JPH10255324A - Phase transition type recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase transition type optical recording medium which is improved in respective characteristics of recording, erasing an reproducing even when the recording is executed at a high line speed. SOLUTION: A protective layer 2, boundary reflection control layer 3, recording layer 4, light absorption layer 7, protective layer 5 and reflection layer 6 are formed in this order on a substrate 1. The recording layer 4 comprises an alloy contg. at least Ge, Sb, Te and N. The boundary reflection control layer 3 comprises a mixture composed of >=1 kinds of the dielectric substances selected from ZnS, SiO2 , SiO, SiC, SiN and TiO2 and >=1 kinds of the metals selected from W, Mo, Nb, Ta and Hf.

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 recording medium capable of obtaining a high quality reproduced signal in overwriting by mark edge recording at a high linear velocity.

[0002]

2. Description of the Related Art In recent years, as a means for recording an enormous amount of information, research and development on an optical recording medium have been actively conducted. In particular, a so-called phase-change optical recording medium that performs recording and erasing of information by using a recording layer in which the recording layer reversibly changes phase between two states, crystalline and amorphous, uses the power of laser light. It is promising because it has the advantage that it is possible to simultaneously record new information (hereinafter referred to as "overwriting") while erasing old information only by changing it.

As a material of a recording layer used for a phase change type optical recording medium, for example, a Ge-Te-Sb alloy described in JP-A-62-53886 and an alloy disclosed in JP-A-61-258787 are disclosed.
In the publication, Ge-Te-Sb-M (M is Al, Si, T
i, V, Cr, Mn, Fe, Co, Ni, Cu, Zn,
Y, Zr, Nb, Mo, Ru, Rh, Pd, Ag, T
a, W, Au, Tl, Pd, and a metal selected from Bi).

On the other hand, when recording / erasing is actually performed by using these chalcogen alloys, deformation of the substrate due to heat during recording / erasing is prevented, oxidation of the recording layer, mass transfer along the guide groove. Or, in order to prevent deformation, usually, at least one of metal or metalloid oxides, carbides, fluorides, sulfides, and nitrides at least one or both immediately above and immediately below the recording layer. Is provided.

On a transparent substrate, a recording layer made of a chalcogen alloy, a protective layer provided immediately below and / or immediately above the recording layer, and a cooling layer provided on the opposite side of the recording layer from the substrate side are also used. A three-layer or four-layer structure having a reflective layer (for example, an Al alloy) has become the mainstream of the phase-change optical recording medium because the signal amplitude can be increased and the repetition characteristics can be improved.

However, when overwriting is performed with a single beam in a phase-change recording medium having such a structure, a new recording mark is formed between a crystalline portion and an amorphous portion according to the previous recording state. It is formed on both of the parts. The effect of the magnitude of thermal conductivity and latent heat differs depending on whether the recorded part is crystalline or amorphous. Differences result, resulting in different maximum temperatures of the parts. This causes a problem that the size and shape of the recording mark, that is, the recording state is different, which may adversely affect the erasing characteristics. Further, at the time of mark edge recording for the purpose of high-density recording, there may be a problem that information cannot be reproduced correctly.

In general, a recording layer in a crystalline state has a higher thermal conductivity than a recording layer in an amorphous state, and requires latent heat to melt. Therefore, a recording mark is formed in a crystalline state. In this case, a larger amount of heat is required than when forming a recording mark in an amorphous state.

In order to solve this, for example, Japanese Patent Laid-Open No.
No. 149238 discloses that the light absorption coefficient in a crystalline state of a recording layer (hereinafter referred to as “Ac”) is equal to the light absorption rate in an amorphous state (hereinafter referred to as “Aa”), or It is disclosed to be higher than Aa. As a method therefor, it is mentioned that the film thickness of each layer constituting the phase change recording medium is appropriately selected. Specifically, the film thickness of the metal reflection layer is made thinner than usual, and the metal reflection layer is formed directly above and below the recording layer. Is changed, the ratio of the light absorptivity in the crystalline state to the light absorptivity in the amorphous state (Ac / A
An example in which a) is increased to about 1.1 is disclosed.

