JPH01162255A - Ferroelectric polymer optical recording media - Google Patents

Abstract

PURPOSE:To improve the light absorption efficiency of an optical recording medium and to obtain the optical recording medium which allows writing, reading out and erasing and has a high sensitivity by using an electrode material having specific conditions to at least one the electrode layers of the optical recording medium. CONSTITUTION:The material having the properties satisfying the formula I is used as the material to constitute at least one electrode of a pair of the electrodes 2, 3 which sandwich the recording layer 1 constituted of a vinylidene polymer. The material to satisfy the formula I is exemplified by materials having a small thermal conductivity and relatively large specific heat and density, for example, tellurium, bismuth, titanium, niobium, nickel, platinum, antimony, chromium, germanium, silicon, aluminum, etc. The light absorption efficiency of the ferroelectric high-polymer optical recording medium is thereby improved and the diffusion of the generated heat is decreased, by which the sensitivity of the optical recording medium is increased.

Description

Detailed Description of the Invention [Technical Field] The present invention relates to a highly ferroelectric material using a vinylidene polymer (hereinafter abbreviated as PVD polymer) useful for optical cards, optical discs, displays, etc. as a recording layer. Related to molecular optical reversible recording media.

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

This is an epoch-making optical memory that utilizes the ferroelectric properties of PVD polymers, and its recording principle is based on Japanese Patent Application Laid-Open No. 59-215098.
Publication No. 59-215097, or IE
E E trans, Elcetr, Ins,,P
I-21, 359° 198B, polymer processing 35.418
(198B), the ferroelectric polymer material is polarized in one direction by applying a high electric field, taking advantage of the property that the ferroelectric polymer material is polarized by an electric field. , enabling writing by irradiating and heating an arbitrary part with a light beam while applying a weak reverse electric field below 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.

When using such a ferroelectric polymer as an optical memory, the absorption efficiency of the light irradiated onto the memory is an important factor, but since PVD polymer films generally have high light transmittance, Even when high-power laser light is irradiated, there is a lot of loss, which poses a major problem when it comes to practical application.

Furthermore, due to the functionality of this recording medium, electrode layers must be provided on both sides of the recording layer, but no study has been conducted on the electrode material, and the generated heat may easily diffuse through the electrodes. This makes it difficult to raise the temperature of the recording layer.
When used as a memory, there were problems such as a decrease in S/N ratio and recording density.

In view of these circumstances, the present invention provides an optical recording medium made of a PVD polymer in which at least one of the electrodes sandwiching the recording layer has absorption in the wavelength range of the semiconductor laser light that is the light source. The object of the present invention is to provide a highly sensitive ferroelectric polymer optical recording medium that functions both as an electrode and as a heat source.

[Configuration] The present inventors have been conducting research in order to put the optical recording medium into practical use. By improving the light absorption efficiency of the optical recording medium and establishing a method for retaining the generated heat for a certain period of time, we succeeded in producing a highly practical ferroelectric polymer recording medium.

That is, the present invention provides an optical recording medium made of a PVD polymer, in which a material constituting at least one of a pair of electrodes sandwiching a recording layer made of the PVD polymer satisfies the following conditional expression: A ferroelectric polymer optical recording medium characterized by having physical properties satisfying the following.

k≦1. OX 10' w * m 2/ J/J
``C However, k: Thermal conductivity (we m'' 11 K-') ρ:
Density (g-m-3) C: Specific heat (J-g-'-1').

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

FIG. 1 is a structural model diagram of the ferroelectric polymer recording medium of the present invention. 1 in this figure is a portion consisting of a PVD polymer film which is the recording layer of the optical recording medium. 2 is a lower electrode, and 3 is an upper electrode. Further, 4 is a substrate that supports the lower electrode 2.

The electrode material used in the present invention may be either the upper or lower electrode in FIG. 1, and the picture electrode may also be made of the above material. Furthermore, the present inventors have previously reported that dyes can be dispersed in a PVD polymer recording layer to improve its light absorption efficiency, and the present invention can also be applied to this case. In this case, it is desirable to use a transparent electrode as the electrode on the incident side of the irradiation light, and use the above material for the other electrode.

