JPH11254833A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To determine a composition which enables a high frequency of repeated overwrite at a high writing density to be performed in an Ag-In-Sb-Te phase changing recording material and further, make available the appropriate material of a protecting layer and a medium structure which helps determine the composition. SOLUTION: This photorecording medium is structured of a first dielectric protecting layer 2, a recording layer 3, a second dielectric protecting layer 4 and a reflective heat radiation layer 6 formed, in that order, on a base 1. The recording layer 3 is composed of a material represented by a chemical formula: AgαInβSbγTeδ. In the formula, α, β and γ are independently a composition ratio (atomic %) and satisfy the following requirements: 1<=α<10, 1<β<=20, 35<=γ<=70, 20<=δ<=35, α+β+γ+δ=100, 4β-δ<=0, γ-2δ>=0, γ-8α>=0.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large-capacity and rewritable phase-change optical recording medium.

[0002]

2. Description of the Related Art An optical recording medium capable of recording / reproducing and erasing information by irradiating a semiconductor laser beam has a magneto-optical recording system in which magnetization is reversed by utilizing heat, and a recording / erasing method is used. There is a phase-change optical recording system that can record and erase data using a specific phase change. The latter is advantageous in that it allows single-beam overwriting and is compatible with CD-ROM and CD-R media. Therefore, a standard has been established today as a rewritable medium for CD-RW media. Has been commercialized.

On the other hand, studies have been made on increasing the capacity of a phase change optical recording medium, and with the release of DVD-ROM media, a rewritable DVD medium called a DVD-RAM has been developed. A DVD-RAM with a capacity of 2.6 GB is about to appear,
A capacity of M or more is desired. Materials used for the recording layer of the phase change recording medium are chalcogen-based Ge-Sb-Te,
In-Sb-Te, Ge-Se-Te, Ge-Te-B
i, Sb-Se-Te, and In-Te-Au have been investigated so far, but among them, Ge-Sb-Te has reached a practical level. However, even with Ge-Sb-Te, it is desired to improve the recording sensitivity and erasing sensitivity, and to improve the characteristics such as a reduction in the erasing ratio due to the unerased portion during overwriting.

Accordingly, Ag-In-Sb has been proposed as a material capable of further improving the erasing ratio during overwriting.
-Te system (JP-A-4-78031, JP-A-9-2)
63055). The improvement in the erasing ratio in this system is due to the two-phase state of microcrystalline AgSbTe ₂ and amorphous In—Sb during erasing. Ag-In-Sb-
Te-based recording materials are more excellent in high-density recording, and are expected to be applied to large-capacity optical recording media and DVD-RWs in the future. Therefore, the present applicant has also proposed a composition having a high density and a composition range having more excellent recording and reproduction characteristics.

Further, the improvement in the number of repetitions required for a recording medium cannot be achieved by using only the recording material described above, and the improvement is achieved by laminating the upper and lower protective layers and the heat radiation layer. Heretofore, as the material of the protective layer, ZnS.SiO ₂ (Japanese Patent Publication No. 7-114031), metal oxides, metal sulfides, and metal nitrides alone or in mixtures have been considered. The mixing ratio of ZnS and SiO ₂ is particularly 80: 2.
It is said that a ratio of 0 is good. Further, the reflective heat dissipation layer represented by AlTi improves the reflectance and the repetitive overwrite characteristics.

[0006]

The present invention relates to a large-capacity and rewritable phase-change optical recording medium expected in the future. The phase-change recording medium is commercialized as a CD-RW and is used for an external memory of a personal computer. Today, DVD-ROM players have begun to appear, and commercialization of large-capacity and rewritable DVD media is expected. The present invention relates to a recording layer material and composition excellent in recording / reproducing characteristics, particularly for increasing the number of repeated overwrites, using a phase change recording method usable for these media. Further, these characteristics relate to the configuration, material, and composition of the protective layer so that the characteristics are not deteriorated even in high-speed recording / reproducing.

