JP2001159878A - El display device and electronic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EL display device which can display images of bright colors good in balance of light emission luminance of red, blue and green. SOLUTION: The EL display device having plural pixels respectively including plural El elements executes intensity levels by controlling the time when the plural El elements emit light. The voltages impressed to the plural El elements are varied by the colors displayed by the plural pixels respectively including the plural El elements.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EL (electroluminescence) display device formed by forming a semiconductor element (an element using a semiconductor thin film) on a substrate, and an E-display device.
The present invention relates to an electronic device (electronic device) having an L display device as a display.

[0002]

2. Description of the Related Art In recent years, the technology for forming a TFT on a substrate has been greatly advanced, and its application to an active matrix type display device has been developed. In particular, a TFT using a polysilicon film is a conventional TFT using an amorphous silicon film.
Since the field-effect mobility (also referred to as mobility) is higher than that of the FT, high-speed operation is possible. Therefore, the control of the pixel, which has been conventionally performed by the drive circuit outside the substrate, can be performed by the drive circuit formed on the same substrate as the pixel.

Such an active matrix type display device has various advantages such as reduction in manufacturing cost, downsizing of the display device, increase in yield, and reduction in throughput by forming various circuits and elements on the same substrate. Is obtained.

Further, active matrix EL display devices having EL elements as self-luminous elements have been actively studied. The EL display device is an organic EL display (OELD: Organic EL Display) or an organic light emitting diode (OLED: Organic Light Em
It is also called itting Diode.

[0005] The EL display device is of a self-luminous type unlike the liquid crystal display device. An EL element has a structure in which an EL layer is sandwiched between a pair of electrodes. The EL layer usually has a stacked structure. A typical example is a laminated structure of “hole transport layer / light emitting layer / electron transport layer” proposed by Tang et al. Of Eastman Kodak Company. This structure has a very high luminous efficiency, and is currently under research and development.
Most L display devices adopt this structure.

In addition, a hole injection layer / hole transport layer / light emitting layer / electron transport layer, or a hole injection layer / hole transport layer / light emitting layer / electron transport layer / electron injection layer is provided on a pixel electrode. May be used. The EL layer may be doped with a fluorescent dye or the like.

Then, a predetermined voltage is applied to the EL layer having the above structure from a pair of electrodes, whereby recombination of carriers occurs in the light emitting layer to emit light. Note that in this specification, emission of an EL element is referred to as driving of the EL element.

In this specification, a light-emitting element formed by an anode, an EL layer, and a cathode is called an EL element.

[0009]

[Problems to be solved by the invention]

EL display devices are roughly classified into four color display methods, a method of forming three types of EL elements corresponding to R (red), G (green), and B (blue), and a white light emitting EL.
A method in which a device and a color filter are combined, an EL device emitting blue or blue-green light and a phosphor (fluorescent color conversion layer: CC
M) and a method in which a transparent electrode is used as a cathode (opposite electrode) and EL devices corresponding to RGB are stacked.

However, in many organic EL materials, the luminance of red emission is generally lower than that of blue and green. When an organic EL material having such light emission characteristics is used for an EL display device, the luminance of a displayed image in red becomes low.

Further, since red light emission luminance is lower than blue and green light emission luminances, a method of using orange light, which has a slightly shorter wavelength than red light, as red light has been conventionally performed. However, also in this case, the luminance of the red color itself of the image displayed by the EL display device is low, and when an attempt is made to display a red image, the image is displayed as orange.

In view of the above, in an EL display device using organic EL materials having different emission luminances of red, blue, and green, an EL display that displays a desired image with a good balance of emission luminances of red, blue, and green is provided. It is an object to provide a device.

[0014]

The applicant of the present invention uses an EL display device which performs time-division gray scale display and applies a voltage applied to an EL element for displaying a color having a low light emission luminance to a color having a relatively high light emission luminance. Is higher than the voltage applied to the EL element that performs the display.

An EL driving TFT for controlling a current to the EL element is provided with an EL driving TFT for causing the EL element to emit light.
A relatively larger amount of current flows than the switching TFT that controls the driving of the FT. Note that controlling the driving of a TFT means that the TFT is turned on or off by controlling a voltage applied to a gate electrode included in the TFT. In particular, the invention of the present application, in the above configuration, the EL driving TFT of a pixel displaying a color with low emission luminance includes:
A larger amount of current flows than the EL driving TFT of the pixel displaying another color. This raises a problem that the EL driving TFT of a pixel displaying a color with low emission luminance is deteriorated earlier by hot carrier injection than the EL driving TFT of a pixel displaying another color.

Therefore, the present inventor has proposed, in addition to the above-described configuration, an EL driving TF for a pixel displaying a color with low emission luminance as a measure against deterioration of the EL driving TFT due to hot carrier injection.
The length of the LDD region of T is longer than the length of the LDD region of the EL driving TFT of the pixel displaying a color with high emission luminance.

In this specification, the length of the LDD region refers to the length of the LDD in the direction connecting the source region and the drain region.
It means the length of the D area.

At the same time, the channel width (W) of the EL driving TFT of a pixel displaying a color with low emission luminance is changed to the channel width (W) of the EL driving TFT of a pixel displaying a color with relatively high emission luminance. Made larger.

In this specification, the channel width (W) means the length of the channel region in the direction perpendicular to the direction connecting the source region and the drain region.

According to the present invention, with the above structure, even if the amount of current controlled by the EL driving TFT increases due to an increase in the applied voltage, the deterioration of the EL driving TFT can be suppressed. Further, it is possible to adjust the emission luminance of the EL element by the value of the voltage applied to the EL element, and to display a colorful image with a good balance of red, blue, and green emission luminance. Becomes possible. Note that the configuration of the present invention can be used for other than the time-division gray scale display.

The configuration of the present invention will be described below.

According to the present invention, there is provided an EL display device having a plurality of pixels each including a plurality of EL elements, wherein the EL display apparatus performs gradation display by controlling the light emission time of the plurality of EL elements. An EL display device is provided, wherein the voltage applied to the plurality of EL elements differs depending on the color displayed by a plurality of pixels each including the plurality of EL elements.

According to the present invention, a plurality of EL elements, a plurality of EL driving TFTs for respectively controlling the light emission of the plurality of EL elements, and a plurality of switching TFTs for respectively controlling the driving of the plurality of EL driving TFTs. An EL display device having a plurality of pixels, each of which includes a plurality of pixels, wherein the EL display device performs gradation display by controlling a light emitting time of the plurality of EL elements, and is applied to the plurality of EL elements. Voltage varies depending on colors displayed by a plurality of pixels including the plurality of EL elements, respectively.
The L driving TFT is an n-channel TFT, and the length of the LDD region of the plurality of EL driving TFTs in the channel length direction increases as the voltage applied to the plurality of EL elements increases. An EL display device is provided.

According to the present invention, a plurality of EL elements, a plurality of EL driving TFTs for respectively controlling the light emission of the plurality of EL elements, and a plurality of switching TFTs for respectively controlling the driving of the plurality of EL driving TFTs An EL display device having a plurality of pixels, each of which includes a plurality of pixels, wherein the EL display device performs gradation display by controlling a light emitting time of the plurality of EL elements, and is applied to the plurality of EL elements. Voltage varies depending on colors displayed by a plurality of pixels including the plurality of EL elements, respectively.
The EL display device is characterized in that the L driving TFT is an n-channel TFT, and the width of the channel region of the plurality of EL driving TFTs is larger as the voltage applied to the plurality of EL elements is larger. Provided.

According to the present invention, a plurality of EL elements, a plurality of EL driving TFTs for controlling light emission of the plurality of EL elements, and a plurality of switching TFTs for controlling driving of the plurality of EL driving TFTs, respectively. An EL display device having a plurality of pixels, each of which includes a plurality of pixels, wherein the EL display device performs gradation display by controlling a light emitting time of the plurality of EL elements, and is applied to the plurality of EL elements. Voltage varies depending on colors displayed by a plurality of pixels including the plurality of EL elements, respectively.
The L driving TFT is formed of an n-channel TFT, and the length of the LDD region of the plurality of EL driving TFTs in the channel length direction increases as the voltage applied to the plurality of EL elements increases. An EL display device is provided, wherein the width of the channel region of the EL driving TFT increases as the voltage applied to the plurality of EL elements increases.

According to the present invention, a plurality of EL elements, a plurality of EL driving TFTs for respectively controlling the light emission of the plurality of EL elements, and a plurality of switching TFTs for respectively controlling the driving of the plurality of EL driving TFTs An EL display device having a plurality of pixels, each of which includes a plurality of pixels, wherein the EL display device performs gradation display by controlling a light emitting time of the plurality of EL elements, and is applied to the plurality of EL elements. Voltage varies depending on colors displayed by a plurality of pixels including the plurality of EL elements, respectively.
An EL display device is provided, wherein the width of the channel region of the L driving TFT increases as the voltage applied to the plurality of EL elements increases.

The present invention may be characterized in that the time during which the plurality of EL elements emit light is controlled by a digital signal input to a switching TFT.

The present invention may be an electronic device using the EL display device.

