JP2000352612A - Multilayered film filter - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayered film filter which is formed on a glass bulb surface such as a halogen lamp for night vision and which selectively transmits the wavelength region of IR rays. SOLUTION: The multilayered film filter 2 is produced by alternately laminating high refractive index films 2a and low refractive index films 2b each having the optical film thickness controlled to λ/4 so that the center wavelength λof the light to be reflected ranges 600 to 900 nm. At least one layer of the high refractive index films 2a consists of a light-absorbing film 3 having such characteristics that the upper limit of absorption characteristics for light is present in a 600 to 1000 nm wavelength region and that the film absorbs light at wavelengths under the upper limit. Thus, an IR-transmitting multilayered film filter 2 which certainly cuts visible rays in a 380 to 780 nm wavelength range and which can transmit IR rays in >=800 nm wavelength with high transmittance characteristics, can be realized with a small number of films.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a film formed on the surface of a glass bulb of a lamp used as a light source of an infrared irradiation apparatus such as a halogen lamp for night vision, for cutting a visible light wavelength range and selecting an infrared wavelength range. The present invention relates to a multi-layer filter that transmits light.

[0002]

2. Description of the Related Art Conventionally, a multilayer filter 91 of this type has
For example, the glass bulb is configured as shown in FIG.
90, for example, Ta₂O₅, TiO₂, Zr
O₂High-refractive-index film 91a made of a metal oxide film such as ZnS or ZnS
And SiO₂, MgF₂, AlF ₆Metal oxide film
Reflection wavelengths that the low refractive index film 91b
1/4 of λ (hereinafter referred to as design wavelength) is used as the optical film thickness.
The inner surface of the glass bulb 1 is formed by laminating a plurality of layers on each other.
Is provided with a filament (not shown). Like this
Emitted from the filament by the laminated film
Of the light in the wavelength region around the design wavelength λ,
Reflected in the wavelength range.
Light is transmitted. The optical film thickness
Is the physical thickness of the layer times the value of the refractive index.

The above film is formed by an appropriate film forming method such as a vacuum evaporation method, a sputtering method, a dipping method, and an ion plating method.

[0004] Table 1 shows a specific configuration example of the conventional multilayer filter 91. For example, the design wavelength λ of the visible light to be reflected is set in the range of 400 to 700 nm, and the high refractive index film 91 is formed.
As a, a metal oxide film TiO ₂ having a refractive index n _H = 2.3 is set within an optical thickness λ / 4 = 100 to 175 nm,
Similarly, as the low refractive index film 94b, SiO ₂ having a refractive index n _L = 1.46 is set within an optical thickness λ / 4 = 100 to 175 nm. The layer numbers are given in order from the side closer to the surface of the bulb 90.

In this conventional example, first, layer numbers 2 to 19
The layers are formed by alternately stacking high-refractive-index films 91a and low-refractive-index films 91b with an optical film thickness of 112.5 nm. Next, in the layer numbers 20 to 33, the low refractive index films 91b and the high refractive index films 91a are alternately set to have an optical film thickness of 13 layers.
Set to 7.5 nm, and further layer numbers 34 to 4
The eight layers are formed by alternately laminating low-refractive-index films 91b and high-refractive-index films 91a, each having an optical film thickness of 154 nm. The optical film thickness of the high refractive index film 91a of the layer number 1 closest to the surface of the valve 90 is formed as λ / 8 = 56.3 nm, and the high refractive index film 91a of the layer number 49 which is the uppermost layer.
Is formed as λ / 8 = 77 nm.
This configuration is generally called an LW type, which makes it possible to make the infrared light wavelength portion of the transmittance characteristics of the entire film flat. The reference numerals in the table in the table correspond to the reference numerals in FIG.

[Table 1]

The multilayer filter 91 thus formed
First, the design wavelength λ =
112.5 × 4 = reflects light in a wavelength range centered on 450 nm, and then, by layer numbers 20 to 33, light in a wavelength range centered on a design wavelength λ = 137.5 × 4 = 550 nm By reflecting the light in the wavelength range centered on the design wavelength λ = 154 × 4 = 616 nm by the portions of the 34th to 48th layers, the wavelength range of visible light as the whole film (1 to 49 layers) is reflected. Is reflected in the range of 400 nm to 700 nm.

