JPH01191101A - Reflection preventive film - Google Patents

Abstract

PURPOSE:To realize the reflection preventive film which has high transmissivity and provides excellent heat generation as a cloud-preventive film by specifying the film thickness of the transparent conductive film of the reflection preventive film including the transparent conductive film. CONSTITUTION:The reflection preventive film consists of films 1-3 provided on an optical element 4, and one layer among the films is the transparent conductive film 3, whose film thickness is 45-120nm. Thus, the conductive film 3 among the reflection preventive films 1, 2, and 3 is formed to <=120nm thickness, so the light absorption by the transparent conductive film 3 is reduced to obtain sufficient transmissivity which is used for the optical element 4. Further, the film thickness range is set to 45-120nm, and consequently the surface resistance is smaller than before and suitable for the heat generation of the optical element 4 such as an optical lens, thereby realizing the reflection preventive films 1-3 including the transparent conductive film 3 which is used excellently as the cloud preventive film.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to an optical thin film that is formed on the surface of an optical element and improves the characteristics of the optical element.

(Prior Art) Increasing the characteristics of optical elements, especially the light transmittance, is essential in order to increase the efficiency of incident light in camera lens systems, semiconductor exposure apparatus optical systems, etc., which are composed of a plurality of optical elements.

Conventionally, in order to increase the transmittance of an optical element, an antireflection film composed of a single layer or a plurality of films was formed on the optical element, thereby reducing the light reflected on the surface of the optical element.

Recently, transparent conductive films such as In20s and 5n02 have been increasingly used as transparent electrodes of liquid crystal panels, heating films for preventing dew condensation (anti-fog films) on window glasses, and the like. This transparent conductive film alone does not have a sufficiently high transmittance (In203
(90% for SnO2, 85% for SnO2) A method for reducing the reflectance of glass, etc. on which a transparent conductive film is formed is to use a transparent conductive film as a component film of a multilayer antireflection film formed on the substrate surface as a high refractive index layer. Alternative membrane configurations are known.

For example, λ. Let be the center wavelength of anti-reflection and integer layer (λ.

Optical film thickness that is an integral multiple of 1/4 of (actual film thickness x refractive index)
(1) Substrate glass-InzOs(λ./2)-Mg'F
2'(λ./4) (2) Substrate glass-AjZ2os(λ./4)-In,
03 (λo/2) −M g F 2(λ./
4) (The optical film thickness is in parentheses) is known.

[Problem that the invention is trying to solve] However,
With these configurations, it is possible to reduce the reflectance of the transparent conductive film, but it is not possible to reduce the light absorption of the film itself. The material constituting the transparent conductive film is such that electrons are easily excited from the valence band to the conductive band, and absorbs light energy during this excitation, so the transparent conductive film is a common optical film, such as MgF2, Zf"02, It absorbs light more easily than An20s etc. This transparent conductive film must be provided in the anti-reflection film with a thickness corresponding to λ6/2 with respect to the center wavelength λ.If λo = SOO, the refractive index is 1.9. ITO
The film requires a thickness of 132%, and the decrease in transmittance due to light absorption is so large that it cannot be ignored, making it difficult to use it in optical elements that require a transmittance of nearly 100%, for example, as an anti-fog film.

In view of the above-mentioned problems, the present application is characterized by providing an antireflection film that can obtain sufficiently high light transmittance even if it includes a transparent conductive film.

[Means and effects for solving the problem] The present invention provides an anti-reflection film including a transparent conductive film whose thickness is 120% m.
Since the structure is as follows, it is possible to reduce light absorption by the transparent conductive film and obtain sufficient transmittance for use in an optical element. In addition, by setting the film thickness range to 45% to 120% m, the sheet resistance is larger than that of conventional ones, and an appropriate sheet resistance for heat generation can be obtained in optical elements such as optical lenses.
An antireflection film containing a transparent conductive film that is suitable for use as an antifogging film becomes possible.