[0007] DV as rewritable DVD media
D-RAM has appeared. It has a capacity of 2.6 GB and performs recording and reproduction at a linear velocity of about 6 m / sec. DVD-ROM
, A linear velocity of about 3.5 m / sec and a capacity of 4.7 GB
It is. What is required of rewritable DVD media is to enable recording and reproduction at a capacity larger than ROM and at double speed or higher,
Further, compatibility with the ROM can be obtained. To satisfy such specifications, low jitter, even at high linear density,
A wide margin of characteristics and a high number of repeated overwrites are fundamental, and the requirements are becoming stricter.
In particular, the number of repetitive overwrites is one of the major issues in a phase change recording medium, and it is necessary to improve this characteristic in order to increase the reliability. Ag-I
The n-Sb-Te phase change recording material is a material suitable for high-density recording, and the problem is how to increase the number of repetitive overwrites. In the present invention, Ag-In-Sb-
It is an object of the present invention to find a composition having a high density and a high number of repetitive overwrites in a Te-based phase change recording material, and to further propose a material and a configuration of a protective layer for enabling the composition.

[0008]

Means for Solving the Problems The present inventors have developed an optical recording medium comprising a first dielectric protective layer, a recording layer, a second dielectric protective layer, and a reflective heat dissipation layer which are laminated on a substrate in this order. As a result of examining the material represented by the formula AgαInβSbγTeδ used for the recording layer, it is assumed that a material having α, β, γ and δ representing the composition ratio (atomic%) of each element of the above formula satisfying the following requirements is used. It has been found that an optical recording medium having excellent recording and reproduction characteristics can be obtained even at high density, and the present invention has been achieved. 1 ≦ α <10 1 <β ≦ 20 35 ≦ γ ≦ 70 20 ≦ δ ≦ 35 α + β + γ + δ = 100 4β-δ ≦ 0 γ-2δ ≧ 0 γ-8α ≧ 0

Hereinafter, the configuration of the optical recording medium of the present invention will be specifically described with reference to FIG. 1 is a substrate, 2 is a first dielectric protection layer, 3 is a recording layer, 4 is a second dielectric protection layer, 5 is a heat dissipation layer, 6 is a reflection heat dissipation layer, and 7 is an organic environment protection layer.
Each of the layers, for example, the five heat dissipation layers, may have a laminated structure of two or more layers as necessary.

[0010] The first, second dielectric protective layer _{2,4, SiOx, ZnO, SnO 2} , Al 2 O 3, TiO 2,
Metal oxides such as In ₂ O ₃ , MgO, ZrO ₂ and Ta ₂ O ₅ , nitrides such as Si ₃ N ₄ , AlN, TiN, BN and ZrN, sulfides such as ZnS and TaS ₄ , SiC, TaC, B ₄
Carbides such as C, WC, TiC, ZrC and the like can be mentioned. These materials are used alone or as a mixture thereof. As the mixture, for example, ZnS
SiOx, Ta ₂ O ₅ and SiOx and the like and. These material properties include thermal conductivity, specific heat, thermal expansion coefficient, refractive index, and adhesion to the substrate material or recording layer material, etc., high melting point, high thermal conductivity, low thermal expansion coefficient, and low adhesion. Good things are required. In particular, the second dielectric protection layer affects repeated overwrite characteristics and sensitivity.

Although the thickness of the protective layer is more important,
The thickness of the first dielectric protection layer 2 is in the range of 50 to 250 nm, preferably 75 to 200 nm. If the thickness is less than 50 nm, the protective function for environmental resistance is reduced, the heat resistance is reduced, and the heat storage effect is reduced. On the other hand, if the thickness is more than 250 nm, in the film manufacturing process by a sputtering method or the like,
Undesirably, an increase in the film temperature causes film peeling or cracking, or lowers the sensitivity during recording. The thickness of the second dielectric protection layer 4 is in the range of 10 nm to 100 nm, preferably 15 nm to 50 nm. In the case of the second protective layer, if the thickness is less than 10 nm, the heat resistance basically decreases, which is not preferable. When the thickness exceeds 100 nm, the overwrite characteristics are repeatedly deteriorated due to a decrease in recording sensitivity, film peeling, deformation and heat dissipation due to a rise in temperature.

The reflective heat radiation layer 6 is made of Al, Au, C
u, Ag, Cr, Sn, Zn, In, Pd, Zr, F
e, Co, Ni, Si, Ge, Sb, Ta, W, Ti,
A simple substance or alloy of a material mainly composed of a metal such as Pb,
Mixtures can be used. If necessary, a plurality of different metals, alloys or mixtures may be laminated. It is important for this layer to efficiently release heat, and the thickness is 30
nm to 250 nm. Preferably 50 nm to 150
nm is good. If the film thickness is too thick, the heat radiation efficiency is too good, resulting in poor sensitivity. If the film thickness is too thin, the sensitivity is good, but the repetitive overwrite characteristics deteriorate. As the characteristics, high thermal conductivity, high melting point, good adhesion to the protective layer material, and the like are required.

