JP2002123219A - Display device and its driving method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress effect of dispersion in characteristics of TFTs(thin film transistors) constituting pixels, variation in display periods and fluctuation of luminance of EL elements die to the change of ambient temperature under which a display device is used in the active matrix type EL(electroluminescence) display device. SOLUTION: In this display device, one frame period is divided into plural sub-frame periods and display is performed by changing a voltage to be applied to EL elements of pixels for every sub-frame period and by using a time gradation system. Thus, a display device in which fluctuation of luminance of the EL elements due to the change of the ambient temperature is suppressed by using a gradation display method which is hardly affected by dispersion in the characteristics of the TFTs of a pixel part and variation in display periods is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an electronic display device formed by forming an EL (electroluminescence) element on a substrate and a driving method thereof. In particular, the present invention relates to an EL display device using a semiconductor element (an element using a semiconductor thin film) and a driving method thereof. Further, the present invention relates to an electronic device using the EL display device for a display portion.

[0002]

2. Description of the Related Art In recent years, the development of EL display devices having EL elements as self-luminous elements has been activated. The EL display device is an organic EL display (OELD: Organic EL Dis
play) or organic light emitting diode (OL
It is also called ED (Organic Light Emitting Diode).

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

[0004] In addition, a "hole injection layer / hole transport layer / light emitting layer / electron transport layer" or "hole injection layer /
A structure in which the layers are stacked in the order of “hole transport layer / light emitting layer / electron transport layer / electron injection layer” may be used. The light emitting layer may be doped with a fluorescent dye or the like.

In this specification, all layers provided between a cathode and an anode are collectively called an EL layer. Therefore, the above-described hole injection layer, hole transport layer, light-emitting layer, electron transport layer, electron injection layer, and the like are all included in the EL layer.

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 including an anode, an EL layer, and a cathode is referred to as an EL element.

[0007] In this specification, the anode and the cathode of the EL element may be referred to as both electrodes of the EL element.

[0008] In this specification, an EL element refers to an element utilizing both light emission (fluorescence) from a singlet exciton and an element utilizing light emission (phosphorescence) from a triplet exciton. And

As a driving method of the EL display device, there is an active matrix method.

FIG. 6 is a block diagram showing an example of an active matrix type display device. In the pixel portion, a source signal line to which a signal is input from a source signal line driver circuit and a gate signal line to which a signal is input from a gate signal line driver circuit are formed in a matrix. Further, a power supply line is formed in parallel with the source signal line. In this specification, the potential of a power supply line is referred to as a power supply potential.

FIG. 5 shows a configuration of a pixel portion of an active matrix EL display device. Gate signal lines (G1 to Gy) for inputting a selection signal from the gate signal line driving circuit are connected to the gate electrode of the switching TFT 301 included in each pixel. Further, one of a source region and a drain region of the switching TFT 301 included in each pixel is connected to a source signal line (S1 to Sx) for inputting a signal from a source signal line driving circuit, and the other is connected to a gate electrode of the EL driving TFT 302 and It is connected to one electrode of a capacitor 303 included in the pixel. The other electrode of the capacitor 303 is connected to power supply lines (V1 to Vx).
One of a source region and a drain region of the EL driving TFT 302 included in each pixel is connected to a power supply line (V1 to Vx).
The other is connected to the EL element 304 of each pixel.

The EL element 304 has an anode, a cathode, and an EL layer provided between the anode and the cathode. EL element 3
When the anode 04 is connected to the source or drain region of the EL driving TFT 302, the anode of the EL element 304 is a pixel electrode and the cathode is a counter electrode. Conversely, when the cathode of the EL element 304 is connected to the source region or the drain region of the EL driving TFT 302, the EL element 30
The cathode 4 is a pixel electrode, and the anode is a counter electrode.

In this specification, the potential of the counter electrode is called a counter potential. Note that a power supply that applies a counter potential to the counter electrode is referred to as a counter power supply. The potential difference between the potential of the pixel electrode and the potential of the counter electrode is the EL drive voltage, and this EL drive voltage is applied to the EL layer.

As a gradation display method of the above EL display device,
There are an analog gray scale method and a time gray scale method.

First, the analog gray scale method of the EL display device will be described. FIG. 7 shows a timing chart when the display device shown in FIG. 5 is driven by an analog gray scale method. The period from when one gate signal line is selected to when the next gate signal line is selected is called one line period (L). Further, a period from when one image is selected to when the next image is selected corresponds to one frame period. In the case of the EL display device of FIG. 5, the gate signal line is y
Since there are books, y line periods (L
1 to Ly) are provided.

As the resolution increases, the number of line periods in one frame period increases, and the driving circuit must be driven at a high frequency.

The power supply lines (V1 to Vx) are kept at a constant potential. The opposing potential is also kept constant. The opposing potential has a potential difference from the power supply potential to such an extent that the EL element emits light.

In the first line period (L1), a selection signal from the gate signal line driving circuit is input to the gate signal line G1. Then, analog video signals are sequentially input to the source signal lines (S1 to Sx). Gate signal line G
1 are turned on, the analog video signals input to the source signal lines (S1 to Sx) are
The signal is input to the gate electrode of the EL driving TFT 302 through T301.

When the switching TFT 301 is turned on, the analog video signal input into the pixel becomes the gate voltage of the EL driving TFT 302. At this time, the drain current is determined one-to-one with respect to the gate voltage according to the Id-Vg characteristics of the EL driving TFT 302. That is, the potential of the drain region (ON EL drive potential for ON) is determined in accordance with the voltage of the analog video signal input to the gate electrode of the EL drive TFT 302, and the predetermined drain current becomes EL.
The EL element emits light at a light emission amount corresponding to the amount of current flowing through the element.

When the above operation is repeated and the input of the analog video signal to the source signal lines (S1 to Sx) ends, the first line period (L1) ends. In addition,
The period until the input of the analog video signal to the source signal lines (S1 to Sx) ends and the horizontal retrace period may be combined into one line period. Then, in the second line period (L2), a selection signal is input to the gate signal line G2. Then, analog video signals are sequentially input to the source signal lines (S1 to Sx) in the same manner as in the first line period (L1).

Then, all the gate signal lines (G1 to Gy)
When the selection signal is input to all the line periods (L1 to L1)
Ly) ends. When all the line periods (L1 to Ly) end, one frame period ends. All the pixels display during one frame period, and one image is formed. Note that all the line periods (L1 to Ly) and the vertical flyback period may be combined into one frame period.

As described above, the light emission amount of the EL element is controlled by the analog video signal, and gradation display is performed by controlling the light emission amount. As described above, in the analog gray scale method, gray scale display is performed by changing the potential of the analog video signal input to the source signal line.

Next, the time gray scale method will be described.

In the time gray scale method, a digital signal is input to a pixel, and the digital signal controls the light emission time of an EL element of the pixel to express a gray scale.

Here, an example will be described in which a digital signal of n (n is a natural number of 2 or more) bits is input and 2 ⁿ gray scales are displayed.

FIG. 8 shows a timing chart when the display device shown in FIG. 5 is driven by the time gray scale method. First, one frame period is divided into n (n is a natural number of 2 or more) subframe periods (SF _{1 to} SF _n ). In addition,
A period in which all the pixels in the pixel portion display one image is called one frame period (F). A subframe period is a period obtained by further dividing one frame period into a plurality. 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.

One sub-frame period is divided into a writing period (Ta) and a display period (Ts). The writing period is a period during which a digital signal is input to all the pixels in one sub-frame period, and the display period (also referred to as a lighting period) is a period during which the light emitting or non-light emitting state of the EL element is selected and displayed. Is shown.

The EL driving voltage shown in FIG. 8 represents the EL driving voltage of the EL element whose light emitting state is selected. That is, the EL driving voltage of the EL element whose light emitting state is selected is 0 V during the writing period, and has such a magnitude that the EL element emits light during the display period.

The opposing potential is controlled by an external switch (not shown). The opposing potential is maintained at the same level as the power supply potential during the writing period, and is such a level that the EL element emits light with the power supply potential during the display period. It has a potential difference.

First, the writing period and the display period of each sub-frame period will be described in detail with reference to FIGS. 5 and 8, and then the time gradation display will be described in detail.

First, a signal is input to the gate signal line G1,
All the switching TFTs 301 connected to the gate signal line G1 are turned on. Then, digital signals are sequentially input to the source signal lines (S1 to Sx). The counter potential is kept at the same level as the power supply potential of the power supply lines (V1 to Vx). Digital signal is "0" or "1"
Information. The digital signals “0” and “1” mean signals having a voltage of either Hi or Lo, respectively.

The digital signal input to the source signal lines (S1 to Sx) is a switching T
The signal is input to the gate electrode of the EL driving TFT 302 via the FT 301. Also, a digital signal is input to and held in the capacitor 303.

The above operation is repeated by sequentially inputting the signals to the gate signal lines G2 to Gy, and the digital signals are input to all the pixels, and the input digital signals are held in the respective pixels. In this manner, a period until a digital signal is input to all pixels is called a writing period.

When digital signals are input to all the pixels, all the switching TFTs 301 are turned off. Then, an external switch (not shown) connected to the opposite electrode changes the opposite potential so as to have a potential difference between the power supply potential and the EL element 304 such that the EL element 304 emits light.

When the digital signal has information of "0", the EL driving TFT 302 is turned off and the EL driving TFT 302 is turned off.
The element 304 does not emit light. Conversely, when the information has “1”, the EL driving TFT 302 is turned on. As a result, the pixel electrode of the EL element 304 is kept almost at the power supply potential, and the EL element 304 emits light. As described above, the light emitting state or the non-light emitting state of the EL element is selected by the digital signal, and all the pixels simultaneously perform display. An image is formed when all the pixels perform display. A period in which the pixel performs display is called a display period.

Here, n sub-frame periods (SF ₁
To SF _n ) have respective writing periods (Ta _{1 to} Ta ₁ ).
_n) of length are all the same city, SF ₁ - SF _n display periods each having a (Ts), respectively, and Ts ₁ ~Ts _n.

For example, the length of the display periods Ts _{1 to} Ts _n is
_{Ts 1: Ts 2: Ts 3} : ...: Ts (n- 1): Ts n = 2 0: 2
^-1 : 2 ^-2 : ...: 2- ^(n-2) : 2- ^(n-1) A desired gradation display out of 2 ⁿ gradations can be performed by the combination of the display periods.

The display period is any one of Ts ₁ to Ts _n . Here, it is assumed that by lighting periods Ts _1, the predetermined pixel.

Next, the writing period is started again, and after the digital signals are input to all the pixels, the display period is started. Any one period of this time Ts ₂ ~Ts _n is the display period. Here, it is assumed that by lighting periods Ts _2, a predetermined pixel.

Hereinafter, the same operation is repeated for the remaining n-2 sub-frames, and sequentially Ts ₃ , Ts ₄ ... Ts _n
And a display 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, the gradation of the pixel is determined by integrating the length of the display period in which the pixel is lit. For example, when n = 8, if the pixel at all the display periods is 100% of luminance in the case where the light emission, the pixels in Ts ₁ and Ts ₂ emitted 75
% Luminance can be expressed, in the case of selecting the Ts ₃ and Ts ₅ and Ts ₈ can be expressed 16% luminance.

