JPH02145399A - Ferro-dielectric polymer optical memory - Google Patents

Abstract

PURPOSE:To prevent thermal diffusion in an electrode layer and to make the thicknesswise temperature of a recording layer uniform by so providing a gap at the electrode of incident side that part of incident light is absorbed at the incident side electrode and the remainder is absorbed at the other electrode. CONSTITUTION:In an optical memory of the type for absorbing light to an electrode layer, the electrode layer of the incident light side is formed of flat plates distributed with gaps or aligned with slender flat plates via gaps to absorb part of the incident light to the other electrode layer through the electrode layer of incident light side. Since the light of suitable ratio of the incident light is not absorbed by the electrode, but passed and absorbed by the electrode layer of opposite side, the recording layer can be uniformly heated from both sides, and S/N ratio for writing and reading information is improved. Since the thermal diffusion in the electrode layer can be suppressed, its recording density can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ferroelectric polymer optical memory useful for optical memory cards, optical disks, and the like.

[Prior art] Polymer optical memory using PVD polymer as a recording medium is
Already known.

This is a revolutionary optical memory that utilizes the ferroelectric properties of PVD polymers, and its recording principle is based on Japanese Patent Application Laid-Open No. 59-21509.
8 and No. 59-215097, or IEEE
Trans, Elcctr, Ins, El-21 (
3), 539 (198B), Polymer Processing 35.418 (
1981i), utilizing the property of ferroelectric polymer materials to be polarized by an electric field, applying a high electric field to the ferroelectric polymer materials to polarize them in one direction, Enables writing by irradiating and heating an arbitrary part with a light beam while applying a weak reverse electric field less than the coercive electric field and selectively inverting the polarization of only the light irradiated part,
Furthermore, it can be read using the pyroelectric effect caused by light or heat.

In this optical memory, it is necessary to place electrode layers above and below the layer consisting of the recording medium in order to apply an electric field and detect the pyroelectric effect, but the heat generated by light beam irradiation is easily absorbed within the electrode layer. Because it is diffused, the recording density and S/N
The problem was that the ratio decreased.

[Problem to be solved by the invention]

Another problem was that the recording layer was not heated uniformly in the thickness direction of the recording layer.

As described above, in this optical memory, writing and reading are performed by heating the recording layer by irradiating it with a light beam, and at this time, it is desirable that the temperature distribution be as uniform as possible in the thickness direction of the recording layer. Methods of heating the recording layer with incident light include a method of mixing a light absorbent into the recording layer to absorb light, a method of providing a light absorbing layer inside the recording layer or in contact with the recording layer, and a method of heating the recording layer with light on the electrode layer. There are methods to absorb light, such as: ∎ In the case of a method in which a light absorber is mixed in the recording layer to absorb light, when the light absorber is mixed uniformly, the amount of attenuation of light within the recording layer is Unless it is sufficiently small, the incident light side will be hotter than the opposite side.

It is extremely difficult and impractical to adjust the temperature distribution in the thickness direction of the recording layer to be -like by changing the concentration of the light absorbent in the thickness direction of the recording layer.

■ In the case of a method in which a light absorption layer is provided inside or in contact with the recording layer, multiple light absorption layers are arranged within the recording layer or in contact with the recording layer, and the ratio of light absorption among them is adjusted. If this is done, it is possible to make the temperature distribution in the thickness direction of the recording layer approximate to a - shape, but if there is only one light absorption layer, the temperature distribution in the thickness direction of the recording layer can be made to approximate a - shape. It cannot be made into any shape.

(2) In the case of a method in which the electrode layer absorbs light, unless the electrode on the incident light side is transparent or translucent, the side of the recording layer closer to the electrode on the incident light side will be hotter than the other side. When the electrode on the incident light side is transparent or slightly opaque, the side of the recording layer closer to the electrode on the side opposite to the incident light side becomes hotter. If the opacity of the electrode on the incident light side is appropriate and the electrodes on both sides absorb light equally, the temperature distribution in the thickness direction of the recording layer can be shaped like -, but this is not the case for this optical memory. There are no such electrodes among the materials that have desirable properties as electrodes.