In particular, when the ratio of In / (In + Mg) is 0.1.
Mg-In-O-based oxides having a resistivity in the range of 60 to 1.0 have a capability of 10 ^-4 Ω · cm or less, and are particularly preferable because they are high melting point materials. The range of 0.60 to 1.0 corresponds to mixing MgO with In ₂ O ₃ at a molar ratio of 0.40 or less. Although the In ₂ O ₃ thin film has a high light transmittance, it cannot be said that the resistivity is sufficiently low. MgO is not suitable for mass production because the film formation speed when forming a thin film is slow. In / (In
+ Mg) is preferably 0.8 to 0.9. On the other hand, the Mg—In—O-based oxide is In / (In
+ Mg) in the range of 0.6 to 1, the electrical conductivity is known to be high, and the refractive index is around 2. Therefore, Mg containing high MgO having a high melting point and having a light transmittance of 80% is used.
-In-O-based oxide is used as a heat dissipation layer having higher thermal conductivity than the second protective layer. The refractive index of the heat radiation layer 5 is the second
1.9 to obtain a refractive index equivalent to that of the dielectric protective layer of
Those in the range of 2.1 are preferred.

Next, the second dielectric protection layer ZnS.S
It is necessary to optimize the film thickness ratio between iO ₂ and the MgO—In ₂ O ₃ based heat dissipation layer 5. In particular, the film thickness ratio becomes more important as the linear density is higher and the linear velocity is higher. In this case, power is required because the recording frequency increases and the laser pulse width during recording decreases. However, as the power is increased, the temperature rises accordingly. However, heat may be trapped, the number of repetitive overwrites may be reduced, the edge of the recording mark may be blurred, or the mark position may be shifted, resulting in poor jitter. These Mg-In-O
When the oxide heat dissipation layer 5 and the ZnS.SiO ₂ second dielectric protection layer 4 are stacked, the effect is exhibited, and there is a range of the optimum thickness ratio of each layer. Protective layer thickness: heat dissipation layer thickness = 5
0:50 to 90:10, preferably 60:50.
The range is 40 to 80:20. When the heat radiation layer is thicker than the protective layer film thickness, it becomes difficult to store heat, and the sensitivity or jitter deteriorates. Further, even if the heat radiation layer is too thin, the effect is small.

The optical recording medium having the above-mentioned materials and constitutions includes a semiconductor laser having a wavelength of 635 nm, an NA of 0.6.
Alternatively, recording and reproduction are performed using a 650 nm semiconductor laser and a NA 0.6 pickup. The recording method is pul
The modulation code is recorded in the EFM + [8/16, RLL (2, 10)] system by the second width modulation.

[0016]

Examples 1 to 9 and Comparative Examples 1 to 6 These were made of polycarbonate, and had a substrate thickness of 0.6 mm, a track pitch of 0.74 μm, a groove width of 0.45 μm, and a groove depth of 50.
After dehydration treatment at 70 to 80 ° C. using a substrate of nm, a film was formed by sputtering. ZnS as the first dielectric protection layer
- attached to a layer thickness of 170nm using a SiO ₂ target. Next, an AgInSbTe target having a predetermined composition ratio was irradiated with an argon gas pressure of 3 × 10 ⁻³ torr and an RF power of 30.
Sputtering was performed at 0 W to provide a recording layer having a thickness of 18 nm. Furthermore, ZnS.SiO is formed thereon similarly to the first dielectric protection layer.
₍₂ ) A second dielectric protection layer, on which an AlTi alloy film having a thickness of 120 nm was formed as a reflective heat dissipation layer. Finally, an ultraviolet-curable resin film was used as a protective film and used as a medium. The recording layer after the film formation was amorphous, and was initialized for crystallization. Recording was performed at λ = 635 nm and NA of 0.6, and the recording method used was a pulse modulation method, and the modulation method was EFM + [8/1
6, RLL (2, 10)]. The linear velocity at the time of recording / reproduction is 3.5 m / sec to 7 m / sec depending on the composition.
c. The ratio of recording power / erasing power is about 2 to 2.2.
Then, recording was performed with the bottom power equal to or lower than the reproduction power. The recording power was applied up to a maximum of 15 mW. The recording frequency was 23.3 MHz to 46.6 MHz, and recording was performed in the group. Recording / reproduction is performed for each recording layer composition, and d
The data to clk jitter was measured. Jitter σ
Recording was performed at an optimum recording power at which / Tw (Tw: window width) was minimized, and overwriting was repeated. The number of overwrites is the number of times when the jitter becomes 10% or less. Table 1 shows Examples 1 to 9 and Comparative Examples 1 to 6,
Table 2 shows a conventional example. The comparative example and the conventional example are cases where any one of the composition conditions described in claim 1 is out of the range. By limiting to such a composition range, a higher number of overwrites can be obtained and data reliability can be increased.

