JPH05205316A - Rewritable optical information recording medium - Google Patents

Abstract

PURPOSE:To enable recording, erasing and reproduction with a high reflectance and small light energy. CONSTITUTION:A rewritable optical information recording medium 10 is formed by successively laminating a multilayer lower layer protective film 2 consisting of two transparent lower layer protective films (I)2a and (II)2b with different refractive indexes, a recording film 3, an upper layer protective film 4 and a reflective film 5 on a substrate 1. Each thickness of the multilayer lower layer protective film 2 is set so that the reflectances of both the part corresponding to a crystal part of the recording film and the amorphous part at the time of the wavelength of the light for recording and erasing between two light with different wavelengthes are low and the reflectance of either one between both parts of the recording film at the time of the wavelength of the light for reproduction is high and the reflectance of the other part is low. Thus since the subject rewritable optical information recording medium can be made high in light absorbability at the time of recording and erasing and sufficiently high in the reflectance at the time of reproduction, the light energy required at that time can be small enough.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable optical information recording medium capable of recording / erasing and reproducing.

[0002]

2. Description of the Related Art Conventionally, a compact disc (hereinafter referred to as a CD) has been widely used as an optical disc which is a read-only optical information recording medium, and is also used as a vehicle. Here, vibration resistance is one of the performances required for an optical disk mounted on a vehicle. In order to improve this vibration resistance,
High reflectivity is required on the optical disk side. As a rewritable optical information recording medium, Japanese Patent Laid-Open No. 2-165
The one disclosed in Japanese Patent No. 444, "Rewritable optical disk" is known. This is a phase-change type optical disk which utilizes a reversible change in the crystalline state upon irradiation with light, that is, a phase transition between amorphous and crystalline, and a change in reflectance that accompanies the phase transition. To obtain an amorphous portion (for example, a recorded state portion), a recording film (optical recording layer) is irradiated with a large amount of light energy (high laser power) for a short period of time and rapidly cooled from a high temperature molten state. Further, in order to obtain a crystalline portion (for example, an erased portion), the recording film (optical recording layer) is irradiated with medium optical energy (medium laser power) to heat and gradually cool the amorphous state. Achieved by.

[0003]

However, the reflectance of the portion corresponding to the crystalline portion (for example, erased portion) of the recording film of the phase change type rewritable optical information recording medium is about 50% at the highest. , Lower than the CD standard of 65%. Further, in the high reflectance state, the light absorptance is naturally small, so that there is a problem that the light energy during recording / erasing becomes very large. In the state where the difference in light absorptance between the crystalline portion and the amorphous portion is large, the light energy required for recording or erasing is largely different between the crystalline portion and the amorphous portion. There is a problem that it is difficult to perform so-called overwriting in which re-recording is performed on the recording medium instead of once erasing it.

The present invention has been made to solve the above problems, and an object of the present invention is to achieve high reflectance in a rewritable optical information recording medium and to record with a small optical energy. -To be able to erase and reproduce.

[0005]

The constitution of the invention for solving the above problems is a rewritable optical information recording medium in which a lower protective film, a recording film, an upper protective film and a reflective film are sequentially formed on a substrate. The lower protective film is composed of a plurality of films that are transparent to two lights having different wavelengths and have different refractive indexes, and have a multilayer structure in which the one having a larger refractive index is arranged alternately on the incident light side. At the wavelength of the light for recording / erasing of light, the reflectance of both portions corresponding to the crystalline portion and the amorphous portion of the recording film is low, and the portion of the light for reproducing of the two light rays is low. It is characterized in that the film thicknesses are set so that the reflectance is high in either one of the crystalline portion and the amorphous portion of the recording film at the wavelength and the reflectance is low in the other portion. And

[0006]

