JPH04286732A - Optical disk - Google Patents

Abstract

PURPOSE:To improve recording characteristics by specifying the refractive index in the amorphous state of recording layers at the wavelength of the laser beam to be used within a 2<=n<=3 range and the attenuation coefft. k within a 1.0<=k<=1.7 range. CONSTITUTION:The recording layers 2a, 2b and protective layers 3a, 3b are formed on substrates 1a, 1b and the substrates are stuck to each other by an adhesive 4 in such a manner that the layers 2a, 2b are positioned on the inner side with each other. The recording layers 2a, 2b are formed of TeOPd, etc. The refractive indext at the wavelength of the laser beam to be used in the amorphous state of the layers 2a, 2b is set within the 2<=n<=3 range and the attenuation coefft. k within the 1.0<=k<=1.7 range.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical disc on which information can be recorded and reproduced using a laser beam.

0002

2. Description of the Related Art In recent years, so-called optical disks have been rapidly put into practical use as new high-density, large-capacity information recording media. Optical disks are steadily becoming popular in various fields, with combinations of various usage formats such as write-once type and rewritable type, and various recording methods such as perforated type and phase change type.

One of the various types of optical discs is a phase change type optical disc. That is, it is known that once a metal is heated and then rapidly cooled, it becomes an amorphous state, and when it is slowly cooled, it becomes a crystalline state. In some alloys, this phenomenon can occur at relatively low temperatures, and furthermore, the optical properties of the surface change between the amorphous and crystalline states, making it difficult to reconcile this phenomenon. It can be used as a variable optical storage medium. Note that both writing and reading of information is performed non-contact using laser light.

The phase change type optical disk as described above is considered to be more advantageous than other systems, especially in terms of recording density, and is highly expected to be put into practical use in the future.

[0005]

[Problems to be Solved by the Invention] However, in general, phase change optical discs that do not use a reflective film structure have a high transmittance of the optical disc itself, so the reflectance and recording characteristics are affected by the protective layer and adhesive layer. Therefore, there is a problem that the recording characteristics are unstable.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to solve the problems of the prior art described above and provide a phase change optical disk having a novel structure with stable recording characteristics at a high level.

[0007]

[Means for Solving the Problems] That is, according to the present invention,
In an optical disc configured by laminating a pair of substrates including a substrate loaded with a recording layer that records information by phase change so that the recording layer is on the inside, the recording layer is
For the wavelength of the laser beam used in the amorphous state, 2≦n≦
has a refractive index n that satisfies the range of 3, and 1.0≦
An optical disc characterized by having an extinction coefficient k satisfying the range k≦1.7 is provided.

[0008]

[Function] In the phase change optical disk according to the present invention, the refractive index of the recording layer in the amorphous state at the wavelength of the laser beam used is 2.
≦n≦3, and the extinction coefficient k is 1.0≦k≦
It is characterized by being within the range of 1.7.

That is, in a phase change type optical disk, the refractive index n of the amorphous state of the recording layer at the used laser wavelength is 2.
If it is lower than , the reflectance of the unrecorded area is too low.
When reading recorded information, a sufficient amount of reflected light cannot be obtained in this area, and servo defects such as tracking errors are likely to occur. On the other hand, when the refractive index n is higher than 3, the reflectance of the unrecorded area becomes too high. For this reason, in order to record information, there are areas where the recording layer is crystallized and has a high reflectance.
A problem arises in that a sufficient reflectance difference with the unrecorded area cannot be ensured, and the reproduced signal amplitude obtained when reading recorded information becomes small.

[0010] Furthermore, in the optical disc, if the extinction coefficient k of the recording layer is lower than 1.0, physical deformation of the recording layer occurs during writing with a laser beam of high optical power, resulting in Noise level rises and C/N
ratio decreases. Therefore, the power margin becomes narrow, which is not preferable. On the other hand, when the extinction coefficient k is larger than 1.7, the crystallization temperature of the recording layer becomes low, so that the recording sensitivity becomes too high and the thermal stability of the recording layer deteriorates. Furthermore, since the change in reflectance after writing becomes smaller, the C/N ratio becomes lower. Note that the extinction coefficient k here refers to the complex refractive index n−ki
It means the imaginary part when expressed as .

For the above reasons, the optical disc according to the present invention is superior to conventional phase change optical discs in terms of maximum C/N ratio, power margin of C/N ratio, recording sensitivity, and thermal stability. It has superior properties compared to

[0012] Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing a typical configuration example of an optical disc according to the present invention.

As shown in the figure, this optical disc includes a pair of substrates 1a each loaded with a recording layer 2a, 2b.
, 1b are bonded together using an adhesive 4 so that the recording layers 2a and 2b are on the inside of each other. Furthermore, protective layers 3a and 3b are formed on each recording layer 2a and 2b.

In the optical disk constructed as described above, the substrates 1a and 1b are made of a transparent plastic material such as polycarbonate resin, polymethyl methacrylate resin, epoxy resin, or amorphous polyolefin resin, or glass. can do.

Further, the recording layers 2a and 2b can be formed of TeOPd or the like. Here, C/N of the recording layer
From the viewpoint of maintaining high ratio and recording sensitivity, the content of Pd in the recording layer is preferably within the range of 5 to 50 atomic %. In addition to the above characteristics, from the viewpoint of obtaining a good power margin, the thickness of the recording layer is 100 nm.
It is preferable that it is more than m.

Furthermore, the protective layers 3a and 3b are provided for the purpose of improving the weather resistance of the recording layer, and can be formed from a photocurable resin. In addition, the protective layers 3a and 3b
can be formed by a spin coating method or the like.

