JPH07153576A - Organic electroluminescent panel - Google Patents

Abstract

PURPOSE:To provide respective circuits on the same substrate, and exhibit excellent display capacity by connecting electrically a negative electrode to a box body of a panel covering an organic electroluminescent element and an active matrix circuit. CONSTITUTION:An organic electroluminescent element composed of an organic light emitting layer 4 sandwiched by a positive electrode 2 and a negative electrode 5 and an active matric circuit to drive the organic electroluminescent element, are arranged on the same substrate 1. The negative electrode 5 is electrically connected to a panel covering the substrate 1, the electroluminescent element and the matric circuit. Here, metal having a low work function is used as the negative electrode 5, and an electron is efficiently implanted. Picture elements composed of an XY matrix are selected line by line in the X direction, and display signals of the respective picture elements are imparted from the electrode in the Y direction, and after a round of it is made, the whole image screen is displayed. Then, a memory is arranged to maintain a display condition until the next selection time after making a round of the image screen from selection time, and is used as an electric current drivable circuit. Thereby, excellent display capacity can be attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an organic electroluminescent panel, and more particularly, to a thin film type device which emits light by applying an electric field to a light emitting layer made of an organic compound.

[0002]

2. Description of the Related Art Conventionally, as a thin film type electroluminescent (EL) element, Zn which is a II-VI group compound semiconductor of an inorganic material has been used.
It is general that S, CaS, SrS, etc. are doped with Mn or a rare earth element (Eu, Ce, Tb, Sm, etc.), which is the emission center, but the EL element made from the above inorganic material is 1). AC drive is required (50 to 1000 Hz), 2) high drive voltage (up to 200 V), 3) full colorization is difficult (especially blue is a problem), and 4) peripheral drive circuit costs are high. ing.

However, in recent years, in order to improve the above problems,
EL devices using organic thin films have been developed. In particular, the electrode type was optimized to improve the efficiency of carrier injection from the electrode in order to increase the luminous efficiency, and an organic hole transport layer made of an aromatic diamine and a light emitting layer made of an aluminum complex of 8-hydroxyquinoline. Of an organic electroluminescence device provided with a light emitting diode (Appl. Phys. L
ett. , 51, p. 913, 1987), the luminous efficiency is significantly improved as compared with a conventional EL device using a single crystal such as anthracene.

[0004]

In order to use the above organic electroluminescent device as a display panel,
Generally, a matrix address method (Japanese Patent Laid-Open No. 2-66873)
Publication, Technical Report of IEICE, OME89-4
6, 37, 1989) is adopted, but the brightness decreases as the duty decreases with the increase in the number of pixels (Technical Research Report of the Institute of Electrical Communication, OME88-4).
7, 35, 1988), crosstalk occurs. Therefore, it is conceivable to drive the organic electroluminescent element by an active matrix circuit, but the method disclosed so far (see Japanese Patent Laid-Open No. 2-148687).
In order to control the brightness with a digital signal by connecting a memory element composed of a plurality of MOS transistors to each organic electroluminescent element, mount these circuits on the same substrate as the organic electroluminescent element. Is very difficult because the aperture ratio becomes small and a large amount of wiring is required. Therefore, a panel in which an organic electroluminescent device and an active matrix circuit are provided on the same substrate is conceivable (see Japanese Patent Application No. 5-116208). In this panel, since the anode, which is a transparent electrode, and the active matrix circuit are on the same substrate, the connection between each anode arranged in the XY matrix and the external drive circuit is formed in advance around the substrate. It is made by the wiring pattern. The other electrode, the cathode, need not have an XY matrix structure and may have a solid structure. However, since the driving currents of all pixels are collected in the cathode, an external circuit is formed by utilizing the narrow gap around the substrate. There was a problem in terms of the amount of current to make an electrical connection with.

In view of the above situation, the present inventors have an object to provide an organic electroluminescent panel having an organic electroluminescent element and an active matrix driving circuit thereof on the same substrate.

[0006]

The summary of the present invention is as follows.
What is claimed is: 1.An organic electroluminescent panel comprising an organic electroluminescent device comprising an organic luminescent layer sandwiched by an anode and a cathode, and an active matrix circuit for driving the organic electroluminescent device, the organic electroluminescent panel comprising: , An organic electroluminescent panel characterized in that it is electrically connected to a casing portion of the panel covering the substrate, the organic electroluminescent element and the active matrix circuit.