FIG. 10 shows the transmittance characteristics of the multilayer filter 91 actually formed in this manner.
Visible light in the range of nm to 700 nm is cut, and only infrared light is selectively transmitted.

[0008]

However, in the case of such a conventional multilayer filter 91, 400 nm to 70 nm is required.
In order to reliably cut off visible light in the wavelength range of 0 nm, it is necessary to laminate a total of 49 layers of the high refractive index film 91a and the low refractive index film 91b, and cut the entire visible light wavelength range of 380 nm to 780 nm. To do this, 30 more
It is necessary to add up to 40 layers, which causes a problem that an enormous film formation time is required and workability is poor. When the number of films is 50 or more, since the film is formed directly on the surface of the glass bulb 90, thermal stress is applied when the lamp is turned on, and film peeling and cracks occur, resulting in uneven color of the lamp. There is also the problem of solving such problems.

[0009]

According to the present invention, as a specific means for solving the above-mentioned conventional problems, a plurality of high refractive index films and low refractive index films are alternately laminated on a light transmitting substrate. The high refractive index film and the low refractive index film have a center wavelength λ of reflected light of 600 nm to 900 nm.
a high-refractive-index film and a low-refractive-index film each having an optical thickness set to λ / 4 so as to be in the range of nm. At least one of the layers has an upper limit of an absorption characteristic for light having a wavelength of 600 nm to 1000 nm, and is provided with a light-absorbing film having a characteristic of absorbing light of a wavelength less than the upper limit. This solves the problem.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described in detail based on an embodiment shown in the drawings.

FIG. 1 is a sectional view showing a main part of a first embodiment of a multilayer filter 2 according to the present invention. As in a conventional example, Ta ₂ O ₅ , TiO ₂ , ZrO ₂ ,
A high refractive index film 2a made of a metal oxide film material such as ZnS;
A low-refractive-index film 2b made of a metal oxide film material such as iO ₂ , MgF ₂ , or AlF ₆ is alternately laminated.

Here, in the present invention, the high refractive index film 2a
And the low-refractive-index film 2b have a center wavelength λ of reflected light of 60
The optical film thickness is set to λ /
4, and at least one of the high-refractive-index films, in this embodiment, the high-refractive-index film closest to the glass bulb 1, has an upper limit of absorption characteristics for light having a wavelength of 600 nm to 1000 nm. And a light absorbing film 3 having a characteristic of absorbing light having a wavelength smaller than that.

Table 2 shows a specific example of the structure of the film in the first embodiment of the multilayer filter 2 of the present invention. As the high refractive index film, Ta ₂ O ₅ having a refractive index n _H = 2.1 is used. And SiO ₂ having a refractive index n _L = 1.46 as a low refractive index film, and an amorphous film having a refractive index n _H = 3.4 as a high refractive index film as a first layer (a layer closest to the glass bulb 1). A silicon (hereinafter a-Si) film is used. The layer numbers are given in order from the side closer to the surface of the glass bulb 1, and the reference numerals in the figure correspond to FIG. 1 and the above description.

[Table 2]

The a-Si film generally has a characteristic of absorbing light having a wavelength of about 800 nm or less, and almost all short-wavelength light of 600 nm or less is absorbed. Therefore, as shown in the configuration example of Table 2, the low refractive index film 2b and the high refractive index film 2a are formed on the a-Si film 3 by optical thicknesses λ such that the design wavelength λ is set to 700 nm. / 4 = 175 nm
By alternately laminating the second to fourteenth layers, light having a wavelength in the range of approximately 600 nm to 800 nm is reflected by the multilayer film, so that the visible light wavelength range of 380 to 380 is reflected.
Of the 780 nm light, light on the short wavelength side is absorbed by the a-Si film 3 and part of the light on the long wavelength side is transmitted through the a-Si film 3, but the high refractive index film 2 a and the low refractive index 800 nm when cut by reflection of light by the multilayer film with the film 2b.
The infrared transmission type multilayer filter 2 in which only the infrared light described above is selectively transmitted is formed.

