JPH09101761A - El display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an EL display device which utilizes an EL dot matrix display panel and thereby allows high-luminance and half-tone display by active matrix driving. SOLUTION: The transistor drive circuit 3 is composed from a selection TFT 3a and a memory TFT 3b. The gate electrode G and the drain electrode D of the TFT 3a are respectively connected to an address line and a data line. In this TFT 3a, the gate is made on by the selection signal inputted from the address line to accumulate the input image data inputted from the data line in the memory TFT 3b. In the memory TFT 3b, the memory depth (the shift of the ON threshold voltage due to writing/erasure) of the gate electrode controls the emission luminance of the organic EL diode element 1 based on the gradation information included in the input image data inputted into its gate electrode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an EL display device, and more particularly, to an EL display device having a dot matrix display panel with EL elements.

[0002]

2. Description of the Related Art Conventionally, an organic thin film E which is a self-luminous display device.
A dot matrix display panel using an L (Electro Luminescence) element has been proposed. In this organic EL dot matrix display panel, a cathode scan line (metal electrode side) is used as a common line and an anode data line (ITO side) is used. A positive voltage is applied all at once during the cathode selection period to line-sequentially drive the EL elements in the portion where the common line and the data line are orthogonal to each other to display an image. In this case, each organic EL element has a duty H = τ / T
(Τ is a positive voltage application time on the data line side, and T is one cycle period of common line selection).

[0003]

However, in such a conventional organic EL dot matrix display panel, the E of the portion where the common line and the data line are orthogonal to each other is used.
Since the L element is line-sequentially driven to display an image, the selection time (duty H) per pixel becomes shorter as the number of common lines and the number of data lines increase, and the luminance required for the display device is reduced. There was a problem that I could not get. Therefore, it is necessary to increase the value of the duty H, but it becomes difficult as the number of common lines and the number of data lines increase. Further, if the duty H is not increased, a high-brightness EL element is required, and it is difficult to realize an organic EL dot matrix display panel.

An object of the present invention is to provide an EL display device using an EL dot matrix display panel which enables high brightness and intermediate gradation display by active matrix driving.

[0005]

E of the invention according to claim 1
In the L display device, a predetermined power source is connected to one electrode of a pair of terminals of the EL element, and a voltage control means for storing image data selected by address data is connected to the other electrode of the EL element. As a result, an EL display circuit for one pixel is formed, the voltage control means stores a voltage corresponding to the magnitude of the image data signal for a predetermined time, and outputs the stored image data to the EL element. The brightness of the EL element is controlled.

According to the EL display device of the present invention, a predetermined power source is connected to one electrode of a pair of terminals of the EL element, and the other electrode of the EL element is selected by address data. By connecting the voltage control means for storing the recorded image data, the EL for one pixel is connected.
A display circuit is formed, and the voltage control means stores a voltage corresponding to the magnitude of the signal of the image data for a predetermined time,
The stored image data is output to the EL element,
The brightness of the EL element is controlled. Therefore, the input image data can be surely held for each EL display circuit that configures each pixel, the light emitting state of each EL element can be improved, and an EL display device without using a high-luminance EL element. It is possible to increase the brightness.

In this case, the EL of the invention described in claim 2
Like the display device, the voltage control means, the address data is input to the gate electrode at predetermined time intervals, and a selection transistor that outputs image data input to the drain electrode to the memory transistor based on the address data, It is effective that a plurality of the EL display circuits are arranged in a matrix, and a memory transistor that writes, erases, and stores the image data input from the selection transistor.

According to the EL display device of the second aspect of the invention, in the voltage control means, the address data is input to the gate electrode at predetermined time intervals, and is input to the drain electrode based on the address data. A selection transistor that outputs image data to a memory transistor, and writes the image data input from the selection transistor.
A plurality of the EL display circuits are arranged in a matrix form, and a memory transistor for erasing and storing. Therefore, the holding state of the image data can be maintained in each EL display circuit, a high-brightness EL dot matrix display panel can be configured, and a high-brightness E
The L display device can be easily realized.

