JPH0817574A - Method for manufacturing thin film electroluminescent device - Google Patents

Abstract

(57) [Summary] [Objective] A thin-film electroluminescent device having excellent emission brightness is obtained by improving the production method of the emitting layer. [Structure] When forming a zinc sulfide ZnS thin film added with a dopant serving as an emission center, a mixed gas of hydrogen sulfide and argon gas is introduced from a gas inlet 13 and a target 8 of zinc and dopant is sputtered with argon gas. At the same time, the temperature of the glass substrate 1 is maintained in the range of 380 to 480 ° C. to react the sputtered zinc, the vapor of the dopant and the hydrogen sulfide gas to form the light emitting layer on the glass substrate 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a light emitting layer of a thin film electroluminescent device, and more particularly to a method for manufacturing a light emitting layer having excellent emission brightness.

[0002]

2. Description of the Related Art Recently, a thin film electroluminescent device, which is an all-solid-state device, has been attracting attention as a flat-panel display device capable of high-resolution and large-capacity display. FIG. 7 is a sectional view showing a thin film electroluminescent device. As shown in the figure, the thin film electroluminescent device includes a transparent electrode 2, a first insulating layer 3, a light emitting layer 4 on a glass substrate 1,
It has a double insulating structure in which the second insulating layer 5 and the back surface electrode 6 are laminated. Among them, the light emitting layer of the thin film electroluminescent device is composed of a material in which zinc sulfide (ZnS) is used as a base material and a small amount of emission center (Mn) is added thereto.

At present, a method of manufacturing a light emitting layer of such a thin film electroluminescent device is one of a vacuum deposition method and a CVD method, ALE.
Methods and sputtering methods are being studied. Among them, the sputtering method is a manufacturing method excellent in productivity because it can form a uniform film over a large area and the film formation rate is very high.

[0004]

However, when the light emitting layer of the thin film electroluminescent device is formed by the sputtering method, there is a problem that the emission brightness is low (ACTA POL).
YTECHNICA SCANDINAVICA Applied Physics Series No.17
0 "5th International Workshop on Electroluminescen
ce "pp41-48).

Upon studying the cause of this, the constituent elements zinc Zn, sulfur S, and manganese Mn have different physical characteristics such as sputtering rate and vapor pressure, so that the composition of the formed film is significantly different from the composition of the target. It was found that stoichiometry deviates from the stoichiometric composition and causes a decrease in brightness. As a countermeasure against this, the formation of a zinc sulfide ZnS light emitting layer by reactive sputtering was examined and it was found that the emission brightness was improved. However, when the substrate temperature is set to 300 to 350 ° C. which is the conventional condition when forming the light emitting layer, the light emitting brightness is improved, but the dead layer, which is a region with a small crystal grain size, is reduced at the beginning of the film formation. It is generated with a thickness of about 100 nm, and the crystal grain size of the light emitting layer is about 260 n.
Since it is as small as about m, there is a problem that a practically usable level of emission luminance cannot be obtained. If there is a dead layer and the crystal grain size is small, the acceleration of electrons is hindered, the excitation of the dopant is insufficient, and the emission brightness is reduced.

FIG. 6 is a sectional view showing a main part of a conventional thin film electroluminescent device. Dead layer 4A is generated in the light emitting layer. The present invention has been made in view of the above points, and an object thereof is to improve the substrate temperature in reactive sputtering to prevent the formation of a dead layer at the early stage of light emitting layer formation and to prevent zinc sulfide during light emitting layer formation. An object of the present invention is to provide a thin film electroluminescent device having a large crystal grain size and excellent emission brightness.

[0007]

According to the present invention, the above object is to provide zinc sulfide Z to which a dopant serving as an emission center is added.
In a method for manufacturing a thin film electroluminescent device using an nS thin film as a light emitting layer, a mixed gas of a gas containing a sulfur element and a rare gas is used by sputtering zinc and a dopant and maintaining a substrate temperature in a range of 380 to 480 ° C. This is achieved by forming the light emitting layer by a reactive sputtering method.

