JPH05217214A - Material for substrate reflection layer in optical recording medium - Google Patents

Abstract

PURPOSE:To provide the material for a substrate reflection layer which enables a high reflectivity by imparting a good push-pull signal characteristic to an optical disk having the film of the material for the substrate reflection layer which exhibits a high reflectivity and high transmittance with a good balance on the substrate. CONSTITUTION:The substrate reflection layer 2, then a recording layer 3 are formed on the substrate 1 and light is made incident from the substrate 1. Grooves 4 for tracking servo are directly formed on this substrate 1. The substrate 1 consists of an acrylic resin, polycarbonate resin, glass, etc. The film formation of the reflection layer 2 is executed by a sputtering method, vacuum vapor deposition method, etc. Further, the material to be used for the recording layer 3 generates a certain optical change by the photon energy or thermal energy generated by photoirradiation. Namely, a change in the reflectivity or transmittance arises from a color change, phase change, pit formation, shape change, etc. As a result, the high reflectivity is enabled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a material for a reflective layer of a substrate which enables high reflectance and high transmittance in an optical recording medium.

[0002]

2. Description of the Related Art Optical discs capable of high density recording are expected to become the mainstream of recording media in the future.
Read-only optical discs have already formed a large market in the audio field. Research and development have also been conducted on a write-once optical disc capable of recording information and a rewritable optical disc capable of recording and erasing information. Among them, a write-once optical disc for recording by a pit formation method using a Te-based or organic dye as a recording material and a TbFeCo-based for a recording material,
A rewritable optical disk of a magneto-optical system using a rare earth system has already been put into practical use.

Most optical discs have a recording layer formed directly on a substrate.
The push-pull signal characteristics necessary for performing tracking servo may not be obtained due to the optical constants, film thickness, film forming properties, etc. of the recording material used for the recording layer. For example, when the difference in the complex refractive index between the substrate and the recording layer is small and the difference in the complex refractive index between the recording layer and the air or the recording layer and the layer laminated thereon (for example, the reflective layer or the protective layer) is large, the push-pull It is difficult to get a signal. In addition, when the film forming property of the recording material is poor, there arises a problem that the noise becomes high due to a minute roughness of the film or the tracking shifts. Therefore, if the recording layer is formed directly on the substrate, the characteristics may be inferior. In such a case, it is effective to form a material having a refractive index different from that of the substrate and having a good film-forming property as the substrate reflecting layer between the substrate and the recording layer. As a result, the push-pull signal required for tracking servo can be satisfactorily detected and noise can be reduced.

As such a substrate reflecting layer, one having a refractive index which is largely different from that of the substrate in the wavelength range of the light source used is preferable. For example, in JP-A-1-276443,
An optical disc having a substrate reflection layer made of a metal such as u, Ag or Cu is disclosed. However, these metals have a poor balance between light transmittance and reflectivity as materials for the substrate reflecting layer. That is, if the film thickness is increased to obtain a sufficient reflectance, the transmittance is lowered, and conversely, if the film thickness is reduced to obtain a sufficient transmittance, the reflectance is lowered.

[0005]

The inventors of the present invention have conducted extensive studies in view of the above problems, and as a result, found that silicon or silicon nitride has excellent properties as a material for a substrate reflection layer, and complete the present invention. Came to. The present invention is based on this knowledge, and for an optical recording medium in which optical recording and erasing are performed using a semiconductor laser, a substrate reflection layer for which the film thickness of the recording layer can be arbitrarily set and which enables stable tracking servo. It provides the material.

[0006]

A material for a substrate reflection layer in the present invention is used for a substrate reflection layer in an optical recording medium including at least a substrate, a substrate reflection layer formed on the substrate, and a recording layer. It is made of silicon.

The substrate reflection layer material preferably has an extinction coefficient of 0.2 or less at the wavelength of the light source used, and is particularly 0.
Or, almost 0 is preferable. The refractive index is preferably different from the refractive index of the substrate by 0.4 or more.

