JPH03152736A - Optical information recording medium and protective film for optical information recording medium - Google Patents

Abstract

PURPOSE:To prevent thermal deformation of protective films due to repetition of recording and erasing, to avoid movement of a recording film, and to obtain stable characteristics of repetition of recording and erasing by using a mixture of SiO2 and Al2O3 as the material of protective films to be provided on both sides of the recording film. CONSTITUTION:For example, the first protective layer 2 consists of a mixture film of about 1500 Angstrom thickness comprising SiO2 and 5 mol% Al2O3. The recording medium layer 3 is a mixture thin film comprising GeTe alloy and Sb, with about 300 Angstrom thickness. The second protective layer 4 of <=300Angstrom thickness consists of the same material as the first protective layer 2. A reflecting layer 5 used to cause multiple interference of laser light is a thin film of about 500 Angstrom thickness comprising Al, Au, or Cu. Namely, by providing protective layers adjacent to the recording layer, and by adding small amt. of Al2O3 to SiO2 which has small coefft. of thermal expansion, the total coefft. of thermal expansion can be made smaller. Thereby, thermal deformation of protective films due to repetition of recording and erasing can be suppressed, and segregation due to movement of the recording film can be prevented.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to an optical information recording medium capable of recording, reproducing, and erasing information in a high-density, large-capacity manner using a laser beam or the like. A recording medium layer is formed on one side of a disk substrate, and a laser beam is irradiated from the disk substrate side to form minute holes in the recording medium layer, or bits with varying optical density are formed for recording. Even though discs that perform playback have been put into practical use, erasable discs that allow for repeated writing and erasing by reversibly changing the optical density of the recording medium layer are being put into practical use. By melting and rapidly cooling it, it becomes amorphous and records information, and by heating and slowly cooling it, it crystallizes and erases it.This material is S, R0vsh.
Although materials such as Ge + s Tes + 5b2S2 made by Mr.
Thin films made of a combination of a chalcogen element such as es and a group V element of the periodic table or a group W element such as Ge are widely known. In order to record information on these thin films by modulating laser light and then erase that information, the thin film is crystallized in advance, and the intensity of the laser light focused at approximately 1 μm is modulated in accordance with the information. For example, by rotating a disc-shaped disk and irradiating it, the temperature of the laser beam irradiated area 1-1 is raised above the melting point of the thin film, and then rapidly cooled, resulting in an amorphous mark that records information but erases this information. There is a known method for heating the thin film by irradiating it with a long spot light in the direction of the rotating track of the disk, and then crystallizing it again by the gradual cooling effect of the long spot light. Although it is in a small area, the temperature becomes high,
For example, if a resin substrate is used as the disk substrate and the recording medium layer is directly formed, the heat deforms the disk substrate and makes it impossible to repeat recording and erasing.For this reason, when fishing on a boat, the disk substrate and recording medium layer are Even if a dielectric layer is formed as a protective layer between the recording medium layer and the protective member that protects the recording medium layer in order to prevent thermal deformation of the substrate, this dielectric layer is also formed on the protective member side. A reflective layer is provided on the dielectric layer to improve the sensitivity of recording and erasing as an optical layer that utilizes multiple interference of laser light to perform recording and erasing. The problem with information recording and erasable recording media that uses means of heating, melting, quenching, amorphization, and heating and temperature raising is that the signal quality fluctuates in response to heating cycles. This may be caused by repeated rapid cooling of 400°C or more by the recording spot light and the erasing spot light.In particular, during recording, for example, the recording medium layer 13 in FIG. When heated above the melting point and melted, the first protective layer 12 and the second protective layer 14 sandwiching the recording medium layer 13 from both sides become a recording film represented by the recording medium layer 13 as shown in FIG. It is thought that the laser irradiated area 1 expands and deforms due to the heat of the disk.Also, because the disk is rotating, the temperature is different at the beginning and end of the mark, and even though the end of the mark is higher and the beginning of the mark is lower. For this reason, the expansion and deformation of the dielectric layer shown in the protective layer 12.14 becomes asymmetrical, and it is thought that the melted recording film moves due to the temperature difference, but this phenomenon is repeated by irradiation with laser light for recording and erasing. The recording layer has a thick part and a thin part, and the thick part has a large heat capacity, so sufficient recording and erasing cannot be done, while the thin part has a small heat capacity, so it is overheated. However, even with the erasing power, the recording film becomes molten and the erasing rate decreases.Also, the dielectric layer in the thinner part of the recording film is thermally damaged and destroyed, making it impossible to record. The present invention solves these problems.Even if the temperature of the recording film during recording and erasing rises above or near the melting point, the dielectric layer does not undergo deformation due to thermal expansion, and recording and erasing is possible. It is an object of the present invention to provide a highly reliable disk with excellent cycle characteristics.A protective layer is formed in contact with a recording medium layer, and a 5i (A It uses a mixed material of isOs, and by adding a small amount of AlaOs to 5iOe, which has a high heat resistance as a protective layer, strong mechanical strength, and a small coefficient of thermal expansion, the coefficient of expansion becomes even smaller. By using a material with such properties as a protective layer, it is possible to suppress the deformation of the protective layer due to heat during recording and erasing.Therefore, it is possible to prevent L-bending due to movement of the recording film. EXAMPLE An optical information recording medium according to an embodiment of the present invention will be described below with reference to the drawings. In FIG. 1, 1 is a disk substrate made of a resin substrate such as Boligar carbonate or a glass substrate, and 71o2 is a first protective layer. So 5i (A to h
12 (It is a mixed film containing 5 mo1% of h, and the film thickness is approximately 1
3 is the recording medium layer, which is a mixed thin film made of GeTe alloy and sb, and the film thickness is approximately 300 layers.
4 is the second protective layer, which is made of the same material as the first protective layer and has a thickness of 3
00 Å or less. 5 is a reflective layer that utilizes multiple interference of laser light, and is a thin film made of metals such as AI, Au, and Cu, and the film thickness is approximately 500 mm. Vacuum evaporation and sputtering methods are used to form these thin films. 2106 can be used as a protection plate, which is the same as the disk substrate 1 and can be attached to the disk substrate 1 with adhesive 7. In the configuration shown in Fig. 1, the wiring can be erased by irradiating laser light from the direction of arrow 8. At this time, the recording medium layer 3 is a minute spot of about 1μ, but it is
℃ or higher, and as the temperature of the recording medium layer increases, the first and second protective layers are also heated.a
In this way, each protective film is repeatedly heated and cooled as recording and erasure are repeated. A to 5ins of the present invention
l! The linear expansion coefficient of the thin film mixed with 03 is close to zero, and no deformation occurred and no movement of the recording film was observed even after repeated power distribution and erasure.9 In this way, 5
By mixing AlaOs into i(h, the force that can obtain a linear expansion coefficient smaller than 5i(h) <, AIto
When s was reduced to 2 mo1% or less, movement of the recording film was observed due to repeated recording and erasing.
When the mo content is 1% or more, it is observed that the properties of Ah (h) increase, the thermal conductivity increases, the recording sensitivity tends to decrease, and the rate during film formation slows down.
The appropriate amount of AbO3 relative to i(h) is 2 to 30 mo1%9, and the coefficient of linear expansion in this range is almost zero.Also, the material and film thickness of the first protective layer 2 and the second protective layer 4 This is a major factor that determines the cooling conditions for the recording medium layer 3. In particular, the second protective layer is in contact with a reflective layer made of metal, and this reflective layer has a high thermal conductivity, so it is a major factor in determining the cooling conditions of the recording medium layer 3. Therefore, if the second protective layer 4 is thin, the recording medium 3 whose temperature has been raised by the laser beam will easily lose heat, be rapidly cooled, and become amorphous. As a result, the coefficient of linear expansion of the second protective layer 4 is reduced.The film thickness is 300 Å or less, and the effect is large.As described in detail, according to the present invention, on both sides of the recording film. The material of the protective layer provided was 5i (Als in h).

By using a mixture of 100% and 100%, it is possible to prevent thermal deformation of the protective film due to repeated power distribution and erasure, which eliminates movement of the recording film and provides stable cycle characteristics of power distribution and erasure.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of an information carrier disk according to an embodiment of the present invention, and FIG. 2 is a schematic cross-sectional view of a conventional information carrier disk showing movement of the recording film due to thermal deformation of the protective layer due to power distribution and erasure. A connection... Disc board 2...
・First protection #3...Recording medium #4...Second protection IL5...Reflection layer

Claims (6)

[Claims] (1) A recording thin film that has the property of absorbing the energy of laser light when irradiated with the laser beam, heating it, melting it, rapidly cooling it, and becoming amorphous; and the property of crystallizing the amorphous state by heating it; Si in contact with the recording thin film layer
An optical information recording medium comprising a protective film containing O_2 mixed with Al_2O_3. (2) A protective film for an optical information recording medium characterized by being made of a mixture of SiO_2 and Al_2O_3. (3) The ratio of TiO_2 in the protective film is 2 mol% or more 30
2. The optical information recording medium according to claim 1, wherein the optical information recording medium has a content of mol% or less. (4) The optical information recording medium according to claim 1, wherein a material consisting of Te-Ge or Sb is used as the recording film. (5) The optical information recording medium according to claim 1, further comprising a reflective layer provided on the surface opposite to the surface irradiated with laser light. (6) The optical information recording medium according to claim 1, wherein the film thickness between the recording film and the reflective layer is 300 Å or less.