In this specification, a display period in which the EL element of a pixel is in a light emitting state or a non-light emitting state by a higher bit signal of a digital signal input to a display device is referred to as a higher bit display period. Also, the lower bit signal of the digital signal input to the display device allows
A display period in which the EL element of the pixel is in a light emitting state or a non-light emitting state is referred to as a lower bit display period.

[0043]

When the conventional analog gray scale method is used, there are the following problems.

The analog gray scale method has a problem that variations in TFT characteristics greatly affect gray scale display. For example, the Id-Vg characteristic of the switching TFT is
It is assumed that two pixels displaying the same gradation are different (a characteristic of one of the pixels is entirely shifted to the plus or minus side with respect to the other).

In this case, even if the same voltage is applied to the gate electrode of each switching TFT, each switching TFT
The drain current of the FT has a different value, and a different value of gate voltage is applied to the EL driving TFT of each pixel. That is, a different amount of current flows to each EL element, resulting in a different amount of light emission, making it impossible to perform the same gradation display.

Even if the same gate voltage is applied to the EL driving TFT of each pixel, the EL driving TF
If the Id-Vg characteristics of T vary, the same drain current cannot be output. Therefore, Id−Vg
If the characteristics are slightly different, even if the same gate voltage is applied, a situation may occur in which the amount of output current is significantly different. Then, even if a signal of the same voltage is input, the light emission amount of the EL element greatly differs between adjacent pixels due to a slight variation in the Id-Vg characteristics.

In practice, the switching TFT and the EL driving TFT have a synergistic effect, and the gradation display is further greatly varied. Thus, analog gray scale display is extremely sensitive to variations in TFT characteristics. Therefore, when this EL display device performs gradation display, there is a problem that the display has many irregularities.

On the other hand, when the conventional time gray scale method is used,
There are the following problems.

As the number of gradations increases, the number of divisions per frame also increases. Then, the display period of the lower bits is particularly shortened.

At this time, the rounding of the waveform of the voltage applied to the EL element poses a problem.

After the writing period, in the display period, the EL
When a voltage is applied to the elements, the voltage of the counter electrode of the EL elements of all the pixels is changed at the same time, so that the load applied to the EL elements and the wiring is very large, and the waveform of the voltage applied to the EL elements of all the pixels is very large. Calm down.

As described above, when the waveform of the voltage applied to the EL element is rounded, a predetermined voltage is sufficiently applied to the EL element during the display period, especially in the display period corresponding to the lower bits in which the display period is shortened. Since it cannot be applied, accurate gradation display becomes difficult.

Further, the voltage applied from the power supply line to the EL element in the pixel portion varies due to the wiring resistance of the power supply line and the like. Therefore, the current flowing through the EL element in the pixel portion changes due to the fluctuation of the applied voltage, and the luminance varies.

The magnitude of the current flowing through the EL element is:
It also depends on the temperature.

Here, the luminance of the EL element is proportional to the current flowing through the EL element. Therefore, when the current flowing through the EL element changes, the luminance of the EL element also changes.

FIG. 4 is a graph showing a change (temperature characteristic) of the IV characteristic of the EL element with temperature. From this graph, it is possible to know the amount of current flowing through the EL element with respect to the voltage applied between both electrodes of the EL element at a certain temperature. Here, the temperature T ₁ is higher than the temperature T ₂ and the temperature T _1
2 is higher than the temperature T _3. From this graph, the EL of the pixel portion
Even when the voltage applied between the electrodes of the element is the same, the higher the temperature of the EL layer, the higher the current flowing through the EL element due to the temperature characteristics of the EL element. As described above, the current flowing through the EL element in the pixel portion varies depending on the environmental temperature at which the EL display device is used, and the luminance of the EL element in the pixel portion changes.

For these reasons, accurate gradation expression cannot be performed, which is one of the causes of deteriorating the reliability of the EL display device.

Therefore, a gradation display method which does not need to change the EL drive voltage at high speed, which is hardly affected by the variation in the characteristics of the TFTs in the pixel portion, is used, and a display in which the fluctuation of the luminance due to the environmental temperature of the EL element is suppressed. It is an object to provide a device.

[0059]

Means for Solving the Problems One frame period is divided into a plurality of sub-frame periods, and a voltage applied between both electrodes of an EL element (first EL element) of a pixel whose light emission state is selected is applied to a sub-frame. Display is performed using a time gray scale method, which changes every frame period.

In the lower bit display period, the voltage applied between the two electrodes of the EL element (first EL element) of the pixel whose light emission state is selected is set to the light emission state in the upper bit display period. EL element of pixel (first EL
The voltage is set smaller than the voltage applied between both electrodes of the element. Thus, the display period of the lower bits can be made longer as compared with the conventional time gray scale method.

The voltage applied between both electrodes of the EL element (first EL element) of the pixel whose emission state has been selected is:
A plurality of constant current sources serving as gradation references are provided between both electrodes of a monitor EL element (second EL element) formed on the same substrate as a substrate on which a pixel portion including the first EL element is formed. And generating a current by flowing a constant current.

Further, the E of the pixel is
The voltage applied between both electrodes of the L element (first EL element) is kept constant.

This makes it possible to provide a display device in which the variation in luminance due to the environmental temperature of the EL element is suppressed by a gradation display method which is not easily affected by the variation in the characteristics of the TFT in the pixel portion and does not require a high-speed response of the EL drive voltage. Can be provided.

The configuration of the present invention will be described below.

According to the present invention, a first EL element is constituted by a first electrode, a second electrode, and an EL layer provided between the first electrode and the second electrode. And a method for driving a display device having a second EL element, wherein one frame period is divided into a plurality of sub-frame periods, and the first E period is set for each of the plurality of sub-frame periods.
The L element enters a light emitting state or a non-light emitting state, and a constant current flows between the first electrode and the second electrode of the second EL element during each of the plurality of subframe periods, thereby causing the light emitting state. The first electrode of the first EL element and the second electrode
The voltage between the electrodes of the second
The constant current value is different from each other in two sub-frame periods of the plurality of sub-frame periods, the voltage being equal to the voltage between the first electrode and the second electrode of the EL element. A method for driving a display device is provided.

According to the present invention, a first EL element is constituted by a first electrode, a second electrode, and an EL layer provided between the first electrode and the second electrode. And a method of driving a display device having a second EL element, wherein one frame period is divided into a plurality of sub-frame periods, and the first EL device is provided for each of the plurality of sub-frame periods.
The element is in a light emitting state or a non-light emitting state, and the first EL element of the second EL element
A constant current flows between the first electrode and the second electrode, and the constant current flows as a voltage between the first electrode and the second electrode of the first EL element in the light emitting state. A method of driving a display device, wherein the constant current value is different in each of the plurality of sub-frame periods and equal to a voltage between a first electrode and a second electrode of the second EL element. Is provided.

The driving method of a display device may be characterized in that the plurality of sub-frame periods have the same length.

According to the present invention, a first EL element is constituted by a first electrode, a second electrode, and an EL layer provided between the first electrode and the second electrode. And a method of driving a display device having a second EL element, wherein one frame period is divided into n (n is a natural number of 2 or more) subframe periods, and each subframe period is divided into n subframe periods. , The first EL element is in a light emitting state or a non-light emitting state, and in each of the n subframe periods,
A constant current flows between a first electrode and a second electrode of the second EL element, and the first EL element in the light emitting state is turned on.
The voltage between the first electrode and the second electrode of the element is equal to the voltage between the first electrode and the second electrode of the second EL element through which the constant current flows.
Equal to the voltage between the electrodes, the n in each sub-frame period number, the ratio of the value of the constant current 2 ^0: 2 ^{- 1:
2−2} :...: 2 ^{− (n−2)} : 2− ⁽ⁿ⁻¹⁾ is provided.

A video camera, an image reproducing device, a head-mounted display, a personal computer, or an information terminal device characterized by using the method for driving the display device may be used.

According to the present invention, a plurality of pixels each having a TFT and a first EL element, a power supply line, a buffer amplifier, and a second EL element output constant currents having different values from each other. A display device having a first constant current source A1 and a second constant current source A2, wherein the first EL device
The element and the second EL element each include a first electrode, a second electrode, and an EL layer provided between the first electrode and the second electrode. Constant current source A
1 is connected to the first electrode of the second EL element, or the output terminal of the second constant current source A2 is connected to the first electrode of the second EL element. A first electrode of the second EL element is connected to a non-inverting input terminal of the buffer amplifier;
An output terminal of the buffer amplifier is connected to the power supply line, and a potential of the power supply line is supplied to a first electrode of the first EL element via the TFT. A display device is provided.

According to the present invention, a plurality of pixels each having a TFT and a first EL element, a power supply line, a buffer amplifier, and a second EL element each output a constant current of the same value. n (n is a natural number of 2 or more) constant current sources, and wherein the first EL
The element and the second EL element each include a first electrode, a second electrode, and an EL layer provided between the first electrode and the second electrode. M (m is a natural number not more than n) of the output terminals and the first electrode of the second EL element are connected, or k (m is a natural number) of the n constant current sources. k is a natural number of n or less different from m) and a switch for selecting whether to connect to the first electrode of the second EL element, and a switch for selecting whether to connect the first electrode of the second EL element. Are connected to the non-inverting input terminal of the buffer amplifier, the output terminal of the buffer amplifier is connected to the power supply line, and the potential of the power supply line is set to the first EL via the TFT. A display device is provided, wherein the display device is provided to a first electrode of an element.

The display device may be characterized in that the first electrode of the first EL element and the second EL element is an anode, and the second electrode is a cathode.

The display device may be characterized in that the first electrode of the first EL element and the second EL element is a cathode, and the second electrode is an anode.

A video camera, an image reproducing device, a head-mounted display, a personal computer or an information terminal device characterized by using the display device may be used.

[0075]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The configuration of the present invention will be described with reference to FIG.

Here, 2 ⁿ (n is a natural number of 2 or more)
Although a gray scale display device will be described, the present invention is not limited to 2 ⁿ gray scales and can be freely applied to display devices using other gray scales.

Reference numeral 101 denotes a monitor EL element (a second EL element).
Element), 102 is a buffer amplifier (buffer amplifier), A ₁
To A _n are each a constant current source for supplying a constant current I ₁ ~I _n.

Here, in this specification, a constant current source is an element that always outputs a constant current from its output terminal.

As the constant current source included in the display device of the present invention, a device having a known configuration can be used freely.

Here, the EL element (first EL element) of each pixel in the pixel portion and the EL element for monitoring (second EL element)
L element) 101 includes a first electrode, a second electrode, and an EL layer provided between the first electrode and the second electrode, and has an IV characteristic. , At the same temperature.

[0081] Further, 103 denotes a switch, and select one of the constant current source A ₁ to A _n, and the output terminal, monitoring EL element (the second EL element) one electrode of 101 (the 1 electrode).