[0029]

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows a circuit configuration of the EL display device of the present invention. The EL display device in FIG. 1A includes a pixel portion 101 formed by a TFT formed over a substrate, a data signal side driving circuit 102 and a gate signal side driving circuit 103 arranged around the pixel portion. In this embodiment, EL
The display device has one data signal side drive circuit and one gate signal side drive circuit, but in the present invention, there may be two data signal side drive circuits. Further, there may be two gate signal side drive circuits.

The data signal side driving circuit 102 basically includes a shift register 102a, a latch (A) 102b, and a latch (B) 102c. The shift register 102a has a clock pulse (CK) and a start pulse (SP).
, A digital data signal (Digital Data Signals) is input to the latch (A) 102b, and a latch signal (Latch Signals) is input to the latch (B) 102c.

A digital data signal input to the pixel portion is formed by a time division gray scale data signal generation circuit 114. This circuit converts a video signal (a signal including image information) composed of an analog signal or a digital signal into a digital data signal for performing a time-division gradation, and a timing pulse necessary for performing a time-division gradation display. And the like.

Typically, the time-division grayscale data signal generating circuit 114 includes means for dividing one frame period into a plurality of subframe periods corresponding to n-bit (n is an integer of 2 or more) grayscales. Means for selecting an address period and a sustain period in the plurality of subframe periods, and selecting the sustain period as Ts1: Ts2: Ts3: ...: Ts
(n-1): Ts (n) = 2 ⁰ : 2 ^-1 : 2 ^-2 : ...: 2- ^(n-2) : 2
^-(n-1) .

This time division gray scale data signal generation circuit 114
May be provided outside the EL display device of the present invention. In that case, the digital data signal formed there is input to the EL display device of the present invention. In this case, an electronic device having the EL display device of the present invention as a display includes the EL display device of the present invention and the time-division grayscale data signal generation circuit as separate components.

The time-division gradation data signal generation circuit 11
4 may be mounted on the EL display device of the present invention in the form of an IC chip or the like. In that case, a digital data signal formed by the IC chip is input to the EL display device of the present invention. In this case, an electronic device having the EL display device of the present invention as a display includes the EL display device of the present invention mounted with an IC chip including a time-division grayscale data signal generation circuit as a component.

Finally, the time division gray scale data signal generating circuit 114 is connected to the pixel section 101 and the data signal side driving circuit 1.
02 and the gate signal side drive circuit 103 can be formed using TFTs on the same substrate. In this case, if a video signal including image information is input to the EL display device, all the signals can be processed on the substrate. Of course, in this case, it is desirable that the time-division grayscale data signal generating circuit is formed of a TFT having a polysilicon film as an active layer used in the present invention. In this case, in the electronic device having the EL display device of the present invention as a display, the time-division grayscale data signal generating circuit is
Since the electronic device is incorporated in the L display device itself, the size of the electronic device can be reduced.

In the pixel portion 101, a plurality of pixels 104 are arranged in a matrix. FIG. 1 is an enlarged view of the pixel 104.
It is shown in (B). In FIG. 1B, reference numeral 105 denotes a switching TFT. The gate electrode of the switching TFT 105 is connected to a gate wiring 106 for inputting a gate signal. One of a source region and a drain region of the switching TFT 105 is connected to a data wiring (also referred to as a source wiring) 107 for inputting a digital data signal, and the other is connected to a gate electrode of the EL driving TFT.

The digital data signal is "0" or "1"
One of the digital data signals “0” and “1” has a potential of Hi and the other has a potential of Lo.

The source region of the EL driving TFT 108 is connected to the power supply line 111, and the drain region is the EL region.
Connected to element 110.

The EL element 110 is an EL driving TFT 108.
And a counter electrode provided opposite the pixel electrode with the EL layer interposed therebetween. The counter electrode is connected to a common power supply 112 maintained at a constant potential (common potential). It is connected.

When the anode of the EL element 110 is used as a pixel electrode and the cathode is used as a counter electrode, the EL driving TFT 108 is preferably a p-channel TFT.

When the cathode of the EL element 110 is used as a pixel electrode and the anode is used as a counter electrode, the EL driving TFT 108 is preferably an n-channel TFT.

The potential applied to the power supply line 111 is called an EL drive potential. The EL drive potential when the EL element emits light is called an ON EL drive potential. An EL driving potential when the EL element does not emit light is referred to as an OFF EL driving potential.

Further, the difference between the EL drive potential and the common potential is called an EL drive voltage. The EL drive voltage when the EL element is emitting light is called an ON EL drive voltage. Also E
The EL driving voltage when the L element does not emit light is referred to as an OFF EL driving voltage.

The value of the ON EL drive voltage applied to the power supply line 111 changes depending on the color (red, green, blue) displayed by the corresponding pixel. For example, organic EL used
When the red light emission luminance of the material is lower than the blue and green light emission luminances, the ON EL drive voltage applied to the power supply line connected to the red display pixel is connected to the blue and green display pixels On the power supply line
It is set higher than the L drive voltage.

Note that a resistor may be provided between the drain region of the EL driving TFT 108 and the pixel electrode of the EL element 110. By providing a resistor, EL
By controlling the amount of current supplied from the driving TFT to the EL element, it is possible to prevent the influence of variations in the characteristics of the EL driving TFT. The resistor may be any element having a resistance value sufficiently larger than the ON resistance of the EL driving TFT 108, and thus the structure is not limited. The on-resistance is T
This is a value obtained by dividing the drain voltage of the TFT by the drain current flowing at that time when the FT is in the ON state. The resistance value of the resistor is 1 kΩ to 50 MΩ (preferably 10 kΩ).
10 MΩ, more preferably 50 kΩ to 1 MΩ). It is preferable to use a semiconductor layer having a high resistance value as the resistor because formation is easy.

When the switching TFT 105 is in a non-selected state (OFF state), the EL driving TFT 108
Capacitor 113 is provided to hold the gate voltage. This capacitor 113 is a switching TFT
The drain region 105 is connected to the power supply line 111.

Next, the time division gray scale display will be described with reference to FIGS. Here, a case where 2 ⁿ gray scale display is performed by the n-bit digital driving method will be described.

First, one frame period is divided into n sub-frame periods (SF1 to SFn). Note that a period in which all the pixels in the pixel portion display one image is referred to as one frame period. In a normal EL display, the oscillation frequency is 6
A frame period of 0 Hz or more, that is, 60 or more frames per second is provided, and 60 or more images are displayed per second. When the number of images displayed per second becomes less than 60, flickering of the image such as flicker starts to be noticeable visually. Note that a period obtained by further dividing one frame period into a plurality is referred to as a sub-frame period. As the number of gradations increases, the number of divisions in one frame period also increases, and the driving circuit must be driven at a high frequency. (Fig. 2)

One subframe period is divided into an address period (Ta) and a sustain period (Ts). The address period is a time required to input data to all pixels in one subframe period, and the sustain period (also called a lighting period) indicates a period during which the EL element emits light.

The n subframe periods (SF1 to SF)
n) address periods (Ta1 to Tan) respectively
Are all constant in length. The sustain periods (Ts) of SF1 to SFn are represented by Ts1 to Tsn, respectively.
And

The length of the sustain period is Ts1: Ts
2: Ts3:...: Ts (n−1): Tsn = 2 ⁰ : 2 ⁻¹ :
2 ^-2 : ...: 2- ^(n-2) : Set so as to be 2- ^(n-1) .
However, SF1 to SFn may appear in any order. A desired gray scale display out of 2 ⁿ gray scales can be performed by the combination of the sustain periods.

First, the power supply line 111 is kept at the OFF EL drive potential, and the gate wiring 106 is turned off.
, And all the switching TFTs 105 connected to the gate wiring 106 are turned on. Note that the OFF EL driving potential is almost the same as the common potential so that the EL element does not emit light.

Then, the switching TFT 105 is turned on.
After the state is turned on or simultaneously with the ON state, a digital data signal having information of “0” or “1” is input to the source region of the switching TFT 105.

The digital data signal is a switching TF.
The signal is input to and held by the capacitor 113 connected to the gate electrode of the EL driving TFT 108 via T105.
A period until a digital data signal is input to all pixels is an address period.

When the address period ends, the power supply line 1
11 is kept at the ON EL driving potential, the switching TFT is turned off, and the digital data signal held at the capacitor 113 is transmitted to the EL driving TFT 1.
08 is input to the gate electrode.

Note that the height of the ON EL drive potential is a height having a potential difference from the common potential that the EL element emits light. More preferably, the potential applied to the anode is higher than the potential applied to the cathode. That is, when the anode is used as the pixel electrode, it is desirable that the ON EL drive potential is higher than the common potential. Conversely, when the cathode is used as the pixel electrode, it is desirable that the ON EL drive potential is lower than the common potential.

In this embodiment, when the digital data signal has information of "0", the EL driving TFT
Reference numeral 108 denotes an OFF state, and the ON EL drive voltage applied to the power supply line 111 is not applied to the anode (pixel electrode) of the EL element 110.

Conversely, if the information has the information “1”,
The L driving TFT 108 is turned on, and the power supply line 1
The ON EL drive voltage applied to 11 is applied to the anode (pixel electrode) of the EL element 110.

