JPS62290096A - 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 [Field of Industrial Application] The present invention relates to a thin film EL device, and in particular to a λ film El element with high contrast and high breakdown voltage.

[Prior art and its problems]

Thin-film phosphors have replaced dispersion-type EL elements using curved lead sulfide (ZnS)-based phosphor powder, which had problems with brightness and had to be abandoned in its development as a light source for illumination. Thin-film type ``1-elements'' using layers are currently attracting attention because they can obtain high brightness.

Thin film F [The device has a light-emitting layer that is transparent and thin and has no graininess, so light entering from the outside and light emitted inside the light-emitting layer are scattered, causing halation and bleeding. Due to its high reliability, it is attracting attention for use in vehicles, display devices such as computer terminals, and lighting devices.

The basic structure of a conventional thin film FL device is a transparent electrode made of a tin oxide (SnO2) layer or the like on a transparent substrate, a first dielectric layer, a Jff optical layer made of a ZnS:Mn thin film, and a second dielectric layer. The dielectric layer and the back electrode made of an aluminum (A1) layer or the like are sequentially laminated to form a two-layer dielectric 4vi structure.

The process of light emission is as shown below.

When a voltage is applied between the transparent electrode and the back electrode, the electric field induced in the light-emitting layer pulls out the electrons trapped in the W-plane, speeds them up to h0, and obtains sufficient energy. It collides with the orbital electrons of Mn (optical center) and excites them.

Then, when this excited luminescent center returns to the ground state, it emits light.

In a thin film EL element with such a structure, all layers except the back electrode are transparent, and artificial light from the outside is reflected by the back electrode, and this reflected light interferes with light from the light emitting layer. However, the disadvantage is that sufficient contrast cannot be obtained and only low display quality can be obtained.

Therefore, in order to improve the contrast, the present invention contemplated that the second dielectric layer was made of black tantalum oxide (TaOx).
: x < 2.5), or forming a composite film by attaching a high-resistance insulating film on top of this tantalum oxide film.

Although the method provided by the inventor has good contrast, it has the disadvantage that the withstand voltage is low.

In the latter method, it is possible to improve both the withstand voltage, but when using a composite film like this, dielectric breakdown occurs at the interface when an electric field is applied. Contrast 1 due to relaxation and reflection at this interface
Problems such as a decrease in .

The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a thin film "L strand" with high contrast and high voltage resistance.

(Means for Solving and Overcoming the Problems) Therefore, in the present Komei, the second dielectric layer is continuously changed from a black tantalum oxide film to a transparent kuntal oxide film.

[Effect]

For example, when the second dielectric layer is formed by sputtering using tantalum pentoxide (T205) and flowing a mixed gas of Arcon (Ar) and 02, it is difficult to remove the second dielectric layer. In order to lower the oxygen partial pressure in the reaction chamber, a black tantalum oxide film (TaOx:
Transparent tantalum oxide film (Ta205
) is obtained.

Since the stoichiometric ratio changes continuously, dielectric breakdown does not occur at the interface, and a thin film EL element with high contrast and high breakdown voltage can be obtained.

(Embodiments) Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a diagram showing a thin film "1-element" according to an embodiment of the present invention.

This thin film EL element consists of a light-transmitting glass substrate 1, a transparent electrode made of a tin oxide (SnO2) layer, etc., a first dielectric layer made of a yttrium oxide (Y203) layer, etc.; V
Curved lead monochloride (ZnS):? A second dielectric layer 5 having a composition ratio continuously changing from black to transparent, and a back electrode 6 consisting of a )Iluminium layer are sequentially laminated. It is constructed according to the following.

The second dielectric layer has a stoichiometric composition starting from a black tantalum oxide film (TaOx + It changes continuously, with a total of 50
The film thickness is approximately 0.00.

The deposition of this second dielectric layer is carried out by R' sputtering, using tantalum pentoxide as a target and initially depositing a 3000A tantalum oxide film (TaOx: x<2. After depositing 5>
The partial pressure of oxygen was increased for removal, and the tantalum oxide film (TaOx:
Let it be multiplied.

Here, the transmittance (%) and resistivity (0 cm ) for light with a wavelength of λ-600 nm when the amount of oxygen is changed when forming a tantalum oxide film using a target of Quntal pentoxide using the RF sputtering method. The relationship is shown in FIGS. 2 and 3. As is clear from this figure, when the amount of oxygen decreases, the transmittance decreases, but so does the resistivity, and when the amount of oxygen increases, the resistivity also increases.

The luminance-voltage characteristics of the lung ■φ[1-element thus formed are shown by curve IIAa in FIG. Second for comparison
The dielectric diagram is composed of one layer of (black) tantalum oxide film (TaOx:x<2.5) with a film thickness of 5,000 yen. A black tantalum oxide film (TaOx:x<2.5) and a transparent tantalum oxide film (Ta20s) with a thickness of 1000
) and a thin film Fl having a two-layer structure with
- The luminance-voltage characteristics of the device are shown by curves c in FIG. 4, respectively.