Examples 10 to 14 A substrate made of polycarbonate, having a substrate thickness of 0.6 mm, a track pitch of 1.48 μm, a groove width of 0.74 μm, and a groove depth of 65
Using a substrate of nm, a film was formed by sputtering after dehydration treatment at a high temperature. ZnS · Si as the first dielectric protection layer
The thickness was set to 170 nm using an O ₂ target.
Next, the recording layer having the composition ratio of Example 1 was applied to a gas pressure of 3 × 10 ⁻³ ton.
Sputter at rr, RF power 300 mW. At this time, Ar gas and nitrogen gas were flowed at 0.5 sccm to obtain a mixed gas of Ar + N ₂ . The recording layer was formed with a thickness of 18 nm. Further, the thickness was 250 nm in the order of the Mg—In—O heat radiation layer, and the thickness ratio of each layer was set in the range of 50:50 to 90:10. Further, an AlTi alloy film having a thickness of 120 nm was formed thereon as a reflective heat dissipation layer. The measured refractive index of the Mg—In—O heat radiation layer was about 2.1. An ultraviolet-curable resin film was applied thereon as a protective film to serve as a medium. Recording and reproduction conditions are such that recording and reproduction are performed at a wavelength of 635 nm and an NA of 0.6.
The recording method uses a pulse modulation method, and the modulation method is EFM +
[8/16, RLL (2, 10)] The modulation method was used.
The recording power / erasing power ratio was about 2 to 2.2, the reproducing power was 1 mW, and the bottom power was equal to or lower than the reproducing power. Linear velocity 3.5m / s
ec, recording was performed at a recording frequency of 23.3 MHz, and overwriting was repeatedly performed at a recording power that minimized jitter. Jitter measured the data to clk jitter. Table 3 shows examples. As a result, In / (In +
Mg) was in the range of 0.96 to 0.98, and the number of overwrites was the largest when the thickness ratio of the protective layer to the heat radiation layer was around 80:20. Similar to the above, the number of repeated overwrites is a case where the jitter is 10% or less. Table 3 shows Examples 10 to 14.

[0018]

[Table 1]

[0019]

[Table 2]

[0020]

[Table 3]

[0021]

[Effect] Excellent recording / reproducing characteristics even at high density, and
An optical recording medium with an improved number of overwrites was obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a configuration of an optical recording medium used in the present invention.

[Description of Signs] 1 Substrate 2 First Dielectric Protective Layer 3 Recording Layer 4 Second Dielectric Protective Layer 5 Heat Dissipation Layer 6 Reflective Heat Dissipation Layer 7 Organic Environmental Protection Layer

Claims (4)

[Claims] A first dielectric protection layer, a recording layer,
In the recording layer of the optical recording medium formed by laminating the second dielectric protective layer and the reflective heat dissipation layer in this order, the recording layer has a chemical formula of AgαIn
An optical recording medium comprising a material represented by βSbγTeδ. In the above formula, α, β, and γ represent the respective composition ratios (atomic%), and satisfy the following requirements. 1 ≦ α <10 1 <β ≦ 20 35 ≦ γ ≦ 70 20 ≦ δ ≦ 35 α + β + γ + δ = 100 4β-δ ≦ 0 γ-2δ ≧ 0 γ-8α ≧ 0 2. A heat radiation layer made of a material made of Mg, In, and O is provided between the second dielectric protection layer and the reflection heat radiation layer, and the material has a ratio represented by In / (In + Mg). 2. The optical recording medium according to claim 1, satisfying the following requirements. 0.60 <In / (In + Mg) <1.0 3. The optical recording medium according to claim 2, wherein the thickness ratio between the reflective heat dissipation layer and the second dielectric protection layer is 10:90 to 50:50. 4. The optical recording medium according to claim 2, wherein the reflective heat radiation layer has a refractive index of 1.9 to 2.1.