As a result, the EL element 110 of the pixel to which the digital data signal having the information “0” is applied does not emit light. Then, the EL element 110 included in the pixel to which the digital data signal having the information “1” is applied emits light. A period until the light emission ends is a sustain period.

The period in which the EL element 110 emits light (the pixel is turned on) is one of Ts1 to Tsn. Here, it is assumed that a predetermined pixel is turned on during a period of Tsn.

Next, the address period is started again, and after the data signals are input to all the pixels, the sustain period is started. At this time, any of the periods Ts1 to Ts (n-1) is the sustain period. Here, it is assumed that a predetermined pixel is turned on during a period of Ts (n-1).

Thereafter, the same operation is repeated for the remaining n-2 subframes, and Ts (n-2), Ts
(N-3)... It is assumed that Ts1 and a sustain period are set, and a predetermined pixel is turned on in each subframe.

When n sub-frame periods appear, one frame period has ended. At this time, by integrating the length of the sustain period during which the pixel is lit, in other words, the length of the sustain period immediately after the address period in which the digital data signal having the information of “1” is applied to the pixel, the floor of the pixel is integrated. The tone is determined. For example, when n = 8, if the luminance when the pixel emits light in all sustain periods is 100%, if the pixel emits light in Ts1 and Ts2, 75% luminance can be expressed, and Ts3 and Ts
When 5 and Ts8 are selected, 16% luminance can be expressed.

Further, in the present invention, the power supply line 1
The value of the ON EL drive voltage applied to the pixel 11 is changed depending on the color (red, green, blue) displayed by the corresponding pixel. For example, when the emission luminance of red of the organic EL material used is lower than the emission luminance of blue and green, the ON EL drive voltage applied to the power supply line connected to the pixel displaying red is
It is set to be higher than the ON EL drive voltage applied to the power supply line connected to the pixels displaying blue and green.

It is important to change the value of the potential of the digital data signal and the value of the gate signal at the same time as changing the value of the ON EL drive potential.

Next, the EL driving TFT according to the present invention is described.
Will be described. In the present invention, the EL driving TFT is a p-channel TFT or an n-channel TF.
It is composed of T. EL composed of p-channel TFT
The driving TFT has no LDD region and is an n-channel type TF
The EL driving TFT composed of T has an LDD region.

The EL driving TFT is a switching TFT.
The amount of current to be controlled is greater than that. In particular, the amount of current controlled by the EL driving TFT of a pixel displaying a color with low emission luminance is larger than that of the EL driving TFT of a pixel displaying another color.

When the EL driving TFT is a p-channel type TFT, the EL driving TFT of a pixel displaying a color having a low emission luminance is used.
The channel width (W) of the FT is set to be larger than the channel width (W) of the EL driving TFT of a pixel displaying a color having a relatively high emission luminance. With the above structure, even if the amount of current controlled by the EL driving TFT of a pixel displaying a color with low emission luminance is larger than that of the EL driving TFT of a pixel displaying another color, a color with low emission luminance is displayed. T for EL drive of pixel
It is possible to prevent the FT from being quickly deteriorated by hot carrier injection.

Even when the EL driving TFT is an n-channel TFT, the channel width (W) of the EL driving TFT of a pixel displaying a color having a low emission luminance is determined by changing the channel width (W) of the pixel displaying a color having a relatively high emission luminance. Channel width of EL driving TFT (W)
By making it larger, it is possible to prevent the EL driving TFT of a pixel displaying a color with low emission luminance from being quickly deteriorated by hot carrier injection.

In the case where the EL driving TFT is an n-channel TFT, the length of the LDD region of the EL driving TFT of a pixel displaying a color with low emission luminance can be obtained without having the above configuration.
T for EL driving of a pixel displaying a color having a relatively high emission luminance
By making the length longer than the length of the LDD region of the FT, it is possible to prevent the EL driving TFT of a pixel displaying a color with low emission luminance from being deteriorated by hot carrier injection. EL
When the driving TFT is an n-channel TFT, the above-described configuration in which the channel width (W) of the EL driving TFT differs depending on the pixel, and the configuration in which the EL driving TFT differs depending on the pixel.
A configuration in which the length of the LDD region of the FT is different may be provided.

According to the present invention, the emission luminance of an EL element included in a target pixel can be adjusted by the value of an ON EL drive potential applied to the EL element. And a bright image with a good balance of light emission luminance can be displayed. Further, even if the amount of current controlled by the EL driving TFT increases due to the increase of the ON EL driving voltage, the EL
Deterioration of the driving TFT can be suppressed.

Further, according to the present invention, it is possible to perform clear multi-tone display by time-division tone display. Further, even if the amount of current controlled by the EL driving TFT increases due to an increase in the applied voltage, deterioration of the EL driving TFT can be suppressed.

[0074]

Example (Example 1)

In this embodiment, a description will be given of a time-division gray scale display in the case of performing 256-color (16.770,000 colors) full-color display by an 8-bit digital drive system. In this embodiment, the driving of an EL display device using an organic EL material whose emission luminance of red is lower than emission luminance of blue and green will be described.

First, one frame period is divided into eight sub-frame periods (SF1 to SF8). EL of this embodiment
In the display device, the oscillation frequency is set to 60 Hz and 6
0 frame periods are provided, and 60 images are displayed per second. (Fig. 3)

One subframe period is divided into an address period (Ta) and a sustain period (Ts). S
Address periods (Ta1 to Ta8) of F1 to SF8 respectively.
The length of Ta8) is all constant. The sustain period (Ts) of each of SF1 to SF8 is represented by Ts1.
To Ts8.

The length of the sustain period is Ts1: Ts
2: Ts3: Ts4: Ts5: Ts6: Ts7: Ts8
= 1: 1/2: 1/4: 1/8: 1/16: 1/32:
1/64: Set to be 1/128. Where S
The order in which F1 to SF8 appear may be any order. A desired gradation display among the 256 gradations can be performed by the combination of the sustain periods.

First, the power supply line is kept at the OFF EL drive potential, a gate signal is applied to the gate wiring, and all the switching TFTs connected to the gate wiring are turned on. In this embodiment, the OFF EL
The driving potential is set to 0V. In this embodiment, the anode of the EL element is connected to a power supply line as a pixel electrode, and the cathode is connected to a common power supply as a counter electrode.

After the switching TFT is turned on or at the same time as the switching TFT is turned on, a digital data signal having information “0” or “1” is input to the source region of the switching TFT.

The digital data signal is a switching TF
Via T, it is input to and held by a capacitor connected to the gate electrode of the EL driving TFT. A period until a digital data signal is input to all pixels is an address period.

After the end of the address period, the power supply line is maintained at the ON EL drive potential and the switching TF
T is turned off, and the digital data signal held in the capacitor is input to the gate electrode of the EL driving TFT. In this embodiment, during the sustain period,
The power supply line connected to the red display pixel is maintained at the ON EL drive potential of 10 V. The power supply lines connected to the green and blue display pixels are maintained at a 5V ON EL drive potential.

In the present embodiment, when the digital data signal has information of “0”, the EL driving TFT is turned off, and the ON EL applied to the power supply line is turned off.
The driving voltage is not applied to the anode (pixel electrode) of the EL element.

On the other hand, when the information has “1”,
The L driving TFT is turned on, and the ON EL driving voltage applied to the power supply line is applied to the anode (pixel electrode) of the EL element.

As a result, the EL element of the pixel to which the digital data signal having the information of “0” is applied does not emit light. Then, the EL element included in the pixel to which the digital data signal having the information “1” is applied emits light. A period until the light emission ends is a sustain period.

The period in which the EL is made to emit light (the pixels are turned on) is any one of Ts1 to Ts8. Here, it is assumed that a predetermined pixel is turned on during the period Ts8.

Next, the address period is entered again, and after the data signals are inputted to all the pixels, the sustain period is entered. At this time, any of the periods Ts1 to Ts7 is a sustain period. Here, it is assumed that a predetermined pixel is turned on during Ts7.

Hereinafter, it is assumed that the same operation is repeated for the remaining six sub-frames, Ts6, Ts5... Ts1 are sequentially set, and a predetermined pixel is turned on in each sub-frame.

When eight sub-frame periods appear, one frame period has ended. At this time, by integrating the length of the sustain period during which the pixel is turned on, in other words, the length of the sustain period immediately after the address period in which the digital data signal having the information of “1” is applied to the pixel, the gradation of the pixel is increased. Decided. For example, assuming that the luminance when the pixel emits light in all the sustain periods is 100%, when the pixel emits light in Ts1 and Ts2, it becomes 7%.
5% luminance can be expressed, and when Ts3, Ts5 and Ts8 are selected, 16% luminance can be expressed.

It is important to change the values of the potentials of the digital data signal and the gate signal at the same time as changing the value of the EL drive potential.

With the above configuration, the present invention makes it possible to adjust the emission luminance of the EL element included in the target pixel by the value of the EL drive voltage applied to the EL element, and furthermore, it is possible to perform time-division gradation display. It has become possible to perform clear multi-tone display. Specifically, an EL element using an organic EL material whose emission luminance of red is lower than emission luminance of blue and green has a good balance of emission luminance of red, blue, and green, and displays a colorful image. Becomes possible. In addition, time-division gradation display is performed by a digital signal, and a high-definition image with good color reproducibility without gradation failure due to variation in characteristics of the EL driving TFT can be obtained.

