JPH07130002A - Optical recording medium and recording and reproducing method using the same - Google Patents

Abstract

PURPOSE:To obtain an optical recording medium having such recording and reproducing characteristics as satisfactory erasure ratio with a laser light source emitting light of <=600nm wavelength. CONSTITUTION:This optical recording medium has a 1st dielectric layer, a phase change type recording layer, a 2nd dielectric layer and a reflecting layer in order on the substrate. The thickness of the recording layer is 15-50nm, the 2nd dielectric layer is made of a material having >5.0X10<-4> pJ.mum<-1>.K<-1>.ns<-1> heat conductivity and the thickness of the 2nd dielectric layer is 10-250nm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium capable of recording, reproducing and erasing information at high speed and high density by irradiating a laser beam and the like and a recording and reproducing method using the same.

[0002]

2. Description of the Related Art In recent years, an optical disk using a laser beam has been developed as a recording medium that meets the demands for increasing the amount of information and increasing the recording and reproducing density and speed. There are two types of optical disks: a write-once type that allows recording only once and a rewritable type that allows recording / erasing as many times as desired.

Examples of the rewritable optical disk include a magneto-optical recording medium utilizing a magneto-optical effect and a phase change medium utilizing a reversible change in crystal state. The phase change medium does not require an external magnetic field, and recording / erasing can be performed only by modulating the power of laser light. Further, there is an advantage that it is possible to perform one-beam overwriting in which erasing and re-recording are simultaneously performed with a single beam.

In the one-beam overwritable phase change recording method, it is general that the recording film is made amorphous to form a recording bit and is crystallized to erase. As a recording layer material used in such a phase change recording method, a chalcogen-based alloy thin film is often used. For example, Ge-Te system, Ge-Te-
Sb type | system | group, In-Sb-Te type | system | group, Ge-Sn-Te type | system | group alloy thin film etc. are mentioned.

A write-once type phase change medium can also be realized by applying almost the same material and layer structure as the rewritable type. In this case, since the reversibility is not used, information can be recorded and stored for a longer period of time, and in principle, it can be stored almost semipermanently. When using a phase change medium as a write-once type,
Unlike the hole-drilling type, there is an advantage that a signal rim called a rim does not form a bulge around the recording pit, which is excellent in signal quality, and an air sandwich structure is not necessary because no void is required above the recording layer.

Generally, in a rewritable phase change recording medium,
Two different laser light powers are used to achieve different crystalline states. This method will be described by taking as an example the case of recording amorphous pits in the crystallized initial state and erasing by crystallization. Crystallization is performed by heating the recording layer to a temperature sufficiently higher than the crystallization temperature of the recording layer and lower than the melting point. In this case, the cooling layer is sandwiched between dielectric layers or an elliptical beam long in the beam moving direction is used so that the crystallization is slow enough to cause sufficient crystallization.

On the other hand, the amorphization is performed by heating the recording layer to a temperature higher than the melting point and quenching it. in this case,
The dielectric layer also has a function as a heat dissipation layer for obtaining a sufficient cooling rate (supercooling rate). In addition, in order to prevent deformation of the recording layer due to melting and volume change in the heating / cooling process, thermal damage to the plastic substrate, and deterioration of the recording layer due to moisture as described above, Body layers are important.

The material of the dielectric layer is such that it is optically transparent to laser light, has a high melting point / softening point / decomposition temperature, is easy to form, and has suitable thermal conductivity. Selected from the perspective.

[0009]

The beam diameter of a laser that can be assumed to be a Gaussian beam is 0.82 × λ ÷ NA (λ
Is the wavelength and NA is the numerical aperture of the lens. Therefore, when a laser having a short wavelength such as 600 nm or less is used for high density recording, the beam spot diameter becomes small.

In the phase change type optical disk, the amorphous bits of the recording layer are annealed at the crystallization temperature and crystallized to erase the recording. However, when the beam spot diameter is small, the recording layer has a crystallization temperature higher than the crystallization temperature. There is a problem in that the crystallization time does not go well because the time kept for 2 hours is shortened.

[0011]

By optimizing the thermal conductivity of the second dielectric layer, the present inventors can prolong the time during which the recording layer is kept at the crystallization temperature or higher. I found that As a result, it has been found that the recording layer can be sufficiently heated above the crystallization temperature, and an optical recording medium suitable for short wavelength recording of less than 600 nm can be obtained.
The present invention has been reached.

