JPS62285396A - Dc driven thin film el device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a DC-driven thin-film FL device, and more particularly to a DC-driven thin-film EL device that has excellent contrast and stability and is easy to drive.

2. Description of the Related Art] AC drive thin film FL elements have been actively researched as flat panel displays used in computer terminals and the like. Conventionally, such thin film EL elements have a transparent electrode made of indium and tin mixed crystal oxide (hereinafter referred to as ITO) on a glass substrate, yttrium oxide, titanium oxide, strontium titanate, mental oxide, silicon oxide, aluminum oxide and a first dielectric layer made of silicon nitride or the like;
It has a structure in which a phosphor layer made of zinc sulfide doped with manganese, terbium, samarium, etc., a second dielectric layer made of the same material as the first dielectric layer, and a back electrode made of a thin aluminum film are sequentially laminated. be.

To form a dot matrix, the ITO electrodes and aluminum electrodes are processed into stripes and are perpendicular to each other. By applying an AC pulse voltage between the two electrodes, the intersection between the two electrodes is made to emit light, thereby displaying characters and figures. Such AC-driven thin film EL devices have the great characteristics of high brightness and stable operation over long periods of time, but because they have a high operating voltage and are driven by AC pulses, the drive circuit is complicated and expensive. There was a drawback. Another drawback was that it was difficult to modulate the brightness.

On the other hand, DC-driven thin-film EL devices have a structure in which the EL light emitting layer is directly sandwiched between electrodes without using a dielectric layer, or a structure in which a resistor layer or a semiconductor layer is used instead of the dielectric layer. has been prototyped (Japanese Unexamined Patent Publication No. 181486/1986).

A DC-driven thin film EL element has the characteristics that when a matrix type display device is configured, a low-cost display device with a simple drive circuit is possible, and brightness modulation is easy.

Problems to be Solved by the Invention Although the DC-driven thin film EL device has the above-mentioned advantages,
The disadvantage is that it lacks stability. In other words, when a voltage is applied to cause the device to emit light, dielectric breakdown is likely to occur, and when the device is operated for a long time, there are problems in that pixel elements are missing or wire breaks occur. Further, although thin film EL elements generally have poor contrast in both AC and DC driven types, the present invention also improves the contrast of DC driven EL elements.

Means for Solving the Problems An element is constructed in which a transparent electrode, an EL light emitter layer, a current control layer made of a mixed oxide thin film of Pr and Ni, and a back electrode are arranged in sequence.

Function: The mixed oxide thin film of Pt and Ni has a resistivity of 4X103.
It has a value of ~1 x 106 ohms, has a high dielectric breakdown field strength, and operates as a stable resistor for a long period of time.

As a result, it is thought that by using it as a current control layer of a DC-driven EL element, a DC EL element that stably emits light over a long period of time will become possible. In addition, this material exhibits a completely black color and has a large absorption coefficient of more than 1057m', so it can effectively absorb external light and reduce the external light reflectance of the panel to form a high-contrast element. .

Example FIG. 1 shows a cross-sectional view of the thin film EL device of the present invention.

On a glass substrate 1 made of Corning 7059 glass, a tin-doped indium oxide thin film (hereinafter abbreviated as ITO thin film) with a thickness of 2,000 wafers is formed by sputtering and processed into stripes by photolithography to form transparent electrodes 2.
And so. Thereon, an EL phosphor layer 3 consisting of a manganese-doped zinc sulfide thin film having a thickness of 4,000 wafers was formed at a substrate temperature of 200° C. by co-evaporation of manganese and zinc sulfide. Thereafter, heat treatment was performed in vacuum at 450'C for 1 hour to activate the EL light emitting layer 3. A current control layer 4 made of a mixed oxide thin film of Pr and Ni was formed thereon. The preparation method and characteristics thereof will be explained in detail below.

P so that the atomic ratio of Pr and Ni is 6o atoms each.
r6O11 and NiO oxide were weighed out and mixed well. Then, it was heat treated in air at 1200°C for 2 hours to effect atomic diffusion, and then pulverized to form a sputtering target. Using RF sputtering equipment, the substrate temperature is 20
A Pr/Ni mixed oxide thin film with a thickness of 400 μm was formed by sputtering in Ar gas at 3×10 Torr at 0′C. This mixed oxide thin film current control layer of Pr and Ni is a completely black resistor, and a separate experiment showed that the resistivity was 4×1♂Ω・σ, so when the thickness was 4000, the sheet resistance was 1010Ω/ It is the mouth. The specific resistance varies greatly depending on the composition ratio, and decreases rapidly when N1 exceeds 70 atoms. 4 x 103Ω with a composition below 7o atomic coefficient
- A specific resistance of σ or more and a sheet resistance value of 1080/mouth or more with a film thickness of 4000 can be obtained with good reproducibility under the above sputtering conditions. In order to absorb external light as a black resistor and lower the external light reflectance of the element, a light absorption coefficient of 105 crrT1 or more is desired at a wavelength of around 6000 A. It has been found that for this purpose, the Ni content must be 20 atoms or more. Therefore, the composition of the mixed oxide current control layer of Pr and N1 suitable for the present invention is one containing 20 to 7 atoms of Ni.