(Example 2)

Next, regarding the EL display device of the present invention,
The outline of the cross-sectional structure will be described with reference to FIG. In this embodiment, an example in which the cathode of the EL element is connected to the drain region of the EL driving TFT will be described.

In FIG. 4, reference numeral 11 denotes a substrate, and 12 denotes an insulating film serving as a base (hereinafter, referred to as a base film). As the substrate 11, a translucent substrate, typically, a glass substrate, a quartz substrate,
A glass ceramic substrate or a crystallized glass substrate can be used. However, it must withstand the maximum processing temperature during the manufacturing process.

The base film 12 is particularly effective when a substrate containing mobile ions or a substrate having conductivity is used, but may not be provided on a quartz substrate. As the base film 12, an insulating film containing silicon (silicon) may be used. Note that, in this specification, the “insulating film containing silicon” refers specifically to silicon such as a silicon oxide film, a silicon nitride film, or a silicon nitride oxide film (SiOxNy: x and y are arbitrary integers). On the other hand, it refers to an insulating film containing oxygen or nitrogen at a predetermined ratio.

Reference numeral 201 denotes a switching TFT, and reference numeral 202 denotes an EL driving TFT, both of which are formed by n-channel TFTs. In the present invention, the switching TF
The T and EL driving TFTs may be either n-channel TFTs or p-channel TFTs.

However, since the field-effect mobility of the n-channel TFT is larger than the field-effect mobility of the p-channel TFT, the operation speed is high and a large current can easily flow. Further, even when the same amount of current flows, the TFT size can be made smaller in the n-channel TFT. Therefore, the n-channel TFT is changed to E
It is more preferable to use the TFT as the L driving TFT because the effective light emitting area of the image display unit is increased.

The switching TFT 201 includes a source region 13, a drain region 14, LDD regions 15a to 15d,
An active layer including an isolation region 16 and channel formation regions 17a and 17b, a gate insulating film 18, and gate electrodes 19a and 19a.
9b, a first interlayer insulating film 20, a source wiring 21, and a drain wiring 22. The gate insulating film 1
8 or the first interlayer insulating film 20 may be common to all TFTs on the substrate, or may be different depending on the circuit or element.

The switching TFT 2 shown in FIG.
Reference numeral 01 denotes a so-called double gate structure in which the gate electrodes 19a and 19b are electrically connected. Of course, not only a double gate structure but also a so-called multi-gate structure (a structure including an active layer having two or more channel forming regions connected in series) such as a triple gate structure may be used.

The multi-gate structure is extremely effective in reducing the off-state current. If the off-state current of the switching TFT is made sufficiently low, the EL driving TFT 202
The minimum capacitance required by the capacitor connected to the gate electrode can be suppressed. That is, since the area of the capacitor can be reduced, the multi-gate structure is effective in increasing the effective light emitting area of the EL element.

Further, in the switching TFT 201, the LDD regions 15a to 15d
Are provided so as not to overlap with the gate electrodes 17a and 17b through the gate electrode. Such a structure is very effective in reducing off-state current. The length (width) of the LDD regions 15a to 15d is 0.5 to 3.5 μm, typically 2.0 to 2.0 μm.
The thickness may be set to 5 μm.

It is more preferable to provide an offset region (a region made of a semiconductor layer having the same composition as the channel formation region and to which a gate voltage is not applied) between the channel formation region and the LDD region in order to reduce off-state current. Also,
In the case of a multi-gate structure having two or more gate electrodes, an isolation region 16 provided between channel formation regions
(A region where the same impurity element is added at the same concentration as the source region or the drain region) is effective in reducing off-state current.

Next, the EL driving TFT 202 includes an active layer including a source region 26, a drain region 27, an LDD region 28, and a channel forming region 29, and a gate insulating film 18.
, A gate electrode 30, a first interlayer insulating film 20, a source wiring 31 and a drain wiring 32.
In this embodiment, the EL driving TFT 202 is an n-channel TFT.

The drain region 14 of the switching TFT 201 is connected to the gate electrode 3 of the EL driving TFT 202.
Connected to 0. Although not shown, specifically, the gate electrode 30 of the EL driving TFT 202 is electrically connected to the drain region 14 of the switching TFT 201 via a drain wiring (also referred to as a connection wiring) 22. The gate electrode 30 has a single gate structure, but may have a multi-gate structure. The source wiring 31 of the EL driving TFT 202 is connected to a power supply line (not shown).

The EL driving TFT 202 is an element for controlling the amount of current injected into the EL element, and a relatively large amount of current flows. Therefore, it is preferable that the channel width (W) is designed to be larger than the channel width of the switching TFT. It is preferable that the channel length (L) is designed to be long so that an excessive current does not flow through the EL driving TFT 202. Desirably 0.5 to 2 per pixel
μA (preferably 1 to 1.5 μA).

In particular, in the present invention, the EL drive TFT of a pixel displaying a color having low emission luminance has a larger control current than the EL driving TFT of a pixel displaying another color. Therefore, the pixel E that displays a color with low emission luminance
The L driving TFT is deteriorated earlier by hot carrier injection than the EL driving TFT of a pixel displaying another color.

Therefore, in the present invention, the length of the LDD region of the EL driving TFT of the pixel displaying a color with low emission luminance is set to the length of the LDD region of the EL driving TFT of the pixel displaying a color with relatively high emission luminance. Longer than the length. This makes it possible to suppress the deterioration of the EL driving TFT due to an increase in the amount of current controlled by the EL driving TFT.

Further, the thickness of the active layer (particularly, the channel forming region) of the EL driving TFT 202 is increased (preferably 50 to 100 nm, more preferably 60 to 80).
nm), deterioration of the TFT may be suppressed. Conversely, in the case of the switching TFT 201, from the viewpoint of reducing the off current, the thickness of the active layer (particularly, the channel formation region) is reduced (preferably 20 to 50 n).
m, more preferably 25 to 40 nm) is also effective.

In the above, the structure of the TFT provided in the pixel has been described. At this time, a drive circuit is also formed. FIG. 4 shows a CMO as a basic unit for forming a driving circuit.
The S circuit is shown.

In FIG. 4, a TFT having a structure for reducing hot carrier injection while keeping the operating speed as low as possible is replaced with an n-channel type TFT 204 of a CMOS circuit.
Used as Note that the drive circuit here refers to a data signal side drive circuit and a gate signal side drive circuit. Of course, other logic circuits (level shifter, A / D converter,
It is also possible to form a signal dividing circuit or the like.

An n-channel TFT 204 of a CMOS circuit
The active layer is composed of a source region 35, a drain region 36, an LD
The LDD region 37 includes a D region 37 and a channel forming region 38, and overlaps with the gate electrode 39 via the gate insulating film 18.

The LDD region 37 is formed only on the drain region 36 side.
Is formed in order not to lower the operation speed. Further, the n-channel TFT 204 does not need to care much about the off-current value, and it is better to give much importance to the operation speed. Therefore, it is desirable that the LDD region 37 is completely overlapped with the gate electrode and the resistance component is reduced as much as possible. That is, it is better to eliminate the so-called offset.

Also, a p-channel type TFT of a CMOS circuit
In the case of 205, since the deterioration due to hot carrier injection is hardly noticed, it is not necessary to particularly provide an LDD region. Therefore, the active layer includes the source region 40, the drain region 41, and the channel forming region 42, and the gate insulating film 18
And a gate electrode 43 are provided. Of course, n-channel type T
It is also possible to provide an LDD region similarly to the FT 204 and take measures against hot carriers.

Further, the n-channel TFT 204 and the p-channel TFT 205 have source wirings 44 and 45 on the source region with the first interlayer insulating film 20 interposed therebetween. The drain regions of the n-channel TFT 204 and the p-channel TFT 205 are electrically connected to each other by the drain wiring 46.

Next, a first passivation film 47 has a thickness of 10 nm to 1 μm (preferably 200 to 50 μm).
0 nm). As a material, an insulating film containing silicon (in particular, a silicon nitride oxide film or a silicon nitride film is preferable) can be used. The passivation film 47 has a role of protecting the formed TFT from alkali metals and moisture. Finally, TFT (especially TF for EL driving)
The EL layer provided above T) contains an alkali metal such as sodium. That is, the first passivation film 47 converts these alkali metals (mobile ions) into TFTs.
Also acts as a protective layer that does not penetrate the side.

Reference numeral 48 denotes a second interlayer insulating film, and TF
It has a function as a flattening film for flattening a step formed by T. As the second interlayer insulating film 48, an organic resin film is preferable, and polyimide, polyamide, acrylic, B
It is preferable to use CB (benzocyclobutene) or the like. These organic resin films have an advantage that a good flat surface is easily formed and the relative dielectric constant is low. Since the EL layer is very sensitive to irregularities, it is desirable that the step due to the TFT is almost completely absorbed by the second interlayer insulating film. In order to reduce the parasitic capacitance formed between the gate wiring or data wiring and the cathode of the EL element, it is desirable to provide a thick material having a low relative dielectric constant. Therefore, the film thickness is preferably 0.5 to 5 μm (preferably 1.5 to 2.5 μm).

