JPS61165995A - El panel - 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 Industrial Application This invention relates to an EL panel that is applied to computer terminals and the like as a character and graphic display.Prior art Generally, an EL panel consists of transparent electrodes on a glass substrate. (indium tin mixed crystal oxide: ITO), a lower insulator layer, a phosphor layer, an upper insulator layer, and a back electrode (usually an Al metal electrode). However, when this EL panel is viewed from the glass substrate side on the observation side, it looks like a mirror due to the transparency of the thin film and the effect of the A4 electrode on the back electrode, and it easily reflects external light (ambient light), making it susceptible to high external light. The disadvantage is that the contrast tends to be low in environments such as For example, if external light is incident perpendicularly to the panel surface, theoretically about 8% will be reflected by the surface glass and thin film interface just before it enters the Al electrode, and the remaining 92% will be reflected by the surface glass and thin film interface.
Since 90% of the light is reflected by the AI electrode, if all of it were to come out to the surface, the panel would have a high reflectance of 91 cm, but in reality, light is lost due to absorption within the thin film and scattering at the interface. The length is 80 to 90 inches. Therefore, a panel with a standard brightness of 100 nits when there is no outside light has the disadvantage that the contrast is as low as about 2=1 when the surface illuminance is the same as the bright office illuminance of 4001x.

Generally, a contrast of 6:1 or more is desirable even when the panel surface has an illuminance of 4o011x.

Therefore, a method of arranging a circularly polarizing filter in front of the panel has been considered in order to improve the contrast. However, circular polarizing filters have a number of drawbacks, such as being expensive, having low mechanical strength, deteriorating due to ultraviolet rays and turning yellow, and reducing brightness to below 40 inches, so they are not suitable for practical use. Although the brightness is reduced to about 50%, there is a method of interposing a black insulating film between the back electrodes of the phosphor layer to overcome the above problems. The material is a S 1 x C1-x:
H membrane (JP 58-216392), chalcogenide compound (US Patent 3,560,784)
is proposed.

Problems to be Solved by the Invention In such a conventional black insulating film, its dielectric constant is 10.
Since it is small, it has a big drawback of increasing the driving voltage of the EL panel. An object of the present invention is to provide an EL panel that uses a black film with a sufficiently high dielectric constant to provide high contrast without increasing the driving voltage.

Means for Solving the Problems In order to solve the above problems, the present invention provides a thin film layer made of an oxygen-deficient oxide of tantalum between the phosphor layer and the back electrode.

Function The oxygen-deficient oxide of tantalum is black and has a dielectric constant of over 100. By using it for the black layer, the film thickness can be increased to several hundred nanometers due to its high dielectric constant and ability to absorb external light. To a certain degree, the contrast of the EL panel can be increased by increasing the drive voltage by only a few volts.

Example The figure shows one embodiment of the EL panel of the present invention.

In the figure, 1 is a black film made of a thin film of tantalum oxygen-deficient oxide, and 2 and 3 are transparent insulating layers, each made of S r
T 103. Consists of B a T a 20 e. 4
5 is a light emitting layer made of ZnS:Mn, 5 is a transparent electrode made of ITO, and 6 is a back electrode made of Al. These are laminated on a glass substrate Y. In the EL panel of the present invention, external light from indoor lighting and white wall paper, etc., which conventionally lowered the contrast of the EL panel, is absorbed by the black film 1.
It cannot reach the back electrode 6. Only the light emitted from the light emitting layer 4 is visible. Here, the thickness of each layer is 300 nm for black film 1,
Insulating layer 2 has a thickness of 500 nm.

The insulating layer 3 has a thickness of 100 nm, the light emitting layer 4 has a thickness of 450 nm,
When an AC pulse with a width of 3oμ was applied at 60V and a charge density of 1.8μC/cM per cycle was passed through the phosphor layer, the driving voltage was 11oVO, and the luminance was 56cd/m.
It was 2. In addition, in a conventional type EL panel that does not have the black film 1 and has the same film structure, under the same conditions, the driving voltage is 107 Vo-, and the luminance is 10
It was 0 Cd/m2.