The above explanation is about a thin film formed by sputtering in Ar gas, but it is not preferable to mix oxygen into Ar gas because the resistor thin film has a P-type property, although the light absorption coefficient does not change. This causes the resistance to drop somewhat, and the oxygen plasma has an adverse effect on the underlying phosphor layer. In addition, the sputtering rate decreases, resulting in poor manufacturing efficiency. The substrate temperature and Ar gas pressure of the sputtering conditions are the commonly used 200°C, 3X 10
It may be carried out at around -2 Torr. Although the resistivity changes to some extent depending on these conditions, it is very small compared to the change due to the composition, so it may be selected within the commonly used range mentioned above.

When examined by X-ray diffraction, a thin film prepared in the above composition range shows a halo pattern and is amorphous from an X-ray perspective. It is thought that there are few.

After forming the current limiting layer in the above manner, aluminum is finally vacuum-deposited to a thickness of 2,000 yen, and a striped back electrode 5 is formed in a direction perpendicular to the Q I To transparent electrode using photolithography technology. Then, a thin film EL device was completed.

For comparison, F and L elements were also fabricated with exactly the same configuration, except that only the current control layer was changed to a well-known T a 206 thin film with a thickness of 2000 mm.

The Ta 20s thin film was prepared by Ar using a Ta metal target.
Formed by active sputtering method in +02 atmosphere,
The manufacturing conditions have been optimized for use as a DC ELL child.

The EL element of the present invention has a duty ratio of 1/620 as shown in FIG. 2, using the back electrode as an anode. Frequency 60Hz.

When line sequential driving was performed using pulses with a pulse width of 32 μs, brightness voltage characteristics as shown in FIG. 3 were obtained. The light-emitting portion of the EL element corresponds to 64 areas of the total area, and the average brightness including the light-emitting and non-light-emitting portions is shown. Rising from 50V 7
Practical 45Cd/- was obtained at 0V. 100 at 70V
The brightness voltage characteristics after driving for 0 hours are all shown by broken lines. As shown in the figure, the change is small and the brightness is 10 at 70V.
It operated stably during 1,000 hours of driving, with only a slight decrease of more than 10%, and no electrode breakage due to dielectric breakdown was observed.

In addition, in the EL element of the present invention, the current control layer is provided between the phosphor and the aluminum back electrode, and since it is black, reflection of external light by the aluminum electrode is effectively prevented, and the external light reflectance is 6%. It was low. Therefore, a high contrast EL element can be obtained.

On the other hand, a conventional EL element using a Ta205 thin film has 66
Luminescence rises from V, and unlike the case of the black-brown current control layer of the present invention, it is transparent and the reflection of the emission from the aluminum back electrode is also effective, so a brightness of 80 Cd7m'' can be obtained at ssV, but it also lasts for 1000 hours. When driven at , ssV, the brightness decreased to 60% and some disconnections occurred.Also, the external light reflectance was as high as 67%.If 200Cd/
rr? If the external light source is specularly reflected on the surface of the element, then
The device of the present invention provides a contrast of 3.8:1 at a luminance of 4s Cd/-. On the other hand, the conventional EL element has a luminance of 80 Cd/Z, 6:1, which is very low.

As explained above, the DC thin film EL device of the present invention has more stable luminance voltage characteristics, drive stability, and better contrast characteristics than the conventional example. To create a high-contrast DC-driven thin-film EL device that operates stably using zinc sulfide added with rare earth elements such as terbium and samarium, as well as calcium sulfide and strontium sulfide also added with rare earth elements, in addition to zinc sulfide. was completed.

Effects of the Invention According to the present invention, it is possible to form a shadow of a DC-driven thin film EL element that has high contrast and can be driven stably over a long period of time. Since it is a DC drive type, brightness gradation control is easy, the drive circuit can be configured at low cost, and the element configuration is simple and small, so it can be put to practical use as an inexpensive thin display with excellent visibility.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a DC-driven thin film EL device according to Example 3 of the present invention, FIG. 2 is a waveform diagram showing the DC pulse used to drive the device, and FIG. 3 is a brightness voltage of the device of the present invention. It is a graph showing characteristics. 1...Glass substrate, 2...Transparent electrode, 3.
River: EL light emitting layer, 4: Current control layer, 5:
...Back electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person 2nd
figure

Claims (3)

[Claims] (1) A direct current driven thin film EL device characterized in that it is constructed by sequentially arranging a transparent electrode, an EL light emitter layer, a current control layer made of a mixed oxide thin film of Pr and Ni, and a back electrode. (2) In a mixed oxide thin film of Pr and Ni, Ni
2. The DC-driven thin film EL device according to claim 1, wherein the content of the thin film EL device is 20 to 70 at.%. (3) The mixed oxide thin film of Pr and Ni is created by heat-treating a mixture of Pr oxide and Ni oxide in an air atmosphere and then using it as a target by sputtering in an Ar atmosphere. A DC-driven thin film EL device according to claim 1, characterized in that: