JPS61153842A - Recording and reproducing method of optical recording medium - Google Patents

Abstract

PURPOSE:To carry out high-density recording with high sensitivity by irradiating light on an optical recording medium using a thin film wherein fine particles showing a metal-insulator transition are dispersed as the recording film, and utilizing the change in the optical characteristic at that time. CONSTITUTION:Mass movement of electrons of fine particle is caused, when light is irradiated on a film wherein the fine particles are dispersed in a medium. Consequently, plasma resonance absorption is produced, and the light absorption results. The absorption wavelength and absorption coefficient of the light absorption depend on the property of the medium, the space occupation ratio of the fine particles, the diameter of the fine particle, the concn. of free electrons, the effective mass, etc. Accordingly, the film contg. fine particles is fixed to a substrate, light is irradiated on the film to generate a metal-insulator transition at the irradiated site by the heating effect, the absorption wavelength and absorption coefficient of the plasma resonance absorption are changed to record a signal, the light of wavelength of the plasma resonance absorption is transmitted to read the presence and absence of the light absorption, and the reproduction of the recorded information is carried out.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention relates to a recording/reproducing method for an optical recording medium, and more specifically, a method for recording and reproducing an optical recording medium by using a plasma resonance absorption phenomenon that occurs in a recording film due to light irradiation. It relates to a method that allows recording, reproducing recordings, and also erasing them.

[Technical background of the invention and its problems] Fine particles of various inorganic materials are highly chemically reactive.

Since these particles have the characteristics of poor thermal diffusion, easy concentration of heat, and high light absorption, a highly sensitive optical recording medium in which these particles are fixed as a film 7 on a substrate has been proposed. For example, in Japanese Patent Application Laid-open No. 57-94944,
A recording SS containing fine particles of various inorganic materials dispersed on a substrate is formed.

Here, a method of recording and reproducing information by forming deformed, altered, or discolored parts in a thin film by irradiating it with a wood beam such as a laser beam or an electron beam is disclosed. Furthermore, Japanese Patent Laid-Open No. 58-74392 discloses a method in which a laser beam is irradiated onto an island-like agglomerated film of fine metal or metalloid particles, and the irradiated area is melted or evaporated to form a depression. It is.

However, in these optical recording media, the changes in the fine particles or the recording film containing them before and after recording are irreversible, so once information is recorded by light irradiation, it is impossible to erase the information. Can not,
That is, there is a problem in that the optical recording medium cannot be used repeatedly.

[Object of the Invention] The present invention solves the above-mentioned problems in the conventional prior art, and provides a recording film containing dispersed fine particles of a substance whose change upon irradiation with light exhibits a reversible metal '-'-edge body transition. By doing so, the sensitivity during recording is high and the signal/noise ratio during playback (
S/N ratio) is large.

In addition, recording and reproduction of optical recording media that can be erased,
The purpose is to provide an erasure method.

[Summary of the Invention 1 In the course of intensive research to achieve the above object, the present inventors discovered an island formed by discontinuously adhering fine particles to a film or substrate in which fine particles such as metal are dispersed in a medium. In a film of microparticles, when light is irradiated here, the electrons of the microparticles cause collective movement, resulting in

Light absorption occurs due to the plasma resonance absorption phenomenon caused by dispersed fine particles, and the absorption wavelength and absorption coefficient in this light absorption are determined by the properties of the medium, the space occupancy rate of fine particles, the particle size of all particles, and the total particle size. We focused on the fact that it depends on the electrical properties of the electrons, especially the free electron concentration and their effective mass.