Panel surface illuminance is 4001! The contrast determined as the ratio of the brightness when the light-emitting segment is emitting light and when it is not emitting light at x is 6°6:1 for the panel of the present invention.
The ratio was 2.2:1 for conventional type panels. In this way, by introducing the black tantalum oxygen-deficient compound layer of the present invention, contrast can be increased without increasing the driving voltage.

The method for producing the tantalum oxygen-deficient oxide of the present invention will be described below.

Active sputtering is performed using tantalum metal as a target and introducing oxygen and argon as sputtering gases into the sputtering chamber. The tantalum oxide thin film has a larger amount of oxygen and is closer to the stoichiometric composition of Ta205, the less light it absorbs and the more transparent it becomes. On the other hand, if the arsenic content of oxygen is too low, its properties become close to that of tantalum metal, resulting in increased reflectance, metallic luster, and decreased electrical resistance. T a 2
Although there are compositions between 0 s and metallic tantalum that have a high light absorption rate, a low return rate, and a high electrical resistance, the preferable composition range is a relatively narrow range. Film composition tends to shift due to slight fluctuations in sputtering parameters such as gas pressure and discharge current during film formation. Therefore, it is desirable to constantly monitor the film formation state and adjust the sputtering parameters to achieve a constant sputtering state. A suitable method for this purpose is to use plasma light during sputtering to monitor the state of film formation. The plasma light is divided into spectra, and the oxygen gas flow rate is controlled to keep the intensity of the mentally excited atomic spectrum constant. Discharge power, sputtering pressure, etc. may be controlled.

In this example, the emission of tantalum having a wavelength of 300 mm K was monitored, and the oxygen flow rate was controlled so that the intensity of the emission was kept at a constant value. The emission intensity of tantalum at this time was maintained at 44% of the intensity when no oxygen gas was flowed.

A 6'x15'' target was used, discharge current was 4 A, and sputtering pressure was 0.4 Pa.

Sputtering was performed with an Alcon flow rate of 60 SCCM and an oxygen flow rate of 35 to 383 CCM. Sputtering time is 45 seconds. The film formation rate is extremely fast at 400 nm/min.

The obtained film had a dielectric constant of 19o.

Sheet resistance 2 x 10'Ω/mouth (film thickness 300 nm)
, the light absorption coefficient in the visible range was 6×10′/cm.

The emission intensity of tantalum was preferably 40% to 50% of the intensity when no oxygen gas was flowed as a black film for the purpose of the present invention. If it is less than 40%, light absorption will be weak, and if it is more than 50%, the sheet resistance will be low, which is not preferable. Further, in this example, the luminescence intensity of the mental beam was measured as a means for monitoring the sputtering state, but similar results can be obtained by measuring the excitation light of the metal beam by spectrally dispersing the plasma light.

Effects of the Invention As described above, the ML panel of the present invention has a power efficiency of 400 lx because a thin film made of black tantalum oxygen-deficient oxide is provided between the phosphor layer and the back electrode of the EL panel.
Even in ambient light, the contrast can be improved to the extent that it has a contrast of 5:1 or more, which is more than twice that of the conventional EL panel, which is easy to see even in bright places and can be driven at a low voltage. Such a large contrast has the effect of improving display image quality and further enhancing the practicality of the EL panel as a character or graphic display.

[Brief explanation of drawings]

The figure is a sectional view schematically showing the structure of an EL panel in an embodiment of the present invention. 1... Black film, 2, 3... Insulating layer, 4
...No light emission, 6...Transparent electrode, 6.
...Back electrode, 7. River, glass substrate.

Claims (1)

[Claims] A phosphor layer, a transparent electrode and a back electrode formed between the phosphor layer, and a black tantalum oxygen-deficient oxide formed interposed between the phosphor layer and the back electrode. An EL panel comprising a black film made of a thin film made of a material.