JP2004006362A - Color el display - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a color EL display requiring less number of production steps. <P>SOLUTION: An anode 7 and a light emitting layer 15 are formed for each pixel, and a hole transport layer 14, an electronic transport layer 16, and a cathode 17 are formed extendedly over a plurality of pixels. Accordingly, steps for etching back the hole transport layer 14 and the electronic transport layer 16 are eliminated. Also, since a partition wall 68 which was installed before is not formed, a step for forming the partition wall can also be eliminated. Since the anode 7 and the cathode 17 are separated from each other by the hole transport layer 14 and the electronic transport layer 16, they are not short-circuited even if the partition wall 68 is absent. In addition, since the light emitting layer 15 is formed in shape larger than and same as the anode 7, a leak current and the concentration of field can be prevented from occurring at the end part of the anode. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an active color EL display device that drives an electroluminescence (EL) element using a thin film transistor (TFT).
[0002]
[Prior art]
Since the organic EL element emits light by itself and does not require a backlight necessary for a liquid crystal display device, it is most suitable for thinning, and there is no restriction on the viewing angle, so that its practical use as a next-generation display device is greatly expected. ing.
[0003]
Currently, three methods have been proposed as methods for realizing color display in a display device using such an organic EL element.
[0004]
The first method is to use a different light-emitting material for the light-emitting layer for each of the three primary colors of RGB to independently form each pixel that directly emits RGB light. A method of realizing light emission and dividing it into three primary colors by a color filter, and a third method is a method of converting light from a blue light emitting layer into three primary colors by a color conversion layer (CCM). Of these three methods, the second and third methods use a color filter or a color conversion layer, so there is a loss of light, but the first method has the highest efficiency because the required light is directly emitted.
[0005]
By the way, there are two types of driving methods of the organic EL display device, a passive type using a simple matrix and an active type using a TFT, and the active type generally has a circuit configuration shown in FIG.
[0006]
FIG. 11 shows a circuit configuration per pixel. The organic EL element 20, a first switching TFT 21 which is turned on / off by a selection signal Scan applied to a drain while a display signal Data is applied to a drain, When the TFT 21 is turned on, the capacitor 22 is charged by the display signal Data supplied. When the TFT 21 is turned off, the capacitor 22 holding the charging voltage Vh, the drain is connected to the drive power supply voltage COM, and the source is connected to the anode of the organic EL element 20. The second TFT 23 drives the organic EL element 20 by supplying a holding voltage Vh from the capacitor 22 to the gate.
[0007]
The selection signal Scan is at the H level during one selected horizontal scanning period (1H), and when the TFT 21 is turned on, the display signal Data is supplied to one end of the capacitor 22, and the voltage Vh corresponding to the display signal Data is supplied to the capacitor 22. 22 is charged. This voltage Vh continues to be held in the capacitor 22 for one vertical scan (1 V) even if the scan goes low and the TFT 21 is turned off. Then, since this voltage Vh is supplied to the gate of the TFT 23, the EL element is controlled to emit light at a luminance corresponding to the voltage Vh.
[0008]
Therefore, a conventional configuration for realizing color display by the above-described first method in such an active EL display device will be described below.
[0009]
FIG. 8 is a plan view showing a conventional configuration, and FIG. 9 is a cross-sectional view taken along line CC in FIG. 8, showing three pixels of RGB.
[0010]
In the figure, 50 is a drain line for supplying the display signal DATA, 51 is a power supply line for supplying the power supply voltage COM, 52 is a gate line for supplying the selection signal Scan, and 53 is the first TFT 21 and 54 in FIG. The capacitors 22 and 55 in FIG. 11 represent the anodes of the EL element 20 constituting the pixel electrodes, and the second TFTs 23 and 56 in FIG. The anode 56 is formed separately for each pixel on the planarization insulating film 60, and a hole transport layer 61, a light emitting layer 62, an electron transport layer 63, and a cathode 64 are sequentially stacked thereon to obtain EL. An element is formed. Then, the holes injected from the anode 56 and the electrons injected from the cathode 64 are recombined inside the light emitting layer 62 to emit light, and the light is emitted as shown by the arrow in FIG. Radiated from outside. The hole transport layer 61, the light emitting layer 62, and the electron transport layer 63 are formed separately for each pixel in substantially the same shape as the anode 56, and the light emitting layer 62 is formed by using a different light emitting material for each of RGB. Is emitted from each EL element. Since the cathode 64 applies a common voltage to each pixel, the cathode 64 extends over each pixel. The light emitting layers 62 are separated from each other by partition walls 68. Here, 65 is a transparent glass substrate, 66 is a gate insulating film, and 67 is an interlayer insulating film.
