JPH06325869A - Organic electroluminescent panel - Google Patents

Abstract

PURPOSE:To provide an organic BL panel having an excellent displaying ability by furnishing an active matrix circuit consisting of a thin film transistor and a capacitor on the same base board as an organic EL element. CONSTITUTION:An organic EL element consisting of an organic light emitting layer 4 pinched by an anode 2 and a cathode 5 and an active matrix circuit to drive this organic EL element are installed on a base board 1, and thereby an organic BL panel is formed. The arrangement is characterized by this active matrix circuit composed of the first thin film transistor TFT1, which is to charge and discharge an accumulative capacitor C in conformity to the light emission signal, and the second thin film transistor TFT2 which is turned on and off in compliance with the discharge voltage from the accumulative capacitor C and controls the light emission and non-emission of the organic EL element.

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 device,
ZnS and Ca which are II-VI group compound semiconductors of inorganic materials
In S, SrS, etc., Mn, which is the emission center, and rare earth elements (E
(u, Ce, Tb, Sm, etc.) is generally doped, but an electroluminescent device made of 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 color is a problem), and 4) Peripheral drive circuit cost is high. Have

However, in recent years, in order to improve the above problems,
Electroluminescent devices using organic thin films have been developed. In particular, the electrode type was optimized for the purpose of improving the efficiency of carrier injection from the electrode in order to increase the light emission efficiency, and an organic hole transport layer composed of an aromatic diamine and a light emitting layer composed of an aluminum complex of 8-hydroxyquinoline. Of an organic electroluminescent device provided with (Appl. Phys.
Lett. , 51, p. 913, 1987, etc.), the luminous efficiency is greatly improved as compared with the conventional electroluminescent 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, Technical Research Report of the Institute of Electrical Communication, OME89-46, is used.
37, 1989, etc.), but the brightness decreases with the decrease of the duty as the number of pixels increases (Technical Research Report of the Institute of Electrical Communication, OME88-47, 3).
5, 1988, etc.) and the occurrence of crosstalk has become a serious problem in practical use.

In order to solve the above problem, it is considered to drive the organic electroluminescent element by an active matrix circuit, but in the methods disclosed so far (see Japanese Patent Laid-Open No. 2-148687, etc.), Since each organic electroluminescent element is connected to a memory element composed of a plurality of MOS transistors to control the brightness with a digital signal, it is possible to mount these circuits on the same substrate as the organic electroluminescent element. It is very difficult because the aperture ratio becomes small and a large amount of wiring is required.

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.

[0007]

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 light emitting layer sandwiched between an anode and a cathode and an active matrix circuit for driving the organic electroluminescent device, the organic electroluminescent panel comprising: ,
A first thin film transistor that turns on in response to a switching signal and charges and discharges a storage capacitor in response to a light emission signal; and turns on and off in response to a discharge voltage from the storage capacitor to emit light from the organic electroluminescent element. A second thin film transistor for controlling non-light emission, and an organic electroluminescent panel.

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, and 4 is a hole transport layer.
Represents a light emitting layer, and 5 represents a cathode. The substrate 1 serves as a support for the organic electroluminescence device, and a plate of quartz or glass 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, N ', described in column 14
-(3-Methylphenyl) -1,1'-biphenyl-
Aromatic amine compounds such as 4,4′-diamine: 1,1′-bis (4-di-p-tolylaminophenyl) cyclohexane: 4,4′-bis (diphenylamino) quadrophenyl, JP-A-2- Examples thereof include the hydrazone compound disclosed in Japanese Patent No. 311591 and the silazane compound disclosed in US Patent No. 4,950,950. These compounds may be used alone or, if necessary, may be mixed and used. In addition to the above compounds, polyvinylcarbazole and polysilane (Appl. Phys. Let)
t. , Vol. 59, page 2760, 1991) and the like.