In the above-described method for manufacturing a thin film electroluminescent device, it is effective that the dopant is manganese, manganese sulfide, manganese halide, rare earth element, rare earth sulfide or rare earth halide. Furthermore, it is preferable that the mixed gas of the gas containing the elemental sulfur and the rare gas is a mixed gas of hydrogen sulfide and argon.

[0009]

[Function] The melting point of each element of zinc Zn and sulfur S is Zn = 420
C., S = 120.degree. C. However, if the substrate temperature is set above the melting point of zinc, which is usually considered to be difficult to form a film, the crystal growth rate increases due to the high substrate temperature, and excess zinc and sulfur are generated. Easily evaporated.

[0010]

【Example】

Example 1 FIG. 1 is a layout view showing a sputtering apparatus for producing a thin film electroluminescent element according to an example of the present invention. In the figure, the cathode 9 on which the target 8 is attached is connected to the 13.56 MHz RF power supply 11 via the matching circuit 12. On the other hand, the anode 10 is at a position facing the target,
The substrate 1 is placed on the anode 10.

FIG. 5 is a sectional view showing a main part of a thin film electroluminescent device according to an embodiment of the present invention. I which is the transparent electrode 2
TO is deposited to a thickness of 1700Å, the first insulating film 2 made of silicon oxide or silicon nitride is 2100Å, the light emitting layer 4 is 7000Å,
The second insulating film 5 made of silicon nitride or silicon oxide is formed by 2100
A back electrode 6 made of Å and aluminum was sequentially laminated to a thickness of 7,000 Å.

For forming the light emitting layer, manganese is added to zinc as a target, and the Mn concentration in the target [Mn /
As (Zn + Mn)], one adjusted to be 0.3 wt% was used. The sputtering gas is a mixed gas of a gas containing a sulfur element and a rare gas, and the gas from the gas inlet 13 is 2
Argon gas containing 0-40% hydrogen sulfide was introduced into the reaction chamber 14. The sputtering conditions were adjusted to a gas pressure of 10 mTorr, a substrate temperature of 350 to 500 ° C., and a discharge power of 3 W / cm ² . Under this condition, the target surface is sulfided and the zinc sputter rate is reduced, and a zinc sulfide film having a stoichiometric composition is obtained. After forming the light emitting layer, heat treatment was further performed at a temperature of 500 ° C.

The light emitting layer thus obtained has a large crystal grain size of about 450 nm and a substrate temperature of 380 to 48.
A high emission luminance of 200 cd / m ² or more was exhibited in a wide range of 0 ° C. This value is twice as high as the emission luminance when the film is formed under the conventional substrate temperature of 350 ° C. FIG. 4 is a diagram showing the substrate temperature dependence of the emission brightness of the thin film electroluminescent device according to the embodiment of the present invention.

When the substrate temperature is 380 ° C. or higher, the emission brightness is about 2
It can be seen that it is over 00 cd /. Since the substrate temperature is high, the crystal growth rate increases, and excess zinc and sulfur evaporate. In this way, a large crystal of about 450 nm grows directly from the surface of the first insulating layer, the dead layer disappears, and the stoichiometry of the crystal is controlled to the stoichiometric composition. Embodiment 2 FIG. 2 shows a target of a manufacturing method according to another embodiment of the present invention. FIG. 2A is a plan view and FIG. 2B is a sectional view. Terbium fluoride TbF ₃ 42 is placed in a zinc target 41.

As the apparatus, the same apparatus as in Example 1 was used. As the target used here, TbF ₃ was appropriately arranged on Zn, and the average Tb concentration [Tb / (Zn
+ Tb)] was adjusted to about 2.5 wt%. As the sputtering conditions, an argon gas added with 40% hydrogen sulfide was used, the gas pressure was 10 mTorr, the substrate temperature was 400 ° C., and the discharge power was 3 W / cm ² . After the film formation, the light emitting layer was heat-treated at a temperature of 600 ° C.

