JPH08271701A - Environmental resistant infrared ray transmissive structural body suing zinc sulfide as substrate - Google Patents

Abstract

PURPOSE: To provide an infrared transmissive structural body having excellent infrared ray transmissivity, free from the generation of stripping or scratch of a reflection preventive film even in use under a severe environmental conditions and excellent in environmental resistance. CONSTITUTION: The infrared ray transmissive structural body is provided with an innermost layer of Y2 O3 formed directly on a ZnS substrate, an intermediate layer of YF3 thereon and an outermost layer of MgF2 thereon or a shock mitigating layer composed of a material >=100GPa in elastic module on the ZnS substrate and an outermost layer of diamond or diamondike carbon thereon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure having an excellent infrared transparency used as an optical window or the like in an infrared detector such as an infrared sensor, and more particularly to an infrared transparent structure used in a harsh environment. is there.

[0002]

2. Description of the Related Art In recent years, various infrared detecting devices for detecting infrared rays due to heat radiated or radiated from an object have been developed. The infrared transmissive structure forming the optical windows of these infrared detection devices is required to be made of a material that transmits infrared rays in a necessary wavelength band.

Zinc sulfide (ZnS) is one of such infrared transmitting materials. Zinc sulfide has a refractive index of 2.2
The linear transmittance is not so large because the surface reflection loss is large. For example, the linear transmittance of about 70% is the maximum in a zinc sulfide substrate having a thickness of 5 mm. Therefore, ZnS
When used as an optical window or the like, a treatment for improving the linear transmittance is generally performed by providing an antireflection film coated with a fluoride such as MgF ₂ or an oxide such as TiO ₂ on the surface. .

[0004]

Since the conventional general infrared detectors are intended for indoor use, such as infrared radiation thermometers and entrance / exit detection sensors, the antireflection film also has a linear transmittance. However, there were few things that considered the environment resistance.

Recently, however, infrared ray detecting devices have been used more and more outdoors, and have been installed in high speed flying objects such as aircraft. As a result, when used in a high temperature and high humidity environment for a long time or in an environment subject to a sudden temperature change, and even when exposed to raindrop collision conditions during high-speed flight, the zinc sulfide substrate should be used in a short time. There is a problem that the antireflection film is peeled off or the antireflection film is scratched.

In view of the above conventional circumstances, the present invention has an excellent infrared transmittance and, at the same time, does not cause peeling or scratches of the antireflection film even when used in a harsh environment. It is an object of the present invention to provide an infrared transmitting structure excellent in heat resistance.

[0007]

In order to achieve the above object, the first infrared transmitting structure provided by the present invention is Zn
An S substrate, an innermost layer of Y ₂ O ₃ formed in direct contact with the ZnS substrate, an intermediate layer of YF ₃ formed on the innermost layer, and an outermost layer of MgF ₂ formed on the intermediate layer. It is characterized by having.

A second infrared transmitting structure provided by the present invention is a ZnS substrate, an impact relaxation layer formed on the ZnS substrate and made of a material having an elastic modulus of 100 GPa or more, and a diamond formed on the impact relaxation layer. Alternatively, the outermost layer made of diamond-like carbon is provided.

As the material having an elastic modulus of 100 GPa or more, which constitutes the shock absorbing layer of the infrared transmitting structure, Ge, S
i, GaP, BP, Y ₂ O ₃ , Al ₂ O ₃ , TiO ₂ , Y
F ₃ , LaF ₃ , CeF ₃ or the like can be used.

Further, the first or second infrared transmitting structure may be a ZnS substrate in which the ZnS substrate is subjected to a transparentizing treatment, and in that case, the infrared ray having excellent transparency to visible light as well as infrared light. It becomes a transparent structure.

[0011]

The ZnS substrate alone has an infrared transmittance of only about 70%. Therefore, it is well known that coating the surface of a ZnS substrate with a material having a low refractive index as an antireflection film improves the transmittance. However, in consideration of the environment resistance, the adhesion between the antireflection film and the ZnS substrate, the abrasion resistance of the antireflection film itself, etc. are required. Z
PbF ₂ is a material having good adhesion to nS, but it is not useful in a humid environment because it absorbs water and turns white.

Therefore, in the first infrared transmitting structure of the present invention, MgF ₂ that is resistant to water and stable at high temperature is used for the outermost layer, and the intermediate layer is transparent in the infrared region and has good adhesiveness with MgF _2. Uses excellent YF ₃ . These two layers act as an antireflection film at the target wavelength, for which the outermost layer of MgF ₂ has a thickness of 0.02 to 0.80 μm, and the intermediate layer of YF ₃ has a thickness of 0.1 to 2 A range of 0.2 μm is preferable, and a film thickness that improves the transmittance with respect to a target infrared wavelength in this range is appropriately selected.