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-59-194393), a cyclopentadiene derivative (JP-A-2-289).
675), and a perinone derivative (JP-A-2-2896).
76), oxadiazole derivatives (JP-A-2-2)
16791), a bisstyrylbenzene derivative (JP-A 1-245087, JP-A-2-222484), a perylene derivative (JP-A-2-189890, JP-A-3-791), and a coumarin compound (JP-A-1). Two
No. 191694, No. 3-792), rare earth complexes (JP-A-1-256584), distyrylpyrazine derivatives (JP-A-2-252793), p-phenylene compounds (JP-A-3-33183). , A thiadiazolopyridine derivative (JP-A-3-37292),
Examples thereof include a pyrrolopyridine derivative (JP-A-3-37293) and a naphthyridine derivative (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. In addition to the structure shown in FIG. 1, an organic electroluminescent device having the following layer structure is used in the organic electroluminescent panel of the present invention.

[0012]

[Table 1] Anode / organic light emitting layer / cathode, organic light emitting layer / cathode consisting of anode / polymer, organic light emitting layer / cathode dispersed in anode / polymer, anode / hole transporting layer / organic electron transporting light emission 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, then organic electroluminescence in the present invention An active matrix circuit that drives the elements will be described.

In the organic electroluminescent panel of the present invention, one line is selected in the X direction 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 in the device is 10 compared with the drive circuit for liquid crystal.
It is more than 00 times.

The above is the basic circuit function, but further, the contrast is sufficiently large as a display panel,
Further consideration was 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 TFs for each pixel.
It is composed of T and one capacitor, and realizes current drive and memory performance. Two electrodes (SCAN) for drive signals
Electrode, DATA electrode) and similar to those for liquid crystal,
In addition, there is a COM electrode for supplying current, which is different in that a 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 (SCA
When the input signal of the N electrode is HIGH, the TFT1 is in the ON state and the potential of the intermediate electrode FE is HIGH when the DATA signal is HIGH.
If it is H, 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. Also, D
If the ATA signal is LOW, the TFT2 is turned off and the output potential becomes LOW. After that, the SCAN signal becomes LO
When W, that is, in the non-selected state, the TFT 1 is turned off, but the potential of the intermediate electrode FE is held by the capacitor C and does not change, and the state of the output potential does not change even if the DATA signal changes. The output potential changes when the line including this pixel is in the selected state again, that is, when the SCAN signal becomes HIGH and a different signal from before is applied to the DATA 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 laminated. 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 so that the capacitor and the electrode intersecting portion can be formed simultaneously with the fabrication of the TFT. 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.

[0019]

(A) Lower electrode forming step: patterning of the ITO pixel electrode 12 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 8 / i type a-
Si layer 9 / n ⁺ type a-Si layer 10 (c) a-Si patterning step: TFT (8a-10
a) and storage capacitor (8b to 10b) (d) upper electrode forming step: source electrode and drain electrode 11a, 11b of TFT and electrode 11 of storage capacitor
c) (e) TFT channel formation: n ⁺ type a-Si layer 10
Etching off of a (f) Organic light emitting layer film forming step: formation of organic light emitting layer 13 (g) Cathode forming step: formation of cathode 5 In the above example of the process, the final cathode formation may be a uniform film formation over the entire surface. No patterning of the cathode as in the matrix structures disclosed up to now is required, thus avoiding a photolithography process that damages the organic light emitting layer after forming the organic light emitting layer, and To be simplified.

[0020]

EXAMPLES Next, the present invention will be described in more detail by way of examples, but the present invention is not limited to the following examples unless it exceeds the gist thereof. 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 On a non-alkali glass (NA-40 made by HOYA) substrate,
A pixel electrode (anode) was patterned by sputtering ITO with a film thickness of 120 nm (sheet resistance ˜20 Ω / □) by wet etching using ordinary photolithography technology and hydrochloric acid. Next, it is performed by the usual photolithography technique and electron beam evaporation, and 100 nm
To form a gate electrode in which an Al layer and a Cr layer having a thickness of 50 nm were sequentially laminated. (B) a-Si continuous film forming step The substrate produced in the step (a) was set in a plasma CVD apparatus, and a-Si layers were continuously formed under the conditions shown in Table 1 below.

[0022]

[Table 3]

(C) a-Si patterning step The substrate was taken out from the above plasma CVD apparatus, and a-Si patterning was carried out by the usual photolithography technique and plasma etching using SF ₆ gas. (D) Step of forming upper electrode A drain and source electrode in which a Cr layer of 50 nm and an Al layer of 100 nm were sequentially stacked were formed by a normal photolithography technique and electron beam evaporation. (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. (F) Organic electroluminescent layer forming step Ultrasonic cleaning of the drive circuit board completed in the steps up to (e) with acetone, ultrasonic cleaning with methanol, water cleaning with pure water, drying with dry nitrogen, UV / ozone cleaning. After that, it was installed in a vacuum vapor deposition apparatus with a contact mask for limiting the vapor deposition portion, and exhausted using an oil diffusion pump until the degree of vacuum in the apparatus became 2 × 10 ⁻⁶ Torr or less. An organic electroluminescence device portion having the structure shown in FIG. 1 was produced below.

As the organic hole transport layer material, N, N'-diphenyl-N, N '-(3 represented by the following structural formula (H1) is used.
-Methylphenyl) -1,1'-biphenyl-4,4 '
-Diamine

[0025]

[Chemical 1]

[0026] was placed in a ceramic crucible and heated by a tantalum wire heater around the crucible for vapor deposition. The temperature of the crucible at this time was controlled in the range of 160 to 170 ° C. The degree of vacuum during vapor deposition was 2 × 10 ⁻⁶ Torr, and the hole transport layer 3 having a film thickness of 60 nm was obtained with the vapor deposition time of 3 minutes and 20 seconds.

Next, as a material for the light emitting layer 4, an aluminum 8-hydroxyquinoline complex Al (C ₉ H ₆ NO) ₃ represented by the following structural formula (E1) is used.

[0028]

[Chemical 2]

The above was vapor-deposited on the hole transport layer 3 in the same manner. The temperature of the crucible at this time is 230-270 ° 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. (G) Cathode forming step The film formed in (f) is taken out from the above vacuum vapor deposition apparatus, placed in another vacuum vapor deposition apparatus with a contact mask that limits the cathode vapor deposition portion, and an alloy of magnesium and silver. 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. <Driving Characteristics of Organic Electroluminescent Panel> Above (a) to (g)
A-SiTFT of organic electroluminescent panel manufactured by the process of
When the characteristics of were evaluated, the mobility (μFE) was 0.5c.
m ² / V · sec and the threshold value was 3V.

Next, as the input signal waveform, when the selection time for one line is 0.2 msec and the time (field time) for one cycle of the selection state is 10 msec, the SCAN signal, D
FIG. 6 shows input waveforms of the ATA signal and the COM signal. The input signal voltage was LOW = 0V and HIGH = 36V for the DATA signal and the SCAN signal, and 25V for the COM signal. This input signal waveform corresponds to a field frequency (frequency for rewriting the screen) of 100 Hz in a display of 100 lines (when the screen is divided and driven), and this field frequency is sufficient for displaying moving images and still images. Is a possible value for.
The voltage waveform of the pixel electrode is shown in FIG. The falling response from ON to OFF is slow, but it does not cause a problem according to the current-voltage characteristics of the organic electroluminescent element, and the emission waveform from the actual organic electroluminescent element also has a steep falling edge, which is satisfactory for a display. Yes (Figure 8). The same measurement was carried out for an input signal corresponding to 200 lines and a field frequency of 50 Hz, and satisfactory operating characteristics were obtained.

[0031]

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 an input signal waveform according to an embodiment.

FIG. 7 is a pixel voltage signal waveform according to an embodiment.

FIG. 8 is a pixel light emission output waveform in the example.

[Explanation of symbols]

 1 Substrate 2 Anode 3 Hole transport layer 4 Light emitting layer 5 Cathode 6 Glass substrate 7a TFT gate electrode, 7b Storage capacitor electrode 8, 8a, 8b SiNx insulating film 9, 9a, 9b i layer a-Si 10, 10a , 10b n + layer a-Si 11a source electrode 11b drain electrode 11c storage capacitor electrode 12 ITO pixel electrode 13 organic light emitting layer

Claims (1)

[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, the organic electroluminescence panel comprising: An active matrix circuit is turned on in response to a switching signal, and is turned on / off in response to a discharge voltage from the storage capacitor, and a first thin film transistor for charging / discharging the storage capacitor in response to a light emission signal. Emission of electroluminescent device,
An organic electroluminescent panel comprising a second thin film transistor for controlling non-light emission.