JP2985096B2 - Zn lower 2 SiO lower 4: Method of manufacturing AC driven thin film electroluminescent device using Mn thin film as light emitting layer - Google Patents

Description

The present invention relates to an AC-driven thin-film electroluminescence device using a Zn ₂ SiO ₄ : Mn thin film as a light-emitting layer.

[Prior art] Electroluminescence element (hereinafter referred to as EL element)
Has been studied for a long time for application to a flat panel solid-state light-emitting display device, and there is a strong expectation for its practical use. This EL device is characterized in that a crystalline thin film of phosphor is formed on a glass or plastic film substrate in structure, and the thin film and phosphor powder are uniformly dispersed and mixed in an organic dielectric binder. And an inorganic dispersion type wherein the phosphor powder is bound with an inorganic binder such as glass. Inorganic dispersion type EL
It is often referred to as a ceramic EL, but is merely a dispersion of the phosphor powder particles in the inorganic binder. In these conventional EL devices, a thin film or powder made of a manganese-doped zinc sulfide (ZnS: Mn) or copper-doped zinc sulfide (ZnS: Cu) phosphor is used as a light emitting layer. The former is practically used as an AC-driven thin-film EL element having a double insulation structure, and the latter is practically used as an organic dispersed-type AC driven EL element, which emits yellow-orange light and blue-green light.
As the phosphor, many materials such as an oxyacid salt type, an oxide type or the above-mentioned sulfide type are known. The former two hardly function as a light emitting layer for an EL element, so they are exclusively used as phosphors for CRTs or lamps. Except for the above-mentioned part, the latter sulfide-based phosphor hardly serves as a light emitting layer for an EL element at a practical level.

[Problems to be Solved by the Invention] Since the EL element is expensive and uses a sulfide-based phosphor as the light-emitting layer, only the above-described yellow-orange or blue-green light-emitting elements can be used. The sulfide-based phosphor has a small amount of the doping activator and is therefore sensitive to impurities. Weak against water and oxygen and extremely poor in stability. Sulfide-based phosphors are likely to chemically react with oxides such as transparent electrodes and insulating layers due to sulfides, causing damage such as oxidation to the light-emitting layer. There have been problems such as the occurrence of catastrophic dielectric breakdown and the failure of obtaining a sufficient luminance for practical use in the case of the dispersed type. Therefore, in order for EL elements to be widely put to practical use, it is essential to develop an inexpensive and highly stable element that realizes multicolor light emission. For this reason, in the conventional EL element, the thin film type is used only for limited applications such as an expensive computer terminal display, and the dispersed type has a low luminance. It was only partially used for light-emitting panels for interior decoration.

By the way, multi-color emission, high brightness, high efficiency and stable EL
It is impossible to obtain a device except by developing a new light emitting layer material for an EL device.

In the present invention, an inexpensive and extremely stable green light emitting EL device is realized by using a high quality crystalline thin film composed of an oxyacid salt-based phosphor or an oxide phosphor as the light emitting layer for the EL device. It is.

[Means for Solving the Problems] As a result of intensive research, the present invention has found that high-quality crystalline Zn ₂ SiO ₄ : Mn is optimal as a material for solving the above problems. . High quality crystalline Zn ₂ SiO ₄ : Mn thin films can be deposited on various substrates in various controlled atmospheres, for example, electron beam evaporation, activated reactive evaporation (ARE), sputtering, cluster ion beam (ICB), ion Beam sputter (I
BS) method, chemical vapor crystal growth (CVD) method, atomic layer epitaxial (ALE) growth method, molecular beam epitaxial growth (MB
E) method, gas source MBE (or CBE) method, crystal growth method using electron cyclotron resonance (ECR), etc., can be formed on a relatively high temperature substrate using a known crystal growth technique. After that, the thin film together with the substrate material and the like is formed in a non-oxidizing gas atmosphere containing at least one kind of phosphor component element or a non-oxidizing gas atmosphere partially containing an oxidizing gas constituting the thin film, or with these atmospheres. In an equivalent atmosphere, 750 ° C to 1200 ° C, preferably 900 ° C to 10 ° C
It can be obtained by heat treatment in a temperature range of 50 ° C.