Reference numeral 49 denotes a protection electrode, which is an electrode for connecting the pixel electrode 51 of each pixel. Protection electrode 49
It is preferable to use a low-resistance material containing aluminum (Al), copper (Cu), or silver (Ag). The protective electrode 49 can also be expected to have a heat radiation effect of reducing heat generation of the EL layer. The protection electrode 49 is a TFT for EL driving.
It is formed to be connected to the drain wiring 32 of 202.

On protective electrode 49, a third interlayer insulating film 50 made of a silicon oxide film, a silicon nitride oxide film or an organic resin film is provided with a thickness of 0.3 to 1 μm. The third interlayer insulating film 50 has an opening formed by etching on the protective electrode 49, and the edge of the opening is etched so as to have a tapered shape. The angle of the taper is preferably 10 to 60 ° (preferably 30 to 50 °).

The pixel electrode (E) is formed on the third interlayer insulating film 50.
An L element cathode 51 is provided. As the cathode 51,
Magnesium (Mg), lithium (L
i) or a material containing calcium (Ca) is used.
Preferably, MgAg (Mg and Ag are Mg: Ag = 10:
An electrode made of the material mixed in step 1) may be used. Other examples include a MgAgAl electrode, a LiAl electrode, and a LiFAl electrode.

On the pixel electrode 51, an EL layer 52 is provided. The EL layer 52 is used in a single layer or a laminated structure.
Luminous efficiency is better when used in a laminated structure. Generally, a hole injection layer / a hole transport layer / a light emitting layer / an electron transport layer are formed in this order on a pixel electrode. A structure such as a hole transport layer / light emitting layer / electron transport layer / electron injection layer may be used. In the present invention, any known structure may be used, and the EL layer may be doped with a fluorescent dye or the like.

The EL display device can be roughly classified into four color display methods, R (red), G (green), B (blue).
A method of forming three kinds of EL elements corresponding to the above, a method of combining a white light emitting EL element and a color filter, and a combination of a blue or blue-green light emitting EL element and a phosphor (fluorescent color conversion layer: CCM) Method, cathode (counter electrode)
There is a method of superposing EL elements corresponding to RGB using transparent electrodes.

FIG. 4 shows three types of E corresponding to RGB.
This is an example in which a method of forming an L element is used. In addition,
Although only one pixel is shown in FIG. 4, pixels having the same structure are formed corresponding to the respective colors of red, green and blue, whereby color display can be performed.

The present invention can be carried out irrespective of the light emitting method, and all the above four methods can be used in the present invention. However, since the fluorescent substance has a slow response speed as compared with the EL and may cause a problem of afterglow, a method using no fluorescent substance is desirable.

Next, a counter electrode (anode of an EL element) 53 made of a transparent conductive film is formed on the EL layer. In this embodiment, ITO (Indium Tin Oxi) is used as the transparent conductive film.
de) was used.

The laminated body composed of the EL layer 52 and the counter electrode 53 needs to be formed individually for each pixel.
Is extremely weak to moisture, so that ordinary photolithography cannot be used. Therefore, it is preferable to selectively form the film by a vapor phase method such as a vacuum evaporation method, a sputtering method, and a plasma CVD method using a physical mask material such as a metal mask.

As a method for selectively forming the EL layer, an ink jet method, a screen printing method, a spin coating method, or the like can be used.

Numeral 54 denotes a second passivation film having a thickness of 10 nm to 1 μm (preferably 200 to 50 μm).
0 nm). The purpose of providing the second passivation film 54 is mainly to protect the EL layer 52 from moisture, but it is also effective to have a heat radiation effect. However,
As described above, since the EL layer is weak to heat, it is desirable to form the film at a temperature as low as possible (preferably in a temperature range from room temperature to 120 ° C.). Therefore, it can be said that a plasma CVD method, a sputtering method, a vacuum evaporation method, an ion plating method, or a solution coating method (spin coating method) is a preferable film forming method.

The present invention is not limited to the structure of the EL display device shown in FIG. 4, but the structure shown in FIG. 4 is only one of preferred embodiments for carrying out the present invention.

With the above configuration, the present invention makes it possible to adjust the emission luminance of the EL element included in the target pixel by adjusting the value of the ON EL drive voltage applied to the EL element, The display makes it possible to perform clear multi-tone display. Specifically, depending on the value of the ON EL drive voltage applied to the EL element,
By adjusting the light emission luminance of, it is possible to display a colorful image with a good balance of the light emission luminances of red, blue and green. In addition, time-division gradation display is performed by a digital signal, and a high-definition image with good color reproducibility without gradation failure due to variation in characteristics of the EL driving TFT can be obtained.

Further, the configuration of the present embodiment can be freely combined with the configuration of the first embodiment.

(Embodiment 3) In this embodiment, a method for simultaneously manufacturing TFTs of a pixel portion and a driving circuit portion provided around the pixel portion will be described. However, for the sake of simplicity, a CMOS circuit, which is a basic unit for the drive circuit, is illustrated.

First, as shown in FIG. 5A, a substrate 501 having a base film (not shown) provided on the surface is prepared. In this embodiment, a silicon nitride oxide film having a thickness of 100 nm and a silicon nitride oxide film having a thickness of 200 nm are stacked as a base film over crystallized glass. At this time, the nitrogen concentration in contact with the crystallized glass substrate is preferably set to 10 to 25 wt%. Of course, the element may be formed directly on the quartz substrate without providing the base film.

Next, an amorphous silicon film 502 having a thickness of 45 nm is formed on the substrate 501 by a known film forming method. Note that the present invention is not limited to an amorphous silicon film, and may be any semiconductor film including an amorphous structure (including a microcrystalline semiconductor film). Further, a compound semiconductor film having an amorphous structure such as an amorphous silicon germanium film may be used.

The steps from here to FIG. 5 (C) can completely refer to Patent No. 3032801 by the present applicant. This patent discloses a technique related to a method for crystallizing a semiconductor film using an element such as Ni as a catalyst.

First, a protective film 504 having openings 503a and 503b is formed. In this embodiment, a silicon oxide film having a thickness of 150 nm is used. Then, a layer (Ni-containing layer) 505 containing nickel (Ni) is formed on the protective film 504 by spin coating. Regarding the formation of the Ni-containing layer, the above publication may be referred to.

Next, as shown in FIG. 5B, a heat treatment is performed at 570 ° C. for 14 hours in an inert atmosphere to crystallize the amorphous silicon film 502. At this time, the regions in contact with Ni (hereinafter, referred to as Ni added regions) 506a, 50
Starting from 6b, crystallization proceeds substantially parallel to the substrate,
A polysilicon film 507 having a crystal structure in which rod-like crystals are gathered and arranged is formed.

Next, as shown in FIG.
Using Group 04 as a mask, an element belonging to Group 15 (preferably phosphorus) is added to the Ni-added regions 506a and 506b. Thus, regions 508a and 508b to which phosphorus is added at a high concentration (hereinafter, referred to as phosphorus added regions) are formed.

Next, as shown in FIG. 5C, heat treatment is performed at 600 ° C. for 12 hours in an inert atmosphere. As a result of this heat treatment, Ni existing in the polysilicon film 507 moves, and finally, almost all of the Ni is captured in the phosphorus-added regions 508a and 508b as indicated by arrows. This is considered to be a phenomenon due to the gettering effect of the metal element (Ni in this embodiment) by phosphorus.

By this step, the concentration of Ni remaining in the polysilicon film 509 is reduced to at least 2 × 10 ¹⁷ atoms / cm ³ as measured by SIMS (Secondary Mass Ion Analysis). Ni is a lifetime killer for semiconductors, but if it is reduced to this extent, there is no adverse effect on TFT characteristics. Further, since this concentration is almost the measurement limit of the current SIMS analysis, it is considered that the concentration is actually lower (2 × 10 ¹⁷ atoms / cm ³ or less).

Thus, the crystallization is carried out using the catalyst, and
The polysilicon film 509 whose catalyst is reduced to a level that does not hinder the operation of the TFT is obtained. afterwards,
Active layer 510 using only this polysilicon film 509
513 is formed by a patterning step. At this time, a marker for performing mask alignment in the subsequent patterning may be formed using the polysilicon film.
(FIG. 5 (D))

Next, as shown in FIG.
A thick silicon nitride oxide film is formed by a plasma CVD method, and a heat treatment is performed thereon at 950 ° C. for one hour in an oxidizing atmosphere to perform a thermal oxidation step. Note that the oxidation atmosphere may be an oxygen atmosphere or an oxygen atmosphere to which a halogen element is added.

In this thermal oxidation step, oxidation proceeds at the interface between the active layer and the silicon nitride oxide film, and the polysilicon film having a thickness of about 15 nm is oxidized to form a silicon oxide film having a thickness of about 30 nm. That is, a silicon oxide film having a thickness of 30 nm and a silicon nitride oxide film having a thickness of 50 nm are stacked.
A gate insulating film 514 having a thickness of nm is formed. The thickness of the active layers 510 to 513 is set to 30 by this thermal oxidation step.
nm.

