JPH05234130A - Optical recording medium - Google Patents

Abstract

PURPOSE:To provide an optical recording medium which does not increase information error rate due to repeated recording and vanishing. CONSTITUTION:When a first protective layer 2, a phase change recording layer 4, a second protective layer 5 and a reflecting layer 6 are successively laminated on a substrate 1 to obtain a phase change optical recording medium, a ZnS layer 3 is interposed at least between the first protective layer 2 and the recording layer 4. At the time when the recording layer 4 crystallizes, many crystal nuclei are generated by the presence of the ZnS layer 3 and a fine-grained layer is formed. As a result, the occurrence of voids in the recording layer 4 due to repeated recording and vanishing is inhibited and information error rate is not increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable optical recording medium for recording and erasing information by utilizing the phase change of a recording layer caused by irradiation of laser light.

[0002]

2. Description of the Related Art In an optical recording medium represented by a magneto-optical disk and a phase change type optical disk, a method of recording and reproducing information by converging a laser beam is used. The density and recording capacity have improved dramatically. Currently, it is 128 for 3.5-inch magneto-optical disk.
Those having a capacity of megabytes are commercially available, and have a recording capacity far exceeding that of a magnetic disk. At the same time, it has a large capacity, but it also has the advantage of being convenient to carry like a floppy disk. Further, since recording / reproducing is performed in a non-contact manner in the optical recording medium, there is no fear that the recorded information is lost due to a head crash unlike a magnetic disk. Optical recording media having such advantages are forming a new market in the field of information filing systems and the like.

Among such optical recording media, a phase change type optical disk is a recording medium characterized by recording information by phase change of a recording layer. That is, the structure of the phase change type optical disk is generally as shown in FIG. 2, and a first dielectric material is formed on a substrate 1 made of plastic such as polycarbonate or glass having a guide groove for laser light on one side. A protective layer 2 and a recording layer 4 made of a phase change material are provided, and a second protective layer 5 and a reflective layer 6 are sequentially laminated. With such a film structure, recording and reproduction are performed as follows. First, the laser light incident from the substrate side is transparent to the first protective layer 2
The light is condensed by the light to form a light spot of about 1 μm and reaches the recording layer 4. A part of the light is transmitted through the recording layer 4, but the transmitted light is reflected by the reflective layer 6 to the recording layer 4 through the second protective layer 5. Therefore, the recording layer is efficiently irradiated with the laser beam, the laser beam having a high energy density is absorbed, and the recording layer 4 is heated. At this time, the first protective layer 2 and the second protective layer 5 act as a heat insulating layer, assist in increasing the temperature of the recording layer 4, and further, the substrate 1 or the reflective layer or the like undergoes a thermal irreversible change. Prevent it from reaching. Thus, the temperature of the recording layer 4 rises above the melting point, and the temperature generally reaches 400 degrees or higher. In the recording layer that has reached the melting point or higher, mass transfer occurs,
When the recording layer is rapidly cooled in the cooling process, it becomes an amorphous phase, and when gradually cooled, it becomes a crystalline phase, and information is recorded. On the other hand, at the time of reproducing information, the strength of reflected light is reproduced as a digital signal by utilizing the fact that the amorphous phase and the crystalline phase have different reflectances. In the phase change type optical disc,
Since the single beam overwriting is possible by selecting the material of the recording layer, it has attracted great attention.

For the above-mentioned reasons, the protective layer of such a phase-change optical disk is required to have a small thermal diffusivity, good heat resistance and a high refractive index. However, conventional single films of SiO ₂ , ZrO ₂ , ZnS, etc. have not been sufficient to fulfill such a role at the same time. For example,
SiO ₂ has a too small refractive index, and ZrO ₂ has a large refractive index but a large thermal diffusivity. ZnS also has a large refractive index like ZrO ₂ , but has poor heat resistance. Therefore, various attempts have been made to improve the performance of the protective layer. For example, in Japanese Patent Laid-Open No. 2-7240, Si
It has been proposed to secure the required refractive index and thermal diffusivity by selecting the composition of O _x . In addition, JP-A-2-22
In Japanese Patent No. 3033, Cu, Al, T is added to SiO _x.
Attempts have been made to further improve the refractive index and the thermal diffusivity by adding another metal element such as i.