A typical EL device according to the present invention is basically a substrate 5 / transparent electrode layer 1 / thin film light emitting layer 2 / insulating layer 3 / back electrode layer 4 as shown in FIG. 1 or as shown in FIG. A substrate 5 / transparent electrode layer 1 / insulating layer 3 / thin film light emitting layer 2 / insulating layer 3 / back electrode layer 4 can be exemplified, and the substrate 5 of FIG. Side or the thin film light emitting layer 2
And the insulating layer 3 can be exchanged. Further, as shown in FIG. 3, the structure in which the insulating layer 3 also serves as the substrate 5 (substrate / insulating layer 6) has no problem as long as the function as the EL element is not impaired. . If necessary, as a charge supply layer between the thin-film light emitting layer 2 and the insulating layer 3 or as a protective film of the insulating layer 3, for example, a single layer of a ZnO-based transparent conductive film having conductivity and excellent environmental resistance characteristics. Alternatively, it is effective to insert a multilayer film layer. In order to obtain a higher contrast ratio, a black thin film can be formed or inserted between the insulating layer 3 and the thin film light emitting layer 2, for example.

Further, an insulating or charge blocking layer may be inserted between the transparent electrode layer 1 and the thin-film light emitting layer 2 without any problem.

[Function] The Zn ₂ SiO ₄ : Mn phosphor, which is a silicate phosphor employed as the light emitting layer for the EL device according to the present invention, is extremely chemically stable unlike the sulfide phosphor and is easy to handle. Therefore, it has long been used on the other side as a phosphor for exciting an electron beam. However, it is known that even if this phosphor is used as it is as a light emitting layer for an EL element, no light is emitted. In order to function as a light-emitting layer for an EL element, first, the crystallinity of the light-emitting layer itself must be improved, the element structure must be such that a high electric field can be effectively applied to the light-emitting layer, and carriers can be efficiently injected. It has been essential to remarkably improve the interface state between the light emitting layer and the insulating layer. When a high dielectric constant BaTiO ₃ ceramic plate is used as the insulating layer, heat treatment can be performed at a high temperature of 750 ° C. or more, unlike a conventionally used glass substrate. Therefore, in this case, the light emitting layer formed on the ceramic is formed by a known film forming method. In the present invention, the crystallinity is further enhanced by high-temperature heat treatment, and an appropriate barrier is provided by controlling the atmosphere. Is thought to be possible. High electric field (~10 ⁶ V / cm) by Zn ₂ Si in the result insulating layer near the interface
Hot electrons can be injected into the O ₄ : Mn phosphor, the Mn emission center can be efficiently excited, and the distribution state of Mn, which is the emission center, in the film is good, and high-brightness emission can be realized. Inferred. In addition, even when a single-insulation type or double-insulation type thin-film EL element is formed on a substrate such as a glass substrate as conventionally performed, the high-quality crystal growth technique described above and the post-crystal growth The heat treatment can be expected to have an effect equivalent to that of the high-temperature treatment described above, and can also be expected to modify the state of the interface between the insulating layer and the light emitting layer.

The following is a summary of these functions and effects.
The crystallinity and composition of the compound base material of the phosphor thin film can be optimized. The state of introduction of the luminescent center of the phosphor film can be optimized. Damage to the sintered oxide ceramics of the insulating layer introduced during the process of forming the phosphor thin film can be recovered. In addition, between the sintered oxide ceramic and the phosphor thin film light emitting layer,
Insertion of various thin film layers having a thickness of 1 μm, preferably 50 nm to 500 nm is effective as a buffer layer, a charge supply layer or a protective layer, and as a result, high emission luminance can be realized with low voltage driving and high efficiency. . As a result, high-quality green light emission can be realized, and a wide range of applications can be expected. As described above, the present invention provides an extremely innovative manufacturing technique for an EL element such as a surface-emitting illuminating lamp, a surface-emitting display panel, or a flat-panel display having a flat light source.