Monitor EL element (second EL element) 1
01 is formed on the same substrate as the substrate on which the pixel portion is formed. Note that in this specification, a substrate on which a pixel portion is formed is referred to as a pixel substrate.

Here, the monitor EL element (the second EL element)
The element and the EL element (first EL element) in the pixel portion can be manufactured at the same time.

The constant current sources A _{1 to An} and the buffer amplifier 10
2 are collectively indicated by 1001. 1001 may be formed over a pixel substrate, may be formed over a single crystal IC chip, may be attached to a pixel substrate, or may be formed over an external substrate.

Here, the monitor EL element (the second E
One electrode of the L element) 101 (first electrode), and is connected to the output terminal of the constant current source A ₁ by the switch 103. At this time, a constant current I ₁ is input between both electrodes (first electrode and second electrode) of the monitoring EL element (second EL element) 101.

Monitor EL connected to constant current source A ₁
When the temperature of the surrounding environment changes, the element (second EL element) 101 has both electrodes (first electrode and second electrode) of the element.
Instead of the current I ₁ flowing between does not change, monitor EL element due to the temperature characteristic of the EL element shown in FIG. 4 (second
The voltage between both electrodes (the first electrode and the second electrode) of the EL element changes.

Here, the monitor EL element (the second EL element)
In the electrode of the device), on the side not connected to the constant current source A ₁ electrode (second electrode), it is supplied with a predetermined potential.
This constant potential is set to be substantially the same as the potential of the counter electrode (second electrode) of the EL element (first EL element) in the pixel portion during the display period.

Here, the buffer amplifier 102 has a non-inverting input terminal (+), an inverting input terminal (-), and an output terminal. The buffer amplifier 102 has a function of suppressing a change in the potential input to the non-inverting input terminal (+) due to a load connected to the output terminal, wiring resistance, or the like.

As the buffer amplifier included in the display device of the present invention, a buffer amplifier having a known configuration can be used freely.

Non-inverting input terminal (+) of buffer amplifier
Is an electrode (first electrode) on the side of the monitor EL element (second EL element) connected to the output terminal of the constant current source A1
And the potential of the electrode (first electrode) of the monitoring EL element (second EL element) is input. The potential of the electrode (first electrode) of the monitor EL element (second EL element) is input to the power supply line 104 via the buffer amplifier 102. Here, when the EL driving TFT of the pixel connected to the power supply line 104 is turned on, the potential of the electrode (first electrode) of the monitor EL element (second EL element) 101 becomes the EL of the pixel portion. Element (first EL
Element).

The potential of the electrode (first electrode) on the side connected to the output terminal of the constant current source of the monitor EL element (second EL element) is set to a constant value set by the connected constant current source. It changes according to the temperature so that a current flows. This potential is used as the potential of the pixel electrode (first electrode) of the EL element (first EL element) of the pixel. Accordingly, in the display period, the same voltage as the voltage applied between both electrodes (the first electrode and the second electrode) of the monitor EL element (the second EL element) is applied to the pixel whose emission state is selected. Is applied between both electrodes (first electrode and second electrode) of the EL element (first EL element). Thus, a constant current flows between both electrodes (the first electrode and the second electrode) of the EL element (the first EL element) of the pixel.

As described above, the EL element (the first EL element) in the pixel portion is used.
The element is also applied with a voltage that changes so that a constant current flows between the first electrode and the second electrode in response to a temperature change. Thus, the current flowing through the pixel portion EL element (first EL element) can be kept constant with respect to the temperature change.

Here, the EL element in the pixel portion and the monitor E
Since the L element is formed on the same substrate, its I element
The same -V characteristics can be obtained at the same temperature. Therefore, the monitor EL element (second EL element)
By adjusting the current flowing between the first electrode and the second electrode, the pixel portion EL element (first EL element) can be turned on with required brightness.

[0094] Also, by switching the switch 103 sequentially selects the remaining constant current source A ₂ to A _n, and inputs a constant current I ₂ ~I _n to monitor the EL element (the second EL element) . The voltage generated between the first electrode and the second electrode of the monitor EL elements by constant current I ₂ ~I _n (second EL element) using a buffer amplifier, the EL element of the pixel portion (first Is applied between the first electrode and the second electrode.

Here, the driving method of the present invention will be described with reference to FIG.
This will be described with reference to the timing chart of FIG. In addition, some
The same reference numerals as those used in FIG. 1 are used.

One frame period is divided into a plurality of sub-frame periods SF _{1 to} SF _n . One of the constant current source A ₁ to A _n shown in each the sub-frame periods SF ₁ - SF _n in FIG. 1, the switch 103 are sequentially selected,
The output terminal of the selected constant current source is connected to the first electrode of the monitor EL element (second EL element). At this time, the power supply line, the voltage V ₁ ~V _n corresponding to the constant current I ₁ ~I _n is applied.

[0097] sub-frame period, a write period Ta ₁ to Ta _n each pixel signal is written into all the pixels to select whether or not to emit light, the write period Ta ₁
EL elements of all pixels (the first EL element) and a display period Ts ₁ ~Ts _n to whether or not to emit light respectively by the signal written in to Ta _n.

[0098] The length of the writing period Ta ₁ to Ta _n are all the same, and all the length of the display period Ts ₁ ~Ts _n is the same.

[0099] is the sub every frame period to a constant current source A ₁ to A _n are sequentially selected, constant current, each of which outputs I ₁ ~I _n
By changing the potential of the first electrode of the monitoring EL element (the second EL element), in response to the potential, the potential of the power supply line is changed to V ₁ ~V _n.

[0100] counter electrode potential (second electrode), the potential V ₁ ~V _n each power supply line of each during each write period Ta ₁ to Ta _n, the pixel portion EL element (a first EL element) And are kept the same. Therefore, the writing period Ta ₁
The EL drive voltage is 0 V during the period from ~ Ta _n . On the other hand, during the display periods Ts _{1 to} Ts _n , the potential of the counter electrode (second electrode) of the pixel EL element (first EL element) is between the potential of the power supply line and the EL element. It is set so that a small potential difference occurs.

Here, the potential of the counter electrode (the second electrode) of the pixel EL element (the first EL element) during the writing period changes according to the potential of the power supply line which differs for each sub-frame period. I do. Note that the potential of the counter electrode during the display period may be the same in all subframe periods.

Here, the potential of the counter electrode of the pixel EL element (first EL element) during the display period Ts _{1 to} Ts _n is set to 0.
V. Then, the EL driving applied during the display periods Ts _{1 to} Ts _n is applied between both electrodes (first electrode and second electrode) of the EL element (first EL element) of the pixel whose light emission state is selected. voltage changes of the value of V ₁ ~V _n for each sub-frame period.

This EL drive voltage V₁~ V_nBy the pixel part
(The first EL element) has a constant current source A₁~ A_n
Constant current I output by₁~ I_nConstant current I proportional to
_EL1~ I_ELnFlows. Here, the EL element flows through the element.
Current I_EL1~ I_ELnThe emission luminance is almost directly proportional to
There is a property. Therefore, the current I₁~ I_n, That is, constant current
Source A₁~ A_nCurrent I flowing through₁~ I_nRatio I₁: I_Two: ・ ・
・ ： I_n-1: I_n, 2 ⁰: 2^-1: ・ ・ ・: 2^-(n-2): 2
^-(n-1)Is set so that the EL element of the pixel portion (the
1 EL element) in each display period Ts₁~ Ts_nThe place where light was emitted
Light emission luminance Lm₁~ Lm_nRatio Lm₁: Lm_Two: ・ ・ ・:
Lm_(n-1): Lm_nAlso 2⁰: 2^-1: ・ ・ ・: 2^-(n-2):
2^-(n-1)Becomes

At this time, the luminance of the pixel is determined by integrating the light emission amounts in the display periods Ts _{1 to} Ts _n in which the pixel is lit during one frame period. For example, when n = 8, if the luminance when the pixel emits light in all display periods Ts _{1 to} Ts _n is 100%, if the pixel emits light in Ts ₁ and Ts ₂ , about 75% luminance is obtained. Can be expressed. On the other hand, if you select Ts ₃ and Ts ₅ and Ts ₈ it can be expressed luminance of about 16%.

The display periods Ts _{1 to} Ts _n may appear in any order. For example, during one frame period, the next Ts _1, Ts _4, Ts _3, it is possible to reveal the display period in the order such as Ts ₂ · · ·.

Further, as described above, when there are a plurality of constant current sources outputting currents of different values, the same constant current source is selected in a plurality of subframe periods in one frame period, and the same constant current source is selected. It is also possible to express gradation by making the length of the display period of each sub-frame period in which the current source is selected different.

For example, as shown in the timing chart of FIG. 19, the same constant current source is selected in a plurality of subframe periods out of n subframe periods in one frame period.
It is also possible to express gradation by changing the length of the display period of each sub-frame period in which the same constant current source is selected.

In FIG. 19, subframe period SF1
And SF2, the same constant current source A1 is selected. At this time, the display period Ts of the sub-frame periods SF1 and SF2
1 and Ts2 have different lengths.

As described above, the method of changing the length of the display period in different sub-frame periods and the method of monitoring EL element (second E) in different sub-frame periods are described.
A constant current source required for a longer display period of lower bits and a gradation display by combining with a method of changing a current flowing between both electrodes (first electrode and second electrode) of the L element). Can be reduced.

Further, when the current values output from n (n is a natural number of 2 or more) constant current sources are the same, and m (m is n
The following natural numbers) output terminals of constant current sources and monitor E
Connecting the first electrode of the L element (the second EL element) to output terminals of k (k is a natural number of n or less different from m) constant current sources in another subframe period; E for monitor
The first electrode of the L element (the second EL element) is connected.

As described above, the sum of the output currents of the selected plurality of constant current sources is used as the monitor EL element (the second EL element).
The current may flow between the first electrode and the second electrode of the element.

[0112]

Embodiments of the present invention will be described below.

(Embodiment 1) In this embodiment, the structure of a buffer amplifier included in a display device of the present invention will be described.

FIG. 3 shows an example in which a buffer amplifier is manufactured using TFTs.

The buffer amplifiers are TFTs 1901 to 190
9. Capacitor 1910, constant current sources 1911, 1912
And so on. TFT 1901, 1902, 19
Reference numerals 06 and 1909 denote n-channel TFTs.
Reference numerals 1903 to 1905, 1907, and 1908 denote p-channel TFTs.

Reference numeral 1930 denotes a high potential side power supply line.
1931 is a low potential side power supply line.

The operation of the buffer amplifier will be described in detail below.

The differential amplifier circuit 1921 constituted by the TFTs 1901 and 1902 will be described. The amount of current flowing between the drain and source of each TFT due to the difference between the voltage input to the gate electrode of TFT 1901 corresponding to the non-inverting input terminal of the buffer amplifier and the gate electrode of TFT 1902 corresponding to the inverting input terminal of the buffer amplifier Are different. This current is referred to as i1 and i2, respectively.

