JPH0224852A - Ferroelectric polymer optical memory - Google Patents

Abstract

PURPOSE:To speed up the response of recording, reproducing and erasing operations by providing a layer consisting of a material having the thermal conductivity smaller than the thermal conductivity of a substrate between the substrate and an electrode layer in contact with the substrate. CONSTITUTION:The recording layer 1 consisting of a ferroelectric high-polymer film is crimped by the upper electrode 2 and the lower electrode 3 and further, the lower electrode 3 is held on the substrate 5 via a heat insulating layer 4, by which the optical memory is constituted. The diffusion of the heat generated in the recording layer 1 by irradiation light is decreased in such a manner, by which the recording sensitivity is increased and the response of the recording, reproducing and erasing operations are speeded up.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention relates to a ferroelectric polymer optical memory using a vinylidene polymer (hereinafter referred to as PVD polymer) as a recording layer, and relates to an optical memory card. It can also be applied to optical discs, etc.

[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.
6 and No. 59-215097, or IIEI
EE Trans, Electr, Ins, El-
21(3), 539(191i6), Polymer Processing 35.
418 (198B), by utilizing the property of ferroelectric polymer materials to be polarized by an electric field, a high electric field is applied to the ferroelectric polymer materials to polarize them in one direction. By applying a weak reverse electric field below the coercive electric field, a light beam is irradiated onto an arbitrary part to heat it, selectively inverting the polarization of only the light irradiated part, thereby making writing possible. It can be read using the electric effect.

In this optical memory, the recording medium must be held on a substrate that supports it, but the generated heat easily diffuses into the substrate, which prevents the temperature of the recording layer from increasing and reduces the recording density and S/S. The problem was that the N ratio decreased.

[Problems to be Solved by the Invention] The present invention provides an optical memory that uses a ferroelectric polymer material as a recording medium by providing a heat insulating layer between an electrode layer and a substrate to prevent the thermal diffusion and improve recording performance. The aim is to increase the temperature rise rate of the layer and speed up the response of recording, reproducing, and erasing operations.

[Means for Solving the Problems] The present inventors have been conducting research in order to put the optical memory into practical use. By providing a layer made of a small material, we succeeded in reducing the amount of heat diffusion into the substrate and increasing the temperature rise rate of the recording layer.

In other words, the configuration of the present invention is such that 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, there is a gap between the substrate and the electrode layer in contact with the substrate. Another example is a ferroelectric polymer optical memory having a layer made of a material with a lower thermal conductivity than the substrate.

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

FIG. 1 is a schematic diagram of the structure of the ferroelectric polymer optical recording medium of the present invention. 1 in this figure is a portion made of a PVD polymer film which is the recording layer of the optical recording medium. 2 is an upper electrode, and 3 is a lower electrode. 4 is a heat insulating layer provided between the lower electrode and the substrate. Further, 5 is a substrate that supports the lower electrode 3.

Methods for heating the recording layer with incident light include 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,
There are methods of making the electrode layer absorb light, but the present invention is not limited to these heating methods.

Normally, the thermal conductivity of the material used as the electrode layer is very high, so a considerable part of the heat generated in the above method diffuses within the electrode layer and further into the substrate, causing the recording layer to be heated. The problem existed that the temperature rise was impaired. One way to improve this is to use a material with as low a thermal conductivity as possible for the electrode layer, but within the range of materials that have desirable properties as an electrode and are inexpensive, there is no choice. is limited. Similarly, it is desirable to use a material with as low a thermal conductivity as possible for the substrate, but there are limited choices within the range of materials that have desirable properties for the substrate. Therefore, it would be advantageous if heat conduction between the layers could be prevented by inserting a different type of substance between the recording layer and the electrode layer or between the electrode layer and the substrate.