On the other hand, since the phase change type optical disk is used as a rewritable recording medium, repeated stability of recording and erasing is required for the purpose of ensuring the reliability of recorded information. On the other hand, as described above, in the phase change type optical disk, since the recording layer is heated to a high temperature of 400 degrees or more, oxidation of the recording layer material, a chemical reaction with the protective layer material, a reaction to the substrate and the protective material, This causes an irreversible change, which causes a problem that the information error rate increases as recording and erasing are repeated. Therefore, Japanese Patent Application Laid-Open No. 62-76038 proposes that the protective layer is formed by laminating a soft dielectric film and a hard dielectric film. Further, JP-A-3-52138 proposes to use a nitride thin film, a passive metal oxide thin film or the like of a recording film material as a protective layer in order to prevent the recording film from being oxidized. Furthermore, JP-A-2-270144 proposes a composite protective film in which AlN is mixed with SiO ₂ .

[0006]

However, when the conventionally proposed protective layer is used, the density of generation of crystal nuclei is reduced when the recording layer is crystallized, resulting in coarse crystal grains. However, there is a problem that a void is generated near the recording bit. Further, as recording and erasing are repeated, voids on the surface of the recording layer grow and become large voids, and finally appear as noise in a reproduced signal, which causes a problem in repeated recording and erasing stability. For example, when recording and erasing were repeated on a disk using SiO ₂ as a protective layer, submicron-sized voids were generated on the surface of the recording layer.

The problem to be solved by the present invention is to provide an effective protective layer material, thereby suppressing the occurrence of voids due to repeated recording and erasing, and providing an optical recording medium having sufficient repeated recording and erasing characteristics. It is in.

[0008]

In order to solve the above problems, the present invention provides an optical recording medium in which a first protective layer, a recording layer, a second protective layer and a reflective layer are sequentially laminated on a substrate. An optical recording medium in which information is recorded by utilizing the fact that the recording layer undergoes a phase change between a crystalline phase and an amorphous phase upon irradiation with laser light, and the information is recorded between the first protective layer and the recording layer. Provided is an optical recording medium characterized in that a vapor-deposited layer made of ZnS (hereinafter referred to as ZnS layer) is provided.

[0009]

The present invention will be described in detail below. The layer structure of the optical recording medium of the present invention is shown in FIG. A first protective layer 2 is formed on a substrate 1 made of polycarbonate, glass or the like. Since the first protective layer plays a role of preventing thermal influence on the substrate as in the conventional case, a dielectric material having a small thermal diffusivity is preferable. In addition, it is preferable to increase the refractive index as much as possible in order to narrow the laser light. However, since the laser light is incident on the recording film, it is necessary that the refractive index is smaller than the refractive index (n = 2.3) of ZnS. Furthermore,
The first protective layer 2 needs to have a sufficient film thickness to suppress heat conduction to the substrate. In forming the protective layer, it is effective to form a dense film as it prevents moisture and the like from entering and at the same time suppresses the generation of voids to some extent. The ZnS layer 3 is formed on the protective layer by a vapor deposition method. Since crystal nuclei are generated at high density when the recording film is cooled by the ZnS layer, generation of voids is suppressed. Further, providing the ZnS layer having a large refractive index in contact with the recording film is also effective in narrowing the laser light. When forming the ZnS layer, good characteristics can be obtained if a dense film is formed as in the first protective layer. The thickness of the ZnS film is preferably 0.5 to 100 nm. When the film thickness is less than 0.5 nm, it tends to form islands and it is difficult to obtain a uniform film. When the film thickness is more than 100 nm, the first protective layer 2 and the first ZnS layer 3 are formed. Since it is necessary to make both film thicknesses optically advantageous in terms of recording and erasing characteristics, it is necessary to set the film thickness of the first protective layer 2 thin, and as a result, effective heat resistance is obtained. It is not preferable because it tends not to occur. Z laminated on the substrate in this way
The phase-change recording layer 4 is formed on the nS layer 3, and the second protective layer 5 and the reflective layer 6 are formed in this order by a vapor deposition method and laminated. If a ZnS layer is similarly provided between the second protective layer 5 and the phase-change recording layer 4, the above-mentioned effects are synergized and better characteristics can be obtained. The second protective layer 5 functions as a heat insulating layer when the recording layer is crystallized and has a function of releasing heat to the reflective layer when the recording layer is made amorphous. And need to.