Furthermore, when the fine particles are composed of a substance that exhibits a metal-insulator transition, when the substance is in a metallic phase and has a high free electron concentration and a small effective mass, the film-
When irradiated with light, a plasma resonance absorption phenomenon occurs and large absorption occurs at wavelengths from the infrared to visible light.If the material is in an insulator phase, the free electron concentration is small and the effective mass is large, so when irradiated with light, In other words, a film containing fine particles of a substance exhibiting a metal-insulator transition may or may not cause plasma resonance absorption when irradiated with light, depending on the state of the phase of the fine particle material. We focused on

Therefore, the inventors fixed a thin film containing such fine particles on a substrate, irradiated it with light, and caused a metal-insulator transition in the fine particles at the irradiated site due to the heating effect of the light energy, thereby changing the thin film. Signals can be recorded by changing the absorption wavelength and absorption coefficient of plasma resonance absorption, and recorded information can be reproduced by transmitting light at the wavelength of plasma resonance absorption and reading whether or not the light is absorbed. Furthermore, he came up with the idea that if the light irradiated area is cooled, a phase transition opposite to the above case will occur, the recorded signal will be erased, and the particulate matter will be restored to its original state before the light irradiation. Based on this idea, we have developed the method of the present invention.

That is, the method for recording and reproducing an optical recording medium of the present invention is based on a method for recording and reproducing an optical recording medium in which fine particles of a substance exhibiting a metal-insulator transition are dispersed.
irradiating light onto an optical recording medium having No. 19 as a recording film to cause a metal-insulator transition of the substance due to the heating effect, and utilizing changes in optical properties based on plasma resonance absorption of the thin film at that time. It is characterized by

First, in the optical recording medium to which the method of the present invention is applied, the recording film is a fine particle dispersion film in which fine particles of a substance exhibiting metal-insulator transition are dispersed in the medium, and is fixed on a substrate. Something that is or.

This is a so-called island-like particulate film formed by discontinuously depositing particulates on a substrate.

The fine particles that make up these films, which exhibit a metal-insulator transition, are preferably those whose free electron concentration and effective mass change greatly during the transition, but for practical use, it is even more desirable to have a transition temperature near room temperature. preferable.

For such a substance, the linear formula = (V 1-
! ) 02 (A represents at least one of No and W, and X represents a number satisfying O≦x<0.1), or the following formula: (VlyBy)2O3 (B is Cr', AnO') represents at least one species, and y is O<
(representing a number satisfying Y < 0.03) can be mentioned.

The former has a transition temperature around 70°C, with the low temperature side being an insulating phase and the high temperature side being a metal phase. Therefore, when this material is irradiated with light and the irradiated area is heated, that area becomes a metal phase and exhibits plasma resonance absorption, whereas this phenomenon does not occur in the insulator phase. It is a component that shifts the transition temperature to the lower temperature side, and is effective for maintaining the recording state in the room temperature range, which will be described later.

The latter has a transition temperature of −20 to 15 depending on the value of y.
Varies within a range of 0°C. When y=o+7≧0.03, no metal-insulator transition occurs (l/), and the metal phase is on the low temperature side and the insulator phase is on the high temperature side. Even if the content of Cr and An is small, the effect can still be exhibited, but it is practically preferable that X≧0.0001.

In order to form a recording film with such a substance,

Eight types of commonly used film forming techniques may be applied to the substrate. For example, in the case of the latter membrane, a given filtration under low oxygen partial pressure
ti, (7) V-Cr alloy, V-A 1 alloy, V
A method for vacuum-depositing the -Or-^ alloy; reactive deposition of V under low oxygen partial pressure and sputtering can be applied.

In addition, by appropriately selecting conditions such as the evaporation source, target composition, atmosphere, substrate temperature, and arrangement during this film formation process, thin films in which fine particles exist discontinuously in the form of islands or various types of glass can be formed. , 5n02, CaF2゜ or PM
Using a substance (dispersion medium) such as an organic substance such as A as an evaporation source or target, alternately applying or sputtering it with the substance 1 of (Vl-yB,) 203, or combining polymerization by a vapor phase method. Accordingly, a thin film in which fine particles of the substance (VlyBy)2O3 are dispersed and present in the dispersion medium can be formed. Furthermore, depending on condition settings, it is also possible to form a thin film in which both are laminated.

