JPH05159363A - Optical recording medium - Google Patents

Abstract

PURPOSE:To provide the optical recording medium being able to surely record and erase without lowering a recording sensitivity. CONSTITUTION:The medium is an optical disk having a recording layer 3, heat resistant protective layers 2 and 4 and a reflectively radiating layer 5 on a base plate 1, and the layer 5 is made of one of an Ag-Ni alloy, an Ag-Mn alloy and an Ag-Ti alloy. A suitable thermal conductivities for reflectively radiating layer is 9X10<-2>-3.2W/cm.deg in case of the Ag-Ni alloy, 4.0X10<-2>-3.2 W/cm.deg in case of the Ag-Mn alloy, 7.0X10<-2>-3.2W/cm.deg in case of the Ag-Ti alloy.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change type optical recording medium and can be applied to an optical memory.

[0002]

2. Description of the Related Art Generally, a phase change type optical recording system utilizes a change in an optical constant associated with a phase transition of a substance due to heat. Specifically, the chalcogen-based compound material is irradiated with light corresponding to the energy band cap of the material to absorb the light, which is exchanged with heat to increase the temperature of the irradiated part, and after melting and quenching, it is amorphous. Turn into. This amorphized portion (pit) is generally recorded.

Next, in the case of erasing, the amorphous portion may be irradiated with light with low power to be crystallized. In this way, the phase change optical recording is a crystal of the recording material due to the intensity modulation of the incident light.
The basis is to utilize an amorphous phase change. In order to improve the sensitivity of recording and erasing, there is a method of providing a metal reflection layer so that incident light can be efficiently absorbed by the recording layer. For example, a method has been proposed in which a metal such as Al, Ag, and Rh is used as the reflective layer and a chalcogen-based material is used as the recording layer (Japanese Patent Publication No. 61-18262). However, since metals such as Al and Ag have large thermal conductivity, it is difficult to use heat efficiently, and high sensitivity cannot be expected so much. Therefore, a method of reducing the thermal conductivity of the reflective layer to realize high sensitivity has also been proposed (JP-A-63-58639). However, also in this case, if the thermal conductivity is not properly adjusted, the thermal conductivity becomes too small and the cooling effect at the time of recording becomes insufficient, so that there is a possibility that amorphization becomes difficult.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical recording medium that can surely record and erase without lowering the recording sensitivity.

[0005]

The constitution of the present invention for solving the above-mentioned problems is an optical recording medium as described in the claims.

That is, according to the present invention, in a phase-change type optical recording medium, the medium is composed of a recording layer, a dielectric protective layer, and a reflection heat dissipation layer, and the reflection heat dissipation layer is Ag-Ni alloy, Ag-.
It is characterized by being made of any alloy selected from a Mn alloy and an Ag-Ti alloy. The phase-change type optical recording medium utilizes a change in optical constant between two phases by causing a recording layer to absorb light and generate heat when irradiated with light to cause a phase transition between crystal and amorphous. Therefore, how to record and erase information with low energy light irradiation (that is, to increase sensitivity) is important. For this purpose, it depends on how effectively the light applied to the recording layer is absorbed.

As a concrete method, by reducing the thickness of the recording layer, the heat capacity is reduced and the light energy required for recording and erasing information is reduced, and at the same time, a reflection heat dissipation layer is provided to form a recording portion. It is considered that the transmitted light is reflected and the emitted light is effectively used as much as possible. Further, since the reflective layer is generally made of metal, it has a large thermal conductivity, so that a rapid cooling effect can be expected, and it has an effect of amorphizing at the time of recording information. However, Au,
When a metal having a large thermal conductivity such as Al, Ag, or Cu is used as the reflective layer, heat diffuses before the temperature of the recording portion during recording sufficiently rises, that is, before reaching the temperature required for melting. Therefore, the recording sensitivity will be reduced. On the other hand, if Ti, Mn or the like having a relatively low thermal conductivity is used, heat conduction is reduced, so that the quenching effect is not efficiently performed, so that recording, that is, amorphization becomes difficult, and at the same time, the reflectance is reduced. Therefore, the role of the reflective layer is lost. Therefore, as a method of solving these problems,
By alloying a metal with a high reflectance and a high thermal conductivity with a metal with a relatively low thermal conductivity, a decrease in reflectance is prevented, and at the same time, the thermal conductivity records information, that is, the temperature rises rapidly to the melting point. Then, it becomes possible to adjust to a value having a quenching effect necessary for amorphization, and high sensitivity can be expected.
In addition, by adjusting the alloy composition, it becomes possible to provide a recording medium corresponding to the linear velocity of the disc (from low speed to high speed).

