JP2645664B2 - Thin-film optical imaging device - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention relates to the conversion of an incoherent image into a coherent image using the photoconductivity and electro-optic effect of a crystal having a silenate type crystal structure, spatial frequency filtering, The present invention relates to an optical image element for performing an optical logic operation or the like.

(Prior Art) For example, as shown in FIG. 1, Bi ₁₂ MO ₂₀ (M = Si, Ge, Ti) having both photoconductive effect, electro-optical effect and high dark resistivity
Etc., a single crystal plate 1 having a silenate type crystal structure, an insulating layer 2 provided on at least one side thereof, and a transparent film provided on those side surfaces for applying an electric field to the single crystal plate 1 and the insulating layer 2. An element composed of the electrode 3 has been conventionally known. This element can perform writing, reading, erasing, and the like of an optical image, and is used for, for example, converting an incoherent light image to a coherent light image, spatial frequency filtering, optical logic operation, and the like.

The principle of writing and reading of this element is as follows.

First, when a voltage is applied to the transparent electrode 3 by the power supply 4,
In the dark state, since both the single crystal plate 1 and the insulating layer 2 have high resistance, the voltage is divided according to the capacitance of the insulating layer 2 and the single crystal plate 1 based on the principle of series connection of capacitors. When an image of blue light is formed on the single crystal plate 1 in this state, the single crystal plate 1 has a photoconductive effect, so that electrons and holes excited according to the light intensity are antiparallel to the incident light. In the symmetrical device shown in FIG. 2A, the positive charge distribution and the vicinity of the interface (2) are close to the interface (1) between the single crystal plate 1 and the insulating film 2 in the symmetrical device of FIG. A negative charge distribution is formed corresponding to the image, and only the positive charge distribution is formed corresponding to the image in the vicinity of the interface (1) in the asymmetric device of FIG.
That is, the potential distribution corresponding to the image is written in the single crystal plate 1.

To read the written image, red light that does not contribute to the photoconductive effect is used, and the electro-optic effect of the single crystal plate 1 is used. That is, since the single crystal plate 1 has an electro-optic effect, the potential distribution in the single crystal plate 1 is converted into a refractive index distribution. Therefore, the linearly polarized red light is incident on the single crystal plate 1 using the polarizer 5, and the light detected by the analyzer 6 has a light intensity corresponding to the refractive index distribution in the single crystal plate 1. Is played. If an image is input using incoherent light and reproduction is performed using coherent light such as laser light, conversion from an incoherent image to a coherent image can be performed in real time.

However, when coherent light is used as the reading light, interference fringes occur due to multiple reflections occurring between the incident side surface and the outgoing side surface of the single crystal plate 1, thereby deteriorating the image quality of the read image. FIG. 2 is a configuration diagram of an optical image element according to a conventional example for removing the interference fringes, which is configured by adding a taper angle to the side surface of the single crystal plate 1. An intersection point between the optical axis of the readout light and the projection plane is defined as an origin O, and a direct transmission image (0-order image) and an image (N-order image) reflected N times on the incident side surface and the exit side surface of the single crystal plate 1, respectively. h _n Expressing position on the projection surface at a distance h _n from the origin O of) is, h _n = L · tan [[arcsin {n · sin ((2N + 1) · δ)} ] - [delta]] ... ( 1) Here, n is the refractive index of the single crystal plate 1, δ is the taper angle, L is the distance from the single crystal plate 1 to the projection plane, and it is assumed that the center thickness d << L of the single crystal plate 1 is satisfied.

The effective diameter of the single crystal plate 1 D, and the distance of the distance h _0, 1 primary image direct transmission image from the origin 0 (0 primary image), respectively and _{h 1 h 1 -h 0> D} ...... (2 ), The multiple reflection image does not directly overlap the transmission image, so that no interference fringes occur. For example, n = 2.55 (Bi ₁₂ SiO ₂₀ ), D = 3
The taper angle δ when 5 mm and L = f = 1,000 mm (focal length of the lens) is as follows from Expressions (1) and (2): δ> 0.38 ゜ (3) Accordingly, the central thickness d of the single crystal plate 1 is set to a general value of 30.
If it is 0 μm, the thinnest part is 200 μm and the thickest part is 400 μm.

