JPH03263626A - Optical information recording, reproducing and erasing member - Google Patents

Abstract

PURPOSE:To decrease the pulsation by the thermal deformation of dielectric layers and to make improvement in repetitive characteristics by forming the dielectric layer of the thin layer between a recording thin film and a reflecting layer into two layers, selecting a material of a coefft. of thermal expansion for any one layer and making the film thickness adding the film thicknesses of the 2nd and 3rd dielectric layers smaller than the film thickness of the 1st dielectric layer. CONSTITUTION:The 1st dielectric layer 2, the recording thin film 3, the 2nd dielectric layer 4, the 3rd dielectric layer 5 consisting of the material different form the material of the 2nd dielectric layer, and the reflecting layer 6 are successively formed on one surface of a transparent substrate 1. The 3rd dielectric layer 5 is formed of the material having the smaller coefft. of thermal expansion than the coefft. of thermal expansion of the 1st, 2nd dielectric layers 2, 4 or the 2nd dielectric layer 4 is constituted of the material having the smaller coefft. of thermal expansion than the coefft. of thermal expansion of the 1st and 3rd dielectric layers 2, 5. Namely, the 3rd dielectric layer 5 is formed by providing the dielectric layer of the small coefft. of thermal expansion between the 2nd dielectric layer 4 and the reflecting layer 6. Or the 2nd dielectric layer 4 is formed by providing the this layer between the recording thin film 3 and the 3rd dielectric layer 5. The thermal deformation of the dielectric layers on both sides of the recording thin film by the heat of the recording thin film at the time of recording and erasing is decreased in this way and the repetitive characteristics are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical information recording/reproducing/erasing member capable of recording/reproducing/erasing information with high density and large capacity using a laser beam or the like. Regarding it, there is a write-once disk using a Te0x (0<x<2.0) thin film whose main components are Te and TeO2.Furthermore, the recording thin film is heated with laser light and melted! IL, % By rapid cooling,
A chalcogen material Ge+5Tes+5b by S. RoOvshinsky et al. is a material that can record information by becoming amorphous and then crystallize and erase it by heating and slowly cooling it.
aS2 etc. are known. MaL As2S3 and As2
Although recording thin films made of a combination of a chalcogen element such as Ses or 5b2Set and a group V element of the periodic table or a group I element such as Ge are widely known, these recording thin films are used on a substrate with grooves for guiding laser light. However, the method of recording information on these disks with laser light and erasing that information is to crystallize the recording thin film in advance, and then apply a laser focused to a diameter of about 1 μm to this disk. For example, when a disc-shaped recording disk is rotated and irradiated with intensity modulation according to information, this peak power laser beam irradiation area (
Information can be recorded as marks that are heated above the melting point of the recording thin film and rapidly cooled to become amorphous. In addition, the area irradiated with this modulated bias power laser beam is heated to a temperature higher than the crystallization temperature of the recording thin film, and the recording thin film has the function of erasing low recorded signal information, allowing reoverwriting. Because the temperature rises above the crystallization temperature, it is common to provide a dielectric layer with excellent heat resistance on both sides of the recording thin film as a protective layer for the substrate and adhesive layer. Recording/erasing special repeatability characteristics are affected by characteristics such as thermal conductivity or thermal expansion coefficient. Therefore, recording/erasing characteristics and repeatability characteristics can be improved by changing the material or layer structure of the dielectric. Problems to be Solved by the Amo Invention The first problem in information recording and erasable override recording media using means of heating and heating a recording thin film, melting, rapidly cooling, and crystallizing it and heating and slowly cooling it to crystallize it is to erase the recording thin film. poetry
The second issue is the repeatability of recording and erasing. Crystallization can be achieved by irradiating the film with a laser beam and gradually cooling it.This temperature is generally in the crystallization temperature range lower than the melting point.Also, by irradiating this crystallized film with a high power level laser beam, the film can be crystallized. If heated above the melting point, that part will melt and then rapidly cool down, becoming amorphous again and forming a mark.If amorphous recording is selected as the recording mark, this mark will be formed by the recording thin film melting and rapidly cooling. The faster the cooling rate, the more uniform the amorphous state will be obtained and the higher the signal amplitude.If the cooling rate is slower, there will be a difference in the degree of amorphization between the center and the periphery of the mark. When erasing crystallization, the temperature of the amorphous mark part where recording has already been made is raised to a temperature higher than the crystallization temperature by irradiation with laser light, crystallizing it and erasing the mark.At this time, the amorphous part of the mark When the quality state of the mark is uniform (i) The mark is more likely to be uniformly crystallized and the erasing properties are improved.When the amorphous state of the mark is uneven (y) The crystallization and erasing state is uneven and the erasing properties are deteriorated. There is one task that I said I would do.
．． Regarding the repeated recording/erasing characteristics, there is thermal damage to the disk substrate or dielectric layer due to rapid heating and cooling repeated many times. If the disk substrate or dielectric layer is thermally damaged, there is a problem in that noise increases and characteristics deteriorate during repeated recording and erasing. An object of the present invention is to provide an optical disc with stable characteristics.

