JPH11134713A - Optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a phase transition type optical disk which lessens cross erasure and is excellent in repeating characteristics by successively laminating a dielectric layer, lower reflection layer, dielectric layer, recording layer, dielectric layer and upper reflection layer on a substrate and using at least one kind of the metals selected from Au, Al, Ti, Cu and Cr or their alloys for the reflection layer. SOLUTION: The constitution obtd. by successively laminating the dielectric layer 2, the lower reflection layer 3, the dielectric layer 4, the recording layer 5, the dielectric layer 6 and the upper reflection layer 7 on the substrate 1 is adopted for the recording medium 10. The dielectric layer 2 suppresses the thermal deformation of the substrate 1 by heating up of the lower reflection layer 3 at the time of recording. The lower reflection layer 3 acts to suppress the cross erasure by making the absorptance at the time the recording layer 5 is in an amorphous state lower than the absorptance at the time the recording layer is in a crystalline state. Materials or metallic materials having a high refractive index and having a small coefft. attenuation are usable for the lower reflection layer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium for recording and reproducing information by irradiating a laser beam.
In particular, it relates to a phase change optical disk.

[0002]

2. Description of the Related Art A retrospective study of the prior art relating to the present invention from a past patent application shows that the ratio between the absorptivity Aa in the amorphous state and the absorptivity Ac in the crystalline state is improved to reduce cross erasure. As the application,
149238 and JP-A-7-93804. In addition, as an application for expanding the applicable range of the linear velocity, Japanese Patent Application Laid-Open No. 8-156423 has recently been proposed.
Japanese Patent Application Laid-Open No. 9-63119 is an application aimed at improving the erasing rate, particularly the jitter characteristics after overwriting.
Recently, Japanese Patent Application Laid-Open No. 9-73660 has been filed as an application that proposes a configuration capable of performing the “verification operation during recording”.

Further, there are the following academic papers relating to the optical information recording medium of the present invention. Author: Naoki Morishita Naomasa Nakamura Katsumi Suzuki Title of publication: Fifth Meeting of the Phase Change Recording Society Symposium Proceedings Publication date: November 25, 1993 Applicable parts and drawings; Page 94, FIG. 1

[0004]

By the way, in the prior art, if the track pitch is reduced for higher density, the information on the adjacent track is erased when the information is recorded. The problem of so-called cross erasure was serious. To reduce cross erasure, it is effective to make the absorption rate Aa in the amorphous state lower than the absorption rate Ac in the crystalline state.

In a conventional phase change optical disk, generally, Aa
Is higher than Ac, but techniques for lowering Aa than Ac include techniques described in JP-A-1-149238 and JP-A-7-93804, and the 5th Symposium on Phase Change Recording Research Symposium. The technology described on page 94 is known. In these inventions, Ac is made higher than Aa for the purpose of improving the overwrite characteristic at the time of mark edge recording, but Aa is not made lower for the purpose of improving the cross erase characteristic.
Since it is lower, it is an effective technique for reducing cross erase.

[0006] However, these conventional techniques have the following problems. The first problem is that the track pitch cannot be reduced. The reason that the above problem occurs is that when information is rewritten, cross erasure that erases data recorded on an adjacent track occurs. In addition, the second of the prior art
The problem is that, in a conventional phase-change optical disc capable of suppressing cross erasure, the number of times that information can be rewritten is greatly limited particularly at a low linear velocity.

The second problem occurs because the conventional phase-change optical disc capable of suppressing cross erasure has a structure in which the heat load is increased. For example, the fifth
94 pages of the proceedings of the Symposium
FIG. In the example disclosed by No. 1, a layer called “absorptive semi-transparent metal layer” is provided immediately above the substrate as a structure that may be a reflective layer. However, since this layer is an extremely thin gold thin film, However, when recording information, the reflective layer absorbs the laser beam and raises the temperature, so that a thermal load is applied to the substrate immediately below the reflective layer, and the number of times of rewriting information repeatedly is limited. Further, since a layer acting as a buffer for preventing heat transfer is not provided between the substrate and the “absorptive translucent metal layer”, the substrate accompanying the temperature rise of the reflective layer is also considered from this point. However, the problem of suppressing thermal deformation and improving repetition characteristics has not been achieved.