An application example of the material for the substrate reflecting layer in the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing an example of the structure of an optical disc using the material for a substrate reflecting layer in the present invention. In FIG. 1, a substrate reflective layer 2 and then a recording layer 3 are laminated on a substrate 1. In this optical disc, light is incident from the substrate side.

Although the groove 4 for tracking servo is directly formed on the substrate 1, it may be a pit. Further, the groove forming layer may be laminated on the substrate without directly forming the groove on the substrate 1. The groove may be a simple groove, or pits corresponding to the format signal may be formed in the groove. Pits corresponding to this format signal may be formed in the land portion of the substrate. When forming a pit instead of the groove for tracking servo, a pit corresponding to the format signal may be further included. The substrate 1 may be made of synthetic resin such as acrylic resin, polycarbonate resin, epoxy resin, polyolefin resin, or glass.

The substrate reflective layer can be formed by a sputtering method, a vacuum vapor deposition method, or the like. In particular, the silicon nitride film can be formed by a sputtering method in an atmosphere containing nitrogen gas.

The material used for the recording layer 3 is not particularly limited as long as it causes some kind of optical change due to photon energy or heat energy generated by light irradiation, and it is a rewritable material even if it is a write-once material. It may be a material. Examples of such a material include materials that cause a change in reflectance or transmittance due to color change, phase change, pit formation, shape change, and the like. Furthermore, specifically, as a color-changing substance, a spiropyran-based compound,
A photochromic compound such as a fulgide-based compound, a photochromic compound dispersed in a polymer compound,
There are those having a photochromic group in the side chain, there are polymer compounds blends, polymer liquid crystals, etc. that undergo phase changes, and phthalocyanine dyes, naphthalocyanine dyes, cyanine dyes, etc. that form pits. There are organic dyes, polymer compounds in which such organic dyes are dispersed, and shape memory resins that change in shape,
There is one having a two-layer structure of an expansion layer made of a material capable of thermal expansion and contraction such as polyurethane and a holding layer made of a resin capable of being thermally deformed and having a high glass transition point such as an epoxy resin. The recording layer 3 can be formed by a spin coating method, a dipping method, a vacuum deposition method, or the like.

A reflective layer and / or a protective layer may be laminated on the recording layer 3. The respective layers of the optical disc described above are stacked under the condition that the film thickness is optimized in consideration of the optical constant of the material used and the push-pull signal.

[0013]

EXAMPLES Next, examples of optical constants (refractive index and extinction coefficient) of an example of the material for a substrate reflecting layer of the present invention and characteristics evaluation of an optical disk manufactured using this material for a substrate reflecting layer will be shown. However, the present invention is not limited to these.

Example 1 A silicon thin film having a thickness of about 50 nm was formed on a slide glass substrate by a sputtering method to form a substrate reflection layer.
A reflection spectrum (aluminum relative value) and a transmission spectrum were measured using the glass substrate having this substrate reflection layer. Figure 2 shows the reflection spectrum and Figure 3 shows the transmission spectrum.
Show. At a wavelength of 780 nm, the reflectance is 62% (aluminum relative value) and the transmittance is 50%.
In nm, the reflectance was 63% (aluminum relative value) and the transmittance was 48%. In each case, the balance between reflectance and transmittance was good.

Example 2 A polycarbonate substrate having a diameter of 120 mm and having a groove (made by Idemitsu Petrochemical Co., Ltd., refractive index of 1.59 at 830 nm) having a thickness of about 50 was formed on a disk substrate.
nm silicon thin film (refractive index at 830 nm is 3.15,
A film having an extinction coefficient of 0.05) was formed to form a substrate reflection layer. Next, 10 parts by weight of a block copolymer of polystyrene and trans-1,4-polybutadiene (Asmer, trade name of Asahi Kasei Corporation), 1 part by weight of bis (triethylsiloxy) silicon-tetrakis (decylthio) naphthalocyanine, and toluene 320 It was dissolved in 1 part by weight to obtain a uniform solution.
This solution was applied by spin coating on the substrate reflection layer to form a recording layer having a thickness of about 290 nm, and an optical disc was produced.