(Problems to be Solved by the Invention) As described above, when coherent light is used for readout light, the thickness of the crystal differs in the plane of the element because a taper angle is added to the single crystal plate 1 in the conventional element. . Therefore, the voltage distributed to the single crystal plate 1 also differs in the element plane. The resolution of the element does not depend directly on the charge distribution formed corresponding to the written image in the vicinity of the interface between the single crystal plate 1 and the insulating layer 2. Determined by distribution. Therefore, in the thin portion of the single crystal plate 1, the spread of the potential distribution in the direction perpendicular to the thickness is small compared to the charge distribution, so that the resolution is good. On the contrary, in the thick portion, the spread of the potential distribution is large and the resolution is poor. As described above, there is a problem that the resolution becomes non-uniform in the element surface.
Further, since the sensitivity of image writing depends on the voltage distributed to the single crystal plate 1, there is a problem that the writing sensitivity becomes non-uniform due to the non-uniform crystal thickness.

Further, as is clear from the above description, it is desirable to reduce the thickness of the single crystal plate 1 from the viewpoint of improving the resolution of the element, but the physical strength required for element preparation and handling is limited. The thickness of the conventional single crystal plate 1 is 100 μm.
It was difficult to:

In addition, it is desirable that the written image can be erased only by applying the applied voltage, because the peripheral optical system can be simplified when using the element. Could not be erased.

As described above, the conventional optical image element has problems in resolution, writing sensitivity, and erasing.

The present invention has been made in view of the above-described problems of the related art, and provides a thin-film optical image element that has excellent in-plane uniformity and resolution of image writing sensitivity and can be erased only by applying an applied voltage. With the goal.

(Means for Solving the Problems) In order to achieve this object, the present invention provides a method for writing an incident optical image using the photoconductive effect and the electro-optical effect of a single crystal plate having a silenate type crystal structure. In the optical imaging device, the dark resistivity is equal to or less than the resistivity in the state where the photoconductive effect occurs without Bi ₁₂ MO ₂₀ (where M = Si, Ge, Ti). Bi ₂₀ MO ₂₀ (provided that
M = Si, Ge, Ti) composed of a crystal obtained by adding a pentavalent element,
And a low-dark-resistance single-crystal plate having a tapered shape, disposed on the incident side of the low-dark-resistance single-crystal plate, having the same crystal structure as the low-dark-resistance single-crystal plate, and having a lattice formed by crystal growth. A high dark resistance layer having a uniform thickness and a high dark resistivity capable of matching, an insulating layer provided on the other end side of the high dark resistance layer, the low dark resistance single crystal plate and the high dark resistance layer, And a transparent electrode for applying a voltage to the substrate.

 Hereinafter, the present invention will be described in detail.

(Principle of the Invention) First, the principle of the present invention will be described. The thin-film optical image element used in the present invention has a structure formed of a low-dark-resistance single crystal plate and a high-dark-resistance layer, which were previously applied for a patent by the same applicant (Japanese Patent Application No. 1-441616). The structure will be described in detail. In the following description, the same components as those of the conventional example shown in FIG.

FIG. 3 is a structural view of the thin film type optical image element used in the present invention. The low dark resistance single crystal plate 7 having a silenate type crystal structure in which the dark resistivity is significantly reduced by adding P is provided on the incident side of the low dark resistance single crystal plate. It has a structure in which a high dark resistance layer 8 which is lattice-matched to the single crystal plate 7 and has a photoconductive effect, an electro-optical effect, and a high dark resistivity is provided.