Here, the current mirror circuit 1922 is
It is composed of TFTs 1903 and 1904. TF
Since the gate electrode of T1903 and the gate electrode of TFT1904 are connected, the potentials of the gate electrodes of the two TFTs are equal. Therefore, the TFT 1903 and the TFT
The amount of current flowing between the source and the drain in 1904 becomes equal. Therefore, T of the differential amplifier circuit 1921
Currents i1 and i2 flowing through FT1901 and TFT1902
Must be input to the differential amplifier circuit 1921.

The current i3 is supplied from the capacitor 1910. Thereby, the potential difference V between the electrodes of the capacitor 1910 increases. The potential difference V is equal to
923.

The common source amplifier circuit 1923 is connected to the TFT 1
905. The input potential difference V is T
This is the potential difference between the source and the drain of the FT 1905. A current i4 flows in accordance with the potential difference V. here,
The constant current source 1912 passes only a constant current i0. Therefore, the difference i5 between the currents i4 and i0 is input to the source follow buffer circuit 1924. This current i5 is
It increases in accordance with the amplified potential difference V.

The source follow buffer circuit 1924 is
It is composed of TFTs 1906 and 1907.
An input i5 from the common source amplifier 1923 is a TFT
Input to the gate electrode of 1906. This input current i5
Accordingly, the amount of the current i6 flowing between the source and the drain of the TFT 1906 increases. That is, a larger current is output from the buffer amplifier.

As described above, the buffer amplifier amplifies and outputs the current.

Although the differential circuit is composed of n-channel TFTs here, it may be composed of p-channel TFTs.

(Embodiment 2) In this embodiment, the TFs of the pixel portion of the display device of the present invention and the drive circuit portions (source signal line side drive circuit and gate signal line side drive circuit) provided around the pixel portion are provided.
A method for simultaneously manufacturing T will be described. However, for the sake of simplicity, a CMOS circuit, which is a basic unit for the drive circuit unit, is illustrated.

First, as shown in FIG. 9A, oxidation is performed on a substrate 5001 made of glass such as barium borosilicate glass represented by Corning # 7059 glass or # 1737 glass or aluminoborosilicate glass. A base film 5002 made of an insulating film such as a silicon film, a silicon nitride film, or a silicon oxynitride film is formed. For example, a plasma CVD method _{SiH 4, NH 3, N 2} O silicon oxynitride film 5002a made from 10 to 20
0 [nm] (preferably 50 to 100 [nm]) is formed, similarly SiH _4, N ₂ O hydrogenated silicon oxynitride film 5002b made from 50 to 200 [nm] (preferably 100 to
150 [nm]). Although the base film 5002 has a two-layer structure in this embodiment, the base film 5002 may have a single-layer structure or a structure in which two or more insulating films are stacked.

The island-shaped semiconductor layers 5003 to 5006 are formed of a crystalline semiconductor film formed by using a semiconductor film having an amorphous structure by a laser crystallization method or a known thermal crystallization method.
The thickness of the island-shaped semiconductor layers 5003 to 5006 is 25 to 8
It is formed with a thickness of 0 [nm] (preferably 30 to 60 [nm]). The material of the crystalline semiconductor film is not limited, but is preferably formed of silicon or a silicon germanium (SiGe) alloy.

In order to form a crystalline semiconductor film by a laser crystallization method, a pulse oscillation type or continuous emission type excimer laser, a YAG laser, or a YVO ₄ laser is 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 30 [Hz], and the laser energy density is 100 to 400 [mJ / cm ² ] (typically, 2
00 to 300 [mJ / cm ² ]). When a YAG laser is used, the second harmonic is used, the pulse oscillation frequency is set to 1 to 10 [kHz], and the laser energy density is set to 30.
0 to 600 [mJ / cm ² ] (typically 350 to 500 [mJ / c]
m ² ]). And a width of 100 to 1000 [μm],
For example, a laser beam condensed linearly at 400 [μm] is irradiated over the entire surface of the substrate, and the superposition rate (overlap rate) of the linear laser beam at this time is set to 80 to 98 [%].

Next, island-like semiconductor layers 5003 to 5006
Is formed to cover the gate insulating film 5007. The gate insulating film 5007 is formed by a plasma CVD method or a sputtering method.
It is formed of an insulating film containing silicon with a thickness of 40 to 150 [nm]. In this embodiment, a silicon oxynitride film is formed with a thickness of 120 [nm]. Needless to say, the gate insulating film is not limited to such a silicon oxynitride film, and another insulating film containing silicon may be used as a single layer or a stacked structure. For example, 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]) and a 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.].

[0130] Then, a first conductive film 5008 and a second conductive film 5009 for forming a gate electrode are formed over the gate insulating film 5007. In this embodiment, the first conductive film 5008 is formed of Ta to a thickness of 50 to 100 [nm],
A second conductive film 5009 is formed with W to a thickness of 100 to 300 [nm].

The Ta film is formed by a sputtering method by sputtering a Ta target with Ar. in this case,
When an appropriate amount of Xe or Kr is added to Ar, the internal stress of the Ta film can be relaxed and the film can be prevented from peeling. Also, α
The phase Ta film has a resistivity of about 20 [μΩcm] and can be used as a gate electrode, but the β phase Ta film has a resistivity of about 180 [μΩcm] and is not suitable for a gate electrode. . In order to form an α-phase Ta film, tantalum nitride having a crystal structure close to the Ta α-phase is formed on a Ta base with a thickness of about 10 to 50 [nm]. Can be easily obtained.

When a W film is formed, it is formed by a sputtering method using W as a target. Alternatively, it can 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.
[μΩcm] or less is desirable. 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, the crystallization is inhibited and the resistance is increased. From this, in the case of using the sputtering method, a W target having a purity of 99.9999 [%] is used, and a W film is formed by giving sufficient consideration so as not to mix impurities from the gas phase during film formation. Resistivity 9-20
[μΩcm] can be realized.

In this embodiment, the first conductive film 500
8 was Ta, and the second conductive film 5009 was W. However, there is no particular limitation, and any of Ta, W, Ti, Mo, Al, and Cu was used.
Alternatively, it may be formed of an element selected from the above, or an alloy material or a compound material containing the element as a main component. Also,
A semiconductor film typified by a polycrystalline silicon film doped with an impurity element such as phosphorus may be used. As a desirable example of another combination other than this embodiment, a combination in which the first conductive film 5008 is formed of tantalum nitride (TaN) and the second conductive film 5009 is W, Is formed of tantalum nitride (TaN), the second conductive film 5009 is made of Al, the first conductive film 5008 is made of tantalum nitride (TaN), and the second conductive film 5009 is made of Cu. No.

Next, a mask 5010 is formed using a resist, and a first etching process for forming electrodes and wirings is performed. In this embodiment, ICP (Inductively Coupled)
d Plasma: Inductively coupled plasma) etching method,
CF ₄ and Cl ₂ are mixed as an etching gas, and RF (13.56 [MH]) of 500 [W] is applied to the coil-type electrode at a pressure of 1 [Pa].
z]) Power is supplied to generate plasma. 100 [W] RF (13.56 [MH] also on the substrate side (sample stage)
z]) Apply power and apply a substantially negative self-bias voltage. When CF ₄ and Cl ₂ are mixed, the W film and Ta
The film is etched to the same extent.

Under the above-mentioned etching conditions, the shape of the resist mask is made appropriate, so that the ends of the first conductive layer and the second conductive layer are tapered due to the effect of the bias voltage applied to the substrate side. Become. The angle of the tapered portion is 15 to 45 °. In order to perform etching without leaving a residue on the gate insulating film, the etching time may be increased by about 10 to 20%. Since the selectivity of the silicon oxynitride film to the W film is 2 to 4 (typically 3), the exposed surface of the silicon oxynitride film is etched by about 20 to 50 [nm] by over-etching. become. Thus, by the first etching process, the first conductive layer and the second conductive layer
Conductive layers 5011 to 5016 (first conductive layer 50
11a to 5016a and second conductive layers 5011b to 501
6b) is formed. At this time, in the gate insulating film 5007, a region which is not covered with the first shape conductive layers 5011 to 5016 is etched to a thickness of about 20 to 50 [nm] to form a thinned region. (FIG. 9 (B))

Then, a first doping process is performed to add an impurity element imparting n-type. The doping may be performed by an ion doping method or an ion implantation method. The condition of the ion doping method is that the dose is 1 × 10 ^{13 to} 5 × 10
¹⁴ [atoms / cm ² ] and an acceleration voltage of 60 to 100 [keV]. An element belonging to Group 15 of the periodic table, typically phosphorus (P) or arsenic (As) is used as the n-type impurity element. Here, phosphorus (P) is used. In this case, the conductive layers 5011 to 5015 serve as a mask for the impurity element imparting n-type, and are self-aligned in the first impurity region 50.
17 to 5025 are formed. First impurity region 501
For 7 to 5025, 1 × 10 ²⁰ to 1 × 10 ²¹ [atoms / cm ³ ]
Is added in the concentration range of n.
(FIG. 9 (B))

Next, as shown in FIG. 9C, a second etching process is performed without removing the resist mask. Using CF ₄ , Cl ₂ and O _{2 as an} etching gas,
The film is selectively etched. At this time, the second shape conductive layers 5026 to 5031 are formed by the second etching process.
(First conductive layers 5026a to 5031a and second conductive layers 5026b to 5031b) are formed. At this time, in the gate insulating film 5007, the second shape conductive layer 50 is formed.
The area not covered by 26 to 5031 is further 20 to 50 [n
m] to form a thinned region.

The etching reaction of the W film or the Ta film by the mixed gas of CF ₄ and Cl ₂ can be estimated from the generated radicals or ionic species and the vapor pressure of the reaction product.
Comparing the vapor pressures of fluorides and chlorides of W and Ta, W
WF ₆ is extremely high and other WC
l ₅ , TaF ₅ and TaCl ₅ are comparable. Therefore, C
With the mixed gas of F ₄ and Cl ₂ , both the W film and the Ta film are etched. However, when an appropriate amount of O ₂ is added to this mixed gas, CF ₄ and O ₂ react to form CO and F, and a large amount of F radicals or F ions are generated. As a result, the etching rate of the W film having a high fluoride vapor pressure increases. On the other hand, in Ta, the increase in the etching rate is relatively small even if F increases. Further, since Ta is more easily oxidized than W, the surface of Ta is oxidized by adding O ₂ .
Since the oxide of Ta does not react with fluorine or chlorine,
The etching rate of the a film decreases. Therefore, the W film and Ta
It is possible to make a difference in the etching rate with the film, and it is possible to make the etching rate of the W film larger than that of the Ta film.