An optical disk manufactured as described above by an optical recording characteristic evaluation device (OMS2000, trade name of Nakamichi Co., Ltd., which is designed to irradiate laser light from the substrate side) equipped with a semiconductor laser having a wavelength of 830 nm. When a tracking servo was attempted with a laser power of 1 mW, a good push-pull signal excellent in waveform and signal strength was obtained, and stable tracking servo could be performed. This optical disc has a rotation speed of 3 m / s and a frequency of 1
When recording was performed while changing the laser power at MHz and a duty of 50%, C / N showed recording power dependency and 45 dB was obtained at a laser power of 5 mW. Then, for erasing, the entire circumference of the recorded track was irradiated with a laser beam of 2 mW at a rotation speed of 3 m / s. C / N decreases, erase ratio is 25 dB
showed that. Furthermore, C / N is 45 with re-recording power of 5 mW.
It showed dB. Such recording characteristics and erasing characteristics could be repeatedly measured. That is, since the tracking servo is stable, good recording and erasing can be repeated.

Example 3 On a disk substrate made of polycarbonate having a diameter of 120 mm (made by Idemitsu Petrochemical Co., Ltd., refractive index 1.59 at 830 nm), a mixed gas flow of argon gas and nitrogen gas (flow rate ratio, argon gas: A silicon nitride thin film with a thickness of about 50 nm (refractive index 2.6 at 830 nm, extinction coefficient 0.
02) was formed into a film to form a substrate reflection layer. Next, poly (3
10 parts by weight of -dodecylthiophene and 1 part by weight of bis (triethylsiloxy) silicon-tetrakis (decylthio) naphthalocyanine were dissolved in 490 parts by weight of toluene to obtain a uniform solution. This solution was applied by spin coating to form a recording layer having a thickness of about 100 nm on the substrate reflective layer to prepare an optical disc.

Using the same optical recording characteristic evaluation device as in Example 2, an attempt was made to perform tracking servo on the above-produced optical disk with a laser power of 1 mW, and a good push-pull signal excellent in waveform and signal strength was obtained and stable. I was able to perform a proper tracking servo. This optical disc has a rotation speed of 3 m / s, a frequency of 1 MHz and a duty of 5
When recording was performed by changing the laser power at 0%, C /
N indicates the recording power dependence and is 40 at a laser power of 8 mW.
dB was obtained. Then, for erasing, the entire circumference of the recorded track was irradiated with a laser beam of 2 mW at a rotation speed of 3 m / s. C
/ N decreased and the erase ratio was 25 dB. Furthermore, the C / N was 40 dB at a re-recording power of 8 mW. Such recording characteristics and erasing characteristics could be repeatedly measured. That is, since the tracking servo is stable, good recording and erasing can be repeated.

Example 4 A polycarbonate substrate having a diameter of 120 mm and having a groove [a refractive index of 1.59 at 830 nm manufactured by Idemitsu Petrochemical Co., Ltd.] having a thickness of about 50 was formed by a sputtering method.
nm silicon thin film (refractive index at 830 nm is 3.15,
An extinction coefficient of 0.05) was formed and used as a reflective layer. next,
10 parts by weight of 1,2-polybutadiene [JSR RB810, trade name of Japan Synthetic Rubber Co., Ltd.] and 1 part by weight of bis (triethylsiloxy) silicon-tetrakis (decylthio) naphthalocyanine were dissolved in 320 parts by weight of toluene to form a uniform solution. Was spin-coated to form a recording layer having a thickness of about 250 nm on the surface of the silicon film of the substrate to form an optical recording medium. Wavelength 830n
Optical recording characteristics evaluation device [OM
S2000 (trade name of Nakamichi Co., Ltd., this device is adapted to irradiate laser light from the substrate side) according to the recording characteristics of the optical recording medium obtained as described above under the same conditions as in Example 1. The erasing characteristics were measured, and as a result, the recording power was 7
C / N shows 40 dB at mW and C at erasing power of 2 mW
/ N decreased and the erase ratio was 20 dB. Furthermore, C / N was 40 dB at a re-recording power of 7 mW. Such recording characteristics and erasing characteristics could be repeatedly measured. That is, since the tracking servo is stable, good recording and erasing can be repeated.