[0009]

However, in this method, Aa is kept low by reducing the thickness of the reflective layer and increasing the amount of transmitted light from the reflective layer. As the reflection layer becomes higher, the amount of return light entering the recording layer from the opposite side of the reflection layer from the recording layer increases, causing noise at the time of reproduction, or causing the reflection layer to be thinner. Because cooling performance decreases,
There may be a problem that the recording / erasing and reproducing characteristics are deteriorated.

In order to increase the transfer rate at the time of recording, it is necessary to perform recording at a high linear velocity. In particular, when performing recording at a high linear velocity in mark edge recording,
It is necessary to increase the light absorption ratio (Ac / Aa) of the phase change recording medium. For example, the light absorption ratio (Ac / Aa) required when the recording linear velocity is 5.5 m / s is about 0.85, but the light absorption ratio required when the recording linear velocity is 15 m / s. (Ac / Aa) is said to be about 1.45 (sponsored by the Japan Society of Applied Physics, Phase Change Recording Research Group, 1995 [1995], Proceedings of the 7th Phase Change Symposium, “High Density Phase Change Light”). Fundamentals and Applications of Recording Technology ”P23-28
reference).

However, the recording layer is made of Ge-Sb-Te
When it is composed of an alloy, the light absorption ratio (Ac / A
If recording is performed at a high linear velocity by setting a) extremely high, there is a problem in that noise during reproduction is large and a good reproduction signal cannot be obtained.

The present invention has been made in view of such a point, and provides a phase-change type optical recording medium having good recording / erasing and reproducing characteristics even when recording is performed at a high linear velocity. The task is to provide.

[0013]

According to the present invention, there is provided a recording layer having a reversible phase change between a crystalline state and an amorphous state according to the intensity of irradiation light. And a substrate supporting the recording layer, wherein the recording layer is made of an alloy containing at least Ge, Sb, Te, and N in a phase change type optical recording medium for recording, erasing, and reproducing information by light irradiation. , Just below the recording layer, ZnS, SiO
_2, SiO, SiC, SiN, and the one or more dielectric selected from _{TiO 2, W, Mo, Nb} , Ta, and interface reflection control consisting of a mixture of one or more metals selected from Hf A phase-change type optical recording medium characterized in that a layer is provided and a protective layer made of a transparent dielectric material is provided between the interface reflection control layer and the substrate.

In the present invention, the reflectance at the light incident side interface of the recording layer is defined as Ra when the recording layer is in an amorphous state, and Rc when the recording layer is in a crystalline state. By providing the control layer immediately below the recording layer (on the light incident side),
Interface on the light incident side of the recording layer (interface with the interface reflection control layer)
, The reflectance difference (Rc-Ra) becomes smaller, and the light absorption ratio (Ac / Aa) can be set to a high value (for example, 1.40 or more) that can cope with recording at a high linear velocity.

On the other hand, immediately below the recording layer (on the light incident side)
When the recording layer is provided immediately above the protective layer without providing the interface reflection control layer as described above, for example, the reflectance difference at the light incident side interface of the recording layer (the interface with the protective layer). (Rc-R
a) becomes large, and as a result, light absorption in the recording layer is larger in the case where the recording layer is in the amorphous state than in the case where the recording layer is in the crystalline state.

In the present invention, the above-mentioned dielectric materials constituting the interface reflection control layer all have a melting point, a sublimation point, and a transition point of 1000 ° C. or more, and have high durability against heat. Further, the above-mentioned metals constituting the interface reflection control layer all have a melting point of 2000 ° C. or higher, and are hardly diffused into the recording layer heated and melted during recording. Since such an interfacial reflection control layer is formed immediately below the recording layer, the material constituting the interfacial reflection control layer does not diffuse into the recording layer during recording, and the recording / erasing characteristics are maintained even by repeated overwriting. Good retention.

