JPH03165493A - Double insulation thin film electroluminescence device - Google Patents

Abstract

PURPOSE:To attain a low voltage drive and a high dielectric strength by forming a front side dielectric layer with a dielectric of a dielectric constant higher than that of a back side dielectric layer. CONSTITUTION:A first dielectric area or a front side dielectric layer 36 is formed out of dielectric of a high dielectric constant such as Sm2O3 of a relative dielectric constant of 15 and the like. A second dielectric layer or a back side dielectric layer 40 is formed out of dielectric such as Y2O3 of a dielectric strength of 3MV/cm or greater and the like. Since the voltage drop in a dielectric layer 36 decreases with this constitution, the energy differential corresponding to the effective voltage applied to a light emitting area 38 increases. Therefore, the voltage to be applied may be relatively low. The dielectric strength is prevented from lowering as the insulation property is maintained by the dielectric layer 40.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film electroluminescent device, and more particularly to a double insulated thin film electroluminescent device having a structure in which a light emitting region is sandwiched between dielectric materials.

[Prior Art] Electroluminescent devices that emit light by causing electrons to collide with a light-emitting center by applying an alternating current electric field are attracting attention as panels for thin display devices because they have high brightness, high resolution, and can form thin light-emitting layers. has been done.

The conventional double insulated thin film electroluminescent device
This will be explained with reference to the figures.

FIG. 5 shows a cross section of a double insulating thin film electroluminescence device, in which an ITO is placed on a glass substrate 2.
A transparent electrode 4 made of (Indium Tin Oxide) is formed, and Y2O or AA203 is formed on this.
Alternatively, the front dielectric layer 6 made of 5izNn or the like is formed by sputtering, vacuum evaporation, or the like. Next, Zn
S (zinc sulfide) is used as a base material, and M becomes the luminescent center.
The light emitting layer 8 is formed by electron beam evaporation using a material to which transition metals such as n and rare earth elements are added. Next, on this light emitting layer 8, a back side dielectric layer 10 made of the same material as the front side dielectric layer 6 is formed. Finally, this back side dielectric layer 1
A back electrode 12 made of Aρ is formed on the Aρ.

The double insulating thin film electroluminescent device thus formed emits light by applying an alternating current voltage 14 between the transparent electrode 4 and the back electrode 12, and the light emitting layer 8 is Since it is insulated by the body layer 610, no excess current flows and generation of Joule heat can be suppressed, thereby preventing a decrease in luminous efficiency and extending the life of the element.

[Problem to be solved by the invention]

The conventional double-insulated thin film electroluminescent device described above has the following problems.

In order to ensure the reliability and long life of the device, dielectric materials such as Y2O3 or Al2O, Si, N, etc., which have a high breakdown voltage, are used for the dielectric layers 6.10 on the front and back sides. However, when these dielectrics are used, the driving voltage of the element becomes high, so the AC applied voltage must be increased, and an expensive high-voltage driving IC or the like is required.

FIG. 6 shows the relationship between the emission intensity and driving voltage of a conventional double-insulated thin film electroluminescent device. Each curve A to D shows the characteristics of a double insulating thin film electroluminescent device having the same structure using Mn-doped ZnS as the light emitting layer 8. Here, the curve A shows the case where Y2O3 is used as the material of the dielectric layer 610 on the front side and the back side, and the curve B shows the case where AfzO3 is used. In the case of these curves A and B, the dielectric breakdown voltage of this device is 360■ for curve A and 440■ for curve B. Although both have high break-out voltages, as shown in Figure 6, they are not sufficient. The driving voltage required to obtain a certain luminous intensity is 150 .mu. or more. In order to reduce such a high driving voltage, it is known to use a dielectric material having a large dielectric constant for the dielectric layers 6.10 on the front side and the back side. 6th
Curve C in the figure is Sm20. (relative permittivity=1.5), and the curve is a characteristic curve when TazOs (relative permittivity=23) is used for the dielectric layers 6 and 10 on the front side and back side.

In the case of curves C and D, the driving voltage of the element is as low as 100 .ANG. or less. However, the dielectric breakdown voltage of these dielectric layers is extremely low, from 90 V in curve C to 80 V in curve C, resulting in poor reliability of the device and affecting the life of the device.

As described above, if a material with high withstand voltage is used for the dielectric layers 6.10 on the front side and back side that sandwich the light emitting layer 8, the driving voltage will become high, and if a material with a high dielectric constant is used, Since the withstand voltage is lowered, it has been impossible for conventional double-insulated thin film electroluminescent devices to achieve both low driving voltage and high green withstand voltage.

SUMMARY OF THE INVENTION The present invention is intended to solve the above-mentioned problems.The purpose of the present invention is to make the front dielectric layer and the back dielectric layer different from each other in terms of materials and properties, thereby achieving a low driving voltage.
Moreover, the objective is to realize a double-insulated thin film electroluminescent device with a high breakdown voltage.

[Means to solve the problem] In order to solve the above problem, a small (also known as transparent electrode,
The present invention provides a double insulated thin film electroluminescent device having a structure in which a first dielectric region, a light emitting region, a second dielectric region and a back electrode are sequentially laminated, and the light emitting region is sandwiched between two dielectric layers. The measure taken is to form the first dielectric region with a dielectric material having a higher dielectric constant than the second dielectric region.

Further, in this case, the first dielectric region has a relative permittivity of 1.
It is desirable that the second dielectric region is formed of a dielectric material having a breakdown voltage of 3 MV/cm or more.

[Effect]

According to such means, the following effects can be obtained.

FIG. 4(a) shows an energy band diagram of a conventional double-insulated thin film electroluminescent device, and FIG. 4(b) shows an energy band diagram of a conventional double-insulated thin film electroluminescent device, and FIG. FIG. 3 shows an energy band diagram of a double insulated thin film electroluminescent device according to the present invention formed.

When a high voltage is applied between the transparent electrode 34 and the back electrode 42, the light emitting region 38 and the first and second dielectric regions 36, 4
It is thought that the electrons 20 trapped at the boundary with 0 and the electrons 22 generated by thermal excitation are accelerated by the high electric field in the light emitting region, collide with the light emitting center in the light emitting region, and emit light.

Here, in the means of the present invention, the first dielectric region 3
6 is formed of a dielectric material having a higher dielectric constant than the second dielectric region 40, the voltage drop within the first dielectric region 36 is reduced as shown in FIG. 4(b). Therefore, even if the energy difference 24 corresponding to the applied voltage is equal, the energy difference 2 corresponding to the effective voltage applied to the light emitting region 38 is
8 is larger than the energy difference 26 in the case of FIG. 4(a). Therefore, a relatively low applied voltage is sufficient;
The driving voltage of the device can be lowered.

On the other hand, since the second dielectric region 40 is formed of a dielectric material with a high breakdown voltage similar to the conventional one, the second dielectric region 40 maintains insulation properties and prevents a drop in breakdown voltage. It can be prevented.

Therefore, the device simultaneously satisfies the requirements for driving voltage and breakdown voltage of the element, operates at a low drive voltage, and has a high breakdown voltage, improving reliability and durability.

〔Example〕

Next, the present invention will be described in detail with reference to FIGS. 1119 to 3.

First, a first embodiment of the present invention will be described. As shown in FIG. 1, IT◯ is deposited on a glass substrate 32 by sputtering to form a transparent electrode 34 having a film thickness of 2,000. Next, as the first dielectric material, Sm with a film thickness of 4000
, O, is formed by electron beam evaporation, and on top of this is a ZnS layer containing 0.5% by weight of Mn.
A light-emitting layer 38 having a thickness of 5,000 wafers is formed using the material by electron beam evaporation.

Further, on this light-emitting layer 38, a back side dielectric layer 40 made of Y2O3 with a thickness of 4000 nm is formed as a second dielectric layer by electron beam evaporation method, and Af is sputtered on this to make the film thickness. 5ooo back electrodes 42 are deposited.

The emission brightness-driving voltage characteristic of the double insulated thin film electroluminescent device according to the first embodiment is expressed by the curve X in FIG.
Shown below. Here, curves A and C are shown in FIG.
It is the same as , and is included for reference. In this way, when Sm,03 (relative permittivity=15) with a high dielectric constant is used for the front side dielectric layer 36, the drive voltage is lowered by about 100V than curve A, and the front side dielectric layer 36 is lower than curve A. body layer 36
It is possible to emit light at substantially the same driving voltage as when SmzO is used for both the back side dielectric layer 40 and the rear side dielectric layer 40.

On the other hand, the dielectric breakdown voltage of this example is 310 V, which is more than 220 V higher than that of curve C (when Y2O3 is used for both the front dielectric layer 36 and the back dielectric layer 40 (curve A). ) is almost the same as

Therefore, the double-insulated thin film electroluminescent device of this embodiment has a high breakdown voltage even though the driving voltage is low, so it is highly reliable and durable, and does not require a high-voltage power source.

Next, a second embodiment of the present invention will be described.

This embodiment has the same structure as the first embodiment, but the front dielectric layer 36 is made of Taz O, with a thickness of 4000 mm, and the back dielectric layer 40 is made of A2□03 with a thickness of 4000 mm. The difference is that each is deposited by electron beam evaporation.

The emission brightness-driving voltage characteristic of the double insulating thin film electroluminescent device according to this example is shown by curve Y in FIG. Here, curves B and D are the same as B and D shown in FIG. 5, and are added for reference. In this way, the front side dielectric layer 36 has a high dielectric constant TazQ, (relative permittivity=
In the case of curve Y using 23), the driving voltage is about 100 cm lower than that of curve B, and TazQ is applied to both the front dielectric layer 36 and the back dielectric layer 40, which are represented by curved lines. It is possible to emit light at almost the same driving voltage as when using the device.

On the other hand, the dielectric breakdown voltage of this embodiment is 330V, which is 250cm higher than that of the curved case.
Although it is lower than the case where AI20 is used for both the curve B and the back side dielectric layer 40 (curve B), there is no problem in practical use.

Various materials other than those described above can be used in embodiments of the present invention.

The front dielectric material preferably has a dielectric constant of 15 or more, and has a S mt 03. In addition to T az Os,
HfO,, PbTi0. , BaTiOs BaTaZ
Oh, SrTiO3, PbNbz06, etc. can be used.

The dielectric on the back side has a breakdown voltage of 3 MV/c.
m or more is desirable, YZ O:l, Alz O
In addition to z, SiO□, 313 N4, S +A10N
etc. can be used.

As the transparent electrode, in addition to ITO, 5nOz or an organic conductive material can also be used.

In addition to ZnS, the light-emitting layer may include CaS, SrS, etc., and Mn.
, Tb, Sm, Eu, Tm, Ce, etc. can be used.

As the back electrode, films made of various metals and formed by electron beam evaporation, sputtering, CVD, or the like can be used.

Note that when a dielectric with a high breakdown voltage was used for the front dielectric layer and a dielectric with a high dielectric constant was used for the back dielectric layer, the drive voltage did not decrease much.

(Effects of the Invention) In the double insulating thin film electroluminescent device according to the present invention, the first dielectric region and the second dielectric region sandwiching the light emitting region are made of different materials, and the first dielectric region is made of different materials. Since a dielectric material with a high dielectric constant is used and a high breakdown voltage material with a low dielectric constant is used in the second dielectric region, the following effects are achieved.

■ Since we were able to simultaneously achieve a low drive voltage and a high breakdown voltage, which were previously impossible, there is no need for a high-voltage AC power supply, and we can manufacture inexpensive light-emitting devices.

(2) It has a high breakdown voltage and can emit light at a low voltage, so it has improved durability and durability as a light emitting device.

[Brief explanation of the drawing]

FIG. 1 is a structural cross-sectional view of a double insulation thin film electroluminescent device according to a first and second embodiment of the present invention. FIG. 2 is a characteristic diagram showing the relationship between luminance and driving voltage of the double-insulated thin film electroluminescent device according to the first embodiment of the present invention. FIG. 3 is a characteristic diagram showing the relationship between luminance and driving voltage of a double-insulated thin film electroluminescent device according to a second embodiment of the present invention. Figure 4(a) is an energy band diagram showing the light emitting mechanism of a conventional double-insulated thin film electroluminescent device.
Figure (b) is an energy band diagram showing the light emitting mechanism of the double insulating thin film electroluminescent device according to the present invention. FIG. 5 is a cross-sectional view of the structure of a conventional double-insulated thin film electroluminescent device. FIG. 6 is a characteristic diagram showing the relationship between emission brightness and driving voltage of a conventional double-insulated thin film electroluminescent device. [Explanation of symbols] 32...Glass substrate 34...Transparent electrode 36=...Front side dielectric layer (Smz 03, Ta2o
s) 38...Light emitting layer 40...Front side dielectric layer (Yz Oz, Afz 0
3) 42...Back electrode is T az Os and the back side dielectric layer is A/l! Emission brightness when formed with , O, -
Drive voltage characteristic curve.

Claims (2)

[Claims] (1) In a double constant green thin film electroluminescent device having a structure in which at least a transparent electrode, a first dielectric region, a light emitting region, a second dielectric region and a back electrode are sequentially laminated, the first 2, wherein the dielectric region is formed of a dielectric material having a higher dielectric constant than the second dielectric region.
Heavy green thin film electroluminescence device. (2) In claim 1, the first dielectric region is formed of a dielectric material having a dielectric constant of 15 or more, and the second dielectric region has a break-through voltage of 3 MV/cm or more. A double insulating thin film electroluminescent device characterized in that it is formed of a dielectric material.