[0011]
[Problems to be solved by the invention]
However, in the conventional color EL display device, the number of manufacturing steps is such that a hole transport layer 61, a light emitting layer 62, and an electron transport layer 63 are formed for each pixel, a partition wall 68 is formed, and a cathode 64 is formed on the entire surface. Therefore, there is a demand for a color EL display device having a simpler structure.
[0012]
Therefore, an object of the present invention is to provide a color EL display device whose manufacturing process is easy.
[0013]
[Means for Solving the Problems]
The present invention has been made to solve the above problems, and has an active element including an EL element in which an anode, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode are stacked, and a thin film transistor for driving the EL element. In a color EL display device of the type, an anode, a light emitting layer, and a thin film transistor are formed for each pixel, a flattening insulating film is formed on the thin film transistor, and a hole transport layer, an electron transport layer, and a cathode are formed on the flattening insulating film. This is a color EL display device formed over a plurality of pixels.
[0014]
Further, in an active type color EL display device including an EL element in which an anode, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode are stacked, and a thin film transistor for driving the EL element, the anode, the light emitting layer, and the thin film transistor Is formed for each pixel, a power supply line connected to an anode via a thin film transistor is formed, a hole transport layer, an electron transport layer, and a cathode are formed over a plurality of pixels, and the color EL does not overlap the anode and the power supply line. A display device.
[0015]
Further, in an active type color EL display device including an EL element in which an anode, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode are stacked, and a thin film transistor for driving the EL element, the anode, the light emitting layer, and the thin film transistor Is formed for each pixel, a planarizing insulating film is formed on the thin film transistor, a power supply line connected to the anode through the thin film transistor is formed, and the hole transport layer, the electron transport layer, and the cathode are formed on the planarizing insulating film. Is a color EL display device formed over a plurality of pixels, wherein a planarizing insulating film, a hole transport layer, and an electron transport layer are formed between a power supply line and a cathode.
[0016]
Further, by using a different light emitting material for each of the RGB in the light emitting layer, each of the EL elements directly emits the RGB light.
[0017]
The anode and the light emitting layer have substantially the same planar shape.
[0018]
Alternatively, the light emitting layer is larger than the anode and is formed so as to cover an end of the anode.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a plan view showing one embodiment of a color EL display device according to the present invention, and shows three RGB pixels. FIG. 2 is a sectional view taken along line AA in FIG. This embodiment is an example of the stripe arrangement shown in FIG.
[0020]
The driving circuit of each pixel is exactly the same as the circuit shown in FIG. 11, and the points different from the conventional example of FIGS. 8 and 9 are the pattern arrangement and the cross section.
[0021]
In FIGS. 1 and 2, 1 is a drain line made of aluminum for supplying a display signal DATA, 2 is a power line made of aluminum for supplying a power supply voltage COM, and 3 is a gate line made of chromium for supplying a selection signal Scan. Reference numeral 4 denotes the first TFT 21 in FIG. 11, 5 denotes the capacitor 22 in FIG. 11, 6 denotes the second TFT 23 in FIG. 11, and 7 denotes the anode of the EL element 20 made of ITO and constituting a pixel electrode. . In FIG. 1, a dotted line indicates chromium, a dashed line indicates ITO, and a solid line other than the drain line 1 and the power supply line 2 indicates a polysilicon thin film.
[0022]
First, the second TFT 6 is formed as follows. That is, a chromium gate electrode 9 is formed on a transparent glass substrate 8, and a gate insulating film 10 is formed thereon. Next, a polysilicon thin film 11 is formed on the gate insulating film 10, and a drain line 1 and a power supply line 2 are formed on the polysilicon thin film 11 covered with an interlayer insulating film 12. Further, a flattening insulating film 13 is laminated, and an anode 7 made of ITO is formed thereon. Then, the drain region of the polysilicon thin film 11 contacts the power supply line 2 and the source region contacts the anode 7.
[0023]
The structure of the first TFT 4 is the same as that of the second TFT 6, and the capacitor 5 connected to the first TFT 4 is composed of a chrome electrode with a gate insulating film interposed therebetween and a polysilicon thin film.