That is, the conventional single crystal plate 1 has a high dark resistivity, but in the present invention, a low dark resistance single crystal plate 7 having a low dark resistivity and a high dark resistance layer 8 are newly provided. Things. As a means for obtaining an image with good contrast with a small exposure, the same applicant has already applied for a patent by applying a configuration in which an epitaxially grown layer having a large photoconductive effect is arranged on the incident side of the single crystal plate 1 (Japanese Patent Application No. 63-163). -208022). The difference between this image element (JP-A-63-208022) and the present invention is whether the single crystal plate has a high dark resistivity or a low dark resistivity. The low dark resistance single crystal plate 7 used in the present invention is configured so that the incident light enters the low dark resistance single crystal plate 7 and has a resistivity equal to or less than the resistivity when the photoconductive effect occurs. On the other hand, the single crystal plate of the conventional image element (Japanese Patent Application Laid-Open No. 63-208022) is made of a material having a high dark resistivity.

In the present invention, the voltage applied by the power supply 4 between the transparent electrodes 3 is reduced by combining the low dark resistance single crystal plate 7 having a low dark resistivity and the high dark resistance layer 8 having a high dark resistivity. Since the resistivity of the low-dark-resistance single crystal plate 7 is much smaller than that of the insulating layer 2 and the high-dark-resistance layer 8, it is almost divided into the insulating layer 2 and the high-dark-resistance layer 8. That is, the low-dark-resistance single crystal plate 7 functions as a transparent electrode with respect to the read red light, and the high-dark-resistance layer 8 performs the same operation as the conventional single-crystal plate 1. Therefore, in the thin-film optical image element used in the present invention,
The physical strength required for the device can be ensured by increasing the thickness of the low-dark-resistance single-crystal plate 7 and increasing the resolution by improving the high-dark-resistance layer 8 to a thin film having a thickness of 100 μm or less.

First, the reason why the present invention provided with the low dark resistance single crystal plate 7 can be erased only by the applied voltage will be described.

Since the low-dark-resistance single crystal plate 7 and the high-dark-resistance layer 8 are composed of crystals having the same kind of crystal structure, the band structure related to electric conduction also has the same kind of structure. Therefore, when the power supply 4 is removed and the transparent electrodes 3 are short-circuited, the high dark resistance layer 8 corresponding to the image is formed.
The direction of the electric field generated by the positive charge distribution formed near the interface between the substrate and the insulating layer 2 is opposite to the electric field at the time of image writing. Layer 8
Electrons are easily injected into the positive charge distribution to neutralize the positive charge distribution and return to a uniform potential distribution state. That is, when erasing the written image, the purpose can be achieved only by operating the applied voltage without irradiating uniform blue light unlike the element of the conventional example.

Next, a method of manufacturing the thin-film optical image element of the present invention including the low dark resistance single crystal 7 will be described.

Conventionally, a crystal having a low dark resistivity and a silenate type structure that can be used as the low dark resistance single crystal plate 7 of the present invention has not been known. The inventors of the present invention have studied various methods for lowering the dark resistivity, and found that P (phosphorus)
It was found that the addition of a small amount significantly reduced the dark resistivity of the silenate type crystal. FIG. 4 is a characteristic diagram showing the relationship between the P concentration in the crystal of the low-dark-resistance single crystal plate 7 and the dark resistivity according to the present invention.
P-added Bi ₁₂ SiO ₂₀ grown by Czochralski method using 50 mmφ platinum in a crucible using i ₂ O ₃ , BiPO ₄ and SiO ₂
It is an experimental result in a single crystal.

As is clear from the experimental results shown in the same figure, the dark resistivity of the Bi ₁₂ SiO ₂₀ single crystal is from P (phosphorus) concentration of 0.03 atm% to 0.2 atm% ｛a.
tm% = (P atoms / total number of atoms) in the range of × 100%} indicates 1/10 ⁷ times the value of the additive-free crystals, Bi ₁₂ SiO ₂₀ single crystal containing P in this concentration range Can be used as the low dark resistance single crystal plate 7 of the present invention. This P-added crystal
A patent application has already been filed by the present inventor on the low dark resistance single crystal plate 7 sliced to a thickness of 300 to 500 μm (Japanese Patent Laid-Open No. 62-17099).
A method of epitaxially growing a Bi-containing oxide thin film by vapor phase growth using metal Bi or alkylated Bi which has been subjected to (No.) as a raw material, an undoped Bi ₁₂ SiO ₂₀ epitaxial layer is used as the high dark resistance layer 8 of the present invention. It grows about 10 μm. Furthermore, the insulating layer 2 of the present invention is provided on the side of the high dark resistance layer 8.
As an insulating layer of parylene, mica, or the like, or a composition range of 30 ≦ TiO ₂ ≦ 70, 10 ≦ Bi ₂ O ₃ ≦ 40, 10 for which a patent application (Japanese Patent Application No. 63-82834) has already been filed by the present inventor. ≤S
iO ₂ ≦ 50 (However, the unit is TiO ₂ +1/2 Bi ₂ O ₃ + Si in mol%
O ₂ = 100) TiO ₂ —Bi ₂ O ₃ —SiO ₂ -based insulating film for high-voltage driving elements and the like are deposited and an ITO film (In ₂ O ₃
-SnO ₂ based film) or the like can be a thin film type light image device according to the present invention by depositing on both sides.