In the rewritable optical information recording medium of the present invention, the lower protective film, the recording film, the upper protective film and the reflective film are sequentially formed on the substrate. The lower protective film is composed of a plurality of films that are transparent to two lights having different wavelengths and have different refractive indices, and has a multilayer structure in which the one having the larger refractive index is alternately arranged on the incident light side. Each film thickness of the lower protective film having a multi-layer structure is such that reflection of both portions corresponding to a crystalline portion and an amorphous portion of the recording film at the wavelength of light for recording / erasing of the two lights. Both rates are set to be low. Further, each film thickness of the lower protective film having a multilayer structure is
At the wavelength of the reproduction light of the two lights, one of the two parts corresponding to the crystalline part and the amorphous part of the recording film has a high reflectance and the other has a low reflectance. Is set as follows. The optical information recording medium is recorded / erased / reproduced by using the two lights. As a result, the rewritable optical information recording medium of the present invention has a large light absorptance at the time of recording / erasing, and requires a small amount of light energy. In addition, since the reflectance of both of the portions corresponding to the amorphous portion and the crystalline portion of the recording film is low, and the difference in the light absorptance is small, this is easy to overwrite. Further, in the case of reproducing, since the portion corresponding to the crystalline portion of the recording film is in a high reflectance state having strong anti-vibration property at the time of reproducing, it can be reproduced even if the light energy is small.

[0007]

EXAMPLES The present invention will be described below based on specific examples. FIG. 1 is a schematic diagram showing a cross-sectional structure of a rewritable optical information recording medium according to the present invention. The rewritable optical information recording medium 10 is formed by sequentially laminating the following films on a substrate 1 made of, for example, a disc-shaped transparent glass or plastic. Polycarbonate (refractive index 1.
On the substrate 1 composed of 58), the multilayer lower layer protective film 2 was formed as the lower layer protective film. This multilayer lower protective film 2 has a wavelength (685
nm, 780 nm) is a two-layer film which is transparent to two lights having different refractive indices and has a different refractive index. The lower protective film (I) 2a and the lower protective film (I
I) and 2b were laminated so as to form a multilayer structure. The lower protective film (I) 2a was formed with TiO ₂ (refractive index 2.5) to a thickness of 240 nm, and the lower protective film (II) 2b was formed with ZnS—SiO ₂ (refractive index 2.0) to a thickness of 100 nm. .. Next, the lower protective film
(II) A recording film 3 made of GeSbTe was formed on 2b.
An upper protective film 4 made of ZnS—SiO ₂ (refractive index 2.0) was formed thereon with a thickness of 140 nm. Further, a reflective film 5 made of Au was formed to a thickness of 100 nm. Each of the above films was formed by sputtering. Further, an inorganic or organic film may be further formed thereon as an overcoat.
Further, the lower protective film (I) and the lower protective film (II) may be films that are transparent to two lights having different wavelengths and have a different refractive index (different refractive index).

FIG. 2 shows a recording film thickness of a crystalline portion and an amorphous portion in the optical information recording medium 10 having the above structure.
It is a characteristic view showing a simulation result of the dependency of reflectance (%) on (nm). 2 (a) shows the case where the light wavelength λ is 685 nm for recording / erasing, and FIG. 2 (b) shows the case where the light wavelength λ is 780 nm for reproduction. Wavelength of light
At 685 nm, when the film thickness of the recording film 3 was 70 nm, the reflectance of the crystalline portion was 42% and the reflectance of the amorphous portion was 29%. When the wavelength of light is 780 nm, the film thickness of the recording film 3 is 70 nm.
The reflectance of the crystalline portion was 63%, and the reflectance of the amorphous portion was 25%. The reflectance changes as above, and the light absorption rate at the light wavelength of 685 nm is 58% for the crystalline part,
The amorphous portion is 71%. That is, since the optical information recording medium 10 of the present embodiment has a large light absorptance in both the crystalline portion and the amorphous portion, recording / erasing can be easily performed with a small optical energy. Also, overwriting is possible. When the wavelength of light is set to 780 nm, the reflectance of the crystalline portion becomes large, and even if the light energy for reproduction is small, focus servo or tracking servo can be easily performed. The focus servo is a control for moving the objective lens up and down so that the focus is accurately positioned with respect to the vertical movement of the optical information recording medium in the pickup optical system for the optical information recording medium. Further, the tracking servo is a control in which a beam follows a track shake generated in a radial direction when the optical information recording medium rotates in a pickup optical system for the optical information recording medium. As a result, the optical information recording medium 10 has an effect of being resistant to vibration when recording or reproducing.