[0024]
Further, the anode 7 is formed separately on the flattening insulating film 13 for each pixel, a hole transport layer 14 is formed on the entire surface, and the light emitting layer 15 is formed separately on each pixel. The electron transport layer 16 and the cathode 17 are formed on the entire surface, and are laminated in this order to form an EL element. Then, the holes injected from the anode 7 and the electrons injected from the cathode 17 recombine inside the light emitting layer 15 to emit light, and this light is emitted from the transparent anode side to the outside as shown by the arrow. Radiated. Further, the light emitting layer 15 is formed in the same shape as the anode 7 separately for each pixel, and further, by using a different light emitting material for each RGB, each light of RGB is emitted from each EL element.
[0025]
Here, for example, MTDATA, Alq3, MgIn alloy is used as a material of the hole transport layer 14, the electron transport layer 16, and the cathode 17, and a DCM system is used as each of the R, G, and B light emitting layers 15. Alq containing a dopant, Alq containing quinacridone as a dopant, and DPVBi containing a distyrylarylene-based dopant are used.
[0026]
In this embodiment, as shown in the figure, since the second TFT 6 and a part of the capacitor are arranged in the horizontal direction of the anode 7 which is a pixel electrode, the shape of the pixel electrode is smaller than that of the conventional example shown in FIGS. It can be vertical. As described above, since the pixel electrode 7 and the light emitting layer 15 are formed in substantially the same shape, the light emitting region of the pixel has substantially the same shape as the pixel electrode. Therefore, in this case, if the horizontal dimension and the vertical dimension of the light emitting region are EH and EV, respectively, and the horizontal dimension and the vertical dimension of the pixel pitch are PH and PV, respectively, EH / EV <PH / PV.
[0027]
Therefore, when forming each light emitting layer of RGB while shifting the metal mask, the horizontal margin for shifting the metal mask is increased as compared with the conventional case, and even if the films are formed with the same accuracy, the colors may be mixed. Is less. Note that the first TFT 4 may be arranged in the horizontal direction of the anode 7 instead of the second TFT 6.
[0028]
In addition, since the anode 7 and the light emitting layer 15 are formed in substantially the same shape, the formation area of the light emitting layer 15 can be minimized. That is, since the light emitting layer 15 emits light when a current flows between the anode 7 and the cathode 17, even if the light emitting layer 15 is formed in a region other than on the anode, no current flows, that is, no light is emitted. , Hardly contributes to the display. Conversely, when the distance between the light emitting layers 15 of different colors is reduced, the light emitting layers 15 of different colors are mixed with each other, and the color purity may be reduced. If the size of the light emitting layer 15 is minimized, the area of the light emitting layer 15 necessary for display is secured, and the possibility that the light emitting layers 15 of different colors are mixed with each other is reduced.
[0029]
Next, a cross section of the present embodiment will be described with reference to FIG. In the present embodiment, the hole transport layer 14 and the electron transport layer 16 are formed to extend over each pixel. The light emitting layer 15 emits light by the current flowing therethrough. Since the light-emitting layer 15 needs to be formed so as to emit a different color for each pixel, it is provided independently for each pixel, but the hole transport layer 14 and the electron transport layer 16 are provided for each pixel. Whether they are independent or extend over a plurality of pixels, there is no significant difference in operation.
[0030]
When the hole transport layer 14 and the electron transport layer 16 extend over a plurality of pixels, the manufacturing process can be simplified. This is because, in order to form the hole transport layer 14 and the electron transport layer 16 for each pixel, the hole transport layer 14 and the electron transport layer 16 are selectively formed using a metal mask opened in the region, or are formed over the entire surface and then etched back. Either method must be adopted. On the other hand, in the present embodiment, the hole transport layer 14 is formed on the entire surface including the anode 7 formed for each pixel, the light emitting layer 15 is formed by the above-described method, and the electron transport layer 16 is further formed thereon. The cathode 17 may be formed on the entire surface. Therefore, the step of etching back the hole transport layer 14 and the electron transport layer 16 can be reduced.
