JPS63152035A - Optical disk - Google Patents

Abstract

PURPOSE:To improve sensitivity and to reduce a noise level by removing a recording medium interposing between the gaps of guiding grooves each other with etching. CONSTITUTION:In an optical disk which executes the recording and deleting of information on the recording medium 3 on the guiding groove 2 provided on a disk substrate 1 by utilizing the difference of reflection factor caused by the difference of the crystallization of the recording medium 3, the recording medium 3 interposing between the mutual gaps of the guiding grooves 2 is removed with etching so as to be used. Namely, the recording medium 3 formed on the disk substrate 1 is selectively etched in order to form the recording medium 3 only on the part of the guiding groove 2. Thus the reduction of the noise and high sensitivity can be realized.

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] As a method for improving the sensitivity of an optical disc and reducing the noise level, an optical disc is provided in which a recording medium interposed between guide grooves, which are information recording positions, is removed.

[Industrial application field]

The present invention relates to an optical disc with reduced noise level.

An optical disk is a memory that records high-density information using laser light, and has excellent features such as a large recording capacity, non-contact recording and playback, and being unaffected by dust.

Here, the optical disk uses a low-melting point metal or alloy as a recording medium, and is a read-only memory (Write 0nce Memory) that records information by the presence or absence of holes.
In addition to
Erasable Memory) has also been put into practical use.

The present invention relates to the latter, particularly to improvements in optical discs that utilize crystal-to-crystal phase change.

[Conventional technology]

The memory that utilizes the phase change between crystals according to the present invention is made of indium antimony (
A memory that uses an alloy thin film such as In-Sb (In-Sb) or indium-bismuth (In-Bi) as a recording medium, and when this recording medium is irradiated with a laser beam, the crystal structure changes depending on the irradiation conditions and there is a difference in reflectance. It is something that takes advantage of what is generated.

The In-5b system will be explained below as an example.

The feature of this system is that in a solid solution consisting of an In-Sb intermetallic compound and sb gold metal, the dispersion state of sb metal atoms differs depending on the conditions of application of thermal energy, and this difference in state makes use of the fact that the reflectance differs. .

For example, for an optical disk whose recording medium is a thin film with an atomic weight ratio of In and sb of 40:60 and a film thickness of 1,000 mm, a semiconductor laser (wavelength of 830 nm) is used, and an output of 10:60 is used.
mW.

When irradiated with a pulse width of 200 ns, the reflectance of the recording medium was about 30%, but the reflectance of the irradiated area increases to about 40%.

On the other hand, this irradiated part has an output of 5 m and a pulse width of 800 nS.
When irradiated with a laser beam of , the reflectance of the irradiated area is approximately 3
Returns to the value before irradiation of 0%.

However, when a laser beam with an output of 2 mW is irradiated, the reflectance of the irradiated area does not change.

That is, a recording medium made of an In--Sb alloy thin film has an energy level that causes a change in crystalline state, and the reflectance above and below this level is different, and can be changed depending on the energy application conditions.

Here, the reason for the difference in reflectance is the In-Sb compound (I
ns. SbS. ) and sb in the solid solution state.

That is, according to X-ray diffraction, Ins in the low reflectance part (30% part). sb,. The diffraction line of sb appears strongly, and the diffraction line of sb is weak.

On the other hand, in the high reflectance part (40% part), the sb diffraction line is Ins. sbs. It appears stronger than.

Here, since the reflectance of a pure sb thin film is about 70%, it can be seen that the amount of sb precipitated is large in the high reflectance portion.

Utilizing this phenomenon, the recording conditions are the laser beam irradiation conditions that can form a high reflectance area, the reproduction conditions are the irradiation conditions where the reflectance does not change even with irradiation, and the erasing conditions are the conditions that can reduce the reflectance. Optical discs have been developed.

Here, the structure of the optical disc is about 1.6 μm thick on an optical disc substrate made of transparent plastic or glass.
A guide groove (pre-group) is provided concentrically or spirally in a pinch, and an In-Sb recording medium is formed as a film on the optical disk substrate, and a laser beam with a diameter of approximately 1 μm is formed along this guide groove. Information is recorded, reproduced, and erased by beam irradiation.

Here, the necessary conditions for a rewritable memory are: (1) Recording and erasing can be performed with as little laser power and time as possible, that is, the recording medium must have good sensitivity.

■ Little change over time, that is, little increase in noise when recording and erasing is repeated.

Examples include.

However, with conventional optical discs, the noise increases to about 5 dB after about 1000 repetitions, and an improvement is needed.

