JPS5829492B2 - Manufacturing method of optical image conversion element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical spatial filter element and an optical image conversion element using a single crystal having a photoconductive effect and an electro-optic effect, and in particular to an optical spatial filter element and an optical image conversion element that have good performance by reducing the thickness of the single crystal. The present invention relates to a method for obtaining an optical image conversion element.

The sirenite group single crystal of bismuth oxide (Bi203), which has remarkable photoconductive and electro-optic effects, can also be used for the addition of other oxides, such as silicon dioxide (SiO2), germanium dioxide (eeo2), and thus the body-centered cubic crystal ( b, c,
c) becomes a stable compound.

The thus obtained bismuth silicon oxide (Bi1) has remarkable photoconductive and electro-optic effects.
Various studies have been conducted on converting an incoherent light image into a coherent light image using bismuth germanium oxide (Bi1□Ge02o) or bismuth germanium oxide (Bi1□Ge02o) as an optical spatial filter element or an optical image conversion element. ing.

For example, tT, Applie by Feinleib
d 0pticsvo1.11. Nal 2, Dec.
1972, p. 2752, etc., is an example of an optical image conversion element as shown in FIG.

In FIG. 1, 1 is a bismuth silicon oxide single crystal, 2 is a transparent insulating film, and 3 is a transparent or semi-transparent electrode.

Its operating characteristics are as shown in Figure 2, in which a voltage is applied between the electrodes and an image or character pattern is projected onto one side in that state.

In this case, taking advantage of the wavelength dependence of the photoconductive effect of bismuth silicon oxide, in particular the fact that it has a remarkable photoconductive effect for light with a short wavelength of 500 nm or less, the writing wavelength is 500 nm or less. Light with a wavelength distribution is used, but in reality, white light from a xenon or tungsten lamp is sufficient.

The area irradiated with light generates photogenerated electrons as shown in the upper part a of Figure 2.
Since hole pairs diffuse and move toward both poles within the crystal and are trapped at the insulating film interface, the potential distribution within the crystal is 1. The distribution is gentler than that in the lower part of Figure 2 where no light is irradiated.

Since bismuth silicon oxide is an insulator in the dark, charged bodies trapped at the interface remain for a while.

In this state, He as the readout light is
Coherent light with a long wavelength that does not contribute to the photoconductive effect, such as Ne laser light, with a wavelength of 6331 m or more is
By uniformly irradiating the element surface as linearly polarized light with a polarization direction of °, after transmission, the retardation δ due to the electro-optic effect is modulated in accordance with the size of the electrolytic distribution.
For example, by passing the light through an analyzer, an intensity-modulated coherent light image can be obtained.

(In the formula, λ is the optical wavelength, no is the refractive index, γ4 is the electro-optic coefficient, and ■ is the voltage.) Bismuth silicon oxide is a body-centered cubic crystal and has point group symmetry 23, so the crystal plane (100) For an electric field in the perpendicular direction and light in the incident direction, the retardation δ is independent of the crystal thickness as shown in equation (1).

Therefore, the performance improvement as a light conversion element is as follows: (1) By reducing the crystal thickness, the focal point of the image and the electrons or holes trapped at the interface of the insulating film are brought closer to each other, thereby improving the resolution of the image.

■ By making the single crystal film that is the active layer smaller, the absorption loss of continuous light is reduced and a clear image is obtained.
This is achieved by reducing the crystal thickness.

However, in the previously proposed rope structure, the processing technology is limited because the film is made thin by polishing a single crystal wafer, and as the film becomes thinner, the wafer surface becomes curved. The thickness was the limit.

As a result of repeated research in order to efficiently obtain an optical image conversion element having a thin single crystal film, the present inventors found that Nakamoto thin film single crystals can be produced by epitaxial growth on a suitable single crystal substrate. In fact, this substrate single crystal has a similar crystal structure and lattice constant to the target thin film single crystal so that epitaxial growth is possible, and the substrate single crystal has the same optical properties as the thin film single crystal that is the active layer. The present invention was achieved by discovering that it is necessary to have no conduction effect.

That is, the present invention provides a single crystal having a photoconductive effect and an electro-optical effect and having a body-centered cubic crystal structure, and a single crystal having a crystal structure and lattice constant similar to this single crystal and similar to the above-mentioned single crystal. It is characterized by epitaxial growth on a substrate single crystal that does not have a photoconductive effect.

The present invention relates to a method of manufacturing an optical image conversion element in which a thin film single crystal is provided as an active layer on a single crystal substrate.

In this case, the epitaxial growth method itself is carried out according to a known method.

Examples of the single crystal of the active layer in the present invention include bismuth silicon oxide (Bi12SIO2o), bismuth germanium oxide (Bi1□CIeO2o), bismuth zinc oxide (Bi12Zn02o), and examples of the single crystal of the substrate include bismuth silicate [B14(
SiO4)3).

Bismuth silicate [B14(GeO4)3] is mentioned.

These properties are shown in Table 1 below. As shown in Table 1, the substrate single crystal is a cubic crystal, whereas the thin film single crystals that are the active layer are all body-centered cubic crystals, and although their crystal structures are different, they are similar and have similar lattice constants. Therefore, heterogeneous junctions (heteroepitaxy) are possible.

Furthermore, since the melting points of the substrate materials are all higher than the melting points of the thin film single crystal materials, this is an advantageous condition for liquid phase epitaxial growth by direct immersion.

The electro-optic effect of the substrate single crystal is smaller than that of the thin film single crystal.

Regarding the photoconductive effect, the photosensitivity range of the thin film single crystal that is the active layer is large at wavelengths of 500 nm or less, and the photosensitivity range of the substrate single crystal is below 320 nm, so for example,
When irradiated with a writing light having a wavelength of nm, writing is performed in a thin film single crystal, and the photosensitivity of the substrate single crystal can be ignored.