Here, the optical film thickness of the a-Si film 3 is λ / 4 = 175 n with respect to the design wavelength λ = 700 nm of the multilayer film 2.
It has been obtained from experimental results that it is desirable to set it to m or less, whereby it has been confirmed that the transmittance of light in the wavelength region of 800 nm to 1500 nm is always 50% or more. In this embodiment, the optical film thickness of the a-Si film 3 is set to λ / 20 = 35 nm and 800 nm to 150 nm.
Good characteristics are obtained in which the transmittance of light in the wavelength range of 0 nm is 90% or more. The optical film thickness of the high refractive index film 2a of the layer number 15 which is the uppermost layer is set to λ / 8 = 87.5 nm, and the multilayer filter 2 as a whole has an LW type configuration. The wavelength characteristic of the infrared light in the transmittance characteristics of the entire film is made flat.

In order to form the multilayer filter 2 as described above, the cleaned glass bulb 1 is first placed in an apparatus such as a vacuum evaporation apparatus, a plasma CVD apparatus, or a sputtering apparatus.
These devices form the a-Si film 3 by a well-known vacuum deposition method, a plasma CVD method, or a sputtering method. Thereafter, the glass bulb 1 on which the a-Si film 3 is formed is vacuum-deposited using SiO ₂ as a low-refractive-index film and Ta ₂ O ₅ as a high-refractive-index film as a deposition source, and is subjected to a CV method.
It can be obtained by a method of alternately forming a film while controlling the film thickness by a method D, a sputtering method or the like.

Hereinafter, a specific film forming method of the multilayer filter 2 of the present invention will be described using an example using a vacuum deposition method.

First, the cleaned glass bulb 1 is fixed on a substrate in a vacuum vapor deposition apparatus, Si is placed on a crucible as a vapor deposition material, and the interior of the apparatus is evacuated to a vacuum.
-Forming a Si film 3; Here, the substrate to which the glass bulb 1 is fixed rotates around the center (filament position) of the glass bulb 1 so that a film can be uniformly formed on the entire surface of the glass bulb 1. I have.

At this time, the conditions for forming the a-Si film 3 are as follows: the substrate temperature (surface temperature of the valve 1) is 350 ° C .;
An a-Si film 3 is formed on the glass bulb 1 at Å / s, in oxygen-free atmosphere, and at an ultimate vacuum of 5 × 10 ⁻⁴ Pa. Thereafter, the glass bulb 1 on which the a-Si film 3 is formed is subjected to SiO ₂ as a low refractive index film 2b and T as a high refractive index film 2a, which are also placed on a crucible in a vacuum evaporation apparatus.
a ₂ O ₅ is sequentially vapor deposited to form a film. The film formation conditions at this time are as follows: the SiO ₂ film has a substrate temperature of 350 ° C., a film formation rate of 3 ° / s, an oxygen-free atmosphere, an ultimate vacuum of 5 × 10 ⁻⁴ Pa, the Ta ₂ O ₅ film has a substrate temperature of 350 ° C. Film forming speed 10Å
/ S, oxygen partial pressure 0.03 Pa, ultimate vacuum 5 × 10 ⁻⁴
Pa.

FIG. 5 shows the transmittance characteristics of the multilayer filter 2 actually formed in this manner.
Light in the visible light range of 780 nm is reliably cut,
Good characteristics were obtained as an infrared-transmitting multilayer filter having a transmittance of 90% or more for light in the infrared light range of 800 nm to 1500 nm.

The conditions for forming the a-Si film 3 are as follows.
It has been confirmed that substantially the same characteristics can be obtained when the substrate temperature is in the range of room temperature to 500 ° C. and the film formation rate is in the range of 1 to 8 ° / s. The conditions for forming the SiO ₂ film include a substrate temperature of room temperature to 500 ° C., a film forming rate of 1 to 15 ° / s, an oxygen partial pressure of 5 × 10 ⁻³ Pa or less, and a Ta ₂ O ₅ film forming condition. The substrate temperature is from room temperature to 500 ° C., and the film formation rate is from 1 to
It has been confirmed that almost the same characteristics can be obtained within the range of 10 ° / s and the oxygen partial pressure of 0.01 to 0.06 Pa.

FIG. 2 is a cross-sectional view showing a main part of a second embodiment of the multilayer filter 2 according to the present invention, and Table 3 shows a specific film configuration thereof. As the film material, the refractive index _nH = 2.1 as the high refractive index film 2a as in the first embodiment.
Using Ta ₂ O ₅ as the low refractive index film 2b and the refractive index n _L
= 1.46 SiO ₂ is used.

[Table 3]

Here, in this embodiment, the light absorbing film 3
In this configuration, a polysilicon (poly-Si) film is used in place of the a-Si film of the first embodiment, and is further stacked on a seventh layer located in the middle of the 15 multilayer films. Therefore, to form the multilayer filter 2 of the present embodiment,
As in the first embodiment, the cleaned glass bulb 1 is placed in an apparatus such as a vacuum evaporation apparatus, a plasma CVD apparatus, or a sputtering apparatus, and SiO ₂ is deposited as a low-refractive-index film and Ta ₂ O ₅ is deposited as a high-refractive-index film. Vacuum evaporation method, CVD as source
Films are alternately formed while controlling the film thickness by a sputtering method, a sputtering method, etc., and when the sixth layer is laminated, a seventh polysilicon film is formed, and again under the same conditions as the first to sixth layers. 8
It can be obtained by forming the 15th to 15th layers. In addition,
Polysilicon film, after the a-Si film formed under the same conditions as the first embodiment, the substrate temperature is then raised to 700 ℃,
Obtained by placing in air for 4 hours or more.

The polysilicon film is generally about 1000 nm
There is an upper limit of the absorption characteristic for light having a wavelength of, and the light has a characteristic of absorbing light having a wavelength less than that. Therefore, as shown in the configuration example of Table 3, the polysilicon film 3 is stacked in the middle of the multilayer film, and the high refractive index film 2a and the low refractive index film 2b
If the optical film thickness is set to λ / 4 = 200 nm and the first to fifteenth layers are alternately laminated so that the design wavelength λ is set to 800 nm, the multilayer film becomes approximately 700 nm.
Since the light having a wavelength in the range of about 900 nm is reflected, the light is absorbed by the polysilicon film 3 and the light is reflected by the entire multilayer film 2 so that the visible light has a wavelength range of 380 to 780.
nm is reliably cut off, and an infrared transmission type multilayer filter 2 through which infrared light of 900 nm or more is selectively transmitted is formed.

Here, the optical film thickness of the polysilicon film 3 is:
Design wavelength λ = 800 n of the multilayer film 2 as in the first embodiment.
It has been experimentally confirmed that λ / 4 is preferably 200 nm or less with respect to m, whereby the transmittance of light in the wavelength range of 900 nm to 1500 nm is always 50% or more. In this embodiment, the optical thickness of the polysilicon film 3 is λ / 8 = 100 nm and 900 n
Good characteristics with a light transmittance of 80% in a wavelength range of m to 1500 nm are obtained. Further, the high refractive index layer 2a of the layer number 1 closest to the glass bulb 1 and the layer number 15 of the uppermost layer
The optical film thickness of the high refractive index film 2a is λ / 8 = 100, respectively.
nm, and L is set as a whole for the multilayer filter 2.
It has a W-shaped configuration, whereby the wavelength characteristic of the infrared light in the transmittance characteristic of the entire film is made flat.

FIG. 6 shows the transmittance characteristics of the multilayer filter 2 actually formed in this manner.
Light in the visible light range of 780 nm is reliably cut,
Good characteristics were obtained as an infrared-transmitting multilayer filter having a transmittance of 80% or more for light in the infrared region in the range of 900 nm to 1500 nm.

FIG. 3 is a sectional view showing a main part of a third embodiment of the multilayer filter 2 according to the present invention, and Table 4 shows a specific film configuration thereof. As the film material, the refractive index _nH = 2.1 as the high refractive index film 2a as in the first embodiment.
Using Ta ₂ O ₅ as the low refractive index film 2b and the refractive index n _L
= 1.46 SiO ₂ is used.