FIG. 13 shows page 94 of the above-mentioned proceedings, Fi.
g. FIG. 1 is a diagram disclosed in FIG. In the structure shown in FIG. 13, the disk 130 is made of polycarbonate (Po).
An Au layer 132 is placed directly on a lycarbonate substrate 131, and then a ZnS—SiO ₂ layer 133, G
e ₂ Sb ₂ Te ₅ layer 134, ZnS-SiO ₂ layer layer 13
5, an Al alloy layer 136 and a UV resin layer 137 are sequentially stacked. The Au layer 132, which is assumed to play the role of a reflective layer, is as thin as 14 nm.

In Japanese Patent Application Laid-Open No. 1-149238, since a very thin metal is used as the reflective layer, the heat dissipation is poor and the heat load is high, and particularly at a low linear velocity of 8 m / s or less. However, there has been a problem that the number of times of rewriting is limited. Further, in Japanese Patent Application Laid-Open No. Hei 7-93804, although repetition characteristics can be ensured, there has been a problem that when a short wavelength light source is used, Aa cannot be reduced significantly from Ac.

[0010] In addition, Japanese Patent Application Laid-Open No. Hei 8-15 filed recently
Examination of JP-A-6423 and JP-A-9-63119 reveals that the structure of the recording medium disclosed in the technology of the present invention is different in the following points. FIG.
156423 discloses the structure of an optical disc.

[0011] As shown in FIG.
1, a first protective layer 113 on a light-transmitting substrate 112;
Recording layer 114, second protective layer 115, reflective layer 116, U
The V-cured resin protective layers 117 are laminated in this order. In this structure, the reflection layer 116 is the only reflection layer. FIG. 12 shows the structure of an optical recording medium disclosed in Japanese Patent Application Laid-Open No. 9-73660.

As shown in FIG. 12, in the optical recording medium 120, a first protective film 123, a recording film 124, a second protective film 125, a reflection film 126, and an ultraviolet curing resin 127 are formed on a transparent substrate 122. They are stacked in order. Also in this structure, only one of the reflective films 126 is considered to be a reflective layer. Further, JP-A-9-63119 does not disclose any drawings, but according to the description in the specification, there is still only one reflective layer, and the publication specifies the material. Not just.

[0013] Therefore, even in the techniques disclosed in these applications, the above problems are not structurally solved. The present invention has been made in view of the above-mentioned problems in the conventional disk drive technology, and accordingly, a first object of the present invention is to provide a phase change having less cross erasure and excellent repetition characteristics. An optical disk is provided.

It is a second object of the present invention to provide a phase-change optical disc which achieves higher density and which is superior in performance characteristics and reliability to the conventional one.

[0015]

According to an embodiment of the present invention, a dielectric layer, a lower reflective layer, a dielectric layer, a recording layer, a dielectric layer, and an upper reflective layer are provided on a substrate. Are sequentially stacked, thereby providing a phase-change optical disc. As the upper reflective layer of the phase change optical disk, at least one metal selected from Au, Al, Ti, Cu, and Cr or an alloy thereof can be used.

Further, the thickness of the upper reflective layer of the phase-change optical disk can be set to 40 nm or more and 300 nm or less. It is possible to use Si or Ge as the lower reflective layer of the phase change optical disk. Further, the thickness of the lower reflective layer of the phase-change optical disk can be set to 10 nm or more and 120 nm or less.

Further, in addition to the above, Au, Al, Ti, Cu, C
It is also possible to use at least one metal selected from r or an alloy thereof. Further, the thickness of the lower reflective layer of the phase-change optical disk may be 10 nm in addition to the above.
A specification of not less than 30 nm is also possible.

