JP2001196190A - Organic thin film luminous display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To offer an organic thin film luminous display which is prevented from deteriorating display image quality due to generating of a short circuit defect at the time of a long-term drive and is enabled to suppress a short-circuit current. SOLUTION: The organic thin film luminous display comprising a first electrode 7 of two or more rows configured on a transparent substrate 1 in a thin strip shape; a second electrode 8 of two or more rows configured in the thin strip shape in the direction which intersects perpendicularly with the first electrode 7; an organic emission layer sandwiched between the first electrode 7 and the second electrode 8 at least; and a pixel 10 constituted by intersection points of the electrodes 7 and 8 respectively; displays an information by taking out an electro-luminescence by impressing a voltage between the electrodes 7 and 8 which constitute a desired pixel 10, wherein a plural of the first electrodes 7 have at least 3 functions which are an electricity supply function supplying current to the above-mentioned corresponding pixel 10, a transparent electrode function taking out electric luminescence in the pixel 10, and an interception function disconnecting wire by an over-current in the pixel 10 at the time of the short circuit between both the electrodes 7 and 8.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field 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 which can be driven for a long period of time and has high reliability, and a manufacturing technique thereof.

[0002]

2. Description of the Related Art Organic light-emitting devices are self-luminous devices and have high visibility and can be driven at a low voltage. Therefore, research on practical use has been actively conducted (Appl. Phys. .Lett., 51, 913, 1987). Such an organic light emitting device has a structure in which 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 are formed on a transparent substrate. Also, a structure in which an organic layer has a three-layer structure of a hole transport layer, a light emitting layer, and an electron transport layer is known.

The light emitting mechanism of an organic light emitting device is considered as follows. A process in which electrons injected from the cathode and holes injected from the anode recombine near the interface between the hole transport layer and the light-emitting layer to generate excitons, and the excitons are radiatively deactivated. Emits light. This light is emitted to the outside through the transparent conductive film and the transparent substrate serving as the anode, and light emission occurs.

[0004] As one of displays using an organic light emitting element, there is a passive matrix type (simple matrix type) display as shown in FIG. Such a passive matrix type organic light emitting display comprises a plurality of rows of anodes 7 (first electrodes, data lines) on a transparent substrate 1 and a plurality of rows of cathodes 8 (second electrodes, address lines) crossing the anodes.
And an organic layer 5 including an organic light emitting layer sandwiched therebetween. The intersection area between the anode 7 and the cathode 8 forms one pixel 10, and a display portion is formed by arranging a plurality of pixels 10. The anode and the cathode extend 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 via the connection unit.

Recently, research on a high-definition passive matrix type color display utilizing the high light emission response speed of an organic light emitting device has been advanced, and low cost and high quality for information equipment applications such as full color display and moving image display. Expectations for the realization of displays are increasing.

As described above, the organic light-emitting element is a device that obtains electroluminescence (hereinafter, also referred to as "EL") by injecting a current, and a drive circuit capable of controlling a large current as compared with an electric field device such as a liquid crystal display. Requires an anode and a cathode through which a large current can flow.

As an electrode used for a passive matrix type organic light emitting display, a transparent conductive metal oxide such as indium tin oxide (ITO), indium zinc oxide, or tin oxide is used for an anode, and a cathode is used for a cathode. Is a low work function metal such as Al, an Al alloy, and an Mg alloy.
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.

Problems caused by the wiring resistance of the anode include a high driving voltage required for driving the panel due to a voltage drop caused by the wiring resistance, resulting in an increase in power consumption and a joule generated in the wiring. As a result of heat heating the organic layer, the characteristics of the panel are degraded.

As a method of reducing the resistance of the anode,
JP-A-4-82197, JP-A-5-307997
As shown in the examples in Japanese Patent Application Laid-Open No. Hei. That is, when such a method of laminating a transparent conductive film and a metal film is used, in JP-A-5-307997, “the work function of the anode and the anode stacked partly between the hole transport layers is smaller than that of the anode. Japanese Patent Laid-Open Publication No. 6-5369 discloses that the second anode has a work function higher than that of the first anode portion in contact with the transparent first anode portion and the hole transport layer. As described above, the effect of reducing wiring resistance by laminating metal films can be obtained.