Here, in the present embodiment, the light absorbing film 3
Is the same as that of the first embodiment except that the a-Si film 3 is laminated on the 15th layer, which is the uppermost layer, and the optical film thickness is set to λ / 40. =
17.5 nm. Therefore, in order to form the multilayer filter 2 of this embodiment, contrary to the first embodiment, the cleaned glass bulb 1 is connected to a vacuum deposition apparatus or a plasma CVD apparatus.
It is placed in a device such as a device or a sputtering device, and the film thickness is formed by a vacuum deposition method, a CVD method, a sputtering method, or the like using SiO ₂ as a low refractive index film and Ta ₂ O ₅ as a high refractive index film as a deposition source. Films are alternately formed while controlling, and thereafter, a-Si is formed by a vacuum evaporation method, a plasma CVD method, a sputtering method, or the like.
It can be obtained by a method for forming the film 3.

[Table 4]

FIG. 7 shows the transmittance characteristics of the multilayer filter 2 actually formed in the present embodiment. Like the first embodiment, the light in the visible light region in the range of 380 nm to 780 nm is surely emitted. Cut, 800nm ~ 1500
Good characteristics were obtained as an infrared-transmitting multilayer filter having a transmittance of 90% or more for light in the infrared region in the range of nm.

FIG. 4 is a sectional view showing a main part of a fourth embodiment of the multilayer filter 2 according to the present invention, and Table 5 shows a specific film configuration thereof. As the film material, the high-refractive-index film Ta ₂ O ₅ of the first embodiment is a light-absorbing film.
Instead of the Si film 3, the low refractive index film ₂ b is made of SiO ₂ , and the multilayer filter 2 is configured by laminating a total of nine layers. The conditions for forming each film are the same as those in the first embodiment.

[Table 5]

In the above configuration example, nine layers of the a-Si film 3 and the low refractive index film 2b are alternately laminated with the optical film thickness of λ / 4 = 142.5 nm so that the design wavelength λ is set to 570 nm. . As a result, as in the other embodiments, 800
The transmittance of light in the wavelength range from nm to 1500 nm is always 50%.
It has been confirmed that the above results are obtained.
It has been confirmed that a good characteristic of 90% or more in transmittance of light in a wavelength region of 0 nm is obtained. Also in this case, as in the other embodiments, the optical film thickness of the a-Si film 3 of the layer number 1 closest to the glass bulb 1 and the layer number 9 which is the uppermost layer is λ / 8.
= 71.3 nm, and the entire multilayer filter 2 has an LW-type configuration, thereby making the infrared light wavelength portion of the transmittance characteristic of the entire film flat.

FIG. 8 shows the transmittance characteristics of the multilayer filter 2 actually formed in this manner.
Light in the visible light range of 780 nm is reliably cut,
Good characteristics were obtained as an infrared-transmitting multilayer filter having a transmittance of 90% or more for light in the infrared region in the range of 800 nm to 1400 nm.

In each of the above embodiments of the present invention, Ta ₂ O ₅ is used as the high refractive index film and SiO ₂ is used as the low refractive index film, but other materials such as metal oxides are used. And similar characteristics can be obtained. To give a specific example, TiO ₂ , ZrO may be used as the high refractive index film.
₂ , ZnS, Zi ₃ N _{4 and the} like, and examples of the low refractive index film include MgF ₂ and AlF ₆ .

In each of the above embodiments, an a-Si film or a polysilicon film is used as the light absorbing film 3, but the present invention is not limited to this.
As another light absorbing film, any film having a characteristic of absorbing light having a wavelength of 600 nm to 1000 nm having an upper limit and absorbing light of a wavelength less than that may be used. For example, ITO obtained by oxygen-free deposition may be used. Film, ZnO film, In
Metal oxide films such as ₂ O ₃ and Fe ₂ O ₃ may be used. These films are formed under the following conditions to become light absorbing films having the above characteristics. It is the same as the first to fourth embodiments, and it has been confirmed that almost the same characteristics can be obtained.

The ITO film serving as the light absorbing film has a substrate temperature of 200 ° C. (within the range of ordinary temperature to 500 ° C.) and a film forming rate of 5 °.
/ S (within the range of 1 to 10 ° / s), in an oxygen-free condition, at a final vacuum degree of 1 × 10 ⁻³ , and
A ZnO film and an In ₂ O ₃ film can be obtained under the same conditions. Further, with respect to the Fe ₂ O ₃ film, the substrate temperature 20
0 ° C (within the range of room temperature to 500 ° C), film formation rate 5Å / s
(In the range of 1 to 10 ° / s), and each is obtained by forming a film in an atmosphere of oxygen-free to 0.02 Pa under a condition of a degree of ultimate vacuum of 1 × 10 ⁻³ .

[0036]

As described above, according to the present invention, the high-refractive-index film of the multilayer filter in which a plurality of high-refractive-index films and low-refractive-index films are alternately laminated on a light-transmitting substrate. And the low refractive index film, the center wavelength λ of the reflected light is 600 nm to 90 nm.
The optical film thickness is set to λ / 4 so as to be in a range of 0 nm, and a plurality of layers are alternately laminated, and at least one of the high refractive index films has an upper limit of absorption characteristics for light having a wavelength of 600 nm to 1000 nm. , A visible light wavelength of 380 nm to 780 nm by using a multilayer filter constituted by a light absorbing film having a characteristic of absorbing light of a wavelength smaller than that.
Can reliably realize the infrared transmission type multilayer filter capable of transmitting infrared light of 800 nm or more with high transmittance characteristics with a small film configuration of 15 layers or less. Membrane time can be greatly reduced,
Workability is greatly improved. In addition, since the film configuration is as small as 15 layers or less, the heat resistance is significantly improved as compared with the conventional case,
Even when thermal stress is applied to the bulb surface when the lamp is turned on, film peeling and cracking are unlikely to occur, preventing color unevenness when the lamp is turned on.This is an extremely excellent effect for reducing the cost and improving the performance of this type of multilayer filter. To play.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a first embodiment of a multilayer filter according to the present invention.

FIG. 2 is a sectional view showing a second embodiment of the multilayer filter according to the present invention.

FIG. 3 is a sectional view showing a third embodiment of the multilayer filter according to the present invention.

FIG. 4 is a sectional view showing a fourth embodiment of the multilayer filter according to the present invention.

FIG. 5 is a graph showing transmittance characteristics of the first embodiment.

FIG. 6 is a graph showing transmittance characteristics of the second embodiment.

FIG. 7 is a graph showing transmittance characteristics of the third embodiment.

FIG. 8 is a graph showing transmittance characteristics of the fourth embodiment.

FIG. 9 is a cross-sectional view showing a conventional multilayer filter.

FIG. 10 is a graph showing transmittance characteristics of a conventional multilayer filter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Glass bulb 2 ... Multilayer filter 2a ... High refractive index film 2b ... Low refractive index film 3 ... Light absorption film

Claims (7)

[Claims] 1. A multilayer filter comprising a light transmitting substrate and a plurality of high refractive index films and low refractive index films alternately laminated on a light transmitting substrate.
The high-refractive-index film and the low-refractive-index film are a high-refractive-index film and a low-refractive-index film each having an optical film thickness set to λ / 4 such that the central wavelength λ of reflected light is in the range of 600 nm to 900 nm. And a high-refractive-index film having a thickness of 600 nm to 1 nm.
A multilayer filter comprising a light absorption film having a characteristic of absorbing light having a wavelength lower than the upper limit of absorption characteristics of light having a wavelength of 000 nm. 2. The light absorption film according to claim 1, wherein said light absorption film is an amorphous silicon film or a polysilicon film.
The multilayer filter according to any one of the preceding claims. 3. The multilayer filter according to claim 1, wherein said light absorbing film is an ITO film. 4. The multilayer filter according to claim 1, wherein said light absorbing film is a ZnO film. 5. The multilayer filter according to claim 1, wherein said light absorbing film is an In ₂ O ₃ film. 6. The multilayer filter according to claim 1, wherein said light absorbing film is an Fe ₂ O ₃ film. 7. The multilayer filter according to claim 1, wherein the optical thickness of the light absorbing film is λ / 4 or less.