FIG. 3 is a schematic view showing the sectional structure of a second embodiment of the rewritable optical information recording medium according to the present invention. In the rewritable optical information recording medium 30, the lower protective film between the substrate 31 and the recording film 33 is the multilayer lower protective film 32. This multilayer lower protective film 32 has a wavelength (685 nm, 780 nm)
Lower layer protective film (I) 32a and lower layer protective film (II) 32, which are two-layer films that are transparent to two different light rays and have different refractive indices
Four layers were alternately laminated so as to form a multilayer structure in which b was a unit. The lower protective film (I) 32a is made of TiO ₂ (refractive index 2.5).
At a thickness of 87 nm, and the lower protective film (II) 32b is made of ZnS-Si.
A film having a thickness of 100 nm was formed with O ₂ (refractive index 2.0). The substrate 31, the recording film 33, and the upper protective film 3
4. The material of the reflection film 35 and the like are the same as those in the above-mentioned embodiment, and the description thereof will be omitted.

FIG. 4 shows the recording film thickness of the crystalline portion and the amorphous portion in the optical information recording medium 30 having the above structure.
It is a characteristic view showing a simulation result of the dependency of reflectance (%) on (nm). Incidentally, FIG. 4A shows the case where the light wavelength λ is 685 nm for recording / erasing, and FIG. 4B shows the case where the light wavelength λ is 780 nm for reproduction. Wavelength of light
At 685 nm, the reflectance of the crystalline portion was 42% and the reflectance of the amorphous portion was 28% when the film thickness of the recording film 33 was 65 nm. When the wavelength of light is 780 nm, the film thickness of the recording film 33 is 65
In nm, the reflectance of the crystalline portion was 70% and the reflectance of the amorphous portion was 33%. Since the reflectance changes as described above, when the light wavelength is 780 nm, the reflectance of the crystalline portion satisfies the CD standard reflectance of 65% or more. Therefore, recording / playback CD
When a film having the structure of the present invention is formed on a substrate for commercial use, a commercially available CD
It can be played on a playback device.

Next, a third embodiment of the rewritable optical information recording medium according to the present invention will be described. The cross-sectional structure of this optical information recording medium 50 is similar to that of the second embodiment described above,
In FIG. 3, a substrate 51, a multilayer lower layer protective film 52 (lower layer protective film (I) 52a, lower layer protective film (II) 52b), recording film 5
3, the upper protective film 54 and the reflective film 55 are replaced with reference numerals. In the optical information recording media 30 and 50, the film thicknesses of the lower protective films (I) 32a and 52a made of TiO ₂ are different. In the rewritable optical information recording medium 50, the lower protective film between the substrate 51 and the recording film 53 is the multilayer lower protective film 52. This multilayer lower protective film 52 has a wavelength (685n
(m, 780 nm) are transparent to two lights having different m and 780 nm and have different refractive indices, and are alternated to form a multi-layer structure including a lower protective film (I) 52a and a lower protective film (II) 52b as a unit. 4 layers were laminated. That is, the lower protective film (I) 52a is made of TiO 2.
₂ (refractive index 2.5), thickness 240 nm, lower protective film (II) 52
b was ZnS—SiO ₂ (refractive index 2.0) and was formed into a film having the same thickness as 100 nm in the second embodiment.

FIG. 5 shows the recording film thickness of the crystalline portion and the amorphous portion in the optical information recording medium 50 having the above structure.
It is a characteristic view showing a simulation result of the dependency of reflectance (%) on (nm). 5 (a) shows the case where the light wavelength λ is 685 nm for recording / erasing, and FIG. 5 (b) shows the case where the light wavelength λ is 780 nm for reproduction. Wavelength of light
At 685 nm, the reflectance of the crystalline portion was 31% and the reflectance of the amorphous portion was 10% when the film thickness of the recording film 53 was 65 nm. When the wavelength of light is 780 nm, the film thickness of the recording film 53 is 65
In nm, the reflectance of the crystalline portion was 72% and the reflectance of the amorphous portion was 35%. The reflectance changes as above,
The optical absorption at a light wavelength of 685 nm is 69 for the crystalline part.
%, And the amorphous portion is 90%. As described above, in the optical information recording medium 50 of the present invention, the sensitivity of the amorphous portion and the crystalline portion at the time of reproduction is improved, and the optical information recording medium 50 is used as a recording medium of high speed rotation (10 m / sec) such as a video disc. it can. That is, since the optical information recording medium 50 has a high reflectance in the crystalline portion, it can be reproduced by a commercially available video disk reproducing device.