A light emitting layer having a large crystal grain size is obtained,
A thin film thin film electroluminescent device with high emission brightness was obtained. Although Tb is used as the rare earth element, the rare earth element is not limited to Tb, but Sm, Tm, Pr, Ho, Er, Dy,
Eu, Ce, etc. can be similarly used. FIG. 3 is a plan view showing different targets in a manufacturing method according to different embodiments of the present invention. This is a so-called mosaic target in which Tb is arranged in the Zn target so as to have the above concentration. Example 3 A film was formed in the same manner as in Example 1 except that a mixed gas of sulfur vapor and argon gas was used as the sputtering gas instead of the mixed gas of hydrogen sulfide and argon gas.

The light emitting layer thus obtained has a large crystal grain size of about 430 nm and a substrate temperature of 380 to 48.
A high emission luminance of 200 cd / m ² or more was exhibited in a wide range of 0 ° C. This value is approximately twice as high as the light emission luminance when a film is formed under the conventional substrate temperature of 350 ° C. As the sputtering gas, sulfur hexafluoride or the like can be used in addition to the above.

[0018]

According to the present invention, the substrate temperature is 380-4.
Since the light emitting layer is formed by a reactive sputtering method using a mixed gas of a gas containing a sulfur element and a rare gas while maintaining the temperature in the range of 80 ° C., a dead layer is not generated and a light emitting layer having a large crystal grain size is obtained. As a result, the composition of crystals is controlled to a stoichiometric composition, and as a result, a thin film electroluminescent device having an emission luminance about twice that of the conventional one can be obtained.

[Brief description of drawings]

FIG. 1 is a layout view showing a sputtering apparatus for producing a thin film electroluminescent device according to an embodiment of the present invention.

2A and 2B show a target of a manufacturing method according to another embodiment of the present invention, FIG. 2A is a plan view and FIG. 2B is a sectional view.

FIG. 3 is a plan view showing another target in the manufacturing method according to the different embodiment of the present invention.

FIG. 4 is a diagram showing the substrate temperature dependence of the emission brightness of a thin film electroluminescent device according to an example of the present invention.

FIG. 5 is a sectional view showing a main part of a thin film electroluminescent device according to an embodiment of the present invention.

FIG. 6 is a sectional view showing a main part of a conventional thin film electroluminescent device.

FIG. 7 is a cross-sectional view showing a thin film electroluminescent device.

[Explanation of symbols]

 1 Glass Substrate 2 Transparent Electrode 3 First Insulating Layer 4 Light Emitting Layer 4A Light Emitting Layer 5 Second Insulating Layer 6 Back Electrode 7 Driving Power Supply 8 Target 9 Cathode 10 Anode 11 RF Power Supply 12 Matching Circuit 13 Gas Introducing Tube 14 Reaction Chamber 41 Zinc 42 terbium fluoride

Front page continued (72) Inventor Takashi Tsuji 1-1 Tanabe Shinden, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. (72) Inventor Yutaka Terao 1-1 Tanabe-shinden, Kawasaki-ku, Kanagawa Prefecture Fuji Electric Co., Ltd.

Claims (4)

[Claims] 1. A method of manufacturing a thin film electroluminescent device using a zinc sulfide ZnS thin film to which a dopant serving as an emission center is added as a light emitting layer, wherein zinc and the dopant are sputtered and the substrate temperature is maintained in the range of 380 to 480 ° C. A method of manufacturing a thin film electroluminescent device, comprising forming a light emitting layer by a reactive sputtering method using a mixed gas of a gas containing a sulfur element and a rare gas. 2. The method for manufacturing a thin film electroluminescent device according to claim 1, wherein the dopant is manganese, manganese sulfide or manganese halide. 3. The method for manufacturing a thin film electroluminescent device according to claim 1, wherein the dopant is a rare earth element, a rare earth sulfide or a rare earth halide. 4. The method of manufacturing a thin film electroluminescent device according to claim 1, wherein the mixed gas of the gas containing sulfur element and the rare gas is a mixed gas of hydrogen sulfide and argon.