 Hereinafter, the present invention will be described with reference to examples.

[Example 1] A Zn ₂ SiO ₄ : Mn (No. P-1 phosphor) powder compact was used as a target in a pure argon gas atmosphere, and a sputtering gas pressure of 0.
In the range of 4-10Pa, high frequency power 100W, substrate heating temperature 350
At a temperature of 25 ° C. and a substrate-target distance of 25 mm, a high dielectric constant (εs) of 5800 and a thickness (t) of 0.2 mm, a surface smooth sintered BaTiO ₃ ceramic substrate having a thickness of 700 nm was formed on an insulating layer by a high-frequency magnetron sputtering method. A Zn ₂ SiO ₄ : Mn thin film was formed.
Then, Zn ₂ SiO ₄ : Mn was added to the oxide phosphor ZnO: Zn (No. P-15 phosphor) powder charged in the alumina ceramic boat.
BaTiO ₃ ceramics were embedded, set in an electric furnace, and heat-treated at 1000 ° C. for 5 hours in argon to give the thin film a function as a light emitting layer for an EL element. afterwards,
A 500 nm-thick aluminum (Al) -doped zinc oxide (ZnO: A) was formed on the light emitting layer by magnetron sputtering.
l) A transparent electrode layer was formed, and a metal Al back electrode layer was formed on the opposite surface by a vacuum deposition method, respectively, to produce an EL device. As a result of driving the EL elements at 1kHz sine wave AC voltage, light emission start voltage 80V, the maximum emission luminance 2600cd / m ² (200V applied), with luminous efficiency 1.0lm / W, uniform green emission over the transparent electrode over the entire surface to obtain Was done. Further, a Pb (Mg _1/3 Nb _2/3 ) O ₃ sintered ceramic having a smooth surface of εs = 10000 and t = 0.2 mm was adopted as the sintered oxide ceramic substrate / insulating layer to form a similar light emitting layer. In the EL device, the light emission starting voltage is 60
V, maximum emission luminance 2200cd / m ² (200V applied), luminous efficiency 0.9l
At m / W, uniform green light emission was obtained over the entire surface of the transparent electrode. In addition, after forming a ZnO thin film with a thickness of 50 nm to 500 nm on the BaTiO ₃ ceramics in advance by sputtering,
In the case of a device having a Zn ₂ SiO ₄ : Mn light emitting layer formed thereon, the light emission starting voltage can be reduced by 10 V to 30 V, and the EL of the same level or higher can be obtained.
The characteristics were realized.

Example 2 A Zn ₂ SiO ₄ : Mn (No.P-1 phosphor) powder compact pellet was placed on a sintered BaTiO ₃ ceramic substrate / insulating layer having a smooth surface of εs = 6600 and t = 0.2 mm. By electron beam evaporation,
A Zn ₂ SiO ₄ : Mn thin film having a thickness of 600 nm was formed, embedded in a P-15 phosphor powder charged in an alumina ceramic boat, set in an electric furnace, and heat-treated at 1000 ° C. for 2 hours in argon. A function as a light emitting layer for an EL element was imparted to the thin film. Thereafter, a transparent electrode layer was formed on the light-emitting layer, and a metal Al back electrode layer was formed on the opposite surface by a vacuum deposition method, to produce an EL device.

As a result of driving this EL element with a sine wave AC voltage of 1 kHz,
Uniform green light emission was obtained over the entire surface of the transparent electrode with a light emission start voltage of 60 V, a light emission luminance of 1500 cd / m ² (200 V applied), and a light emission efficiency of 0.8 llm / W.