] The trust is almost the same for a and b, and slightly lower for c.

(Here, the vertical axis represents brightness and the horizontal axis represents applied voltage.) Furthermore, the voltage that can be withstood for a long time (withstand voltage)
A is 75V, b is 35V.

C is 60 V, and it can be seen that the resistance U' of the thin film EL element of the present invention in which the second dielectric layer is continuously changed has been significantly improved.

As described above, the thin film El element of this example has high contrast and high breakdown voltage.

Note that the ratio of nψ thickness between the black layer and the continuous layer and the transparent layer in the second dielectric layer is not limited to the example and can be changed as appropriate.

Furthermore, the materials constituting each layer of the layer are not limited to the examples and can be changed as appropriate. In addition, this film El element can be used not only for display devices but also for illumination, for inputting and outputting signals from and reading out optical recording media, and as a light source for students.

In addition, in the case of thin film "1-element" devices used under environmental conditions where the surrounding brightness changes, such as in display devices,
When the surrounding brightness increases, the contrast decreases and it becomes difficult to see, whereas when the illuminance is extremely low, there are problems such as a constant brightness being too bright. For example, as shown in FIG. 5, a photo sensor 7 is arranged on the iron,
Based on the signal from this foot sensor, the voltage applied to the thin film L element is controlled to change the brightness, making it possible to maintain a constant contrast and further enhance the effect. can.

Regarding the control of this applied voltage, as shown in Fig. 6, when the signal from the photosensor reaches a predetermined level, the applied voltage is changed stepwise to maintain the contrast within a certain range (
It is easy to maintain the conditions a-b).

For example, when a thin film El element emits light at a certain brightness A, when the surrounding illuminance, that is, the value detected by the photo sensor 7 reaches 1000 lux, the applied voltage is increased so that the brightness Iσ becomes B, and the illuminance is further increased. 1- When the brightness reaches about 5000 lux, the brightness is changed to C, and so on, and the brightness is changed stepwise from A to R to C to D. In this way, the contrast can be maintained within a more or less constant range without being affected by the surrounding illuminance.

It is also possible to continuously change the applied voltage based on the detection value 11 of the photosensor.

〔effect〕

As explained above, according to the present invention, the dielectric diagram formed between the light emitting layer and the back electrode is changed to tantalum oxide (T).
Since the stoichiometric ratio is continuously changed from black to transparent, it is possible to create a thin film with a high value of 1 to 1 and a high breakdown voltage. ``It becomes possible to use 1-device in IT.

[Brief explanation of drawings]

Figure 1 is a diagram showing a thin film "1-element" of an embodiment of the present invention;
3 and 3 are curves showing the relationship between oxygenation permeability and resistivity during the formation of a tantalum oxide film, and FIG. A comparison diagram of the %n:ilα characteristics of the thin film [1-element and the conventional thin film E1-Suryō, FIG. 5 shows a η diagram of a modification of the present invention, and FIG. 6 shows the thin film shown in FIG. FIG. 1 shows a brightness control curve with respect to the surrounding illuminance (horizontal axis) for maintaining the "1-element] ntruss" at a constant 100 yen. 1...Glass substrate, 2... Transparent electrode, 3...1st
Dielectric layer, 4... Light emitting layer, 5... Second dielectric layer, 6... Back electrode, 7... F41 to center. (與音 i shu) Copperne-I'l (-@”'-口(f) Ln -j F) CD C%J w (田〕U)
Transparent 1f (%) Poro Snoring 3f, continued for city official use (1'fIffff) July 1939
May 211, Name of the invention R membrane [1-Soriko 3, Relationship with the person making the amendment A1 Patent applicant (123) Komatsu Ltd. 4, Agent (104) VAJ 2-chome, Ginza, Chuo-ku, Kyoto No. 11 February Ginza Daisaku Building 6th floor Telephone 03-545-3508 (Representative) 5. Subject of amendment 6. Contents of amendment (1) Line 19 of page 4 and line 10 of page 6 in the specification of the application Correct "-1 for removal" to "gradually". (2) Correct "lower" to "raise" in the 20th line of page 4 of Kaimei@sho. (3) The accompanying drawings cited in the same specification are corrected as shown in the attached sheet.

Claims (2)

[Claims] (1) In a thin film El element in which a dielectric layer is interposed between the light emitting layer and the back electrode and the light emitting layer is made to emit light by supplying an electric field to the light emitting layer, the dielectric layer is changed from black to transparent. A thin film EL device comprising a tantalum oxide film whose stoichiometric ratio changes continuously. (2) Claim (1) characterized in that the electric field applied to the light emitting layer is controlled by a detected value of a photosensor disposed near the light emitting layer. The thin film EL device described in .