Means for Solving the Problems The present invention provides an optical information recording/reproducing/erasing member comprising a recording thin film and a dielectric layer laminated on both sides of the recording thin film, the first dielectric layer recording on one surface of a transparent substrate. Thin film Second dielectric layer Third dielectric layer made of a different material from the second dielectric layer The reflective layer is sequentially formed to form the third dielectric layer with a thermal expansion coefficient higher than that of the second dielectric layer. Alternatively, the second dielectric layer may be made of a material with a smaller coefficient of thermal expansion than the third dielectric layer. forming a third dielectric layer between the dielectric layer and the reflective layer;
Alternatively, by forming a second dielectric layer between the recording thin film and the third dielectric layer, the thermal deformation of the dielectric layers on both sides of the recording thin film due to the heat of the recording thin film during recording and erasing can be reduced. Thermal deformation of these dielectric layers is not permanent; they heat and expand only the moment the laser beam is irradiated, and when the laser is not irradiated, they cool and return to their original state. Since the direction of rotation of the disk is constant, this pulsation of the dielectric layer causes the recording thin film to move in the direction of rotation of the disk, degrading the repeatability. However, by providing one layer of dielectric material with a small coefficient of thermal expansion, thermal deformation of the dielectric material layers on both sides of the recording thin film can be reduced and the repeatability characteristics can be improved. Embodiment Hereinafter, an embodiment of the present invention will be described based on the drawings. In Fig. 1, reference numeral 1 denotes a disk substrate, which may be made of a resin substrate such as polycarbonate, or a resin substrate with grooves formed in advance for guiding laser light, or a glass substrate with grooves formed using the so-called 2P method using photopolymer. Plate It may be a substrate with grooves formed directly on a glass plate. 12 is the first dielectric layer, which is made of a material whose main component is ZnS, which has excellent heat resistance, and has a film thickness of about 150 nIIl.
It is.

Reference numeral 3 denotes a recording thin film, which is an alloy thin film made of Te-Ge-3b and has a film thickness of about 30 nm. 4 is a second dielectric layer;
It is made of the same material as the first dielectric layer and has a thickness of approximately 20 mm.
It is nm. 5 is the third dielectric layer, which is made of 5iO2 with a small coefficient of thermal expansion (coefficient of thermal expansion 0.45 x 10-')
The film thickness is approximately 20 nm7). 6 is AI
The reflective layer is approximately 60 nm thick. GEL vacuum deposition or sputtering can be used to form these thin films. A protective plate 7 is attached to the disk substrate 1 with an adhesive 8. In the configuration shown in Fig. 1, recording, erasing, and reproducing are performed by irradiating a laser beam whose intensity is modulated according to the information in the direction of arrow 9 and by detecting the reflected light. By providing the third dielectric layer 5 with a small coefficient of thermal expansion, it is possible to suppress pulsations caused by thermal deformation of the second dielectric layers 2 and 4 that occur during repeated recording and erasing. Even if the materials of the second dielectric layer 4 and the third dielectric layer 5 are switched, the same effect can be obtained. Furthermore, the total thickness of the second dielectric layer 4 and the third dielectric layer 5 is approximately 40 mm.
As a result, the reflective layer 6, which serves as a heat diffusion layer, and the recording thin film 3 become close to each other, and the heat of the recording thin film 3 during recording and erasing is rapidly transmitted to the reflective layer 6. This is effective in rapidly cooling the thin film 3, and the cooling rate can be controlled by the material and thickness of the dielectric layer between the recording thin film 3 and the reflective layer 6. The override characteristics of a signal of fl-3, 43 MHz and a signal of f2-1.0 MHz were measured using a disc configuration with an external diameter of 130 na and a 18 Q Orprn circuit line speed of 8 m/sec. By modulating the laser beam between a high power level of 1 mW and a low power level of 8 mW, the amorphous mark is crystallized and erased at a low power level. This result was obtained using the simultaneous erasure method.The C/N ratio of the recorded signal was 55 dB or more.As for the erasure characteristics, an override erasure rate of 30 dB or more was obtained. After measuring the rate characteristics, no deterioration was observed after 1,000,000 cycles. The following effects can be obtained by selecting a material with a small coefficient of thermal expansion for the layers and making the combined thickness of the second and third dielectric layers thinner than the first dielectric layer (1). The repetition characteristics are improved by reducing the pulsation caused by thermal deformation of the dielectric layer during recording and erasing.