Example 3 ZnO having a thickness of about 100 nm was formed on a sintered BaTiO ₃ ceramic substrate / insulating layer having a smooth surface of εs = 4600 and t = 0.3 mm.
Under the same conditions as above, and a Zn ₂ SiO ₄ : Mn (No. P-1 phosphor) powder compact was further formed thereon by electron beam evaporation to a thickness of 600 nm.
m Zn ₂ SiO ₄ : Mn thin film was formed and embedded in a P-15 phosphor powder charged in an alumina ceramic boat and heat-treated in an electric furnace at 1000 ° C. for 5 hours in argon,
The thin film was given a function as a light emitting layer for an EL element. Thereafter, a ZnO: Al transparent electrode layer was formed on the light-emitting layer, and a metal Al back electrode layer was formed on the opposite surface by a vacuum evaporation method, to produce an EL device.

As a result of driving this EL element with a sine wave AC voltage of 1 kHz,
Uniform green light emission was obtained over the entire surface of the transparent electrode with a light emission start voltage of 45 V, a light emission luminance of 5800 cd / m ² (300 V applied), and a light emission efficiency of 1.0 lm / W.

Example 4 A Zn ₂ SiO ₄ : Mn (No.P-1 phosphor) powder compact was used as a target on a sintered BaTiO ₃ ceramic substrate / insulating layer having a smooth surface of εs = 4600 and t = 0.15 mm. A 500 nm thick Zn ₂ SiO ₄ : Mn thin film was formed by a high-frequency magnetron sputtering method at a gas pressure of 8 Pa in an argon atmosphere and set in an electric furnace, and hydrogen diluted with argon at 1000 ° C. for 3 hours. Heat treatment was performed in a gas or in a nitrogen gas-diluted ammonia gas to give the thin film a function as a light emitting layer for an EL element. Thereafter, a transparent electrode layer was formed on the light emitting layer, or a metal Al back electrode layer was formed on the opposite surface by a vacuum deposition method, respectively, to produce an EL device.

As a result of driving this EL element with a sine wave AC voltage of 1 kHz,
Uniform green light emission was obtained over the entire surface of the transparent electrode with a light emission start voltage of 70 V, a light emission luminance of 2500 cd / m ² (200 V applied), and a light emission efficiency of 0.9 lm / W.

Example 5 A glass substrate coated with an Al-doped ZnO transparent electrode (HOYA
-NA-40), a 500 nm thick Ta ₂ O ₅ thin film is formed on the transparent electrode by a high frequency magnetron sputtering method, and then a 100 nm thick SiO ₂ thin film is laminated on the insulating layer by the same sputtering method. An 800 nm thick Zn ₂ SiO ₄ : Mn thin film was formed by the high-frequency magnetron sputtering method of the first embodiment. These films were embedded in ZnO: Zn phosphor powder charged in an alumina ceramic boat, set in an electric furnace, and argon gas was introduced into the furnace and heat-treated at 700 ° C. for 5 hours. For 30 minutes at 750 ° C. Then, Al was vacuum-deposited as a back electrode to produce an EL element.

As a result of driving this EL element with a sine wave AC voltage of 1 kHz,
Uniform green light emission was obtained over the entire surface at a light emission start voltage of 90 V, a light emission luminance of 1000 cd / m ² (200 V applied), and a light emission efficiency of 0.5 lm / W.