The organic electroluminescent panel of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a cross-sectional view schematically showing a structural example of a general organic electroluminescent device used in the present invention, where 1 is a substrate, 2 is an anode, 3 is a hole transport layer, 4 is a light emitting layer, and 5 is Each represents a cathode. The substrate 1 serves as a support for the organic electroluminescence device, and a quartz or glass plate or the like is used.

An anode 2 is provided on the substrate 1. As the anode, a metal such as gold, silver, palladium, platinum or the like, or a metal oxide such as an oxide of indium and / or tin (abbreviated as ITO hereinafter) is usually used. Object or copper iodide, or poly (3
-Methylthiophene) and other conductive polymers. Examples of the compound used for the hole transport layer 3 provided on the anode 2 include JP-A-59-194393.
No. 13 to U.S. Pat. No. 4,175,960.
N, N′-diphenyl-N, described in column 14
N '-(3-methylphenyl) -1,1'-biphenyl-4,4'-diamine: 1,1'-bis (4-di-p-
Tolylaminophenyl) cyclohexane: 4,4′-bis (N- (1-naphthyl) -N-phenylamino) biphenyl and other aromatic amine compounds, JP-A-2-3115
The hydrazone compound described in Japanese Patent No. 91, the silazane compound, the quinacridone compound, and the like described in US Pat. No. 4,950,950. These compounds may be used alone, or may be used as a mixture if necessary. In addition to the above compounds, polyvinylcarbazole and polysilane (Appl.Phy
s. Lett. , 59, p. 2760, 1991).

As a material used for the light emitting layer 4, an aromatic compound such as tetraphenyl butadiene (see JP-A-57-57).
No. 51781), a metal complex such as an aluminum complex of 8-hydroxyquinoline (JP-A-59-19439).
3), a cyclopentadiene derivative (Japanese Patent Laid-Open No. Hei 2)
-289675), perinone derivative (see JP-A-2-289676), oxadiazole derivative (see JP-A-2-216791), bis-styrylbenzene derivative (JP-A 1-245087, JP-A 1-245087). 2-222484), perylene derivatives (see JP-A-2-189890, JP-A-3-791), and coumarin compounds (JP-A-2-191694).
JP-A No. 3-792), a rare earth complex (see JP-A 1-256584), a distyrylpyrazine derivative (see JP-A-2-252793),
p-phenylene compound (JP-A-3-33183), thiadiazolopyridine derivative (JP-A-3-372)
92), pyrrolopyridine derivative (JP-A-3-
37293) and naphthyridine derivatives (see JP-A-3-203982).

The cathode 5 plays a role of injecting electrons into the light emitting layer 4. The material used as the cathode 4 is preferably a metal having a low work function in order to efficiently inject electrons, and an appropriate metal such as tin, magnesium, indium, aluminum, silver or an alloy thereof is used. Besides the structure shown in FIG. 1, an organic electroluminescent device having the following layer structure is used in the present invention.

[0011]

[Table 1] Anode / organic luminescent layer / cathode Anode / polymer organic luminescent layer / cathode Anode / polymer dispersed organic luminescent layer / cathode Anode / hole transport layer / organic electron transport luminescent layer / cathode Anode / organic hole-transporting light-emitting layer / organic electron-transporting layer / cathode Anode / hole-transporting layer / organic electron-transporting light-emitting layer / electron-transporting layer / cathode Next, an active layer for driving the organic electroluminescent device of the invention is formed. The matrix circuit will be described.

In the organic electroluminescent panel of the present invention, one line in the X direction is selected for each pixel composed of the organic electroluminescent elements arranged in the XY matrix, and the display signal of each pixel is selected from the electrode in the Y direction. The selection signal in the X direction is operated line by line, and the entire screen is displayed in one cycle. In this panel, each pixel circuit has a memory function. This is because, unlike the case of liquid crystal, if a current is passed only during selection (the scanning electrode of a certain pixel is ON and a display signal is being applied), the pixel will emit light only at the selected moment. , Because the entire screen cannot be displayed continuously. Therefore, it is necessary to provide a memory on the circuit for maintaining the display state from the time of selection to the time of the next selection after making a round of the screen. Then, a circuit that can be driven by current is used. Specifically, the current density flowing through the device is usually 1000 times or more that of a drive circuit for liquid crystal.