Furthermore, the pair of substrates 1a, 1b on which the protective layers 3a, 3b and the recording layers 2a, 2b formed of the above-mentioned materials are mounted can be bonded by hot melt adhesive, especially from the viewpoint of material cost and manufacturing cost. It is preferable to use adhesive or epoxy adhesive.

[Preparation Example 1] A recording layer with a thickness of 150 nm was formed on a spirally grooved polycarbonate substrate with a diameter of 130 mm by reactive RF sputtering using a TePd alloy target. The sputtering gas was a mixed gas of 4.5 SSCM of oxygen gas and 75 SCCM of Ar gas. The recording layer formed by such a method exhibits characteristics such as a refractive index n of 2.5 and an extinction coefficient k of 1.3 with respect to a laser beam having a wavelength of 830 nm.

[0020] Subsequently, an ultraviolet curable resin was coated by spin coating, and then ultraviolet rays were irradiated to cure the resin, thereby forming a protective layer on the recording layer. Finally, two substrates loaded with the recording layers were pasted together so that each recording layer was on the inside of the substrate to produce an optical disk. Hot melt adhesive was used to attach the substrates.

[0021] In the optical disc manufactured as described above, a wavelength of 830n was detected at a position 60 mm from the center of the optical disc.
Using m semiconductor laser, frequency 2.58MHz
, a repetitive signal with a duty ratio of 33% was written. The output of the laser beam was varied under the condition of 1200 rpm, and the maximum value of the C/N ratio and the maximum value of the signal amplitude when read with a laser beam with an output of 1.2 mW were measured. Further, the upper limit Pup and lower limit Pdown of the writing light power at which the C/N ratio becomes 90% or more of its maximum value were measured, and the difference (Pup-Pdown) was recorded as a power margin. The measurement results are shown in Table 1 together with the measurement results of other production examples and comparative examples.

[Preparation Example 2] The sputtering gas during recording layer deposition was 3.5SCC.
A recording layer with a thickness of 150 nm was formed on the substrate using the same materials and manufacturing conditions as in Manufacturing Example 1, except that a mixed gas of M oxygen gas and 75 SCCM Ar gas was used. The obtained TePdO recording layer had an amorphous refractive index n of 2.7 and an extinction coefficient k of 1.5 with respect to a laser beam having a wavelength of 830 nm. Subsequently, after forming a protective layer in the same manner as in Production Example 1, the substrates were bonded together using a hot melt adhesive to produce an optical disc as a sample.

Regarding this optical disc, the maximum value of the C/N ratio, the maximum value of the signal amplitude, and the power margin were measured under the same conditions as in Manufacturing Example 1. The measurement results are shown in Table 1 together with the measurement results of other production examples and comparative examples.

[Comparative Example 1] Sputtering gas during recording layer deposition was 5.0 SCCM of oxygen gas and 75 SCCM.
Preparation Example 1 except that the gas was mixed with Ar gas.
A recording layer with a thickness of 150 nm was formed on the substrate using the same materials and production conditions as in Production Example 2. The obtained TePdO
The recording layer is resistant to laser light with a wavelength of 830 nm.
The refractive index n in the amorphous state is 2.5, and the extinction coefficient k is 0.9.
Met. Subsequently, after forming a protective layer in the same manner as in Production Example 1, the substrates were bonded together using a hot melt adhesive to produce an optical disc as a sample.

Regarding this optical disk, the maximum value of the C/N ratio, the maximum value of the signal amplitude, and the power margin were measured under the same conditions as in Manufacturing Examples 1 and 2, respectively. The measurement results are shown in Table 1 together with the measurement results of other production examples and comparative examples.

[Comparative Example 2] The sputtering gas during recording layer deposition was 7.0SCCM oxygen gas and 75SCCM.
Comparative Example 1 except that the gas was mixed with Ar gas.
150 nm thick on the substrate using the same materials and manufacturing conditions as
A recording layer was formed. The obtained TePdO recording layer had a refractive index n of 2.5 in an amorphous state and an extinction coefficient k of 1.9 with respect to a laser beam having a wavelength of 830 nm. Subsequently, after forming a protective layer in the same manner as in Production Example 1, the substrates were bonded together using a hot melt adhesive to produce an optical disc as a sample.

Regarding this optical disc, the maximum value of the C/N ratio, the maximum value of the signal amplitude, and the power margin were measured under the same conditions as in Comparative Example 1. The measurement results are shown in Table 1 together with the measurement results of other production examples and comparative examples.

[0028]

[Table 1]

[0029]

As explained above, the phase change optical disc according to the present invention has significantly improved recording characteristics by optimizing the characteristics of its recording layer.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view showing a configuration example of an optical disc to which the present invention is applicable.

[Explanation of symbols]

1a, 1b board, 2a, 2b recording layer, 3a, 3b Protective layer, 4 Adhesive material

Claims (4)

[Claims] 1. An optical disk constructed by laminating a pair of substrates including a substrate loaded with a recording layer that records information by phase change so that the recording layer is on the inside,
The recording layer has a refractive index n that satisfies the range of 2≦n≦3 with respect to the wavelength of the laser beam used in an amorphous state, and has a refractive index n that satisfies the range of 1.0≦k≦1.7. Extinction coefficient k that satisfies
An optical disc characterized by having. 2. The optical disc according to claim 1, wherein the recording layer is formed of a Te--Pd composite oxide. 3. The optical disc according to claim 2, wherein the recording layer contains 5 to 50 atomic % of Pd. 4. The optical disc according to claim 1, wherein the thickness of the recording layer is
An optical disc characterized by having a wavelength of 100 nm or more.