JPH04349242A - Optical recording medium - Google Patents

Abstract

PURPOSE:To provide the optical recording medium which is improved in recording and erasing sensitivity and is improved in C/N and erasing ratio. CONSTITUTION:The phase transition type optical recording medium which allows recording, reproducing and erasing of information has further heat resistant protective layers 2 and 4 and a reflection heat radiating layer 5 on the outside of the recording layer 3. Particularly this reflection heat radiating layer consists of any among Al-Ti alloy, Al-Mn alloy, Cu-Ni alloy, and Cu-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 optical recording medium, and is applicable to optical memories.

0002

2. Description of the Related Art When a phase change optical recording medium is irradiated with light, the irradiated portion of the recording layer that absorbs the light is converted into heat, the temperature there rises, and the recording layer melts. When it is rapidly cooled by heat conduction, it becomes amorphous and recording is performed.

Next, when the recorded area is irradiated with a lower intensity of light, the recorded area becomes amorphous and crystallizes, thereby erasing the recording.

In this case, a method has been proposed in which a reflective layer is provided to efficiently absorb incident light into the recording layer in order to save the energy necessary for recording and erasing information in the recording layer. For example, a metal film such as Au, Al, Ag, or Rh is used as the reflective layer, and a chalcogen compound is used as the recording layer (see Japanese Patent Publication No. 61-18262 and Japanese Patent Application Laid-open No. 57-11189).

However, since metals such as Al, Ag, Au, and Cu have high thermal conductivity, it is difficult to heat the recording layer to a sufficiently high temperature with low energy. As a result, recording sensitivity will decrease. On the other hand, a method has also been proposed to achieve high sensitivity by reducing the thermal conductivity of the reflective layer (see JP-A-63-58639).
If a metal with low thermal conductivity, such as Ti or Mn, is used as the reflective layer, the cooling effect of the recording layer will not be sufficient, so there is a problem that it will be difficult to amorphize the recording layer.

[0006]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an optical recording medium that does not reduce recording sensitivity and can perform recording and erasing reliably.

[0007]

[Means for Solving the Problems] The structure of the present invention for solving the above problems is an optical recording medium as described in the claims.

That is, the present invention provides a phase change optical recording medium comprising a substrate, a recording layer provided thereon, a heat-resistant protective layer, and a reflective heat dissipation layer, and the reflective heat dissipation layer is made of an Al-Ti alloy. or Al-Mn alloy, and its thermal conductivity is 9.0 x 10- in the case of Al-Ti alloy.
It is characterized by being between 3 and 1.4 w/cm·deg, and in the case of an Al-Mn alloy, between 7.3×10 −3 and 1.4 w/cm·deg.

[0009] In a phase change optical recording medium, a recording layer absorbs light when irradiated with light and generates heat, thereby performing a crystal-amorphous phase transition and utilizing changes in optical constants between the two phases. Therefore, it is important to know how to record and erase information using low-energy light irradiation (higher sensitivity).

For this purpose, it is important to have a means for effectively absorbing the light irradiated onto the recording layer. One method is to reduce the thickness of the recording layer to reduce its heat capacity, thereby reducing the light energy required to record and erase information, and at the same time providing a reflective heat dissipation layer to reflect the light that has passed through the recording area. The idea is to use the irradiated light energy as effectively as possible. Furthermore, since metal is generally used for the reflective layer, it has a relatively high thermal conductivity and can be expected to have a rapid cooling effect, which is very effective in making the recording layer amorphous when information is recorded.

However, as already explained, when a metal with high thermal conductivity is used for the reflective layer, the recording sensitivity decreases because heat is dissipated before the recording layer irradiated with light reaches a predetermined temperature. . On the other hand, if a metal with low thermal conductivity is used, it becomes difficult for heat to dissipate, making the rapid cooling effect insufficient, making it difficult to make the recording layer amorphous, and at the same time reducing the reflectance, making it less effective as a reflective layer. It will disappear.

In order to solve 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 the reflectance can be prevented and at the same time the thermal conductivity can be increased. The temperature must be the value necessary for recording and erasing information, that is, the value that quickly raises the temperature to the melting point of the material forming the recording layer, and then produces the rapid cooling effect necessary to make it amorphous. This makes it possible to increase the sensitivity of recording media.

Furthermore, by adjusting the alloy composition, it becomes possible to adapt the linear velocity of the disk, which is a recording medium, from a low speed to a high speed range. That is, Al-Ti alloy, Al-
When using a Mn alloy, Cu--Ni alloy, or Cu--Ti alloy, the thermal conductivity changes depending on the composition, and the reflectance also changes at the same time.

For example, in the case of an Al-Ti alloy, high sensitivity corresponding to the linear velocity of the disk can be achieved by adjusting its thermal conductivity between 9.0×10 −3 and 1.4 w/cm·deg. If this can be achieved and the thermal conductivity is within this range, the reflectance will also be a value of 65 to 85%, and the function as a reflective layer will be sufficient.

In the case of Al-Mn alloy, by setting its thermal conductivity to 7.3 x 10-3 to 1.4 w/cm・deg, the reflectance becomes 60 to 85%, and the reflective heat dissipation layer It works well as a.