As described above, the thin-film optical image element used in the present invention is:
Since it has a structure in which the low dark resistance single crystal plate 7 and the high dark resistance layer 8 are arranged, the resolution is good and erasing can be performed only by a voltage application operation. Further, in the present invention, the thin-film optical image element described in detail (Japanese Patent Application No. 1-41616) is improved to make the resolution and the writing sensitivity uniform in the element surface.

(Example) Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 5 is a structural view of a thin-film type optical image element according to the present invention, in which a low-dark-resistance single crystal plate 7 having a silenate-type crystal structure in which P is added to greatly reduce the dark resistivity is formed into a tapered low-dark single crystal plate. This is a resistance single crystal plate 7a.

That is, in the element of the conventional example, the single crystal plate 1 having a high dark resistivity is used.
Is a tapered shape in order to remove interference fringes due to multiple reflection, but in the present invention, the low dark resistance single crystal plate 7 having a low dark resistivity of the thin film type optical image element previously applied is tapered. is there. Incidentally, when the refractive index of the low dark resistance single crystal plate 7a (n ₇₎ and the refractive index of the high dark resistance layer 8 (n ₈₎ are largely different, multiple reflections inside the high dark resistance layer 8 of uniform thickness Causes interference fringes. However, Bi ₁₂ MO ₂₀ (where M = Si, Ge, T
i) and the refractive index of Shireneto type crystal such as P added Bi ₁₂ MO _20, since the range of about 2.2 to 2.6, multiple reflection is not a problem.

The taper angle δ is obtained by calculating the sum of the thickness (average value) of the center of the low dark resistance single crystal plate 7a and the thickness of the high dark resistance layer 8 as the center thickness d.
As in the conventional example, it can be obtained from Expressions (1) and (2).

By applying a configuration in which a low-dark-resistivity single-crystal plate 7a having a low-dark-resistivity and a high-dark-resistivity layer 8 having a high-dark-resistivity is combined with the power supply 4 between the transparent electrodes 3, as in the present invention. The applied voltage is almost divided by the insulating layer 2 and the high dark resistance layer 8 because the resistivity of the low dark resistance single crystal plate 7a is much smaller than that of the insulating layer 2 and the high dark resistance layer 8. Therefore, in the thin-film optical image element according to the present invention, the low-dark-resistance single crystal plate 7a acts as a transparent electrode for the read-out red light, removes interference fringes by multiple reflections, and Is applied uniformly, and a charge distribution corresponding to the written image is formed inside similarly to the single crystal plate 1 of the conventional example, so that the image writing sensitivity and the resolution can be made uniform within the element surface. .

As the low dark resistance single crystal plate 7a and the high dark resistance layer 8, in addition to _{Bi 12 GeO 20, Bi 12 TiO} 20 , etc. Other Shireneto type crystal of Bi ₁₂ SiO ₂₀ it can also be applied. Further, it is not necessary that the low dark resistance single crystal plate 7a and the high dark resistance layer 8 have exactly the same composition, and as long as the refractive indices are substantially the same, the composition may be different between materials of the same kind of crystal structure. .

When producing the tapered low-dark-resistance single crystal plate 7a, a pentavalent element such as Sb (antimony) or Nb (niobium) may be used instead of P (phosphorus).