In this specification, the optical film thickness λ/4°λ/2 is a general term, and strictly speaking, the film thickness deviates from this value to some extent depending on the characteristics required for the optical element used. Specifically describing the range of each film thickness, film thickness λ/4: 0.18λ or more, 0.27
λ or less film thickness λ/2: 0.39λ or more and 0.6λ or less.

〔Example〕

FIG. 1 is a schematic diagram of the structure of an antireflection film according to a first embodiment of the present invention, in which 1 represents the antireflection center wavelength λ. On the other hand, films 2 and 3 are low refractive index films with an optical thickness of λo/4, and have a refractive index of 1.38. Films 2 and 3 have antireflection center wavelengths λ.

The sum of their optical thicknesses is λ. /2 is a high refractive index layer, that is, an equivalent film, where 2 is a Z r O2 film with a refractive index higher than the transparent conductive film of 3 and has a refractive index of 2.1'2, and 3 is a transparent film with a refractive index lower than that of 2. This is a conductive film with a tin oxide-containing indium oxide film (hereinafter collectively referred to as ITO film) with a refractive index of 1.9, and is a power supply that heats the surface of the study lens and prevents condensation. be.

When a current is supplied from the power supply 6 through the electrode 5 to the ITO film 3 of the anti-reflection film provided on the optical lens 4, the I-To film 3 generates heat and the heat is transmitted to the MgF film 1, which is the outermost layer of the anti-reflection film. Dew condensation on the surface of the MgF2 film 1 is prevented.

Here, the wavelength of the ITO film manufactured by varying the film thickness with a mixed weight ratio of SnO of 5% is 400°450.650% m.
The transmission loss rate and sheet resistance for light are shown in FIG. 7 (the broken line is the sheet resistance value).

It can be seen from this figure that the transmission loss rate is a low value in the visible light region when the film thickness is 120 nm or less. Further, the sheet resistance value increases rapidly when the film thickness is 45 nm or less, and sufficient heat generation cannot be obtained unless the voltage is increased. Therefore, it is effective to set the thickness of the ITO film in the range of 45 to 120% m.

For example, for the film structure of the antireflection film shown in Figure 1, the center wavelength λ
-552 nm, the optical thickness of each layer is 190.55.138% m from the optical lens side, and the anti-reflection properties when an optical lens with a refractive index of 1.52 is used as the base material 4 are as follows.
The actual thickness of the ITO film shown in the figure is 1100n.
It is.

For comparison, λ in Figure 1. /2 film, ITO film 3 and ZrO,
Film 2 has an optical thickness λ. FIG. 6 shows the antireflection properties of the antireflection film replaced with a single layer of ITO film of /2. Comparing the two, 450-650 nm is important for optical lenses.
It can be seen that sufficient antireflection properties are obtained in this example in the range of . In addition, the thickness of the ITO film in the comparative film is 132 nm, while in the present example it is 1100 nm. The amount of light absorbed by an ITO film increases depending on the film thickness, so
This example has less light absorption and higher transmittance.

When a current of 0.5 A was actually applied to an ITO film with a sheet resistance of 20 Ω/sq, the film surface temperature reached 40°C approximately 10 minutes after the current was applied.
The optical lens was heated to a temperature of 25° C. and the humidity was supersaturated, and no fogging was observed on the optical lens, confirming the antifogging effect. In addition, the satisfactory antireflection function required for optical lenses was maintained.

As a modification of the film structure of the antireflection film shown in FIG.
．． 52. An optical lens 4 with a diameter of 50 mm has a center wavelength λ. =
For light of 476 nm, the optical thickness of the ITO film as a transparent conductive film is 90 nm, and Zr with a higher refractive index of 2.1 is used as a transparent conductive film.
With the optical thickness of the O□ film being 194 nm, these two films form a λo/2 film, and the final layer has a low refractive index of 1.38.
FIG. 3 shows the antireflection properties of the M g F 2 film having an optical thickness of 119 nm and a λ/4 film. The ITO film thickness was increased to 47 mm while maintaining good anti-reflection properties.
It is as thin as nm. Comparing FIG. 3 with FIG. 2, it can be seen that the antireflection properties have changed. In this way, by changing the thickness of the ITO film between 45 and 120 nm, it is possible to finely adjust the characteristics without changing the basic film configuration, that is, without significantly changing the antireflection characteristics.

