JPS62285395A - 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 3. Detailed Description of the Invention Industrial Application Field The present invention relates to a DC-driven thin-film EL device, and particularly relates to a DC-driven thin-film EL device that has excellent contrast and stability and is easy to drive. .

BACKGROUND OF THE INVENTION AC-driven thin film EL devices are being actively researched as flat panel displays used in computer terminals and the like. Conventionally, such a thin film EL element has a transparent electrode made of indilum, tin G crystal oxide (hereinafter referred to as IT○) on a glass substrate, yttrium oxide, titanium oxide, strontium titanate, tantalum oxide, silicon oxide, aluminum oxide. and a first dielectric layer made of silicon nitride, 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 thin aluminum film. It has a structure in which rear baskets are sequentially stacked.

To form a dot matrix, the ITo electrodes and aluminum electrodes are processed into stripes and are orthogonal to each other. By applying an alternating current 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 elements 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 driving 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 in place of the dielectric layer. has been prototyped (Japanese Unexamined Patent Publication No. 181485/1985).

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 direct current driven thin film EL device has the above-mentioned advantages, it has the drawback of lacking 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. Furthermore, thin film EL elements generally have poor contrast in both AC and DC single drive types, but 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 thin Mn2O3 oxide film, and a back electrode are arranged in sequence.

Function: The MnO oxide thin film has a resistivity of 3×1Q8Ω-a, and also has a large dielectric breakdown field strength and operates as a stable resistor for a long period of time. As a result, the DC drive EL
By using it as a current control layer of the device, it becomes possible to create a DC EL device that emits light stably over a long period of time.

This material also exhibits a blackish brown color and has a thickness of about 1 x 105 (m-
Since it has a large light absorption coefficient of 1, it can effectively absorb external light, reduce the external light reflectance of the panel, and form an element with high contrast.

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

A tin-doped indium nitride film (abbreviated as IrO2 film) with a thickness of 200 OA is formed on a glass substrate 1 made of Corning A059 glass by a sputtering method, and is processed into a stripe shape by a photolithography technique to form a transparent electrode 2.
And so. Thereon, due to co-evaporation of manganese and zinc sulfide, an EL phosphor layer 3 consisting of a manganese-added zinc sulfide thin film having a thickness of 4000 was formed at a substrate temperature of 200°C. 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 M n 203 oxide thin film was formed thereon. The method for making it and its characteristics will be explained below.

Mn2O3 may be used as a starting material, but MnCO3, which is easier to obtain, is used and heated in air at 1100 °C.
The Mn2O3 target, 71-, was created by heating at ~1250'C. MnC2O4 and Mn are used as starting materials in the pond.
(OH)2 may also be used. The target was heated to a substrate temperature of 200° CAr using an RF magnetron
Spano sauce at gas pressure 3 x 10-2 Torr, thickness 2
A thin film of 000 people was formed. The thin film is blackish brown and about 3
It has a specific resistance of X1Q8Ω・bacteria, so with a film thickness of 2000Å, it is 1.5X10! It becomes η. In addition, the light absorption coefficient is about 10, which is desired to increase the contrast of the EL element.
A value of 50I+= was obtained at a light wavelength of 6000 people. The substrate temperature and gas pressure of the sputtering conditions are 2Oo''G, '3X10 Torr, which are commonly used as mentioned above.
It can be selected as desired since it does not have a large effect on resistivity or light absorption coefficient. Oxygen may be mixed into the Ar gas, but since M n 203 exhibits P-type semiconductivity, the resistivity decreases, but this is not a problem because the charge control layer of the present invention has a wide resistivity range. However, since oxygen plasma during sputtering has an adverse effect on the underlying phosphor layer, it is better not to mix oxygen. Furthermore, since the sputtering rate is higher when using Ar only gas than when oxygen is mixed, it is more efficient in terms of forming a thin film, and M n 20 with the same characteristics.
3 Thin films can be created with good reproducibility. When examined by X-ray diffraction, the thin film was found to be composed of polycrystalline particles with a pattern matching ASTM cards 10-69 and 24-508 and different from gamma type Mn2O3.

