KR100292324B1 - Electroluminescent Devices with Multilayer Insulators - Google Patents

Abstract

The present invention is a transparent electrode on a glass substrate, a dielectric layer, a phosphor layer, an insulating layer, as a method of manufacturing a double insulation structure AC thin film electroluminescent device formed of a metal electrode in order, an insulation layer of aluminum oxide (Al ₂ O ₃₎ By alternately growing with and tantalum oxide (Ta ₂ O ₅ ), the breakdown field strength is slightly reduced compared to the Al ₂ O ₃ single dielectric, but the dielectric constant is increased to increase the maximum accumulated charge and lower the driving voltage of the electroluminescent device. Maximum luminance was obtained at low modulation voltage. Such an insulator can also be applied to an insulating layer of an active matrix type electroluminescent device in which a multicolor electroluminescent device having two or more fluorescent layers or an electroluminescent device is formed on a silicon substrate.

Description

Electroluminescent element with multilayer insulator

The present invention relates to an electroluminescent device, and more particularly, to an electroluminescent device having a heterogeneous multilayer insulator as an insulating layer in contact with a fluorescent layer.

Due to the rapid development of the information and communication field, the importance of the display industry for displaying desired information is increasing day by day. Until now, the main dominant type of information display device is a cathod ray tube (CRT). CRTs have enjoyed popularity ever since they were developed because of their ability to display a variety of colors and provide excellent screen brightness. However, the desire for large, portable and high resolution displays is urgently needed to develop flat panel displays instead of CRTs, which are bulky and bulky. These flat panel displays have a wide range of applications from computer monitors to displays used in aircraft and spacecraft.

Currently produced or developed flat panel displays include liquid crystal display (LCD), electroluminescent display (ELD), field emission display (FED), plasma display panel (PDP), etc. have. To be an ideal flat panel display, light weight, high brightness, high efficiency, high resolution, high speed response characteristics, long life, low driving voltage, low power consumption, low cost and color display characteristics are required. Liquid crystal displays, which are widely used as portable computer monitors, are passive light emitting devices, and require an extra light source, have a slow response characteristic, and have a narrow viewing angle. Plasma displays, which are often used for large displays over 30 inches, have poor spatial resolution. Field emission displays and electroluminescent displays have great advantages as high resolution displays due to their excellent spatial resolution and response speed, but lack of high luminance and natural color phosphors.

Among the flat panel displays mentioned above, the electroluminescent display is completely solid, and thus has a much wider operating temperature than other flat panel displays, and has been used in medical and military equipment and measuring equipment used in harsh environments due to its resistance to shock and vibration. Recently, ultra-small AMEL displays for high-resolution head-mounted displays have also been developed. However, in order to expand the use of the electroluminescent display, it is required to develop a high-luminance blue phosphor comparable to red and green and to develop an insulating material that can improve driving voltage and emission stability.

The electroluminescent display is driven by applying an alternating voltage, and the structure has a double insulation structure in which an insulation layer is wrapped above and below the fluorescent layer. In order to realize high luminance and high efficiency electroluminescence, good light emitting material selection and fluorescent layer thin film properties are important, but the insulating layer plays an important role as well. The role of the insulating layer is to easily induce breakdown when the applied electric field is applied directly to the fluorescent layer, thereby injecting electrons present at the interface between the insulating layer and the fluorescent layer by the external electric field into the fluorescent layer. This method serves to increase the lifetime of the electroluminescent device. Since the driving voltage of the electroluminescent device is determined by the sum of the voltage required to excite the fluorescent layer and the voltage applied to the insulating layer, the higher the dielectric constant of the insulating layer is advantageous to effectively apply the applied voltage to the fluorescent layer.

In order to lower the driving voltage and increase the luminance of the EL device, it is necessary to develop high quality insulating materials. The physical properties of these insulators should be such that the leakage current is small so that the insulation layer is not destroyed even at high electric field strengths, and the dielectric constant is high to minimize the driving voltage. The most commonly used numerical value is the maximum accumulated charge that corresponds to the product of the breakdown field strength and permittivity. In addition, the insulating layer should have good adhesion with the fluorescent layer or the electrode, and should be transparent in the visible light region to transmit the emitted light well. Oxide and nitride insulators have excellent stability to electric fields, but have a low dielectric constant and high dielectric constants have a low breakdown field for electric fields. Since the breakdown field strength and the dielectric constant represent opposite physical quantities, it is quite difficult to produce materials with good physical properties at the same time.