The above is the basic circuit function, but the contrast is sufficiently large as a display panel.
Further consideration is given to the large aperture ratio of the screen and the absence of crosstalk. FIG. 2 shows an active matrix drive circuit including a thin film transistor (TFT) for one pixel and a capacitor. This circuit uses two Ts for each pixel.
FT (TFT1, TFT2) and one capacitor (C)
It realizes current drive and memory performance. Two electrodes (SCAN electrode, DATA electrode) for driving signals
However, it is similar to that for liquid crystal, but is different in that there is a COM electrode for supplying current, and voltage is always applied.

The operation of the device will be described below. Although the TFT is expressed as an FET in the circuit diagram of FIG.
Has basically the same structure and operation as the MOS-FET, and can switch between the source and drain electrodes by the gate potential. The method of giving a signal for driving is selected for each line, and an ON or OFF signal is given for each pixel in the selected line. The electrodes for selection are SCAN electrodes, and the electrodes that give signals are DATA.
It is an electrode. Now, the selected state, that is, the SCAN signal (S
When the input signal of the CAN electrode is HIGH, the TFT1 is
The N state is set, and the potential of the intermediate electrode FE is H when the DATA signal is H.
If it is IGH, it becomes HIGH, and if it is LOW, it becomes LOW. Therefore, if the DATA signal is HIGH, the TFT 2 is turned ON and the output potential (pixel electrode potential) becomes HIGH. If the DATA signal is LOW, the TFT2 is turned off and the output potential is LOW. After that, when the SCAN signal becomes LOW, that is, in the non-selected state, the TFT1 is turned off, but the potential of the intermediate electrode FE is held by the capacitor C and does not change, and even if the DATA signal changes, the output potential The state does not change. The output potential changes
Again, the line containing this pixel is in the selected state, that is, SCA
The N signal becomes HIGH, and a different signal from before is DA
It is when applied to the TA electrode. With this circuit, it is possible to drive an active matrix system even if it is a current drive type.

FIG. 3 shows the above circuit embodied on a substrate in consideration of the aperture ratio. In the figure, patterns for four circuits are shown. Examples of the material of the TFT used in the active matrix circuit of the present invention include amorphous silicon (a-Si), polycrystalline silicon (poly-Si), and cadmium selenide (CdSe). As the TFT structure, what is called an inverted stagger type is preferably adopted.

As a typical example, an inverted stagger type a-
The SiTFT is shown in FIG. A-Si on the glass substrate 6
The TFT is formed. As the gate electrode 7, Mo, T
A, Al, Cr, a laminated film or alloy thereof, or the like is used. The gate electrode is usually formed by an electron beam evaporation method or a sputtering method. A silicon nitride film (SiN _x ) is used as the gate insulating film 8, and the i-type aS
The i layer 9 and the n ⁺ type a-Si layer 10 are stacked. Silicon nitride film (SiN _x ), i-type a-Si layer and n ⁺ -type a-S
The i layer is usually continuously formed by the plasma CVD method. After forming the window in the n ⁺ type a-Si layer 10, the source and drain electrodes 11a and 11b are formed. The same metal as the gate electrode is used for the source and drain electrodes. In the above a-Si TFT, electric charges are induced on the surface of the i-type a-Si semiconductor layer by the gate potential,
A switch operation between the source and drain electrodes is performed depending on the presence or absence of the charge. The n ⁺ type a-Si is a contact layer for facilitating the transfer of charges to the electrodes.