[0016] Cu-Ni alloy also has a wide range of thermal conductivity depending on its composition ratio, for example, from 3 x 10-2 to 1.0 w/cm・d.
eg, and can realize high sensitivity corresponding to the linear velocity of the disk.

[0017] The thermal conductivity of the Cu-Ti alloy can also be varied between 9.0 x 10-3 and 1.0 w/deg cm depending on its composition ratio, and it also has a high thermal conductivity that corresponds to the linear velocity of the disk. Sensitization can be realized.

FIG. 1 shows the structure of the recording medium of the present invention. The substrate used in the present invention is usually made of glass, ceramics, or resin, and resin substrates are preferred in terms of moldability, cost, and the like. Typical examples of resins include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicone resin,
Examples include fluororesins, ABS resins, urethane resins, etc., but polycarbonate resins and acrylic resins are preferable in terms of processability, optical properties, etc. Further, the shape of the substrate may be a disk, a card, or a sheet.

[0019] As the material of the heat-resistant protective layer, SiO, S
iO2, ZnO, SnO2, Al2O3, TiO2, I
Metal oxides such as n2O3, MgO, ZrO2, Si3N
4. Nitride such as AlN, TiN, BN, ZrN, Zn
S, In2S3, sulfides such as TaS4, SiC, TaC
, B4C, WC, TiC, ZrC, diamond-like carbon, or a mixture thereof. Further, it may contain impurities as necessary. Such a heat-resistant protective layer can be formed by various vapor phase growth methods, such as vacuum evaporation, sputtering, plasma CVD, photo-CVD,
It can be formed by an ion plating method, an electron beam evaporation method, or the like.

[0020] The thickness of the heat-resistant protective layer is 200 to 50
00 Å, preferably 500 to 3000 Å. If it becomes thinner than 200 Å, it will not function as a heat-resistant protective layer, and if it becomes thicker than 5000 Å, sensitivity will decrease or interfacial peeling will easily occur. or,
The protective layer can also be multilayered if necessary.

The recording material used was a system in which Sb was added to AgInTe2, which had a chalcopyrite structure that we had discovered. The film is preferably formed by sputtering. The thickness of the recording layer is 100 to 2000 Å, preferably 50 Å.
The thickness is preferably 0 to 1500 Å.

The reflective heat dissipation layer is formed by vacuum evaporation or sputtering, and its film thickness is 300 to 2000 Å, preferably 500 to 100 Å, depending on the heat capacity, refractive index, etc. of the heat dissipation layer material.
It is preferable to set it to 0 Å.

Several types of electromagnetic waves can be used for recording, reproducing, and erasing, such as laser light, electron beams, X-rays, ultraviolet rays, visible light, infrared rays, and microwaves. Therefore, a compact semiconductor laser is optimal.

[0024]

[Examples] The present invention will be specifically explained below with reference to Examples. However, this example does not limit the present invention in any way.

Example I Grooves with a pitch of 1.6 μm and a depth of 700 Å, thickness of 1.2
RF on a polycarbonate substrate with a diameter of 86 mmφ
A heat-resistant protective layer, a recording layer, a heat-resistant protective layer, and a reflective layer were sequentially laminated by sputtering to produce an optical disc for evaluation. Also, when preparing the reflective layer, a 20 mm
A cover glass measuring 20 mm x 1 mm was attached.

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

[0027] For evaluation of optical discs, a semiconductor laser beam of 830 nm is passed through a lens of NA=0.5 at 1 on the medium surface.
This was done by reducing the spot diameter to μmφ and irradiating it from the substrate side.

Although the recording film after film formation was amorphous, in the measurement, the entire surface of the disk was first sufficiently crystallized with 10 mW of DC light on the medium surface to bring it into an initial (unrecorded) state.

The linear velocity of the disk is 5 m/s, 7 m/s,
The speeds were 9 m/s and 11 m/s. The conditions for writing records are:
For each linear velocity, the frequency is 2.6 MHz (linear velocity 5
m/sec), 3.7 MHz (linear velocity 7 m/sec), 4
．． 8 MHz (linear velocity 9 m/sec), 5.8 MHz (linear velocity 11 m/sec), and the laser power (Pw) was 7~
The power was varied up to 14 mW.

[0030] The read power (PR) was 1.0 mW. Tables I-1 and 2 show the laser power (PW) and optimal erasure power (PE) when the C/N (carrier-to-noise ratio) value is saturated or maximum, as well as the obtained C/N value and erasure ratio. , 3 and 4.

[0031] Furthermore, it is difficult to measure the thermal conductivity of the reflective layer if the film is thin. The electrical resistivity was measured and calculated using the Wiedemann-Franz law. This is because it was thought that the Wildman-Franz equation would hold since the reflective layer was made of a metal material.

[0032]

[Table 1]

[0033]

[Table 2]

[0034]

[Table 3]

[0035]

[Table 4] As can be seen from Table I-1, Table I-2, Table I-3, and Table I-4, Al-Ti alloys can be used for disks by adjusting the composition ratio and controlling the thermal conductivity. It becomes possible to provide a reflective heat dissipating layer that corresponds to the linear velocity of the disk without deteriorating its characteristics.

[0036]Also, if the composition ratio of the Al-Ti alloy is adjusted to control the thermal conductivity to ~1.2 x 10-1 or less even when the linear velocity is 11 m/sec or more, the disk characteristics can be fully satisfied. It goes without saying that you should.

Example II Al-Mn was used instead of Al-Ti as an alloy for the reflective heat dissipation layer.
An optical disc for evaluation was produced under the same conditions as in Example I, except that the following was used, and it was evaluated under the same conditions. The results are shown in Tables II-1 to II-4 below.

[0038]

[Table 5]

[0039]

[Table 6]

[0040]

[Table 7]

[0041]

[Table 8] Above Table II-1, Table II-2, Table II-3, Table II-4
As can be seen from the above, by adjusting the composition ratio of the Al-Mn alloy and controlling the thermal conductivity, it is possible to provide a reflective heat dissipation layer that corresponds to the linear velocity of the disk without deteriorating the disk characteristics. .

[0042] Also, even when the linear velocity is 11 m/sec or more, the thermal conductivity is 7.3 × 10-3 to 1.4 w/cm・d.
It goes without saying that the disc characteristics can be fully satisfied if the control is performed between eg and eg.

Example III: Cu-Ni was used instead of Al-Ti as the alloy for the reflective heat dissipation layer.
An optical disc for evaluation was prepared under the same conditions as in Example I, except that the following was used, and it was evaluated under approximately the same conditions. In other words, the light when initializing the recording medium (unrecorded state) is 4 to 1
The conditions were the same as in Example I, except that 0 mW DC light was used, the energy when writing to the disk was 7 to 17 mW, and the erasing of recording was performed using DC light.

[0044]

[Table 9]

[0045]

[Table 10]

[0046]

[Table 11]

[0047]

[Table 12] As can be seen from Tables III-1 to 4 above, the Cu-Ni alloy can adapt to the linear speed of the disk without deteriorating the disk characteristics by adjusting its composition ratio and adjusting the thermal conductivity. It becomes possible to provide a reflective heat dissipation layer with a high reflectance. Furthermore, it was confirmed that the Cu--Ni reflective heat dissipation layer had a durability of 105 or more in terms of repetition characteristics in the overwrite mode.

Example IV Example I except that the alloy of the reflective heat dissipation layer was changed to Cu-Ti.
An optical disc for evaluation was produced under the same conditions as in II, and evaluated under the same conditions.

[0049]

[Table 13]

[0050]

[Table 14]

[0051]

[Table 15]

[0052]

[Table 16]

[0053]

[Table 17] As can be seen from Tables IV1 to IV5 above, the Cu-Ti alloy allows reflective heat dissipation that corresponds to the linear velocity of the disk without deteriorating the disk characteristics by adjusting the composition ratio and controlling the thermal conductivity. It becomes possible to provide layers. In addition, the repetition characteristics in the overwrite mode also showed that Cu-
It was confirmed that the Ti-based reflective heat dissipation layer had durability of 105 times or more.

[0054]

Effects of the Invention As explained above, the optical recording medium of the present invention can be applied to Al-Ti, Al-Mn alloy, Cu-Ni alloy,
By providing a reflective heat dissipation layer made of any one of Cu--Ti alloys, it is possible to use the disc in accordance with the linear velocity of the disc without deteriorating its characteristics. Furthermore, the corrosion resistance of the recording layer is also good.

[Brief explanation 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 Board 2 and 4 Heat-resistant protective layer 3 Recording layer 5　Reflective heat dissipation layer 6 Protective layer

Claims (5)

[Claims] 1. A phase-change optical recording medium in which the optical constants of a recording material are changed by irradiating a recording layer provided on a substrate with light, and information can be recorded, reproduced, and erased by the change. In addition to the recording layer, this optical recording medium further has a heat-resistant protective layer and a reflective heat dissipation layer, and this reflective heat dissipation layer is made of Al-Ti alloy, Al-Mn alloy, Cu-Ni alloy, etc.
An optical recording medium comprising any one of the group consisting of alloys and Cu-Ti alloys. [Claim 2] The reflective heat dissipation layer has a thermal conductivity of 9.0×10
2. The optical recording medium according to claim 1, wherein the optical recording medium is made of an Al-Ti alloy of -3 to 1.4 w/cm·deg. [Claim 3] The reflective heat dissipation layer has a thermal conductivity of 7.3×10
2. The optical recording medium according to claim 1, wherein the optical recording medium is made of an Al-Mn alloy of -3 to 1.4 w/cm·deg. Claim 4: The reflective heat dissipation layer has a thermal conductivity of 2.0×10
2. The optical recording medium according to claim 1, wherein the optical recording medium is made of a Cu-Ni alloy of −2 to 1.0 w/cm·deg. [Claim 5] The reflective heat dissipation layer has a thermal conductivity of 9.0×10
2. The optical recording medium according to claim 1, wherein the optical recording medium is made of a Cu-Ti alloy of -3 to 1.0 w/cm·deg.