The substrate used in the present invention is, for example,
Examples thereof include a substrate in which a guide groove is directly formed in resin or glass such as polycarbonate, polymethylmethacrylate, and amorphous polyolefin, and a substrate in which a guide groove is formed on a flat plate of glass or resin by a photopolymer method.

[0011] As the material of the first and second protective layer, typically the optical constants and the transmittance is large, large SiN _X effect of protecting the recording _{layer, SiO X, Al 2 O 3} , Ta 2 O 5, B
N, ZnSe, GeO ₂ , TeO ₂ , TiN, ZnTe,
Examples include SnO ₂ and SiC.

As a material for forming the phase change recording layer,
For example, GeTeSb, GeTe, SbTe, GeTe
S, GeSbTeSe, TeGeSnAu, InSe,
InSbTe, InSbSe, etc. are mentioned.

The material of the reflective layer is Al, Al, Au.
And alloys with other metals, etc., but an alloy in which Ti is added to Al, which has a large effect of protecting the recording film, is particularly preferable.

The first and second protective layers, the phase-change recording layer and the reflective layer are formed by physical vapor deposition (PVD) such as sputtering or ion plating, chemical vapor deposition (CVD) such as plasma CVD, or the like. .

If necessary, a protective coat layer may be provided on the reflective layer.

Both organic and inorganic materials are used for the material of the protective coating layer. When forming an organic protective coat layer, methods such as a dipping method, a spin coat method, a roll coater method, and a vapor deposition method are used. on the other hand,
When forming the inorganic protective coat layer, a method such as a sputtering method, a vapor deposition method, an impregnation method or the like is used.

Of these protective coating methods, the spin coating method using an ultraviolet curable resin is preferable because it is a simple and quick method. In this method, an ultraviolet curable resin is discharged onto a substrate using a dispenser, the magneto-optical recording medium is rotated at a high speed, and the resin is spread by centrifugal force for application. The applied resin is then cured by UV irradiation. The spin coating method can also be suitably used for resins other than the ultraviolet curable resin. In any case, the resin used for the protective coat layer preferably has a pencil hardness of H or higher after curing.

The plastic substrate has insufficient scratch resistance, and in order to overcome such drawbacks, a hard coat layer is provided on the surface opposite to the recording layer using a transparent material having high hardness. Is desirable. As a means for hard coating, a method of applying and curing an organic polymer such as a UV-curable resin containing a polyfunctional urethane acrylate and a photopolymerization initiator by a spin coating method, a 2P method or the like, a silicon dioxide by a precipitation method or a sputtering method, etc. And the like, a ceramic hard coat layer is not suitable for mass production due to poor productivity, and thus a hard coat layer using an ultraviolet curable resin is preferable.

The optical disk thus formed with a film may be used alone or may be used by laminating two optical disks.

[0020]

By providing a uniform ZnS layer on the surface of the recording layer as described above, the occurrence of voids during repeated recording and erasing can be suppressed, and at the same time, the heat resistance, which is a problem with the ZnS layer alone, can be improved. Sufficient characteristics could be secured by laminating a protective film having excellent properties. In this way, the optical recording medium according to the present invention has no increase in noise due to repeated recording and erasing, so that the information error rate is not deteriorated and good repeating characteristics are obtained.

