JPS62285398A - Dc driven thin film el device - Google Patents

Abstract

(57) [Abstract] 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 EL device, and more particularly 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 indium and tin mixed crystal oxide (hereinafter referred to as ITO) 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, etc., a phosphor layer made of zinc sulfide doped with mangen, 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 back electrodes are sequentially laminated.

To form a dot matrix, the ITO electrodes and aluminum electrodes are processed into stripes and are perpendicular 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. AC-driven thin-film EL elements have the major 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 brightness modulation was difficult.

On the other hand, DC-driven thin film EL devices have a structure in which the EL light emitter 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. A prototype has been manufactured (Japanese Patent Application Laid-open 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 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. In addition, thin film EL elements generally have poor contrast in both AC and DC driven types, but the present invention also improves the contrast of DC driven EL elements.

Means for Solving the Problems Transparent electrodes, EL emitter layers, and PrO'! or P r
a current control layer consisting of a mixture layer of e○11+PrO2;
The element has a structure in which back electrodes are arranged in sequence.

Function The Pr6O11 or Pr6O11+PrO2 mixed oxide thin film has a resistivity value on the order of 10 Ω·crn, has a large dielectric breakdown field strength, and operates as a stable resistor over a long period of time. As a result, it is thought that by using it as a current control layer of DC-driven E and L elements, a DC EL element that stably emits light over a long period of time will become possible. In addition, this material has a dark brown color and a large light absorption coefficient of around 10 cm, so it can effectively absorb light and reduce the external light reflectance of the panel to form elements with high contrast. can.

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

A tin-doped indium oxide thin film (hereinafter abbreviated as ITO thin film) with a thickness of 2,000 thick was formed on a glass substrate 1 made of Corning 7059 glass by sputtering, and processed into stripes by photolithography to form a transparent electric fence 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 20° C. by co-evaporation of manganese and zinc sulfide. Thereafter, heat treatment was performed at 460° C. for 1 hour in vacuum to activate the EL light emitting layer 3. On top of that, a Pr6O11 ceramic target was sputtered in an argon atmosphere containing 60% oxygen at a substrate temperature of 200°C and a pressure of 3X10-2 Torr to form a 200OA thick Pr e○.
11 A current control layer 4 made of a thin film was formed. This current control layer is a thin film with a blackish-brown color, and a separate experiment showed that the resistivity was 8.
×108Ω·cm, so when the thickness is 2000 people, the sheet resistance is 4×10 Ω/mouth.

The optical absorption coefficient has a large value of about 105c,-i at a wavelength of 5000A.

The composition of this current control layer can be changed by changing the sputtering conditions or target. When using Pr6011 oxide ceramic target, it is usually Pr6O1
1 A thin film is formed, but if the proportion of oxygen in the sputtering gas is increased or the sputtering rate is low, some P r O2 is generated and P r 6011+P
It becomes an r02 mixed oxide thin film. When active sputtering is performed in an oxidizing atmosphere using fPr metal as the target, a Pr6O11 thin film is formed, although the crystal orientation of the thin film changes depending on the sputtering conditions. The films formed under the various sputtering conditions mentioned above have a resistivity of 10
A thin film having a value on the order of Ω·cm and containing PrO2 becomes more dark brown and has a greater light-absorbing ability, which is convenient for producing a high-contrast EL element. It is trivalent Pr that turns black and brown, and 4, which has a large light absorption ability.
This is because the value Pr increases relatively.

Finally, aluminum with a thickness of 2000 A is vacuum-deposited, and a striped back electrode 5 is formed in a direction perpendicular to the transparent electrode 2 using photolithography.
A thin film EL device was completed.

For comparison purposes, an EL element was also fabricated with the same structure, except that only the current control layer was replaced with a well-known T a 206 thin film. The Ta2O thin film was formed by active sputtering in an Ar +02 atmosphere using a Ta metal target, 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 a duty of 11520, a frequency of 60 Hz, and a pulse width of 32 μB as shown in FIG. 2 using the back electrode 6 as an anode, the brightness voltage characteristics as shown in FIG. 3 were obtained. 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. Start up 62V, a
A practical value of 50 cd/- was obtained at oV. 1000 at 80V
The brightness change characteristics after time driving are shown by broken lines. As shown in the figure, the change was small and the luminance was only about 10% lower at aoV, and the device operated stably during 1000 hours of operation, with no electrode breakage due to dielectric breakdown. Further, 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 7. It was low. Therefore, a high contrast EL element can be obtained.

On the other hand, in the conventional EI device using the T a 206 thin film, luminescence rises at ssV, and unlike the case of the black-brown current control layer of the present invention, it is transparent and the reflection of luminescence by the aluminum back electrode is also effective. 80 c d/m at 90 V”
The brightness of 90V is obtained for 1000 hours.
When I drove it, the brightness decreased to 60 inches, and some wires broke. Also, the external light reflectance is as high as 67%. If 2
If an external light source of 00 cd/- is specularly reflected on the surface of the element, the element of the present invention has a luminance of 3.6 at a luminance of 50 cd/-.
A contrast of 1 is obtained. On the other hand, the luminance of the conventional EL element mentioned above is 80Cd/rr? However, it is very small at 0.6:1.

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.

In the above embodiment, a case was explained in which a Pr es○11 current control layer was used, but even if a PrO+PrO2 mixed thin film was used, the contrast would only be improved and other characteristics would not change.

In addition to the manganese-doped zinc sulfide mentioned above, the EL light-emitting layer can also be made of zinc sulfide doped with rare earth elements such as terbium or samarium, or calcium sulfide or strontium sulfide also doped with rare earth elements. 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 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, 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 an embodiment of the present invention, FIG. 2 is a waveform diagram showing the DC pulse used to drive the device, and FIG. 3 is a diagram showing the brightness voltage characteristics of the device of the present invention. This is a graph showing. 1...Glass substrate, 2...Transparent electrode,
3... EL light emitter layer, 4... Current control layer, 5... Back electrode. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 1
Figure 2 Figure 3 Electric 7mi (1/)

Claims (3)

[Claims] (1) Transparent electrode, EL light emitter layer, Pr_6O_1
1. A DC-driven thin film EL device comprising a current control layer made of a thin film of _1 oxide or Pr_6O_1_1+PrO_2 mixed oxide, and a back electrode arranged in sequence. (2) Pr_6O_1_1 oxide or Pr_6O_
1_1+PrO_2 mixed oxide thin film is Pr_6O_1_
2. The DC-driven thin film EL device according to claim 1, which is produced by sputtering in an oxidizing atmosphere using monooxide as a target. (3) The DC-driven thin film EL device according to claim 1, wherein the Pr_6O_1_1 oxide thin film is produced by active sputtering in an oxidizing atmosphere using Pr metal as a target.