The content of the metal in the mixture constituting the interface reflection control layer is preferably 5% by volume to 60% by volume, more preferably 10% by volume to 40% by volume. If the metal content is less than 5% by volume, the effect of increasing the light absorption ratio (Ac / Aa) cannot be substantially obtained. On the other hand, when the metal content is more than 60% by volume, the amount of light that passes through the interface reflection control layer and reaches the recording layer is significantly reduced, deteriorating the sensitivity at the time of recording / erasing or reducing the signal amplitude at the time of reproduction. May be.

The thickness of the interface reflection control layer is 2 nm or more and 10
It is preferably in the range of 0 nm or less. If the thickness is less than 2 nm, it is difficult to form a uniform continuous film.
If it exceeds 300, the amount of light absorbed by the interface reflection control layer becomes too large, and there is a possibility that the recording sensitivity is reduced or the optical contrast is reduced. The more preferable thickness of the interface reflection control layer is from 2.5 nm to 20 nm.

In the phase change type optical recording medium of the present invention, the light absorption ratio (Ac / Aa) is extremely increased by forming the recording layer from an alloy containing at least Ge, Sb, Te and N. Even when recording is performed at a high linear velocity, it is possible to form a recording mark with a small displacement of a mark forming position and a small shape distortion. As a result, noise at the time of reproduction can be reduced.

Such a recording layer is made of, for example, Ge-Sb
-Forming a thin film by sputtering or the like by mixing nitrogen in an atmosphere gas with
a target made of an e-Sb-Te alloy and Ge, Sb,
Alternatively, it can be obtained by forming a thin film by sputtering or the like using both targets made of Te nitride.

This recording layer may be made of a material to which a small amount of another element is added in addition to Ge, Sb, Te, and N. The thickness of the recording layer is 10 nm or more and 5
It is preferably 0 nm or less.

The phase-change type optical recording medium of the present invention further comprises a protective layer made of a transparent dielectric material between the interface reflection control layer and the substrate.
Conventionally known materials can be used as the protective layer material, such as any of S, SiO ₂ and SiO, or a mixture thereof. The thickness of the protective layer is arbitrarily set so as to obtain appropriate optical characteristics, but is preferably 50 nm or more in order to suppress deformation of the substrate surface due to thermal diffusion during recording.

As the material of the substrate, a conventionally known material such as glass, polycarbonate resin, and acrylic resin can be used. As shown in FIG. 1, the phase-change optical recording medium of the present invention comprises at least a substrate 1, a protective layer 2, an interface reflection control layer 3 made of the above-described material, and a recording layer 4 made of the above-described material. The protective layer 2, the interfacial reflection control layer 3, and the recording layer 4 exist in this order from the substrate 1 side, and no intervening layer exists between the interfacial reflection control layer 3 and the recording layer 4. However, in addition, it is preferable that the recording layer 4 has a protective layer, a light absorption layer, a reflection layer, and the like for the purpose of increasing the signal amplitude and improving the overwrite repetition characteristics.

As a specific example, as shown in FIG. 2, a protective layer 2, an interface reflection control layer 3, a recording layer 4, a protective layer 5, and a reflective layer 6 are formed on a substrate 1 in this order. As shown in FIG. 3, a protective layer 2, an interface reflection control layer 3, a recording layer 4, a light absorbing layer 7, and a reflective layer 6 are formed on a substrate 1 in this order. As shown in FIG. 5, a protective layer 2, an interface reflection control layer 3, a recording layer 4, a light absorbing layer 7, a protective layer 5, and a reflective layer 6 are formed on a substrate 1 in this order, as shown in FIG. In addition, a substrate in which a protective layer 2, an interfacial reflection control layer 3, a recording layer 4, a protective layer 5, a light absorbing layer 7, and a reflective layer 6 are formed in this order on a substrate 1 is exemplified.

The protective layer 5 on the recording layer 4 is made of ZnS, Si, similarly to the protective layer 2 between the substrate 1 and the interface reflection control layer 3.
Conventionally known materials can be used as the protective layer material, such as O ₂ or SiO, or a mixture thereof. The thickness of the protective layer 5 is set to 50 nm in order to obtain a quenching effect advantageous to the overwrite repetition characteristics.
The following is preferred.