FIG. 6 is a schematic view showing the cross-sectional structure of a fourth embodiment of the rewritable optical information recording medium according to the present invention. The rewritable optical information recording medium 60 is a multilayer lower protective film 62 in which four lower protective films of a substrate 61 and a recording film 63 are laminated. The multilayer lower layer protective film 62 is formed by forming a lower layer protective film (I) 62a made of TiO ₂ (refractive index 2.5) on a substrate 61 made of polycarbonate with a thickness of 200 nm and SiO ₂ (refractive index
1.46) lower protective film (II) 62b with a thickness of 150 nm, T
It was deposited respectively at a thickness 200nm the lower protective layer (III) 62c made of iO _2. These films are formed by the sputtering method, and T is used for the target that is the material source.
io ₂ and io ₂ were used. Furthermore, ZnS-SiO ₂ (refractive index 2.
A lower protective film (IV) 62d consisting of 0) was formed to a thickness of 90 nm. This film is also formed by the sputtering method, but a target which is a material source is a mixture of ZnS and SiO ₂ and sintered. Next, a recording film 63 made of GeSbTe was formed. This film is also formed by the sputtering method, and the target that is the material source is Ge, S
Appropriate mixed sintering of b and Te (GeSb ₂ Te _4, Ge ₂ S
b ₂ Te ₅ ) was used. ZnS-Si is formed on the recording film 63.
An upper protective film 64 made of O _{2 was formed} to a thickness of 135 nm. The method of forming this film was the same as that of the lower protective film (IV) 62d. Further, a reflective film 65 made of Au was formed to a thickness of 100 nm. This film was formed by a sputtering method or a vacuum evaporation method.

FIG. 7 shows the recording film thickness of the crystalline portion and the amorphous portion in the optical information recording medium 60 having the above structure.
It is a characteristic view showing a simulation result of the dependency of reflectance (%) on (nm). Incidentally, FIG. 7 (a) shows the case where the light wavelength λ is 780 nm for reproduction, and FIG. 7 (b) shows the case where the light wavelength λ is 850 nm for recording / erasing. Wavelength of light
At 780 nm, the reflectance of the crystalline portion was 72% and the reflectance of the amorphous portion was 31% when the thickness of the recording film 63 was 65 nm. When the wavelength of light is 850 nm, the film thickness of the recording film 63 is 65
In nm, the reflectance was 30% for both the crystalline part and the amorphous part. Since the reflectance changes as described above, the light wavelength
At 80 nm, the reflectance of the crystalline part is the CD standard reflectance of 65.
Satisfies at least%. Also, when the wavelength of light is 850 nm, the light absorption is large, so recording / erasing becomes easy.

Next, a fifth embodiment of the rewritable optical information recording medium according to the present invention will be described. The cross-sectional structure of this optical information recording medium 80 is similar to that of the above-mentioned fourth embodiment,
In FIG. 6, a substrate 81, a multilayer lower protective film 82 (lower protective film (I) 82a, lower protective film (II) 82b, lower protective film (I)
II) 82c, the lower protective film (IV) 82d), the recording film 83, the upper protective film 84, and the reflective film 85 are replaced with the reference numerals. In addition, the lower protective film (II) 82b is the above-mentioned SiO 2
₂ (refractive index 1.46) lower MgF ₂ (refractive index 1.3
In 8), the film thickness is set to 160 nm, and the TiO ₂ that is vertically adjacent to the film is
The refractive index difference with the film is made larger.

