JP5303818B2 - Organic electroluminescent display panel and manufacturing method thereof - Google Patents

Description

  The present invention uses an organic EL material electroluminescence (hereinafter referred to as EL) that emits light by current injection, and is an organic EL device in which organic EL elements having a light emitting layer made of a thin film of an organic EL material are arranged in a matrix. It relates to a display panel.

  In recent years, organic EL displays are promising as display devices such as mobile terminals, mobile PCs, and mobile phones. The organic EL display is self-luminous, so no backlight is required and full color display is possible without using a color filter, so it has features such as a wide viewing angle, high contrast, and excellent color reproducibility. Because of its high brightness, thinness, and excellent response characteristics, it has been actively developed by various companies for mobile phones and PDAs (personal digital assistants).

  For example, as described in JP-A-9-115672 and JP-A-8-227276, an organic EL display has an organic electroluminescent element (hereinafter referred to as an organic EL element) on individual pixel electrodes arranged in a matrix. In this case, electrons are injected from the cathode by a voltage applied to the pixel electrode and holes are injected from the anode, and light is emitted by recombination of the electrons and holes, and display is performed. This occurs at the portion where the cathode and the anode overlap with the organic electroluminescent material layer in between.

  FIG. 4 shows a configuration of a conventional organic EL display panel.

  On the glass substrate 30 which is a transparent substrate, a plurality of island-shaped transparent electrodes 31 made of indium tin oxide (ITO) arranged side by side in a matrix and a non-linear element 32 connected to the transparent electrode 31, for example, Thin film transistors (TFTs) connected to each other are formed by photolithography, vacuum deposition technique, or the like. A planarizing film 39 made of a photosensitive resin is formed on the nonlinear element for planarization by several microns, and the nonlinear element 32 and the transparent electrode 31 are electrically connected through an opening in which the planarizing film 39 is opened by photolithography. Yes. On the planarizing film 39 and the transparent electrode 31, a projection 38 made of a photosensitive resin is formed. On the transparent electrode 31 to be the anode, an organic medium of a hole transport layer 33, a light emitting layer 34 and an electron transport layer 35 is formed as a thin film, and a metal thin film which is a cathode 36 is formed in the uppermost layer. These thin films are sequentially formed by, for example, a vacuum deposition method. By selectively applying a direct current voltage between the transparent electrode 31 serving as the anode and the cathode 36, holes injected from the transparent electrode 31 are formed. Electrons injected from the cathode 36 through the hole transport layer 33 and the electron transport layer 35 reach the light-emitting layer 34 to cause recombination of electrons and holes, respectively, thereby generating light emission 37 having a predetermined wavelength, Light emission can be displayed from the transparent substrate 30 side. At this time, the light emitting layers 34 having different light emitting materials for red (37-R), green (37-G), and blue (37-B) are individually arranged in parallel on the transparent electrode 31. Full color display can be performed.

  Next, FIGS. 5 and 6 show a method for manufacturing an EL display panel.

  In FIG. 5A, nonlinear elements 32 arranged in a matrix are formed on a glass substrate 30. The nonlinear element 32 is formed by photolithography or vacuum evaporation.

  A flattening film 39 is formed on the non-linear element 32 to relieve unevenness due to the formation of the non-linear element, and a transparent film made of indium tin oxide (ITO) electrically connected to the non-linear element 32 is formed on the flattening film 39. The electrode 31 is formed. Therefore, an opening is provided in a part of the planarizing film 39.

  In FIG. 5B, a projection 40 made of a photosensitive resin is formed on the planarizing film 39 and the transparent electrode 31 by a photolithography method. The protrusion 40 is formed in order to prevent damage caused by the film formation mask coming into contact with the transparent electrode 31 and the formed organic EL layer when the organic EL layer is formed in a subsequent mask vapor deposition step. The protrusion 40 has a thickness of 0.5 to 10 microns.

  5C, an organic medium to be the hole transport layer 33 is formed on each transparent electrode 31, and a light emitting layer 34 and an electron transport layer 35 are sequentially formed thereon (FIG. 5D and FIG. 6). a)). The light emitting layer 34 is formed so that individual light emitting layers 34-R, 34-G, and 34-B having different light emitting substances for each color of red (R), green (G), and blue (B) are juxtaposed. .

