JPH11162011A - Optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical information recording medium of a phase transition type having excellent repetitive overwrite characteristics. SOLUTION: This optical information recording medium of the phase transition type is constituted by holding a recording layer 3 consisting of a phase transition material by plural dielectric protective layers 2, 3, arranging these layers on a transparent substrate 1 and forming a reflection layer 5 on the dielectric protective layer parted from this transparent substrate. At least one dielectric protective layer among the plural dielectric protective layers is constituted to include three components; the first component mainly consisting of ZnS and the second and third components consisting of one or two kinds selected from an oxide, nitride, sulfide and fluoride. As a result, the repetitive overwrite characteristics are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase-change type optical information recording medium for recording and reproducing information by irradiating a laser beam, and is particularly suitable for high-density recording having excellent repetition characteristics of recording, reproducing and erasing. The present invention relates to an optical information recording medium.

[0002]

2. Description of the Related Art Phase-change optical information recording media include:
2. Description of the Related Art An optical disk using a method of performing recording, reproduction, and erasing by utilizing the fact that the optical constant of a recording layer reversibly changes between crystalline and amorphous has been known (Japanese Patent Laid-Open No. 7-7351).
No. 3). When the writing laser light is irradiated on the disk surface, the recording layer, the phase change material layer, is heated to a liquid phase by the irradiation of the writing laser light, and then rapidly cooled to become amorphous. The optical constant changes. A signal is read (reproduced) by detecting a change in the optical constant as a change in reflectance.

In this phase change type optical disk, crystallization and amorphization are selectively performed by changing the power of one laser beam between two levels. That is, by irradiating the recording layer with a high-power laser beam that raises the temperature of the recording layer to a temperature equal to or higher than the melting point, the recording layer becomes a liquid phase, and after being rapidly cooled, becomes an amorphous state. When the recording layer is irradiated with a low-power laser beam that reaches a temperature higher than the crystallization temperature and lower than the melting point, the irradiated portion is in a crystalline state. 2. Description of the Related Art Conventionally, a phase change optical disk has a configuration in which at least a phase change material layer, a dielectric protection layer, and a reflection layer are formed on a transparent substrate, and a protection layer and the like are further formed on the reflection layer.

For a recording layer made of a phase change material, a chalcogenide-based material such as GeSbTe-based, InSbTe-based, or InSe-based material is used. It is formed by a method. Further, the dielectric protective layer is formed of a mixture of ZnS and SiO _{2 by} the same film forming method. Generally, a sputtering method is often used in consideration of productivity. The state of the recording layer immediately after film formation is a kind of amorphous state. In order to perform recording on this recording layer to form an amorphous recording portion, initialization is performed to make the entire recording layer crystalline. Processing is performed. Recording is achieved by forming amorphous portions in this crystallized state.

In a phase-change type optical disk, during recording, the recording layer melts above its melting point as described above and is immediately cooled. Therefore, the dielectric protection film sandwiching the recording layer is repeatedly subjected to thermal stress during the heat mode recording of heating, melting, and cooling of the recording layer. For this reason, a material such as ZnS-SiO ₂ is used for the dielectric protection layer in consideration of heat resistance.

[0006]

As described above, in a phase-change optical disk, a recording layer is melted by laser light irradiation and becomes amorphous by cooling to form recording marks, and the recording marks and the recording marks other than the recording marks are formed. This is to detect the difference in reflectance from the part as a signal, and the dielectric protection layer sandwiching the recording layer
A mixture of ZnS and SiO ₂ with improved heat resistance of ZnS is used,
It showed excellent recording and erasing characteristics. However, when overwriting is repeatedly performed on such an optical disk many times, the recording layer itself flows due to repeated melting and cooling of the recording layer, and as a result, the film thickness of the recording layer fluctuates, and the reflectance decreases. In some cases, the signal amplitude decreases, and the signal amplitude decreases. Further, the dielectric protection layer may be deformed due to thermal damage, thereby damaging the recording layer and increasing jitter.

The cause of the fluctuation of the film thickness due to the flow of the recording layer as described above is considered as follows. That is, it has been confirmed that Ar gas used at the time of sputtering for forming the recording layer and the dielectric protection layer is mixed into the recording layer and the dielectric protection layer. Ar gas gradually aggregates to form voids. When the recording layer is melted and cooled, that is, overwriting is further repeated, minute voids grow while repeating aggregation, and as a result, the volume occupied by the voids in the recording layer gradually increases. The balance of the internal stress is lost, causing the flow of the film and the fluctuation of the film thickness. Also released from the dielectric protective layer
Ar gas infiltrates the recording layer to increase the formation of voids, and similarly causes the flow and thickness of the recording layer to fluctuate.