Example 5 A polycarbonate substrate having a diameter of 120 mm and having a groove [a refractive index of 1.59 at 830 nm manufactured by Idemitsu Petrochemical Co., Ltd.] having a thickness of about 50 was formed by a sputtering method.
nm silicon thin film (refractive index at 830 nm: 3.15, extinction coefficient: 0.05) was formed as a reflective layer. Next, a uniform solution was prepared by dissolving 10 parts by weight of polystyrene (95800 molecular weight Aldrich Chemical Corporation) and 1 part by weight of bis (triethylsiloxy) silicon-tetrakis (decylthio) naphthalocyanine in 320 parts by weight of toluene. An optical recording medium was prepared by applying a film on the surface of the silicon film of the substrate by spin coating to form a recording layer having a thickness of about 200 nm.

Using the optical recording characteristic evaluation apparatus shown in Example 1, the recording characteristic and the erasing characteristic of the optical recording medium obtained above were measured under the same conditions as in Example 1. As a result, the C / N was 40 dB at a recording power of 4 mW. Next, when this optical recording medium was placed in an oven and subjected to heat treatment at 120 ° C. for 5 minutes, C / N was reduced and an erasing ratio of 20 dB was obtained. Furthermore, with a re-recording power of 4 mW, the C / N is 40 d.
B was shown. Such recording characteristics and erasing characteristics could be repeatedly measured. That is, since the tracking servo is stable, good recording and erasing can be repeated.

Comparative Example 1 A 23 Å-thick gold thin film was formed on a slide glass substrate by a vacuum deposition method to form a substrate reflection layer. A reflection spectrum (aluminum relative value) and a transmission spectrum were measured using the glass substrate having this substrate reflection layer. As a result,
At a wavelength of 780 nm, the reflectance was 19% (aluminum relative value) and the transmittance was 53%, and at the wavelength 830 nm, the reflectance was 18% (aluminum relative value) and the transmittance was 56%. In both cases, the balance between reflectance and transmittance was not good.

Comparative Example 2 An optical disk comprising a substrate and a recording layer was prepared in the same manner as in Example 2 except that a glass substrate with a groove having a diameter of 130 mm was used instead of the polycarbonate substrate and the substrate reflection layer was not formed. When this optical disk was evaluated by the same optical recording characteristic evaluation device as that used in Example 2, no push-pull signal was detected and tracking servo could not be performed.

[0024]

The film of the substrate reflective layer material according to claim 1 exhibits high reflectance and high transmittance in a well-balanced manner, and imparts good push-pull signal characteristics to an optical disc having this on the substrate. Enables optical discs with excellent tracking servo.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of an optical disc manufactured using a material for a substrate reflection layer in the present invention.

FIG. 2 is a reflection spectrum of a substrate on which a substrate reflection layer manufactured in Example 1 is laminated.

FIG. 3 is a transmission spectrum of a substrate on which a substrate reflection layer manufactured in Example 1 is laminated.

[Explanation of symbols]

1 ... Substrate, 2 ... Substrate reflective layer, 3 ... Recording layer,
4 ... groove.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masanobu Haburo 48 Wadai, Tsukuba City, Ibaraki Prefecture Tsukuba Development Laboratory, Hitachi Chemical Co., Ltd. (72) Inventor Takeo Toyama 48 Wadai, Tsukuba City, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Incorporated company Tsukuba R & D Labs (72) Inventor Nobuaki Takane 48 No. Wadai, Tsukuba, Ibaraki Prefecture Hitachi Chemical Co., Ltd. Within Tsukuba R & D Labs (72) Inventor, Mitsuo Yamada 48 Wadai, Tsukuba, Ibaraki Hitachi Chemical Co., Ltd. Incorporated company Tsukuba Development Laboratory

Claims (1)

[Claims] 1. A material for a substrate reflection layer, which is used for a substrate reflection layer in an optical recording medium including at least a substrate, a substrate reflection layer formed thereon, and a recording layer, and made of silicon or silicon nitride.