JPH05162451A - Optical recording medium - Google Patents

Abstract

PURPOSE:To realize a good C/N ratio when the relative speed of a recording layer to laser beam is low, in a phase change type optical recording medium, by lowering the crystallizing speed of the recording layer. CONSTITUTION:A recording layer containing Te, Ge and M (Ti and/or Zn) in an atomic ratio represented by formula (Gex Te1-x)100-y M (where x is 0.05<=x<=0.20 and y is 0<y<=10) is used.

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 for recording / reproducing information by utilizing the change in crystal state of a recording layer.

[0002]

2. Description of the Related Art In recent years, an optical recording medium capable of high-density recording and capable of erasing and rewriting recorded information has attracted attention. Among rewritable optical recording media, phase-change optical recording media change the recording layer from crystalline to amorphous or from amorphous to crystalline by irradiating laser light. Then, the change in the reflectance of the recording layer due to such a change in state is detected. The phase-change type optical recording medium drive device has a simpler optical system configuration than that of a magneto-optical recording medium.

In the phase change type optical recording medium, Te and Ge are mainly used because the difference in reflectance between the crystalline state and the amorphous state is large and the stability of the amorphous state is relatively high. A recording layer as a component is usually used.

The following proposals have been made for improving the recording layer of the phase change type optical recording medium.

For example, in claim 2 of JP-A-63-63141,

"A general formula representing the composition of a thin film is defined as at least one selected from (Te _y Ge _100-y ) _100-x M _x M: (Al, Ga, In, Zn, Ni). X is the atomic number of M in the thin film, y is the atomic number of Te in (Te and Ge)%, and the ranges of x and y are 2 ≦ x ≦ 2, respectively.
Information recording medium characterized in that 0, 30 ≦ y ≦ 70 ”

Are disclosed. In the thin film (recording layer) of this information recording medium, recording is usually performed by changing from amorphous to crystalline. Then, the publication discloses that the crystallization transition temperature of the thin film is raised by the above composition in order to prevent the thin film from being crystallized (in a recording state) by the absorption heat of the reading light. .. In the example of the publication, a TeGe alloy with an atomic ratio of 50% is used as a raw material for the thin film.

Further, in Japanese Patent Application Laid-Open No. 3-15591,
According to the recording layer composition disclosed in JP-A-63-63141, C / N and durability are insufficient.

"Te, Ge and Zn contained in the recording layer
When the atomic ratio of is represented by x and y of (Te _x Ge _100-x ) _100-y Zn _y , 20 ≦ x ≦ 90 and 20 <
y ≦ 70 ”

The crystallization temperature of the recording layer is increased.
In the upper left column on page 6 of the publication, "a portion not irradiated with laser light is amorphous, and a portion irradiated with laser light is gradually cooled and partially crystallized to record information. It is possible. ”

On the other hand, an optical recording medium in which recording is performed by changing from a crystalline state to an amorphous state is disclosed in, for example, Japanese Patent Application Laid-Open No. 1-165047. The optical recording medium described in the above publication uses GeTe, which is a 1: 1 compound of Ge and Te, and Ni, Co, Cu, Fe, V, Cr, and T.
i, Mn, Zn, Y, Mo, Pd, Pt, Ag, Au,
It has an optical recording material layer containing 10% or less of at least one of Rh. In the GeTe thin film, compared with the change speed from the crystalline state to the amorphous state at the time of recording (corresponding to a disk peripheral speed of 10 m / s or less), the change speed from the amorphous state to the crystalline state at the time of erasing (disk peripheral speed 2 m / s (equivalent to s or less), it was not possible to increase the peripheral speed of the disk, but the optical recording medium described in this publication was able to increase the crystallization speed, so it was possible to increase the peripheral speed of the disk. The publication discloses that the data transfer rate can be improved by this.

By the way, recently, a compact disc (C
An optical recording disk capable of recording / reproducing at the same linear velocity as in D) is drawing attention because it can be used as a CD and a driving device by simply adding or changing an optical system. As such an optical recording disc, for example, a write-once type optical recording disc and a magneto-optical recording disc using an organic dye in a recording layer have been developed. The phase-change type optical recording disk is rewritable, and the optical system of the driving device has a simpler structure than the magneto-optical recording disk. Therefore, it is considered suitable for such an application.