[0010] Further, by laminating a metal film having a relatively low resistance, the emission current flows more intensively in the metal film than in the transparent conductive film. Accordingly, for the transparent conductive film, the material can be selected and formed with priority given to the transmittance over the conductivity, and the luminous efficiency of the light emitting element can be improved.

As described above, when designing wiring such as the anode and cathode of a passive matrix type organic light emitting display, it is important to reduce the wiring resistance and to improve the aperture ratio and the transmittance at the same time. Was. The operating voltage and power consumption can be reduced by this design guideline.
In addition, it is also possible to improve the driving stability by suppressing the deterioration due to Joule heat and the like.

[0012]

However, there are still important problems in the actual passive matrix type organic light emitting display. It is between the electrodes in the pixel,
The point is that an electrical short may occur due to a structural defect in the process.

For example, a pixel pitch of 0.11 mm × 0.3
3 mm, an aperture ratio of 70%, the number of data lines is 240 using the anode as the data line, the number of address lines is 60 using the cathode as the address line, and the number of pixels formed at the intersection of both electrodes is 1
Consider a 4400 1.25-type passive matrix organic light emitting display. For simplicity, the data line potential is H (positive potential) when selected and zero (ground) when not selected, and the address line potential is zero (ground) when not selected and H (positive potential: same as data potential H). , Scanning line 1
The address line is driven by one power supply at a constant voltage.

In a state where there is no electrical short-circuit defect, the electrode wiring resistance or the internal impedance of the driving circuit is sufficiently smaller than the resistance of the pixel having the organic light emitting element. In the illustrated example, the pixel resistance at the time of selection (light emitting state, forward bias) is several hundred kΩ, and the pixel resistance at the time of non-selection (light-off state, forward bias) or reverse bias is several tens MΩ or more. The electrode wiring resistance or the internal impedance of the driving 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 necessary for injecting electric charge into the pixel, that is, the organic light emitting layer. As described above, by reducing the wiring resistance and the internal impedance of the driving circuit, it is possible to realize a panel with low power consumption and excellent image quality uniformity.

However, when an electric short circuit exists in a pixel, the above-mentioned pixel resistance is almost lost and several hundreds of pixels are lost at most.
About Ω. 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 through the electric path passing through the defective pixel. In the illustrated example, while the pixel current during normal operation is 100 μA at most, the leakage current reaches several mA to several tens mA.

This leakage current not only increases the power consumption, but also causes the organic thin film layer, which is relatively weak in heat, to deteriorate, to increase the electrode short-circuit area in the short-circuit pixel, and to propagate to the neighboring pixels. Thus, a new electrically shorted pixel is induced.

In addition, a pixel having an electrical short circuit is not lit because it is impossible to obtain a potential between electrodes required for light emission, which causes not only a black dot display defect during display but also an image display. Causes various image quality defects. For example, image quality defects such as a data line including a short-circuited pixel continuously lighting in a bright line or an entire address line including a short-circuited pixel are darkened.

As a method of repairing a short-circuited pixel of a passive matrix type organic light-emitting display immediately after fabrication, for example, a method of partially destroying and repairing a short-circuit electrode using a laser, or a method of applying a high voltage exceeding an emission voltage to a short-circuit portion There is a method of repairing.

However, the organic layer used in the passive matrix type organic light emitting display has a thickness of several hundreds.
Since it is extremely thin, such as about nm or less, it is industrially difficult to eliminate short-circuit defects due to dust adhesion and film formation unevenness, and although it can be repaired by the above-described method and the like,
In order to obtain a stable pixel during long-term driving, it is necessary to suppress a short-circuit current in a generated short-circuit defective pixel and to eliminate a display defect caused by a short circuit.

An object of the present invention is to provide an organic thin-film light emitting display which can prevent a deterioration in display image quality due to the occurrence of short-circuit defects during long-term driving and can suppress a short-circuit current.