As described above, the substrate material has different characteristics from the thin film crystal material of the active layer and has good electrical insulation properties, so that it is suitable for the original purpose as a substrate material for an optical image conversion element.

In the present invention, the structure of the optical image conversion device in which a thin film active layer is epitaxially grown on a single crystal substrate is as shown in FIG. 4 and 5 represent electrodes.

Both the substrate single crystal and the thin film single crystal layer are plate-shaped single crystals with a plane having a normal line of <100>.

When manufacturing an optical image conversion element according to this structure, the process of manufacturing the element is simplified because the transparent insulating film layer only needs to be provided on one side, as has been done in the past.

Example 1 A bismuth silicate [B14(SiO4)3] single-crystal (100) wafer of 10 mm diameter x 1 mm thickness was mirror-polished on both sides, and was further chemically polished using hydrochloric acid.

Next, platinum crucible 1 (30φ x 3
81 B112ZnO2 on 0 mountain height x 1.0m7IL thickness)
o Powder raw material having a single crystal composition is charged, heated to about 850° C. by heater 2 of a resistance heating furnace, and kept in a sufficiently molten state for about 3 hours.

A substrate single crystal Bi, a (5104) s is horizontally attached to a substrate crystal holder 3 attached to the upper part of the resistance heating reactor core, and is gradually lowered while rotating at a rotational speed of 3 orpm to be immersed in the melt in a platinum crucible.

Next, gradually lower the furnace temperature at a rate of about 0°C/min.
The temperature is set to 80° C., and then the substrate single crystal is pulled up to just above the crucible, and the furnace temperature is reduced to about 0° C./hour.

A thin crystal layer Bi1□Zn02o was precipitated on the single crystal surface of the substrate, and its thickness was about 10μ. According to fluorescent X-ray analysis, it was approximately Bi2O3: ZnO was 6:
It was confirmed that the composition was 1.

The single crystal thin film was transparent and had a good surface condition.

Next, a transparent insulating film with a thickness of about 3 μm was coated over the entire surface of the thin single crystal surface, and gold was further deposited on the film to a thickness of about 3000 Å to form an electrode.

A gold electrode was similarly deposited on the back surface of the single crystal substrate.

Writing was performed by projecting an image onto the surface of the element using a tungsten lamp (100 W) as a writing light.

At the time of irradiation with writing light, a voltage of about 1500 V was applied between the electrodes.

Immediately after writing, a H e-N e laser 6 polarized at an angle of 45° with respect to the crystal axis of the Bi1□Zn02o single crystal
An image was obtained by irradiating linearly polarized 33 nm light (approximately 3 mW) and passing it through an analyzer after passing through the element.

Since the film thickness of the active layer is 10μ, the image resolution is 300
The film thickness is about 1 µm compared to the conventional film thickness of several hundred microns.
Digit resolution has been improved.

Furthermore, since the absorption of readout light decreased during light transmission, an image with low brightness was obtained.

Example 2 Bismuth silicate (Bi4 (Ge04) 3rd crystal (
Both surfaces of the 100) surface wafer were mirror-polished for 10 minutes φ x 1 thickness, and further chemically polished using hydrochloric acid.

Next, Bi1 was placed in platinum crucible 1 (30φ x 30mm height x 1.0mm thick) in the resistance heating furnace shown in FIG.
A powder raw material having a single crystal composition of □51020 is charged, heated to about 910° C. by the heater 2 of the resistance heating furnace, and kept in a molten state for about 3 hours.

A substrate single crystal Bi4 (Ge04) 3 wafer is horizontally attached to the substrate crystal holder 3, and is gradually lowered while rotating at a rotational speed of 3 Orpm to be immersed into the melt in the platinum crucible 1.

Next, gradually lower the furnace temperature at a rate of about 0℃/min until 9.
After that, the substrate single crystal was pulled up to just above the crucible, and the furnace temperature was decreased to about 0° C./hour.

After cooling, approximately 10μ thick Bi1□Si is deposited on the single crystal surface of the substrate.
It was observed that O□0 was growing.

The surface condition of this thin film single crystal was smooth, showed good crystallinity, and was transparent.

Next, a transparent insulating film with a thickness of about 3 μm was coated on the entire surface of the thin film single crystal surface, and about 3000 gold electrode thin films (7 m7 ILφ) were further deposited thereon.

Writing was performed by projecting an image onto the element surface using a tungsten lamp (100 W) as a writing light.

The applied voltage during writing was 1000V.

After writing, an H e-Ne laser beam (3 mW) linearly polarized at an angle of 45° with respect to the crystal axis of the B112SiO2o single crystal was irradiated, and after passing through the element, the image was reproduced by passing it through an analyzer. .

The image resolution was 300 lines/home. In this example, sufficient writing was obtained with a light energy of 5 erg/i and a small amount of light during writing.

[Brief explanation of drawings]

Fig. 1 shows the structure of a conventional optical image conversion element, Fig. 2 shows the operating characteristics of the optical image conversion element, Fig. 3 shows the structure of the optical image conversion element obtained by the present invention, and Fig. 4 shows the structure of the optical image conversion element obtained by the present invention. 1 shows the structure of a resistance heating furnace for carrying out the method of the present invention.

Claims (1)

[Claims] 1 Bismuth silicate (B t
4 (st 04) a) or bismuth silicate [
B14(GeO4)3] On top, bismuth silicon oxide (Bi1□5iO2o), bismuth germanium oxide (Bil. Ge02o) or bismuth zinc oxide (Bi1
A method for manufacturing an optical image conversion element in which a thin film single crystal is provided as an active layer on a substrate single crystal, the method comprising epitaxially growing a single crystal of □z no 26 ).