Next, as shown in FIG. 6A, a resist mask 515 is formed, and a resist mask 515 is formed via a gate insulating film 514.
An impurity element for imparting a mold (hereinafter referred to as a p-type impurity element) is added. As the p-type impurity element, an element belonging to Group 13 typically, typically, boron or gallium can be used. This step (called a channel doping step) is a step for controlling the threshold voltage of the TFT.

In this embodiment, boron is added by an ion doping method in which diborane (B ₂ H ₆ ) is plasma-excited without mass separation. Of course, an ion implantation method for performing mass separation may be used. By this step, 1 × 1
0 ¹⁵ to 1 × 10 ¹⁸ atoms / cm ³ (typically 5 × 10 ¹⁶ to
Impurity regions 516 to 518 containing boron at a concentration of 5 × 10 ¹⁷ atoms / cm ³ ) are formed.

Next, as shown in FIG. 6B, resist masks 519a and 519b are formed, and a gate insulating film 514 is formed.
Through which an impurity element imparting n-type (hereinafter referred to as an n-type impurity element) is added. Note that as the n-type impurity element, an element belonging to Group 15 typically, typically, phosphorus or arsenic can be used. Note that a plasma doping method is used, plasma excited without mass separation of phosphine (PH ₃₎ In this embodiment, 1 phosphorus × 10 ¹⁸ the atom
Add at a concentration of s / cm ³ . Of course, an ion implantation method for performing mass separation may be used.

In the n-type impurity regions 520 and 521 formed in this step, the n-type impurity element contains 2 × 10 ^{16 to} 5 × 10 ^16.
× 10 ¹⁹ atoms / cm ³ (typically 5 × 10 ^{17 to} 5 × 10
^The dose is adjusted so as to be contained at a concentration of ¹⁸ atoms / cm ³ ).

Next, as shown in FIG. 6C, a step of activating the added n-type and p-type impurity elements is performed. Although there is no need to limit the activation means, furnace annealing using an electric furnace is preferable because the gate insulating film 514 is provided. In addition, since there is a possibility that the active layer / gate insulating film interface in a portion to be a channel formation region in the step of FIG. 6A may be damaged, it is preferable to perform heat treatment at a temperature as high as possible.

In this embodiment, since the crystallized glass having high heat resistance is used, the activation step is performed by furnace annealing at 800 ° C. for 1 hour. Note that thermal oxidation may be performed using a treatment atmosphere of an oxidizing atmosphere, or heat treatment may be performed in an inert atmosphere.

By this step, n-type impurity regions 520, 5
21, that is, a boundary portion between the region around the n-type impurity regions 520 and 521 where the n-type impurity element is not added (the p-type impurity region formed in the process of FIG. 6A). (Joint) becomes clear. This means that when the TFT is completed later, a very good junction can be formed between the LDD region and the channel forming region.

Next, a conductive film having a thickness of 200 to 400 nm is formed and patterned to form gate electrodes 522 to 525. The length of the channel length of each TFT is determined by the line width of the gate electrodes 522 to 525.

Note that the gate electrode may be formed of a single-layer conductive film, but it is preferable to form a two-layer or three-layer laminated film as necessary. A known conductive film can be used as a material for the gate electrode. Specifically, a film made of an element selected from tantalum (Ta), titanium (Ti), molybdenum (Mo), tungsten (W), chromium (Cr), and silicon (Si), or a nitride of the element (Typically, a tantalum nitride film, a tungsten nitride film, a titanium nitride film), an alloy film combining the above elements (typically, a Mo-W alloy, a Mo-Ta alloy), or a silicide film of the element (Typically, a tungsten silicide film or a titanium silicide film) can be used. Of course, they may be used as a single layer or stacked.

In this embodiment, a 50 nm thick tungsten nitride (WN) film and a 350 nm thick tungsten (W)
A laminated film composed of a film is used. This may be formed by a sputtering method. In addition, xenon (X
e), addition of an inert gas such as neon (Ne) can prevent the film from peeling due to stress.

At this time, the gate electrodes 523 and 525 are formed so as to overlap a part of the n-type impurity regions 520 and 521 via the gate insulating film 514, respectively. This overlapping portion later becomes an LDD region overlapping with the gate electrode. Note that the gate electrodes 524a and 524b appear to be two in cross section, but are actually electrically connected.

Next, as shown in FIG. 7A, an n-type impurity element (phosphorus in this embodiment) is added in a self-aligned manner using the gate electrodes 522 to 525 and a mask. The impurity regions 527 to 533 formed in this manner are １ ／ to 1/10 (typically １ ／) of the n-type impurity regions 520 and 521.
Adjust so that phosphorus is added at a concentration of (〜).
Specifically, a concentration of 1 × 10 ^{16 to} 5 × 10 ¹⁸ atoms / cm ³ (typically, 3 × 10 ^{17 to} 3 × 10 ¹⁸ atoms / cm ³ ) is preferable.

Next, as shown in FIG. 7B, resist masks 534a to 534d are formed so as to cover the gate electrodes and the like, and an n-type impurity element (phosphorus in this embodiment) is added to increase the concentration. The impurity regions 535 to 541 containing phosphorus are formed. Also in this case, the ion doping method using phosphine (PH ₃ ) is performed, and the phosphorus concentration in this region is 1 × 10 ²⁰ to 1
× 10 ²¹ atoms / cm ³ (typically 2 × 10 ^{20 to} 5 × 10
Adjust so as to be ²¹ atoms / cm ³ ).

In this step, the source region or the drain region of the n-channel TFT is formed, but the switching TFT leaves a part of the n-type impurity regions 530 to 532 formed in the step of FIG. This remaining region corresponds to the LDD regions 15a to 15d of the switching TFT in FIG.

Next, as shown in FIG. 7C, the resist masks 534a to 534d are removed, and a new resist mask 543 is formed. Then, a p-type impurity element (boron in this embodiment) is added to form impurity regions 544 and 545 containing boron at a high concentration. Here, diborane (B
3 × 10 ²⁰ to 3 × by ion doping using ₂ H ₆ )
10 ²¹ atoms / cm ³ (typically 5 × 10 ²⁰ to 1 × 10 ²¹ a
toms / cm ³ ) Add boron to a concentration.

Note that phosphorus is already added to the impurity regions 544 and 545 at a concentration of 1 × 10 ²⁰ to 1 × 10 ²¹ atoms / cm ³ , and the boron added here is at least three times as large as that. It is added at a concentration. Therefore, the n-type impurity region formed in advance is completely inverted to P-type and functions as a P-type impurity region.

Next, as shown in FIG. 7D, after removing the resist mask 543, a first interlayer insulating film 546 is formed. As the first interlayer insulating film 546, an insulating film containing silicon may be used as a single layer or a stacked film in which the insulating film is combined. The film thickness may be 400 nm to 1.5 μm. In this embodiment, an 800 nm thick silicon oxide film is stacked over a 200 nm thick silicon nitride oxide film.

Thereafter, the n-type or p-type impurity element added at each concentration is activated. As an activation means, a furnace annealing method is preferable. In this embodiment, heat treatment is performed in an electric furnace at 550 ° C. for 4 hours in a nitrogen atmosphere.

Further, in an atmosphere containing 3 to 100% of hydrogen, a heat treatment is performed at 300 to 450 ° C. for 1 to 12 hours to perform a hydrogenation treatment. This step is a step of terminating dangling bonds of the semiconductor film with thermally excited hydrogen.
As another means of hydrogenation, plasma hydrogenation (using hydrogen excited by plasma) may be performed.

The hydrogenation process is performed for the first interlayer insulating film 546.
May be inserted during formation. That is, a hydrogenation treatment may be performed as described above after a 200-nm-thick silicon nitride oxide film is formed, and then a remaining 800-nm-thick silicon oxide film may be formed.

Next, as shown in FIG. 8A, contact holes are formed in the first interlayer insulating film 546, and source wirings 547 to 550 and drain wirings 551 to 553 are formed.
To form In this embodiment, this electrode is made of a Ti film of 100 nm, a Ti-containing aluminum film of 300 nm,
A 150 nm Ti film is continuously formed by a sputtering method to form a three-layer laminated film. Of course, other conductive films may be used.

Next, 50 to 500 nm (typically 20 to 500 nm)
The first passivation film 55 with a thickness of
4 is formed. In this embodiment, the first passivation film 5
A silicon nitride oxide film having a thickness of 300 nm is used as 54. This may be replaced by a silicon nitride film.

At this time, it is effective to perform a plasma treatment using a gas containing hydrogen such as H ₂ and NH ₃ before forming the silicon nitride oxide film. Hydrogen excited by this pretreatment is supplied to the first interlayer insulating film 546, and the heat treatment is performed, whereby the quality of the first passivation film 554 is improved. At the same time, the hydrogen added to the first interlayer insulating film 546 diffuses to the lower layer side, so that the active layer can be effectively hydrogenated.