However, the above-mentioned Japanese Patent Laid-Open No. 1-165047.
In a phase-change type optical recording disk for recording by changing from a crystalline state to an amorphous state, as described in Japanese Patent Publication No. JP-A-2003-264, a good C / N is obtained when used at a linear velocity equivalent to that of a CD. I can't. For CD, the linear velocity is 1.4m / s
Below, this is extremely slow compared to conventional phase change optical recording disks. Therefore, when a phase change type optical recording disk is used at a linear velocity equivalent to that of a CD, the influence of heat from the laser beam extends outside the irradiation area. In the signal recording part, the region heated by the laser beam is rapidly cooled and becomes an amorphous state. However, when the signal recording part is long, for example, in the recording part such as 11T signal, the irradiation end regions are adjacent to each other. Since it is slightly heated by the influence of the irradiation part, the state of gradual cooling cannot be achieved and good amorphization cannot be performed. Therefore, good C /
N cannot be obtained.

In order to solve such a problem, it is necessary to slow down the crystallization rate of the recording layer to widen the range of cooling rate at which the recording layer can be made amorphous. However, as described above, although proposals for improving the crystallization rate for high-density recording have been made, proposals for decreasing the crystallization rate have not been made.

[0015]

The present invention has been made under such circumstances, and in a phase change type optical recording medium, the crystallization speed of the recording layer is reduced to thereby form a recording layer against a light beam. Good C when relative speed is low
/ N is realized.

[0016]

The above objects are achieved by the present invention described in (1) to (3) below.

(1) An optical recording medium having a recording layer on a substrate, wherein recording is performed by changing the crystalline state of the recording layer by irradiation with a light beam, wherein the recording layer is Te, Ge and M ( M is Ti and / or Zn), and the atomic ratio of Te, Ge and M in the recording layer is represented by the following formula. Formula (Ge _x Te _1-x ) _100-y M _y (In the above formula, 0.05 ≦ x ≦ 0.20 and 0 <y ≦ 10.)

(2) In the recording layer, the signal non-recorded portion is crystalline and the signal recorded portion is amorphous.
The optical recording medium according to 1.

(3) The optical recording medium as described in (1) or (2) above, wherein the relative velocity of the recording layer with respect to the light beam is 1.2 to 2.8 m / s.

[0020]

In the optical recording medium of the present invention, the recording layer is formed by adding Ti and / or Zn in addition to Te and Ge. When Ti and / or Zn in the above range is added to the recording layer containing Te in the above range, the crystallization rate of the recording layer decreases. Therefore, good C / N can be obtained when the present invention is applied to an optical recording disk having a low linear velocity.

[0021]

[Specific Structure] The specific structure of the present invention will be described in detail below.

The optical recording medium of the present invention is an optical recording medium having a recording layer on a substrate, and recording is performed by changing the crystal state of the recording layer by irradiation of a light beam.

The recording layer is Te, Ge and M (M is
Ti and / or Zn. ), And the atomic ratio of Te, Ge and M in the recording layer is represented by the following formula.

Formula (Ge _x Te _1-x ) _100-y M _{y In the} above formula, 0.05 ≦ x, preferably 0.10 ≦
x, and x ≦ 0.20, preferably x ≦ 0.15. Further, 0 <y ≦ 10, preferably 5 ≦ y ≦ 8.

If x exceeds the above range, that is, if the content of Te with respect to Ge is insufficient, the crystallization rate becomes too high, and the 11T signal having a long signal length cannot be fixed as an amorphous state. Good C / N cannot be obtained.
In addition, the difference in reflectance between the crystalline state and the amorphous state becomes insufficient. If x is less than the above range, that is, if the content of Te with respect to Ge is too large, the bonding between Tes increases, the amorphous state becomes unstable, and crystallization occurs soon after recording.

When the Te and Ge contents are within the above ranges and the M content is within the above ranges, the crystallization rate of the recording layer can be lowered. Therefore, when the relative velocity of the recording layer with respect to the recording light beam is low, that is, in the recording with a low linear velocity, good C / N is obtained. M
If y representing the content of is less than the above range, the C / N improving effect cannot be realized, and if it exceeds the above range, the difference in reflectance between the crystalline state and the amorphous state becomes insufficient.

Since Ti has a stronger effect of increasing the crystallization transition temperature than Zn, it is advantageous in improving reliability.

Although the thickness of the recording layer is not particularly limited, it is usually 100 to 2000 A, preferably 150 to 1500 A.

The method of forming the recording layer is not particularly limited and may be appropriately selected from the sputtering method, the vapor deposition method and the like.

In the optical recording medium of the present invention, it is preferable that the recording layer is irradiated with the recording light and the reproducing light through the substrate. Therefore, the substrate is made of a material which is substantially transparent to these lights, for example, Preferably, it is made of resin, glass, or the like. Of these, resin is preferable as the material of the substrate because it is easy to handle and inexpensive.
Specifically, various resins such as acrylic resin, polycarbonate, epoxy resin and polyolefin may be used.

The shape and dimensions of the substrate are not particularly limited, but they are usually disk-shaped, and their thickness is usually 0.
The diameter is about 5 to 3 mm and the diameter is about 50 to 360 mm. On the surface of the board, for tracking and address,
A predetermined pattern such as a groove is provided as needed.

Between the recording layer and the substrate and on the recording layer,
It is preferable to provide a dielectric thin film. The dielectric used is not particularly limited, and examples thereof include silicon oxide such as SiO ₂ and Si.
Other than these, silicon nitride such as ₃ N ₄ or various transparent ceramics or various glasses may be used. For example, so-called LaSiON containing La, Si, O and N,
So-called SiAlON containing Si, Al, O and N, or SiAlON containing Y can be preferably used.

Such a dielectric thin film has a function of protecting the recording layer, and also has a function of promptly releasing the heat remaining in the recording layer after recording by heat conduction.

The thickness of the dielectric thin film is preferably about 500 to 2000 A, and the dielectric thin film is preferably formed by a vapor phase growth method such as a sputtering method or a vapor deposition method.

If necessary, a reflective thin film may be provided on the recording layer or on the dielectric thin film provided on the recording layer as required. Although the material of the reflective thin film is not particularly limited, it may be usually composed of a high reflectance metal such as Al, Au, Pt, or Cu. The thickness of the reflective thin film is 300 to 150.
It is preferably 0A. When the thickness is less than the above range, it becomes difficult to obtain sufficient reflectance. Further, even if it exceeds the above range, the improvement in reflectance is small, which is disadvantageous in cost. The reflective thin film is preferably formed by a vapor phase growth method such as a sputtering method or a vapor deposition method.

If necessary, a protective film may be provided on the dielectric thin film or the reflective thin film in order to improve scratch resistance and corrosion resistance. This protective film is preferably composed of various organic substances, but in particular, it is composed of a substance obtained by curing a radiation-curable compound or a composition thereof with radiation such as electron beams or ultraviolet rays. preferable. The thickness of the protective film is usually about 0.1 to 100 μm, and may be formed by a usual method such as spin coating, gravure coating, spray coating, dipping or the like.

With the optical recording medium of the present invention, recording and reproduction are performed as follows.

In the optical recording medium of the present invention, the entire recording layer is crystallized in the initialized state. By irradiating the recording layer in the crystallized state with the recording light beam (laser light beam), the irradiated portion is melted. Then, since the temperature of the portion is rapidly lowered after passing through the recording light beam, the portion becomes substantially amorphous and becomes a signal recording portion. In the optical recording medium of the present invention, the crystallization rate of the recording layer is low, so that even if the relative speed of the recording light beam to the recording layer is low and the cooling rate of the irradiated portion is relatively low, good amorphization is achieved. , High C / N is obtained.