For the above reasons, the phase change type optical disk has a problem that the overwrite characteristics are repeatedly deteriorated. An object of the present invention is to solve the above problems and provide a phase change type optical information recording medium having excellent repetitive overwrite characteristics.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies on the causes of jitter, and as a result, it is possible to suppress the damage to the recording layer by controlling the properties of the dielectric protective layer sandwiching the recording layer. Thus, the present invention has been accomplished by obtaining the above-mentioned knowledge.

That is, according to the present invention, a recording layer made of a phase change material is interposed between a plurality of dielectric protection layers on a transparent substrate, and a reflection layer is formed on the dielectric protection layer remote from the transparent substrate. In a phase-change type optical information recording medium in which is formed, at least one of the plurality of dielectric protective layers has ZnS as a main first component, and has an oxide, a nitride, and a sulfide. One or two types selected from among substances and fluorides as the second and third components.
It is one that contains components.

In this case, each of the second and third components has a Young's modulus greater than ZnS of the first component and is 1.0 × 10 ^5.
1.01.0 × 10 ⁷ kgf / cm ² , and the Knoop hardness should be 500 or more. The thermal conductivity of the dielectric protection layer is in the range of 6 × 10 ⁻⁴ to 8 J / cmKs.

As described above, in a phase-change optical information recording medium in which at least a phase-change material layer, a dielectric protective layer and a reflective layer are formed on a transparent substrate, the dielectric protective layer is made up of three components. By selecting the Young's modulus, Knoop hardness, and thermal conductivity of the two components other than the components within predetermined ranges, the overwrite characteristics can be repeatedly stabilized. That is, by the above-described configuration, the deformation of the film is suppressed by increasing the mechanical strength of the dielectric protection layer,
Raising the thermal conductivity improves the heat dissipation characteristics, resulting in melting of the phase change material contained in the recording layer, damage to the dielectric protection layer caused by repeated cooling,
Furthermore, it is possible to suppress damage to the recording layer itself due to damage to the dielectric protection layer, and to achieve repeated overwrite characteristics.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the optical information recording medium of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a diagram showing a basic configuration of a phase change type optical information recording medium of the present invention. As shown in FIG. 1, an optical disc as an optical information recording medium includes a first dielectric protection layer 2, a recording layer 3 made of a phase change material, a second dielectric protection layer 4, a reflection layer 5, The protective layer 6 made of resin is sequentially laminated. In the illustrated example, the upper and lower parts are shown upside down.

The transparent substrate 1 has a groove and is made of a polycarbonate resin, a polyolefin resin,
Acrylic resin, quartz, glass and the like can be used. The phase change material of the recording layer 3 is, for example, a chalcogenide-based material.
GeSbTe-based, InSbTe-based, and InSe-based materials can be used. The first dielectric protection layer 2 or the second dielectric protection layer 4 or both of these dielectric protection layers 2 and 4 are mainly composed of ZnS, and the second and third components are oxides and nitrides. , Sulfide,
It is selected from fluorides and comprises a mixture of a total of three components. Specifically, oxides such as Al ₂ O ₃ and Ta
₂ O ₅ , SiO ₂ , ZrO ₂ , TiO ₂ , BeO, MgO, Y ₂ O ₃ , HfO ₂ etc.
AlN As the _{nitride, Si 3 N 4, TiN,} GeN, ZnN like, CdS as sulfide, PdS, Sb ₂ S ₃ or the like, as the fluoride, MgF _2,
LiF, NdF ₃ , NaF and the like, but are not limited thereto. Among the above dielectric materials, Young's modulus is 1.0 × 10 ^{5 to} 1.0 × 1
0 ⁷ kgf / cm ² and Knoop hardness of 500
Satisfies ~ 3000 and thermal conductivity is 6 × 10 ^-4 -8
Any material within the range of J / cmKs can be used.

The reflective layer 5 is made of a metal film having a good reflectivity to the irradiated laser beam, such as Cu, C
Mixtures with metals such as r, Ni, Ti, Mo, W and the like, or Au and the like can be used. In addition, as the protective layer 6 made of resin,
A thermosetting or ultraviolet curable resin can be used. The Young's modulus and Knoop hardness can be adjusted by controlling, for example, film forming conditions during sputtering film forming, such as Ar gas pressure, film forming speed, and distance between target substrates.

As described above, by forming the dielectric protective layers 2 and 4 from the ternary mixture as described above, the mechanical strength of the layers 2 and 4 is increased to suppress deformation, and the durability against thermal stress is improved. (Deformation resistance) can be improved. Accordingly, it is possible to improve the overwrite characteristics while suppressing an increase in jitter.

In particular, the mechanical strength can be further improved by setting the Young's modulus and Knoop hardness of the second and third components of the dielectric protective layers 2 and 4 within the ranges described above, respectively. Further, by setting the thermal conductivity of the dielectric protection layers 2 and 4 within the above-described range, heat radiation characteristics can be improved, and as a result, durability against thermal stress can be improved. Also, the dielectric protection layers 2, 4
Of the above three components is 70 mol% to 85 mol% for the first component.
Preferably, the second component is in the range of 5 to 20 mol%, and the third component is in the range of 5 to 20 mol%. Note that the second component and the third component may have the opposite relationship. The phase-change optical information recording medium having the above-described configuration will be described in detail with reference to specific examples.

The thickness is 1.2 mm and the track pitch is 1.6 μm
A first dielectric protection layer 2, a recording layer 3 made of a phase change material, a second dielectric protection layer 4, and a reflection five layer are sequentially laminated on a transparent substrate 1 made of polycarbonate to form a phase change optical recording medium. An optical disk was formed. At the time of film formation, ZnS
, Al ₂ O ₃ , SiO ₂ using a target consisting of three components,
A first dielectric protective layer 2 having a thickness of 100 nm was formed on the transparent substrate 1 by RF sputtering. In this case, the ratio of the three components is approximately 8: 1: 1 in terms of mol%. Next, a GeSbTe-based alloy was formed as a phase-change material with a thickness of 20 nm on the dielectric protective layer 2 to form the recording layer 3. Next, ZnS, Al ₂ O
_{3. A} second dielectric protective layer 4 composed of three components of SiO ₂ was formed to a thickness of 20 nm in the same manner as the first dielectric protective layer 2. Further, a reflective layer 5 of Al alloy was formed thereon to a thickness of 150 nm. Finally, on this, UV curable resin is spin-coated to 5-10μm
The resin was applied and cured by ultraviolet rays to form a resin protective layer 6.
Through the above process, a phase change optical disk was manufactured.

The disk thus manufactured was rotated, and dynamic measurement and evaluation were performed. The wavelength of the irradiation laser light is
685nm, numerical aperture NA of the objective lens is 0.60, linear velocity is 6.0m / s,
The recording power was 11.0 mW, the erasing power was 4.5 mW, and an 8-16 modulated signal was recorded. The reproduction power was 1.0 mW. The repetitive overwrite characteristic is measured by measuring the jitter σ of the 3T signal, which is the shortest mark (which is a normalized absolute value in FIG. 1 and preferably 1 or less) after recording and erasing a large number of times. Was observed. Here, T is a window width.
For comparison, the characteristics of a conventional optical disk were also measured. In this conventional optical disk, the first and second dielectric protection layers are made of Zn.
It is composed of two components of S-SiO ₂ , and other configurations are the same as the optical disk of the present invention.

FIG. 2 shows the measurement results. As a result, conventional optical disk sharply increases and characteristics are deteriorated when overwriting number exceeds ¹⁰⁵ times. In contrast, the phase change type optical disk prepared in Example of the present invention is significantly less than the increase in jitter conventional even beyond the number of overwriting times 10 ⁵ times, that shows good properties found. In the above embodiment, an optical disk having a single recording layer 3 has been described as an example. However, the present invention is not limited to this, and it is needless to say that the present invention can be applied to an optical disk having a plurality of recording layers, for example, two layers.

[0021]

As described above, according to the optical information recording medium of the present invention, the following excellent operational effects can be exhibited. Since the dielectric protection layer is a mixture containing three components mainly composed of ZnS, the mechanical strength can be increased to suppress deformation, and the durability against thermal stress can be improved. Therefore, it is possible to improve the overwrite characteristics repeatedly while suppressing an increase in jitter. Also, by selecting the Young's modulus, Knoop hardness, and thermal conductivity of the substance constituting the dielectric protective layer within predetermined ranges, the overwrite characteristics can be further improved repeatedly, and as a result, a phase with high reliability can be obtained. A variable-type optical information recording medium can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of a phase change type optical information recording medium of the present invention.

FIG. 2 is a diagram showing the relationship between the number of overwrites and jitter.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Transparent substrate, 2, 4 ... Dielectric protection layer, 3 ... Recording layer, 5
... reflective layer, 6 ... protective layer.

Claims (2)

[Claims] 1. A recording layer comprising a phase change material sandwiched between a plurality of dielectric protection layers on a transparent substrate, and a reflection layer is formed on the dielectric protection layer remote from the transparent substrate. In a phase-change optical information recording medium, at least one of the plurality of dielectric protective layers has ZnS as a main first component, and includes oxides, nitrides, sulfides, and fluorides. An optical information recording medium, characterized in that one or two types selected from the group consisting of these three components are included as second and third components. 2. The second and third components each have a Young's modulus greater than ZnS of the first component and are 1.0 × 10 ^{5 to} 1.0 × 1.
0 ⁷ kgf / cm ² , the Knoop hardness is 500 or more, and the thermal conductivity of the dielectric protective layer is 6 × 10 ^-4 to 8
2. The optical information recording medium according to claim 1, wherein the optical information recording medium is in a range of J / cmKs.