KR100198803B1 - Ac thin film electroluminescent display structure for blue-emitting - Google Patents

Abstract

The present invention is to solve the problems of the prior art that the market efficiency is lowered due to the disadvantage of the luminous efficiency of the blue thin film electroluminescent display which is still insufficient commercialization compared to the red and green and the expensive high voltage IC required to drive the ELD. And the heterojunction layer of red and green emitters are composed of emitters to improve blue light emission efficiency, and the insulating film also has a dual structure of ferroelectric and low dielectric constant amorphous layer formed by atomic layer epitaxy to increase the amount of charge required for light emission, The structure of a white AC drive type thin film electroluminescent element for improving blue light emission efficiency for lowering the driving circuit by lowering the threshold voltage by reducing the breakdown characteristics is also proposed.

Description

Structure of White AC Driven Thin Film EL Device for Improving Blue Luminous Efficiency

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information communication display, and more particularly, to a structure of an AC thin film electroluminescent display (ACTFELD) for improving blue light emission efficiency.

A thin film electroluminescent display (ELD) has a wider viewing angle, an operating temperature range, and a higher color contrast than a conventional CRT. However, while the brightness of red and green is not a problem in commercialization, the brightness of blue is still insufficient in commercialization. In addition, in order to drive the ELD, a high voltage circuit of about 150 V is usually required, and the price of this high voltage IC has been a major cause of deteriorating the market economy of the ELD element. Complementing these two shortcomings, ELD will build a wide market from the current major market for measuring devices to industrial, military, propulsion, telecommunications and vehicle.

The main technologies of the conventional information communication display field are as follows.

1.Orange-yellow emitter of ZnS: Mn

The ZnS: Mn emitter may utilize only red or may transmit red-green multicolor light using a filter suitable for emitting light in the orange-yellow region.

2. Blue-green emitter of SrS: Ce

Since the SrS: Ce emitter emits light in the blue-green region, a suitable filter may be used to emit only blue, or may emit multiple colors of the green-blue broadband spectrum.

3. White-emitting emitter

The red-green-blue filter is used for SrS: Ce and Eu, and the red-green-blue filter is used for ZnS: Mn / SrS: Ce.

In the case of ZnS: Mn, which only utilizes red or transmits red-green additive color light, the efficiency and brightness of light emission are good without any problem in practical use, and when grown by atomic layer epitaxy or chemical vapor deposition, red or red- Green light can be obtained. On the other hand, in the case of SrS: Ce, only blue light is emitted, when the red-green-blue filter is used for SrS: Ce and Eu, or when the red-green-blue filter is used for ZnS: Mn / SrS: Ce, the efficiency of blue light is low and the brightness is low. Weak and not enough for practical use. In order to improve the efficiency and brightness of blue light, the electron excitation efficiency and frequency of Ce, which directly contributes to light emission in the SrS: Ce layer, must be increased.

Accordingly, the present invention improves the efficiency and brightness of blue light to be suitable for practical use to realize full three-color light emission with improved blue light emission efficiency and brightness, and induces lower voltage of the driving circuit to lower the cost of the driving IC, thereby making the ACTFELD practical. And its purpose is to increase marketability.

According to the present invention for achieving the above object, the insulator adjacent to the light emitter uses a high dielectric constant material and grows an insulator having a low dielectric constant in a heterogeneous layer to increase the amount of effective interfacial electron level, while at the same time, electrical breakdown at a high electric field. Even if is generated is characterized in that the self-recovery in the low dielectric constant insulating layer is configured to maintain the electric field.

1 is a structural diagram of a light emitting body including an electrode, a glass substrate, and a double insulating layer at both ends according to a first embodiment of the present invention.

2 is a structural diagram of a light-emitting body including an electrode, a silicon substrate, and a double insulation layer at both ends according to the second embodiment of the present invention.

3 is a structural diagram of a light-emitting body heterogeneously bonded to an insulating film showing portions of FIGS. 1 and 2 (a) enlarged.

4 is a structural diagram of an energy band according to thickness in the light emitting structure of FIG.

5 is an energy band structure diagram when an electric field is applied and electrons are incident from the first insulating film / cyan light emitting interface.

FIG. 6 is a structural diagram of an energy band when electrons are incident from the second insulating film / cyan light emitter interface by applying an electric field as opposed to the case shown in FIG.