Further, as in the EL display device according to a third aspect of the present invention, it is effective that the memory transistor keeps the EL element in the light emitting state at all times except when the image data is written / erased. .

According to the EL display device of the third aspect of the present invention, in the memory transistor, the EL element is always in a light emitting state except when writing / erasing the image data. Therefore, even when the address selection line is not selected, the light emitting state of the EL element can be maintained, and thus even if the EL display panel is made finer, the surface emitting state can be maintained without increasing the brightness of the EL element. .

[0011] Furthermore, E of the invention described in claim 4
Like the L display device, the memory transistor stores a voltage corresponding to the magnitude of the image data until the next image data is input, and controls the brightness of the EL element by the stored image data. Is effective.

According to the EL display device of the present invention, the voltage corresponding to the magnitude of the image data is stored in the memory transistor until the next image data is input, and the stored image is stored. The EL according to the data
The brightness of the device is controlled to be controlled. Therefore, halftone display can be performed according to the tone setting included in the input image data, and the image expressiveness of the EL display device can be improved.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to FIGS. 1 to 8 are diagrams showing an embodiment of an organic EL display device to which the present invention is applied. First, the driving principle for driving the organic EL matrix display panel constituting the organic EL display device of the present embodiment will be described with reference to the equivalent circuit for one pixel shown in FIG.
FIG. 1 is a diagram showing an equivalent circuit for one pixel of a drive circuit for driving an organic EL matrix display panel.
It is composed of an L diode element 1 and a power control element 2. The organic EL diode element 1 has a cathode electrode side connected to a constant power source -Vdd, an anode electrode side connected to the power control element 2, and the power control element 2 grounded.

In this equivalent circuit, the organic EL diode element 1 is constantly turned on by the power source -Vdd, and the power control element 2 changes the light emission luminance of the organic EL element 1 according to the gradation data based on the input image data at the time of selection. To control the power.

FIG. 2 is a diagram showing a specific example of a drive circuit of the equivalent circuit for one pixel shown in FIG. In FIG. 2, the power control element 2 shown in FIG. 1 is configured by a transistor drive circuit 3 having an EEPROM memory function. This transistor drive circuit 3 is a selection TFT
It is composed of a (Thin Film Transistor) 3a and a memory TFT 3b, and an address line is connected to the gate electrode G of the selection TFT 3a and a data line is connected to its drain electrode D. In the selection TFT 3a, the gate is turned on by the selection signal input from the address line, so that the input image data input from the data line is accumulated in the memory TFT 3b. In the memory TFT 3b, the light emission brightness of the organic EL diode element 1 is determined by the memory depth of the gate electrode (ON threshold voltage Vt shift amount due to writing / erasing) according to the gradation information included in the input image data input to the gate electrode. To control.

Therefore, in one frame, except for the pixel data writing time, an output (light emission) is performed according to the writing information. The electrical characteristics of each element shown in FIG. 2 are shown in FIGS.

FIG. 3 shows the organic EL diode element 1 of FIG.
Is a graph showing the electrical characteristics of the above, and the voltage-luminance characteristics are shown by setting the anode-cathode voltage Vdd on the horizontal axis and the luminance on the vertical axis. As shown in FIG. 3, in the organic EL diode element 1 of the present embodiment, the brightness characteristic is controlled by controlling the anode-cathode voltage Vdd in the range of 1/2 Vdd to Vdd. FIG.
It is a figure which shows the electric characteristic of the selection TFT3a of FIG. 2, and the ON-OFF characteristic is shown by setting the gate voltage Vdd on the horizontal axis and the LOG channel current on the vertical axis. This figure 4
In the case where the gate voltage Vdd is small, almost no current flows at 0V or + 2Vdd even in the normal TFT.

FIG. 5 is a diagram showing the electrical characteristics of the memory TFT 3b of FIG. 2, in which the horizontal axis shows the gate voltage Vdd and the vertical axis shows the LOG channel current, which shows the write-erase characteristics. As shown in FIG. 5, the gate voltage characteristics are shifted during writing and erasing, and the shift amount (hysteresis width) is determined by the electric field strength applied to the memory gate insulating film during writing and erasing and the application time. It
Therefore, as shown in FIG. 4 and FIG.
Both 3a and the memory TFT 3bF have PMOS characteristics.