In the case of such island-shaped fine particle aggregation films and fine particle dispersed films, the space occupation rate of the VA particles in the thin film is small, so the thermal conductivity of the thin film is low. As a result, the sensitivity to light irradiation increases when the temperature rises due to light irradiation during recording, making it possible to use a low-output light source such as a semiconductor laser. Furthermore, for the same reason, the expansion of the irradiated area due to thermal diffusion is suppressed, making high-density recording possible.

In such a thin film, it is desirable that the particle size be smaller than the wavelength of the light used for reproduction in order to suppress the scattering of the light, so 50 to 7000 people,
Preferably 100 to 800 people, particularly preferably 20
0 to 700 people, and the volume occupancy of the fine particles in the thin film is 10 to 80%, preferably 20 to 80%.
It is set to 70%, particularly preferably in the range of 30 to 80%.

The film thickness also depends on the wavelength of the light source used for reproduction, and whether the light transmitted through the thin film is emitted from the opposite side of the light source during light detection, or whether a reflective layer is provided between the thin film and the substrate and the film is formed on the light source side. An appropriate value can be selected depending on the method of detecting the reflected light after transmission, the particle size of the fine particles, and the difference in volume occupancy, but in general, it is 0.5 to 50, preferably 1. ~20. Set to the mouth range.

Recording and reproduction can be performed as follows using the optical recording medium as described above. Namely.

First, the thin film is irradiated with light. The area irradiated with light is heated and its temperature rises, causing a metal-insulator transition at the transition temperature.
In other words, at this time, the record was stored as a phase transition of the microparticles.

Next, the light irradiation is stopped and the optical recording medium is cooled to room temperature. However, in the metal-insulator transition of the above substances, the transition temperature during heating is not the same as the transition temperature during cooling, that is, there is warm-eating hysteresis of the phase transition, and the transition temperature during cooling is different from that during heating. Since the temperature has shifted to the lower temperature side in comparison, even during this cooling, the recorded state, that is, the light irradiated area, remains in the phase transformed by the light irradiation, so that the recorded state is maintained.

In recording and reproducing, for example, if the fine particles at the light irradiation site are in a metal phase, plasma resonance absorption occurs at that site.
This can be done by irradiating light having an absorption wavelength of the plasma resonance absorption thereon and detecting whether or not the transmitted light is absorbed at that time.

Note that if the cooling temperature is lowered to below the transition temperature of the particulate matter during cooling, the light irradiated area returns to the state of the phase before the light irradiation, and the record is erased accordingly. In other words,
It is possible to prepare for rewriting recorded information and repeating recording and reproduction.

Furthermore, the transition temperature during cooling of particulate matter depends on its cooling rate. That is, when a region in a recorded state is rapidly cooled by light irradiation, the recorded state is maintained at a temperature lower than the transition temperature during normal cooling, so to speak, and is frozen. This can be explained by using the Funo phenomenon, which can be thought of as a phenomenon that occurs when the laser spot during light irradiation is narrowed down to an extremely small size, and when that spot cools down, it becomes rapidly cooled in relation to its surroundings. Select a substance with a composition whose transition temperature during slow cooling is just above room temperature. During recording, it is rapidly cooled to maintain the recorded state of the light irradiated area, and when erasing, the temperature is raised again and slowly cooled, resulting in a phase transition at the transition temperature of normal cooling. can be made to do so. That is, recording, reproducing, and erasing operations can be performed without using a special cooling device.

[Examples of the Invention] Example 1 In an argon atmosphere with an oxygen partial pressure of 2 x 10-'' Torr, a quartz substrate cooled with liquid nitrogen was subjected to evaporation treatment for 20 seconds using metal vanadium as an evaporation source.

Subsequently, a thin film having a thickness of 1.5 mm was formed on the quartz substrate by repeating 12 times 0 or more operations in which a 60-second sexual treatment was performed using boron trioxide (B203) as an evaporation source. When this thin film was observed using an electron microscope, the particle size was 200 to 40.
0 people's VO2 particles are 820 at intervals of 400 to eoo
It turned out to be a fine particle dispersed film dispersed in 3.

