JPH06251873A - Forming method of electroluminescent element - Google Patents

Abstract

PURPOSE:To provide a method for forming a light emitting layer for EL element with excellent luminous efficiency which has a luminescence center consisting of zinc sulfide by means of spattering. CONSTITUTION:A target obtained by adding and mixing a material forming a luminescence center into zinc sulfide fine powder followed by sintering is spattered with a pure inert gas reduced in pressure. The spattered molecules are formed on a base kept at 500-650 deg.C at a film forming speed of 70nm/min-150 nm/min to form a light emitting layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming an electroluminescence (hereinafter referred to as EL) element used as a display device of an electronic device on a substrate. More specifically, an EL element having improved luminous efficiency is provided. A method of forming on a substrate.

[0002]

2. Description of the Related Art A zinc sulfide thin film containing an active substance such as manganese (Mn) or a rare earth element is used as a light emitting layer of an EL element and is formed by a vacuum deposition method or a high frequency sputtering method. It is known that a light emitting layer made of a zinc sulfide thin film can be formed by a vacuum vapor deposition method and has excellent light emitting characteristics, but a method by sputtering has not been obtained. For example, page 21 of the 2nd study group material of the characteristic evaluation standard subcommittee of the 125th committee of photoelectric conversion and the Jpn.J.Appl.Phys.27.
(1988) p.592. T. Matsuoka's paper (prior art 1) uses a pure inert gas as a sputtering gas, the substrate temperature is 200 ° C. to 350 ° C., and the deposition rate is 20 nm. An EL device has been reported which uses zinc sulfide as a light emitting layer and is formed at a rate of / min to 65 nm / min. The conditions for forming the light emitting layer according to the prior art 1 are shown in the range of the shaded portion 2 in FIG. Further, the crystal structure of the obtained zinc sulfide is a zinc blend type.

Further, a method using a mixed gas of argon and hydrogen sulfide which is an inert gas as a sputtering gas is known as SID (SOCIETY FOR INFORMATION DISPLAY) 84, Diges.
T., p. 245 in M. Abdalla's paper (Prior Art 2).

[0004]

In order to obtain a light emitting layer exhibiting good EL characteristics by a sputtering method, the crystal grain size is increased and a zinc sulfide film having a small deviation from the stoichiometric composition is formed. This is very important. In order to increase the crystal grain size of zinc sulfide, a high substrate temperature is required to remove the unstable nuclei that cause the grain size to decrease in the initial stage of film growth. However, in the zinc sulfide thin film, the vapor pressure of sulfur is higher than the vapor pressure of zinc as the temperature of the substrate for forming the film is increased, so that the re-evaporation amount of sulfur from the substrate surface is zinc. There is a drawback that the amount becomes larger and the deviation from the stoichiometric composition of the formed film occurs. Therefore, there is an upper limit to the substrate temperature necessary for improving the crystallinity of the film, which is an obstacle to obtaining a thin film with good crystallinity, and the EL device obtained has low emission luminance and emission efficiency. was there.

In the prior art 2 described in the above-mentioned article of MIAbdalla, in which hydrogen sulfide is mixed at the time of sputtering to compensate for the lack of sulfur in the film (the amount of sulfur is less than the stoichiometric amount), hydrogen sulfide gas is used. Therefore, there has been a problem in corroding the film forming apparatus and implementing it industrially. The present invention is
The present invention has been made in order to solve the above-mentioned problems, and an object thereof is to provide a method for manufacturing an EL element having a high light emission efficiency by forming its light emitting layer by a sputtering method.

[0006]

The present invention provides a method for forming on a substrate an electroluminescent device having a light emitting layer made of zinc sulfide doped with an emission center, comprising:
The substrate in which the light emitting layer is sputtered with a pure inert gas under reduced pressure by sputtering a target obtained by adding and mixing a substance to be an emission center to zinc sulfide fine powder, and maintaining the sputtered molecules at 500 ° C to 650 ° C. 70nm above
The method for forming an electroluminescence element is characterized in that the electroluminescence element is formed at a film formation rate of from 1 / min to 150 nm / min.