* Explanation of symbols for main parts of the drawings

11: opaque metal electrode 12: low dielectric constant insulating film

13 high dielectric constant insulating film 14 light emitting body

14A: Cyan light emitter 14B: Yellow light emitter

15 transparent metal electrode 16 glass substrate

17 silicon substrate 18 Fermi energy level

19: 1st insulating film / cyan light emitter interface 20: 2nd insulating film / cyan light emitter interface

According to the present invention, a yellow light emitting layer such as ZnS: Mn is grown between a cyan light emitting layer such as SrS: Ce, and hot energy incident from the insulating film and the cyan light emitting layer passes through the hot electrons, thereby obtaining energy and accelerating the acceleration layer itself. Utilize the light emission of the. The reason why the hot electrons are accelerated in the ZnS: Mn layer is that the band gap of SrS is larger than the band gap of ZnS, so that the energy difference from the lowest conduction band energy is increased as electrons incident from SrS enter the ZnS layer. This is because the energy of the electrons increases. The effect of this acceleration is increased in the direction in which the energy band is lowered according to the slope of the energy band due to the applied potential difference. As compared with the case where there is no ZnS layer, electrons accelerated to a higher energy have a greater effect of exciting electrons in the light emitting center the next time they enter the adjacent SrS layer. That is, it can be expected that the luminous efficiency from Ce, which is the emission center of the SrS layer, will be improved. On the other hand, the thicker the SrS layer, the greater the number of light emission centers participating in light emission, so that the brightness increases. Therefore, if the thickness of the SrS layer is increased in the direction of lowering the energy band due to the potential difference, the luminous efficiency of the SrS layer is increased by the acceleration effect due to the difference in the band gap, and the thickness of the SrS layer is thickened in the same direction, so that the brightness of light emission is increased. Is increased. In the AC-driven type, the polarity of the electricity is reversed according to the set frequency, so that the thickness of the SrS layer is made thickest and the symmetrical growth of the SrS layer in order to increase luminous efficiency and brightness in both directions. On the other hand, the insulating material in contact with the light emitter becomes a layer that determines the amount of electrons incident on the light emitter in the applied electric field. The interfacial electron level present at the interface between the insulator and the light emitter serves as a source for supplying electrons incident to the light emitter. The higher the concentration of the interfacial electron level, the greater the probability that electrons enter the light emitter. The amount of this effective interfacial electron level is proportional to the dielectric constant of the insulator. However, an insulator having a high dielectric constant has a disadvantage in that when an electric breakdown occurs in a high electric field required for light emission, it propagates as a whole and leakage of current causes the electric field to disappear. On the other hand, an insulating material having a low dielectric constant has a small amount compared to the effective interfacial electron level, but has an advantage that the electric field does not disappear even in a high electric field because of its self-healing property when an electrical breakdown occurs.

Hereinafter, with reference to the accompanying drawings will be described in detail the present invention.

1 is a structural diagram of a light emitting body including an electrode, a glass substrate, and a double insulating layer at both ends according to the first embodiment of the present invention. As shown, ITO (Indium Tin Oxide), ZnO, or the like is formed on the glass substrate 16 having a thickness of about 1 mm by the lower transparent electrode 15. On the lower transparent electrode 15, a low dielectric constant insulating film 12 having a thickness of 2000 to 3000 GPa is formed of Al ₂ O ₃ , SiO ₂ , or Si ₃ N ₄ . On the upper side of the low dielectric constant insulating film 12, a high dielectric constant insulating film 13 of SrTiO ₃ , Ta ₂ O ₅ , or the like is formed to a thickness of about 1000 to 2000 kPa. The light emitting body 14 is formed on the high dielectric constant insulating film 13. At this time, the light emitter 14 is composed of a heterojunction structure of a cyan light emitter such as SrS: Ce and a red yellow light emitter such as ZnS: Mn. A high dielectric constant insulating film 13 is formed on the light emitter 14, and a low dielectric constant insulating film 12 is formed on the high dielectric constant insulating film 13. The formation conditions of the high dielectric constant insulating film 13 and the low dielectric constant insulating film 12 are the same as the formation conditions described above. An opaque metal electrode 11 is formed on the low dielectric constant insulating film 12 to form an A1 of about 1000 to 2000 mW.