In fact, when a current of 0.3 A is supplied from a stabilized power supply to an ITO film, the surface temperature of the film is heated to 40°C in about 10 minutes after the current is applied, and even when the humidity reaches a supersaturated state in an atmosphere at a temperature of 25°C, the optical lens remains intact. No fogging occurred and satisfactory anti-reflection function was maintained.

As a third example, the design wavelength λ. On the other hand, the film thickness λ of the antireflection film consisting of an integral number of layers is higher than the refractive index of the base material from the base material side. /4 layer, the film thickness λ consisting of a layer with a higher refractive index than this. /2 layer, film thickness λa consisting of a lower refractive index than the base material /
4, the first layer is replaced with a transparent conductive film 13 made of a non-integer layer and a non-integer layer 15 with a lower refractive index, and the second layer is replaced with a non-integer layer 15 made of two high refractive index layers. A non-integer layer 14 having a lower refractive index between the integer layers 12a and 12b.
FIG. 4 shows a schematic diagram of the structure of the antireflection film replaced with one consisting of three non-integer layers including .

Specifically, the center wavelength λ. -The refractive index of the base material for light of 540 nm is 1.70.The refractive index of each film is 1.9. Au□Os 1.6°ZrO22,1,Al
1203 1.6. Zr022.1. MgF21.38
The respective optical film thicknesses are 90.20, 159, 23, 66.
．． 135nm.

Further, the diameter of the base material was 60 mm. The antireflection properties of this film are shown in FIG.

By combining an ITO film consisting of a non-integer layer with a non-integer layer having the same intermediate refractive index to make it equivalent to an integer layer having an intermediate refractive index lower than a high refractive index layer, it is possible to achieve good results without changing the optical film thickness. It has excellent anti-reflection properties.

When a current of 0.35 A is supplied to the ITO film from a stabilized power supply, the surface temperature of the film is heated to 40°C in about 10 minutes after the current is applied, and the temperature rises to 2.
Even when the humidity was supersaturated in an atmosphere at a temperature of 5°C, the optical lens did not fog up, exhibited efficient anti-fog function with a power consumption of 8 W, and maintained sufficient anti-reflection function.

(Effects of the invention) As explained above, by configuring the antireflection film including a transparent conductive film so that the thickness of the transparent conductive film is 45 to 120 nm, (1) an antireflection film with high transmittance can be obtained. become.

(2) An anti-reflection film that generates good heat as an anti-fog film becomes possible.

There is an effect.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the film structure of the anti-reflection film of the first embodiment of the present invention, FIG. 2 is a diagram showing the anti-reflection properties of the film structure of the first embodiment, and FIG. FIG. 4 is a schematic diagram showing the film structure of the anti-reflection film of the third embodiment of the present invention; FIG. 5 is a diagram showing the film structure of the film structure of the third embodiment of the present invention. FIG. 6 is a diagram showing the antireflection characteristics of a conventional antireflection film. FIG. 7 is a diagram showing the transmission loss rate characteristics due to changes in the thickness of the ITO film. In the figure, 1 is M g F 2 film, 2 is ZrO2 film, 3 is I
4 is an optical glass, 5 is an electrode, and 6 is a power source.

Claims (1)

[Claims] (1) In an antireflection film composed of a plurality of films provided on an optical element, one layer of the plurality of films is a transparent conductive film, and the thickness of the transparent conductive film is 45 to 120 nm. Features an anti-reflection film.