In the phase-change optical disk, the absorption of the recording layer in the amorphous state may be set to be lower than the absorption of the recording layer in the crystalline state. To describe the operation of the phase change optical disk of the present invention,
First, attention has been paid to the fact that it is effective to reduce the absorptance of the amorphous portion to suppress cross erasure. Therefore,
By using a material having a high transmittance such as Si or Ge or a very thin metal having a film thickness of 10 to 30 nm as the lower reflective layer, the reflectance of the amorphous portion is increased and the absorptance of the amorphous portion is reduced. It is possible.

Since the lower reflective layer also absorbs light, the temperature of the lower reflective layer rises when recording information. By providing a dielectric layer as a heat transfer preventing layer between the lower reflective layer and the substrate, the heat load on the substrate can be reduced, and the repetition characteristics can be improved.

[0020]

Next, an embodiment of a phase change optical disk according to the present invention will be described with reference to FIGS. FIG. 1 is a configuration diagram of a phase-change optical disc according to the first embodiment of the present invention. In the embodiment shown in FIG. 1, a recording medium 10 includes a first dielectric layer 2, a lower reflective layer 3, a second dielectric layer 4, a recording layer 5, a third dielectric layer 6, A configuration in which the reflective layers 7 are sequentially stacked is adopted.

The first dielectric layer 2 comprises a lower reflective layer 3 for recording.
The thermal deformation of the substrate 1 due to the temperature rise is suppressed. Lower reflective layer 3
Has the function of increasing the reflectivity when the recording layer 5 is in the amorphous state and lowering the absorptance when in the amorphous state than the absorptivity when in the crystalline state, thereby suppressing cross erasure. doing.

The lower reflective layer 3 has a large refractive index,
A material having a small extinction coefficient or a metal material can be used. In order to secure an absorptivity when the recording layer 5 is in a crystalline state, the thickness of the lower reflective layer 3 should be 10 nm or more and 120 nm in the case of a material having a large refractive index and a small extinction coefficient.
In the case of a metal material, the thickness is preferably 10 nm or more and 30 nm or less.

This is because if the absorptance of the recording layer in the crystalline state is too low, recording cannot be performed using laser light. The recording layer 5 is a phase change material whose reflectivity changes reversibly by irradiation with laser light. Upper reflective layer 7
For this purpose, a metal material is used in order to enhance heat dissipation and improve repetition characteristics.

The thickness of the upper reflective layer 7 is desirably 40 nm or more and 300 nm or less from the viewpoint of improvement of repetition characteristics and film quality. This is because if the thickness of the upper reflective layer 7 is less than 40 nm, sufficient heat dissipation cannot be obtained, and the repetition characteristics are deteriorated.
This is because the reflective layer is likely to be peeled off when the thickness is more than m.

FIG. 2 is a configuration diagram of a phase change optical disk according to a second embodiment of the present invention. In the embodiment shown in FIG. 2, the upper reflective layer 7 in the first embodiment described above is used.
Is specified, and at least one metal selected from Au, Al, Ti, Cu, and Cr or an alloy thereof is used. FIG. 3 is a configuration diagram of a phase-change optical disc according to the third embodiment of the present invention.

In the embodiment shown in FIG. 3, the thickness of the upper reflective layer 7 in the first or second embodiment is specified, and is 40 nm or more and 300 nm or less. FIG. 4 is a configuration diagram of a phase-change optical disc according to the fourth embodiment of the present invention. In the embodiment shown in FIG. 4, the material of the lower reflective layer 3 in any one of the first to third embodiments is specified, and Si or Ge is used.

FIG. 5 is a configuration diagram of a phase-change optical disc according to a fifth embodiment of the present invention. In the embodiment shown in FIG. 5, the film thickness of the lower reflective layer 3 in any one of the first to fourth embodiments is specified, and
It is set to 0 nm or less. FIG. 6 is a configuration diagram of a phase-change optical disc according to the sixth embodiment of the present invention.

In the embodiment shown in FIG. 6, the material of the lower reflective layer 3 in any one of the first to third embodiments is specified, and at least one selected from Au, Al, Ti, Cu, and Cr is selected. One kind of metal or an alloy thereof is used. FIG. 7 is a configuration diagram of a phase-change optical disc according to the seventh embodiment of the present invention. In the embodiment shown in FIG. 7, the film thickness of the lower reflective layer 3 in the above-described first, second, third or sixth embodiment is specified, and is 10 nm or more and 30 n or more.
m or less.