An insulating film for a TFT is used for the capacitor and the electrode crossing portion, and the structure can be formed at the same time when the TFT is manufactured. Since the capacitor is formed between the constant potential COM electrode and the constant potential COM electrode, it has a circuit structure resistant to noise. An example of the manufacturing process of the organic electroluminescent panel is shown in FIG. (A) Lower electrode forming step: patterning of the ITO pixel electrode 2a and the gate electrode 7a (the electrode 7b becomes an electrode of the storage capacitor.) (B) a-Si continuous film forming step: SiN _x layer 8a / i type a -Si layer 9a / n ⁺ type a-Si
Layer 10a (c) a-Si patterning step: TFT (8b to 10)
b) and storage capacitors (8c-10c)

(D) Step of forming upper electrode: formation of source electrodes and drain electrodes 11a and 11b of TFT and electrode 11c of storage capacitor (e) Formation of channel of TFT: n ⁺ -type a-Si layer 10
Etch-off of b (f) Insulating film 12 for protecting active matrix circuit
(G) Organic light emitting layer film forming step: formation of organic light emitting layer 13 (h) Cathode forming step: formation of cathode 5a As the material used for the insulating layer 12, patterning by photolithography is possible and sufficient insulation is obtained. A material having a withstand voltage can be used, and specific examples thereof include a silicon oxide film, a silicon nitride film, and the like. These insulating films can be formed by a CVD method, a plasma CVD method, a sputtering method, an evaporation method, or the like. . It is possible to form the insulating layer using a photosensitive resin other than the inorganic material, and in this case, it is sufficient to perform only the step of patterning a normal photoresist, which is simple.

Without the insulating layer 12, the cathode 5a and the TF
An electric field is applied between the source electrode 11a, the drain electrode 11b of T and the electrode 11c of the storage capacitor, so that an unnecessary leak current flows or a short circuit due to dielectric breakdown occurs, resulting in the operation of the active matrix circuit. Or, in the worst case, disables active matrix driving. The insulating film 12 for protecting the active matrix circuit prevents the leak current and the dielectric breakdown as described above and guarantees the complete operation of the active matrix circuit.

In the above process example, patterning of the cathode 5a as in the matrix structure disclosed so far is not necessary, and the cathode 5a and the organic light emitting layer 13 may be formed uniformly over the entire surface. Therefore, it is possible to avoid a photolithography process that damages the organic light emitting layer after forming the organic light emitting layer 13, and the entire process is simplified.

FIG. 6 shows a plane structure of a panel having the above active matrix circuit. DATA line and S
Wiring leads for connecting the CAN line to the external drive power source are densely located around the substrate as shown in FIG.
Although not shown in FIG. 6, it is also necessary to take out the wiring of the COM line. Since the voltage required to drive the organic electroluminescent element is 5 to 20 V and the current density is 5 to 30 mA / cm ^2, it is extremely difficult to provide a cathode wiring for collecting the current flowing in each pixel on the substrate. Since it is provided in a portion having a small area, it is difficult to obtain a sufficient current density through this wiring portion.

FIG. 7 shows a panel structure in which the cathode 25 is electrically connected to the back conductive casing 27 through the electrical connection layer 26. The casing 27 is configured to cover the substrate, the organic electroluminescent element, and the active matrix circuit together with the sealing portion 28 made of epoxy resin, acrylic resin, or the like. The material of the casing 27 is not particularly limited as long as it has conductivity and mechanical strength, but preferably, stainless steel, aluminum, or an equivalent metal is used. In the structure of FIG. 7, since the cathode is grounded to the entire casing, the voltage applied to the anode which is the pixel electrode through the active matrix circuit may be a positive potential.
Since the cathode is electrically connected to the entire panel, a sufficient current density required for driving the panel can be supplied, and there is no problem such as local heat generation.

It is desirable that the electrical connection layer 26 has a low resistivity, good contact with the cathode 25, and a high thermal conductivity. The resistivity is 10 Ω · cm or less, preferably 1 Ω · c
A value of m or less is desirable. In order to improve the contact with the cathode, an elastic material that is easily mechanically deformable is desirable,
For example, conductive rubber can be used. The conductive rubber may be anisotropic or isotropic. The use of conductive rubber also avoids the risk of damaging the cathode. In addition, conductive rubber usually has a thermal conductivity of 10 ⁻³ cal / (cm · sec · ° C.).
In addition, it has a function of releasing heat generated from the active matrix circuit and the organic electroluminescent element to the casing 27, and also functions as a heat sink, which contributes to prolonging the life of the element.