Next, as shown in FIG. 8B, a second interlayer insulating film 555 made of an organic resin is formed. As the organic resin, polyimide, acrylic, BCB (benzocyclobutene) or the like can be used. In particular, since the second interlayer insulating film 555 needs to flatten a step formed by the TFT, an acrylic film having excellent flatness is preferable. In this embodiment, an acrylic film is formed with a thickness of 2.5 μm.

Next, a contact hole reaching the drain wiring 553 is formed in the second interlayer insulating film 555 and the first passivation film 554, and then a protection electrode 556 is formed. As the protective electrode 556, a conductive film containing aluminum as a main component may be used. The protective electrode 556 may be formed by a vacuum evaporation method.

Next, an insulating film containing silicon (a silicon oxide film in this embodiment) having a thickness of 500 nm is formed, and an opening is formed at a position corresponding to a portion to be a pixel electrode, thereby forming a third interlayer insulating film. 557 are formed. When forming the opening, a tapered side wall can be easily formed by using a wet etching method. If the side wall of the opening is not sufficiently gentle, the deterioration of the EL layer due to the step becomes a significant problem.

Next, a pixel electrode (Mg) which is a cathode of the EL element is used.
(Ag electrode) 558 is formed. The MgAg electrode 558 is formed to have a thickness of 180 to 300 nm (typically 200 to 250 nm) by using a vacuum evaporation method.

Next, an EL layer 559 is formed by using a vacuum evaporation method without opening to the atmosphere. Note that the thickness of the EL layer 559 is 800 to 200 nm (typically 100 to 120 nm).
m).

In this step, pixels corresponding to red, pixels corresponding to green, and pixels corresponding to blue are sequentially subjected to E
An L layer is formed. However, since the EL layer has poor resistance to a solution, it must be formed individually for each color without using a photolithography technique. Therefore, it is preferable that a metal mask is used to hide portions other than the desired pixels and an EL layer is selectively formed only at a necessary portion.

That is, first, a mask for hiding all pixels other than pixels corresponding to red is set, and a red light emitting EL layer is selectively formed using the mask. Next, a mask for hiding all pixels other than pixels corresponding to green is set, and a green light-emitting EL layer is selectively formed using the mask. Next, a mask for covering all pixels other than the pixel corresponding to blue is similarly set, and an EL layer for emitting blue light is selectively formed using the mask. Note that all the masks are described herein as being different, but the same mask may be used again. In addition, it is preferable that processing be performed without breaking vacuum until an EL layer is formed in all pixels.

A known material can be used for the EL layer 559. As a known material, it is preferable to use an organic material in consideration of a driving voltage. For example, a four-layer structure including a hole injection layer, a hole transport layer, a light emitting layer, and an electron injection layer may be used as the EL layer.

Next, a counter electrode 560 (anode) is formed. The counter electrode (anode) 560 may have a thickness of 110 nm. In this embodiment, the counter electrode (anode) 56 of the EL element is used.
As 0, an indium tin oxide (ITO) film is formed. Also, 2-20% of zinc oxide (Z
A transparent conductive film mixed with nO) may be used, or another known material may be used.

Finally, a second passivation film 561 made of a silicon nitride film is formed to a thickness of 300 nm.

In this way, the E of the structure shown in FIG.
The L display device is completed. Actually, when the package is completed as shown in FIG. 8 (C), it is packaged with a housing material such as a highly airtight protective film (laminate film, ultraviolet curable resin film, etc.) or a ceramic sealing can so as not to be further exposed to the outside air. (Encapsulation). At this time, the reliability (lifetime) of the EL layer is improved by setting the inside of the housing material to an inert atmosphere or disposing a hygroscopic material (for example, barium oxide) inside.

When the airtightness is enhanced by processing such as packaging, a connector (flexible printed circuit: FPC) for connecting terminals routed from elements or circuits formed on the substrate to external signal terminals. To complete the product. Such an EL display device that can be shipped is referred to as an EL module in this specification.

The configuration of the present embodiment can be freely combined with the configuration of the first embodiment.

(Example 4)

In this embodiment, the structure of the EL display device of the present invention will be described with reference to the perspective view of FIG.

The EL display device according to this embodiment uses the glass substrate 6
01, a pixel portion 602, a gate side drive circuit 603, and a source side drive circuit 604.
The switching TFT 605 of the pixel portion 602 is an n-channel TFT, and is disposed at an intersection of a gate wiring 606 connected to the gate driver circuit 603 and a source wiring 607 connected to the source driver circuit 604. Also,
One of a source region and a drain region of the switching TFT 605 is connected to the source wiring 607, and the other is connected to a gate electrode of the EL driving TFT 608.

Further, the source region of the EL driving TFT 608 is connected to a power supply line 609. A capacitor 616 connected to the gate electrode of the EL driving TFT 608 and the power supply line 609 is provided. In this embodiment, the power supply line 609 is supplied with an EL drive potential. Further, a common potential (0 in this embodiment) of a common electrode is applied to a counter electrode (cathode in this embodiment) of the EL element 611.
V) is added.

The FPC 61 serving as an external input / output terminal
2 is provided with input / output wirings (connection wirings) 613 and 614 for transmitting signals to the drive circuit, and input / output wirings 615 connected to the power supply line 609.

Further, the EL module of this embodiment including the housing material will be described with reference to FIGS. 10 (A) and 10 (B). The reference numerals used in FIG. 9 will be referred to as needed.

On the substrate 1200, the pixel portion 1201, the data signal side drive circuit 1202, and the gate signal side drive circuit 12
03 is formed. Various wirings from the respective drive circuits are supplied to the FPC 612 via input / output wirings 613 to 615.
And connected to the external device.

At this time, the housing member 120 is formed so as to surround at least the pixel portion, preferably the drive circuit and the pixel portion.
4 is provided. Note that the housing member 1204 has a shape having a concave portion whose inner size is larger than the outer size of the EL element or a sheet shape, and is fixed to the substrate 1200 by an adhesive 1205 so as to form a closed space in cooperation with the substrate 1200. Is done. At this time, the EL element is completely sealed in the closed space, and is completely shut off from the outside air. Note that a plurality of housing members 1204 may be provided.

The material of the housing member 1204 is preferably an insulating material such as glass or polymer. For example, amorphous glass (borosilicate glass, quartz, etc.), crystallized glass,
Examples include ceramic glass, organic resins (acrylic resin, styrene resin, polycarbonate resin, epoxy resin, etc.) and silicone resins. Further, ceramics may be used. If the adhesive 1205 is an insulating material, a metal material such as a stainless alloy can be used.

As the material of the adhesive 1205, an adhesive such as an epoxy resin or an acrylate resin can be used. Further, a thermosetting resin or a photocurable resin can be used as the adhesive. However, it is necessary that the material does not transmit oxygen and moisture as much as possible.

Further, a gap 1206 between the housing material and the substrate 1200 is formed by an inert gas (argon, helium,
Nitrogen or the like). Further, not only gas but also an inert liquid (liquid fluorinated carbon represented by perfluoroalkane or the like) can be used. As the inert liquid, a material such as that used in JP-A-8-78519 may be used.

It is also effective to provide a desiccant in the space 1206. As a desiccant, JP-A-9-1480
No. 66 can be used. Generally, barium oxide is used.

Further, as shown in FIG. 10B, a plurality of pixels having individually isolated EL elements are provided in the pixel portion, and all of them have the protective electrode 1207 as a common electrode. In this embodiment, it is preferable that the EL layer, the cathode (MgAg electrode), and the protection electrode are formed continuously without opening to the atmosphere. However, the EL layer and the cathode are formed using the same mask material, and only the protection electrode is separately formed. 10B, the structure shown in FIG. 10B can be realized.

At this time, the EL layer and the cathode are connected to the pixel portion 1201.
May be provided only on the drive circuits 1202, 1203
There is no need to place it on Of course, there is no problem even if the EL layer is provided on the driving circuit, but it is preferable not to provide the EL layer in consideration of the fact that the EL layer contains an alkali metal.

Note that the protection electrode 1207 is connected to the input / output wiring 1210 via a connection wiring 1209 made of the same material as the pixel electrode in a region 1208. The input / output wiring 1210 is a power supply line for applying an EL driving potential to the protection electrode 1207, and is a conductive paste material 1
It is connected to FPC 611 via 211.

The structure of the present embodiment can be freely combined with the structure of the first embodiment.

(Embodiment 5) The present invention can be applied to organic EL materials having different emission luminances of red, green and blue. For example, in the case of an organic EL material having the lowest emission luminance of red and the highest emission luminance of blue, the luminance of the pixel displaying red and the luminance of the pixel displaying green are adjusted to the luminance of the pixel displaying blue. In addition, the EL display device performs time-division gray scale display, and the EL driving voltage applied to the EL element for displaying red and the EL element for displaying green is changed to the EL driving applied to the EL element for displaying blue. What is necessary is just to set so that it may become larger than a voltage. As a countermeasure against deterioration of the EL driving TFT due to hot carrier injection, in addition to the above configuration, the channel width (W) of the EL driving TFT of the pixel for displaying red and the EL driving TFT of the pixel for displaying green is set as follows. The width is set to be larger than the channel width (W) of the EL driving TFT of the pixel displaying blue. EL drive TFT
Is an n-channel TFT, the E of the pixel displaying red is
L driving TFT and EL driving TF for green display pixel
The length of the LDD region of T may be longer than the length of the LDD region of the EL driving TFT of the pixel displaying blue. E
The channel width (W) of the L driving TFT and the length of the LDD region of the EL driving TFT can be appropriately set by a practitioner.