2 is a structural diagram of a light-emitting body including an electrode, a silicon substrate, and a double insulating layer at both ends according to the second embodiment of the present invention. As shown, an opaque metal electrode 11 is formed on the opaque silicon substrate 17 having a thickness of 600 to 700 µm with an A1 of about 1000 to 2000 microns, and a low dielectric constant, which is an upper layer in the double layer insulating film, on the opaque metal electrode 11. The insulating film 12 is formed. The low dielectric constant insulating film 12 is made of Al ₂ O ₃ , SiO ₂ , Si ₃ N ₄ , or the like, and has a thickness of about 2000 to 3000 kPa. On the upper side of the low dielectric constant insulating film 12, a high dielectric constant insulating film 13 of SrTiO ₃ , Ta ₂ O ₅ , or the like is formed to a thickness of about 1000 to 2000 kPa. The light emitting body 14 is formed on the high dielectric constant insulating film 13. At this time, the light emitter 14 is composed of a heterojunction structure of a cyan light emitter such as SrS: Ce and a red yellow light emitter such as ZnS: Mn. A high dielectric constant insulating film 13 is formed on the light emitter 14, and a low dielectric constant insulating film 12 is formed on the high dielectric constant insulating film 13. The formation conditions of the high dielectric constant insulating film 13 and the low dielectric constant insulating film 12 are the same as the formation conditions described above. On the low dielectric constant insulating film 12, a transparent metal electrode 11 such as ITO of about 1000 to 2000 kPa is formed.

In the case of FIG. 1, the light emission direction is toward the glass substrate, while in FIG. 2, the position of the transparent metal electrode and the opaque metal electrode is changed to view the light emission from the transparent metal electrode. The structure proposed in the present invention can be applied to both of the above cases.

FIG. 3 is a structural diagram of a light emitting body heterogeneously bonded to the insulating film, in which portions of FIGS. 1 and 3 (a) are enlarged. As shown, the light emitter has a repeating structure of the cyan light emitter 14A and the red yellow light emitter 14B. The cyan light emitter 14A may be SrS: Ce, CaS: Ce or the like, and the red yellow light emitter 14B may be ZnS: Mn or the like. The repetition frequency and thickness of each layer are different depending on the light emitting growth method and the process conditions. For example, growth by the atomic layer epitaxy method proposed in the present invention may be performed by using SrS: Ce / ZnS: Mn / SrS: Ce / ZnS. : Mn / SrS: Ce / ZnS: Mn / SrS: Ce / ZnS: Mn / SrS: Ce is 250/250/500/250/1000/250/500/250/250 각각 respectively, and the total thickness of the illuminant is 3500 Å . Light emitting growth methods include sputtering, electron beam deposition, chemical vapor deposition, and the like, but in the present invention, the structure of the low dielectric constant insulating film 12 to the light emitting body 14 is all reacted using atomic layer epitaxy (ALE). Grow continuously in the chamber. The ALE growth method accurately adjusts the composition of the light emitter, and there is an advantage that the insulating film can be continuously grown in one chamber only by changing the reaction source. The polycrystalline structure of the light-emitting body grown by the ALE method is formed to be movable in the depth direction and is known as the most ideal form for light emission.

The characteristics of the double-layered insulating films 12 and 13 proposed in the present invention are to increase the concentration of the trapped charge density at the phosphor / insulator interface by contacting the high-k dielectric film with the light emitter and to bring the low-k dielectric film into contact with the electrode layer. This is to take advantage of the self-healing property even when an electrical breakdown occurs in the electric field. The highest interfacial electron level concentration is expressed as the product of dielectric constant and fracture electric field, which is about 5-6 times higher than Al ₂ O ₃ for SrTiO ₃ . Therefore, when the electric field is applied to emit light, the concentration of the effective electrons that may be incident on the light emitter is higher than that of only the low dielectric constant insulation layer deposited, thereby lowering the threshold voltage required for initiating light emission.

4 is a structural diagram of an energy band according to thickness in the light emitting structure of FIG. The insulating films at both ends have a much higher energy gap than the light emitter, and the band gaps of SrS and ZnS are 4.3 and 6.3 eV, respectively. As shown, the Fermi energy level 18 is arranged horizontally in the center of the bandgap when no electric field is applied.

5 is an energy band structure diagram when an electric field is applied and electrons are incident from the first insulating film / SrS interface. The electric field is larger than the threshold electric field, so the energy band is inclined as shown, and electrons are incident to the conduction band of SrS: Ce at the interface of SrTiO ₃ / S _i S: Ce on the left side. Once the incident electrons are accelerated for the electric field and excite the outermost electrons of Ce inside SrS: Ce at a high energy state, the excited electrons are restored to their original positions and emit light. When the accelerated electron is incident on the ZnS: Mn layer, the lowest energy level of the conduction band of ZnS is lower than that of SrS, and electrons acquire energy, thereby further accelerating the excitation of the outermost electron of Mn in ZnS, and also emitting the ZnS layer Done. In the present invention, by utilizing the acceleration effect of the electron due to the difference in the energy gap between SrS and ZnS to increase the energy when the electron is admitted into the SrS layer to increase the excitation probability of Ce in the SrS blue light emission by Ce Increase the efficiency In addition, since the thickness of SrS increases in the direction in which the electrons proceed, the amount of Ce participating in the light emission is increased, thereby increasing the luminance of light emission.