(Example 1) As shown in FIG. 1, a SiN _x layer 90 nm, a ZnS layer 10 nm as a first protective layer, and a GeTeSb layer 100 nm as a phase-change recording layer were formed on a polycarbonate disk substrate having a diameter of 130 mm as shown in FIG. , A SiN _x layer 100 nm as a second protective layer and an Al layer 50 as a reflective layer
A phase change type optical recording medium was manufactured by sequentially forming a film with a thickness of nm by a vapor deposition method.

For this optical recording medium, 1800 rpm
At the rotation speed of f1-3.43 MHz signal, f2-
High power level of 14m using 1.0MHz signal
Repetitive recording and erasing were performed 1 million times by modulation between power levels of W and a low power level of 6 mW. At this time, overwriting was performed by a method of forming an amorphous mark at a high power level and crystallizing and erasing the amorphous mark at a low power level. As a result, no change in information error rate was observed due to repeated recording and erasure.

Example 2 Example 2 is different from Example 1 except that the ZnS layer 10 nm is provided between the phase-change recording layer and the second protective layer and the thickness of the second protective layer is 90 nm. A phase change type optical recording medium was manufactured in the same manner as in 1.

This optical recording medium was repeatedly recorded and erased 1 million times in the same manner as in Example 1, but no change in the information error rate was observed.

Comparative Example 1 As shown in FIG. 2, a SiN _x layer having a thickness of 100 nm was used as a first protective layer and a GeTeS layer was used as a phase change recording layer on a polycarbonate disc substrate.
b layer 100 nm, SiN _x layer 100 n as second protective layer
A phase-change optical recording medium was manufactured by sequentially depositing m and an Al layer of 50 nm as a reflective layer by a vapor deposition method.

When this optical recording medium was repeatedly recorded and erased 100,000 times in the same manner as in Example 1, it was confirmed that voids were generated at the interface between the bit forming portion and the initializing portion.

Comparative Example 2 A phase change type optical recording medium was manufactured in the same manner as in Comparative Example 1 except that ZnS layers were used as the first protective layer and the second protective layer in Comparative Example 1.

With respect to this optical recording medium, recording and erasing were repeated 1 million times in the same manner as in Example 1,
It was confirmed that the laminated structure was deformed.

The relationship between the number of times recording and erasing is repeated and the information error rate is shown in FIG.

[0030]

According to the phase change type optical recording medium of the present invention,
As a result of providing the ZnS layer between the recording layer and the protective layer, when the recording layer is crystallized, crystal nuclei are generated at a high density due to the presence of the ZnS layer, so that the crystal grains become small and even if recording and erasing are repeated. , The occurrence of voids on the recording layer surface is suppressed,
The information error rate no longer deteriorates.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an example of a layer structure of a phase-change optical recording medium of the present invention.

FIG. 2 is a schematic cross-sectional view showing an example of a layer structure of a conventional phase change optical recording medium.

FIG. 3 is a table showing the relationship between the number of repeated recording and erasing operations and the information error rate of the phase-change optical recording media of Examples and Comparative Examples.

[Explanation of symbols]

 1 Substrate 2 First Protective Layer 3 ZnS Layer 4 Phase Change Recording Layer 5 Second Protective Layer 6 Reflective Layer

Claims (2)

[Claims] 1. An optical recording medium in which a first protective layer, a recording layer, a second protective layer and a reflective layer are sequentially laminated on a substrate, and the recording layer has a crystalline phase and an amorphous phase when irradiated with laser light. An optical recording medium in which information is recorded by utilizing a phase change between the two layers, characterized in that a vapor deposition layer made of ZnS is provided between the first protective layer and the recording layer. recoding media. 2. The optical recording medium according to claim 1, wherein a vapor deposition layer made of ZnS is provided between the recording layer and the second protective layer.