The substrate temperature at the time of forming the light emitting layer according to the present invention is maintained at 500 ° C. to 650 ° C., and sputtering is applied to the target so that the film forming rate of the light emitting layer is 70 nm / min to 150 nm / min. The power is adjusted. The shaded area 1 in FIG. 1 shows the range of the film formation rate and the substrate temperature when the light emitting layer according to the present invention is formed. By setting the substrate temperature to 500 ° C. or higher, the crystallinity of the film is improved. Also, raising the substrate temperature above about 650 ° C.
The amount of re-evaporation of both zinc and sulfur from the substrate surface becomes large, the target cannot be used effectively, and it is necessary to apply a large sputtering power to the target. Not preferable. Furthermore, when Hoya NA40 or Corning Glass 7059 glass plate is used as the substrate, the substrate is deformed, which is not preferable.

When the film formation rate of the light emitting layer is less than 70 nm / min, the formed light emitting layer has a large deviation from the stoichiometric composition, and it is difficult to obtain a light emitting layer exhibiting good light emitting efficiency. Become. When the film formation rate is higher than 150 nm / min, the deviation from the stoichiometric composition is small, but the disadvantage is that the crystal grain size of the formed light emitting layer becomes small. The crystal structure of zinc sulfide formed within the film forming conditions of the sputtering method of the present invention is a wurtz type crystal structure.

[0009]

According to the present invention, zinc sulfide is deposited on a substrate maintained at a high substrate temperature and a film is formed while performing sufficient creeping motion, so that the crystal grain size is relatively large from the initial stage of film growth. A zinc sulfide thin film can be obtained. The substrate surface tends to form a zinc sulfide thin film having many sulfur defects (more zinc than stoichiometric amount) due to the difference in vapor pressure between sulfur and zinc. By increasing the value, a zinc sulfide thin film with a small deviation from the stoichiometric composition can be obtained. That is, in the present invention, at the same time when the substrate temperature is set to a high temperature, the film formation rate is set so that a much larger amount of zinc and sulfur than the re-evaporated amount of zinc and sulfur from the substrate surface reaches the substrate surface. Since it is selected, the amount of zinc and sulfur deposited on the surface of each substrate and growing as a thin film can be made approximately the same amount, and the deviation from the stoichiometric amount of the zinc sulfide thin film formed on the substrate can be made. Can be made smaller.

[0010]

【Example】

Example 1 An EL device shown in the schematic sectional view of FIG. 5 was manufactured. The heating temperature of the transparent glass substrate was 500 ° C. First, an ITO transparent conductive film (IT
(O: tin-doped indium oxide film) is formed by sputtering an ITO target under a pressure of argon of 3 mTorr, and a silicon target as an insulating film is 6: 2: 2 of argon, nitrogen, and oxygen at a pressure of 5mT
A silicon oxynitride film having a thickness of 220 nm is formed by sputtering in a mixed gas of orr, and a zinc sulfide target mixed with 0.125% by weight of manganese is deposited on the silicon oxynitride target with an argon gas of 20 mTorr to about 85 nm /
The manganese-doped zinc sulfide light-emitting layer having a thickness of 700 nm is formed by sputtering at a film forming speed of 1 minute, a second layer of silicon oxynitride insulating film is formed thereon in the same manner as the first layer, and finally, The aluminum electrode film was formed in vacuum by an electron gun vapor deposition method. The obtained EL element was cooled to room temperature, taken out from the sputtering device, and then, as shown in FIG.
A bipolar pulse wave is applied between the ITO electrode and the aluminum electrode as shown in FIG.
By measuring the amount of mobile charge flowing in the L element, E
The luminous efficiency of the L element was determined. Table 1 shows the film forming conditions of the light emitting layer of Example 1, the crystal structure of the obtained light emitting layer, the crystal grain size, the energy band gap Eg, the chemical composition ratio, and the light emission efficiency of the EL device. Further, the dependence of the luminous efficiency of this EL element on the applied voltage at the time of driving the element is shown by 1 in FIG. 4 so that it can be compared with the EL element obtained by the conventional technique 1 (shown by 2 in FIG. 4). .

[0011]

[Table 1]

Examples 2 to 7 EL elements were prepared in the same manner as in Example 1 except that the film formation rate of the zinc sulfide light emitting layer and the substrate temperature during film formation were variously changed. Table 1 shows the film forming conditions and the obtained results. Each of the light emitting layers of Examples 2 to 7 has a wurtz type crystal structure,
It can be seen that the crystal grain size is as large as 150 nm or more, and the chemical composition ratio of Zn and S of the film shows a value close to 1 which is a stoichiometric amount. The luminous efficiency is 1.9 lumen /
It was a large value of watt (lm / W) or more.

