JPH0224851A - Optical recording medium consisting of ferroelectric high polymer - Google Patents

Abstract

PURPOSE:To allow high sensitivity and high density recording by consisting a recording layer of a vinylidene polymer and a light absorbent which absorbs light and converts the same to heat and specifying the thickness of the recording layer. CONSTITUTION:This optical vinylidene polymer consisting of a ferroelectric high polymer is formed by crimping the recording layer 1 with an upper electrode 3 and a lower electrode 2 and supporting the lower electrode 2 on a substrate 4. The recording layer 1 is heated and recording is executed by absorbing irradiation light in the recording layer 1. The recording layer 1 is formed on the vinylidene polymer and the light absorbent which absorbs light and converts the same to heat. The thickness of the recording layer 1 is set in the range expressed by equation I when the thickness of the recording layer 1 is designated as Dmum and the irradiation time of the irradiation light for recording 1 bit as tns. The dispersion of the heat generated in the recording layer 1 is decreased and the high sensitivity and high density recording is executed in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ferroelectric polymer optically reversible recording medium using a vinylidene polymer (hereinafter referred to as PVD polymer) as a recording layer.

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

This is an innovative 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, EIcctr, Ins, El-21 (
3), 539 (1986), Polymer Processing 35.418 (
19H), taking advantage of 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, Writing is possible by irradiating and heating an arbitrary part with a light beam while applying a weak reverse electric field that is less than the coercive electric field, and selectively inverting the polarization of only the light irradiated part.Additionally, writing is enabled by the pyroelectric effect caused by light or heat. can be read using 111.

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 with 6".

[Problems to be Solved by the Invention] The present invention provides an optical recording medium made of a PVD polymer,
The present invention aims to provide a ferroelectric polymer optical recording medium with high sensitivity and high recording density by appropriately selecting the thickness of the recording layer.

[F-stage for solving the problem] That is, the structure of the present invention is that in an optical recording medium of a type in which a recording layer is heated by absorbing irradiated light, the recording layer is made of a vinylidene polymer and a light-emitting material. A ferroelectric polymer optical recording medium comprising a light absorbing agent that absorbs and converts into heat, and having a thickness within the following range: 0.15 10g1o (L+10.0) <
D< 0.5 10g+u (L+10.O)
+1.0 However, D=thickness of the recording layer (μff1), light irradiation time for recording tel bits (nS).

The thickness of the recording layer is the electrode (hereinafter, the electrode on the light source side is called the first electrode, and the electrode on the opposite side across the recording layer is called the second electrode).
The effects on thermal diffusion and the temperature within the recording layer can be summarized as follows.

(+) As the thickness of the recording layer increases, the total amount of light absorbed within the recording layer increases, and the amount of light that penetrates the recording layer and is absorbed by the second electrode decreases, so the temperature of the second electrode increases. The amount of heat diffused within the second electrode layer is reduced.

(2) As the thickness of the recording layer increases, the proportion of the amount of heat retained within the recording layer increases relative to the amount of heat conducted within the first and second electrode layers.

(3) The effects of (1) and (2) above do not increase much even if the recording layer is made thicker after the thickness of the recording layer reaches a certain value.

(4) If the thickness of the recording layer becomes too thick, the heat capacity within the recording layer will increase, making it difficult to raise the temperature within the recording layer sufficiently.

(5) It is desirable that the temperature distribution be as uniform as possible in the thickness direction of the recording layer, but if the thickness of the recording layer becomes too thick, most of the light will be absorbed in the middle of the recording layer. The light will no longer reach the part on the opposite side from the incident light, and the temperature of that part will not rise sufficiently.

As shown in (1) to (5) above, until the thickness of the recording layer reaches a certain value, the thicker the recording layer, the less the thermal diffusion effect caused by the electrodes, which is advantageous, but beyond a certain value. On the contrary, the undesirable effects become stronger. Therefore, there is an optimum recording layer thickness, but the thickness varies depending on the light irradiation time and the physical properties of the recording layer (light absorption coefficient, thermal conductivity, specific heat, etc.). The energy density of the incident light is 2
By reducing the exposure time required for optical recording, the optimal recording layer thickness decreases because the effects of thermal conduction are reduced. For this recording medium, the optimum thickness was found to satisfy the above formula.

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 optical 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.

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 with a constant dielectric hysteresis. Examples include vinylidene butylene homopolymers and vinylidene butylidene copolymers containing 50% by weight or more of vinylidene fluoride. Examples of such copolymers 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)] is most preferable.

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 the recording layer, the PVD polymer is a part that exhibits ferroelectricity, which can be called the basis of this recording medium, so the light absorber contains the following to prevent the ferroelectricity of the PVD polymer. characteristics are required accordingly.

2) It should have absorption near the wavelength of irradiated light, especially semiconductor laser light, 2) It should have low electrical conductivity, and 3) It should be thermally stable. In particular, it is desirable that it satisfies condition 1. As such light absorbers, organic substances such as cyanines,
Polymethine compounds such as pyridiniums, birylliums, quinoliums, rhodamines, porphyrins, chlorophylls, crown ethers, phthalocyanines,
Metal complex compounds such as squaliriums, thiafulvalenes, dithiols, azo compounds, spiro compounds, fluorenone compounds, fulgide compounds, imidazole compounds, perylene compounds, phthaloperinone compounds, ferrocene compounds, phenazine compounds, phenothiazines -based compounds, phenoxazine-based compounds, polyene-based compounds, indigo-based compounds, quinone-based compounds, quinacridone-based compounds, quinophthalone-based compounds, diphenylamine-based compounds, triphenylamine-based compounds, diphenylmethane-based compounds, triphenylmethane-based compounds, acridine-based compounds compounds, acridinone compounds, carbostyril compounds, coumarin compounds, and the like. More specifically, among the dyes and materials, phthalocyanines and diothyl-based nickel complexes are preferred.