[0021]

In order to solve the above-mentioned problems, an organic thin-film light emitting display according to the present invention comprises a plurality of rows of first electrodes arranged in a strip shape on a transparent substrate. Having a plurality of rows of second electrodes arranged in a strip shape in a direction orthogonal to the electrodes, comprising at least an organic light emitting layer sandwiched between the first electrode and the second electrode, and An intersection of the two electrodes constitutes a pixel, and a voltage is applied between the two electrodes constituting a desired pixel to extract electroluminescence, thereby displaying information by extracting information. The first electrodes each have a power supply function of supplying a current to the corresponding pixel, a transparent electrode function of extracting electroluminescence in the pixel, and a break in the pixel caused by an overcurrent when a short circuit occurs between the two electrodes. 3 functions as ability is characterized in that at least provided.

In the present invention, the plurality of rows of first electrodes may include a power supply portion extending from the plurality of first electrodes, the power supply portion being made of an electrically continuous conductor, and the electrode being provided without being in electrical contact with the power supply portion. A transparent electrode portion made of a transparent conductor arranged in the pixel portion, and a blocking portion made of a low melting point conductive material arranged to electrically connect the power supply portion and the transparent electrode portion, It preferably comprises

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the organic thin-film light emitting display of the present invention will be described with reference to specific embodiments. As shown in FIG. 1, the organic thin-film light-emitting display of the present invention includes 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. A plurality of rows of second electrodes 8 similarly arranged in a strip shape, comprising at least an organic layer 5 including an organic light emitting layer sandwiched between two electrodes 7 and 8; Each intersection constitutes a pixel 10, and information is displayed by extracting electroluminescence by applying a voltage between the electrodes 7 and 8 constituting a desired pixel 10 and injecting a current.

In the present invention, each of the plurality of rows of first electrodes 7 supplies a current to a corresponding pixel 10, a transparent electrode function for extracting electroluminescence from the pixel 10, and a function of the pixel 10. It is necessary to have at least three functions, namely, a cutoff function that causes a disconnection due to an overcurrent when the first electrode 7 and the second electrode 8 are short-circuited.

FIG. 2 is a partially enlarged view of a preferred example of the organic thin-film light emitting display of the present invention. The transparent electrode portion 4 made of a transparent conductive film and an electric material such as a metal film are provided independently for each unit light emitting pixel. FIG. 4 is a schematic plan view showing a first electrode 7 including a power supply unit 2 made of a continuous conductor and a blocking unit 3 for electrically connecting the transparent electrode unit 4 and the power supply unit 2 in the pixel. In this case, the transparent electrode portion 4 is formed in each pixel 10 without making electrical contact with the power supply portion 2, and the blocking portion 3 connecting them is made of a low melting point conductive material.

With the above-described structure, when a short circuit occurs between the electrodes in the pixel 10 during long-term driving, the interruption section 3 made of a low melting point conductive material causes the interruption section 3 due to Joule heat. An electrical disconnection accompanied by melting occurs, and the short-circuit pixel is disconnected from the power supply.

Thus, a large short-circuit current flowing through the short-circuited pixel can be prevented, and further, the occurrence of poor image quality such as a bright linear defect caused by a potential change of the electrode array including the short-circuited pixel can be prevented. It becomes possible.

Further, 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 cut-off section 3, so that a low-cost drive IC can be used.

The design value of the cut-off section 3 in the present invention is determined according to the above principle. That is, the design is made so that the melting point is quickly exceeded 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 power supply resistance of the power supply unit 2, the light emission threshold voltage of the light emitting element, the internal impedance of the driver IC used for the drive circuit, the heat capacity of the low melting point conductive material and The melting point, heat radiation from the blocking portion 3 to the adjacent structure or atmosphere, and the like are important.

As the low melting point conductive material used for the blocking portion 3, a metal, alloy or metal oxide that can be formed by a method having high productivity such as a sputtering method or a vapor deposition method and that can be patterned by a photolithography method is preferable.

A 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). An alloy or an oxide containing as a main component may be used.

FIGS. 3A to 3C are enlarged views of the unit light-emitting pixel portion according to the present invention, and show examples of different arrangement positions and shapes of the blocking portions 3. FIG. The blocking unit 3
It is in electrical contact with the transparent electrode part 4 and the power supply part 2,
In addition, the transparent electrode portion 4 and the power supply portion 2 need only be formed so as not to directly contact with each other, and the arrangement position and shape are not limited to these examples.

In the organic thin-film light-emitting display of the present invention, the first electrode 7 may have the above-described structure, and the materials of the other components, the manufacturing procedure, and the like can be conventionally used.

[0034]

Hereinafter, the present invention will be described in more detail with reference to examples. The number of pixels (80 × RGB) × 60 dots, the pixel pitch 110 × 330 μm, and the number of sub-dots 14400, the organic EL of the example and the comparative example as shown below.
A display panel was manufactured.

Example 1 First, a substrate having the electrode structure shown in FIG. On a glass substrate, a Mo film having a resistivity of 1.5 × 10 ⁻⁵ [Ω · cm] as a power supply unit 2 was formed to a thickness of 3
It was formed with a thickness of 00 nm and a width of 20 μm. The DC magnetron sputtering method was used for the film formation of the power supply unit 2, and the ordinary photolithography method was used for the patterning.

Next, the resistivity 4.1 as the transparent electrode portion 4 is set.
× 10 ⁻³ [Ω · cm] indium-tin-oxide (IT
O) was formed with a thickness of 100 nm, a width of 80 μm, and a length of 280 μm. The DC magnetron sputtering method was used for the film formation of the transparent electrode part 4, and the usual photolithography method was used for the patterning.

Further, the cutoff section 3 has a resistivity of 2.1 × 10
^-4 [Ωcm] indium-tin alloy (indium 50
%) With a thickness of 200 nm, a width of 10 μm, and a length of 80 μm. A resistance heating method was used for forming the pixel electrode portion, and a normal photolithography method was used for patterning.

Subsequently, an organic layer 5 and a cathode 8 as a second electrode were formed on the substrate by the following procedure, and sealing and connection were performed. The above substrate is mixed with an oxygen / nitrogen mixed gas (20%
(Oxygen and water content 20 ppm or less)) After UV irradiation cleaning in a purge environment, the mixture was immediately introduced into a vapor deposition apparatus.

Next, an organic hole injecting layer, an organic light emitting layer, an organic electron injecting layer and an Al cathode were successively formed without breaking a vacuum of the order of 10 × 10 ⁻⁵ Pa. All film formation was performed by using a resistance heating type evaporation method, and a quartz oscillator type film thickness meter was used for film thickness detection. A 20 μm-thick electroformed Ni mask was used to form the cathode as the second electrode.

The substrate on which film formation has been completed is transferred to a glove box under a nitrogen gas atmosphere without being exposed to the atmosphere.
Sealing was performed using a V-curing / thermo-curing combined sealant and a glass sealing plate. Nitrogen gas (water content 5 ppm or less, oxygen content 5 ppm) which is an environmental gas in the glove box
Below). The sealed substrate was taken out into the atmosphere and connected to the drive circuit terminals using an anisotropic conductive adhesive (ACF).

COMPARATIVE EXAMPLE 1 A glass substrate was provided with a resistivity of 1.5 × 10
^-5 [Ωcm] Mo film with a thickness of 300 nm and a width of 20 μm
Formed. The DC magnetron sputtering method was used for the film formation of the power supply unit 2, and the ordinary photolithography method was used for the patterning.

Next, the resistivity of the transparent electrode portion 4 is 2 × 1.
An indium-zinc-oxide of 0 ^-2 [Ω · cm] was formed in a rectangular shape having a thickness of 100 nm, a width of 100 µm, and a length of 280 µm such that the long side of 280 µm was in contact with the power supply unit 2. The DC magnetron sputtering method was used for the film formation of the transparent electrode part 4, and the usual photolithography method was used for the patterning. Subsequently, an organic layer 5 and a cathode 8 as a second electrode were formed on this substrate in the same manner as in Example 1, and sealing and connection were performed.