[0031]
Further, in the present embodiment, the partition wall 68 shown in FIG. 9 is unnecessary. The reason why the partition wall 68 is provided is to prevent the insulation between the anode 7 and the cathode 17 from being mixed with the light emitting layers 15 of the adjacent pixels of different colors from lowering the color purity. On the other hand, in the present embodiment, as described above, since the light emitting layer 15 has substantially the same shape as the anode 7, the possibility that the light emitting layers 15 are mixed with each other is low. Further, the hole transport layer 14 and the electron transport layer 16 are formed between the anode 7 and the cathode 17. Since the hole transport layer 14 and the electron transport layer 16 have high resistance, short-circuiting can be prevented by disposing them between the anode 7 and the cathode 17. Therefore, the partition wall 68 becomes unnecessary, and the step of forming the partition wall 68 can be reduced.
[0032]
Next, a second embodiment will be described with reference to FIGS.
[0033]
FIG. 3 is a plan view showing another embodiment, and FIG. 4 is a sectional view taken along line BB in FIG. The same components as those in FIGS. 1 and 2 are denoted by the same reference numerals, and this embodiment differs from the above-described embodiment only in the pattern arrangement.
[0034]
That is, in FIGS. 3 and 4, reference numeral 4 denotes a first TFT 21 in FIG. 11, 5 denotes a capacitor 22 in FIG. 11, 6 denotes a second TFT 23 in FIG. 20 anodes are represented. In particular, FIG. 4 clearly shows that the capacitor 5 is composed of the chrome electrode 500 and the polysilicon thin film 501 with the gate insulating film 10 interposed therebetween.
[0035]
In this embodiment, as shown in the figure, since the capacitor 5 is arranged in the horizontal direction of the anode 7 serving as the pixel electrode, the shape of the pixel electrode can be made vertically long as compared with the conventional example of FIGS. Therefore, also in this case, similarly to the above-described embodiment, when the horizontal dimension and the vertical dimension of the light emitting region are EH and EV, respectively, and the horizontal dimension and the vertical dimension of the pixel pitch are PH and PV, respectively. EH / EV <PH / PV.
[0036]
Therefore, when forming each light-emitting layer of RGB while shifting the metal mask, the horizontal margin for shifting the metal mask is increased as compared with the related art, and the possibility that colors are mixed even if the film is formed with the same accuracy is reduced. Become.
[0037]
Also in the present embodiment, the hole transport layer 14 and the electron transport layer 16 are formed on the entire surface, and the anode 7 and the light emitting layer 15 are formed for each pixel.
[0038]
Next, a third embodiment will be described with reference to FIGS.
[0039]
FIG. 3 is a plan view showing another embodiment, and FIG. 6 is a cross-sectional view taken along lines AA and BB in FIG. The same components as those in FIGS. 1 and 2 are denoted by the same reference numerals, and this embodiment differs from the above-described embodiment only in the pattern arrangement.
[0040]
That is, in FIGS. 3 and 4, reference numeral 4 denotes a first TFT 21 in FIG. 11, 5 denotes a capacitor 22 in FIG. 11, 6 denotes a second TFT 23 in FIG. 20 anodes are represented.
[0041]
In this embodiment, as shown in the figure, the capacitor 5 is arranged in the vertical direction of the anode 7 which is a pixel electrode. Therefore, in the case of an arrangement in which pixels of different colors are adjacent in the vertical direction such as a delta arrangement, The margin in the direction is increased, and the possibility that colors are mixed even when the film is formed with the same accuracy is reduced.
[0042]
Also in the present embodiment, the hole transport layer 14 and the electron transport layer 16 are formed on the entire surface, and the anode 7 and the light emitting layer 15 are formed for each pixel.
[0043]
In the above-described embodiment, the anode 7 and the light emitting layer 15 are completely drawn in the same shape. However, it is preferable that the light emitting layer 15 is formed to be slightly larger than the anode 7 as shown in FIG. By doing so, even if the misalignment of the metal mask when forming the light emitting layer 15 occurs, the light emitting layer 15 can be reliably arranged on the anode 7. In addition, although the hole transport layer 14 and the electron transport layer 16 have high resistance, they are not complete insulating films. Therefore, when the anode 7 and the cathode 17 face each other without passing through the light emitting layer 15, a leak current flows from an end of the anode 7. Or incorrect electric field concentration may occur. By forming the light emitting layer 15 one size larger and covering the end of the anode 7 with the light emitting layer 15, it is possible to prevent leakage current and electric field concentration. As described above, since it is better to keep the light emitting layer 15 in a minimum necessary area, the difference in size between the anode 7 and the light emitting layer 15 depends on the accuracy of metal mask alignment, the thickness of the anode 7 and the like. It is necessary to optimize and determine according to.