(Effects of the Invention) As described in detail above, the present invention relates to a method of forming a crystal of Bi ₁₂ MO ₂₀ (M = Si, Ge, Ti) or the like having a silenate type crystal structure.
A low dark resistance is provided on the incident light side of a tapered low dark resistance single crystal plate 7a in which P is added in the range of 0.03 ≦ P ≦ 0.2 in m% so that the dark resistivity is significantly smaller than that of the non-doped crystal. By providing a high dark resistance layer 8 having the same kind of crystal structure as the single crystal plate 7a and having both a photoconductive effect, an electro-optical effect and a high dark resistivity, the writing sensitivity and resolution of an image can be made uniform within the element surface. It becomes possible to.

When the high dark resistance layer 8 is made of Bi ₁₂ MO ₂₀ (where M = Si, Ge, Ti), the photoconductive effect, the electro-optical effect, and the high dark resistivity can be provided together.

By forming the low-dark-resistance single-crystal plate 7a from a crystal in which a pentavalent element is added to Bi ₁₂ MO ₂₀ , a single-crystal plate having a low dark-resistivity sileneate-type crystal structure can be realized.

When the pentavalent element is at least one of P (phosphorus), Sb (antimony), and Nb (niobium), the dark resistivity of a single crystal plate having a silenate-type crystal structure can be reduced.

The low-dark-resistance single crystal plate 7a adds P (phosphorus) to Bi ₂ MO ₂₀ by 0.03.
By doping in a concentration range of 0.2 atm% or less, a single crystal plate having a silenate-type crystal structure in which the dark resistivity is significantly reduced can be realized.

Therefore, the thin-film optical image element according to the present invention can be widely applied to optical information processing fields such as conversion from an incoherent image to a coherent image, spatial frequency filtering, and optical logic operation, and the effect is extremely large. is there.

[Brief description of the drawings]

1 (a) and 1 (b) are structural views of a conventional symmetrical element and asymmetrical element, FIG. 2 is a structural view of a conventional optical image element in which a single crystal plate 1 is tapered, and FIG. FIG. 4 is a structural diagram of a thin-film optical image element for explaining the principle of the present invention. FIG. 4 is a characteristic diagram of P (phosphorus) concentration and dark resistivity of a low dark resistance single crystal plate used in the present invention. FIG. 5 is a configuration diagram of the thin-film optical image element according to the present invention. 1 ... single crystal plate, 2 ... insulating layer, 3 ... transparent electrode, 4 ...
… Power supply, 5… polarizer, 6… analyzer, 7… low dark resistance single crystal plate, 7a… tapered low dark resistance single crystal plate, 8…
High dark resistance layer.

Claims (4)

(57) [Claims] 1. An optical image device for writing an incident optical image by using a photoconductive effect and an electro-optical effect of a single crystal plate having a silenate type crystal structure, wherein Bi ₁₂ MO ₂₀ (where M = Si , Ge, Ti) in a state where the photoconductive effect is occurring in a state where no Bi is added to the Bi ₁₂ MO ₂₀ (however, M
= Si, Ge, Ti) and a low-dark-resistance single-crystal plate having a tapered shape and comprising a crystal obtained by adding a pentavalent element to the pentavalent element; A high dark resistance layer having the same kind of crystal structure as the dark resistance single crystal plate and having a high dark resistivity and uniform thickness capable of achieving lattice matching by crystal growth; and a high dark resistance layer provided on the other end side of the high dark resistance layer. And a transparent electrode for applying a voltage to the low-dark-resistance single crystal plate and the high-dark-resistance layer. 2. The high dark resistance layer is made of Bi ₁₂ MO ₂₀ (where M =
2. The thin-film optical image device according to claim 1, wherein the device is made of Si, Ge, Ti). 3. The thin-film optical image according to claim 1, wherein said pentavalent element is at least one of P (phosphorus), Sb (antimony), and Nb (niobium). element. 4. The low dark resistance single crystal plate is formed by doping the Bi ₁₂ MO ₂₀ with the P (phosphorus) in a concentration range of 0.03 to 0.2 atm%. 2. The thin-film optical image element according to claim 1.