JPH0544158B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an electroluminescent (hereinafter referred to as EL) display panel that is used in display devices and the like and is capable of displaying images with good contrast.

(Prior Art) Conventionally, as this type of technology, there is a technology disclosed in Japanese Patent Application No. 1983-193135 filed earlier by the applicant of the present application.

Conventionally, this type of device has a transparent electrode 12 formed on a glass substrate 11 as shown in FIG. 2, and a transparent high-low resistance SiO ₂ insulating layer 13 formed by sputtering.
Transparent low resistivity film formed by electron beam evaporation
A Ta ₂ O ₅ insulating layer 14 is sequentially formed. Then, on the low resistivity Ta ₂ O ₅ insulating layer 14, a light emitting layer 15 is formed using ZnS as a base material and having Mn as the light emitting center,
Furthermore, a transparent low resistivity Ta ₂ O ₅ insulating layer 16 and a transparent high resistivity SiO ₂ insulating layer 17 are successively formed. Furthermore, a back electrode 18 made of aluminum (hereinafter referred to as Al) is provided on the high resistivity SiO ₂ insulating film 17. The back electrode 18 and the transparent electrode 12 are provided to intersect at right angles, and the transparent electrode 1
When an AC voltage is applied between the back electrode 18 and the back electrode 18, light is emitted from the light emitting layer 15 sandwiched between the intersections of both electrodes, and is visible from the glass substrate 11 side. The light emitted from the light emitting layer 15 travels not only to the glass substrate 11 side but also to the back electrode 18 side. Therefore, the light traveling to the back electrode 18 side is transmitted to the back electrode 18 made of Al.
, and the side of the glass substrate 11 that is viewed becomes brighter by the amount of the reflected light.

By the way, low resistivity Ta ₂ is formed on both sides of the light emitting layer 15.
Since the EL display panel provided with O ₅ and an insulating film can obtain high-intensity light emission, characters or pixels can be displayed with brightness that does not require reflected light from the back electrode 18 side. However, since the back electrode 18 can be formed inexpensively and easily, it is formed of Al by vapor deposition or sputtering.

(Problems to be Solved by the Invention) However, in the EL display panel having the above configuration, the light emitting part is formed by the transparent electrode 12 and the back electrode 18.
The back electrode 18 that is at the intersection with the
When displaying in a bright room where the Al can also be seen,
External light is also reflected by the back electrode 18, and areas that are not emitting light (the back electrode 18 where the two electrodes do not intersect and the light emitting area that is not emitting light) become brighter, and the contrast of the light emitting part deteriorates, causing text or pixel display to become unclear. The drawback was that it was difficult to see.

The present invention eliminates the difficulty of viewing the display described above,
The aim is to provide an EL display panel with excellent contrast.

(Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention has a transparent electrode and a transparent high resistivity (resistance at an electric field strength of 10 ⁴ to ^{10 6} V/cm) on a transparent substrate. rate 10 ¹² ~ 10 ¹⁴ Ωcm)
and _a transparent resistivity (electric _{field strength of} ¹⁰ ₄
A second insulating layer with a resistivity of 10 ⁷ to 10 ⁹ Ωcm at ˜10 ⁶ V/cm), a light-emitting layer, a third insulating layer with a low resistivity, and a high resistivity (electric field strength of 10 ⁴ to ^{10 6} In an EL display panel formed by sequentially laminating a fourth insulating layer having a resistivity of 10 ¹² to 10 ¹⁴ Ωcm) in V/cm) and a back electrode, the third insulating layer is made of Ta ₂ O ₅ ,
It is a black or dark brown layer made of a mixture of either SiO ₂ or Al ₂ O ₃ and MnO _2-X , and its electrical properties (resistivity) are equivalent to those of the second insulating layer. It is what it is.

(Function) With the above-described configuration of the present invention, there is no light reflected by the back electrode made of metal such as Al, so the non-light-emitting portion becomes dark and the contrast ratio with the light-emitting portion increases.

(Embodiment) FIG. 1 is a structural diagram of an EL display panel showing an embodiment of the present invention.
A transparent electrode 2 made of In ₂ O ₃ , SnO _{2 ,} etc. and patterned as a plurality of electrodes is provided, and transparent high resistivity SiO ₂ , an insulating material, etc. A layer 3 is formed, and a transparent low resistivity Ta ₂ O ₅ insulating layer 4 is further formed thereon by electron beam evaporation. Then, on the low resistivity Ta ₂ O ₅ insulating layer 4, a light emitting layer 5 is formed using ZnS as a base material and Mn as a light emitting center by electron beam evaporation. Next, on the _light emitting layer 5, _0.1 ~
Low resistivity ( _{Ta 2}
O ₅ +MnO _2-X ) insulating layer 6 is formed. here
MnO2 _-X means a mixture of MnO and _MnO2 .

The high and low resistivity SiO ₂ insulating layer 3 is deposited on this low resistivity (Ta ₂ O ₅ +MnO _2-X ) insulating layer 6 by sputtering.
An insulating film 7 made of high resistivity SiO ₂ similar to that shown in FIG.

Here, low resistivity Ta ₂ O ₅ provided on both sides of the light emitting layer 5
The insulating layer 4 and the low resistivity (Ta ₂ O ₅ +MnO _2-X ) insulating layer 5 have the function of an electron supply source for easily injecting electrons into the light emitting layer 5. As shown in No. 193135, experiments show that its electrical properties have a resistivity of 10 ⁷ to 10 ⁹ Ωcm (at an electric field strength of 10 ⁴ to ^{10 6} V/cm), which is a low resistivity for an insulating layer. By providing a low resistivity Ta ₂ O ₅ insulating layer, high brightness light emission can be obtained.
The Ta ₂ O ₅ insulating layer has the advantage of being easily obtained by electron beam evaporation using Ta ₂ O ₅ pellets, and the low resistivity Ta ₂ O ₅ insulating layer 4 of this example was also formed in this way. There is. However, the low resistivity Ta ₂ O ₅ insulating layer is transparent.

Therefore, the present invention provides a low resistivity layer on the upper side of the light emitting layer 5.
It makes the color of the Ta ₂ O ₅ insulating layer black or blackish brown without changing its electrical properties (resistivity).
Ta ₂ O ₅ powder with 0.1 to 5 weight percent MnO ₂ or
MnO is mixed, pressed into pellets, and fired at a temperature of at least 500°C. Using the fired pellets, electron beam evaporation is used to easily produce a thin film with low resistivity (Ta ₂ O) that becomes black or dark brown. ₅₊
MnO _2-X ) insulating layer 6 can be formed. Firing may be performed in vacuum, in the air, or in an oxygen atmosphere, but in order to reduce outgassing during electron beam evaporation, it is better to perform firing at a temperature of 1000°C or higher in vacuum. Here, when the amount of MnO ₂ or MnO mixed is increased, the electrical characteristics of the low resistivity MnO insulating film change, and the light emitting characteristics of the EL panel change. The amount of Ta ₂ O ₅₂ or Ta ₂ O ₅ is determined based on the required contrast ratio.

In addition, the high resistivity SiO ₂ insulating layers 3 and 7 limit the current flowing to the EL panel, and have a resistivity of 10 ¹² ~
It is an insulating film with a high resistivity of 10 ¹⁴ Ωcm (at an electric field strength of 10 ⁴ to ^{10 6} V/cm), and is formed with a film thickness of 400 Å to 1000 Å.

To make an EL panel with this configuration emit light,
When a voltage is applied between the transparent electrode 2 and the back electrode 8, the light-emitting layer 5 at the intersection of both electrodes emits light, and a plurality of intersections selected in this way are made to emit light, forming characters or pixels. Display. In addition, instead of Ta ₂ O ₅ used for the low resistivity insulating layers 4 and 6 in the above embodiment, Al ₂ O ₃ or SiO ₂ was used to form the low resistivity insulating layers 4 and 6 (however, 6 is MnO _{2 -X-} containing layer) can also be formed using electron beam evaporation to provide a layer having electrical properties (resistivity) equivalent to those using Ta ₂ O ₅ . By the way, it is possible to mix carbon (hereinafter referred to as C) instead of MnO ₂ or MnO, but it is not suitable because C may have a negative effect on the EL layer 15.

(Effects of the Invention) As described in detail above, according to the present invention, the low resistivity Ta ₂ O ₅ insulating layer 6 on the back electrode 8 side is made of MnO _2-X
By mixing these, the EL display panel becomes black or blackish brown, so even if the EL display panel is displayed in a bright room, the indoor light will not be reflected by the back electrode 8 made of metal such as Al, so the non-emitting parts will be dark and emit light. It has a large contrast ratio with other parts, making the display easy to see even in a bright room.

In addition, in the above-mentioned example, a case was described in which MnO _2-X was mixed into a low resistivity Ta ₂ O ₅ insulating layer, but
EL display panels using a low resistivity SiO ₂ insulating layer mixed with MnO _2-X or a low resistivity Al ₂ O ₃ insulating layer mixed with MnO _2-X are similar in terms of the purpose of increasing contrast. effective.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of an embodiment of the present invention, and FIG. 2 is a sectional view showing the structure of a conventional EL display panel. 1... Glass substrate, 2... Transparent electrode, 3... Transparent high resistivity SiO ₂ insulating layer, 4... Transparent low resistivity Ta ₂
O ₅ insulating layer, 5... light emitting layer, 6... low resistivity (Ta ₂
O ₅ +MnO _2-X ) Insulating layer, 7...Transparent high resistivity SiO ₂
Insulating layer, 8... back electrode.

Claims (1)

[Claims] 1. A transparent electrode with a transparent high resistivity (resistivity of 10 12 to 10 ¹² at an electric field strength of ^{10 4} to ^{10 6} V/cm) on a transparent substrate.
10 ¹⁴ Ωcm) and a first insulating layer of Ta ₂ O ₅ , SiO ₂ ,
Transparent low resistivity (resistivity 10 ⁷ ~ at electric field strength 10 ⁴ ~ _{10 6} V/cm) consisting of any of Al ₂ O ₃
10 ⁹ Ωcm), a light emitting layer, a third insulating layer with low resistivity, and a high resistivity (field strength 10 ⁴ to 10 Ω cm).
4th resistivity (10 ¹² to 10 ¹⁴ Ωcm) at 10 ⁶ V/cm
EL is made by sequentially laminating an insulating layer and a back electrode.
In the display panel, the third insulating layer is made of one of Ta ₂ O ₅ , SiO ₂ , and Al ₂ O ₃ .
An EL display panel characterized in that it is a black or blackish brown layer made of a mixture with MnO _2-X and whose electrical properties (resistivity) are equivalent to those of the second insulating layer.