Conventionally, in order to create a material having a high dielectric constant and a high breakdown electric field, a method of manufacturing a new composite thin film by sputtering or evaporating two materials having a satisfactory breakdown field and a dielectric constant, respectively, has been studied. .

However, the prior art of using a mixed thin film as an insulator of a light emitting device has a problem that it is difficult to artificially and easily control the physical properties of the thin film.

The present invention devised to solve the above problems is to provide an electroluminescent device having a multi-layer insulator that can be artificially easily controlled high dielectric constant and high breakdown electric field in order to lower the driving voltage and increase the brightness.

1 is a cross-sectional view of a double insulation structure thin film electroluminescent device according to the present invention.

2 is a cross-sectional view of an Al ₂ O ₃ and Ta ₂ O ₅ multilayer insulating thin film according to the present invention.

Figure 3 is a cross-sectional scanning electron microscope (SEM) photograph of the multilayer insulating thin film according to the present invention.

4 is a graph measuring luminance-voltage characteristics according to the present invention;

5 is a cross-sectional view of a multicolor electroluminescent device according to the present invention.

6 is a cross-sectional view of an active matrix type electroluminescent device according to the present invention;

<Explanation of symbols for main parts of the drawings>

1, 10: glass substrate 2, 11, 15, 25: transparent electrode

3, 5, 12, 14, 16, 18, 22, 24: insulation layer 4, 13, 17, 23: fluorescent layer

6, 19, 21: metal electrode 20: silicon substrate

According to an aspect of the present invention, there is provided an electroluminescent device including at least one phosphor and an insulator formed in contact with the at least one phosphor, wherein the insulator is formed of a first insulating layer and a second insulating layer of different materials. This is a heterogeneous multilayer insulator that is alternately stacked several times, and the first insulating layer is a material having a lower relative dielectric constant and a larger breakdown electric field than the second insulating layer.

Preferably, the first insulating layer uses a material having a relative dielectric constant of at most 10 and a breakdown field of at least 5 MV / cm, and the second insulating layer having a relative dielectric constant of at least 20 and a breakdown field of at most 2 MV / cm.

For example, Al ₂ O ₃ may be used as the first insulating layer and Ta ₂ O ₅ may be used as the second insulating layer. At this time, the total thickness of the Al ₂ O ₃ and Ta ₂ O ₅ layer is 1500 ~ 4000Å, the maximum storage charge can be obtained when the thickness ratio of the Ta ₂ O ₅ layer in the total thickness is 20 to 80%. have. Each thickness of the single Al ₂ O ₃ and Ta ₂ O ₅ layer is 10 to 300 kPa.

In addition, in the present invention, by further forming a Ta ₂ O ₅ thin film having a thickness of up to 100Å at the interface between the insulator and the fluorescent layer can maximize the electron supply efficiency to the fluorescent layer.

In addition, in the present invention, the first insulating layer may use any one of Si ₃ N ₄ , SiON, and SiAlON, and the second insulating layer may use a high dielectric or steel dielectric thin film.

In addition, the electroluminescent device of the present invention, a transparent electrode formed on a glass substrate; A first insulator formed on the transparent electrode and including an Al ₂ O ₃ thin film and a Ta ₂ O ₅ thin film alternately stacked a plurality of times; A fluorescent layer formed on the first insulator; A second insulator formed on the fluorescent layer and including an Al ₂ O ₃ thin film and a Ta ₂ O ₅ thin film alternately stacked a plurality of times; And a metal electrode formed on the second insulator. Here, the thin film of the transparent electrode, the first insulator, the phosphor, the second insulator, and the metal electrode is sequentially stacked at least once more, thereby realizing a multicolor light emitting device.

In addition, an active matrix type electroluminescent device of the present invention comprises: a metal electrode formed on a semiconductor substrate; A first insulator formed on the metal electrode and including an Al ₂ O ₃ thin film and a Ta ₂ O ₅ thin film alternately stacked a plurality of times; A fluorescent layer formed on the first insulator; A second insulator formed on the fluorescent layer and including an Al ₂ O ₃ thin film and a Ta ₂ O ₅ thin film alternately stacked a plurality of times; And a transparent electrode formed on the second insulator.

The present invention having the above-described structure can be manufactured by using the atomic layer growth (ALE) technique, which has recently matured during its manufacture, thereby injecting chemical samples required for thin film growth alternately at the atomic layer level. Form a thin film and control its properties. In particular, by controlling the thickness of each laminated thin film, it is possible to artificially easily control the high dielectric constant and high breakdown electric field.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings so that those skilled in the art may easily implement the technical idea of the present invention. do.

1 is a cross-sectional view of a double insulation structure thin film electroluminescent device using a glass substrate according to a first embodiment of the present invention.

Referring to FIG. 1, the glass substrate 1 is formed in the order of the transparent electrode 2, the insulating layer 3, the fluorescent layer 4, the insulating layer 5, and the metal electrode 6. The glass substrate 1 uses aluminosilicate or borosilicate glass free of alkali metal ions, and the transparent electrode 2 is 1500-thick indium-tin-oxide (ITO). In the fluorescent layer 4, green ZnS: Tb was formed to a thickness of about 4000 to 6000 GHz and aluminum was used as the metal electrode 6. Generally, a voltage of 150 to 250 V is used for driving the electroluminescent device. This can be applied, the strength of the corresponding electric field is about 1 ~ 2MV / cm.

The insulating layers 3 and 5 may have a single aluminum oxide (Al ₂ O ₃ ) having excellent electric field stability or tantalum oxide (Ta ₂ O ₅ ) having a relatively high relative dielectric constant with the aluminum oxide (Al ₂ O ₃ ). Several layers are grown by alternating two materials in thickness. The total thickness of the insulating layers 3 and 5 was 1500 to 4000 GPa, and the thickness of one layer of each of Al ₂ O ₃ -Ta ₂ O ₅ was about 10 to 300 GPa.

Figure 2 is a cross-sectional view of a multi-layered insulating thin film having a different thickness of Al ₂ O ₃ and Ta ₂ O ₅ according to the present invention, Figure 2 (A) is a layer thickness of 100 Å each of Al ₂ O ₃ and Ta ₂ O ₅ 2 (B) shows a thickness ratio of 1: 3 with 50 Å Al ₂ O ₃ and 150 Å Ta ₂ O ₅ , and FIG. 2 (C) shows an insulating layer structure having a 30 Å Ta ₂ O ₅ thin film on the fluorescent layer side.

In the structures of FIGS. 2A and 2B, the upper and lower layers of the multilayer structure were both 100 Å or more Al ₂ O ₃ , which indicates that Al ₂ O ₃ has adhesion to the fluorescent layer 4 and the electrodes 2 and 6. Because this is good. However, since the Ta ₂ O ₅ thin film has a high dielectric constant and a large amount of polarized charge exists in an electric field, it may facilitate supply of electrons. Therefore, as shown in FIG. 2 (C), when a thin film within 100 μs is inserted between the fluorescent layer and the insulating layer, the field emission performance may be improved without significantly deteriorating the surface adhesive force. Al ₂ O ₃ and Ta ₂ O ₅ thin films are formed using atomic layer growth as AlCl ₃ , H ₂ O and TaCl ₅ , H ₂ O precursors, respectively.

FIG. 3 is a cross-sectional scanning electron microscope (SEM) photograph of a multilayer thin film manufactured according to the present invention. FIG. 3 (A) is a sample obtained by growing 1000 μs Al ₂ O ₃ and 1000 μs Ta ₂ O ₅ on a silicon substrate. B) is a case in which 100 Å Al ₂ O ₃ and 100 Å Ta ₂ O ₅ were repeatedly grown 10 times on a silicon substrate. In case of FIG. 3 (B), the thick layer of the surface was etched using hydrofluoric acid to distinguish the two oxide layers, and the etching was performed considerably at the surface edge of Ta ₂ O ₅ with Al ₂ O _{3 which} is relatively fast. The two oxide layers are indistinguishable, and the horizontal line below them shows each oxide layer.

Relative dielectric constants and breakdown field strengths were measured to evaluate the performance of multi-layered Al ₂ O ₃ -Ta ₂ O ₅ thin films as insulators for field emission displays.

Table 1 shows the relative dielectric constants and breakdown field strengths of the thin films prepared by varying the total thickness ratios of the two oxides and the thickness of one layer. It also shows the maximum accumulated charge, which is the product of two physical quantities.

The results show that as the Ta ₂ O ₅ thickness ratio increases, the relative dielectric constant increases from 8 to 29 with pure Al ₂ O ₃ and the breakdown field strength decreases. The maximum accumulated charge corresponding to the figure-of-merit is larger in the case of a multi-layered Al ₂ O ₃ -Ta ₂ O ₅ thin film compared to pure Ta ₂ O ₅ or Al ₂ O ₃ , and has a high Ta ₂ O ₅ thickness ratio. Highest at 6.2 It was confirmed that. It was also observed that if the thickness is too thin, the electric field strength distribution causing field breakage is scattered.

4 is a result of measuring the luminance-voltage characteristics after fabricating an electroluminescent device using the multilayered structure insulator (FIG. 2B) of the present invention and a pure Al ₂ O ₃ single thin film as an insulating layer.

As shown in FIG. 4, since the sample A using the multilayer insulator in both the upper and lower insulating layers emits light at the lowest voltage, the driving voltage is about 10 to 50 V lower than the other samples B, C, and D. In the case where only one layer has a multilayer structure, the driving voltage of Sample B used for the upper insulating layer is lower than that of the lower insulating layer by about 30V. This difference is thought to be due to the fact that the lower insulating layer is subjected to a 500 ° C. heat treatment during the subsequent fluorescence layer growth process, but the upper insulating layer is not affected and that the electrodes ITO and Al which are in contact with the two insulating layers are different.

The Al ₂ O ₃ -Ta ₂ O ₅ multilayer structure insulator manufactured according to the present invention is used for phosphors of materials doped with transition metals or rare metals using any one of ZnS, SrS, and CaS as a parent material, for example, SrS: Ce. Excellent performance can be obtained with respect to SrS: Eu, CaS: Eu and CaS: Pb.

5 is a cross-sectional view of a multicolor field emission device according to a second embodiment of the present invention.

As shown in FIG. 5, the transparent electrode 11, the insulating layer 12, the fluorescent layer 13, the insulating layer 14, the transparent electrode 15, the insulating layer 16, and the fluorescence are disposed on the glass substrate 10. The layer 17, the insulating layer 18, and the metal electrode 19 are formed in this order.

6 is an active matrix electroluminescent device structure according to a third embodiment of the present invention.

As shown in FIG. 6, a metal electrode 21, an insulating layer 22, a fluorescent layer 23, an insulating layer 24, and a transparent electrode 25 are formed on the silicon substrate 20.

The same effect can be expected when using Si ₃ N ₄ , SiON, SiAlON, which has high stability against fracture electric field instead of Al ₂ O ₃ , and using TiO ₂ or other steel dielectric materials, which are high dielectric constants, instead of Ta ₂ O _5. have.

Although the technical idea of the present invention has been described in detail according to the above preferred embodiment, it should be noted that the above-described embodiment is for the purpose of description and not of limitation. In addition, those skilled in the art will understand that various embodiments are possible within the scope of the technical idea of the present invention.

The present invention can reduce the driving voltage by using the Al ₂ O ₃ and Ta ₂ O ₅ multilayer dielectric as a material having a suitable high field breakdown and high dielectric constant as an insulator for the field emission device, to obtain the maximum brightness at low modulation voltage Can be. Increasing the luminance makes it possible to use the field emission device even in a bright environment, and the reduction of the driving voltage facilitates the fabrication of the driving circuit and reduces the power consumption.