The gist of the present invention is to provide a first dielectric on a substrate.
Layer, phase change recording layer, second dielectric layer and reflective layer in that order
An optical information recording medium having a film of a phase change recording layer
A thickness of 15 to 50 nm and heat conduction as the second dielectric layer
Rate is 5.0 × 10^-FourpJ · μm ^-1・ K^-1・ Ns^-1Greater than
Use a threshold and set the thickness of the second dielectric layer to 10 to 2
An optical recording medium characterized by having a thickness of 50 nm;
And information on this using a laser with a wavelength of less than 600 nm
A recording / reproducing method characterized by performing recording / reproducing of
It

The phase change recording layer is made of GeSbTe or InSb.
Te-based materials and the like are preferably used, and Sn, for improving the crystallization rate, easiness of amorphization, crystal grain size, storage stability, etc.
In, Ge, Pb, As, Se, Si, Bi, Au, T
You may add i, Cu, Ag, Pt, Pd, Co, Ni, etc. If the thickness of the recording layer is less than 15 nm, the heat retaining property by the recording layer itself is reduced, and the formation of crystal nuclei for crystallization of the recording layer is suppressed to suppress crystallization, and further sufficient contrast cannot be obtained. The problem arises.

On the other hand, when the thickness is more than 50 nm, mass transfer easily occurs during overwriting. Recording layer thickness is 1
5 to 50 nm is preferable. The recording layer is provided on the substrate while being sandwiched by the dielectric layers, but a reflective layer, a protective layer made of an ultraviolet curable resin, and the like may be further provided. The first and second dielectric layers are transparent and have an optical constant n of 1.5 to 2.4, k of 0 to 0.05, and a thermal expansion coefficient of 1.
It is preferable to use a dielectric of 0 × 10 ⁻⁵ or less.

The second dielectric layer has a thermal conductivity of 5.0 × 1.
It is necessary to be larger than 0 ⁻⁴ pJ · μm ⁻¹ · K ⁻¹ · ns ⁻¹ . Thermal conductivity of 5.0 × 10 ^-4 pJ ・ μm ^-1・ K ^-1
-By setting it to be larger than ns ^-1 , the heat can be quickly released from the recording layer along the second dielectric layer, so that the width for keeping the temperature for crystallization of the recording layer can be widened. Become.

As a result, it is possible to increase the time required for sufficient crystallization and improve the erase characteristic.
The second dielectric layer has a film thickness of 10 to 250 nm. Second
When the film thickness of the dielectric layer is less than 10 nm, it becomes impossible to suppress the mass transfer of the recording layer which occurs when the overwrite is repeatedly performed.

On the other hand, if the second dielectric layer exceeds 250 nm, cracks are likely to occur. The thickness of the first dielectric layer is preferably 50 to 250 nm. As the substrate of the recording medium in the present invention, glass, plastic,
It may be any of those provided with a photocurable resin on glass, but the dielectric layer used in the present invention has excellent heat resistance,
Because of the effect of preventing the substrate from being thermally deformed, it is possible to use a polycarbonate resin substrate that is currently generally used as a substrate for optical disks.

The reflective layer is made of Al and Al alloy, Au, A
It is preferable to use a substance having high thermal conductivity such as g,
Its thickness is usually selected in the range of 100 to 200 nm.
The recording layer, the dielectric layer, and the reflective layer are formed by a sputtering method or the like. It is desirable to perform film formation by an in-line apparatus in which the target for recording film, the target for dielectric film, and the target for reflective layer material, if necessary, are installed in the same vacuum chamber in order to prevent oxidation and contamination between layers. It is also excellent in terms of productivity.

The thermal conductivity described in the present invention is not the bulk value of the material, but the thermal conductivity of the thin film. A method for measuring the thermal conductivity of a thin film is described in J. C. Lambprowl
os, et. al. J. Appl. Phys. , 6
6, 4230 (1989), I.S. Hatta, et. a
l. Rev. Sci. Instrum. , 56, 16
43 (1985) and M.N. Horie, et. al. ，
Mitsubishi Kasei R & D Review
w, 4 (2), 68 (1990) and the like. Specifically, a thermal conductivity measuring device by an optical alternating current excitation method may be used.

[0020]

The present invention will be described in detail with reference to the following examples. Example 1 (ZnS) ₈₀ (Si
O ₂ ) ₂₀ (numbers indicate component proportions and unit is mol%) composition,
The first dielectric film having optical constants n = 2.2 and k = 0 at a wavelength of 488 nm is 160 nm, Ge ₂ Sb ₂ Te ₅ (composition is shown by a ratio) recording film is 30 nm, and Ta ₂ O ₅ ( Thermal conductivity 7.39 × 10 ^-3 pJ · μm ^-1 · K ^-1 · ns ^-1 , wavelength 4
The second dielectric film having an optical constant at 88 nm of n = 2.2 and k = 0) is 20 nm, and the Al alloy reflection film is 200 n.
m and the sputtering method were sequentially formed. Further, an ultraviolet curable resin layer was provided on the reflective layer.