That is, in the Ag-Ni alloy of the present invention, the thermal conductivity can be widely changed depending on the composition ratio (9.0 × 10 to ² W / cm · deg to 3.2 W / cm · deg), It is possible to provide a highly sensitive recording medium corresponding to the linear velocity of the disc.

The structure of the recording medium of the present invention is shown in FIG. Here, the substrate used in the present invention is usually glass, ceramics or resin, and a resin substrate is preferable in terms of moldability, cost and the like. Typical examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicon resin,
Fluorine-based resins, ABS resins, urethane resins and the like can be mentioned, but polycarbonate resins and acrylic resins are preferable from the viewpoints of processability and optical characteristics. The shape of the substrate may be disk-shaped, card-shaped or sheet-shaped.

Materials for the heat-resistant protective layer include SiO and S.
iO ₂ , ZnO, SnO ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O
₃ , metal oxides such as MgO and ZrO ₂ , Si ₃ N ₄ , Al
Nitride such as N, TiN, BN, ZrN, ZnS, In
₂ S ₃ , sulfides such as TaS ₄ , SiC, TaC, B ₄ C, W
Examples thereof include carbides such as C, TiC, and ZrC, diamond-like carbon, or a mixture thereof. Moreover, you may contain impurities as needed. Such a heat resistant protective layer can be formed by various vapor phase film forming methods such as a vacuum vapor deposition method, a sputtering method, a plasma CVD method, a photo CVD method, an ion plating method and an electron beam vapor deposition method.

The thickness of the heat resistant protective layer is 200 to 50.
00Å, preferably 500 to 3000Å.
When the thickness is less than 200Å, the function as the heat resistant protective layer is not fulfilled, and when the thickness is more than 5000Å, the sensitivity is lowered and the interfacial peeling is likely to occur. or,
If necessary, the protective layer can be multi-layered.

On the other hand, the reflection heat dissipation layer is formed by a vacuum evaporation method or a sputtering method, and its film thickness depends on the heat capacity and the refractive index of the heat dissipation layer material, but is 300 to 2000 Å, preferably 50 to 10 Å.
It is good to set it to 00Å. The recording material is AgInTe ₂ which has a chalcopyrite type structure that we have discovered and is Sb.
Was used. The film is preferably formed by sputtering. The film thickness at this time is preferably 100 to 2000Å, more preferably 200 to 1000Å.

As the electromagnetic waves used for recording, reproducing and erasing, several kinds such as laser light, electron beam, X-ray, ultraviolet ray, visible ray, infrared ray, microwave can be adopted, but when they are mounted on the drive, they are small. The beam of a compact and compact semiconductor laser is optimal.

[0014]

EXAMPLES The present invention will be specifically described below with reference to examples. However, this example does not limit the present invention in any way.

Example 1 Pitch of 1.6 μm, depth of 700 Å with groove, thickness of 1.2
mm on a polycarbonate substrate with a diameter of 86 mm and rf
A heat-resistant protective layer, a recording layer, a heat-resistant protective layer, and a reflective layer were sequentially laminated by a sputtering method to produce an optical disc for evaluation. Also, 20m for measuring the thermal conductivity when making the reflective layer
A cover glass measuring m × 20 mm × 1 mm was attached.

The materials and film thicknesses used for each layer are shown in Table 1- (1) below.
Shown in.

The evaluation of the optical disk was performed by passing a semiconductor laser beam of 830 nm through a lens of NA = 0.5 at 1 μm on the medium surface.
It was performed by squeezing a spot diameter of mφ and irradiating from the substrate side.

Although the recording film after film formation was amorphous, at the time of measurement, the entire surface of the disk was first crystallized sufficiently by DC light of 4 to 10 mW on the medium surface to make it an initial (unrecorded) state. did.

The linear velocity of the disk is 5 m / s, 7 m / s,
It was set to 9 m / s, 11 m / s, and 15 m / s. The write condition for recording is 2.6 MHz for each linear velocity,
3.7MHz, 4.8MHz, 5.8MHz, 7.9M
Hz and the laser power (Pw) was changed from 7 to 17 mW.

The reading power (P _R ) was 1.0 mW. Table 1- () shows the laser power (P _W ) and the optimum erase power (P _E ) when the C / N (carrier to noise ratio) value becomes saturated or maximum, and the obtained C / N value and erase ratio. Shown in 1) (2) (3) (4) (5). Also, erasing is DC light.