In FIG. 2, the EEPROM is
In the TFT portion having the function, a pixel driving portion TFT 3b as a memory TFT having a SiN film of Si-rich composition having a hysteresis characteristic in a gate insulating film, and writing / erasing to / from the memory gate of the memory TFT 3b is selectively executed. Therefore, a selection T having a selection gate electrode having a SiN film having a stoichiometric (chemically stable region) composition without hysteresis in the gate insulating film
It is composed of FT3a.

The source electrode of the selection TFT 3a is connected to the gate electrode of the memory TFT, and the write / erase voltage is applied to the drain electrode. This allows the selection TFT 3a to write data in each pixel memory line-sequentially.
Bias of the drain electrode of the image data, the selection TFT
If the gate electrode of 3a is used for address selection, in the organic EL display panel, all the pixels in the area other than the selected line continue to emit light with a gradation according to the data of the memory gate.

Next, FIG. 6 shows a plan view of a drive circuit for one pixel when the transistor drive circuit 3 shown in FIG. 2 is formed as a TFT on an organic EL display panel, and FIG. FIG. 7 shows a sectional view taken along the line A-A '. 6 and 7, 10 is a glass substrate, 11 is an anode electrode, 12 is a cathode electrode, 13 is an organic light emitting layer,
Reference numeral 14 is a selection TFT source electrode, 15 is a selection TFT drain electrode, 16 is a selection TFT gate electrode, and 17 is a selection TF.
T gate insulating film, 18 is a memory TFT source electrode, 19
Is a memory TFT drain electrode, 20 is a memory TFT gate electrode, 21 is a memory TFT SiN film, 22 is a semiconductor layer, 23 is an interlayer insulating film, 24 is an address line, 25 is a data line, 26 is a GND line, and 27 is a selection TFT source. Reference numeral 28 is a contact hole between the electrode and the memory TFT gate electrode, and 28 is a contact hole between the source / drain metal of the memory TFT and the organic EL anode electrode (ITO transparent electrode).

FIG. 8 shows the TF shown in FIGS. 6 and 7.
It is a figure which shows the circuit structure of the organic EL display panel which mounts the drive circuit for 1 pixel in case it is formed as T. The organic EL display panel 30 shown in FIG. 8 shows a display circuit for four pixels, and each display pixel includes a selection TFT 31, a memory TFT 32, and an organic EL diode 33 having the structure shown in FIGS. 6 and 7. An address selection line 34 is connected to the gate electrode of each selection TFT 31, and a data line 35 is connected to the drain electrode of each selection TFT 31. Further, a driving power supply -Vdd is connected to the cathode electrode of the organic EL diode 33 as shown in the figure.

The address selection signal input to the address selection line 34 of FIG. 8 is Vaddress when selected.
M = -Vdd, Vaddress M + 1 = V when not selected
It is set to dd and controlled. In addition, the data line 35
The image data signal input to the
aN = Vdd, and at the time of erasing, VdataN + 1 = -Vdd is set and controlled.

Next, the operation of this embodiment will be described. First, the operation of the selection TFT 31 and the memory TFT 32 shown in FIGS. 6, 7 and 8 will be described. In the circuit of FIG. 8, when the address selection signal is set to −Vdd or less when selected, the selection TFT 31 to the memory TFT 32
During electron injection (hole extraction) into the data line 3,
By applying the positive bias of the write voltage + Vdd to 5, a voltage of + Vdd is applied to both ends of the memory gate insulating film from the gate electrode of the memory TFT 32 toward the source electrode, electron injection is achieved, and image data writing is performed. To be achieved. In this case, in the memory TFT 32, the electric current is shifted in the direction in which the electric current flows, like the electric characteristics shown in FIG.

On the other hand, at the time of erasing, a negative bias of the erase voltage -Vdd is applied to the data line 35, a voltage of -Vdd is applied to both ends of the memory TFT 32 at the time of selection, and hole injection (electron extraction) is achieved. . As a result, the memory TFT 32 is shifted in the direction in which no current flows. Further, regardless of the voltage applied to the data line 35, the address selection signal + Vdd in the non-selected state
As a result, the selection TFT 31 becomes high impedance, and the memory state of the memory TFT 32 when not selected does not change.
As a result, writing and erasing can be performed for each data line by selecting the address line once.

In the above description, the Si in the TFT memory SiN film 21 shown in FIG.
The region trapped by the rich is assumed to be in the vicinity of the memory channel Si layer of the TFT memory gate electrode 20, and electron injection and hole injection are performed for the channel Si and the gate SiN.
I explained that it was a career transfer between the two.

Next, the organic EL display panel 3 shown in FIG.
The operation at 0 will be described. In FIG. 8, the source electrode of the memory TFT 32 is at ground potential, and the driving power supply −Vdd is applied to the cathode electrode of the organic EL diode element 33. Then, the address selection signal input to the address selection line 34 is Vadd.
When the address selection line 34 is selected in response M (-Vdd), the gate electrode of the selection TFT 31 connected to the address selection line 34 is turned on. At that time, the data voltage according to the image data input to the drain electrode of the selection TFT 31 is applied to the gate electrode of the selection TFT 31.

Electrons and holes are trapped or extracted in the TFT memory gate electrode 20 in the selected TFT gate insulating film 17 of the selected TFT 31 due to the potential difference between the data voltage and the source electrode side GND of the memory TFT 32. Or As a result, the ON threshold voltage Vt changes (shifts) in the memory TFT gate electrode 20 of the memory TFT 32 connected in series with the selection TFT 31. As a result, the potential difference (potential difference between −Vdd and Vdd) between the anode electrode and the cathode electrode of the organic EL diode 33 connected in series to the memory TFT 32 changes, and the emission brightness of the organic EL diode 33 changes according to the image data. It is adjusted according to the gradation.

On the other hand, the address selection signal input to the address selection line 34 is VaddressM + 1 (Vd
When the address selection line 34 becomes non-selected in d), the selection TF connected to the address selection line 34.
The gate electrode of T31 is turned off. The selection TFT 31 whose gate electrode is turned off has a high impedance, and the memory TF connected in series to this selection TFT 31.
T32 also becomes high impedance, and this memory TFT
The image data accumulated in 32 is held, and the light emitting state of the organic EL diode 33 connected to this memory TFT 32 is maintained.

As described above, in the organic EL display panel 30 of this embodiment shown in FIG.
Since the light emitting state of the organic EL diode 33 can be maintained even when 4 is not selected, it is possible to maintain the surface light emitting state without increasing the brightness of the organic EL diode 33 even if the organic EL display panel 30 is made finer. You can For example, in a conventional line-sequential organic EL display panel, a surface luminance of 100
When trying to obtain cd, the number of address selection lines is 48
If there are 0 pieces, the light emission luminance of 48000 cd is required, but if the organic EL display panel 30 of the present embodiment is used, even if no light is emitted at the time of selection, it is about 100.
cd is good. (Actually, the emission brightness at the time of selection is indefinite, and depends on the gradation setting of the previous image data and the next image data.) Also, even when the number of address selection lines is 1000, the conventional emission brightness of 48000 cd is required. However, if the organic EL display panel 30 of the present embodiment is used, 100 cd is sufficient. However, assuming that 60 Hz is one frame, the time for writing / erasing image data becomes insufficient as the number of address lines increases. Assuming that both writing and erasing can be performed in 50 μs, the maximum number of addresses is about 333 in the non-interlace system and about 667 in the interlace system.

Incidentally, since the holding time of the memory TFT using the SiN film trap as shown in FIG. 7 of the above embodiment is very long (usually 1 to 10 years), only the changed portion of the screen is rewritten. With this method, even if the writing / erasing speed is in the order of msec, OA display panel level display is possible without flicker, and a high-quality still image can be displayed. Therefore, the organic EL display panel 30 of the present embodiment maintains a surface emission state without using an organic EL element having high brightness, as compared with the organic EL matrix display panel of the line-sequential drive type that has been conventionally proposed. be able to.