However, YF ₃ which constitutes the intermediate layer is ZnS.
The adhesive strength to the substrate is not so excellent, and the YF ₃ film is easily peeled off at the interface of the ZnS substrate under a severe environment such as high temperature and high humidity or rapid temperature change. Therefore, in the first infrared transmissive structure, Y ₂ O ₃ which has a very high adhesive force with YF ₃ and ZnS and is stable against water and temperature change is used as the innermost layer in direct contact with the ZnS substrate.

It has been confirmed that by interposing the Y ₂ O ₃ layer as the innermost layer, peeling at the interface with the ZnS substrate can be prevented even when exposed to a harsh environment for a long time. However,
The Y ₂ O ₃ layer, which is the innermost layer, is used to improve the adhesive force, so the film thickness is made as thin as about 0.02 to 0.20 μm that does not significantly affect the transmittance at the target infrared wavelength.

Furthermore, in the above-mentioned first infrared transmitting structure, if a ZnS substrate subjected to a transparency treatment (HIP treatment) is used as the ZnS substrate, the ZnS substrate is about 60 to 75% from visible to infrared region. Since it has a transmittance of
It is possible to obtain an infrared transmissive structure having excellent visible light transmittance. Further, by setting the refractive index of the intermediate layer to be 1.4 or more and the refractive index of the outermost layer to be 1.4 or less, the transmittance is improved in two wavelength bands of visible and infrared regions.

In this case, the film thickness of the outermost layer of MgF ₂ is 0.0.
_{3 to} 1.50 μm, and the film thickness of the YF ₃ intermediate layer is 0.03.
.About.1.50 .mu.m is preferable, and by adjusting these film thicknesses to the optimum values, the transmittance is improved in the two wavelength bands of visible and infrared regions. Since the innermost Y ₂ O ₃ layer is used to improve the adhesive strength, the film thickness is preferably 0.02 to 0.20 μm, which does not significantly affect the transmittance at the target infrared wavelength.

Conventionally, an antireflection film having a multi-layer structure of three layers or more has been required to improve the transmittance over both visible and infrared wavelengths. With the infrared-transmissive structure of (3), an excellent transmittance was obtained at both wavelengths with an antireflection film having only three layers, and at the same time, a structure was obtained in which film peeling did not occur even under high temperature and high humidity and rapid temperature changes.

In the manufacture of the first infrared transmitting structure, all layers can be formed by a known sputtering method, vacuum vapor deposition method, ion plating method or the like.

Next, the second infrared ray transmitting structure of the present invention has an excellent infrared ray transmittance, and at the same time, has an excellent durability especially against the collision of raindrops and the like. That is,
The surface hardness of the ZnS substrate and the ZnS substrate subjected to the clarification treatment are as low as Knoop hardness of 150 to 350, and the elastic modulus is also low of 70 to 90 GPa. Occurs, and the transmittance sharply decreases.

To improve this, in the second infrared transmitting structure, a material having an elastic modulus of 100 GPa or more, such as Ge or S, is used for the purpose of mitigating the impact of raindrop collision on the ZnS substrate.
i, GaP, BP, Y ₂ O ₃ , Al ₂ O ₃ , oxides such as TiO ₂ and fluorides such as YF ₃ , LaF ₃ and CeF ₃ .
A shock absorbing layer is provided. Here, the elastic modulus is 100 GP
The reason why it is set to a or more is that it is necessary to have a hardness that rebounds and relaxes the impact at the time of raindrop collision.

In addition, in order to provide rain drop abrasion resistance, diamond-like carbon (Di
A layer of amond-like carbon) or diamond is provided. The surface hardness of diamond-like carbon and diamond is 2000 or more in Knoop hardness, it is chemically stable, and has excellent transparency from the visible to the infrared region, and it adheres well to the material forming the impact relaxation layer. It is also excellent in sex.

The thickness of the shock absorbing layer is 0.02 to 25.0.
μm, and the film thickness of the diamond-like carbon or diamond layer is preferably in the range of 0.20 to 20.0 μm. By setting the film thickness of these layers within the above range, the optimum film thickness can be selected according to the visible to infrared wavelength band used.

Further, between the ZnS substrate and the shock absorbing layer, Y
It is also possible to provide an intermediate layer made of ₂ O ₃ or MgF ₂ . In order to suppress the impact on the substrate due to the collision of raindrops,
It is preferable to make the thickness of this intermediate layer as thick as possible, but if it is 0.2 μm or more, it affects the infrared transmittance and should be avoided.

Also in the second infrared transmitting structure,
As in the case of the first infrared transmissive structure, it is possible to obtain an infrared transmissive structure having excellent transparency to visible light by using a transparent ZnS substrate as the ZnS substrate. .

All the layers in the second infrared transmitting structure are formed by a known sputtering method, vacuum vapor deposition method, ion plating method, CVD method, plasma CVD method or the like.