Then, a second doping process is performed as shown in FIG. In this case, the dose is lower than that of the first doping process, and n is set as a condition of a high acceleration voltage.
Doping with an impurity element for giving a mold. For example, the acceleration voltage is set to 70 to 120 [keV], and 1 × 10 ¹³ [atoms / cm]
² ], a new impurity region is formed inside the first impurity region formed in the island-shaped semiconductor layer in FIG. 9B. The doping is performed in the second shape conductive layer 5026-
5030 as a mask for the impurity element,
The regions below the conductive layers 5026a to 5030a are also doped so as to add an impurity element. Thus,
Third impurity regions 5032 to 5036 are formed. The concentration of phosphorus (P) added to third impurity regions 5032 to 5036 depends on that of first conductive layers 5026 a to 5030.
It has a gentle concentration gradient according to the film thickness of the tapered portion a. Note that in the semiconductor layer overlapping the tapered portions of the first conductive layers 5026a to 5030a, the first conductive layer 5
Although the impurity concentration slightly decreases from the end of the tapered portion of 026a to 5030a toward the inside, the impurity concentration is almost the same.

A third etching process is performed as shown in FIG. This is performed using a reactive ion etching method (RIE method) using CHF ₃ as an etching gas. Third
Of the first conductive layers 5026a to 5026a-5
031a is partially etched to form the first portion.
The region where the conductive layer overlaps with the semiconductor layer is reduced. By the third etching treatment, the third shape conductive layer 5037 is formed.
To 5042 (first conductive layers 5037a to 5042a and second conductive layers 5037b to 5042b). At this time, in the gate insulating film 5007, a region that is not covered with the third shape conductive layers 5037 to 5042 is two more.
A region that is etched and thinned by about 0 to 50 [nm] is formed.

By the third etching process, third impurity regions 5032a to 5036a overlapping with first conductive layers 5037a to 5041a are formed in third impurity regions 5032 to 5036 before the third etching. Second impurity region 5 between impurity region and third impurity region
032b to 5036b are formed.

Then, as shown in FIG. 10C, island-shaped semiconductor layers 5004 and 50 forming a p-channel TFT are formed.
In 06, fourth impurity regions 5043 to 5054 having a conductivity type opposite to the first conductivity type are formed. Third shape conductive layer 5
Using 038b and 5041b as masks for impurity elements, impurity regions are formed in a self-aligned manner. At this time, the island-shaped semiconductor layer 500 forming the n-channel TFT is formed.
3, 5005 and the wiring portion 5042
The entire surface is covered with 200. Impurity regions 5043-5
054 has already been doped with different concentrations of phosphorus, but the impurity concentration is 2 × 10 5 in any of the regions using diborane (B ₂ H ₆ ) and ion doping.
^It is formed so as to be ^{20 to} 2 × 10 ²¹ [atoms / cm ³ ].

Through the above steps, impurity regions are formed in each of the island-shaped semiconductor layers. Third overlapping with the island-shaped semiconductor layer
The conductive layers 5037 to 5041 each having the shape described above function as gate electrodes. 5042 functions as an island-shaped source signal line.

After removing the resist mask 5200, a step of activating the impurity element added to each island-shaped semiconductor layer is performed for the purpose of controlling the conductivity type. 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 400 to 700 in a nitrogen atmosphere of 1 [ppm] or less, preferably 0.1 [ppm] or less.
In this embodiment, the heat treatment is performed at 500 ° C. for 4 hours.
However, when the wiring material used for the third shape conductive layers 5037 to 5042 is weak to heat, activation is performed after an interlayer insulating film (mainly containing silicon) is formed to protect the wiring and the like. It is preferred to do so.

Further, a heat treatment is performed at 300 to 450 ° C. for 1 to 12 hours in an atmosphere containing 3 to 100% of hydrogen to hydrogenate the island-like semiconductor layer. In this step, dangling bonds in the semiconductor layer are terminated by thermally excited hydrogen. As another means of hydrogenation, plasma hydrogenation (using hydrogen excited by plasma) may be performed.

Next, as shown in FIG.
Of the interlayer insulating film 5055 from the silicon oxynitride film to 100
It is formed with a thickness of about 200 [nm]. After a second interlayer insulating film 5056 made of an organic insulating material is formed thereon, the first interlayer insulating film 5055, the second interlayer insulating film 5056,
And a contact hole is formed in the gate insulating film 5007, and each wiring (including a connection wiring and a signal line) 5057 is formed.
After patterning 5062 and 5064, the pixel electrode 5063 in contact with the connection wiring 5062 is formed by patterning.

As the second interlayer insulating film 5056, a film made of an organic resin is used. As the organic resin, polyimide, polyamide, acrylic, BCB (benzocyclobutene), or the like can be used. In particular, since the second interlayer insulating film 5056 has a strong meaning of flattening, acrylic having excellent flatness is preferable. In this embodiment, an acrylic film is formed with a thickness that can sufficiently flatten a step formed by a TFT. Preferably, it is 1 to 5 [μm] (more preferably, 2 to 4 [μm]).

The contact holes are formed by dry etching or wet etching. The contact holes reach the n-type impurity regions 5017, 5018, 5021, 5023 or the p-type impurity regions 5043 to 5054, the contact holes reach the wiring 5042, A contact hole (not shown) reaching the power supply line and a contact hole (not shown) reaching the gate electrode are formed.

In addition, wiring (connection wiring) 5057 to 506
2, 5064, a three-layer laminated film in which a Ti film was continuously formed by a sputtering method, a Ti-containing aluminum film having a thickness of 100 nm, a Ti-containing aluminum film having a thickness of 300 nm, and a Ti film having a thickness of 150 nm was patterned into a desired shape. Use something. Of course, another conductive film may be used.

In this embodiment, an ITO film having a thickness of 110 [nm] was formed as the pixel electrode 5063, and was patterned. Contact is established by arranging the pixel electrode 5063 so as to be in contact with and overlap with the connection wiring 5062. Alternatively, a transparent conductive film in which 2 to 20% of zinc oxide (ZnO) is mixed with indium oxide may be used. This pixel electrode 5063 becomes the anode of the EL element. (FIG. 11
(A))

Next, as shown in FIG. 11B, an insulating film containing silicon (a silicon oxide film in this embodiment) is formed to a thickness of 500 [nm], and is formed at a position corresponding to the pixel electrode 5063. An opening is formed, and a third interlayer insulating film 5065 functioning as a bank is formed. When the opening is formed, a tapered side wall can be easily formed by using a wet etching method. Care must be taken because if the side wall of the opening is not sufficiently smooth, deterioration of the EL layer due to the step will become a significant problem.

Next, the EL layer 5066 and the cathode (MgA
g electrode) 5067 is continuously formed using a vacuum deposition method without opening to the atmosphere. Note that the thickness of the EL layer 5066 is 80
The thickness of the cathode 5067 is 180 to 300 [nm] (typically, 20 to 200 [nm] (typically 100 to 120 [nm]).
0 to 250 [nm]).

In this step, an EL layer and a cathode are sequentially formed for a pixel corresponding to red, a pixel corresponding to green, and a pixel corresponding to blue. 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 that the EL layer and the cathode are selectively formed only in necessary portions.

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.

Here, a method of forming three types of EL elements corresponding to RGB was used. However, a method of combining a white light emitting EL element and a color filter, a blue or blue-green light emitting EL element and a phosphor (fluorescent And a method in which an EL element corresponding to RGB is stacked on a cathode (a counter electrode) using a transparent electrode.

Note that a known material can be used for the EL layer 5066. 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 cathode 5067 is formed using a metal mask on a pixel having a switching TFT in which a gate electrode is connected to the same gate signal line (a pixel on the same line). In this embodiment, MgA is used as the cathode 5067.
Although g was used, the present invention is not limited to this. Cathode 50
Other known materials may be used as 67.

Finally, a passivation film 5068 made of a silicon nitride film is formed to a thickness of 300 [nm]. By forming the passivation film 5068, the EL layer 50
66 can be protected from moisture and the like, and the reliability of the EL element can be further improved.

According to the above steps, the monitor E
The L element (the second EL element) can be formed over the same substrate at the same time as the EL element of the pixel (the first EL element).

Thus, an EL display device having a structure as shown in FIG. 11B is completed. Note that EL in this embodiment is
In the manufacturing process of the display device, Ta, which is a material forming the gate electrode,
The source signal line is formed of W, and the gate signal line is formed of Al, which is a wiring material forming the drain and source electrodes, but different materials may be used.

By the way, the EL display device of this embodiment exhibits very high reliability and can improve the operating characteristics by arranging the TFT having the optimum structure not only in the pixel portion but also in the drive circuit portion. It is also possible to add a metal catalyst such as Ni in the crystallization step to enhance the crystallinity. Thereby, the driving frequency of the source signal line driving circuit is set to 10 [MH].
z] or more.

First, a TFT having a structure in which hot carrier injection is reduced so as not to lower the operation speed as much as possible,
N-channel type TF of CMOS circuit forming drive circuit section
Used as T. In addition, as the drive circuit here,
It includes a shift register, a buffer, a level shifter, a latch in line-sequential driving, a transmission gate in point-sequential driving, and the like.

In the case of this embodiment, the activity of the n-channel TFT is
The conductive layer is between the source region, the drain region, and the gate insulating film.
Overlap LDD region that overlaps with the gate electrode
(L _OVRegion), with the gate electrode sandwiching the gate insulating film
Offset LDD areas (L_OFFArea) and
Including a channel forming region.

Also, a p-channel type TFT of a CMOS circuit
Since there is almost no concern about deterioration due to hot carrier injection, it is not necessary to provide an LDD region. Needless to say, it is also possible to provide an LDD region similarly to the n-channel type TFT and take measures against hot carriers.

In addition, when a CMOS circuit in which current flows bidirectionally in the channel formation region, that is, a CMOS circuit in which the roles of the source region and the drain region are exchanged is used in the driver circuit, n In the channel type TFT, it is preferable to form an LDD region on both sides of the channel formation region so as to sandwich the channel formation region. An example of such a transmission gate is a transmission gate used for dot sequential driving. Further, in the case where a CMOS circuit in which off-state current needs to be suppressed as low as possible is used in the driver circuit, the n-channel TFT forming the CMOS circuit preferably has an L _OV region. As such an example,
A transmission gate used for point-sequential driving is exemplified.

[0166] When the structure shown in Fig. 11 (B) is actually completed, the protective film (laminate film, ultraviolet curable resin film, etc.) with high airtightness and low degassing is used to prevent further exposure to the outside air. It is preferable to package (enclose) with an optical sealing material. At this time, the reliability of the EL element is improved by setting the inside of the sealing material to an inert atmosphere or disposing a hygroscopic material (for example, barium oxide) inside.

When the airtightness is improved 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 a state in which the product can be shipped is referred to as a display device in this specification.

According to the steps described in this embodiment, the number of photomasks required for manufacturing a display device can be reduced. As a result, the process can be shortened, which can contribute to a reduction in manufacturing cost and an improvement in yield.

Embodiment 3 In this embodiment, the EL of the present invention is used.
An example in which a display device is manufactured will be described.

FIG. 12A is a top view of the EL display device of the present invention. In FIG. 12A, reference numeral 4010 denotes a substrate;
4011 is a pixel portion, 4012 is a source signal side driving circuit,
Reference numeral 4013 denotes a gate signal side driving circuit. The pixel portion and each driving circuit are connected to the FP through wirings 4014 to 4016.
It reaches C4017 and is connected to an external device.

At this time, the cover member 600 is formed so as to surround at least the pixel portion, preferably, the driving circuit and the pixel portion.
0, sealing material (also referred to as housing material) 7000,
A sealing material (a second sealing material) 7001 is provided.

FIG. 12B shows a cross-sectional structure of the EL display device of this embodiment.
A driving circuit TFT 4022 (here, a CMOS circuit combining an n-channel TFT and a p-channel TFT is illustrated) 4022 and a pixel portion TFT 40
23 (however, here, TF for controlling the current to the EL element)
Only T is shown. ) Is formed. These T
The FT may use a known structure (top gate structure or bottom gate structure).

Driving circuit TFT 4022, pixel portion TF
When T4023 is completed, a pixel electrode 4027 made of a transparent conductive film electrically connected to the drain of the pixel portion TFT 4023 is formed on an interlayer insulating film (flattening film) 4026 made of a resin material. As the transparent conductive film, a compound of indium oxide and tin oxide (called ITO) or a compound of indium oxide and zinc oxide can be used. After the pixel electrode 4027 is formed, an insulating film 4028 is formed, and an opening is formed over the pixel electrode 4027.

Next, an EL layer 4029 is formed. The EL layer 4029 is formed of a known EL material (a hole injection layer, a hole transport layer,
A light emitting layer, an electron transport layer, or an electron injection layer) may be freely combined to form a stacked structure or a single layer structure. A known technique may be used to determine the structure. EL materials include low molecular weight materials and high molecular weight (polymer) materials. When a low molecular material is used, an evaporation method is used. When a high molecular material is used, a simple method such as a spin coating method, a printing method, or an ink jet method can be used.

In this embodiment, an EL layer is formed by an evaporation method using a shadow mask. By forming a light-emitting layer (a red light-emitting layer, a green light-emitting layer, and a blue light-emitting layer) capable of emitting light having different wavelengths for each pixel using a shadow mask, color display becomes possible. In addition, the color conversion layer (CC
M) and a color filter are combined, and a white light-emitting layer and a color filter are combined. Either method may be used. Needless to say, a monochromatic EL display device can be used.

After forming the EL layer 4029, the cathode 4030 is formed thereon. Cathode 4030 and EL layer 4029
It is desirable to remove as much as possible moisture and oxygen existing at the interface. Therefore, the EL layer 4029 and the cathode 40 in vacuum
It is necessary to devise a method of continuously forming the film 30 or forming the EL layer 4029 in an inert atmosphere and forming the cathode 4030 without opening to the atmosphere. In this embodiment, the above-described film formation is made possible by using a multi-chamber type (cluster tool type) film formation apparatus.

In this embodiment, as the cathode 4030,
A laminated structure of a LiF (lithium fluoride) film and an Al (aluminum) film is used. Specifically, a 1-nm-thick LiF (lithium fluoride) film is formed over the EL layer 4029 by a vapor deposition method, and a 300-nm-thick aluminum film is formed thereover. Of course, a MgAg electrode which is a known cathode material may be used. The cathode 4030 is connected to the wiring 4016 in a region indicated by 4031. A wiring 4016 is a power supply line for applying a predetermined voltage to the cathode 4030, and the FPC 401 via the conductive paste material 4032.
7 is connected.

In the region indicated by 4031, the cathode 40
In order to electrically connect the wiring 30 and the wiring 3016, it is necessary to form contact holes in the interlayer insulating film 4026 and the insulating film 4028. These are at the time of etching the interlayer insulating film 4026 (at the time of forming the contact hole for the pixel electrode).
Or when the insulating film 4028 is etched (when an opening is formed before the EL layer is formed). Also, the insulating film 40
When etching 28, etching may be performed all at once up to the interlayer insulating film 4026. In this case, the interlayer insulating film 40
If the same resin material is used for the insulating film 26 and the insulating film 4028, the shape of the contact hole can be made good.

The passivation film 6003 and the filler 600 cover the surface of the EL element thus formed.
4. The cover material 6000 is formed.

Further, a sealing material 70 is provided between the cover material 6000 and the substrate 4010 so as to surround the EL element portion.
The sealing material (second sealing material) 7001 is formed outside the sealing material 7000.

At this time, the filler 6004 also functions as an adhesive for bonding the cover material 6000.
As the filler 6004, PVC (polyvinyl chloride), epoxy resin, silicone resin, PVB (polyvinyl butyral), or EVA (ethylene vinyl acetate) can be used. It is preferable to provide a desiccant inside the filler 6004 because a moisture absorbing effect can be maintained.

Further, a spacer may be contained in the filler 6004. At this time, the spacer may be a granular substance made of BaO or the like, and the spacer itself may have hygroscopicity.

When a spacer is provided, the passivation film 6003 can reduce the spacer pressure.
In addition to the passivation film 6003, a resin film or the like for relaxing a spacer pressure may be provided.

As the cover member 6000, a glass plate, an aluminum plate, a stainless steel plate, FRP (Fiber)
rglass-Reinforced Plastic
s) plate, PVF (polyvinyl fluoride) film,
Mylar film, polyester film or acrylic film can be used. The filling material 600
When PVB or EVA is used as 4, it is preferable to use a sheet having a structure in which aluminum foil of several tens of μm is sandwiched between PVF films or Mylar films.

However, depending on the direction of light emission (the direction of light emission) from the EL element, the cover material 6000 needs to have translucency.

The wiring 4016 is made of a sealing material 700.
0 and through the gap between the sealing material 7001 and the substrate 4010, and is electrically connected to the FPC 4017. Although the wiring 4016 has been described here, the other wiring 401
4, 4015 are similarly electrically connected to the FPC 4017 under the sealant 7000 and the sealant 7001.

In FIG. 12, the sealing material 7000 is attached so as to cover the side surface (exposed surface) of the filling material 6004 after the filling material 6004 is provided, and then the cover material 6000 and the sealing material are attached. 700
After attaching 0, the filler 6004 may be provided.
In this case, an injection port for a filler is provided to communicate with a space formed by the substrate 4010, the cover material 6000, and the sealing material 7000. Then, the gap is evacuated to a vacuum (10 ⁻² T).
or less), the inlet is immersed in a water tank containing the filler, and the pressure outside the gap is made higher than the pressure inside the gap to fill the gap with the filler.

(Embodiment 4) Next, FIGS. 12A and 12B
An example of manufacturing an EL display device having a different form from
This will be described with reference to FIGS. FIG.
Elements having the same numbers as (A) and (B) indicate the same parts, and thus description thereof will be omitted.

FIG. 13A is a top view of the EL display device of this embodiment, and FIG. 13B is a cross-sectional view taken along line AA ′ of FIG.

According to FIG. 12, a passivation film 6003 is formed to cover the surface of the EL element.

[0191] Further, a filler 6004 is provided so as to cover the EL element. This filler 6004 is used as the cover material 6
000 also functions as an adhesive for bonding. As the filler 6004, PVC (polyvinyl chloride), epoxy resin, silicone resin, PVB (polyvinyl butyral), or EVA (ethylene vinyl acetate) can be used. It is preferable to provide a desiccant inside the filler 6004 because a moisture absorbing effect can be maintained.

[0192] The filler 6004 may contain a spacer. At this time, the spacer may be a granular substance made of BaO or the like, and the spacer itself may have hygroscopicity.

In the case where a spacer is provided, the passivation film 6003 can reduce the spacer pressure.
Further, a resin film or the like for relaxing the spacer pressure may be provided separately from the passivation film.

As the cover material 6000, a glass plate, an aluminum plate, a stainless steel plate, FRP (Five)
rglass-Reinforced Plastic
s) plate, PVF (polyvinyl fluoride) film,
Mylar film, polyester film or acrylic film can be used. The filling material 600
When PVB or EVA is used as 4, it is preferable to use a sheet having a structure in which aluminum foil of several tens of μm is sandwiched between PVF films or Mylar films.

However, depending on the light emitting direction (light emitting direction) from the EL element, the cover material 6000 needs to have a light transmitting property.

Next, the cover material 6
After bonding 000, the side surface of filler 6004 (exposed surface)
Frame material 6001 is attached so as to cover. The frame material 6001 is a sealing material (functions as an adhesive)
Glued by 6002. At this time, a photocurable resin is preferably used as the sealing material 6002, but a thermosetting resin may be used as long as the heat resistance of the EL layer is allowed. Note that the sealing material 6002 is preferably a material that does not transmit moisture or oxygen as much as possible. Further, a desiccant may be added to the inside of the sealing material 6002.

The wiring 4016 is made of a sealing material 600.
2 is electrically connected to the FPC 4017 through a gap between the substrate 2 and the substrate 4010. Note that although the wiring 4016 has been described here, the other wirings 4014 and 4015 are also electrically connected to the FPC 4017 under the sealing material 6002 in the same manner.

In FIG. 13, the frame material 6001 is attached so as to cover the side surface (exposed surface) of the filler material 6004 after the filler material 6004 is provided and then the cover material 6000 is bonded. After the 6001 is attached, the filler 6004 may be provided. In this case, an inlet for a filler is provided to communicate with a gap formed by the substrate 4010, the cover member 6000, and the frame member 6001. Then, the gap is evacuated to a vacuum (10 ^-2 Torr).
After filling the filler in the water tank containing the filler, the pressure outside the gap is made higher than the pressure inside the gap, and the filler is filled into the gap.

Embodiment 5 In this embodiment, the EL of the present invention is used.
4 illustrates an example of a structure of a pixel portion of a display device.

FIG. 14 shows a detailed sectional structure of the pixel portion.
In FIG. 14, a switching TFT 3502 provided over a substrate 3501 is manufactured by a known method. 46 is a gate insulating film. This embodiment has a double gate structure. Although the double gate structure is used in this embodiment, a single gate structure, a triple gate structure, or a multi-gate structure having more gates may be used.

In this embodiment, the switching TFT
Has a laminated structure of a first conductive layer 38a and a second conductive layer 38b.

The EL driving TFT 3503 is an n-channel TFT, and is manufactured by using a known method.
At this time, the source wiring 41 of the switching TFT is
It is connected to the source signal line 39. In this embodiment, the source signal line has a stacked structure of the first conductive layer 39a and the second conductive layer 39b. Switching TF
The drain wiring 35 of T3502 is an EL driving TFT 35
03 is electrically connected to the gate electrode 37. EL
The drain wiring 40 of the driving TFT 3503 is connected to the cathode 43 of the EL element. The EL driving TFT 35
The source wiring 34 is connected to a power supply line (not shown) and is supplied with a voltage.

In this embodiment, the TFT 3503 for EL driving is shown in a single gate structure, but a multi-gate structure in which a plurality of TFTs are connected in series may be used. Further, a structure in which a plurality of TFTs are connected in parallel to substantially divide the channel formation region into a plurality of regions so that heat can be radiated with high efficiency may be employed. Such a structure is effective as a measure against deterioration due to heat.

In this embodiment, the gate electrodes of the EL driving TFTs are formed by the first conductive layer 37a and the second conductive layer 37b.
Has a laminated structure.

On the switching TFT 3502 and the EL driving TFT 3503, an interlayer insulating film 49 and a flattening film 42 made of a resin insulating film are formed. Flattening film 42
It is very important to flatten the step due to the TFT by using the method. Since an EL layer formed later is extremely thin, poor light emission may be caused by the presence of a step. Therefore, it is desirable that the EL layer be flattened before forming the pixel electrode so that the EL layer can be formed as flat as possible.

Reference numeral 43 denotes a pixel electrode (cathode of an EL element) made of a highly reflective conductive film. As the pixel electrode 43, a low-resistance conductive film such as an aluminum alloy film, a copper alloy film, or a silver alloy film, or a stacked film thereof is preferably used. Of course, a stacked structure with another conductive film may be employed.

A light emitting layer 45 is formed in a groove formed by banks 44a and 44b formed of an insulating film (preferably resin). Although only one pixel is shown here, light emitting layers corresponding to each of R (red), G (green), and B (blue) may be separately formed. Organic E to be a light emitting layer
As the L material, a π-conjugated polymer material is used. Typical polymer materials include polyparaphenylene vinylene (PPV) and polyvinyl carbazole (PVK).
And polyfluorenes.

There are various types of PPV-based organic EL materials, for example, “H. Shenk, H. Becker, O. Ge.
lsen, E. Kluge, W. Kreuder, and H. Spreitzer, “Polymers
forLight Emitting Diodes ”, Euro Display, Proceeding
s, 1999, p.33-37 "and JP-A-10-92576.

As a specific light emitting layer, cyanopolyphenylene vinylene is used for a light emitting layer emitting red light, polyphenylene vinylene is used for a light emitting layer emitting green light, and polyphenylene vinylene or polyalkylphenylene is used for a light emitting layer emitting blue light. Good. The film thickness is 30-150n
m (preferably 40 to 100 nm).

However, the above example is an example of the organic EL material that can be used for the light emitting layer, and it is not necessary to limit the invention to this. An EL layer (a layer for performing light emission and carrier movement therefor) may be formed by freely combining a light emitting layer, a charge transport layer, or a charge injection layer.

For example, in this embodiment, an example is shown in which a polymer material is used for the light emitting layer, but a low molecular organic EL material may be used. It is also possible to use an inorganic material such as silicon carbide for the charge transport layer and the charge injection layer. Known materials can be used for these organic EL materials and inorganic materials.

In this embodiment, an anode 47 made of a transparent conductive film is provided on the light emitting layer 45. In the case of this embodiment, since the light generated in the light emitting layer 45 is emitted toward the upper surface side (toward the upper side of the TFT), the anode must be translucent. As the transparent conductive film, a compound of indium oxide and tin oxide or a compound of indium oxide and zinc oxide can be used; however, it is possible to form after forming a light-emitting layer or a hole-injecting layer with low heat resistance. A material that can form a film at a temperature as low as possible is preferable.

When the anode 47 is formed, the EL element 3
504 is completed. Note that the EL element 3504 mentioned here
Is formed of a pixel electrode (cathode) 43, a light emitting layer 45, and an anode 47.

In the present embodiment, a passivation film 48 is further provided on the anode 47. As the passivation film 48, a silicon nitride film or a silicon nitride oxide film is preferable. The purpose of this is to shut off the EL element from the outside, and has both the meaning of preventing the organic EL material from being deteriorated due to oxidation and the effect of suppressing outgassing from the organic EL material. Thereby, the reliability of the EL display device is improved.

(Embodiment 6) In this embodiment, a structure in which the EL element 3504 is inverted in the pixel portion shown in Embodiment 5 will be described. FIG. 15 is used for the description.
It is to be noted that the point different from the structure of FIG.
Since only the L element portion and the EL driving TFT are used, other explanations are omitted.

Referring to FIG. 15, an EL driving TFT 450 is provided.
Reference numeral 3 denotes a p-channel TFT, which can be manufactured by using a known method. In this embodiment, the EL driving TFT
The drain wiring 440 of 4503 is connected to the anode 447 of the EL element.
, And the source wiring 434 of the EL driving TFT is connected to a power supply line (not shown).

In this embodiment, a transparent conductive film is used as the pixel electrode (anode) 447. Specifically, a conductive film formed using a compound of indium oxide and zinc oxide is used. Needless to say, a conductive film made of a compound of indium oxide and tin oxide may be used.

Then, the banks 44a and 44b made of an insulating film are used.
Is formed, a light emitting layer 445 made of polyvinyl carbazole is formed by solution coating. A cathode 443 made of an aluminum alloy is formed thereon. In this case, the cathode 443 also functions as a passivation film. Thus, an EL element 3701 is formed.

In the case of this embodiment, the light generated in the light emitting layer 445 is radiated toward the substrate on which the TFT is formed as indicated by the arrow.

(Embodiment 7) In the EL display device of the present invention, the material used for the EL layer included in the EL element is not limited to the organic EL material, but may be 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.

(Embodiment 8) In the present invention, the organic substance used for the EL layer may be a low molecular organic substance or a polymer (high molecular) organic substance. As the low molecular weight organic substance, materials mainly including Alq ₃ (tris-8-quinolilite-aluminum), TPD (triphenylamine derivative) and the like are known. Examples of the polymer-based organic substance include a π-conjugated polymer-based substance. Typically, PPV (polyphenylene vinylene), PVK (polyvinyl carbazole), polycarbonate and the like can be mentioned.

The polymer (polymer) organic substance can be formed by a simple thin film forming method such as a spin coating method (also referred to as a solution coating method), a dipping method, a dispensing method, a printing method or an ink jet method. High heat resistance compared to substances.

[0224] In the EL element included in the EL display device of the present invention, when the EL layer included in the EL element has an electron transport layer and a hole transport layer, the electron transport layer, the hole transport layer, May be made of an inorganic material, for example, an amorphous semiconductor such as amorphous Si or amorphous Si _1-x C _x .

A large amount of trap levels exist in an amorphous semiconductor, and a large amount of interface states are formed at an interface where the amorphous semiconductor is in contact with another layer. Therefore, the EL element can emit light at a low voltage and can achieve high luminance.

Further, a dopant (impurity) may be added to the organic EL layer to change the light emission color of the organic EL layer. As a dopant, DCM1, Nile Red, Rubrene,
Coumarin 6, TPB, quinacridone and the like.

Embodiment 9 In this embodiment, an example in which an EL display device is manufactured by using the present invention will be described with reference to FIGS.
This will be described with reference to FIG. FIG. 16A is a top view showing a state in which the steps up to encapsulation of the EL element are performed on the active matrix substrate on which the EL element is formed. Reference numeral 6801 indicated by a dotted line denotes a source signal line driver circuit, 6802 denotes a gate signal line driver circuit, and 6803 denotes a pixel portion. Also,
6804 is a cover material, 6805 is a first seal material, 680
Reference numeral 6 denotes a second seal material, and a filler 6807 (see FIG. 16B) is provided between the inner cover material surrounded by the first seal material 6805 and the active matrix substrate.

[0228] Reference numeral 6808 denotes a source signal line driver circuit 6801, a gate signal line driver circuit 6802, and the pixel portion 6.
A connection wiring for transmitting a signal input to the external device 803, and receives a video signal and a clock signal from an FPC (flexible print circuit) 6809 serving as a connection terminal with an external device.

Here, FIG. 16B is a cross-sectional view corresponding to a cross section taken along line AA ′ of FIG. In addition,
16A and 16B, the same reference numerals are used for the same parts.

As shown in FIG. 16B, the substrate 6800
Over the pixel portion 6803, a source signal line driver circuit 6801
Are formed. The pixel portion 6803 includes an EL driving TFT 6851 for controlling a current flowing to the EL element and a pixel electrode 6852 electrically connected to a drain region thereof.
And the like. In this embodiment, the EL driving TFT 6851 is a p-channel TFT. In addition, the source signal line driver circuit 6801 is formed using a CMOS circuit in which an n-channel TFT 6853 and a p-channel TFT 6854 are complementarily combined.

Each pixel has a color filter (R) 6855, a color filter (G) 6856, and a color filter (B) (not shown) below the pixel electrode. Here, the color filter (R) is a color filter for extracting red light, the color filter (G) is a color filter for extracting green light, and the color filter (B) is a color filter for extracting blue light. Note that the color filter (R) 6855 is provided for a pixel emitting red light, the color filter (G) 6856 is provided for a pixel emitting green light, and the color filter (B) is provided for a pixel emitting blue light.

The effect of providing these color filters is that the color purity of the emitted light is improved. For example, a red light-emitting pixel emits red light from the EL element (in this embodiment, is emitted toward the pixel electrode side), and the red light is passed through a color filter that extracts red light to emit red light. Can be improved in purity. This applies to other green light and blue light.

In the conventional structure without using a color filter, visible light entering from the outside of the EL display device excites the light emitting layer of the EL element, which may cause a problem that a desired color cannot be obtained. However, by providing a color filter as in this embodiment, only light of a specific wavelength can enter the EL element. That is, it is possible to prevent a problem that the EL element is excited by external light.

Although a structure in which a color filter is provided has been conventionally proposed, an EL element having a white light emission was used. In this case, in order to extract the red light, light of other wavelengths is cut, which causes a decrease in luminance. However, in the present embodiment, for example, the red light emitted from the EL element is passed through the color filter that extracts the red light, so that the luminance does not decrease.

Next, the pixel electrode 6852 is formed of a transparent conductive film and functions as an anode of an EL element. Further, an insulating film 6857 is formed at both ends of the pixel electrode 6852, and a light-emitting layer 6858 that emits red light and a light-emitting layer 6859 that emits green light are formed. Although not shown, a light-emitting layer that emits blue light is provided in adjacent pixels, and color display is performed by pixels corresponding to red, green, and blue. Of course,
The pixel provided with the blue light emitting layer is provided with a color filter for extracting blue.

Note that not only organic materials but also inorganic materials can be used as EL materials. Further, not only the light emitting layer but also a layered structure combining an electron injection layer, an electron transport layer, a hole transport layer, or a hole injection layer may be used.

The cathode 6 of the EL element is provided on each light emitting layer.
860 is formed of a conductive film having a light shielding property. This cathode 6860 is common to all the pixels,
It is electrically connected to the FPC 6809 via the 808.

Next, a first sealing material 6805 is formed with a dispenser or the like, and a spacer (not shown) is scattered to attach a cover material 6804. Then, a filler 6807 is filled in a region surrounded by the active matrix substrate 6800, the cover material 6804, and the first sealant 6805 by a vacuum injection method.

In this embodiment, barium oxide is added to the filler 6807 in advance as the hygroscopic substance 6861. In this embodiment, the hygroscopic substance is used by adding to the filler. However, the substance may be dispersed in a lump and sealed in the filler. Although not shown, it is also possible to use a hygroscopic substance as a material of the spacer.