'5 By adding the light absorber into the PVD polymer, the light absorption efficiency against irradiation is improved, but the value is at least lX104 or more in terms of absorbance per 111, which is not practical as a memory. Considering this, the amount added must be adjusted so that it becomes 5 or more. However, as the content of the light absorber increases, the absorbance improves, but the insulation of the recording layer decreases, resulting in an increase in noise components and a decrease in stability in terms of memory performance. will arise. Therefore, it is desirable that the amount of the light absorbent be 50vt% or less based on the weight of the PVD polymer, and more specifically, 15vt% or less.
It is desirable that

In order to respond sensitively to light irradiation and enable high-density recording, the recording layer must be thick enough to retain heat against diffusion within the electrode layer. On the other hand, if it is too thick, the temperature will become non-uniform in the thickness direction of the recording layer and a low temperature region will remain, which is not preferable. For this reason, it is desirable that the thickness of the recording layer be optimally suited to the light irradiation time during recording.

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 includes tin-doped indium oxide (ITO), tin oxide, vapor deposition of undoped indium oxide, etc., CVD1 sputtering film, etc. The semi-transparent electrode includes gold, platinum, silver, etc. Copper, lead, zinc, aluminum, nickel, tantalum, titanium, cobalt,
Vapor deposition and CVD of various metals such as niobium, palladium, and tin
, sputtering film, 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, polyamide,
Various plastics such as polyimide, polyolefin, acrylic resin, phenol resin, epoxy resin, and the above derivatives, glass, quartz plate, ceramic, etc. are suitable, but like the electrode, it is desirable that they are transparent to irradiated light, and the electrode Although it is preferable that the material also serves as insulation from the electrode, the present invention is not particularly limited thereto, as is the case with the electrode.

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 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.

FIG. 2 shows an example in which a protective layer 5 is provided on the upper electrode 3. This protective layer 5 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.

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

Example 1 On an ITO-deposited polystyrene substrate with a thickness of about 1 IIl, a P (VDF-TrFE) film with a dye dispersed therein so as to have a light absorption coefficient of 1×106 m”1 was formed with a scratch of 2.5 μm in thickness by a spin-coding method. The recording layer 1 was formed by coating.

The upper electrode of this sample was made of chromium with a thickness of 0.1Bts.
The P (VDF-TrFE) film was evaporated with 200
A poling process was performed by applying a voltage of V. 40 more
While applying a reverse electric field of V, the irradiation light intensity was 1.8 using a semiconductor laser (hereinafter abbreviated as LD) with an oscillation wavelength of 8300 rin.
Information was recorded by heating the P (VDF-TrFE) layer from the lower electrode side with a Gaussian beam of +w% and e-' radius of 2.5 μm until the temperature of the center of the recording layer at the irradiation point reached 100° C.

(-After (7), reduce the LD light intensity by 0.16sWl: Te1
P again while chopping at 0kHz (VDF-
When the pyroelectric current generated between the electrodes was measured by irradiating the LD light on the (TrFE) layer and the recorded information was read out, the size of the recorded area (the area where the polarization was reversed) was 3.5 mm in diameter. It turned out to be 1μ■. Note that the light irradiation time required for recording was 8 μs.

Example 2 An optical memory was prepared in the same manner as in Example 1 with a recording layer thickness of 1.0 μm, and subjected to a poling process by applying a voltage of 1 oov, except that the strength of the reverse electric field was 25 V. Information was recorded in the same manner as in Example 1.

When the information was read out using the same method as in Example 1, it was found that the size of the recorded area (the area where the polarization was reversed) was 3.4 μI in diameter. Note that the light irradiation time required for recording was 13 μs.

Example 3 The same optical memory as in Example 2 was irradiated with a light intensity of 1.6 mW using an LD with an oscillation wavelength of 830 nm while applying a reverse electric field of 25 V until the temperature of the center of the recording layer at the irradiation point reached 100°C. Information was recorded by heating the P (VDF-TrFE) layer from the lower electrode side using a Gaussian beam with a radius of 1.5 μ.

Information was then read out using the same method as in Example 1, and it was found that the size of the recorded area (the area where the polarization was reversed) was 1.8 μm in diameter. Note that the light irradiation time required for recording was 1.69 μs.

Comparative Example An optical memory was prepared in the same manner as in Example 1 with a recording layer thickness of 0.5 μm, and subjected to a poling process by applying a voltage of 50 V, except that the strength of the reverse electric field was 12 V. Information was recorded in the same manner as in Example 1.

Information was then read out using the same method as in Example 1, and it was found that the size of the recorded area (the area where the polarization was reversed) was 5.2 μm in diameter. Note that the light irradiation time required for recording was 107 μs.

[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]

FIGS. 1 and 2 are explanatory diagrams of the specific structure of the ferroelectric polymer optical recording medium of the present invention. ■... Recording layer, 2... Lower electrode, 3... Upper electrode, 4... Substrate, 5... Protective layer.

Claims (1)

[Claims] In an optical recording medium of a type in which a recording layer is heated by absorbing irradiated light, the recording layer is made of a vinylidene polymer and a light absorbing agent that absorbs light and converts it into heat. A ferroelectric polymer optical recording medium having a thickness within the following range: 0.15log_1_0(t+10.0)<D<0.5
log_1_0(t+10.0)+1.0 where D: thickness of the recording layer (μm), t: light irradiation time (nS) for recording 1 bit.