Example 6 A thin film of Ta ₂ O ₅ and SiO ₂ was formed on an ITO transparent electrode-coated HOYA glass (NA-40) substrate in the same manner as in Example 5 to 400 nm and 10 nm, respectively.
After the formation of 0 nm, a Zn ₂ (SiO ₄ ): Mn light emitting layer was formed at a substrate temperature of 450 ° C. by MBE, which is a film forming method under ultrahigh vacuum. afterwards,
Heat treatment was performed at 650 ° C. for 2 hours in a vacuum in the same apparatus. ZnS
iO ₄ : As a result of driving an EL element with an Al electrode on a Mn light emitting layer with a 1 kHz sine wave, a light emission start voltage of 70 V and a light emission luminance of 2000 cd / m
² (200 V applied), a luminous efficiency of 0.9 lm / W, and uniform green luminescence was obtained. In addition, after the above-described heat treatment of the ZnSiO ₄ : Mn light emitting layer,
Further, a Ta ₂ O ₅ thin film was formed on the light emitting layer in the same manner as in Example 5 to a thickness of 500 nm, and then an EL device having an Al electrode formed thereon was produced.

As a result of driving this EL element with a sine wave AC voltage of 1 kHz,
Light emission start voltage 140V, light emission luminance 2200cd / m ² (300V applied),
At a luminous efficiency of 1.1 lm / W, uniform green luminescence was obtained over the entire surface of the electrode.

The Zn ₂ SiO ₄ : Mn light emitting layer of Example 6 was formed by alternately using SiCl ₄ as a source, ZnCl ₂ as a Zn source, and MnCl ₂ as a Mn source, and Zn and Si in an ultra-high vacuum. 450
Mn is doped in the range of 0.1 to 5% with respect to Zn atoms while being supplied onto a substrate heated to ℃ 550 ° C., and Zn ₂ SiO ₄ : M
Even when n was performed by the atomic layer controlled film formation method, an EL device equivalent to or more than that of Example 6 could be obtained.

[Effects of the Invention] According to the present invention, it is possible to provide a way to use a Zn ₂ SiO ₄ : Mn phosphor which could not be conventionally used as a light emitting layer material of an EL element, and the effect is remarkable. That is, the existing CR
As a result of using Zn ₂ SiO ₄ : Mn phosphor, which is known as a phosphor for T and lamps, as a light-emitting layer for EL devices, extremely stable green light emission is easily achieved in an oxidizing atmosphere or an oxidizing atmosphere containing moisture. Can be realized. As a result, passivation processing of the element can be extremely simplified, and an inexpensive EL element can be provided. As a result, it is extremely effective as an EL element for a light-emitting flat display, or as an illuminating lamp that makes use of its features as a surface light emitter, various application devices that require a pattern display or a flat light source, and a commercial power supply driven light-emitting element. It can be used in a variety of ways, such as being done, and has the effect of creating a wide range of applications that have never been seen before.

[Brief description of the drawings]

1 and 2 are cross-sectional views showing a structural example of an EL element according to the present invention, and FIG. 3 is a cross-sectional view showing a structural example of an EL element according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Transparent electrode layer, 2 ... Thin film light emitting layer, 3 ... Insulating layer, 4 ... Back electrode layer, 5 ... Substrate, 6 ... Substrate / insulating layer,

Claims (4)

(57) [Claims] After a Zn ₂ SiO ₄ : Mn thin film is formed on a substrate, the thin film together with the substrate material and the like is converted into a non-oxidizing gas or a part thereof containing at least one kind of phosphor component element constituting the thin film. In a non-oxidizing gas atmosphere containing an oxidizing gas, or in an atmosphere equivalent to these atmospheres, 750 ° C ~ 1200
A method for producing an AC-driven thin-film electroluminescent device using a Zn ₂ SiO ₄ : Mn thin film as a light-emitting layer, characterized by performing a heat treatment at a temperature of ° C. 2. The method according to claim 1, wherein the light emitting layer is formed on an insulating layer made of a sintered oxide ceramic having a relative dielectric constant of 4000 or more. Method. 3. The method according to claim 1, wherein the light emitting layer is formed on a thin film insulating layer, or the thin film insulating layer is formed on the light emitting layer. Method. 4. An AC-driven thin-film electroluminescent device according to claim 1, wherein said light-emitting layer is formed on a thin-film insulating layer, and a second thin-film insulating layer is formed on said light-emitting layer. Manufacturing method.