In the present invention, the material constituting the electrode layer preferably has a low thermal conductivity and a relatively high specific heat and density, as can be seen from the above equation. Specifically speaking, metals that meet this condition include tellurium, bismuth, titanium, niobium, nickel,
Examples include platinum, antimony, chromium, germanium, silicon, and aluminum. Using the above materials, the electrode layer is formed by a vapor deposition method, a sputtering method, a CVD method, or the like.

Further, structures other than the electrode layer will also be explained.

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 in dielectric hysteresis measurements, such as vinylidene fluoride. These are a homopolymer and a vinylidene butylene copolymer containing 50 ffl or more of vinylidene butylene. Examples of the copolymer include copolymers of vinylidene butoxide and ethylene trifluoride, propylene hexafluoride, ethylene trifluoride chloride, and the like.

Also included are polyvinylidene cyanide, vinylidene cyanide, and vinyl acetate copolymers, among which vinylidene fluoride and ethylene trifluoride copolymers [hereinafter referred to as P
(abbreviated as VDF-TrFE)] is 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 it not only forms the PVD polymer to a uniform thickness but also allows an ultra-thin film to be obtained.

Regarding other electrode materials employed in the present invention, tin-doped indium oxide (IT) is used as a transparent electrode.
O), tin oxide, undoped indium oxide, etc., and semitransparent electrodes include various metals such as gold, platinum, silver, lead, zinc, aluminum, nickel, tantalum, titanium, cobalt, niobium, palladium, and tin. Examples include vapor deposition, CVD, sputtering films, etc., but the method is not particularly limited to these.

Materials for the substrate 4, which is a support for the electrodes, include polyethylene, polyethylene terephthalate, polypropylene, polystyrene, polyvinyl chloride, polycarbonate, polyvinyl alcohol, polyvinyl acetate, polyamide, polyimide, polyolefin, acrylic resin, phenol resin, and epoxy resin. Various plastics, glass, quartz plates, ceramics, etc., such as and the above-mentioned derivatives, are suitable, but it is preferable that they are transparent to irradiated light; and that they also serve as insulation from the electrodes. However, the present invention is not 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, but in this case, as described above, it may be desirable that the electrode on the light source side be transparent to the irradiated light.

FIG. 2 shows an example in which an undercoat layer 5 is provided on the surface of the lower electrode 2. The undercoat layer 5 is formed by applying or vapor depositing a surface treatment agent on the surface of the lower electrode 2, and its purpose is as follows.

2) Improved contact with the electrode 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 agent used for this purpose is samethyldisilazane (
HMDS),) dimethylchlorosilane (TMC8),
Dimethylchlorosilane (DMCS), dimethyldichlorosilane (DMDCS), bis(trimethylsilyl)acetamide, t-butyldimethylchlorosilane, bis(
Examples include trimethylsilyl)trifluoroacetamide, trimethylsilyldiphenylurea, bistrimethylsilylurea, and the like. In addition to the above-mentioned silylating agents, titanium-based coupling agents (anchor coating agents) have also been confirmed to be effective.

Fig. 3 shows an example in which a protective layer B is provided on the upper electrode 3, and this protective layer protects the recording layer from cow dirt, dust, dirt, etc., and improves the storage stability of the recording layer. For this purpose, it is formed from various polymeric materials, silane coupling agents, glass, etc.

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

Comparative Example A P (VDF-TrFE) film with a thickness of 1 μm was formed by a spin coding method on ITO vapor-deposited glass with a thickness of about 1 μm.
A recording layer 1 was formed by applying the following coating. The upper electrode of this sample was gold (T7-1・3x10'w*m2*J-'
) on the p(vDF-TrFE) film after evaporating 10
A poling process was performed by applying a voltage of 0V. 2 more
While applying a reverse electric field of 5V, a semiconductor laser 4- (hereinafter abbreviated as LD) with an oscillation wavelength of 830rv was used to increase the irradiation light intensity to 5.
Information was recorded by heating several locations in the P (VDF-TrFE) layer from the lower electrode side with 5 mW. After that, the LD light intensity was weakened to 0.55 mW and the P (VDF-TrFE) layer was irradiated with the LD light again while chopping at 10kllz to measure the pyroelectric current generated between the electrodes and read out the recorded information. It was found that the S/N ratio was 25 dB.