FIG. 6 is a structural diagram of an energy band when electrons are incident from the second insulating film / SrS interface by applying an electric field as opposed to the case shown in FIG. In the AC drive type, the electric field is reversed according to a given frequency, so that when the energy levels are arranged in reverse as shown, light emission occurs as described in FIG. Therefore, the thickness of the SrS was the thickest so that the luminous efficiency and luminance of the SrS was maximized when the acceleration of electrons in both directions was increased.

As described above, when the light emitting body is manufactured according to the present invention, luminance and luminous efficiency can be improved, blue light can be obtained and used for manufacturing three primary color light emitting devices. A driving circuit can be formed by lowering the threshold voltage required for light emission by bonding a bilayer insulating film to the light emitting body. It is possible to reduce the high voltage specification of the IC, thereby reducing the manufacturing cost of the ELD device.

Claims (10)

A transparent electrode formed on the glass substrate, a low dielectric constant insulating film formed on the transparent electrode, a high dielectric constant insulating film formed on the low dielectric constant insulating film, a light emitting body formed on the high dielectric constant insulating film, and a high dielectric constant insulating film formed on the light emitting body And a low dielectric constant insulating film formed on the high dielectric constant insulating film and an opaque metal electrode formed on the low dielectric constant insulating film. The structure of claim 1, wherein the light emitter is formed of a heterojunction structure of a cyan light emitter and a red yellow light emitter. The structure of a white alternating current type thin film electroluminescent device for improving blue light emission efficiency according to claim 1, wherein the cyan light emitting body and the junction insulating film at both ends of the light emitter are formed of a double layer of a high dielectric constant film and a low dielectric constant film. The structure of a white AC drive thin film electroluminescent device for improving blue light emitting efficiency according to claim 1, wherein a silicon substrate is formed on the opaque metal electrode instead of the glass substrate formed on the transparent metal electrode. A transparent electrode formed on the glass substrate, a low dielectric constant insulating film formed on the transparent metal electrode, a high dielectric constant insulating film formed on the low dielectric constant insulating film, a first cyan light emitting body formed on the high dielectric constant insulating film, and the first cyan A first yellow light emitter formed on the light emitting body, a second cyan light emitter formed on the first yellow light emitter, a second yellow light emitter formed on the second cyan light emitter, and a third cyan light emitter formed on the second yellow light emitter A third yellow light emitter formed on the third cyan light emitter, a fourth cyan light emitter formed on the third yellow light emitter, a fourth yellow light emitter formed on the fourth cyan light emitter, and an upper portion of the fourth yellow light emitter A fifth cyan light emitting member formed on the upper surface; a high dielectric constant insulating film formed on the fifth cyan light emitting body; The structure of the low dielectric constant insulating film, the low dielectric constant insulating film having an upper white AC-driven thin film electroluminescent device for blue light emission to improve efficiency, characterized by being a non-transparent metal electrode formed on. The structure of a white AC drive thin film EL device for improving blue light emitting efficiency of claim 5, wherein the low dielectric constant insulating film and the high dielectric constant insulating film are formed by an atomic layer epitaxy method. The method according to claim 5, wherein the first, second, third, fourth, and fifth cyan light emitters and the first, second, third, and fourth red yellow light emitters are formed by an atomic layer epitaxy method. The structure of the white AC drive type thin film electroluminescent element for improving blue light emission efficiency. 6. The structure of a white AC driving thin film electroluminescent device for improving blue light emitting efficiency according to claim 5, wherein the insulating film in contact with the first cyan light emitter and the fifth cyan light emitter is formed of a double layer of a high dielectric constant film and a low dielectric constant film. . The structure of a white AC drive thin film electroluminescent device for improving blue light emitting efficiency according to claim 5, wherein a silicon substrate is formed on the opaque metal electrode instead of the glass substrate formed on the transparent metal electrode. 6. The method of claim 5, wherein the thicknesses of the first, second, third and fourth yellow-red emitters are constant, and the first and fifth cyan emitters are formed to have the same thickness as the yellow-red emitters and the second and fourth cyan emitters. Is formed thicker than the first and fifth cyan emitters, and the third cyan emitter is formed thicker than the second and fourth cyan emitters. .