Since the electrode layer and the recording layer must be in contact with each other, a heat insulating layer cannot be inserted between the recording layer and the electrode layer, but it is possible to insert a heat insulating layer between the lower electrode and the substrate. . The inventor of the present invention found that simply inserting a thin heat insulating layer between the lower electrode and the substrate has a large effect on preventing heat diffusion to the board, and the present inventors have discovered that inserting the heat insulating layer between the lower electrode and the substrate has a large effect on preventing heat diffusion to the board. We succeeded in increasing the rate of temperature rise in the recording layer.

The thermal conductivity of the heat insulating layer must be lower than that of the substrate. Further, it is desirable that the thermal conductivity of the heat insulating layer is as low as possible. Furthermore, in an optical memory where incident light is applied from the substrate side, it is desirable that the heat insulating layer be as transparent as possible. If glass or a plastic material with relatively high thermal conductivity is used as the substrate,
Desirable materials for the heat insulating layer include polystyrene homopolymer, styrene copolymer, polypropylene homopolymer, vinyl polymer, and vinyl copolymer. Methods for forming the heat insulating layer using these materials include immersion. coating, roller coating,
Examples include solution coating methods such as curtain coating,
The present invention is not limited to this formation method.

Next, I will describe the parts other than the heat insulating layer.

Various compounds have been reported for the PVD polymer constituting the recording layer, but in this recording medium, it is desirable to use one that has ferroelectricity and exhibits a rectangular shape when measured with dielectric hysteresis. These are vinylidene homopolymers and vinylidene fluoride copolymers containing 50% by weight or more of vinylidene fluoride. Examples of the copolymer include copolymers of vinylidene fluoride and ethylene trifluoride, propylene hexafluoride, ethylene chloride trifluoride, and the like. Also included are polyvinylidene cyanide, vinylidene cyanide and vinyl acetate copolymers, among which vinylidene fluoride and ethylene trifluoride copolymers [hereinafter abbreviated as P (VDF-TrFE)] are also 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, curtain coating, or the like. Among these, methods such as dip coating, spinner coating, and roller coating are preferable because they form a PVD polymer film with a uniform thickness and also provide an ultra-thin film.

In order for the present ferroelectric polymer recording medium to function as an optical memory, it is desirable that at least one of the electrodes sandwiching the recording layer be as transparent as possible to the irradiated light. It is preferable to employ electrodes or semi-transparent electrodes. Of course, both the lower electrode 2 and the upper electrode 3 may be transparent, or only the upper electrode 3 may be transparent.

The transparent electrode employed in the present invention is made of tin-doped indium oxide (ITO), tin oxide, evaporation of undoped indium oxide, etc., or CVD.

Examples include sputtering films, etc., and semitransparent electrodes include vapor deposition, CVD, and sputtering films of various metals such as gold, platinum, silver, copper, lead, zinc, aluminum, nickel, tantalum, titanium, cobalt, niobium, palladium, and tin. etc., but the present invention is not particularly limited to these.

Support materials for these electrodes include polyethylene, polyethylene terephthalate, polypropylene, polystyrene, polyvinyl chloride, polycarbonate, polyvinyl alcohol, polyvinyl acetate 8, polyamide, polyimide, polyolefin, acrylic resin, phenolic resin, epoxy resin, and the above. Various plastics such as dielectrics, glass, quartz plates, ceramics, etc. are suitable, but like the electrodes, it is desirable that they are transparent to irradiated light, and that they also serve as insulation from the electrodes. Similar to the electrodes, the present invention is not particularly limited to these.

The irradiation light source is a semiconductor laser (LD) for mass production and availability.
) is considered optimal. The direction of irradiation of the LD light may be from the upper or lower electrode side, but in this case, it is desirable that at least the electrode on the light source side is transparent to the irradiated light.
- Yes.

FIG. 2 shows an example in which a protective layer 6 is provided on the upper electrode 2. This protective layer protects the recording layer from scratches, dust, dirt, etc., and improves the storage stability of the recording layer. as a goal,
It is formed from various polymer materials, silane coupling agents, glass, etc.