This thin film was irradiated with light with a wavelength of 1.061 Lm, and the relationship between the light absorption rate and temperature was measured. ℃
transfer to the metallic phase occurs.

During cooling, a reverse transition occurs at about 43° C., and the light absorption rate changes significantly.

Next, a semiconductor laser (wavelength: 830 nm) with an output of 10 mW and a spot size of 3 mm in diameter was attached to this thin film.
was irradiated. This light irradiated area (recorded area), the area that was not irradiated with light (unrecorded area), and the above recorded area were
The wavelength t, oe is applied to the part (erasure, part) cooled to 9.
The light absorption rate of each IL intestine was measured using a laser beam with an output of 0.1-1. The measurements were conducted at 50° C. at 9:00 p.m. The light absorption rate of the recorded part, undistributed part, and erased part is 53.
They were 2%, 11.2%, and 11.5%. Sunawa (i,
It has been found that recording is performed with a sharp change in light absorption due to metal-insulator phase transition caused by light irradiation, and is erased by cooling.

Example 2 The thickness was 1.5IL in the same manner as in Example 1 except that the oxygen partial pressure was I x 1 (1', Torr) and the evaporation sources were Vo, 990Cro, olo, and 8203, respectively.
A thin film with a grain size of 200 to 30 m was formed.
It was a fine particle dispersed film in which 203 fine particles of 0 A (V (1,990"rO,olo) were dispersed in E!7Q3 at intervals of 400 to 800 people.

This thin film was irradiated with semiconductor laser light with a wavelength of 1.0 [1 gm], and the relationship between the light absorption rate and temperature was investigated, and the results are shown in FIG.

A recording section was formed by irradiating this thin film with a semiconductor laser beam (wavelength: 830 nm) having an output of jo*W and having a spot size of 3 mm in diameter. Further, the area including this recording area was irradiated with semiconductor laser light (output 10 mW, wavelength 830 nm) with a spot diameter of 20mm and was then slowly cooled to form an erased area. The light absorption rate of each part was measured under the same conditions as in Example 1.

However, the temperature at the time of measurement was 25°C. Recording section 968%
, unrecorded portion 58.2%, erased portion 57.9%.

In other words, in the recording section, the insulator phase is frozen to room temperature and no plasma resonance absorption occurs, so the light absorption rate is small.
In addition, in the erasing part, which is a metal phase, the light absorption rate is increased due to plasma resonance absorption.

[Effects of the Invention J] As is clear from the above description, the method of the present invention is a recording/reproducing method that utilizes plasma resonance absorption of a thin film of fine particles of a substance exhibiting metal-insulator transition. High-sensitivity recording can be performed at high density, and recording and reproduction with a high signal/noise ratio is possible during reproduction.

Moreover, this optical recording medium is a reversible metal-based material made of fine particles.
Since it utilizes insulator transition, it is an erasable optical recording medium that can erase recordings and prepare for recording/reproducing again, and is therefore useful.

[Brief explanation of the drawing]

FIG. 1 and FIG. 2 are diagrams showing the temperature dependence of the light absorption rate of the S films of Example 1 and Example 2, respectively. Figure 1 Figure 2 '°°'- 3LL (@Cl-

Claims (1)

[Claims] 1. Light is irradiated onto an optical recording medium whose recording film is a thin film in which fine particles of a substance exhibiting metal-insulator transition are dispersed, and the metal-insulator transition of the substance is induced by the heating effect. 1. A method for recording and reproducing an optical recording medium, which utilizes changes in optical properties based on plasma resonance absorption by fine particles dispersed within the thin film. 2. The substance has the following formula: (V_1_−_xA_x)O_2
(In the formula, A represents at least one of Mo and W, and x represents a number satisfying the relationship 0≦x<0.1) The method according to claim 1 . 3. The substance has the following formula: (V_1_−_yB_y)_2O
_3 (In the formula, B represents at least one of Cr and Al, and y represents a number that satisfies the relationship 0<y<0.03)
The method according to claim 1, wherein the substance is a substance represented by: