JP3606309B2 - Organic thin film light emitting display - Google Patents

Description

【００４６】
上記表１より、従来技術である比較例に対して、実施例では、短絡画素に起因する短絡電流が完全に遮断され、また、短絡画素を含むデータラインが点灯状態となることにより生ずる明るい線状の画像欠陥についても、発生は認められなかった。
【００４７】
更に、実施例において、配線抵抗の上昇に伴う駆動電圧の上昇は観測されず、構造が複雑となることにより懸念された非点灯画素数についても比較例に対し有意差は見られなかった。
以上の点から、本発明の目的が達成されたことが確かめられた。
【００４８】
【発明の効果】
本発明によれば、長期駆動時における短絡欠陥の発生による表示画質の低下を防止し、短絡電流の抑制を可能とした良好な有機薄膜発光ディスプレイを提供することができる。
【図面の簡単な説明】
【図１】本発明の一例のパッシブマトリクス型有機発光ディスプレイを示す平面図である。
【図２】図１の有機発光ディスプレイの楕円で囲んだ部分を示す部分拡大図である。
【図３】本発明に係る単位発光画素部分の電極構造を示す部分拡大図である。
【符号の説明】
１ 基板
２ 給電部
３ 遮断部
４ 透明電極部
５ 有機層
７ 第一の電極（データライン）
８ 第二の電極（アドレスライン）
１０ 画素[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an organic light-emitting device used as a display, and more particularly to a passive matrix organic light-emitting display that can be driven for a long period of time and has high reliability, and a manufacturing technique thereof.
[0002]
[Prior art]
Since organic light-emitting elements are self-luminous elements and have high visibility and can be driven at a low voltage, research on practical application has been actively conducted (Appl. Phys. Lett., 51 913, 1987). Such an organic light-emitting device has a structure having a two-layer organic layer formed on a transparent substrate, a transparent conductive film as an anode, a hole transport layer and a light-emitting layer made of an organic substance, and a metal film as a cathode. In addition, an organic layer having a structure composed of three layers of a hole transport layer, a light emitting layer, and an electron transport layer is known.
[0003]
The light emission mechanism of the organic light emitting device is considered as follows. A process in which excitons are generated by recombination of electrons injected from the cathode and holes injected from the anode near the interface between the hole transport layer and the light emitting layer, and the excitons are radiatively deactivated. Give off light. This light is emitted to the outside through the transparent conductive film as the anode and the transparent substrate, and light emission occurs.
[0004]
As one of displays using organic light emitting elements, there is a passive matrix type (simple matrix type) display as shown in FIG. Such a passive matrix organic light-emitting display includes a plurality of rows of anodes 7 (first electrodes, data lines) on the transparent substrate 1, a plurality of rows of cathodes 8 (second electrodes, address lines) intersecting the anodes, It is comprised from the organic layer 5 containing the organic light emitting layer pinched | interposed by these. A crossing region between the anode 7 and the cathode 8 forms a single pixel 10, and a plurality of the pixels 10 are arranged to form a display portion, and the anode and the cathode are extended from the display portion to the periphery of the substrate. The display device is configured by connecting the external drive circuit and the display unit through the connection unit.
[0005]
Recently, research on high-definition passive-matrix color displays that take advantage of the high-speed response of organic light-emitting elements is progressing, and realization of low-cost, high-quality displays for information equipment applications such as full-color display and video display. Expectations are growing.
[0006]
As described above, the organic light-emitting element is a device that obtains electroluminescence (hereinafter also referred to as “EL”) by current injection, and has a driving circuit that can control a large current as compared with an electric field device such as a liquid crystal display, It requires an anode and a cathode through which current can flow.
[0007]
As an electrode used for a passive matrix organic light emitting display, the anode includes a transparent conductive metal oxide such as indium tin oxide (ITO), indium zinc oxide, tin oxide, and the cathode includes Al or Low work function metals such as Al alloy and Mg alloy are listed. The resistivity of the transparent metal oxide is larger than that of Al or the like used as a metal wiring material, and the film thickness is limited because it is necessary to maintain a certain degree of visible light transmittance as a transparent conductive film. . For this reason, the wiring resistance of the anode tends to increase.
[0008]
Problems caused by the wiring resistance of the anode include a voltage drop due to the wiring resistance, which requires a high driving voltage when driving the panel, resulting in increased power consumption and Joule heat generated in the wiring. As a result of heating the layer, the characteristics of the panel are deteriorated.
[0009]
As a method for reducing the resistance of the anode, as shown in Examples in JP-A-4-82197, JP-A-5-307997, and JP-A-6-5369, a transparent conductive film and a metal film are used. There is a method of laminating. That is, when the method of laminating such a transparent conductive film and a metal film is used, in Japanese Patent Laid-Open No. 5-307997, “the work function of the anode laminated in a part between the anode and the hole transport layer is higher. And a second anode having a work function higher than that of the first anode portion where the anode is in contact with the transparent first anode portion and the hole transport layer, in JP-A-6-5369. As described in “consisting of parts”, the effect of reducing the wiring resistance by laminating metal films can be obtained.
[0010]
Further, by laminating a metal film having a relatively low resistance, the light emission current flows more concentratedly on the metal film than on the transparent conductive film. Thereby, with respect to the transparent conductive film, the material can be selected and formed with priority over the transmittance, and the light emission efficiency as the light emitting element can be improved.
[0011]
As described above, in designing wirings such as anodes and cathodes of passive matrix organic light emitting displays, it has been important to reduce wiring resistance and improve aperture ratio and transmittance. This is because it is possible to reduce the operating voltage and the power consumption by this design guideline, and to improve the driving stability by suppressing the deterioration due to Joule heat.
[0012]
[Problems to be solved by the invention]
However, there are still important problems in actual passive matrix organic light emitting displays. That is, an electrical short circuit due to a structural defect in the process may occur between both electrodes in the pixel.
[0013]
For example, the pixel pitch is 0.11 mm × 0.33 mm, the aperture ratio is 70%, the anode is the data line, the number of data lines is 240, the cathode is the address line, the number of address lines is 60, and the number of pixels formed at the intersection of both electrodes is Consider a 1.25-inch passive matrix organic light-emitting display of 14400. For simplicity, the data line potential is H (positive potential) when selected and zero (ground) when not selected, and the address line potential is selected when zero (ground) and not selected (positive potential: the same as the data potential H) Suppose that one power supply constant voltage drive of the scanning line 1 address line.
[0014]
In a state where there is no electrical short circuit defect, the electrode wiring resistance or the internal impedance of the drive circuit is sufficiently smaller than the resistance of the pixel having the organic light emitting element portion. In the illustrated example, the pixel resistance at the time of selection (light emitting state, forward bias) is several hundred kΩ, whereas the pixel resistance at the time of non-selection (light-off state, forward bias) or reverse bias is several tens of MΩ or more. The electrode wiring resistance or the internal impedance of the drive circuit is at most several kΩ. Most of the voltage applied to the panel drops between both electrodes in the pixel in order to obtain the electric field strength required for charge injection into the pixel, that is, the organic light emitting layer. As described above, by reducing the wiring resistance and the internal impedance of the drive circuit, a panel with low power consumption and excellent image quality uniformity can be realized.
[0015]
However, when an electrical short circuit exists in the pixel, the pixel resistance described above is almost lost and becomes several hundreds Ω at most. For this reason, there is a drawback that a large current (hereinafter referred to as “leakage current”) determined by the wiring resistance and the internal impedance of the drive circuit flows in the electrical path passing through the defective pixel. In the illustrated case, the pixel current during normal operation is at most 100 μA, whereas the leakage current reaches several mA to several tens mA.
[0016]
This leakage current not only increases the power consumption, but also alters the thermally weak organic thin film layer, increases the electrode short-circuit area in the short-circuited pixel, and further propagates to neighboring pixels to newly In this case, an electrically short-circuited pixel is induced.
[0017]
In addition, a pixel with an electrical short circuit is not lit because the interelectrode potential necessary for light emission cannot be obtained, causing not only a black spot display defect during display but also various image quality when displaying an image. Cause defects. For example, poor image quality is well known, such as a data line including a shorted pixel continues to be lit in a bright line, or an entire address line including a shorted pixel becomes dark.
[0018]
As a method for repairing short-circuited pixels of a passive matrix organic light-emitting display immediately after fabrication, for example, a method of partially destroying the short-circuit electrode using a laser and repairing the short-circuited portion by applying a high voltage exceeding the light emission voltage There are ways to do it.
[0019]
However, since the organic layer used in the passive matrix organic light-emitting display is very thin with a film thickness of about several hundred nm or less, it is industrially difficult to eliminate short-circuit defects due to dust adhesion or uneven film formation. Although it can be repaired by the above method etc., in order to obtain a stable pixel during long-term driving, it is necessary to suppress the short-circuit current in the generated short-circuit defective pixel and eliminate the display defect due to the short circuit It becomes.
[0020]
SUMMARY OF THE INVENTION An object of the present invention is to provide an organic thin film light emitting display capable of preventing display image quality deterioration due to occurrence of a short circuit defect during long-term driving and suppressing a short circuit current.
[0021]
[Means for Solving the Problems]
In order to solve the above-described problems, an organic thin film light emitting display according to the present invention includes a plurality of rows of first electrodes arranged in a strip shape on a transparent substrate, and a strip shape in a direction perpendicular to the first electrode. A plurality of rows of second electrodes, wherein at least an organic light emitting layer is sandwiched between the first electrode and the second electrode, and the intersection of the two electrodes is a pixel. In an organic thin-film light emitting display that displays information by applying a voltage between the electrodes constituting a desired pixel and taking out electroluminescence,
Each of the first electrodes in the plurality of columns has a power supply function for supplying a current to the corresponding pixel, a transparent electrode function for taking out electroluminescence in the pixel, and a disconnection due to an overcurrent when the two electrodes are short-circuited in the pixel. It has at least three functions including a blocking function.
[0022]
In the present invention, the first electrodes in the plurality of rows include a power feeding part made of an electrically continuous conductor extending to the electrode, and the electrode in the electrode without being in electrical contact with the power feeding part. A transparent electrode portion made of a transparent conductor arranged in a pixel portion; and a blocking portion made of a low melting point conductive material arranged to electrically connect the power feeding portion and the transparent electrode portion. Is preferred.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
The organic thin film light emitting display of the present invention will be described below with reference to specific embodiments.
The organic thin film light-emitting display of the present invention has a plurality of rows of first electrodes 7 arranged in a strip shape on a transparent substrate 1 and a direction orthogonal to the first electrodes 7 as shown in FIG. Similarly, a plurality of rows of second electrodes 8 arranged in a strip shape are provided, and an organic layer 5 including at least an organic light emitting layer is sandwiched between two electrodes 7 and 8. Each intersection constitutes a pixel 10, and information is displayed by taking out electroluminescence by applying a voltage between both electrodes 7 and 8 constituting the desired pixel 10 and injecting a current.
[0024]
In the present invention, each of the plurality of first electrodes 7 in the plurality of columns has a power supply function for supplying a current to the corresponding pixel 10, a transparent electrode function for extracting electroluminescence in the pixel 10, and a first function in the pixel 10. It is necessary to have at least three functions, ie, a blocking function that causes disconnection due to overcurrent when the electrode 7 and the second electrode 8 are short-circuited.
[0025]
FIG. 2 is a partially enlarged view of a preferred example of the organic thin film light emitting display according to the present invention. The transparent electrode portion 4 made of a transparent conductive film, which is independent for each unit light emitting pixel, is electrically continuous with a metal film or the like. FIG. 3 is a schematic plan view showing a first electrode 7 including a power feeding unit 2 made of a conductor and a blocking unit 3 that electrically connects the transparent electrode unit 4 and the power feeding unit 2 in the pixel. In this case, the transparent electrode portion 4 is formed in each pixel 10 without being in electrical contact with the power feeding portion 2, and the blocking portion 3 that connects them is made of a low melting point conductive material.
[0026]
With the above-described structure, when an inter-electrode short-circuit occurs in the pixel 10 during long-term driving, the blocking unit 3 made of a low melting point conductive material is melted by the Joule heat. Electrical disconnection occurs and the shorted pixel is disconnected from the power source.
[0027]
As a result, it is possible to prevent a large short-circuit current flowing through the short-circuited pixel, and further it is possible to prevent the occurrence of image quality defects such as bright line defects due to potential fluctuations in the electrode array including the short-circuited pixel. It becomes.
[0028]
Moreover, since the possibility of applying a load to the drive circuit due to a large short-circuit current can be extremely reduced by the function of the interrupting unit 3, it is possible to use a low-cost drive IC.
[0029]
The design value of the blocking unit 3 in the present invention is determined in accordance with the above-described principle. That is, it is designed to quickly exceed the melting point by Joule heat generated by the standard short-circuit current and the resistance value of the interrupting section 3. Factors contributing to the design include the number of matrices of the passive matrix type organic thin film light emitting display, the feeding resistance of the feeding unit 2, the light emitting threshold voltage of the light emitting element, the internal impedance of the driver IC used in the driving circuit, the heat capacity of the low melting point conductive material, and The melting point, heat dissipation from the blocking part 3 to the adjacent structure or atmosphere, etc. are important.
[0030]
The low melting point conductive material used for the blocking portion 3 is preferably a metal, alloy, or metal oxide that can be formed by a highly productive method such as sputtering or vapor deposition and can be patterned by photolithography.
[0031]
The specific metal as the low melting point conductive material according to the present invention is, for example, In (melting point: 429K) or Sn (melting point: 505K), and these are the main components for the purpose of ensuring the above-described productivity. Alloys or oxides contained as may be used.
[0032]
3A to 3C are enlarged views of the unit light-emitting pixel portion according to the present invention, and show configuration examples in which the disposition position and shape of the blocking portion 3 are different. The blocking part 3 may be formed so as to be in electrical contact with the transparent electrode part 4 and the power feeding part 2 and not to be in direct contact with the transparent electrode part 4 and the power feeding part 2. The shape is not limited to these examples.
[0033]
In the organic thin-film light emitting display of the present invention, the first electrode 7 may be configured as described above, and other constituent materials, production procedures, and the like can be performed in accordance with common usage.
[0034]
【Example】
Hereinafter, the present invention will be described in more detail with reference to examples.
As shown below, organic EL display panels of Examples and Comparative Examples were manufactured with the number of pixels (80 × RGB) × 60 dots, the pixel pitch 110 × 330 μm, and the number of subdots 14400.
[0035]
Example 1
First, a substrate having the electrode structure shown in FIG.
On the glass substrate, a Mo film having a resistivity of 1.5 × 10 ⁻⁵ [Ω · cm] as the power feeding unit 2 was formed with a film thickness of 300 nm and a width of 20 μm. A DC magnetron sputtering method was used for film formation of the power feeding unit 2, and a normal photolithography method was used for patterning.
[0036]
Next, indium-tin-oxide (ITO) having a resistivity of 4.1 × 10 ⁻³ [Ω · cm] as the transparent electrode portion 4 was formed with a film thickness of 100 nm, a width of 80 μm, and a length of 280 μm. A DC magnetron sputtering method was used for film formation of the transparent electrode portion 4, and a normal photolithography method was used for patterning.
[0037]
Further, an indium-tin alloy (indium 50%) having a resistivity of 2.1 × 10 ⁻⁴ [Ω · cm] was formed as the blocking portion 3 with a film thickness of 200 nm, a width of 10 μm, and a length of 80 μm. A resistance heating method was used for film formation of the pixel electrode portion, and a normal photolithography method was used for patterning.
[0038]
Subsequently, the organic layer 5 and the cathode 8 as the second electrode were formed on the substrate by the following procedure, and sealed and connected.
The substrate was subjected to UV irradiation cleaning in an oxygen / nitrogen mixed gas (20% oxygen, moisture content 20 ppm or less) purge environment, and then immediately introduced into the vapor deposition apparatus.
[0039]
Next, an organic hole injection layer, an organic light emitting layer, an organic electron injection layer, and an Al cathode were continuously formed without breaking a vacuum of 10 × 10 ⁻⁵ Pa level. All the films were formed by resistance heating vapor deposition, and a crystal oscillator type film thickness meter was used to detect the film thickness. An electroformed Ni mask having a thickness of 20 μm was used for forming the cathode as the second electrode.
[0040]
The substrate after film formation was transferred to a glove box under a nitrogen gas atmosphere without being exposed to the air, and sealed with a UV curing / thermosetting combined sealant and a glass sealing plate. The sealing was filled with nitrogen gas (moisture content of 5 ppm or less, oxygen content of 5 ppm or less) which is an environmental gas in the glove box.
The sealed substrate was taken out into the atmosphere and connected to the drive circuit terminal using an anisotropic conductive adhesive (ACF).
[0041]
Comparative Example 1
On the glass substrate, a Mo film having a resistivity of 1.5 × 10 ⁻⁵ [Ω · cm] as the power feeding unit 2 was formed with a film thickness of 300 nm and a width of 20 μm. A DC magnetron sputtering method was used for film formation of the power feeding unit 2, and a normal photolithography method was used for patterning.