The material of the reflective layer 6 includes metals and semiconductors, but it is preferable to use an Al alloy in order to obtain particularly good overwrite repetition characteristics. Use of a material having an extinction coefficient k of 3.6 or less is preferable because a particularly large light absorption ratio (Ac / Aa) can be obtained. The thickness of the reflective layer 6 is preferably 50 nm or more in order to obtain a high cooling rate.

The material of the light absorbing layer 7 may be any one of dielectric, metal, semiconductor, carbon, boron, etc.
Alternatively, a mixture of these materials can be used, but it is particularly preferable to use one of the above-mentioned materials for the interface reflection control layer 3 or carbon. The thickness of the light absorbing layer 7 is also preferably 50 nm or less in order to obtain a quenching effect advantageous to the overwrite repetition characteristics.

[0028]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described using specific examples. First, the substrate 1 has a center hole with a diameter of 120 mm and a thickness of 0.6 mm.
Made of polycarbonate, 1.4μ in advance
A groove having a pitch of 0.7 μm and a pitch of m was prepared.

Next, various thin films were laminated on the substrate 1 so as to have a layer structure shown in Table 1 below. The thickness of each layer is as shown in Table 2. Table 1 shows that the protective layers 2 and 5
The constituent materials of the layers other than the above are indicated by numbers, and the materials indicated by the numbers are shown in Table 3 for the interface reflection control layer 3, Table 4 for the recording layer 4, and Table 5 for the light absorbing layer 7.
The reflection layer 6 is described in Table 6 respectively. Further, since all of the layers having the protective layer 5 above the recording layer use the same material as the protective layer 2 below,
Table 1 shows only the presence or absence of the protective layer 5.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

[0033]

[Table 4]

[0034]

[Table 5]

[0035]

[Table 6]

The protective layer 2 below the recording layer 4 was formed on the substrate 1 by RF sputtering using a mixture of ZnS and SiO ₂ (SiO ₂ content: 30 mol%) as a target. The atmosphere gas for sputtering was argon gas.

The interface reflection control layer 3 was formed on the protective layer 2 by a simultaneous sputtering method using a target made of a dielectric and a target made of a metal. The target of the dielectric is RF (high frequency) sputtering,
The metal target was formed by a DC (direct current) sputtering method. The atmosphere gas for sputtering was argon gas.

The recording layer 4 was formed on the interface reflection control layer 3 by a DC sputtering method using a target made of a Ge—Te—Sb alloy. Here, in Examples 1 to 5, the recording layer 4 was made of a Ge—Te—Sb—N alloy by using a mixed gas of argon and nitrogen (partial pressure of nitrogen gas: 0.014 Pa) as the atmosphere gas for sputtering. Configured. In Comparative Examples 1 and 2, the recording layer 4 was made of a Ge—Te—Sb alloy by using argon gas (partial pressure of nitrogen gas: 0 Pa) as the sputtering atmosphere gas.

The light absorbing layer 7 was formed on the recording layer 4 only in Examples 1, 3, and 4 and Comparative Example 2. According to the constituent material of the light absorbing layer 7, by using the RF sputtering method when using only the dielectric, by using the DC sputtering method when using metal or carbon.
When a mixture of a dielectric and a metal was used, a film was formed by the same method as that for forming the interface reflection control layer 3 described above. The atmosphere gas for sputtering was argon gas.

The protective layer 5 is provided on the light absorbing layer 7 in Example 4 and Comparative Example 2, and on the recording layer 4 in Examples 2, 5 and Comparative Example 1. 2 were formed in the same manner as in the formation of No. 2.

The reflective layer 6 is provided on the light absorbing layer 7 in Examples 1 and 3, and the protective layer 5 in other cases.
On top of each, using a target made of Al alloy,
It was formed by a DC sputtering method. The atmosphere gas for sputtering was argon gas.

Next, a UV curable resin was applied on the reflective layer 6 by spin coating, and was cured by irradiating ultraviolet rays. Using each sample of the phase change type optical disk (phase change type optical recording medium) thus obtained, the linear velocity was 6 m / s.
At 12 and 12 m / s, overwriting by mark edge recording was performed, and the jitter value of the overwriting signal was measured.