[0044]
【The invention's effect】
According to the present invention, since the hole transport layer, the electron transport layer, and the cathode are formed over a plurality of pixels, the number of manufacturing steps can be reduced. Further, since the hole transport layer and the electron transport layer exist between the anode and the cathode, short-circuit between the anode and the cathode can be prevented.
[0045]
Since the anode and the light-emitting layer have substantially the same planar shape, the area for forming the light-emitting layer can be minimized, and the light-emitting layers of adjacent pixels can be prevented from intersecting with each other. Purity can be increased.
[0046]
Furthermore, since the light emitting layer is formed larger than the anode and the light emitting layer covers the end of the anode, even if an error occurs in the formation of the light emitting layer, the light emitting layer can be reliably disposed on the anode, Further, it is possible to prevent a leak current generated at the anode end and an illegal electric field concentration.
[0047]
Due to these effects, the conventionally formed partition is not required, and the number of manufacturing steps can be further reduced.
[Brief description of the drawings]
FIG. 1 is a plan view showing a first embodiment of the present invention.
FIG. 2 is a sectional view showing a first embodiment of the present invention.
FIG. 3 is a plan view showing a second embodiment of the present invention.
FIG. 4 is a sectional view showing a second embodiment of the present invention.
FIG. 5 is a plan view showing a third embodiment of the present invention.
FIG. 6 is a sectional view showing a third embodiment of the present invention.
FIG. 7 is another cross-sectional view of each embodiment of the present invention.
FIG. 8 is a plan view showing the structure of a conventional color EL display device.
FIG. 9 is a cross-sectional view illustrating a structure of a conventional color EL display device.
FIG. 10 is a diagram illustrating a color arrangement in a color EL display device.
FIG. 11 is a diagram showing a circuit configuration of an active color EL display device.
[Explanation of symbols]
1,50 drain line 2,51 power supply line 3,52 gate line 4,21,53 first TFT
5,22,54 Capacitors 6,23,55 Second TFT
7,56 anode 20 EL element 14 hole transport layer 15 light emitting layer 16 electron transport layer 17 cathode 68 partition wall

Claims (7)

An active color EL display device including an EL element in which an anode, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode are stacked, and a thin film transistor for driving the EL element,
The anode, the light emitting layer, and the thin film transistor are formed for each pixel,
A flattening insulating film is formed on the thin film transistor,
The color EL display device, wherein the hole transport layer, the electron transport layer, and the cathode are formed over a plurality of pixels on the planarization insulating film. An active color EL display device including an EL element in which an anode, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode are stacked, and a thin film transistor for driving the EL element,
The anode, the light emitting layer, and the thin film transistor are formed for each pixel,
A power supply line connected to the anode through the thin film transistor is formed,
The hole transport layer, the electron transport layer, the cathode is formed over a plurality of pixels,
The color EL display device, wherein the anode and the power supply line do not overlap. An active color EL display device including an EL element in which an anode, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode are stacked, and a thin film transistor for driving the EL element,
The anode, the light emitting layer, and the thin film transistor are formed for each pixel,
A flattening insulating film is formed on the thin film transistor,
A power supply line connected to the anode through the thin film transistor is formed,
The hole transport layer, the electron transport layer, and the cathode are formed over the plurality of pixels on the planarization insulating film,
The color EL display device, wherein the planarizing insulating film, the hole transport layer, and the electron transport layer are formed between the power supply line and the cathode. In an active color EL display device including an EL element in which an anode, a hole transport layer, a light emitting layer, an electron transport layer, and a cathode are stacked, a thin film transistor for driving the EL element, and a capacitor,
The light emitting layer is formed by vapor deposition,
The anode, the light emitting layer, the thin film transistor, the capacitor is formed for each pixel,
The light emitting layer does not overlap with the thin film transistor and the capacitor in a plane,
The color EL display device, wherein the hole transport layer, the electron transport layer, and the cathode are formed over a plurality of pixels. 5. The color EL display device according to claim 1, wherein each of said EL elements directly emits RGB light by using a different light emitting material for each of RGB for said light emitting layer. 5. The color EL display device according to claim 1, wherein the anode and the light emitting layer have substantially the same planar shape. The color EL display device according to claim 6, wherein the light emitting layer is formed larger than the anode, and the light emitting layer covers an end of the anode.

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