[Problem that the invention seeks to solve]

As mentioned above, in order to maintain high reliability in rewritable optical discs that utilize phase changes between crystals, the recording medium must have good sensitivity, and when recording and erasing is repeated, noise increases little. This is necessary, and the challenge is to realize this.

[Means for solving problems]

The above problem occurs in optical discs that record and erase information on a recording medium on guide grooves provided on a substrate by utilizing the difference in reflectance due to the difference in crystallization of the recording medium. This can be achieved by using an optical disc in which the intervening recording medium is removed by etching.

[Operation] The present invention was developed as a result of research into the cause of noise increase when recording and erasing are repeated.

In other words, information is recorded and erased by scanning a laser beam with a beam diameter of about 1 μm along a guide groove with a width of about 0.7 μm, and repeatedly turning it on and off depending on the information. Since the beam diameter takes the half width of the intensity distribution, the tail of the distribution extends to the part outside the guide groove.

Therefore, information is recorded and erased mainly on the recording medium in the guide groove portion, but the area other than the guide groove, that is, the area between the guide grooves, is also affected by the laser beam irradiation and gradually Crystallization is progressing.

The inventors believe that the crystallization in this peripheral region is C/N (Carri
It was found that there is a close relationship with a decrease in er-1evel/No1se-1evel).

That is, during reproduction, noise increases due to an increase in reflection from the peripheral portion of the guide groove.

Furthermore, recording and erasing of information is performed by locally heating the recording medium at the irradiation position by irradiating the laser beam, but it is necessary to perform this with as little laser power as possible. It is also necessary to limit the formation position of the recording medium to the guide groove to suppress heat dissipation.

In view of this, the present invention selectively etches the recording medium formed on the disk substrate to form the recording medium only in the guide groove portion.

FIG. 1 is a diagram showing the principle of the present invention, which realizes noise reduction and high sensitivity by forming a recording medium 3 only in the guide groove 2 of a disk substrate 1.

〔Example〕

FIGS. 3(A) and 3(B) show an example of the present invention, in which an acrylic ester is formed on a glass substrate to a thickness of 20 μm by spin coding, and then guided by photolithography. Disc substrate 1 with groove 2
was formed.

On top of this, 10 nm of zinc sulfide (ZnS) was deposited by co-evaporation method.
The base layer 4 was formed by vapor deposition to a thickness of .

This ZnS acts as an interference film and has a refractive index of 2.4.
and higher, improving contrast.

Next, 85% of In, □5bsa was applied on this by co-evaporation method.
After forming the recording layer 5 by vapor deposition to a thickness of nm, the output 51
The laser beam 6 of the guide groove 4 is scanned along the guide groove 4.
The portion of the recording layer 5 was crystallized. (A) Next, when plasma etching is performed in an argon (Ar) gas atmosphere, the recording layer 5 in an amorphous state is more fragile than the crystallized recording layer 7 in the guide groove 2 portion. Therefore, the etching speed is high, and therefore, an optical disk is formed with the crystallized recording layer 7 only in the guide groove 2, as shown in FIG. 2(B).

The conventional recording condition for such optical discs is 10 mW.
x 400ns, and the erase condition is 5 mW x 80
However, the optical disc made in this way can record at 10 mW x 200 ns, and can record at 5 m W x 200 ns.
Erasing could be performed under the condition of 400 ns.

Figure 2 shows the C/C ratio when recording and erasing are repeated under these conditions.
These are experimental results showing changes in N. Conventionally, a decrease of about 5 dB was observed after about 104 repetitions, but in the case of the example, no increase in noise was observed until 105 repetitions.

〔Effect of the invention〕

As described above, by implementing the present invention, the sensitivity and rewriting characteristics of the optical disc were improved, and the quality was improved.

[Brief explanation of the drawing]

Figure 1 is a diagram of the principle of the present invention, Figure 2 is a diagram of the relationship between the number of rewrites and C/N, and Figure 3 (A
), (B) are cross-sectional views of steps for carrying out the present invention. In the figure, 1 is a disk substrate, 2 is a guide groove, 3 is a recording medium,
5 is a recording layer, 6 is a laser beam, 7
is a crystallized recording layer.

Claims (1)

[Claims] In an optical disk that records and erases information on a recording medium on guide grooves provided on a disk substrate by utilizing the difference in reflectance due to the difference in crystallization of the recording medium, an optical disc that is located between the guide grooves. An optical disc characterized in that the recording medium is removed by etching.