JPH0383237A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a medium which has a long life of recorded data even when stored in a bad environment by constituting a cooling layer of aluminum with aluminum oxide dispersed therein. CONSTITUTION:On a disk substrate 1, there are successively laminated a ZnS protective layer 2, Ge2Sb2Te3 medium layer 3, and ZnS protective layer 4. Further a cooling layer 6 comprising Al with Al2O3 dispersed is formed by sputtering an Al target in Ar gas with trace amt. of oxygen added. Then a surface protective layer 5 comprising UV-curing resin is applied thereon. The cooling layer has stability against a bad environment and thus, the obtd. medium has a long life of recorded data and high reliability.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides a medium layer on the side opposite to the substrate in which information is recorded and erased by a reversible optical change caused by light incident through a transparent substrate. The present invention relates to an optical recording medium equipped with a cooling layer that also serves to reflect light that has passed through the medium.

[Conventional technology]

In recent years, there has been an increasing demand for higher density and larger capacity information storage, and research and development has been actively conducted both domestically and internationally.
In particular, optical recording media that use a laser as a light source have a recording density approximately 10 to 100 times that of conventional magnetic recording media, and can record information without contact between the recording/reproducing head and the recording medium.

Because it can be played back, there is little damage to the recording medium, and it has a long lifespan. For this reason, high-density technology is a means of recording and reproducing huge amounts of information.

Optical recording media, which are large-capacity recording systems, are promising.

This optical recording medium can be roughly classified into three types depending on the purpose: read-only type, write-once type, and rewritable type.

The read-only type is a read-only recording medium from which information can only be read, and the write-once type allows information to be recorded and reproduced as needed, but the recorded information cannot be erased. On the other hand, the rewritable type is capable of recording and reproducing information, as well as erasing and rewriting already recorded information, and is desired and has the highest expectations for use as a data file for computers.

There are two types of rewritable optical recording media: magneto-optical and phase change. Among these methods, the phase change method generally focuses a laser beam on the recording surface of a recording medium and heats it, and controls the pulse output and pulse width of the laser beam to change the phase of the recording material, that is, between a crystalline state and a non-crystalline state. It causes transition or phase transition between crystalline states and records and erases information based on the difference in reflectance in each state.

FIG. 2 shows an example of the structure of a phase change type optical recording medium.

Usually, a protective layer 2 made of ceramic such as ZnS is formed on one surface of a substrate 1 made of, for example, polycarbonate, on which many tracking grooves 11 are provided, and a recording layer made of, for example, GeTe compound + InTe compound is formed on the protective layer 2. It has a structure in which a layer of a medium material, that is, a medium layer 3 is provided, and a protective layer 4 made of ceramic or the like and a surface protective layer 5 made of an organic substance are sequentially laminated thereon. To actually write information, first, the medium is sufficiently crystallized and initialized by irradiation with light from a flash lamp, etc. The medium is irradiated with zero-order high-power, short-pulse laser light to rapidly cool the medium to its melting diameter. .

As a result, the medium transforms from crystalline to amorphous and records information. In the case of erasing information, in order to make an amorphous medium crystalline, the medium is heated to a crystallization temperature and annealed using a relatively low output laser beam. The irradiation time at this time is determined by the crystallization rate of the medium.

In order to increase the cooling rate of the medium from the molten state when recording the above information, as shown in Fig.
JP-A-63-214938 discloses that a cooling layer 6 is provided between the Ii layer 5 and the protective layer 4 made of ceramic or the like. At this time, the protective layer 4 acts as a heat insulating layer. In order to ensure the characteristics of the medium, it is important to set the thickness of this heat insulating layer to an optimum value, as described in the above publication.

In addition to the cooling effect, the cooling layer 6 also has a cooling effect on the medium layer 3 through the substrate 1.
It also functions as a reflective layer for light that is incident on the medium layer and transmitted through the medium layer. Regarding its effect, please refer to the magazine “IEEE, J
, Quant, [! ! ect,” Q E 14S
7 (1987), page 487 Alan, E.
As mentioned by Beil et al. The material for the cooling layer 6, which also serves as a reflective layer, is generally aluminum, which is widely used in music compact discs. Aluminum is a cheap material and can be efficiently formed into a bottom film by sputtering, and that film is used for recording media.

It has the characteristic of reflecting a large amount of incident light at the oscillation wavelength of the semiconductor laser used for erasing.

[The invention tries to solve II! In actual use, such optical recording media are often used in environments with high temperatures and high humidity, and in environments where moisture in the air condenses due to rapid temperature changes. According to our experiments, 6
At 0°C and 90% relative humidity, it was observed that aluminum corroded in 250 hours, and when a disc was made using this aluminum and the signal was played back, it was found that the error rate increased. . Also, 80
When the disc was left at a relative humidity of 85% and then brought into a room at 25°C, condensation due to condensation of water was observed inside the disc. It has been observed that such condensation occurs between the organic surface protection layer and the metal cooling layer, and this condensation causes corrosion of the metal cooling layer, which also causes an increase in the signal error rate. Oops.

In order for information written on a recording medium to be stable for 10 years or more at 50°C, for example, a lifetime of 300 to 1000 hours at 100°C is required. The current mainstream recording method is a bit position recording method that determines the presence or absence of pits, but a bit edge recording method that makes the edges of pits correspond to recording points is promising in the future.