That is, each sample is rotated by a driving device so as to have a predetermined linear velocity, and an 8-16 modulation signal is applied to a position 35 mm in the radial direction from the center of the disk using a laser beam having a wavelength of 680 nm. After the mark edge recording, a random signal was recorded on the mark edge recording at the same linear velocity.

The jitter was measured by a jitter analyzer, and Tw of the obtained jitter value (standard deviation σ) was measured.
The ratio (σ / Tw) to (window width) was calculated. The results are shown in Table 7 below. Note that this ratio (σ
If / Tw) is 15% or less, it is a practically good reproduced signal.

From the optical constants of the constituent materials of each sample, the ratio (Ac / Aa) of the light absorption in the crystalline state to the light absorption in the amorphous state in the recording layer 4 was determined by optical calculation. The results are also shown in Table 7 below.

[0046]

[Table 7]

As can be seen from Table 7, in Examples 1 to 5 corresponding to the embodiment of the present invention, the recording layer 4 was formed of Ge-Te-S
Since it is made of a bN alloy and has the interface reflection control layer 3, the light absorption ratio (Ac / Aa) can be increased to 1.25 or more, and the jitter can be increased even when the linear velocity is as high as 12 m / s. The ratio (σ / Tw) becomes 10% or less, and a good reproduced signal is obtained.

On the other hand, in Comparative Example 1, the recording layer 4
The jitter ratio (σ / Tw) at a linear velocity of 6 m / s is as low as 7% because of the e-Te-Sb-N alloy, but the light absorption rate is low because the interface reflection control layer 3 is not provided. Ratio (A
c / Aa) is as low as 0.91, and when the linear velocity is as high as 12 m / s, the jitter ratio (σ / Tw) is as large as 17%, and a high quality reproduced signal cannot be obtained.

In Comparative Example 2, the light absorption ratio (Ac / Aa) was 1.21 because the interface reflection control layer 3 was provided.
However, since the recording layer 4 is made of a Ge—Te—Sb alloy, the jitter ratio is (σ / Tw) = 10% at a linear velocity of 6 m / s, and (σ / Tw) at a linear velocity of 12 m / s. ) =
When the linear velocity is as high as 12 m / s, high quality reproduced signals cannot be obtained.

[0050]

As described above, according to the phase change type optical recording medium of the present invention, a good reproduction signal can be obtained particularly in overwriting by mark edge recording at a high linear velocity.

[Brief description of the drawings]

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

FIG. 2 is a schematic sectional view showing an example (Examples 2 and 5) of a layer structure of a phase change type optical recording medium of the present invention.

FIG. 3 is a schematic cross-sectional view showing an example (Examples 1 and 3) of a layer structure of a phase change type optical recording medium of the present invention.

FIG. 4 is a schematic sectional view showing an example (Example 4) of a layer structure of a phase change type optical recording medium of the present invention.

FIG. 5 is a schematic sectional view showing an example of a layer structure of a phase change optical recording medium of the present invention.

[Description of Signs] 1 Substrate 2 Protective layer below recording layer 3 Interfacial reflection control layer 4 Recording layer 5 Protective layer above recording layer 6 Reflective layer 7 Light absorbing layer

Claims (1)

[Claims] 1. A recording layer in which a phase change between a crystalline state and an amorphous state is reversibly performed in accordance with the intensity of irradiation light, and a substrate supporting the recording layer. In a phase-change optical recording medium for performing recording, erasing, and reproduction of a recording layer, the recording layer is made of an alloy containing at least Ge, Sb, Te, and N, and ZnS, SiO ₂ , S
1 selected from iO, SiC, SiN, and TiO ₂
Or more dielectrics and W, Mo, Nb, Ta, and H
f) providing an interfacial reflection control layer made of a mixture with one or more metals selected from the group consisting of f) and a protective layer made of a transparent dielectric material between the interfacial reflection control layer and the substrate. A changeable optical recording medium.