FIG. 8 shows the recording film thickness of the crystalline portion and the amorphous portion in the optical information recording medium 80 having the above structure.
It is a characteristic view showing a simulation result of the dependency of reflectance (%) on (nm). 8 (a) shows the case where the light wavelength λ is 780 nm for reproduction, and FIG. 8 (b) shows the case where the light wavelength λ is 850 nm for recording / erasing. Wavelength of light
At 780 nm, the reflectance of the crystalline portion was 75% and the reflectance of the amorphous portion was 36% when the thickness of the recording film 83 was 65 nm. Further, when the wavelength of light is 850 nm, the film thickness of the recording film 83 is 65
In nm, the reflectance was 34% for both the crystalline portion and the amorphous portion. Compared with the above-mentioned fourth embodiment, the reflectance could be improved by about 4% by increasing the refractive index difference of the lower protective film. By performing the film structure and the recording / erasing method as described above, the optical information recording medium 80 can perform recording / erasing at an extremely high speed as compared with the conventional one.

As described above, in the rewritable optical information recording medium according to the present invention, the lower protective film (I) and the lower protective film (III) of the multilayer lower protective film are transparent and have a high refractive index. The material is good, and the lower protective film (II) is preferably transparent and has a low refractive index. Furthermore, it was found that the conditions of the materials used for the lower protective film (IV) and the upper protective film should be as follows. Be transparent to light of the above wavelengths. It has a higher melting point than the recording film. Do not react with the recording film.

The material of the recording film in the rewritable optical information recording medium according to the present invention is GeSb as described above.
In addition to the Te system, an InSbTe system or an InSe system phase change film may be used. Furthermore, the rewritable optical information recording medium according to the present invention may be overcoated, and then a protective plate or another similar optical information recording medium may be attached with an adhesive or the like.

[Brief description of drawings]

FIG. 1 is a schematic view showing a cross-sectional structure of a rewritable optical information recording medium according to a specific example of the present invention.

FIG. 2 is a characteristic diagram showing a simulation result of dependence of reflectance on a recording film thickness of a crystalline portion and an amorphous portion in the rewritable optical information recording medium according to the example.

FIG. 3 is a schematic diagram showing a cross-sectional structure of a second embodiment of a rewritable optical information recording medium according to the present invention.

FIG. 4 is a characteristic diagram showing a simulation result of the dependency of reflectance on the recording film thickness of the crystalline portion and the amorphous portion in the second embodiment of the rewritable optical information recording medium according to the present invention. is there.

FIG. 5 is a characteristic diagram showing a simulation result of the dependency of reflectance on the recording film thickness of the crystalline portion and the amorphous portion in the third embodiment of the rewritable optical information recording medium according to the present invention. is there.

FIG. 6 is a schematic view showing a cross-sectional structure of a fourth embodiment of the rewritable optical information recording medium according to the present invention.

FIG. 7 is a characteristic diagram showing a simulation result of dependency of reflectance on recording film thickness between a crystalline portion and an amorphous portion in a fourth embodiment of the rewritable optical information recording medium according to the present invention. is there.

FIG. 8 is a characteristic diagram showing a simulation result of the dependence of reflectance on the recording film thickness of the crystalline portion and the amorphous portion in the fifth embodiment of the rewritable optical information recording medium according to the present invention. is there.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Multilayer lower protective film 2a ... Lower protective film (I) 2b ... Lower protective film (II) 3 ... Recording film 4 ... Upper protective film 5 ... Reflective film 10 ... Rewritable optical information recording medium

Claims (1)

[Claims] 1. A rewritable optical information recording medium in which a lower protective film, a recording film, an upper protective film and a reflective film are sequentially formed on a substrate, wherein the lower protective film protects against two lights having different wavelengths. It has a multi-layered structure composed of a plurality of transparent films having different refractive indexes, and the one having the larger refractive index is arranged alternately with the incident light side as the incident light side. The reflectance of both portions corresponding to the crystalline portion and the amorphous portion of the film is low, and when the wavelength of the light for reproduction of the two lights is low, the crystalline portion and the amorphous portion of the recording film are An optical information recording medium, characterized in that the film thicknesses thereof are set so that one of the corresponding portions has a high reflectance and the other has a low reflectance.