After forming the current control layer as described above, finally, aluminum is vacuum-deposited to a thickness of 2,000 yen, and a striped back electrode 5 in a direction perpendicular to the 5ITO transparent electrode is formed by photolithography. A thin film EL device was completed.

For comparison, an EL element was also fabricated with exactly the same configuration, except that the current control layer was made of a thin Ta 2 Os with a thickness of 2000 mm, which is well known in the art. The Ta,.05 thin film was formed by active sputtering using a Ta metal target in an Ar+02 atmosphere, and the manufacturing conditions were optimized for use in a DC EL device.

When the EL element of the present invention was driven line-sequentially with pulses with a duty of 11520, a frequency of 60 yen, and a pulse width of 32 μs as shown in FIG.
The brightness voltage characteristics shown in the figure were obtained. The light-emitting portion of the EL element corresponds to 64% of the total area, and the figure shows the average brightness including the light-emitting and non-light-emitting portions. 76V rising from 5sV
A practical luminance of 50 Cd/m2+7) was obtained. The brightness change characteristic after driving at 75V for 1000 hours is shown by a broken line. As shown in the figure, the change was small, with only a 12% decrease in brightness at 76 cm, and the device operated stably for 1,000 hours without exhibiting any electrode breakage due to dielectric breakdown. In addition, in the EL element of the present invention, the current control layer is provided between the phosphor and the aluminum backside electrode, and since it is black, the reflection of external light by the aluminum electrode is effectively prevented, and the external light reflectance is reduced. It was as low as 7%. Therefore, a high contrast EL element can be obtained.

On the other hand, in the conventional EI device using the T a 205 thin film, the light emission rises from etsV, and unlike the case of the black-brown current control layer of the present invention, it is transparent and the reflection of the light emission by the aluminum back electrode is also effective. 80cd/rr12 at 85v due to
However, when similarly driven at asV for 1000 hours, the brightness decreased to 60% and some wire breakage occurred. Also, the external light reflectance is as high as 67. If 20Q
If an external light source of cd/m 2 is specularly reflected on the surface of the device, the device of the present invention provides a contrast of 3.6:1 at a luminance of 50 cdA. On the other hand, the conventional EL element has a luminance of 0.6:1, which is extremely low even when the luminance is 80 c d/m'.

As explained above, the DC thin film EL element of the present invention has more stable brightness voltage characteristics, drive stability, and better contrast characteristics than the conventional example.

Furthermore, for the EL emitting layer, in addition to the manganese-doped zinc oxide mentioned above, terbium and samarium can be used, as well as zinc sulfide added with any rare earth element, calcium sulfide or strontium sulfide also added with rare earth elements, and it has a high contrast that operates stably. We were able to create a DC-driven thin film EL device.

Effects of the Invention According to the present invention, it is possible to form a DC-driven thin film EL element that can be stably driven over the range of high contrast and &M. 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, so it can be put to practical use as an inexpensive thin display with excellent visibility.

[Brief explanation of the drawing]

FIG. 1 shows a direct current, oscillating membrane EL in one embodiment of the present invention.
FIG. 2 is a sectional view of the device, FIG. 2 is a waveform diagram showing DC pulses used to drive the device, and FIG. 3 is a graph showing the brightness voltage characteristics of the device of the present invention. 1...Glass substrate, 2...Transparent electrode,
3...EL light emitter layer, 4...Current control layer, 5
・・Back electrographic image. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Kamemi (V)

Claims (2)

[Claims] (1) Transparent electrode, EL emitter layer, Mn_2O_3
A direct current driven thin film EL device characterized in that it is constructed by sequentially arranging a current control layer made of an oxide thin film and a back electrode. (2) A Mn_2O_3 oxide thin film was used, which was created by heat-treating a Mn compound that becomes an oxide through thermal decomposition in air to change it into Mn_2O_3, and using this as a target by sputtering in an Ar atmosphere. A DC-driven thin film EL device according to claim 1.