Evaluation of Performance Passive matrix driving (driving frequency of 6 hours) was performed for the organic light emitting displays of the above Examples and Comparative Examples for 100 hours.
0 Hz, a duty of 1/60, a number of gradations of 32, and a gradation method of frame thinning out), and then the following evaluation was performed. It should be noted that the driving voltage −
Since the luminance characteristics are different, for comparison, evaluation was performed by normalizing the Arial luminance in all lighting states to be 100 cd / m ² .

Evaluation item 1) Driving voltage: An increase in operating voltage due to the introduction of the structure according to the present invention (blocking portion 3) was evaluated. 2) Number of non-lighting pixels in all lighting states: This corresponds to the number of defective pixels accompanied by an electrical short circuit, and the effect of introducing the structure according to the present invention on occurrence of defects was evaluated. The full lighting state is a state in which all data lines are selected. 3) Short-circuit current per defective pixel: The charge / discharge current, circuit current, etc., are subtracted from the panel current in the all-off state (all data lines are driven in a non-selected state), and divided by the number of short-circuit pixels. Value. The short-circuit current limiting ability of the structure according to the present invention was evaluated. 4) Linear image quality defect at the time of display of a test image: In a state where a test image such as a landscape image was given, an image defect caused by a short-circuit pixel was determined. These results are summarized in Table 1 below. In this evaluation, no non-lighting pixels were observed in all displays at the start of driving.

[0045]

[Table 1]

From the above Table 1, it can be seen that, in comparison with the comparative example of the prior art, in the embodiment, the short-circuit current caused by the short-circuited pixel is completely cut off, and the data line including the short-circuited pixel is turned on. No bright linear image defects were found.

Further, in the example, no increase in the driving voltage due to the increase in the wiring resistance was observed, and no significant difference was observed in the number of non-lighting pixels, which was a concern due to the complicated structure, as compared with the comparative example. Was. From the above points, it was confirmed that the object of the present invention was achieved.

[0048]

According to the present invention, it is possible to provide a good organic thin-film light emitting display which can prevent a decrease in display image quality due to the occurrence of short-circuit defects 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.

FIG. 2 is a partially enlarged view showing a portion surrounded by an ellipse of the organic light emitting display of FIG.

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 Substrate 2 Power supply part 3 Interruption part 4 Transparent electrode part 5 Organic layer 7 1st electrode (data line) 8 2nd electrode (address line) 10 pixel

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 3K007 AB05 BA06 CA01 CB01 CB03 DA00 DB03 EB00 FA01 5C094 AA21 AA60 BA27 CA19 DA09 EA05 EB02 HA08

Claims (3)

[Claims] 1. 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 orthogonal to the first electrode. Having at least an organic light-emitting layer sandwiched between the first electrode and the second electrode, and the intersection of the two electrodes constitutes a pixel, respectively, the two electrodes constituting a desired pixel In a thin-film organic light-emitting display for displaying information by applying voltage between electrodes to extract electroluminescence, the plurality of columns of first electrodes each supply a current to a corresponding one of the pixels, An organic thin-film light-emitting display having at least three functions: a transparent electrode function for extracting electroluminescence in a pixel; and a cutoff function for disconnecting due to an overcurrent when the pixel is short-circuited. 2. A power supply unit comprising a plurality of rows of first electrodes, the power supply unit comprising an electrically continuous conductor extending to the electrode, and a power supply unit provided in the electrode without being in electrical contact with the power supply unit. 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 disposed so as to electrically connect between the power supply portion and the transparent electrode portion. Item 2. An organic thin-film light emitting display according to Item 1. 3. The low melting point conductive material is indium,
The organic thin-film light emitting display according to claim 2, wherein the organic thin-film light-emitting display is tin, or an alloy or oxide containing any one of them as a main component.