Next, the characteristics of the phase change optical disk of the present invention will be described with reference to FIGS. FIG. 8 is an explanatory diagram showing a temperature rise when recording is performed by the phase change optical disk of the present invention. When recording information, the temperature of the recording layer 5 has a distribution as shown in the graph of FIG.

At this time, the temperature at the mark end 8 shown in FIG. 8 must be lower than the crystallization temperature of the recording layer so that the data (amorphous mark) recorded on the adjacent track is not erased. There is. The amount of temperature rise at the mark end 8 is proportional to the absorptance Aa in the amorphous state. In the phase change optical disk of the present invention, the lower reflective layer 2 increases the reflectance in the amorphous state and lowers Aa. Erasure can be suppressed.

Next, the configuration and operation of the phase change optical disk of the present invention will be described with reference to the following embodiments. First, a polycarbonate is used as the substrate 1, ZnS—SiO ₂ is 140 nm as the first dielectric layer 2, Si is 40 nm as the lower reflective layer 3, and ZnS—SiO ₂ is the second dielectric layer 4.
₂ is 140 nm, Ge ₂ Sb ₂ Te ₅ is 15 nm as the recording layer 5, and ZnS—SiO ₂ is 2 as the third dielectric layer 6.
An embodiment obtained by sequentially stacking 0 nm and Al as the reflective layer 7 by 100 nm by sputtering will be described.

FIG. 9 is an external view showing the shape of the substrate of the phase change optical disk. As shown in FIG. 9, the pitch (track pitch) of the guide grooves formed on the polycarbonate substrate was 1.1 μm. In the phase change optical disk, the absorption rate Ac in the crystalline state was 60%, and the absorption rate Aa in the amorphous state was 45%. The disk was rotated at a linear velocity of 5 m / s, and the measurement was performed using an optical head having a wavelength of 660 nm and a numerical aperture of the objective lens of 0.6.

First, a signal having a frequency of 1 MHz and a duty ratio of 50% is recorded on the land portion, and a signal having a frequency of 1.5 MHz and a duty ratio of 50% is repeatedly recorded on the adjacent groove portions. Was measured.
FIG. 10 is a graph showing the cross erase characteristics of the phase change optical disk. As is clear from FIG. 10, even when information is repeatedly rewritten in the adjacent groove portion, 1 MH
The signal at z is not affected at all.

FIG. 10 shows a carrier Ci of a 1 MHz signal measured without recording information on an adjacent track, and a 1 MHz signal measured after repeatedly recording a 1.5 MHz signal a predetermined number of times on an adjacent track. (Ci-Cl) from the carrier Cl. When a signal of 1 MHz and a duty ratio = 50% was repeatedly recorded using the above-mentioned phase change optical disk, no change in the carrier or noise of the 1 MHz signal was observed until 500,000 repetitions.

Next, polycarbonate was used as the substrate 1 and ZnS—SiO ₂ was 140 nm as the dielectric layer 2.
Al is 10 nm as the lower reflection layer 3, ZnS—SiO ₂ is 140 nm as the dielectric layer 4, and Ge _{2 is used} as the recording layer 5.
15 nm of Sb ₂ Te ₅ and ZnS—S as the dielectric layer 6
iO ₂ is 20 nm, Al is 100 nm as the reflection layer 7,
An embodiment obtained by sequentially laminating by sputtering will be described.

The track pitch was set to 1.1 μm as in the above embodiment. The absorption rate Ac in the crystalline state is 70
%, And the absorptance Aa in the amorphous state was 45%. The phase change optical disk was rotated at a linear velocity of 5 m / s, and the measurement was performed using an optical head having a wavelength of 660 nm and a numerical aperture of the objective lens of 0.6. As in the above-described embodiment, first, a signal of 1 MHz and a duty ratio = 50% are recorded on the land portion, and then 1.5 MHz and a duty ratio of 1.5 MHz are recorded on the adjacent groove portions.
A signal having a ratio of 50% was repeatedly recorded, and the change in the carrier of the 1 MHz signal was measured.