According to the invention of the present application, with the above structure, the emission luminance of the EL element can be adjusted by the value of the EL drive voltage applied to the EL element, and the red, blue, and green emission luminances are well balanced. Thus, a colorful image can be displayed. Further, even if the amount of current controlled by the EL driving TFT increases due to an increase in the applied voltage, deterioration of the EL driving TFT can be suppressed.

The structure of this embodiment can be freely combined with any of the structures of the first to fifth embodiments.

(Embodiment 6) In the first embodiment, an organic EL material is used for the EL layer. However, the present invention can be implemented by using an inorganic EL material. However, since a current inorganic EL material has a very high driving voltage, a TFT having a withstand voltage characteristic capable of withstanding such a driving voltage must be used.

Alternatively, if an inorganic EL material having a further lower driving voltage is developed in the future, it can be applied to the present invention.

The structure of this embodiment can be freely combined with any of the structures of the first to fifth embodiments.

(Embodiment 7) In the present invention, the organic substance used for the EL layer may be a low molecular organic substance or a polymer (polymer) organic substance. Polymeric (polymeric) organic materials can be formed by simple thin-film forming methods such as spin coating (also known as solution coating), dipping, printing or ink-jet methods, and are more heat-resistant than low-molecular organic materials. Is high.

As the polymer organic substance, typically, P
PV (polyphenylene vinylene), PVK (polyvinyl carbazole), polycarbonate and the like.

The structure of this embodiment can be freely combined with any of the structures of the first to fifth embodiments.

(Embodiment 8) An EL display device (EL module) formed by carrying out the invention of the present application is of a self-luminous type and thus has better visibility in a bright place than a liquid crystal display device. Therefore, the present invention can be applied to a direct-view EL display (which indicates a display incorporating an EL module). Personal computer monitors, TV broadcast reception monitors, and EL displays
An advertisement display monitor and the like can be mentioned.

The present invention can be applied to any electronic device including a display as a component, including the above-described EL display.

Examples of such electronic devices include an EL display, a video camera, a digital camera, a head-mounted display (such as a head-mounted display), a car navigation, a personal computer, and a personal digital assistant (a mobile computer, a mobile phone, or an electronic book). Etc.) and an image reproducing apparatus equipped with a recording medium (specifically, reproducing a recording medium such as a compact disk (CD), a laser disk (registered trademark) (LD) or a digital video disk (DVD), and displaying an image thereof. Device with a display that can be used). FIG. 11 shows examples of these electronic devices.

FIG. 11A shows a personal computer, which includes a main body 2001, a housing 2002, and a display device 200.
3, including the keyboard 2004 and the like. The present invention can be used for the display device 2003.

FIG. 11B shows a video camera, which includes a main body 2101, a display device 2102, an audio input unit 2103, an operation switch 2104, a battery 2105, and an image receiving unit 21.
06 and the like. The invention of the present application can be used for the display device 2102.

FIG. 11C shows a part (right side) of a head-mounted EL display, which includes a main body 2301, a signal cable 2302, a fixed head band 2303, a display monitor 2304, an optical system 2305, and a display device 2306. And so on. The present invention can be used for the display device 2306.

FIG. 11D shows an image reproducing apparatus (specifically, a DVD reproducing apparatus) provided with a recording medium.
1, recording medium (CD, LD, DVD, etc.) 2402,
An operation switch 2403, a display device (a) 2404, a display device (b) 2405, and the like are included. The display device (a) mainly displays image information, and the display device (b) mainly displays character information.
It can be used for (b). The present invention can be applied to a CD reproducing device, a game machine, and the like as an image reproducing device provided with a recording medium.

FIG. 11E shows a portable computer, which includes a main body 2501, a camera section 2502, an image receiving section 2503, operation switches 2504, and a display device 2505.
And so on. The present invention can be used for the display device 2505.

If the emission luminance of the EL material is increased in the future, it can be used for a front-type or rear-type projector.

As described above, the applicable range of the present invention is extremely wide, and can be applied to electronic devices in all fields. Further, the electronic device of the present embodiment can be realized by using a configuration composed of any combination of the first to seventh embodiments.

[0214]

【The invention's effect】

According to the present invention, with the above structure, the emission luminance of the EL element can be adjusted by the value of the EL drive voltage applied to the EL element, and the red, blue, and green emission luminances are well balanced. Thus, a colorful image can be displayed. Further, even if the amount of current controlled by the EL driving TFT increases due to an increase in the applied voltage, deterioration of the EL driving TFT can be suppressed.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an EL display device of the present invention.

FIG. 2 is a diagram illustrating an operation mode of a time division gray scale method according to the present invention.

FIG. 3 is a diagram illustrating an operation mode of a time division gray scale method according to the present invention.

FIG. 4 is a diagram showing a cross-sectional structure of an EL display device of the present invention.

FIG. 5 illustrates a manufacturing process of an EL display device.

FIG. 6 illustrates a manufacturing process of an EL display device.

FIG. 7 illustrates a manufacturing process of an EL display device.

FIG. 8 illustrates a manufacturing process of an EL display device.

FIG. 9 illustrates an appearance of an EL module.

FIG. 10 illustrates an appearance of an EL module.

FIG. 11 illustrates a specific example of an electronic device.

[Explanation of symbols]

 Reference Signs List 101 pixel portion 102 data signal side driving circuit 103 gate signal side driving circuit 104 pixel 105 switching TFT 106 gate wiring 107 data wiring 108 EL driving TFT 110 EL element

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (Reference) G09G 3/20 642 G09G 3/20 642L H01L 21/8234 H05B 33/12 B 27/088 33/14 A 29/786 H01L 27/08 102B 21/336 29/78 614 H05B 33/12 616A 33/14

Claims (7)

[Claims] 1. An EL display device having a plurality of pixels each including a plurality of EL elements, wherein the EL display apparatus performs gradation display by controlling a light emitting time of the plurality of EL elements. The voltage applied to the plurality of EL elements is
An EL display device, wherein a plurality of pixels each including an L element differs depending on a displayed color. 2. A plurality of EL elements, a plurality of EL driving TFTs respectively controlling light emission of the plurality of EL elements, a plurality of switching TFTs respectively controlling driving of the plurality of EL driving TFTs, An EL display device having a plurality of pixels, each of which includes a plurality of pixels, wherein the EL display device performs a gray scale display by controlling a light emitting time of the plurality of EL elements, and a voltage applied to the plurality of EL elements. Is the plurality of E
The plurality of EL driving TFTs include an n-channel TFT, and the length of the LDD region of the plurality of EL driving TFTs in the channel length direction is: An EL display device, wherein the longer the voltage applied to the plurality of EL elements, the longer the voltage. 3. A plurality of EL elements, a plurality of EL driving TFTs for respectively controlling the light emission of the plurality of EL elements, a plurality of switching TFTs for respectively controlling the driving of the plurality of EL driving TFTs, An EL display device having a plurality of pixels, each of which includes a plurality of pixels, wherein the EL display device performs a gray scale display by controlling a light emitting time of the plurality of EL elements, and a voltage applied to the plurality of EL elements. Is the plurality of E
The plurality of EL driving TFTs include n-channel TFTs, and the width of a channel region of the plurality of EL driving TFTs is different from the plurality of EL elements. An EL display device characterized in that the higher the voltage applied to the device, the higher the voltage. 4. A plurality of EL elements, a plurality of EL driving TFTs for respectively controlling the light emission of the plurality of EL elements, a plurality of switching TFTs for respectively controlling the driving of the plurality of EL driving TFTs, An EL display device having a plurality of pixels, each of which includes a plurality of pixels, wherein the EL display device performs a gray scale display by controlling a light emitting time of the plurality of EL elements, and a voltage applied to the plurality of EL elements. Is the plurality of E
The plurality of EL driving TFTs are composed of n-channel TFTs, and the length of the LDD regions of the plurality of EL driving TFTs in the channel length direction is as follows: The EL device is characterized in that the longer the voltage applied to the plurality of EL elements, the longer the width of the channel region of the plurality of EL driving TFTs is. Display device. 5. A plurality of EL elements, a plurality of EL driving TFTs for respectively controlling light emission of the plurality of EL elements, a plurality of switching TFTs for respectively controlling the driving of the plurality of EL driving TFTs, An EL display device having a plurality of pixels, each of which includes a plurality of pixels, wherein the EL display device performs a gray scale display by controlling a light emitting time of the plurality of EL elements, and a voltage applied to the plurality of EL elements. Is the plurality of E
The width of a channel region of the plurality of EL driving TFTs increases as the voltage applied to the plurality of EL elements increases, depending on the color displayed by the plurality of pixels including the L element. Display device. 6. The EL device according to claim 1, wherein a time during which the plurality of EL elements emit light is controlled by a digital signal input to a switching TFT. Display device. 7. An electronic device using the EL display device according to claim 1. [0000]