[0024]

EXAMPLES Next, the present invention will be described more specifically by way of examples, but the present invention is not limited to the description of the following examples unless it exceeds the gist. An example of manufacturing an organic electroluminescent panel is shown below. As the design of the TFT element, in the circuit diagram shown in FIG. 2, the gate length of the first TFT is 20 μm, the gate width is 100 μm, and the second T
The gate length of the FT was 20 μm and the gate width was 600 μm. Pixel area is 600μm x 600μm, pixel spacing is 8
The size was 00 μm × 800 μm, and the aperture ratio was 56%.

Each manufacturing process will be described below. (A) Lower electrode forming step An ITO film having a thickness of 120 nm sputtered (sheet resistance of 20 Ω / □) on a non-alkali glass (7059 manufactured by Corning, USA) substrate was wet using ordinary photolithography technology and hydrochloric acid. The pixel electrode (anode) was patterned by etching. Then, by electron beam evaporation, a Cr layer of 50 nm, an Au layer of 80 nm, 30 n
A Cr layer of m was sequentially laminated, and a gate electrode was formed by a normal photolithography technique and wet etching using cerium nitrate and aqueous ammonia.

(B) a-Si Continuous Film Formation Step The substrate prepared in the step (a) was set in a plasma CVD apparatus, and a-Si layers were continuously formed under the conditions shown in the table below.

[0027]

[Table 2]

(C) a-Si patterning step The substrate was taken out from the plasma CVD apparatus described above, and a-Si patterning was performed by the usual photolithography technique and plasma etching using SF ₆ gas. (D) Upper electrode forming step By electron beam evaporation, Cr layer of 50 nm and 100 nm
The Au layer and the Au layer were sequentially laminated, and the drain and source electrodes were formed by the usual photolithography technique and wet etching. (E) by plasma etching using the n ⁺ a-Si layer etching off process ordinary photolithography technique and SF ₆ gas is performed to etch the layer of n ⁺ a-Si, to form channels.

When the characteristics of the a-SiTFT of the organic electroluminescent panel produced in the steps (a) to (e) were evaluated, the mobility (μFE) was 0.5 cm ² / V · sec and the threshold value was It was 3V. (F) Insulating film forming step for active matrix circuit protection An insulating layer having a film thickness of 1.3 μm is formed by an ordinary photolithography technique using an alkali developing transparent heat-resistant resist material (V-259PA manufactured by Nippon Steel Chemical Co., Ltd.). Was formed. (G) Organic electroluminescent layer forming step The drive circuit board completed in the steps up to (f) is ultrasonically washed with methanol, washed with pure water, dried with dry nitrogen, and U.
After performing V / ozone cleaning, install it in a vacuum vapor deposition device with a contact mask that limits the vapor deposition part, and exhaust using an oil diffusion pump until the degree of vacuum in the device becomes 2 x 10 ^-6 Torr or less. did. An organic electroluminescence device portion having the structure shown in FIG. 1 was produced below.

As the organic hole transport layer material, the following N, N'-diphenyl-N, N '-(3-methylphenyl) -1,1'-biphenyl-4,4'-diamine (H
1) was placed in a ceramic crucible and heated by a tantalum wire heater around the crucible for vapor deposition.

[0031]

[Chemical 1]

The temperature of the crucible at this time is 160 to 170.
The temperature was controlled in the range of ° C. The degree of vacuum during vapor deposition is 2 × 10 ^-6 To
The hole transport layer 3 having a film thickness of 60 nm was obtained with an rr of vapor deposition time of 3 minutes and 20 seconds. Next, as a material for the light emitting layer 4, an aluminum 8-hydroxyquinoline complex A represented by the following structural formula is used.
l (C ₉ H ₆ NO) ₃ (E1) was vapor-deposited on the hole transport layer 3 in the same manner.

[0033]

[Chemical 2]

The temperature of the crucible at this time is 230 to 270 ° C.
Controlled in the range of. The degree of vacuum during vapor deposition is 2 × 10 ^-6 Tor
r, the vapor deposition time was 3 minutes and 30 seconds, and the film thickness was 75 nm. (H) Cathode forming step The film formed in (g) is taken out from the above vacuum vapor deposition apparatus, placed in another vacuum vapor deposition apparatus with an adhesion mask that limits the cathode vapor deposition portion, and an alloy of magnesium and silver is formed. The cathode was vapor-deposited with a film thickness of 150 nm by the two-source simultaneous vapor deposition method.
Vapor deposition uses a molybdenum boat and the degree of vacuum is 3 × 10 ^-6
A glossy film was obtained with Torr and vapor deposition time of 4 minutes and 30 seconds. The atomic ratio of magnesium to silver was 10: 1.5.

Finally, a panel having the structure shown in FIG. 7 was assembled by using the above manufactured element. As the electrical connection layer 26, a conductive silicone rubber EC-A (thickness 0.6 mm) manufactured by Shin-Etsu Silicone Co., Ltd. was used. A stainless steel plate was used as the metallic housing on the back surface of the cathode, and the panel was sealed with an acrylic adhesive 28. The electric wiring 22 on the substrate side was connected to an external drive power source by a flexible wiring 23. In the panel, the selection time for 1 SCAN line is 0.2 msec, the time for one selection state cycle (field time) is 10 msec, and the input signal voltage is LOW = 0 V, HIGH = for the DATA signal and the SCAN signal.
It was driven at 36V, and the COM signal was driven at 25V. The rise and fall of the light emission of each pixel and the memory operation were also good. The above input signal is a field frequency (screen rewriting frequency) on a 100-line (when the screen is divided into two) to be driven.
Is set to 100 Hz, and this field frequency is a value at which moving images and still images can be displayed sufficiently. 20
The same measurement was performed for an input signal corresponding to 0 line and a field frequency of 50 Hz, and satisfactory operating characteristics were obtained.

In the driving of the above panel, the electrical connection between the cathode and the casing and the dissipation of heat are good, and the switching characteristics of each pixel do not change even after continuous driving for a long time. There was no deterioration.

[0037]

According to the present invention, an organic electroluminescent panel having excellent display capability is achieved by providing an active matrix circuit composed of thin film transistors and capacitors on the same substrate as the organic electroluminescent element. Therefore, the organic electroluminescent panel of the present invention is a flat panel
The field of display (for example, computers for OA, FA and LA, and wall-mounted television) and application to display panels of measuring instruments can be considered, and its technical value is great.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of an organic electroluminescence device used in the present invention.

FIG. 2 is a circuit diagram for driving the organic electroluminescent panel of the present invention.

FIG. 3 is a plan view of a TFT drive circuit of the organic electroluminescence panel of the present invention.

FIG. 4 is an example of a TFT structure used in an organic electroluminescence panel driving circuit of the present invention.

FIG. 5 shows an example of steps for manufacturing an organic electroluminescence panel of the present invention.

FIG. 6 is a wiring plan view of the organic electroluminescence panel.

FIG. 7 is a schematic sectional view of an organic electroluminescence panel of the present invention.

[Explanation of symbols]

1 substrate 2 anode 2a ITO pixel electrode 3 hole transport layer 4 light emitting layer 5, 5a cathode 6 glass substrate 7a TFT gate electrode 7b storage capacitor electrode 8, 8a, 8b, 8c gate insulating film 9, 9a, 9b, 9c i layer a-Si 10, 10a, 10b, 10c n ⁺ layer a-Si 11a source electrode 11b drain electrode 11c storage capacitor electrode 12 active matrix circuit protection insulating layer 13 organic light emitting layer 21 substrate 22 on substrate DATA, SCAN and COMMON
Line wiring part 23 Connection wiring with external drive power source 24 Organic electroluminescent element and active matrix circuit part 25 Cathode 26 Electrical connection layer 27 Panel part 28 Panel encapsulation part

Claims (2)

[Claims] 1. An organic electroluminescence panel comprising an organic electroluminescence device comprising an organic luminescence layer sandwiched by an anode and a cathode, and an active matrix circuit for driving the organic electroluminescence device on a substrate. The organic electroluminescent panel is characterized in that the cathode is electrically connected to a casing portion of the panel covering the substrate, the organic electroluminescent element and the active matrix circuit. 2. The active matrix circuit is an SCA.
A first thin film transistor that turns on and off according to an N signal and charges and discharges a storage capacitor according to a DATA signal, and turns on and off according to a discharge voltage from the storage capacitor.
The organic electroluminescent panel according to claim 1, comprising a second thin film transistor that performs FF and controls light emission and non-light emission of the organic electroluminescent element.