This bit edge recording method is expected to be more sensitive to corrosion than the bit position recording method. In order to prevent such corrosion, noble metals such as gold are sometimes used for cooling layers, but such noble metal cooling layers are generally expensive and require thin film formation methods in vacuum such as sputtering. The efficiency of material usage is very low.

The purpose of the present invention is to solve the above-mentioned problems, and to improve the storage life of recorded information without using a noble metal cooling layer, even in a high temperature and high humidity atmosphere, or in a state where dew condensation occurs due to sudden temperature changes. The objective is to provide a long optical recording medium.

(Means for Solving Problem 11B) In order to achieve the above object, the present invention provides a method for recording and erasing information on the opposite substrate side of a medium layer by reversible optical changes caused by light incident through a transparent substrate. In an optical recording medium, the cooling layer is made of a material in which aluminum oxide is dispersed in aluminum.

[Effect]

Materials in which A7, O, are dispersed in M are described, for example, in the book "Physics and Chemistry Dictionary 4th Edition J (1987) 73" published by Iwanami Shoten.
As described on page 8, it is known as SAP and is stable against high temperatures, high temperatures, and moisture for long periods of time, so optical recording media that use this material for the cooling layer cannot be stored in places with poor environmental conditions. However, the signal error rate does not increase, and SAP is not significantly inferior to M in light reflectance.

〔Example〕

As an example of the present invention, an optical recording medium having the structure shown in FIG. 1 was produced. That is, 12On+ of protective N2 made of ZnS is placed on a polycarbonate disk substrate 1.
The medium N3 made of GezSt+gTes is coated with a thickness of 60n+*, and the protective layer 4 made of ZnS is coated with a thickness of 1.
The layers were sequentially laminated to a thickness of 70 ns by sputtering. Furthermore, a bottom film of cooled N6 made of SAP with a thickness of 100 i+m was formed thereon by sputtering using M as a target and a gas containing argon gas to which a small amount of oxygen was added. Finally, a surface-preserving IJW5 made of ultraviolet curable resin and having a thickness of approximately Ion was applied by a spin cord method. This optical recording medium has a circumferential speed of 8■/see T
! While rotating, a laser beam with a wavelength of 830 nm and an output of 81 was irradiated. The laser spot diameter on the optical recording medium surface was approximately 1 μ.

The optical recording material film immediately after sputtering was in an amorphous state and had a light reflectance of about 16%, but the light reflectance increased to about 38% by the above laser irradiation. When the same location on the optical recording medium was irradiated with the laser again under the same conditions, the reflectance remained unchanged from 38%.
The reason why the reflectance changed from 38% to 38% is because the optical recording film changed from an amorphous state to a crystalline state.The reason why the reflectance did not change after the second laser irradiation was because the first laser irradiation caused sufficient crystallization. As for erasing information after writing (hereinafter, this operation will be referred to as initialization), it was possible to erase the information at a circumferential speed of 8Il/SeC, as described above. That is, after the above optical recording medium is sufficiently crystallized, the laser output is 15 mW and the frequency is 3.7 MHz.
When writing a pulse input of
When erased under the condition of mW continuous light, the CN ratio decreased to 13 dB, and it was almost completely erased.

As a comparative example, an optical recording medium was produced which was the same as the optical recording medium of the above-mentioned example, but in which only the cooling layer 6 was formed as a bottom film by vacuum evaporation of aluminum. When this optical recording medium was also written with a pulse input having a frequency of 3.7 MH2 using a laser output of 151 after initialization, a CN ratio of 48 dB was obtained as a reproduction output of the optical recording medium.

The optical recording media of Examples and Comparative Examples were heated at 60°C and at a relative humidity of 8.
Stored in a 0% environment for 2 days and nights, with a relative humidity of 3 at 25°C.
When the disc was left in a 0% environment, a slight amount of dew condensation was observed inside the disc. The block error rate of the signal at this point was in the 10-2 range. However, after 30 days, the block error rate of the signal was on the order of 10-1 in the example, but it deteriorated to on the order of 10-1 in the comparative example.

Note that the present invention is not limited to the above-mentioned embodiments, and can also be implemented in optical recording media in which each layer other than the cooling layer is made of other materials.

〔Effect of the invention〕

According to the present invention, high reliability is achieved by using U-U Z03 cermet, which can be formed into a film by sputtering and is stable even in harsh environments, as the material for the cooling layer that also serves as a reflective layer for light transmitted through the medium layer. It was possible to obtain an optical recording medium with high stability and storage life of recorded information.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of an optical recording medium in which the present invention is implemented, and FIG. 2 is a sectional view of an optical recording medium having another structure. 1: Transparent substrate, 2: Protective layer, medium layer, 4: Protective layer, two-surface protective layer, cooling layer. Figure 1 2v! J

Claims (1)

[Claims] 1) A cooling layer that also serves to reflect the light that has passed through the medium layer on the opposite side of the medium layer that records and erases information through reversible optical changes caused by light that enters through the transparent substrate. An optical recording medium characterized in that the cooling layer is made of a material in which aluminum oxide is dispersed in aluminum.