JP2759477B2 - Electrically erasable optical image element - Google Patents

Description

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

(Prior Art) For example, as shown in FIG. 1, a single crystal plate 1 having a silenate type crystal structure such as Bi ₁₂ MO ₂₀ (M = Si, Ge, Ti) having both a photoconductive effect and an electro-optical effect. An element comprising an insulating layer 2 provided on at least one side surface thereof, and a transparent electrode 3 provided on the side surface thereof for applying an electric field to the single crystal plate 1 and the insulating layer 2 is conventionally known. ing. 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 operation principle of this element is as follows.

First, a voltage is applied to the transparent electrode 3 by the power supply 4. In this state, when an image of blue light is formed on the single crystal plate 1, the single crystal plate 1 has a photoconductive effect, so that electrons and holes excited according to the light intensity are parallel to the incident light and In the symmetrical device shown in FIG. 3A, the positive charge distribution is separated from the vicinity of the interface 1 between the single crystal plate 1 and the insulating film 2 and the negative charge distribution corresponding to the image is formed near the interface 2 in the symmetrical device shown in FIG. On the other hand, in the asymmetric device shown in FIG.
Only a positive charge distribution is formed in the vicinity corresponding to the image formation.
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 the input of an image is performed by using incoherent light and the reproduction is performed by using coherent light such as a laser, conversion from an incoherent image to a coherent image can be performed in real time.

Next, the principle of erasing the written image will be described.
It is considered that the charge distribution formed corresponding to the input image is such that electrons or holes are trapped at the track level, and the trapped charge is easily formed even in the presence of an electric field in the direction opposite to that at the time of writing. Do not move to So, first, power supply 4
And short circuit between the transparent electrodes 3. In this state, when the single crystal plate 1 is irradiated with uniform blue light, electrons and holes, including those trapped in the trap, are excited, and move so as to relax the electric field generated by the charge distribution. To neutralize. That is, the potential distribution in the single crystal plate 1 is returned to a uniform initial state.

(Problems to be Solved by the Invention) As is apparent from the above-described operation principle, in the conventional device, the written image cannot be erased without irradiating uniform blue light simultaneously with the operation of the applied voltage. In this case, there is a disadvantage that the peripheral optical system becomes complicated.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above-described problems of the related art, and has as its object to provide an electrically erasable optical image element capable of erasing in an extremely short time only by operating an applied voltage.

(Means for Solving the Problems) A feature of the present invention is an optical image element which performs writing of an incident optical image using a photoconductive effect and an electro-optical effect of a single crystal plate having a silenate type crystal structure. An insulating layer disposed on the incident side of the single crystal plate, and having the same kind of crystal structure as the single crystal plate directly on part of the single crystal plate on the emission side or outside the single crystal plate, and crystal growth The other ends of the low-dark-resistance layer and the insulating layer and the low-dark-resistance layer, each of which is formed into a semiconductor by adding a pentavalent element P in a concentration range of 0.03 atm% or more and 0.2 atm% or less to the growth layer capable of achieving lattice matching with the above, And the transparent electrode provided in the above.

Embodiment 1 FIG. 2 is a structural diagram of a first embodiment according to the present invention.
What differs from the conventional example is that the single crystal plate 1 has a lattice matching with the surface on the side of the emitted light with the same kind of crystal structure as that of the single crystal plate 1, and a small amount of P (phosphorus) is added to greatly reduce the dark resistivity. This is the point that the low dark resistance layer 7 made into a semiconductor as described above is provided.

The inventor of the present application has studied various methods for obtaining a low dark resistance layer 7 having a low dark resistivity used in the present invention, since a conventional crystal having a silenate structure has a high dark resistivity. As a result, 5
It has been found that the dark resistivity of the silenate type crystal can be reduced by adding a small amount of the chemical element P (phosphorus).

FIG. 3 is a characteristic diagram showing the relationship between the P concentration in the crystal of the low dark resistance layer 7 and the low dark resistivity according to the present invention. As an example, each of the raw materials contains 99.9999% pure Bi ₂ O ₃ , BiPO ₄ and SiO 2. ₂ , in the crucible
P grown by Czochralski method using 50mmφ platinum
Added a Bi ₁₂ SiO ₂₀ experimental results in the 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 0.03 atm% to 0.2 atm% in P (phosphorus) concentration.
It indicates 1/10 ⁷ times the value of the additive-free crystals in the range of {(P atoms / total number of atoms) × 100%}. Therefore, a Bi ₁₂ SiO ₂₀ single crystal containing P in this concentration range can be used as a newly formed low dark resistance layer 7 outside (single side) the single crystal plate 1. As a method for manufacturing a low dark resistance layer 7, the BiSiO ₂₀ single-crystal thin film with the addition of P in the concentration range of above example, already patent application by the present inventors (JP 62-
No. 17099) Metal Bi or alkylated Bi
May be used as a raw material to grow a Bi-containing oxide thin film by an epitaxial growth method by vapor phase growth.

By providing a configuration in which a low dark resistance layer 7 is newly provided outside (emission side) of the single crystal plate 1 as in the present invention, the voltage applied between the transparent electrodes 3 by the power supply 4 can be reduced. Since the resistivity of the low dark resistance layer 7 is much smaller than that of the insulating layer 2 and the single crystal plate 1, the low dark resistance layer 7 is converted into a semiconductor. Therefore, the low dark resistance layer 7 functions as a transparent electrode for the read red light, and can write and read an image according to the same operation principle as that of the conventional element.

Next, the erasure of the written image in the optical image element of the present invention will be described.