  Next, in FIG. 6B, a cathode 36 made of Al is formed so as to cover the hole transport layer 33, the light emitting layer 35, and the electron transport layer. Finally, these organic EL layers were sealed in order to prevent characteristic deterioration due to the influence of humidity.

Problems to be solved by the invention

  As described above, it is possible to realize a self-luminous full-color organic EL display by arranging and forming organic light-emitting layers having different light-emitting substances on transparent electrodes of nonlinear elements arranged in a matrix. The following issues arise.

  The transparent electrode is formed by a vapor deposition method, and is connected to the nonlinear element through an opening of a planarizing film having a thickness of several microns. For this reason, since the surface of the transparent electrode has a recess along the opening of the planarization film, the organic EL layer (hole transport layer, light emitting layer, electron transport layer) formed on the transparent electrode is a planarization film. A step breakage occurs at the edge portion of the shoulder portion of the opening, and this may cause a short circuit between the transparent electrode as the anode and the cathode layer, resulting in a non-lighting pixel defect in pixel units. Similarly, the organic EL layer (hole transport layer, light-emitting layer, electron transport layer) becomes extremely thin in the edge region of the flattening film shoulder, thereby causing a leak path due to low resistance between the anode and the cathode. As a result, it becomes difficult to emit light in the entire region where the organic EL layer (hole transport layer, light emitting layer, electron transport layer) is formed, and the current density per light emitting area increases due to a significant decrease in the light emitting area. As a result, there is a problem in that the display reliability is remarkably lowered, such as a decrease in luminance due to deterioration of the organic EL layer (hole transport layer, light emitting layer, electron transport layer) and an increase in the non-lighting area with time.

  An object of the present invention is to reduce pixel defects due to non-lighted pixels with a simple configuration so as to eliminate such problems, to eliminate luminance deterioration over time and generation of pixel defects, and to achieve high yield and excellent reliability. The object is to provide an organic EL display panel.

Means for solving the problem

  According to the present invention, a contact portion between a transparent electrode and a nonlinear element arranged in a matrix, that is, an opening portion of a planarizing film is covered with an insulating layer or a conductor layer, and the opening portion of the planarizing film is made to have a gentle structure. As a result, the short circuit between the anode and the cathode due to the disconnection of the organic EL layer (hole transport layer, light emitting layer, electron transport layer) and the film thickness of the organic EL layer (hole transport layer, light emitting layer, electron transport layer) become thin. This prevents current leakage between the anode and the cathode. Accordingly, it is possible to realize and provide an organic EL display panel having a high manufacturing yield and high reliability by reducing pixel defects due to non-lighted pixels, a decrease in luminance with time, and a luminance variation in the display area.

  Embodiments of the present invention will be described below with reference to the drawings.

(First embodiment)
FIG. 1 shows a cross-sectional configuration of an organic EL display according to the first embodiment of the present invention.

  On a glass substrate 1 which is a transparent substrate, a thin film transistor 3 which is a nonlinear element arranged in a matrix is formed by photolithography or vacuum deposition technique. Capacitors and wirings are connected to the nonlinear element as necessary, and these are referred to as a nonlinear element circuit. A planarizing film 4 is formed and applied on the nonlinear element circuit including the thin film transistor 3 in order to reduce unevenness due to the film thickness of the thin film transistor 3 itself. The planarizing film 4 is formed of a photosensitive resin by photolithography, and the formed film thickness is several microns. The planarizing film 4 is provided with an opening 7 opened by photolithography, and the transparent electrode 2 electrically connected to the drain electrode 5 of the thin film transistor 3 is formed through the opening 7. The transparent electrode 2 is formed as a pair with the thin film transistor 3, and is arranged side by side in a matrix on the glass substrate 1 as with the thin film transistor 3. The transparent electrode 2 is formed using a material having a small work function, such as indium tin oxide (ITO), and serves as an anode (anode electrode) of an organic EL layer formed in a later step.

