JP3075816B2 - Optical recording medium - Google Patents

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 and reproducing information by utilizing a change in the 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. Of the rewritable optical recording media, the phase-change optical recording medium changes the recording layer from crystalline to amorphous or from amorphous to crystalline by irradiating a laser beam. Then, a change in the reflectance of the recording layer due to such a state change is detected. The drive device of the phase change type optical recording medium has a simpler optical system configuration than that of the magneto-optical recording medium.

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

The following proposals have been made to improve the recording layer of a phase change optical recording medium.

For example, in claim 2 of Japanese Patent Application Laid-Open No. 63-63141,

[0006] "a general formula that indicates the composition of the thin _{film, (Te y Ge 100-y} ) 100-x M x M: (Al, Ga, In, Zn, Ni) selected from among at least one or more X: atomic number% of M in the thin film y: atomic number% of Te in (Te and Ge) When x and y are expressed as 2 ≦ x ≦ 2, respectively.
An information recording medium characterized by satisfying 0, 30 ≦ y ≦ 70 ”

Has been disclosed. In a thin film (recording layer) of this information recording medium, recording is usually performed by a change from amorphous to crystalline. The publication discloses that the crystallization transition temperature of the thin film is increased by the above composition in order to prevent the thin film from being crystallized (becoming a recording state) by the heat absorbed by the readout light. . In the example of the publication, a TeGe alloy having an atomic ratio of 50% is used as a raw material of the thin film.

In Japanese Patent Application Laid-Open No. 3-15591,
Assuming that the recording layer composition disclosed in JP-A-63-63141 has insufficient C / N and durability,

"Te, Ge and Zn contained in the recording layer
The atomic _{ratio, (Te x Ge 100-x} ) 100-y Zn y of x, when expressed in y, 20 ≦ x ≦ 90 and 20 <
y ≦ 70 ”

The crystallization temperature of the recording layer is increased.
The upper left column of page 6 of the publication states, "A portion that is not irradiated with laser light is amorphous, and the portion that is irradiated with laser light is gradually cooled and partially crystallized, whereby information can be recorded. It is possible. "

On the other hand, an optical recording medium on 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 publication discloses that Ge, a 1: 1 compound of Ge and Te, is added to Ni, Co, Cu, Fe, V, Cr, T
i, Mn, Zn, Y, Mo, Pd, Pt, Ag, Au,
It has an optical recording material layer to which at least one of Rh is added by 10% or less. In the case of the GeTe thin film, the speed of change from the amorphous state to the crystalline state during erasure (disk circumferential speed 2 m / s) is lower than the speed of change from the crystalline state to the amorphous state during recording (corresponding to a disk peripheral speed of 10 m / s or less). (equivalent to s or less), the peripheral speed of the disk could not be increased because of the low speed. However, in the optical recording medium described in the publication, the crystallization speed could be increased, so that the peripheral speed of the disk could not be increased. The publication discloses that the data transfer speed can be improved by this.

By the way, recently, a compact disk (C
An optical recording disk capable of recording / reproducing at the same linear velocity as in D) has attracted attention because a drive device can be shared with a CD simply by adding or changing an optical system. As such an optical recording disk, for example, a write-once optical recording disk or a magneto-optical recording disk using an organic dye for a recording layer has been developed. A phase-change type optical recording disk can be rewritten, and the configuration of the optical system of the drive device is simpler than that of a magneto-optical recording disk.

However, Japanese Patent Application Laid-Open No. 1-165047 described above.
In a phase-change type optical recording disk for performing recording by changing from a crystalline state to an amorphous state as described in Japanese Patent Application Laid-Open Publication No. H11-27, good C / N can be obtained when used at a linear velocity equivalent to that of a CD. I can't. For CD, linear velocity is 1.4m / s
This is extremely slow compared to a conventional phase-change optical recording disk. Therefore, when a phase-change optical recording disk is used at a linear velocity equivalent to that of a CD, the influence of heat from the laser beam extends to outside the irradiation area. In the signal recording section, the region heated by the laser beam is rapidly cooled to be in an amorphous state. However, when the signal recording section is long, for example, in the recording section of 11T signal or the like, the irradiation end area is adjacent. Because of the influence of the irradiating section, the heating is continued slightly, so that the state is gradually cooled, and good amorphization cannot be performed. Therefore, a good C /
N cannot be obtained.

In order to solve such a problem, it is necessary to reduce the crystallization speed of the recording layer to widen the range of the cooling speed at which the recording layer can be made amorphous. However, as described above, although a proposal for improving the crystallization speed for high-density recording has been made, no proposal for reducing the crystallization speed has been made.

[0015]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and in a phase change type optical recording medium, the crystallization speed of the recording layer is reduced to reduce the crystallization speed of the recording layer with respect to a light beam. Good C for low relative speed
/ N.

[0016]

This and other objects are achieved by the present invention which is defined below as (1) to (3).

(1) Having a recording layer on a substrate,
The recording is performed by changing the crystalline state of the recording layer by the irradiation.
An optical recording medium, wherein the recording layer is made of Te, Ge and
And M (M is Zn or Zn and Ti).
And Te, Ge and M atoms in the recording layer
An optical recording medium having a ratio represented by the following formula: The formula (Ge_xTe_1-x)_100-yM_y  (In the above formula, 0.05 ≦ x ≦ 0.20 and 0 <y ≦ 10.)

(2) In the recording layer, the signal unrecorded portion is crystalline and the signal recorded portion is amorphous.
An optical recording medium according to claim 1.

(3) The optical recording medium according to the above (1) or (2), wherein the relative speed of the recording layer to the light beam is 1.2 to 2.8 m / s.

[0020]

In the optical recording medium of the present invention, a 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 are added to the recording layer containing Te in the above range, the crystallization speed of the recording layer decreases. Therefore, when the present invention is applied to an optical recording disk having a low linear velocity, a good C / N can be obtained.

[0021]

[Specific Configuration] Hereinafter, a specific configuration of the present invention will be described in detail.

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

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

[0024] In formula _{(Ge x Te 1-x)} 100-y M y above formula, 0.05 ≦ x, preferably 0.10 ≦
x, and x ≦ 0.20, preferably x ≦ 0.15. Also, 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 it is not possible to fix an 11T signal having a long signal length 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, bonds between Tes increase and the amorphous state becomes unstable, and crystallization occurs soon after recording.

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

[0027]

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

The method for forming the recording layer is not particularly limited, and may be appropriately selected from a sputtering method, a 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 reproduction light through the substrate. Therefore, the substrate is made of a material which is substantially transparent to these lights, for example, It is preferable to be made of resin, glass or the like. Among these, resin is preferable as the material of the substrate because it is easy to handle and inexpensive.
Specifically, various resins such as an acrylic resin, a polycarbonate, an epoxy resin, and a polyolefin may be used.

The shape and dimensions of the substrate are not particularly limited, but are usually disk-shaped, and the thickness thereof is usually 0.1 mm.
The diameter is about 5 to 3 mm and the diameter is about 50 to 360 mm. On the surface of the substrate, for tracking, addressing, etc.
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. For example, silicon oxide such as SiO ₂ or Si
₃ N ₄ silicon nitride and the like or other of these, may be used, such as various transparent ceramics and various types of glass, for example, and a so-called LaSiON which containing La, Si, O and N,
A so-called SiAlON containing Si, Al, O and N, or a SiAlON containing Y can be preferably used.

Such a dielectric thin film not only has a function of protecting the recording layer, but also has a function of rapidly releasing the heat remaining in the recording layer by heat conduction after recording.

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 deposition method such as a sputtering method or a vapor deposition method.

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

A protective film may be provided on the dielectric thin film or the reflective thin film, if necessary, for improving scratch resistance and corrosion resistance. This protective film is preferably composed of various organic substances, but in particular, it is preferably composed of a substance obtained by curing a radiation-curable compound or a composition thereof by radiation such as an electron beam 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.

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

On the other hand, when rewriting the recording information, a recording light beam is irradiated on a recording portion of a signal to be newly written, and an erasing light beam is irradiated on other portions.
The erasing light beam has a lower power than the recording light beam, and the irradiated portion is heated to a temperature higher than the crystallization temperature, but the reached temperature is relatively low. Crystallizes. At the time of rewriting, regardless of whether the state before irradiation is crystalline or amorphous, the recording light beam irradiation area is all amorphous, and the erasing light beam irradiation area is all crystalline. Becomes

The crystallization temperature of the recording layer is 80 to 120.
Since the temperature is about ° C, even when a resin substrate having low heat resistance is used, the entire optical recording medium can be heat-treated in a constant temperature bath to initialize the entire recording layer.

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

In the optical recording medium of the present invention, the relative speed 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 the speed to 1.2 to 1.4 m / s, which is equivalent to the linear velocity of the CD. Good C / N at linear velocity in this range
Is obtained.

[0043]

EXAMPLES Hereinafter, the present invention will be described in more detail 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 optical recording disk samples shown in Table 1 were manufactured. The board has
133m diameter with grooves formed simultaneously by injection molding
A disc-shaped polycarbonate having a thickness of 1.2 mm and 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 using SiO ₂ as a target. The recording layer was formed by an RF sputtering method. The target was a Zn chip or Z on the Ge-Te alloy surface.
Those to which n and Ti chips were attached were used. The thickness of the recording layer was 1000A. The composition of the recording layer is shown in Table 1 below. The protective film was formed by applying an ultraviolet curable resin by a spin coating method and then curing the applied resin by ultraviolet 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, and the entire area of the recording layer was crystallized and initialized. The fact that the recording layer was crystallized was confirmed by X-ray diffraction.

Next, 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. Thereafter, the CD signal was further rewritten. The power of the recording light beam was 6 mW, and the power of the erasing light beam was 3 mW.
mW. The wavelength of these light beams was 780 nm.

These signals were reproduced by irradiating a 0.7 mW light beam, and the C / N was measured. Table 1 shows the results.

[0048]

[Table 1]

From the results shown in Table 1, the effect of the present invention is clear. That is, the sample No. in which the ratio of Te to Ge and the content of M were within the range of the present invention. In 1 to 3, good C / N was obtained.

On the other hand, the sample Nos. Sample Nos. 4 and 6, in which the content of M exceeds the range of the present invention. Sample No. 5 in which the ratio of Te is below the range of the present invention. 7 and 8 have extremely low C / N.

[0051]

According to the present invention, a phase change type optical recording medium which can obtain an extremely good C / N even when recording is performed at a low linear velocity equivalent to that of a CD is realized.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-63141 (JP, A) JP-A-3-15591 (JP, A) JP-A 1-165047 (JP, A) JP-A-63-63 155442 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) B41M 5/26

Claims (3)

(57) [Claims] A recording layer is provided on a substrate, and the recording layer
The recording state is changed by changing the crystal state of the recording layer.
An optical recording medium, wherein the recording layer is made of Te, Ge and M (M is Zn or Z
n and Ti. ) In the recording layer.
The atomic ratio of Te, Ge and M is represented by the following formula.
An optical recording medium characterized by the following. The formula (Ge_xTe_1-x)_100-yM_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, a signal unrecorded portion is crystalline and a signal recorded portion is amorphous. 3. The optical recording medium according to claim 1, wherein the relative speed of the recording layer to the light beam is 1.2 to 2.8 m / s.