, The EL element includes a pixel electrode, a counter electrode, and an EL layer provided between the pixel electrode and the counter electrode. When the EL element emits light, a potential applied to the counter electrode is When the EL element is emitting light, a potential is applied from the first power supply to the pixel electrode via the first EL driving TFT, or the potential is applied to the pixel electrode via the second EL driving TFT. By selecting whether to apply a potential to the pixel electrode from the second power source and changing the level of the potential applied to the pixel electrode, the luminance of the EL element in a predetermined period in one frame period can be increased. After a predetermined period The driving method of the light emitting device characterized by higher than the luminance of the plurality of EL elements in the period. 19. A method for driving a light emitting device provided with an EL element, a plurality of pixels having a first EL driving TFT and a second EL driving TFT, a first power supply, and a second power supply, A plurality of sub-frame periods are provided in one frame period; the EL element includes a pixel electrode, a counter electrode, and an EL layer provided between the pixel electrode and the counter electrode; When the EL element emits light, the potential applied to the counter electrode is always constant. When the EL element emits light, the first power supply is applied to the pixel electrode from the first power supply TFT via the first EL driving TFT. By selecting whether to apply a potential or applying a potential to the pixel electrode from the second power supply through the second EL driving TFT, and changing the height of the potential applied to the pixel electrode, Subframe period The EL in a predetermined period in at least one sub-frame period between
A method for driving a light-emitting device, wherein the luminance of an element is higher than the luminance of the plurality of EL elements in a period other than the predetermined period. 20. A method for driving a light-emitting device provided with a plurality of pixels having an EL element, wherein the method operates in a first mode or a second mode, and in the first mode, the EL element In the second mode, the luminance of the EL element is kept constant during a period in which the EL element emits light, and in the second mode, the luminance of the EL element in a predetermined period of the period in which the EL element emits light But,
A driving method of a light emitting device, wherein the luminance of the plurality of EL elements is higher than the luminance of the plurality of EL elements in a period other than a predetermined period in a period in which the EL element emits light. 21. A driving method of a light-emitting device provided with a plurality of pixels having an EL element, wherein the driving method operates in a first mode or a second mode, and in the first mode, the EL element In the second mode, the luminance of the EL element is kept constant during a period in which the EL element emits light, and in the second mode, the luminance of the EL element in a predetermined period of the period in which the EL element emits light But,
The luminance of the plurality of EL elements is higher than the luminance of the plurality of EL elements in a period other than a predetermined period of the period in which the EL element emits light, and a gradation to be displayed is constant among the plurality of pixels. A method for driving a light-emitting device, comprising: operating in a first mode for darker pixels; and operating in a second mode for pixels of a plurality of pixels whose displayed gray scales are brighter than a certain gray scale. 22. A driving method of a light-emitting device provided with a plurality of pixels having an EL element, wherein the driving method operates in a first mode or a second mode, and in the first mode, the EL element In the second mode, the luminance of the EL element is kept constant during a period in which the EL element emits light, and in the second mode, the luminance of the EL element in a predetermined period of the period in which the EL element emits light But,
The luminance of the plurality of EL elements is higher than the luminance of the plurality of EL elements in a period other than a predetermined period of the period in which the EL element emits light, and display is performed in comparison with an adjacent pixel among the plurality of pixels. Only the pixels whose gradations are brighter than a certain value operate in the second mode, and among the plurality of pixels, the pixels other than the pixels whose gradations to be displayed are brighter than a certain value are compared with the first pixels. A method for driving a light-emitting device, which operates in a mode.