Next, after the filler 6807 is cured by irradiating ultraviolet rays or heating, an opening (not shown) formed in the first sealant 6805 is closed. First sealing material 680
After the opening of No. 5 is closed, the connection wiring 6808 and the FPC 6809 are electrically connected using the conductive material 6862. Further, the exposed portion of the first sealing material 6805 and the FPC
A second sealant 6806 is provided so as to cover part of the 6809. The same material as the first sealant 6805 may be used for the second sealant 6806.

By enclosing the EL element in the filler 6807 using the above-described method, the EL element can be completely shut off from the outside, and a substance that promotes the oxidation of organic materials such as moisture and oxygen from the outside. Can be prevented from entering. Therefore, a highly reliable EL display device can be manufactured.

(Embodiment 10) In this embodiment, an example will be described in which, in the EL display device shown in Embodiment 9, the emission direction of light emitted from an EL element and the arrangement of color filters are different. Although FIG. 17 is used for the description, the basic structure is the same as that of FIG.

The pixel portion 6901 is provided with an EL driving TFT 690
2 and a plurality of pixels including a pixel electrode 6903 and the like electrically connected to the drain region thereof.

In this embodiment, an n-channel TFT is used as the EL driving TFT 6902 in the pixel portion 6901. A pixel electrode 6903 is electrically connected to a drain of the EL driving TFT 6902, and the pixel electrode 6903 is formed of a light-shielding conductive film. In this embodiment, the pixel electrode 6903 serves as a cathode of the EL element.

A transparent conductive film 6904 common to each pixel is formed on the light emitting layer 6858 that emits red light and the light emitting layer 6859 that emits green light. This transparent conductive film 690
Reference numeral 4 is an anode of the EL element.

Further, this embodiment is characterized in that a color filter (R) 6905, a color filter (G) 6906, and a color filter (B) (not shown) are formed on a cover material 6804. In the case of the structure of the EL element of this embodiment, the direction of emission of light emitted from the light emitting layer is directed to the cover material 6804 side. Therefore, with the structure of FIG. 17, a color filter can be provided in the light path. .

As in this embodiment, the color filter (R) 6
When the cover material 6905 and the color filter (G) 6906 and the color filter (B) (not shown) are provided on the cover material 6804, the number of steps of the active matrix substrate can be reduced, and the yield and the throughput can be improved. There are advantages.

(Embodiment 11) In this embodiment, an electronic device in which an EL display device formed by using the present invention is incorporated as a display medium will be described.

Examples of such electronic devices include a video camera, a digital camera, a head mounted display (goggle type display), a game machine, a car navigation, a personal computer, a portable information terminal (a mobile computer, a mobile phone or an electronic book, etc.). Is mentioned. One example of them is shown in FIG.

FIG. 18A shows a personal computer, which includes a main body 2001, a housing 2002, a display portion 2003,
And a keyboard 2004 and the like. The EL display device of the present invention can be used for the display portion 2003 of a personal computer.

FIG. 18B shows a video camera, which includes a main body 2101, a display portion 2102, an audio input portion 2103, operation switches 2104, a battery 2105, and an image receiving portion 210.
6 and so on. The EL display device of the present invention can be used for the display portion 2102 of a video camera.

FIG. 18C shows a part (right side) of a head-mounted display device, which includes a main body 2301, a signal cable 2302, a head fixing band 2303, and a display monitor 230.
4, including an optical system 2305, a display unit 2306, and the like. The EL display device of the present invention is a display unit 2 of a head-mounted display device.
306 can be used.

FIG. 18D 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 unit (a) 2404, a display unit (b) 2405, and the like are included. The display unit (a) 2404 mainly displays image information, and the display unit (b) 2405 mainly displays character information. The EL display device of the present invention employs the display unit (a) of an image reproduction device provided with a recording medium. 2404,
(B) Can be used for 2405. Note that the present invention can be applied to a CD playback device, a game machine, and the like as an image playback device provided with a recording medium.

FIG. 18E shows a portable computer, which includes a main body 2501, a camera section 2502, an image receiving section 2503, operation switches 2504, a display section 2505, and the like. The EL display device of the present invention can be used for the display portion 2505 of a portable computer.

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 apparatus according to the present embodiment can be realized by using any combination of the embodiments 1 to 10.

[0256]

In the conventional analog gray scale EL display device, the luminance varies due to the variation in the characteristics of the TFT in the pixel portion. Further, in the conventional time gray scale EL display device, when expressing multiple gray scales, the display period of the sub-frame period corresponding to the lower bit signal is shortened, and the constant EL drive voltage may be continuously applied. It will be difficult. Further, when the ambient temperature at the time of use changes, the amount of current flowing through the EL element changes due to the temperature characteristics of the EL element even when the same voltage is applied to the EL element, causing a variation in luminance. was there.

However, according to the present invention, E
Variation in luminance of the L element can be suppressed. Thereby, a high-quality EL display device can be provided.

[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 showing a timing chart of a gray scale method of the EL display device of the present invention.

FIG. 3 is a diagram showing a configuration of a buffer amplifier of the EL display device of the present invention.

FIG. 4 is a graph showing temperature characteristics of an EL element.

FIG. 5 illustrates a structure of a pixel portion of an EL display device.

FIG. 6 is a block diagram illustrating a structure of an EL display device.

FIG. 7 is a diagram showing a timing chart of a conventional analog gradation method.

FIG. 8 is a diagram showing a timing chart of a conventional time gray scale method.

FIG. 9 illustrates a manufacturing process of an EL display device of the present invention.

FIG. 10 illustrates a manufacturing process of an EL display device of the present invention.

FIG. 11 illustrates a manufacturing process of an EL display device of the present invention.

FIG. 12 is a top view and a cross-sectional view of an EL display device of the present invention.

FIG. 13 is a top view and a cross-sectional view of an EL display device of the present invention.

FIG. 14 is a cross-sectional view of an EL display device of the present invention.

FIG. 15 is a cross-sectional view of an EL display device of the present invention.

FIG. 16 is a top view and a cross-sectional view of an EL display device of the present invention.

FIG. 17 is a cross-sectional view of an EL display device of the present invention.

FIG. 18 illustrates an applied electronic device using the EL display device of the present invention.

FIG. 19 is a diagram showing a timing chart of a gradation method of the EL display device of the present invention.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H05B 33/14 H05B 33/14 A F term (Reference) 3K007 AB02 AB04 AB17 BA06 BB01 BB03 BB04 BB05 BB06 BB07 CA01 CB01 DA01 DB03 EA01 EB00 GA04 5C080 AA06 BB05 DD03 EE28 EE29 FF11 JJ02 JJ03 JJ04 JJ05 JJ06 KK02 KK07 KK43 5C094 AA07 AA08 AA53 AA54 AA56 BA03 BA12 BA27 CA19 CA24 DB01 DB02 DB04 EA04 EA05 EA05 EA04 EA04 EA05 HA10 JA01

Claims (10)

[Claims] A first EL element and a second EL element each including a first electrode, a second electrode, and an EL layer provided between the first electrode and the second electrode. A method for driving a display device having two EL elements, wherein one frame period is divided into a plurality of subframe periods, and the first EL element emits light or does not emit light for each of the plurality of subframe periods. State, and in each of the plurality of subframe periods, the second E
A constant current is passed between the first electrode and the second electrode of the L element, and the voltage between the first electrode and the second electrode of the first EL element in the light emitting state is A voltage equal to the voltage between the first electrode and the second electrode of the second EL element through which a constant current flows, and the value of the constant current in two of the plurality of subframe periods Are different from each other. 2. A first EL element and a first EL element each comprising a first electrode, a second electrode, and an EL layer provided between the first electrode and the second electrode. A method for driving a display device having two EL elements, wherein one frame period is divided into a plurality of sub-frame periods, and the first EL element emits light or does not emit light in each of the plurality of sub-frame periods. In the plurality of subframe periods, the second E
A constant current is passed between the first electrode and the second electrode of the L element, and the voltage between the first electrode and the second electrode of the first EL element in the light emitting state is A constant current is equal to a voltage between a first electrode and a second electrode of the second EL element, and the value of the constant current is different in each of the plurality of subframe periods. A method for driving a display device. 3. The method according to claim 2, wherein the plurality of subframe periods have the same length. 4. A first EL device and a second EL device each comprising a first electrode, a second electrode, and an EL layer provided between the first electrode and the second electrode. A method for driving a display device having two EL elements, wherein one frame period is divided into n (n is a natural number of 2 or more) subframe periods, and the subframe period is divided into n subframe periods. The first EL element is in a light emitting state or a non-light emitting state, and in each of the n subframe periods, the second EL element
A constant current is passed between the first electrode and the second electrode of the L element, and the voltage between the first electrode and the second electrode of the first EL element in the light emitting state is A constant current is equal to the voltage between the first electrode and the second electrode of the second EL element, and the ratio of the constant current value in each of the n subframe periods is 2 ⁰ : ^{2 - 1: 2 -2: ···} : 2 - (n-2): 2
^-(n-1) , a method for driving a display device. 5. A video camera, an image reproducing apparatus, a head mounted display, a personal computer, or an information terminal device, wherein the method for driving the display device according to claim 1 is used. . 6. A plurality of pixels each having a TFT, a first EL element, a power supply line, a buffer amplifier,
A display device comprising: a second EL element; and a first constant current source A1 and a second constant current source A2 that output constant currents having different values from each other, wherein the first EL element and the second 2 EL elements each include a first electrode, a second electrode, and an EL layer provided between the first electrode and the second electrode. The first constant current source A1 output terminal and the second EL
A switch for selecting whether to connect to a first electrode of the element or to connect an output terminal of the second constant current source A2 to a first electrode of the second EL element; The first electrode of the second EL element is connected to a non-inverting input terminal of the buffer amplifier, the output terminal of the buffer amplifier is connected to the power supply line, and the potential of the power supply line is the TFT Through the first
A display device provided to the first electrode of the EL element. 7. A plurality of pixels each having a TFT and a first EL element, a power supply line, a buffer amplifier,
A display device comprising: a second EL element; and n (n is a natural number of 2 or more) constant current sources each outputting a constant current having the same value, wherein the first EL element and the second 2 EL elements each having a first electrode, a second electrode, and an EL layer provided between the first electrode and the second electrode, wherein the n constant current sources M (m is a natural number less than or equal to n)
The number of output terminals and the first electrode of the second EL element, or k (k is a natural number of n or less different from m) out of the n constant current sources. , The second E
A switch for selecting whether to connect to a first electrode of the L element; a first electrode of the second EL element connected to a non-inverting input terminal of the buffer amplifier; The terminal is connected to the power supply line, and the potential of the power supply line is set to the first voltage via the TFT.
A display device provided to the first electrode of the EL element. 8. The device according to claim 6, wherein the first electrode of the first EL element and the second EL element is an anode, and the second electrode is a cathode. Display device. 9. The method according to claim 6, wherein the first electrode of the first EL element and the second EL element is a cathode, and the second electrode is an anode. Display device. 10. A video camera, an image reproducing apparatus, a head-mounted display, a personal computer, or an information terminal device using the display device according to claim 6. Description: