JPH0827973B2 - Optical recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical recording medium, and more particularly to an optical recording medium capable of recording and reproducing information with a laser beam.

[Conventional technology]

The conventional optical recording medium has an excellent feature as a large-capacity recording device because it has a high recording density when recording and reproducing information on the medium with a laser beam. Tantalum and lead were first used as materials for this optical recording medium {Science. 154, 1550,1966}. Since then, various materials have been used, but chalcogen elements such as tellurium or these compounds are often used,
(Japanese Patent Publication No. 47-26897), especially tellurium selenium alloys are often used (Japanese Patent Publication No. 54-41902, Japanese Patent Publication No. 57-7919, and Japanese Patent Publication No. 57-56058).

An example of an optical recording medium using this tellurium-selenium alloy as an optical recording layer has a structure shown in FIG. That is, a recording layer 21 made of tellurium-selenium alloy is provided adjacent to the substrate 1. The recording laser light is focused onto the recording layer 21 through the substrate 1 to form pits 22. As the substrate 1, synthetic resin such as polycarbonate, polyolefin, polymethylpentene, acryl, epoxy resin, or glass is used. Usually, on the substrate 1, pits are concentrically or spirally accurately recorded at regular intervals. A guide groove is provided.

When light enters a groove with a width of about the laser beam diameter, the light is diffracted, and the spatial distribution of the diffracted light intensity changes as the beam center shifts from the groove, so this is detected and the laser beam is incident on the center of the groove. The servo system is configured as follows. The width of the groove is usually 0.3 to 1.3 μm, and the depth of the groove is set in the range of 1/20 to 1/4 of the laser wavelength used.
A servo system is similarly configured for focusing.

Reading of information is performed by irradiating a laser beam having a lower power than at the time of recording so as to pass over the pits, thereby detecting a change in reflectance caused by the presence or absence of the pits.

In recent years, a semiconductor laser has been used as a laser light source in order to miniaturize a recording device. The oscillation wavelength of a semiconductor laser is around 8000 Å, but the tellurium-selenium alloy is relatively well suited to this wavelength band, and can obtain a moderate reflectance and a moderate absorptivity {Physica Stitas Solidai, 7 , 189,1964 (Phys, stat.sol. 7, 189,1964)}.

[Action]

 Various materials can be used for the recording layer 21.

Among them, tellurium has relatively good recording and reproducing characteristics. However, it cannot be put to practical use because it is prone to oxidative deterioration in a high temperature and high humidity environment. Also, the sensitivity was slightly insufficient. As one of the solutions to the lack of sensitivity, it has been proposed to incorporate nitrogen into the tellurium film so that nitrogen is released during heating and the sensitivity is increased (Japanese Patent Laid-Open No. 57-58250).

When an optical recording medium was produced by further testing this known example and the recording / reproducing characteristics were evaluated, the semiconductor laser wavelength (about 8300 Å), which is the light source of a small-sized large-capacity recording device, was almost not absorbed, resulting in insufficient sensitivity. Moreover, since nitrogen is likely to be liberated, its storability was not sufficient in a high temperature and high humidity environment.

Further, it is proposed that the film is formed by sputtering in a mixed gas of argon and nitrogen, instead of the film formation by sputtering in nitrogen gas as in the above proposal (Applied Physic Letters (Appl. .Phyz.
Lett, 45,202,1987)).

However, even with this, sufficient recording sensitivity and sufficient signal quality could not be obtained.

Therefore, by sputtering a tellurium selenium alloy target with a mixed gas of argon and nitrogen, the recording layer is made of tellurium, selenium, and nitrogen, and an optical recording medium having good weather resistance, high sensitivity, and good signal quality can be obtained. The present inventors have already proposed it (Japanese Patent Application No. 61-10
1368).

The reason why this recording layer has good weather resistance, high sensitivity, and good signal quality is that the small melting point of the whole system due to the addition of selenium and the explosiveness of selenium nitride and tellurium nitride are associated with the formation of small holes. It is thought that the sensitivity was enhanced because the expansion of pores due to surface tension began to occur at a relatively low temperature, and the interaction between tellurium, tellurium nitride, selenium, and selenium nitride acted favorably to improve the weather resistance. , It seems that the signal quality has improved.

It has been found that such an optical recording medium also has a problem that its recording sensitivity changes when it is stored in a high temperature and high humidity environment for a long time. The present inventor has crystallized a tellurium-selenium nitrogen film and oxidized its crystal grain boundaries to form a recording film, which has good weather resistance, high sensitivity, good signal quality, and a sufficient recording power margin. It has been found that an optical recording medium having a high degree can be obtained, and has already been proposed.

Even with such a good recording medium, after being stored in an environment of high temperature and high humidity of 85 ° C and 90% for 200 hours, the bit error rate of the stored data does not change, but the film surface has
The granular projections of about 0.1 μm were generated.

[Problems to be Solved by the Invention]

However, such a conventional optical recording medium, although it is a tellurium-selenium alloy film, has the drawbacks of poor weather resistance and unstable recording / reproducing signal quality.

The object of the present invention is good weather resistance, high sensitivity and good signal quality, a large margin of recording power, and changes in medium characteristics even when stored in a high temperature and high humidity environment for a long time. It is an object to provide an optical recording medium that does not have the above.

[Means for solving the problem]

The optical recording medium of the present invention comprises at least a substrate and a recording layer formed on the substrate for recording information by selectively removing a part of the substrate by laser light, wherein the recording layer is tellurium. It is a crystalline film containing selenium, lead, nitrogen, and oxygen as main components, and is configured such that the lead content on the surface side of the recording layer is larger than that in the central portion.

That is, it was found that the optical recording medium of the present invention can suppress the generation of the above-mentioned granular projections by using a crystalline recording film containing tellurium, selenium, lead, nitrogen and oxygen as main components. However, it has been found that the recording film is likely to be oxidized when the lead content is too large, and the present invention has been achieved.The occurrence of particulate projections under a high temperature and high humidity environment is caused by the interface of the recording film substance. Since it is a movement, by increasing the lead content at the recording film interface to suppress the generation of granular projections, and by reducing the lead content in the central part of the recording film to reduce the average content. , The recording film is prevented from being easily oxidized.

〔Example〕

 Next, examples of the present invention will be described.

 First, the first embodiment will be described below.

Annealed at 100 ℃ for 2 hours, inner diameter 15mm, outer diameter 130mm,
On a 1.2 mm-thick injection molded polycarbonate resin disk substrate with guide grooves, a tellurium-selenium-lead target of 71: 20: 9 in atomic% was sputtered with a mixed gas of argon and nitrogen to form about 30 Å thickness. Subsequently, a 75: 20: 5 tellurium-selenium-lead target with an atomic percentage of 75: 20: 5 was sputtered with a mixed gas of argon and nitrogen to about 190.
Å A thick film is formed, and then it is continuously grown on it in atomic% of 71 to 20
A counter 9 tellurium-selenium-lead target was sputtered with a mixed gas of argon and nitrogen to form a film having a thickness of about 30 liters.

Then, an optical recording medium was manufactured by storing it in an environment of a temperature of 85 ° C. and a relative humidity of 90% for 12 hours to make it crystalline and oxidize the crystal grain boundaries.

When the reflectance of the land portion of the optical recording medium which was incident on the substrate at a wavelength of 8300Å was measured, it was about 32%. A semiconductor laser beam with a wavelength of 8300Å enters through the substrate and is focused on the recording layer to a diameter of about 1.6 μm.
_sec, a recording frequency 3.77MHz, the recording pulse width 70n _sec, recorded in the land portions at the conditions of the recording power 5.4 mW, and reproduced at a constant power of 0.7 mW. The carrier-to-noise ratio (C / N) with a bandwidth of 30 KHz was as good as 51 dB.

It was confirmed that even if the optical recording medium was stored in a high temperature and high humidity environment of 85 ° C. and 90% for a long time, no granular projections were generated on the film surface.

In addition, the recording sensitivity characteristics and bit error rate were examined after being stored in an environment of high temperature and high humidity of 85 ° C and 90% for 600 hours, but it was confirmed that the optical recording medium has excellent weather resistance without any change in practical use. It was

The thickness of the recording layer is preferably 160 Å or more and 400 Å or less from the viewpoint of recording / reproducing characteristics, and the selenium content is 9% by atom.
% Or more and less than 35% is desirable from the viewpoint of recording / reproducing characteristics and weather resistance, and the content of lead is preferably in the range of 1% to 10% in terms of atomic% as an average of the entire recording layer from the viewpoint of weather resistance. The nitrogen content is preferably in the range of 0.5% to 10% in atomic% from the viewpoint of recording / reproducing characteristics, and the nitrogen content is in the range of approximately 5% to 25% in atomic% from the viewpoint of recording / reproducing characteristics and weather resistance. From desirable.

〔The invention's effect〕

The optical recording medium of the present invention has good weather resistance because the recording layer is made of crystalline material containing tellurium, selenium, lead, nitrogen and oxygen as main components, and the lead content is varied in the thickness direction. In addition, there is an effect that the sensitivity is high, the signal quality is good, the margin of recording power is large, and the medium characteristics can be prevented from changing even when stored in a high temperature and high humidity environment for a long time.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing an example of the present invention and a conventional optical recording medium. 1 ... Substrate, 21 ... Recording layer, 22 ... Pit.

Claims (1)

[Claims] 1. An optical recording medium comprising a substrate and a recording layer formed on the substrate and comprising a crystalline film containing tellurium, selenium, lead and nitrogen as main components. An optical recording medium characterized in that the lead content on the surface side of is higher than that of the central portion.