(2) Recording signal amplitude increases. L C/N ratio improves to 55 dB or more.

(3) Recorded marks are uniform and override erasure rate is 3
Although the erasing characteristics improve as it becomes more than 0 dB.

[Brief explanation of drawings]

FIG. 1 is a partially omitted sectional view of an optical information recording/reproducing/erasing member according to an embodiment of the present invention. record#! 4
...Second dielectric layer 5...Third dielectric layer
6... Reflective layer 7... Contact 8... Protective plate

Claims (10)

[Claims] (1) When irradiated with laser light, it absorbs the energy, heats up, melts, and rapidly cools to become amorphous, and the amorphous state crystallizes by heating it. An optical information recording/reproducing/erasing member comprising a recording thin film and a dielectric layer laminated on both sides of the recording thin film, the first dielectric layer, the recording thin film, and the second dielectric layer being on one side of a transparent substrate. , a third dielectric layer and a reflective layer made of a different material from the second dielectric layer are sequentially formed, and the third dielectric layer is made of a material with a smaller thermal expansion coefficient than the first and second dielectric layers. An optical information recording/reproducing/erasing member characterized by: (2) The thermal expansion coefficient of the third dielectric layer is 1.0×10^-
2. The optical information recording/reproducing/erasing member according to claim 1, wherein the material is selected from a material having a hardness of ^8k^-^1 or less. (3) The optical information recording/reproducing/erasing member according to claim 1, wherein the combined thickness of the second and third dielectric layers is thinner than that of the first dielectric layer. (4) The optical information recording/reproducing/erasing member according to claim 1, wherein a material containing ZnS as a main component is used as the first and second dielectric layers, and SiO_2 is used as the third dielectric layer. (5) The optical information recording/reproducing/erasing member according to claim 1, wherein a material consisting of Te, Ge, and Sb is used as the recording thin film. (6) When irradiated with laser light, it absorbs the energy, heats up, melts, and rapidly cools to become amorphous, and the amorphous state crystallizes by heating it. An optical information recording/reproducing/erasing member comprising: a recording thin film; and a dielectric layer laminated on both sides of the recording thin film; A layer, a third dielectric layer made of a material different from that of the second dielectric layer, and a reflective layer are sequentially formed, and the second dielectric layer is made of a material with a smaller coefficient of thermal expansion than the first and third dielectric layers. An optical information recording/reproducing/erasing member characterized by: (7) The thermal expansion coefficient of the second dielectric layer is 1.0×10^-
7. The optical information recording/reproducing/erasing member according to claim 6, wherein the material is selected from a material having a hardness of ^8k^-^1 or less. (8) The optical information recording/reproducing/erasing member according to claim 6, wherein the combined thickness of the second and third dielectric layers is thinner than that of the first dielectric layer. (9) The optical information recording/reproducing/erasing member according to claim 6, wherein the first and third dielectric layers are made of a material containing ZnS as a main component, and the second dielectric layer is made of SiO_2. (10) The optical information recording/reproducing/erasing member according to claim 6, wherein a material consisting of Te, Ge, and Sb is used as the recording thin film.