FIG. 3 shows an example in which an undercoat layer 7 is provided on the lower surface of the recording layer 1. The undercoat layer 7 is formed by applying or vapor depositing a surface treatment agent on the surface of the lower electrode 3, and its purpose is as follows.

2) Improved contact with electrodes 2) Improved storage stability of the recording layer 3) Barrier properties against water, gas, solvents, etc. In the above, the main properties are particularly required of l. The surface treatment agents used therein include hexamethyldisilanzane (HMDS), dimethylchlorosilane (TMC),
S), dimethylchlorosilane (DMC5), dimethyldichlorosilane (DMDCS), bis(trimethylsilyl)acetamide, t-butyldimethylchlorosilane, bis(trimethylsilyl)trifluoroacetamide, trimethylsilyldiphenylurea, bistrimethylsilylurea, etc. . In addition to the above-mentioned silylating agents, titanium-based coupling agents (anchor coating agents) have also been confirmed to be effective.

FIG. 4 shows an example in which a light absorption layer 8 is provided below the recording layer l. The light absorption layer is not limited to this diagram, and may be provided on either side of the recording layer, and may form a laminated structure in a state in which it is sandwiched between the recording layer, or vice versa. It doesn't matter if you do.

EXAMPLES The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to these Examples.

EXAMPLE A polystyrene film with a thickness of 2.0 μl was coated on a glass substrate with a thickness of about 1 by the spin-coating method, and I
TO was deposited to a thickness of 500 nm. Furthermore, a P (VDF-TrFE) film in which a dye was dispersed so as to have a light absorption coefficient of 1×10 6 m' was coated thereon to a thickness of 1.0 μm by a spin code method to form a recording layer 1. After evaporating chromium to a thickness of 0.1 μm as the upper electrode of this sample, a voltage of 100 V was applied to the P (VDF-TrFE) film to perform a poling process. Furthermore, while applying a reverse electric field of 25V, the oscillation wavelength is 830rv.
Using a semiconductor laser (hereinafter abbreviated as LD), a Gaussian beam with an irradiation light intensity of 1.6 mW and an e-' radius of 2.5 μm was applied from the lower electrode side until the temperature of the center of the recording layer at the irradiation point reached 100°C. When information was recorded by heating the P (VDF-TrFE) layer, the light irradiation time required for recording was:
The time was 10.6 μs.

After that, the LD light intensity was weakened to 0.16 mW and the frequency was increased to 10 kHz.
P again while chopping with (VDF-TrFE)
When the layer was irradiated with LD light and the pyroelectric current generated between the electrodes was measured and the recorded information was read out, the size of the recorded area (the area where the polarization was reversed) was 3.3 in diameter.
It turned out to be μ■.

Comparative Example When information was recorded in the same manner as in the example in an optical memory without a polystyrene film, which was prepared in the same manner as in the example except that only the process of creating the polystyrene film was omitted, the light irradiation time required for recording was 18. The time was 2 μs. Information was then read out using the same method as in the example, and it was found that the size of the recorded area (the area where the polarization was reversed) was the same as in the example.

[Effects of the Invention] As explained above, by utilizing the present invention, it is possible to reduce the diffusion of heat generated in the ferroelectric polymer optical recording medium and increase the sensitivity of the optical recording medium. It reacts extremely sensitively to low-power irradiation light such as that of a semiconductor laser, and can perform a series of operations such as writing, reading, and erasing smoothly.

[Brief explanation of the drawing]

1 to 4 are schematic cross-sectional views showing the structure of a specific example of the optical memory of the present invention. I... Recording layer, 2... Upper electrode, 3... Lower electrode, 4... Heat insulating layer, 5... Substrate, 6... Protective layer, 7
...Undercoat layer, 8...Light absorption layer. Figure 1

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, there is a gap between the substrate and the electrode layer in contact with the substrate, which has a higher thermal conductivity than the substrate. A ferroelectric polymer optical memory characterized by having a layer made of a small substance.