[0026]

Example 1 On one side of a ZnS substrate having a thickness of 5 mm, the innermost layer made of Y ₂ O ₃ having a thickness of 0.05 μm is in direct contact with the substrate, and YF ₃ having a thickness of 1.30 μm is formed thereon. An intermediate layer and an outermost layer of MgF ₂ having a film thickness of 0.50 μm were formed thereon. Each of these layers was formed at a substrate temperature of 400 ° C. by a vacuum vapor deposition method using an electron beam.

The infrared transmissive structure thus obtained had a reflectance of 7% or less at the intended infrared wavelength. Regarding the environment resistance, if the innermost layer of Y ₂ O ₃ is not used, the temperature is 60 ° C.
The film peeled off in 100 hours when exposed to an environment with a humidity of 95%, and the structure of the present invention using the innermost layer of Y ₂ O ₃ peeled off in the tape test even when exposed to the same environment for 1000 hours. There wasn't. Further, peeling did not occur even after repeating the temperature cycle of -60 ° C to 450 ° C.

Example 2 On one side of a transparent ZnS substrate having a thickness of 5 mm, the innermost layer made of Y ₂ O ₃ having a film thickness of 0.075 μm was formed in direct contact with the substrate, and YF ₃ having a film thickness of 0.030 μm was formed thereon. An intermediate layer and an outermost layer of MgF ₂ having a film thickness of 0.49 to 0.610 μm were formed on the intermediate layer. Each of these layers was formed at a substrate temperature of 400 ° C. by a vacuum vapor deposition method using an electron beam.

As a result, the obtained structure had a reflectance of 8% or less in the intended visible region and infrared region. Regarding the environmental resistance, when exposed to an environment of a temperature of 60 ° C. and a humidity of 95%, film peeling occurred in 80 hours when Y ₂ O ₃ was not used in the innermost layer, but Y ₂ O ₃ was formed in the innermost layer. With 10
The tape test did not peel off even after exposure for 00 hours.
Further, even when repeatedly exposed to a temperature cycle of -60 ° C to 450 ° C, peeling of the film did not occur.

Example 3 On one surface of a ZnS substrate having a thickness of 5 mm, a shock absorbing layer made of Ge having a thickness of 10.0 μm was formed by directly contacting the substrate, and a diamond-like carbon having a thickness of 0.85 μm was formed thereon. The outermost layer consisting of The Ge impact relaxation layer was formed at a substrate temperature of 150 ° C. by a vacuum evaporation method using an electron beam, and the outermost layer of diamond-like carbon was formed at a substrate temperature of 180 ° C. by a plasma CVD method.

The infrared transmissive structure thus obtained had a reflectance of 15% or less with respect to infrared rays having a target wavelength. Also, when this structure was attached to a high-speed flying object and tested for raindrop collision, at a rainfall of 25 mm / h, the speed of the flying object was 2%.
No peeling of the film occurred up to 83 m / s, and the film was not scratched.

[0032]

EFFECTS OF THE INVENTION According to the present invention, while having an excellent infrared ray transmission property, it can prevent reflection even when used in a harsh environment such as high temperature and high humidity, rapid temperature change, and raindrop collision. It is possible to provide an infrared transmitting structure having excellent environment resistance, which does not cause peeling of the film or scratches on the antireflection film.

Therefore, the infrared transmitting structure of the present invention is particularly effective as an optical window for an infrared detecting device for indoor use as well as for an outdoor use, or as an optical window for an infrared detecting device used for a high-speed flying object.

Claims (5)

[Claims] 1. A ZnS substrate, an innermost layer of Y ₂ O ₃ formed in direct contact with the ZnS substrate, and a Y formed on the innermost layer.
Infrared transmission structure that an intermediate layer of F _3, characterized in that a top layer of MgF ₂ formed on the intermediate layer. 2. A ZnS substrate having a transparentized ZnS substrate
The infrared transmissive structure according to claim 1, which is a substrate and is excellent in the transparency of visible light together with infrared light. 3. A ZnS substrate, an impact relaxation layer formed on the ZnS substrate and having an elastic modulus of 100 GPa or more, and an outermost layer formed on the impact relaxation layer and formed of diamond or diamond-like carbon. An infrared transmitting structure characterized by the above. 4. An elastic modulus of 100 which constitutes the impact absorbing layer.
Materials of GPa or higher are Ge, Si, GaP, BP, Y ₂
O ₃ , Al ₂ O ₃ , TiO ₂ , YF ₃ , LaF ₃ , or CeF
Characterized in that it is a _3, infrared transmission structure according to claim 3. 5. A ZnS substrate having a transparentized ZnS substrate
The infrared transparent structure according to claim 3 or 4, wherein the infrared transparent structure is a substrate and has excellent transparency to visible light as well as infrared light.