Since the recording layer of the disk prepared as described above is in an amorphous state, it was crystallized by an Ar laser for initialization, and then the dynamic characteristics of the disk were evaluated by an evaluation device using a laser pickup having a wavelength of 488 nm. did. Recording power 14 mW at linear velocity 10 m / s, erasing power 7 mW, recording frequency 8.58 MHz, pulse width 38 n
The C / N ratio when the sec signal was recorded and the erasing ratio when the erasing power was DC-irradiated were 51 dB and 24, respectively.
It was dB. Further, the erase power margin for the erase ratio of 20 dB or more was 2 mW.

Example 2 (ZnS) ₈₀ (Si
O ₂ ) ₂₀ composition, optical constant at wavelength 488 nm n = 2.
2. Set the first dielectric film of k = 0 to 160 nm by Ge ₂ Sb ₂
Te ₅ recording film 30 nm, SiO ₂ (thermal conductivity 5.40 ×
^{10 -3 pJ · μm - 1 ·} K -1 · ns -1, the optical constants n = 1.6 at a wavelength of 488nm, k = 0) the second dielectric film 20nm made of, 200 nm of Al alloy reflective film Then, they were sequentially formed by a sputtering method. Further, an ultraviolet curable resin layer was provided on the reflective layer.

Since the recording layer of the disk prepared as described above is in an amorphous state, it is crystallized by an Ar laser for initialization and then the dynamic characteristics of the disk are evaluated by an evaluation device using a laser pickup having a wavelength of 488 nm. did. Recording power 15 mW at linear velocity 10 m / s, erasing power 7 mW, recording frequency 8.58 MHz, pulse width 38 n
The C / N ratio when the sec signal was recorded and the erasing ratio when the erasing power was DC-irradiated were 49 dB and 24, respectively.
It was dB. Further, the erase power margin for the erase ratio of 20 dB or more was 3 mW.

Comparative Example 1 (ZnS) ₈₀ (Si
O ₂ ) ₂₀ composition, optical constant at wavelength 488 nm n = 2.
2. Set the first dielectric film of k = 0 to 160 nm by Ge ₂ Sb ₂
Te ₅ recording film 20 nm, (ZnS) ₈₀ (SiO ₂ )
₂₀ (Thermal conductivity 3.5 × 10 ^-4 pJ ・ μm ^-1・ K ^-1・ ns
^-1 , optical constant at wavelength 488 nm n = 2.2, k = 0)
The second dielectric film made of 20 nm and the Al alloy reflection film of 200 nm were sequentially formed by the sputtering method. Further, an ultraviolet curable resin layer was provided on the reflective layer.

Since the recording layer of the disk prepared as described above is in an amorphous state, it was crystallized by an Ar laser for initialization, and then the dynamic characteristics of the disk were evaluated by an evaluation device using a laser pickup having a wavelength of 488 nm. did. Recording power 8 mW at linear velocity 10 m / s, erasing power 4 mW, recording frequency 8.58 MHz, pulse width 38 ns
The C / N ratio when the ec signal was recorded and the erasing ratio when the erasing power was DC irradiated were 56 dB and 20 d, respectively.
It was B. Further, the erase power margin for the erase ratio of 20 dB or more was 0.3 mW.

[0026]

The optical information recording medium of the present invention can obtain recording / reproducing characteristics with a good erasing ratio, especially by using a light source having a laser wavelength of 600 nm or less.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tohwa Horie Sanboshi Kasei Co., Ltd. Research Institute, 1000, Kamoshida-cho, Midori-ku, Yokohama-shi, Kanagawa

Claims (2)

[Claims] 1. A first dielectric layer, a phase change recording layer, and
An optical information recording medium sequentially having a second dielectric layer and a reflective layer, wherein the phase change recording layer has a thickness of 15 to 50 nm.
And has a thermal conductivity of 5.0 × 10 ⁻⁴ as the second dielectric layer.
An optical recording medium, characterized in that it is larger than pJ · μm ⁻¹ · K ⁻¹ · ns ⁻¹ and the second dielectric layer has a thickness of 10 to 250 nm. 2. A recording / reproducing method for recording / reproducing information on / from the optical recording medium according to claim 1, using a laser having a wavelength of less than 600 nm.