On the other hand, when the recorded information is rewritten, the recording light beam for the newly written signal is irradiated with the recording light beam, and the other portion is irradiated with the erasing light beam.
The light beam for erasing has lower power than the light beam for recording, and the irradiated portion is heated up to the crystallization temperature or higher, but the reached temperature is relatively low, so the cooling rate is lower than the crystallization speed and the irradiated portion is Crystallize. At the time of rewriting, regardless of whether the state before irradiation is crystalline or amorphous, all the recording light beam irradiation site becomes amorphous, and all the erasing light beam irradiation site is crystalline. Becomes

The crystallization temperature of the recording layer is 80 to 120.
Since the temperature is on the order of ° C, even if a resin substrate having low heat resistance is used, the entire optical recording medium can be heat-treated in a thermostatic chamber to initialize the entire recording layer.

The reproducing light beam is a low power light beam that does not affect the crystalline state of the recording layer. The reflectance of the amorphous signal recorded portion is lower than that of the crystalline unrecorded portion.

In the optical recording medium of the present invention, the relative velocity of the recording layer with respect to each of the above light beams is about 1.2 to 2.8 m / s,
In particular, it is preferable to set it to 1.2 to 1.4 m / s, which is equivalent to the linear velocity of CD. Good C / N at linear velocity in this range
Is obtained.

[0043]

EXAMPLES The present invention will be described in more detail below by showing specific examples of the present invention.

On the surface of the substrate, a first dielectric thin film, a recording layer, a second dielectric thin film and a protective film were formed, and the optical recording disk samples shown in Table 1 were prepared. On the board
133mm diameter with simultaneous groove formation by injection molding,
A disc-shaped polycarbonate having a thickness of 1.2 mm was used.
The first and second dielectric thin films were formed to a thickness of 1500 A by sputtering with SiO ₂ as a target.
The recording layer was formed by the RF sputtering method. The target is a Ti-chip and / or Z on the surface of the Ge-Te alloy.
The one with an n-chip attached was used. The thickness of the recording layer is 100
It was set to 0A. The composition of the recording layer is shown in Table 1 below. The protective film, after applying a UV curable resin by spin coating,
It was formed by curing with UV irradiation. The protective film thickness after curing was 5 μm.

Each sample was placed in a constant temperature bath, heated to 100 ° C., then taken out of the bath and naturally cooled to crystallize the entire region of the recording layer for initialization. It was confirmed by X-ray diffraction that the recording layer was crystallized.

Then, a CD signal {11T signal (196 kHz)} was recorded while rotating each sample at a linear velocity (1.4 m / s) equivalent to that of a CD. After that, the CD signal was further rewritten. The power of the recording light beam is 6 mW and the power of the erasing light beam is 3 mW.
mW. The wavelength of these light beams was 780 nm.

These signals were reproduced by irradiating a light beam of 0.7 mW and C / N was measured. The results are shown in Table 1.

[0048]

[Table 1]

From the results shown in Table 1, the effect of the present invention is clear. That is, in samples Nos. 1 to 5 in which the ratio of Te and Ge and the content of M are within the range of the present invention, good C / N is obtained.

On the other hand, sample Nos. 6 and 8 not containing M, and sample N having an M content exceeding the range of the present invention
Sample Nos. 10 to 13 in which the ratios of o. 7 and 9 and Te are below the range of the present invention have remarkably low C / N.

[0051]

According to the present invention, it is possible to realize a phase change type optical recording medium capable of obtaining a very good C / N even when recording is performed at a low linear velocity equivalent to that of a CD.

Claims (3)

[Claims] 1. An optical recording medium having a recording layer on a substrate, wherein recording is performed by changing a crystal state of the recording layer by irradiation with a light beam, wherein the recording layer is Te, Ge and M (M Is Ti and /
Or Zn. ), And the atomic ratio of Te, Ge and M in the recording layer is represented by the following formula. Formula (Ge _x Te _1-x ) _100-y M _y (In the above formula, 0.05 ≦ x ≦ 0.20 and 0 <y ≦ 10.) 2. The optical recording medium according to claim 1, wherein in the recording layer, the signal unrecorded portion is crystalline and the signal recorded portion is amorphous. 3. The optical recording medium according to claim 1, wherein the relative velocity of the recording layer with respect to the light beam is 1.2 to 2.8 m / s.