Since the single crystal plate 1 and the low dark resistance layer 7 are composed of crystals having the same kind of structure, the band structures related to electric conduction also have the same kind of structure. Therefore, when the power supply 4 is removed and the transparent electrodes 3 are short-circuited, the direction of the electric field generated by the positive charge distribution formed near the interface between the single crystal plate 1 and the insulating film 2 corresponding to the image is different from the electric field at the time of image writing. Is reversed, electrons are easily injected from the low dark resistance layer 7 having a large free carrier concentration into the single crystal plate 1 to neutralize this positive charge distribution and return to a uniform potential distribution state. Can be.

As described above, according to the present invention, when erasing a written image, the object can be achieved only by operating the applied voltage without irradiating uniform blue light unlike the element of the conventional example.

In the above description, Bi ₁₂ SiO ₂₀ is used as the low dark resistance layer 7.
, But without being limited thereto, Bi ₁₂ GeO ₂₀ , Bi
_It can be applied to other silate-type crystals such as ₁₂ TiO ₂₀ . Further, the same kind of material may have a different composition such as Bi ₁₂ Si _{1 + X} O ₂₀ (−0.3 ≦ X ≦ + 0.1).

Embodiment 2 FIG. 4 shows a second embodiment of the present invention, and is a configuration diagram of an electric erasure type optical image element.

The difference from the first embodiment is that 0.03 atm% to 0.2 atm% of P is added to the single crystal plate 1 by using a technique such as a thermal diffusion method or an ion implantation method, and a part of the single crystal plate 1 on the emission light side is added. The difference is that a low dark resistance layer 8 whose dark resistivity is significantly smaller than that of the other single crystal plate 1 is formed. That is, the first embodiment
In the second embodiment, a low dark resistance layer 7 is newly provided on the outside (outgoing side) of the single crystal plate 1. On the other hand, in the second embodiment, a part of the single crystal plate 1, such as diffusion or ion implantation, is formed. The structure is simplified by providing a low dark resistance layer 8 by technology.

In the electrically erasable optical image device having this structure, as in the device having the structure of Example 1, most of the applied voltage is applied to the single crystal plate 1.
And the insulating layer 2, and the low dark resistance layer 8 acts as a transparent electrode for readout light. Further, since the low dark resistance layer 8 has the same crystal structure as the single crystal plate 1, it is clear that the written image can be erased according to the principle described in the first embodiment. That is, the written image can be erased only by operating the applied voltage without irradiating uniform blue light unlike the element of the conventional example.

(Effects of the Invention) As described in detail above, the present invention has the same kind of crystal structure as the single crystal plate on a part or outside of the exit side in the single crystal plate 1 and can achieve lattice matching by crystal growth. 5 for growth layer
By providing a low-resistivity low-dark-resistance layer 8 (7) which is made into a semiconductor by adding a valence element P in a concentration range of 0.03 to 0.2 atm%, erasing can be performed only by applying an applied voltage.

By forming the single crystal plate 1 from Bi ₁₂ MO ₂₀ (where M = Si, Ge, Ti), a crystal having both the photoconductive effect, the electro-optical effect, and the high dark resistivity can be obtained.

By forming the low dark resistance layer 8 by diffusing or ion-implanting the pentavalent element P into a part of the exit side of the single crystal plate 1, the structure is simple and can be erased only by operating the applied voltage. An electric erasing optical image element can be realized.

By forming the low dark resistance layer 7 with a growth layer obtained by adding a pentavalent element P to Bi ₁₂ MO ₂₀ , an electric erasing optical image element that can be erased only by operating an applied voltage can be realized.

Therefore, since the electric erasing type optical erasing optical image element according to the present invention can be erased only by applying an applied voltage, the field of optical information processing such as conversion from an incoherent image to a coherent image, spatial frequency filtering or optical logic operation. Can be widely applied, and the effect is extremely large.

[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 cross-sectional view showing a structure of an electro-erasable optical image element of a first embodiment according to the present invention, FIG. 3 is a characteristic diagram of the P (phosphorus) concentration and the dark resistivity of the low dark resistance layer used in the present invention, and FIG. 4 is a cross-section showing the structure of the electric erase type optical image element of the second embodiment according to the present invention. FIG. DESCRIPTION OF SYMBOLS 1 ... Single crystal plate, 2 ... Insulating layer, 3 ... Transparent electrode, 4 ... Power supply, 5 ... Polarizer, 6 ... Analyzer, 7,8 ... Low dark resistance layer.

 ────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-53-46047 (JP, A) JP-A-52-141245 (JP, A) JP-A-57-208525 (JP, A) Phys. Status Solid A, Vol. 96, No. 1, (1986), PP. 199-210

Claims (4)

(57) [Claims] 1. An optical image element for writing an incident optical image using a photoconductive effect and an electro-optical effect of a single crystal plate having a silenate type crystal structure, wherein the optical image device is disposed on the incident side of the single crystal plate. And a growth layer having the same kind of crystal structure as the single crystal plate directly on a part of the single crystal plate on the emission side or outside the single crystal plate and capable of achieving lattice matching by crystal growth. Pentavalent element P to 0.03
a low dark resistance layer doped into a semiconductor in a concentration range of atm% or more and 0.2 atm% or less, and transparent electrodes provided on the other end sides of the insulating layer and the low dark resistance layer, respectively. Characteristic electric erasure type optical image element. 2. The method according to claim 1, wherein the single crystal plate is Bi ₁₂ MO ₂₀ (where M = S
2. The electrically erasable optical image element according to claim 1, wherein the element is composed of (i, Ge, Ti). 3. The low dark resistance layer is formed by diffusing or ion-implanting a pentavalent element P into a part of the exit side of the single crystal plate. The electrically erasable optical image element according to the above. 4. The electric erasing light according to claim 1, wherein said low dark resistance layer comprises a growth layer obtained by adding a pentavalent element P to said Bi ₁₂ MO _20. Image element.