Example 1 Similar to the comparative example, P (VD
F-TrFE) film as upper electrode')Ol, (p given c-3-03×10'W"m"J")
was deposited to a thickness of about 500 wafers. After polling the sample by applying an electric field of 100 V, a semiconductor laser beam with an oscillation wavelength HOr+m was applied to the lower ITO layer at an intensity of 5.5 mW while applying a reverse electric field of 25 V. Information was recorded by irradiating the sample from the S pole side and heating several locations on the sample.

When the recorded information was read out using the same method as in the comparative example, it was found that the S/N ratio was 35 dB.

Example 2 Platinum (-"--2,49X 10-' w-m 2-J
-') was used to prepare a sample. When the S/N ratio of the sample was measured, it was found to be 39 dB.

Example 3 Gel manila film (ρ・c−3,53xlO−′ w−m′・J −
) was used to prepare a sample, and its S/N ratio was evaluated and found to be 34 dB.

Example 4 Tellurium (ρ・cm5.03xlo°7w・
When a sample was prepared and evaluated in the same manner as in the comparative example using 2.m2.Jol), it was found that the S/N ratio reached 49 dB.

In Example 5, bismuth (p ・c -6,59X 10-
When a sample was prepared and evaluated in the same manner as in the comparative example below using 6 w・m2・Jol), the S/N ratio was 4.
It turned out to be 5 dB.

Example 6 The above electrode was made of titanium (-only = 7.08X 10-6
When a sample was prepared and evaluated in the same manner as in the comparative example below using the following sample using the following method, it was found that the S/N was 44 dB.

In Example 7, antimony (ρ・c −1,78XIQ
' w * m 2 ・J-1), a sample was prepared and evaluated in the same manner as in the comparative example below, and S
/N ratio was found to be 42 dB.

Example 8 A sample was prepared and evaluated in the same manner as in the comparative example using a 10-5w*m2.J-1n, and it was found that the S/N ratio was 40 dB.

Example 9 Niobium (ρ・c-2, 34X 10-5
When a sample was prepared and subjected to '1P filli in the same manner as in the comparative example below, it was found that the S/N ratio was 40 dB.

Example 10 P (VDF-TrFE) solution represented by the following formula
5vj% of cyanine dye was dispersed onto ITO vapor-deposited glass with a thickness of 1+nn+ using a spin code method.
A recording layer 1 was formed by coating the film in a thickness of .mu.m. Tellurium (ρ・cm5.03XlO-7w-
'm2.J-blind) was deposited. When this sample was produced and evaluated using the same operations as in the comparative example, it was found that the S/N ratio reached 55 dB.

[Effect] As explained above, by utilizing the present invention, the light absorption efficiency of a ferroelectric polymer optical recording medium is improved, and the diffusion of generated heat is reduced, thereby increasing the sensitivity of the optical recording medium. It has the remarkable effect of being able to increase the amount of light it produces, reacting extremely sensitively to low-power irradiation light such as that of a semiconductor laser, and smoothly performing a series of operations such as writing, reading, and erasing. It is something.

[Brief explanation of the drawing]

1 to 3 are structural model diagrams of the ferroelectric polymer recording medium of the present invention. ■... Recording performance, 2... Lower electrode, 3... Upper electrode, 4... Substrate, 5... Undercoat layer, 6... Protective layer.

Claims (1)

[Scope of Claims] In an optical recording medium made of a vinylidene polymer, a material constituting at least one of a pair of electrodes sandwiching a recording layer made of the vinylidene polymer satisfies the following conditional formula: A ferroelectric polymer optical recording medium characterized by having physical properties satisfying the following. k/ρ・c≦1.0×10^-^4w・m^2/J where, k: Thermal conductivity (w・m^-^1・K^-^1) ρ: Density (g・m ^-^3) c: Specific heat (J・g^-^1・K^-^1)