Comparative Examples 1 to 7 EL devices were prepared in the same manner as in Example 1 except that the film formation rate of the zinc sulfide light emitting layer and the substrate temperature during film formation were variously changed. Film-forming conditions of the light-emitting layer, characteristics of the obtained light-emitting layer and E
The L element characteristics are shown in Table 1. From this, the substrate temperature is 500
If the film formation rate of the light emitting layer is less than 70 nm / min even at a temperature of not less than 0 ° C, it is not possible to obtain a zinc sulfide film having good crystallinity and a small deviation from the stoichiometric composition. It can be seen that the device does not show a large luminous efficiency.
Further, even if the film formation rate is 70 nm / min or more, if the substrate temperature is lower than 500 ° C., the deviation of the stoichiometric composition is small, but the crystal grain size is small, and the EL element exhibits high luminous efficiency. I know there isn't.

With respect to the samples obtained in Examples 1 to 7 and Comparative Examples 1 to 7, the influence of the film forming rate of the light emitting layer on the chemical composition ratio of the light emitting layer and the energy band gap Eg is shown in FIG. From FIG. 3, the film formation rate of the light emitting layer is 70 nm /
When it is at least minutes, the atomic composition ratio of Zn and S of zinc sulfide approaches 1 (stoichiometric composition of zinc sulfide), and the energy band gap becomes 3.60 eV or more. In order to obtain light emission with practical brightness, the energy band gap of the light emitting layer must be 3.59 or more, and 3.60 or more is a preferable value. In addition, the light emitting layer formed at a high film forming rate of 70 nm / min or more can reduce contamination of impurities from the outside. FIG. 2 shows the effect of the substrate temperature when forming the light emitting layer on the crystal grain size of the light emitting layer at a constant film forming rate of 70 nm / min. From FIG.
By increasing the substrate temperature, the crystal grain size increases,
The temperature at which a large crystal grain size is obtained is 500 ° C. from FIG.
It can be seen that the temperature is 650 ° C. By setting the substrate temperature in this temperature range and the film formation rate of the light emitting layer to 70 nm / min, the light emitting layer has a composition close to the stoichiometric composition and an energy band gap of 3.60 or more. It can be a zinc sulfide thin film doped with manganese.

[0015]

According to the method of the present invention, zinc sulfide having a small deviation from the stoichiometric composition and a large crystal grain size is used as a light emitting layer without using toxic and corrosive hydrogen sulfide gas as a sputtering gas. It is possible to produce an EL device having high luminous efficiency. In addition, since the light emitting layer with few crystal defects can be obtained in the film forming process, the annealing process after the EL element is not necessary, and since hydrogen sulfide gas is not used, there is no deterioration due to corrosion of the equipment and the equipment cost is small. Become.

[Brief description of drawings]

FIG. 1 is a diagram showing a film formation rate when forming a light emitting layer according to the present invention and a range of a substrate temperature at that time.

FIG. 2 is a diagram showing an influence of a substrate temperature when forming a light emitting layer on a crystal grain size of the light emitting layer.

FIG. 3 is a diagram showing the influence of the film formation rate of the light emitting layer on the chemical composition and energy band gap of the zinc sulfide light emitting layer.

FIG. 4 is a diagram showing the dependence of the luminous efficiency of the EL element obtained in Example 1 on the applied voltage when the element is driven.

FIG. 5 is a schematic cross-sectional view of an EL device prototyped to measure and evaluate the luminous efficiency of the EL device manufactured by using the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Glass plate, 2 ... Transparent electrode, 3 ... Insulating layer, 4 ... Light emitting layer, 5 ... Back electrode, 6 ... AC power supply, 7 ... Sense capacitor

Front Page Continuation (72) Inventor Shiro Kobayashi 3-5-11 Doshomachi, Chuo-ku, Osaka-shi, Osaka Inside Nippon Sheet Glass Co., Ltd.

Claims (1)

[Claims] 1. A method for forming an electroluminescent device having a light emitting layer made of zinc sulfide doped with a light emitting center on a substrate, wherein the light emitting layer is prepared by adding a substance to be a light emitting center to zinc sulfide fine powder. The sintered target is sputtered with a depressurized pure inert gas to form the sputtered molecules on the substrate maintained at 500 ° C. to 650 ° C. at a film formation rate of 70 nm / min to 150 nm / min. And a method for forming an electroluminescent element.