  A projection 6 made of an insulating resin is provided on the transparent electrode. The protrusion 6 is formed in order to prevent the film formation mask from coming into contact with the transparent electrode 2 and the formed organic EL layer when the organic EL layer is formed by vapor deposition in the subsequent mask vapor deposition process, and damaging them. It is what is done. The projection 6 is an insulating resin having photosensitivity, and can be formed using the same material as the planarizing film 4.

  Further, the opening 7 of the planarization film 4 that is connected to the transparent electrode 2 and the drain electrode 5 of the thin film transistor 3 is filled with an opening 8 with an insulating resin so as to cover the entire opening. The hole filling 8 can be formed using the same material as the planarizing film 4 and the protrusion 6. On the transparent electrode 2 serving as an anode of the organic EL layer, organic media of a hole transport layer 9, a light emitting layer 10, and an electron transport layer 11 are sequentially formed as a thin film. And the metal thin film used as the cathode 12 is formed in the uppermost layer so that these organic EL layers 9,10,11 may be covered. The cathode 12 is formed of a metal material such as Al by vapor deposition or the like. The cathode 12 also has the purpose of reflecting the light emitted from the light emitting layer 10 toward the glass substrate 1 to increase the light emission efficiency. Further, in order to make the reflection more reliable, another reflective film can be formed. These thin films are sequentially formed by, for example, a vacuum deposition method. By selectively applying a DC voltage between the transparent electrode 2 as the anode and the cathode 12, holes injected from the transparent electrode 2 are formed. Electrons injected from the cathode 12 through the hole transport layer 9 and the electron transport layer 11 reach the light-emitting layer 10 to cause recombination of electrons and holes, and light emission of a predetermined wavelength occurs from the glass. Light emission can be displayed from the substrate 1 side.

  Further, it is possible to take out the emitted light upward, that is, toward the cathode 12 side. In this case, the cathode 12 is a transparent electrode. And in order to reflect the light which goes out to an anode side, a reflecting film is provided in the outer side (opposite side of a light emitting layer) of an anode.

  The nonlinear element in the above embodiment controls the current applied to the organic EL layers 9, 10 and 11 formed on the transparent electrode 2 and causes the light emitting layer 10 to emit light. The nonlinear element used for this is p. Thin film transistors such as -Si, a-Si, CdSe, and Te can be used, and a circuit using a MOS-FET can also be used. Further, a circuit configuration using a two-terminal type MIM instead of the three-terminal type is also possible.

  Next, a method of manufacturing the organic EL display panel according to the first embodiment of the present invention will be described with reference to the drawings.

  In FIG. 2A, a thin film transistor 3 which is a non-linear element and a gate line, a gate insulating film, a channel layer, a contact layer, a source, a drain line, a signal line, etc. (not shown) are arranged in a matrix on a glass substrate 1. The flattening film 4 is formed and formed on the thin film transistor 3, and the transparent film made of ITO electrically connected to the drain electrode 5 of the thin film transistor 3 through the opening 7 of the flattening film 4 is formed on the flattening film 4. The electrode 2 is formed with a film thickness of 500-1500 angstroms. This transparent electrode 2 will be an anode (anode) of the later organic EL layer, and a material having a small work function such as indium tin oxide (ITO) is used.

  In FIG. 2B, an insulating protrusion 6 is formed on the transparent electrode 2 by photolithography using a resist or a photosensitive polyimide resin. The height of the projection 6 is already formed on the surface of the transparent electrode 2 and the film-forming mask when a film-forming mask (not shown) for forming a later organic EL layer is abutted against the protrusion 6. It is only necessary to have a height (0.5 μm or more) that does not damage the filmed organic EL medium. On the other hand, even if the protrusion 6 is too high, it is easily broken, so it is preferably about 10 μm or less, preferably about 1 to 2 μm. Further, it is desirable that the cross section of the protrusion 6 has a substantially trapezoidal shape so that the cathode grown in the subsequent process does not break due to the taper angle of the protrusion 6. The taper angle at this time is preferably 60 degrees or less. Thus, the protrusions 6 arranged in a matrix can also be formed by a screen printing method in which a light-absorbing substance of glass paste is applied. The planar shape of the protrusion 6 is formed to be a rectangular bottom wall, but any shape such as a square or a circle may be used. The protrusion 6 can also be formed of the same material as the planarizing film 4.

  Next, in FIG. 2C, the opening is filled with an insulating material so as to cover the opening 7 of the planarizing film 4 that electrically connects the transparent electrode 2 and the drain electrode 5 of the thin film transistor 3. 8 is performed. The hole filling 8 in the opening can be formed of the same material as the planarizing film 4 and the protrusion 6. Further, by using a common photolithography mask, it can be formed simultaneously with the protrusion 6. Furthermore, it is also possible to use inorganic materials such as SiO2 and SiNx.

  Next, in FIG. 2 (d), the hole transport layer 9 is formed on the transparent electrode 2 serving as the anode of the organic EL layer, and the light emitting layer 10 is then formed on the hole transport layer 9 as shown in FIG. 3 (a). As shown in FIG. 3B, the electron transport layer 11 is sequentially formed as a thin film on the light emitting layer 10 through a film formation mask having an opening for each pixel.

  In FIG. 3C, a metal thin film that becomes the cathode (cathode) 12 is formed so as to cover these organic EL layers 9, 10, and 11. The cathode 12 is formed by depositing a metal material such as Al by vapor deposition. Thereafter, a glass plate or the like is bonded to the organic EL layers 9, 10, 11 formed on the transparent electrode 2 with a resin in order to prevent deterioration of light emission characteristics due to humidity and material deterioration and generation of defects in non-lighting pixels. Sealing is performed (not shown), and an organic EL display panel can be realized. In addition, as described above, an inorganic material such as SiO2 or SiNx can be used for filling the opening of the planarizing film in addition to the insulating resin having photosensitivity. It can also be formed by a paste-like screen printing method.

  When forming the light emitting layer 10 having different emission colors such as red, green, and blue, the same opening mask is formed by shifting one pixel at a time for each color, so that the film types are not increased. it can.

(Second embodiment)
Further, as a second embodiment, in the first embodiment, the filling 8 of the opening 7 of the planarizing film 4 is formed in a separate process from the protrusion 6, but the protrusion 6 and the opening 7 of the planarizing film 4 are formed. Since the same material can be used for the hole filling 8, it is possible to simultaneously fill the hole 8 in the opening 7 of the planarizing film 4 in the step of forming the protrusion 6.

(Third embodiment)
As a third embodiment, a conductive material such as indium tin oxide (ITO) or aluminum can be used for filling the opening 8 in the opening 7 of the planarizing film 4.

(Fourth embodiment)
Further, as the fourth embodiment, the protrusion 6 on the transparent electrode 2 is not formed, but only the hole filling 8 of the opening 7 of the flattening film 4 is formed, and the hole filling 8 has the function of the protrusion 6. When forming an organic EL layer (hole transport layer 9, light emitting layer 10, electron transport layer 11), the film formation mask is in contact with the transparent electrode 2 and the formed organic EL layer, and damage can be prevented. It is. At that time, the hole filling 8 in the opening 7 of the planarizing film 4 may use either a conductor layer or an insulator layer. At this time, the height and thickness of the hole filling 8 of the opening 7 of the planarizing film 4 are high enough not to damage the transparent electrode 2 and the already formed organic EL medium with the organic EL film forming mask. (0.5 μm or more) is sufficient.

Effect of the invention

  Since the opening of the planarization film formed on the transparent electrode is filled with an insulator layer or a conductor layer, the unevenness of the planarization film surface is alleviated, and an organic EL layer (hole transport layer, light emitting layer, electron) The transport layer is not cut off at the edge of the planarization film opening, and non-lighting failure that does not involve EL light emission in pixel units can be prevented. In addition, the leakage path due to the extremely thin film thickness of the organic EL layer (hole transport layer, light emitting layer, electron transport layer) does not occur in the edge region of the planarization film opening. It is possible to prevent enlargement and increase in power consumption, achieve a high production yield of organic EL panels, and realize an organic EL display panel with high reliability and high image quality and low power consumption with a simple configuration.

Cross-sectional view of the structure of an organic EL display which is an embodiment of the present invention   Process sectional drawing which shows the manufacturing process of the organic electroluminescent display which is one Example of this invention   Process sectional drawing which shows the manufacturing process of the organic electroluminescent display which is one Example of this invention   Cross-sectional structure diagram of an organic EL display which is a conventional example of the present invention   Process sectional drawing which shows the manufacturing process of the organic electroluminescent display which is the prior art example of this invention   Process sectional drawing which shows the manufacturing process of the organic electroluminescent display which is the prior art example of this invention

DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Transparent electrode 3 Thin-film transistor 4 Flattening film 5 Drain electrode 6 Protrusion 7 Opening 8 Opening filling 9 Hole transport layer 10 Light emitting layer 11 Electron transport layer 12 Cathode

Claims (12)

An organic electroluminescence display panel having an image display arrangement composed of a plurality of nonlinear element circuits arranged in a matrix and a light emitting part, corresponding to the light emitting part electrically connected to the nonlinear element circuit In a transparent substrate having a first display electrode formed on a surface in a matrix, an insulating film formed on the nonlinear element circuit and having an opening in a contact region, and an electric insulation projecting on the first display electrode An insulator is formed so as to cover a contact region between the protrusion having the contact point and the non-linear element circuit and the first display electrode, and is formed so as to cover the entire top surface of the insulator. A thin film of at least one organic electroluminescent medium formed on the display electrodes of the organic electroluminescent medium and a thin film of the organic electroluminescent medium. And a second display electrode formed on the protrusions divides the thin film respectively positioned to the light emitting portion adjacent the upper surface of the insulator is located at a position lower than the upper surface of the projection An organic electroluminescence display panel characterized by that.
An organic electroluminescence display panel having an image display arrangement composed of a plurality of nonlinear element circuits arranged in a matrix and a light emitting part, corresponding to the light emitting part electrically connected to the nonlinear element circuit In a transparent substrate having a first display electrode formed on a surface in a matrix, an insulating film formed on the nonlinear element circuit and having an opening in a contact region, and an electric insulation projecting on the first display electrode And a conductor is formed so as to cover a contact region between the protrusion having the contact point and the non-linear element circuit and the first display electrode, and is formed so as to cover the entire top surface of the conductor. A thin film of at least one organic electroluminescent medium formed on the display electrodes of the organic electroluminescent medium and a thin film of the organic electroluminescent medium. The organic electroluminescent display panel, characterized in that and a second display electrode formed.
An organic electroluminescence display panel having an image display arrangement composed of a plurality of nonlinear element circuits arranged in a matrix and a light emitting part, corresponding to the light emitting part electrically connected to the nonlinear element circuit In a transparent substrate having a first display electrode formed on a surface in a matrix, an insulating film formed on the nonlinear element circuit and having an opening in a contact region; the nonlinear element circuit and the first display electrode; A conductor is formed so as to cover the contact region, the conductor is formed so as to cover the entire top surface of the conductor, and a thin film of at least one organic electroluminescent medium formed on the first display electrode; And a second display electrode formed in common on the thin film of the organic electroluminescence medium. Electroluminescent display panel.
The non-linear element circuit of the organic electroluminescent display panel as claimed in any one of claims 1 to 3, characterized in that it consists of a thin film transistor and a capacitor which are connected to each other.
The organic electroluminescence display panel according to any one of claims 1 to 3 , wherein the substrate and the first display electrode are transparent.
The organic electroluminescence display panel according to any one of claims 1 3, characterized in that it has a reflective film formed on the second display electrode.
The organic electroluminescence display panel according to any one of claims 1 to 3 , wherein the second display electrode is transparent.
The organic electroluminescent display panel as claimed in any one of claims 1 to 3, characterized in that it has a reflective film formed on the outer side of the first display electrode.
The organic electroluminescence display panel according to claim 1, wherein the protrusion is a photosensitive resin.
The organic electroluminescence display panel according to claim 1, wherein the insulator is a photosensitive resin.
Claim 2 or 3 organic electroluminescent display panel according to, wherein the conductive member is transparent.
4. The organic electroluminescence display panel according to claim 3, wherein the conductor is made of the same material as the first display electrode.

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