JPH0554428A - Optical recording medium - Google Patents

Abstract

PURPOSE:To improve the heat resistance of a reflection cooling layer and to provide the optical recording medium having excellent repetitive durability for rewriting by forming the reflection cooling layer of an alloy consisting essentially of Al and Ti. CONSTITUTION:The reflection cooling layer 5 is formed of the alloy formed by adding the Ti at 2 atomic % to the Al. A gentle increase in error rate is indicated at 10<5> times the number of repetition times in such a case but there is no sharp increase in the error rate and the error rate is <10<-5> at 10 times. The optical disk formed with the reflection cooling layer 5 by the alloy formed by adding 5 atomic % Ti to the Al is further gentler in the increase in the error rate and additionally smaller in the error rate than in the case of the alloy added with 2 atomic % Ti.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a write-once type which uses as a recording means a change in reflectance, a change in refractive index or a change in shape of an optical recording material, and further, a change in characteristics by an optical method such as a change in magnetic characteristics. Regarding an optical recording medium such as a rewritable type, more specifically, it reflects a laser beam applied to the optical recording medium,
The present invention also relates to the configuration of the reflective cooling layer that also serves to cool the recording material layer.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for higher density and larger capacity of information recording, and the research has been actively conducted in and outside Japan. In particular, the optical recording medium has a higher recording density than the conventional magnetic recording medium, and since the recording and reproducing head and the recording medium can record and reproduce information in a non-contact state, the recording medium is less damaged. In addition, since it has a long life and the like, it is regarded as promising as a high-density, large-capacity recording method for recording and reproducing a huge amount of information. This optical recording medium is classified into a read-only type, a write-once type, and a rewritable type depending on the application.
It can be roughly divided into types. The read-only type is a read-only recording medium that can only read information, while the write-once type is an optical recording that can record and reproduce information as needed, but cannot erase recorded information. It is a medium.
On the other hand, the rewritable type is an optical recording medium capable of recording and reproducing information, and further erasing and rewriting recorded information, which is the most promising for use as a data file for computers. Is.

Optical recording materials include a type in which information is recorded by optical changes such as a change in shape such as a punching type, a bubble type or a texture type, a reflectance such as an organic type or a phase change type, and a change in refractive index. A type in which information is recorded by a magneto-optical effect such as a change in magnetization direction is known. For example, regarding a rewritable optical recording medium, two recording methods, a magneto-optical method and a phase change method, are being developed, and both methods are in the process of research and development in terms of recording material and writing mechanism. is there. Of the above methods,
The phase change method generally focuses and heats a laser beam having a controlled pulse output and pulse width on a recording surface of a medium.
The optical recording material on the surface of the optical recording medium undergoes a phase change due to the heating of the laser beam, causing a transition from a crystalline state to an amorphous state or a phase transition. The optical recording medium is for recording and erasing information by the difference in the reflectance in each state of the phase change state, for example, the crystalline state and the amorphous state.

FIG. 3 shows the structure of a phase change type optical recording disk among such optical recording media.

The magneto-optical disk 10 has a tracking groove 1
A protective layer 2 made of a ceramic such as ZnS is formed on the surface of a base body 1 made of polycarbonate or the like in which 1 is formed. Then, on the protective layer 2, Ge ₂ Sb ₂ T
An optical recording material layer 3 is formed of e ₅ or the like, and a protective layer 4 made of a ceramic such as ZnS, a reflective cooling layer 5 made of Al, and an organic surface protective layer 6 are further formed. The reflective cooling layer 5 is generally laminated on the optical recording material layer 3, that is, on the optical recording material layer 3, or on the protective layer 4.
Discs 10 that are layers stacked through
The laser light incident from the side of the substrate 1 is reflected to improve the utilization efficiency of the laser light, and the cooling rate of the optical recording material layer is increased to promote the phase change from the crystalline state to the amorphous state. .. As described above, in the phase change type optical recording medium, the optical recording material is in a crystalline state in the initial state, and at the time of information recording, the irradiated portion is melted and then rapidly cooled, and the irradiated portion is in an amorphous state. Becomes Therefore, the reflectance differs only in the portion irradiated with the laser beam, and information is recorded by the difference in the reflectance. And when rewriting,
It is annealed to return to a crystalline state by irradiation with a low-power laser beam.

[0006]

One of the problems in recording using such a phase change type optical recording medium is repetitive rewriting durability. That is, in order to put such a rewritable optical recording medium into practical use, 10 ⁵
It is required that the rewriting error rate does not increase sharply after the number of repetitions is about one. However, in the conventional optical recording medium, the error rate increases rapidly before the number of repetitions reaches 10 ^5. There is a problem that it ends up.

The cause of such a rapid increase in the error rate is considered to be the effect of heat damage to the reflective cooling layer. For the above-mentioned purpose, the reflective cooling layer is required to have high reflectance of laser light, high corrosion resistance, high thermal conductivity, and low cost. Therefore, as the material, in addition to Al which has been conventionally used, Au, Ni—C
It is possible to adopt r alloy or the like. As a result of various studies such as Au being expensive and Ni-Cr having low thermal conductivity, Al has been adopted as a material for the reflective cooling layer. However, the Al reflective cooling layer is
The problem remains that the melting point is low.

In the phase change type optical recording disk 10 described above, the lower protective layer 2, the optical recording material layer 3, the upper protective layer 4, and the reflection cooling layer 5 have respective thicknesses of 150,
When the temperature of the reflective cooling layer 5 is calculated by thermal analysis in the case of 20, 20, and 50 nm, the temperature is instantaneously 400 in the writing state under the conditions of the peripheral speed of 9 m / s and the laser output of 16 mW. Rises to ° C. This temperature is close to the melting point of pure Al of 660 ° C., and it is considered that the Al reflection cooling layer is softened. The reflective cooling layer has a stress due to an optical recording material layer having different densities in a crystalline state and an amorphous state, a thermal stress due to a difference in thermal expansion coefficient between layers constituting the optical recording medium, and an optical recording. Since various stresses such as residual stress during the production of the medium are applied, it is considered that the softened reflective cooling layer is deformed by these stresses. Therefore, since the deformed reflective cooling layer causes a change in the film thickness of the optical recording material layer, it is expected that an error such as a significant difference in reflectance due to a phase change will occur.

Therefore, it is an object of the present invention to improve the heat resistance of the reflective cooling layer and to realize an optical recording medium having excellent repetitive rewriting durability.

[0010]

In order to solve the above problems, in the present invention, the reflection cooling layer is formed of an Al-Ti alloy. That is, an optical recording material layer for recording information based on the optical characteristics according to the present invention,
An optical recording medium having at least a reflection cooling layer laminated on the optical recording material layer is characterized in that the reflection cooling layer is formed of an alloy mainly containing Al and Ti.

Then, it is effective to increase the film thickness of the reflective cooling layer in accordance with the Ti ratio. In an optical recording medium in which the optical recording material layer is made of Ge ₂ Sb ₂ Te ₅ , the reflective cooling layer is mainly composed of Al and Ti
It is characterized in that it is formed of an alloy to which is added.

[0012]

In the alloy system mainly composed of Al and Ti, the melting point rises sharply as compared with pure Al. For example,
An alloy obtained by adding 5 atomic% of Ti to Al has a melting point of 1
It has a heat resistance of 200 ° C., which is almost twice as high as that of pure Al having a melting point of 660 ° C.

Therefore, even if laser light is irradiated, Al
-Since the Ti alloy-based reflective cooling layer does not soften,
Less likely to cause thermal deformation. Therefore, even if the rewriting is repeated, the rewriting error rate does not sharply increase, and a practical optical recording medium can be realized.

This Al-Ti type alloy has a slightly lower thermal conductivity than pure Al.

Therefore, in order to maintain the same cooling rate as in the conventional case, the film thickness of the reflective cooling layer may be increased.

[0016]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

The optical recording disk of this example has the same structure as the conventional optical recording disk described above, and was manufactured by RF magnetron sputtering. First, on a disc base 1 made of polycarbonate, ZnSS with a thickness of 140 nm was used.
A protective layer ₂ made of iO ₂ is formed, and a film thickness of 20 nm is formed on the protective layer 2.
Optical recording material layer 3 made of Ge ₂ Sb ₂ Te ₅ with a film thickness of 20 n
A protective layer 4 made of ZnSSiO ₂ was formed by m. further,
On this protective layer 4, under the conditions of Table 1, 3 of cases A to C
Optical discs having a reflective cooling layer made of a type of Al-Ti alloy were produced. This disc has a diameter of 86 mm,
After initialization, overwriting was repeated with a semiconductor laser having a wavelength of 830 nm while rotating at a rotation speed of 3600 rpm, and the error rate was measured. The writing conditions were a frequency of 5.8 MHz, a pulse width of 60 ns, a peak power of 16 mW, and a bias power of 8 mW.

[0018]

[Table 1]

As shown in Table 1, depending on the added amount of Ti,
In order to compensate for the decreasing thermal conductivity of the reflective cooling layer, the thickness of the reflective cooling layer is increased based on the amount of Ti. As a result, as shown in the CN ratio and the erasing ratio, it is possible to secure the same recording characteristics as the conventional one. Further, due to the difference in the reflectance and thermal conductivity of the reflective cooling layer, the optimum values of the write peak power and the erase bias power are slightly changed.

FIG. 1 shows changes in the error rate due to repeated rewriting actually measured in the optical disks of the cases A to C. As can be seen from the figure, the number of repetitions is 1 in the optical disk of case A which is composed of the reflective cooling layer made of pure Al as in the conventional optical disk.
The error rate increases rapidly before reaching 0 ⁵ times,
^The error rate becomes 10 ^-5 or more after ⁵ times. On the other hand, in the optical disk of case B in which the reflective cooling layer is formed of an alloy in which 2 atomic% of Ti is added to Al, a gradual increase in error rate is shown at the number of repetitions of 10 ⁵ , but the error rate increases rapidly. There is no increase in the error rate, and the error rate is 10 even after 10 ⁵ times.
^{-5 or} less. Then, in the optical disk of case C in which the reflective cooling layer is formed of an alloy in which Ti is added at 5 atomic% to Al, the error rate increases more slowly than in case B when the number of repetitions is 10 ⁵ . Even at 10 ⁵ times, the error rate is smaller than that in case B. As described above, in the optical disc in which the reflection cooling layer is formed of the alloy containing Ti, even if the rewriting is repeated 10 ⁵ times, the error rate does not increase rapidly, and the error rate itself is further increased. The value of was less than 10 ⁻⁵ , and an optical disk with no practical problems could be realized.

FIG. 2 shows the relationship between the Al—Ti alloy system composition and the melting point. As can be seen from this figure, the addition of Ti to Al causes the melting point to rise rapidly. And
In an alloy in which 5 atomic% of Ti is added, a pure Al having a melting point of about 1200 ° C and a melting point of 660 ° C.
Which is almost twice as high as the melting point. From the relationship between the experimental result of the error rate shown in FIG. 1 and the melting point of the Al—Ti alloy, by forming the reflective cooling layer using a material with a high melting point,
It has been found that it is possible to realize an optical recording medium that can suppress an increase in error rate and that has excellent durability against repeated rewriting.
As a material for forming the reflective cooling layer, it is needless to say that it has high thermal conductivity, high reflectance, high corrosion resistance, and is inexpensive in addition to the above-mentioned high melting point. Under such conditions, the Al--Ti shown in this example is used.
It can be said that the system alloy is a promising material.

An optical recording medium which can be repeatedly improved in durability by using such a reflective cooling layer is an optical recording medium using the Ge—Sb—Te system of this example as an optical recording material. Not only Te-Ge-Sn-
An optical recording medium, such as an O type or an In-Se-Ti-Co type, that records information by reversible phase change by laser light can be given. Also, depending on the optical recording material,
The protective layer and the reflective cooling layer may be used together.
Further, the reflective cooling layer of the present example is also effective in a magneto-optical medium such as a magneto-optical disk in which magnetic characteristics are changed by laser light to record information.

[0023]

As described above, in the optical recording medium according to the present invention, the reflective cooling layer is formed of a high melting point alloy system mainly containing Al and Ti to improve repetitive durability in rewriting. be able to. Therefore, by making an optical recording medium using such a reflective cooling layer made of an Al—Ti alloy system, the number of times of rewriting is 10 times.
It is possible to realize an optical recording medium in which the error rate does not increase sharply even after ⁵ times or more, and the value of the error rate itself is less than 10 ⁻⁵ without any practical problems.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the number of times rewriting is repeated and an error rate.

FIG. 2 is a graph showing a relationship between a composition of an Al—Ti alloy system and a melting point.

FIG. 3 is a cross-sectional view showing a configuration of a phase change type optical recording disk.

[Explanation of symbols]

 1 ・ ・ ・ Substrate 2 ・ ・ ・ Protective layer 3 ・ ・ ・ Optical recording material layer 4 ・ ・ ・ Protective layer 5 ・ ・ ・ Reflective cooling layer 6 ・ ・ ・ Surface protective layer 10 ・ ・ ・ Optical disk 11 ・ ・ ・ Tracking groove

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Tanio Urushiya 1-1 Tanabe Shinden, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. No. 1 in Fuji Electric Co., Ltd.

Claims (3)

[Claims] 1. An optical recording medium having at least an optical recording material layer for recording information based on optical characteristics and a reflective cooling layer laminated on the optical recording material layer, wherein the reflective cooling layer is Al and Ti. An optical recording medium characterized by being formed of an alloy mainly composed of. 2. The optical recording medium according to claim 1, wherein the film thickness of the reflective cooling layer is increased in accordance with the Ti ratio. 3. The optical recording material layer according to claim 1, wherein the optical recording material layer is formed of Ge ₂ Sb ₂ Te _5, and the reflective cooling layer is formed of an alloy in which Ti is added to Al. Characteristic optical recording medium.