Again, the 1 MHz signal was not affected at all. Using this phase change optical disk, 1
When a signal of MHz and a duty ratio = 50% was repeatedly recorded, no change in carrier or noise was observed up to 500,000 times. As the lower reflective layer 3, other than the above-described embodiment, Ge or Au, Al, Ti, Cu, Cr, or an alloy thereof can be used. Also, the upper reflective layer 7
In addition to the above embodiment, Au, Ti, Cu, Cr
Alternatively, an alloy thereof, or Al and an alloy thereof can also be used.

[0038]

The first effect of the phase change optical disk according to the present invention is that the recording density can be improved by narrowing the track pitch. The reason is that cross erasure can be suppressed. The second effect of the phase change optical disk according to the present invention is that data can be prevented from being erased even when the reproduction laser beam fluctuates and the power becomes high, and the wavelength of the laser light source will be further shortened in the future. In this case, data can be prevented from being erased by the reproduction laser beam.

The reason is that the absorptivity of the amorphous state is lowered.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a phase change optical disc according to a first embodiment of the present invention.

FIG. 2 is a configuration diagram of a phase-change optical disc according to a second embodiment of the present invention.

FIG. 3 is a configuration diagram of a phase-change optical disc according to a third embodiment of the present invention.

FIG. 4 is a configuration diagram of a phase-change optical disc according to a fourth embodiment of the present invention.

FIG. 5 is a configuration diagram of a phase-change optical disc according to a fifth embodiment of the present invention.

FIG. 6 is a configuration diagram of a phase-change optical disc according to a sixth embodiment of the present invention.

FIG. 7 is a configuration diagram of a phase-change optical disc according to a seventh embodiment of the present invention.

FIG. 8 is an explanatory diagram showing a temperature rise when recording is performed by the phase change optical disk of the present invention.

FIG. 9 is an external view showing a shape of a substrate of the phase change optical disk.

FIG. 10 is a graph showing a cross erase characteristic of a phase change optical disk.

FIG. 11 shows the structure of an optical disc disclosed in Japanese Patent Application Laid-Open No. 8-156423.

FIG. 12 shows the structure of an optical recording medium disclosed in JP-A-9-73660.

FIG. 13: Page 94 of the 5th Phase Change Recording Society Symposium Proceedings, FIG. 1 is a diagram disclosed in FIG.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 substrate 2 first dielectric layer 3 lower reflective layer 4 second dielectric layer 5 recording layer 6 third dielectric layer 7 upper reflective layer 8 mark end 10 recording medium

Claims (8)

[Claims] 1. A phase-change optical disk comprising: a dielectric layer, a lower reflective layer, a dielectric layer, a recording layer, a dielectric layer, and an upper reflective layer laminated on a substrate in this order. 2. The method according to claim 1, wherein the upper reflective layer is made of Au, Al, Ti,
The phase-change optical disc according to claim 1, wherein at least one kind of metal selected from Cu and Cr or an alloy thereof is used. 3. The thickness of the upper reflective layer is 40 nm or more and 300
The phase-change optical disk according to claim 1, wherein the diameter is not more than nm. 4. The phase change optical disk according to claim 1, wherein Si or Ge is used as the lower reflective layer. 5. The film thickness of the lower reflective layer is 10 nm or more and 120
The phase change optical disc according to any one of claims 1 to 4, wherein the diameter is not more than nm. 6. As a lower reflection layer, Au, Al, Ti,
4. The phase-change optical disc according to claim 1, wherein at least one kind of metal selected from Cu and Cr or an alloy thereof is used. 7. The thickness of the lower reflective layer is 10 nm or more and 30 n or more.
7. The phase-change optical disk according to claim 1, wherein the value is not more than m. 8. The phase change optical disk according to claim 1, wherein the recording layer in the amorphous state has a lower absorption than the recording layer in the crystalline state.