Claims (18)

An electroluminescent device comprising at least one phosphor and an insulator formed in contact with the at least one phosphor, The insulator is a heterogeneous multi-layered insulator in which a plurality of first and second insulating layers of different materials are alternately stacked, and the first insulating layer has a lower relative dielectric constant and a larger breakdown electric field than the second insulating layer. An electroluminescent device, characterized in that. The method of claim 1, And the first insulating layer has a relative dielectric constant of 10 and a breakdown field of at least 5 MV / cm, and the second insulating layer has a relative dielectric constant of at least 20 and a breakdown field of 2 MV / cm. The method according to claim 1 or 2, The first insulating layer is Al ₂ O _{3 And} the second insulating layer Ta ₂ O ₅ characterized in that the electroluminescent device. The method according to claim 1 or 2, An electroluminescent device comprising a Ta ₂ O ₅ thin film having a thickness of at most 100 kPa at an interface between the insulator and the fluorescent layer. The method of claim 3, The total thickness of the Al ₂ O ₃ and Ta ₂ O ₅ layer is 1500 to 4000Å, the thickness ratio of the Ta ₂ O ₅ layer at the total thickness is 200 to 80%. The method of claim 5, The thickness of each of the single Al ₂ O ₃ and Ta ₂ O ₅ layer is 10 to 300 kPa. The method according to claim 1 or 2, And the first insulating layer is any one of Si ₃ N ₄ , SiON, and SiAlON, and the second insulating layer is a high dielectric or steel dielectric thin film. In the electroluminescent device, A transparent electrode formed on the glass substrate; A first insulator formed on the transparent electrode and including an Al ₂ O ₃ thin film and a Ta ₂ O ₅ thin film alternately stacked a plurality of times; A fluorescent layer formed on the first insulator; A second insulator formed on the fluorescent layer and including an Al ₂ O ₃ thin film and a Ta ₂ O ₅ thin film alternately stacked a plurality of times; And A metal electrode formed on the second insulator Electroluminescent device made, including The method of claim 8, And the thin film made of the transparent electrode, the first insulator, the phosphor, the second insulator, and the metal electrode is sequentially stacked at least once more. The method according to claim 8 or 9, An electroluminescent device comprising a Ta ₂ O ₅ thin film having a thickness of at most 100 kPa at each interface between the first and second insulators and the fluorescent layer. The method of claim 10, In the first and second insulators, the total thickness of the Al ₂ O ₃ and Ta ₂ O ₅ layers is 1500 to 4000 microns, respectively, and the thickness ratio of the Ta ₂ O ₅ layers is 20 to 80% based on the total thickness. Electroluminescent device characterized in that. The method according to claim 8 or 9, The thickness of each of the single Al ₂ O ₃ and Ta ₂ O ₅ layer is 10 to 300 kPa. The method according to claim 8 or 9, The phosphor is an electroluminescent device, characterized in that the transition metal or rare metal doped with any one of ZnS, SrS, CaS as a parent material. In an active matrix type electroluminescent device, A metal electrode formed on the semiconductor substrate; A first insulator formed on the metal electrode and including an Al ₂ O ₃ thin film and a Ta ₂ O ₅ thin film alternately stacked a plurality of times; A fluorescent layer formed on the first insulator; A second insulator formed on the fluorescent layer and including an Al ₂ O ₃ thin film and a Ta ₂ O ₅ thin film alternately stacked a plurality of times; And A transparent electrode formed on the second insulator Active matrix type electroluminescent device comprising a. The method of claim 14, An electroluminescent device further comprising a Ta ₂ O ₅ thin film having a thickness of at most 100 kPa at each interface between the first and second insulators and the fluorescent layer. The method of claim 15, In the first and second insulators, the total thickness of the Al ₂ O ₃ and Ta ₂ O ₅ layers is 1500 to 4000 microns, respectively, and the thickness ratio of the Ta ₂ O ₅ layers is 20 to 80% based on the total thickness. Electroluminescent device characterized in that. The method of claim 16, The thickness of each of the single Al ₂ O ₃ and Ta ₂ O ₅ layer is 10 to 300 kPa. The method according to any one of claims 14 to 17, The phosphor is an electroluminescent device, characterized in that the transition metal or rare metal doped with any one of ZnS, SrS, CaS as a parent material.