[0042]
Next, indium-zinc-oxide having a resistivity of 2 × 10 ⁻² [Ω · cm] as the transparent electrode portion 4 is formed in a rectangular shape having a thickness of 100 nm, a width of 100 μm, and a length of 280 μm, and a long side of 280 μm. Was formed so as to be in contact with the power feeding unit 2. A DC magnetron sputtering method was used for film formation of the transparent electrode portion 4, and a normal photolithography method was used for patterning.
Subsequently, the organic layer 5 and the cathode 8 as the second electrode were formed on the substrate in the same manner as in Example 1, and sealed and connected.
[0043]
Evaluation of performance 100-hour passive matrix drive (driving frequency 60 Hz, duty 1/60, number of gradations 32, gradation method is frame thinning out) for the organic light emitting displays of the above examples and comparative examples. After that, the following evaluation was performed. Note that since the drive voltage-luminance characteristics differ depending on each substrate configuration, for comparison, the evaluation was standardized and evaluated so that the partial luminance in the fully lit state was 100 cd / m ² .
[0044]
Evaluation item 1) Driving voltage: An increase in operating voltage due to the introduction of the structure according to the present invention (blocking part 3) was evaluated.
2) Number of non-lighted pixels in all lighting states: This corresponds to the number of defective pixels with an electrical short circuit, and the influence of the introduction of the structure according to the present invention on the occurrence of defects was evaluated. The all-lit state is a state where all data lines are selected.
3) Short-circuit current per defective pixel: Subtract the charge / discharge current and circuit current from the panel current in the all-off state (all data lines are driven in a non-selected state) and divide by the number of short-circuited pixels. It is the value. The short-circuit current limiting ability of the structure according to the present invention was evaluated.
4) Linear image quality failure when displaying a test image: An image failure caused by a short-circuited pixel was determined in a state where a test image such as a landscape image was given.
These results are summarized in Table 1 below. In this evaluation, no unlit pixels were seen in all displays at the start of driving.
[0045]
[Table 1]

[0046]
From Table 1 above, in contrast to the comparative example which is the prior art, in the embodiment, the short-circuit current caused by the short-circuited pixel is completely cut off, and the bright line generated when the data line including the short-circuited pixel is turned on. No occurrence of image defects was observed.
[0047]
Furthermore, in the examples, no increase in drive voltage due to an increase in wiring resistance was observed, and no significant difference was found with respect to the comparative example with respect to the number of non-lighted pixels, which was concerned due to the complicated structure.
From the above points, it was confirmed that the object of the present invention was achieved.
[0048]
【The invention's effect】
According to the present invention, it is possible to provide a good organic thin-film light-emitting display that can prevent display image quality deterioration due to occurrence of a short-circuit defect during long-term driving and can suppress a short-circuit current.
[Brief description of the drawings]
FIG. 1 is a plan view showing a passive matrix organic light-emitting display according to an example of the present invention.
2 is a partially enlarged view showing a portion surrounded by an ellipse of the organic light emitting display of FIG. 1;
FIG. 3 is a partially enlarged view showing an electrode structure of a unit light emitting pixel portion according to the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Electric power feeding part 3 Blocking part 4 Transparent electrode part 5 Organic layer 7 1st electrode (data line)
8 Second electrode (address line)
10 pixels

Claims (3)

A plurality of rows of first electrodes arranged in a strip shape on a transparent substrate, and a plurality of rows of second electrodes arranged in a strip shape in a direction perpendicular to the first electrodes, At least the organic light emitting layer is sandwiched between the first electrode and the second electrode, and the intersection of the both electrodes constitutes a pixel, and a voltage is applied between the two electrodes constituting the desired pixel. In organic thin-film light-emitting displays that display information by applying and taking out electroluminescence,
Each of the first electrodes in the plurality of columns has a power supply function for supplying a current to the corresponding pixel, a transparent electrode function for taking out electroluminescence in the pixel, and a disconnection due to an overcurrent when the two electrodes are short-circuited in the pixel. An organic thin-film light emitting display comprising at least three functions including a blocking function. The plurality of rows of first electrodes are arranged in a power feeding portion made of an electrically continuous conductor extending to the electrodes and in the pixel portion in the electrode without being in electrical contact with the power feeding portion. The organic material according to claim 1, comprising: a transparent electrode portion made of a transparent conductor, and a blocking portion made of a low melting point conductive material arranged to electrically connect between the power feeding portion and the transparent electrode portion. Thin film light emitting display. The organic thin-film light-emitting display according to claim 2, wherein the low-melting-point conductive material is indium, tin, or an alloy or oxide mainly containing any one of them.

Images