Among the methods (1), (2), and (2) above, method (2) has the advantage that the structure is simple and there are no problems associated with the light absorbing agent or light absorbing layer. The present invention provides a ferroelectric polymer optical memory that can prevent thermal diffusion within the electrode layer and make the temperature of the recording layer uniform in the thickness direction when using the method (2) above. The purpose is to

[Means for Solving the Problems] In order to solve the above problems, the present inventors have conducted extensive research and found that the structure of the electrode layer should not be a --like flat plate, but that a gap should be provided between the electrode layers. found to be effective,
This led to the present invention.

That is, the present invention provides an optical memory in which a recording layer made of a ferroelectric polymer film and an electrode layer sandwiching the recording layer are held on a substrate, in which part of the incident light is absorbed by the electrode on the incident light side. The ferroelectric polymer optical memory is characterized in that at least one of the two electrode layers on the incident light side has a gap so that the remaining portion is absorbed by the other electrode.

The configuration of the present invention will be explained below based on the drawings.

FIG. 1 is a structural model diagram of a ferroelectric polymer optical memory. 1 in this figure is a recording layer made of a PVD polymer. 2 is an upper electrode, and 3 is a lower electrode. 4 is a substrate supporting the lower electrode. Laser light is irradiated from the substrate side or the upper electrode side.

``(Note) The expressions ``upper'' and ``lower'' correspond to cases where the board is used with the board facing down. However, the present invention can be used with the substrate facing up or tilted diagonally. ] As described above, in this optical memory, writing and reading are performed by heating the recording layer by irradiating it with a light beam. The method of heating the recording layer with incident light is as follows:
There are methods such as mixing a light absorbent into the recording layer to absorb light, providing a light absorbing layer inside the recording layer or in contact with the recording layer, and making an electrode layer absorb light. Among these, it is applied to those in which the electrode layer absorbs light.

When the electrode layer absorbs light, if the electrode is opaque, the electrode on the incident light side generates heat. If a transparent electrode is used as the electrode on the incident light side and an opaque electrode is used as the electrode on the opposite side, the opaque electrode generates heat. In either case, only one of the two electrodes generates heat. For this reason, the temperature distribution within the recording layer is not uniform in the thickness direction of the recording layer, and the portion close to the electrode generating heat becomes hotter than the portion close to the other electrode. To solve this problem, the ratio between the amount of light absorbed by the electrode on the incident light side and the amount of light passing through should be set to an appropriate value in some way so that the electrodes on both sides generate heat equally. . However, it is difficult to adjust the opacity of the electrode on the incident light side to an appropriate value by changing the material or thickness of the electrode because it may cause undesirable side effects.

Furthermore, since the thermal conductivity of the material used as the electrode layer is very high, a considerable portion of the heat generated by absorption of light in the electrode layer rapidly diffuses within the electrode, causing the temperature of the recording layer to rise. There is a problem in that the increase in recording density is impaired and the high temperature region unnecessarily expands, resulting in a decrease in recording density.

The present inventors did not make the electrode layer on the incident light side a uniform flat plate,
Either use a flat plate with distributed gaps, or arrange elongated flat plates with gaps so that part of the incident light passes through the electrode layer on the incident light side and is absorbed by the other electrode layer. We have found that the above problem can be solved by doing this. (Figures 2, 3, and 4) At this time, the electrode layer on the side opposite to the incident light may be a flat plate with a uniform thickness, but it has gaps like the electrode layer on the incident light side. A flat plate is preferable from the viewpoint of reducing thermal diffusion within the electrode layer.

In the latter case, it is better to arrange the electrodes so that the overlapping parts of both sides are evenly and densely distributed when viewed from above or below so that the electric field between the picture electrode layers is perpendicular to the recording layer surface. preferable. For example, when the electrode layers on both sides are arranged in the form of long and thin flat plates, it is preferable that the flat plates on both sides form a right angle or an angle close to a right angle. In addition, in order to prevent the ratio of the amount of light absorbed by the lower electrode layer and the amount of light passing through the lower electrode layer from changing significantly depending on the irradiation position of the light, it is necessary to It is desirable that the gaps in the electrode layer be created so that the number of gaps in the electrode layer is approximately the same, and the gaps in the electrode layer are uniformly distributed at small intervals. For example, in the case of electrodes made of elongated flat plates as shown in Figures 2 and 5, it is desirable that the distance between the plates (Ll+L2) be less than or equal to the e-1 radius of the incident light beam, and even shorter. It is more desirable if the number of flat plates falling within the e-+ radius is further increased. In addition, the ratio of the width of the plate to the width of the gap (Ll/L2) is set to a value that allows the incident light to be absorbed equally by both the upper and lower electrodes, taking into account the light absorption rate of the electrode and recording layer material. It is necessary to keep it. The values of Ll and L2 that satisfy these conditions are 6-
1 Radius is 3μ Garden 1 Light absorption rate of recording layer is 01 All the light that hits the lower electrode is absorbed by the lower electrode, and the plate width of the upper electrode and the gap width are equal, then L+ = 0.1μ
m, L2-0.2μ can be cited as an example. In addition, in the case of an electrode with many holes as shown in FIGS. 3 and 4, the size of the holes is determined by the e of the incident light beam.
4 radius is sufficiently small that it cannot be completely contained within it, and the spacing between the holes is such that a circle with radius e-1 of the incident light beam does not touch any of the holes. It is desirable that it be small enough so that there is no damage (Figure 6).

Methods for making such electrode layers include gold, platinum, silver,
Vapor deposition and CVD of various metals such as copper, lead, zinc, aluminum, nickel, tantalum, titanium, cobalt, niobium, palladium, and tin.

Examples include a method of forming a film by sputtering or the like and processing it into a stripe shape, mesh shape, etc. using an ion beam or an electron beam or by etching, etc., but the present invention particularly focuses on these electrode materials and electrode layer forming methods. It is not limited to.

Next, the portions other than the electrode layer will be described.

Various compounds have been reported for the PVDM polymer constituting the recording layer1, but in this recording medium, it is desirable to use one that has ferroelectricity and exhibits a rectangular shape when measured with dielectric hysteresis. vinylidene homopolymer,
And 50ff of vinylidene fluoride! It is a vinylidene fluoride copolymer containing ffi% or more. Examples of the copolymer include copolymers of vinylidene fluoride and ethylene trifluoride, propylene hexafluoride, ethylene trifluoride chloride, and the like. Also included are polyvinylidene cyanide, vinylidene cyanide, and vinyl acetate copolymers, but among these, vinylidene fluoride and ethylene trifluoride copolymer [hereinafter abbreviated as P (VDF-TrFE)] is the most preferred. .

The PVD polymer film of the recording layer can be formed by a solution coating method such as dip coating, spray coating, spinner coating, blade coating, roller coating, or curtain coating. Among these methods, dip coating or spinner coating is preferable because the PVD polymer film can be formed to a uniform thickness and an ultra-thin film can be obtained.

Support materials for the electrode include polyethylene, polyethylene terephthalate, polypropylene, polystyrene, polyvinyl chloride, polycarbonate, polyvinyl alcohol, polyvinyl acetate, polyamide, polyimide,
Various plastics such as polyolefin, acrylic resin, phenol resin, epoxy resin, and the above derivatives, glass, quartz plates, ceramics, etc. are suitable, but it is desirable that they are transparent to irradiated light, and that they are insulated from the electrodes. Although it is preferable that the electrodes also serve as electrodes, the present invention is not particularly limited thereto.

The irradiation light source is a semiconductor laser (LD) in terms of mass production and cost.
) is considered optimal. The direction of irradiation of the LD light may be from either the upper or lower electrode side.

In addition to this, a protective layer can be further provided on the electrode layer if necessary. This protective layer is formed from various polymeric materials for the purpose of protecting the upper electrode layer and the recording layer.

[Example] Next, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples.

Example: On a polystyrene substrate with a thickness of about 1+es, chromium was vapor-deposited as a lower electrode to a thickness of 0.1μ, and then the lower electrode was formed into stripes of 0.5μ- width arranged at 1.0μ-intervals. processed. A P (VDF-Tr-FE) film was applied thereon to a thickness of 1.0 μm to form a recording layer. Furthermore, after evaporating chromium to a thickness of 0.1 μm as an upper electrode on top of this, a width of 1.0 μm is applied in a direction perpendicular to the stripes of the lower electrode.
0 μ-stripe 1. It was processed into a shape arranged at 0 μm intervals.

Furthermore, a polyethylene film with a thickness of 0.0 mm is applied as a protective layer on top of this.
It was applied at 5 m. Then, the P (VDF-TrFE)
The membrane was subjected to poling treatment by applying a voltage of 100V. Furthermore, while applying a reverse electric field of 25V, the oscillation wavelength was 83V.
Using a 0n- semiconductor laser (hereinafter abbreviated as LD), an intensity of 6. Omw.

Information was recorded by heating the picture electrode layer by irradiating a Gaussian beam with e-1 radius of 6.0 μm for 40 μs. After that, reduce the LD light intensity to 0.16 mV and
While chopping with the LD light, the recording layer was heated again by LD light, the pyroelectric current generated between the electrodes was measured, and the recorded information was read out, and the S/N ratio was 45 dB.
The size of the recorded region (region where the polarization was reversed) was 3.5 μm in diameter.

Comparative Example On a polystyrene substrate with a thickness of about 1, chromium was deposited as a lower electrode to a thickness of 0.1μI, and P (VD
A recording layer was formed by applying an F-TrFE film to a thickness of 1.0 μm. Furthermore, chromium was vapor-deposited thereon to a thickness of 0.1 μm as an upper electrode, and a polyethylene film was further applied thereon to a thickness of 0.51 μm as a protective layer. Then, the P
A voltage of 100 V was applied to the (VDF-TrFE) film to perform poling treatment. Furthermore, while applying a reverse electric field of 25 V, a semiconductor laser (hereinafter referred to as L) with an oscillation wavelength of 830 ns was applied.
Strength 6. Osw.

Information was recorded by heating the picture electrode layer by irradiating it with a Gaussian beam of radius e and oμm for 600 μS.

After that, reduce the LD light intensity to 0.18mV to 10kll.
While chopping with z, we irradiated the recording layer with light again to heat the recording layer, measured the pyroelectric current generated between the electrodes, and read out the recorded information, and found that the S/N ratio was 35 dB.
The size of the recorded region (region where the polarization was reversed) was 1010 μm in diameter.

[Effect of the invention] Since the electrode layer on the side where the irradiated light enters has a structure with minute gaps, a suitable proportion of the incident light passes through the electrode layer without being absorbed by the electrode layer and reaches the opposite side. Since the energy is absorbed by the electrode layer, the recording layer sandwiched between them can be heated evenly from both sides, improving the S/N ratio when reading and writing information. Furthermore, compared to the case where the electrode layer is made of a flat plate having a uniform thickness, thermal diffusion within the electrode layer can be suppressed, so that the recording density can be increased.

[Brief explanation of the drawing]

FIG. 1 is a structural model diagram of a ferroelectric polymer optical memory, and FIGS. 2 to 5 are diagrams showing the relationship with the ferroelectric polymer optical memo beam of the present invention. 1... Recording layer, 2... Upper electrode, 3... Lower electrode, 4... Substrate. Figure 5 Figure 3 Figure 2 Figure 4

Claims (1)

[Claims] In an optical memory in which a recording layer made of a ferroelectric polymer film and an electrode layer sandwiching the recording layer are held on a substrate, part of the incident light is absorbed by the electrode on the incident light side, and the remainder is absorbed by the other electrode. 1. A ferroelectric polymer optical memory characterized in that at least one of the two electrode layers on the side of incident light has a gap so that light is absorbed by the incident light.