Since the thermal conductivity of the reflective layer is very difficult to measure when the film thickness is thin, the electrical conductivity of the film was measured by the four-terminal method and calculated from the Wiedemann-Franz law. This is because it was determined that the Wiedemann-Franz rule holds because the reflective layer is made of a metallic material.

[0022]

[Table 1]

[0023]

[Table 2]

[0024]

[Table 3]

[0025]

[Table 4]

[0026]

[Table 5]

As is clear from Tables 1- (1) to (5) above, the Ag-Ni alloy has a composition ratio adjusted to control the thermal conductivity so that the disk characteristics are not deteriorated. It is possible to provide a reflection heat dissipation layer corresponding to the linear velocity. It was also confirmed that the recording medium using the present reflective heat dissipation layer has a durability of 10 ⁴ times or more even in the repeating characteristics in the overwrite mode. Also, no tendency of oxidation was observed even after 500 hours at 80 ° C. and 85% atmosphere.

Example 2 An optical disk for evaluation was produced under the same conditions as in Example 1 except that the material of the reflection / heat dissipation layer was changed to Ag-Mn alloy, and the test was conducted under the same conditions.

The results are shown in Tables 2- (1) (2) (3) (4) (5) below.

[0030]

[Table 6]

[0031]

[Table 7]

[0032]

[Table 8]

[0033]

[Table 9]

[0034]

[Table 10]

As is clear from Tables 2- (1) to (5) above, the Ag-Mn alloy has the same disk characteristics as the Ag-Ni alloy by controlling its thermal conductivity by adjusting its composition ratio. It is possible to provide a reflective heat dissipation layer corresponding to the linear velocity of the disk without decreasing the temperature. It was also confirmed that the recording medium using the present reflective heat dissipation layer has a durability of 10 ⁴ times or more even in the repeating characteristics in the overwrite mode. Also, no tendency of oxidation was observed even after 500 hours at 80 ° C. and 85% atmosphere.

Example 3 An optical disc for evaluation was prepared under the same conditions as in Example 1 except that the material of the reflection / heat dissipation layer was changed to Ag—Ti alloy, and the test was conducted under the same conditions.

The results are shown in Tables 3- (1) (2) (3) (4) (5) below.

[0038]

[Table 11]

[0039]

[Table 12]

[0040]

[Table 13]

[0041]

[Table 14]

[0042]

[Table 15]

As is apparent from Tables 3- (1) to (5) above, Ag-Ti alloys are the Ag-Ni alloys and Ag-Ni alloys described above.
As in the case of the Mn alloy, by adjusting the composition ratio thereof to control the thermal conductivity, it is possible to provide a reflection heat dissipation layer corresponding to the linear velocity of the disk without deteriorating the disk characteristics. It was also confirmed that the recording medium using the present reflective heat dissipation layer has a durability of 10 ⁴ times or more even in the repeating characteristics in the overwrite mode. Also, 80 ℃, 85% atmosphere
Even after 500 hours, no tendency of oxidation was observed.

[0044]

As described above, the optical recording medium of the present invention has an Ag-Ni alloy, an Ag-Mn alloy and an Ag-Ti.
It is possible to provide a highly sensitive recording medium corresponding to the linear velocity of the disk by providing the reflection / heat dissipation layer made of any of alloys.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a configuration example of an optical recording medium of the present invention.

[Explanation of symbols]

 1 Substrate 2 and 4 Heat-resistant protective layer 3 Recording layer 5 Reflective heat dissipation layer 6 Protective layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroko Iwasaki 1-3-6 Nakamagome, Ota-ku, Tokyo Inside Riko Co., Ltd.

Claims (4)

[Claims] 1. A recording layer, a heat-resistant protective layer, and a reflection / radiation layer are provided on a substrate, and when the recording layer is irradiated with electromagnetic waves, the optical constants of the recording material change to record, reproduce, and erase optical information. In the phase change type optical recording medium capable of achieving the above, the reflection and heat dissipation layer has Ag-Ni alloy, Ag-Mn alloy and Ag.
An optical recording medium characterized by comprising any one of Ti alloys. 2. The optical recording medium according to claim 1, wherein the reflection heat dissipation layer made of an Ag—Ni alloy has a thermal conductivity of 9.0 × 10 ^{2 to} 3.2 W / cm · deg. 3. The optical recording medium according to claim 1, wherein the reflective heat dissipation layer made of an Ag—Mn alloy has a thermal conductivity of 4.0 × 10 ^{2 to} 3.2 W / cm · deg. 4. The optical recording medium according to claim 1, wherein the reflective heat dissipation layer made of an Ag—Ti alloy has a thermal conductivity of 7.0 × 10 ^{2 to} 3.2 W / cm · deg.