Therefore, it is possible to easily realize an organic EL display device capable of high-luminance and half-tone display.
The expressive power of the input image of the organic EL display device can be improved.

[0033]

According to the EL display device of the first aspect of the present invention, the input image data can be surely held for each EL display circuit that constitutes each pixel, and the light emission state of each EL element can be improved. Therefore, the brightness of the EL display device can be increased without using a high brightness EL element.

According to the EL display device of the second aspect of the present invention, it is possible to maintain the holding state of the image data in each EL display circuit, and to construct an EL dot matrix display panel with high brightness. A brightness EL display device can be easily realized.

According to the EL display device of the third aspect of the present invention, since the light emitting state of the EL element can be maintained even when the address selection line is not selected, the EL element can be used even if the definition of the EL display panel is increased. It is possible to maintain the surface emission state without increasing the brightness.

According to the EL display device of the fourth aspect of the present invention, it is possible to perform the intermediate gradation display according to the gradation setting included in the input image data, and improve the image expression power of the EL display device. You can

[Brief description of the drawings]

FIG. 1 is a diagram showing an equivalent circuit for one pixel for explaining a driving principle for driving an organic EL matrix display panel constituting an EL display device to which the present invention is applied.

FIG. 2 is a diagram showing a specific example of a drive circuit of an equivalent circuit for one pixel in FIG.

FIG. 3 is a diagram showing electrical characteristics of the organic EL diode element of FIG.

FIG. 4 is a diagram showing electrical characteristics of the selection TFT of FIG.

5 is a diagram showing electrical characteristics of the memory TFT of FIG.

FIG. 6 is a plan view in which the transistor drive circuit 3 of FIG. 2 is formed as a TFT on an organic EL display panel.

7 is a cross-sectional view taken along the line AA ′ of FIG.

8 is a diagram showing a circuit configuration of an organic EL display panel equipped with a drive circuit for one pixel when formed as the TFT shown in FIGS. 6 and 7. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 organic EL diode element 3 transistor drive circuit 3a selection TFT 3b memory TFT (pixel drive part TFT) 10 glass substrate 11 anode electrode 12 cathode electrode 13 organic light emitting layer 14 selection TFT source electrode 15 selection TFT drain electrode 16 selection TFT gate electrode 17 Select TFT gate insulating film 18 Memory TFT source electrode 19 Memory TFT drain electrode 20 Memory TFT gate electrode 21 Memory TFT SiN film 22 Semiconductor layer 23 Interlayer insulating film 24 Address line 25 Data line 26 GND line 27 Contact hole 28 Contact hole 30 Organic EL display Panel 31 Selection TFT 32 Memory TFT 33 Organic EL diode 34 Address selection line 35 Data line

Claims (4)

[Claims] 1. A predetermined power source is connected to one electrode of a pair of terminals of an EL element, and a voltage control means for storing image data selected by address data is connected to the other electrode of the EL element. Therefore, E for one pixel
Forming an L display circuit, wherein the voltage control means stores a voltage corresponding to the magnitude of the signal of the image data for a predetermined time, outputs the stored image data to the EL element, and determines the brightness of the EL element. An EL display device characterized by being controlled. 2. The voltage control means, wherein the address data is input to a gate electrode at predetermined time intervals, and a selection transistor which outputs image data input to the drain electrode to the memory transistor based on the address data, 2. The EL display device according to claim 1, comprising a memory transistor for writing / erasing and storing image data input from the selection transistor, wherein the plurality of EL display circuits are arranged in a matrix. 3. The EL display device according to claim 2, wherein the memory transistor keeps the EL element in a light emitting state except when writing and erasing the image data. 4. The memory transistor stores a voltage according to the magnitude of the image data until the next image data is input, and the EL element is stored according to the stored image data.
The EL display device according to claim 2, wherein the brightness of the element is controlled.