JPH0533675B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording medium on which information can be recorded and reproduced using laser light.

[Prior Art] Optical disk memories, which record and reproduce information on a medium using laser light, have excellent characteristics as large-capacity recording devices because of their high recording density. The material for this optical recording medium is tellurium (Te).
Chalcogen elements such as or compounds thereof are used (Japanese Patent Publication No. 47-26897). In particular, tellurium-selenium alloys with good weather resistance are often used (Japanese Patent Publication No. 41902/1983, Japanese Patent Publication No. 7919/1983).
Publication No. 57-56058).

In recent years, in order to downsize recording devices, semiconductor lasers have been used as laser light sources. Semiconductor lasers have an oscillation wavelength of around 8000 Å, and tellurium-selenium alloys are relatively well suited to this wavelength range, and can provide moderate reflectance and moderate absorption . 189,
1964 (phys.stat.sol. 7 , 189, 1964)}.

An optical recording medium using this tellurium-selenium alloy as an optical recording layer has a structure as shown in FIG. That is, a recording layer 21 made of a tellurium-selenium alloy is provided adjacent to the substrate 1.
The recording laser beam is focused and irradiated onto the recording layer 21 through the substrate 1, and pits 22 are formed. The substrate 1 is made of synthetic resin such as polycarbonate, polyolefin, polymethylpentene, acrylic, or epoxy resin, or glass, and is usually guided so that pits are recorded concentrically or spirally at regular intervals. A groove is provided.

When light enters a groove with a width similar to the diameter of the laser beam, the light is diffracted, and as the beam center shifts from the groove, the spatial distribution of the intensity of the diffracted light changes.This is detected and the laser beam is directed to the center of the groove. The servo system is configured as follows. The width of the groove is usually
The depth of the groove is 0.3 to 1.3 μm, and the depth of the groove is set in the range of 1/12 to 1/4 of the wavelength of the laser used. A servo system is similarly configured for condensing light. Information is read by irradiating laser beams with a weaker power than during recording so as to pass over the pits, and detecting changes in reflectance caused by the presence or absence of pits.

[Problems to be Solved by the Invention] However, optical recording media using only a tellurium-senone alloy layer as a recording layer have not had sufficiently good signal quality.

On the other hand, the present inventors have found that the signal quality can be improved by making the recording layer mainly composed of tellurium, selenium, and nitrogen, and have already proposed this. The present invention is a further improvement on this, and aims to provide an optical recording medium with good weather resistance, high sensitivity, and good signal quality.

[Means for Solving the Problems] The present invention provides an optical recording medium comprising a substrate and a recording layer formed on the substrate, a portion of which is selectively removed by laser light to record information. In,
The recording layer includes at least a layer formed on the substrate side containing fluoride as a main component, and a layer containing tellurium, selenium, and nitrogen as main components adjacent to this layer and formed on the outside of the substrate. An optical recording medium characterized by having:

In the present invention, for example, as shown in FIG. 1, a layer 2 mainly composed of fluoride and a layer 3 mainly composed of tellurium, selenium and nitrogen (hereinafter abbreviated as tellurium-selenium-nitrogen layer) are formed on a substrate 1. The recording layer is formed by sequentially stacking layers. Substrate 1 is made of tellurium-selenium
By providing the fluoride layer 2 between the nitrogen layer 3 and the nitrogen layer 3, pits formed by recording can be prevented from expanding significantly. Therefore, since recording can be performed by filling the pits, high-density recording is possible. Furthermore, since the margin for fluctuations in recording power is increased, the optical recording medium becomes a practical optical recording medium. Furthermore, since no large pits are formed, tracking and focus servo do not become unstable, making it a practical optical recording medium.

Various fluorides can be used as the fluoride layer, and among them, compounds with rare earth elements such as cerium fluoride and lanthanum fluoride, and magnesium fluoride are preferable. It is important to manufacture the film so that its internal stress is small in order to prevent cracks in the film. The thickness of the fluoride layer is 5
A range of Å to 2500 Å is desirable. When the refractive index of the fluoride layer is smaller than the refractive index of the substrate, the medium reflectance can be maximized by setting the thickness to 1/4 or 3/4 of the wavelength in the film. When the refractive index of the fluoride layer is larger than that of the substrate, the medium reflectance can be prevented from becoming small by setting the thickness to 1/2 of the wavelength in the film. On the other hand, if the thickness is set to 1/4 or 3/4 of the wavelength in the film, the medium reflectance will be reduced, but the absorption in the recording film will be maximized, making it possible to achieve high sensitivity.

The thickness of the tellurium-selenium-nitrogen layer is from 100 Å
A range of 1000 Å is desirable from the viewpoint of recording and reproducing characteristics, a nitrogen content of 2% or more and less than 20% in terms of atomic percent is desirable from the viewpoint of recording and reproducing characteristics and weather resistance, and a selenium content of 2% in atomic percent is desirable. A range of from 50% to 50% is desirable from the viewpoint of weather resistance.

The tellurium-selenium-nitrogen layer contains lead, arsenic, tin,
At least one element selected from the group of germanium, cadmium, thallium, antimony, sulfur, phosphorus, indium, gallium, zinc, bismuth, aluminum, copper, silver, magnesium, tantalum, gold, palladium, and cobalt is added. It's okay. In this case, the shape of the pit may be well adjusted. However, the amount added is preferably less than 20% in terms of atomic percent.

Film formation methods include sputtering, vapor deposition,
A responsive vapor deposition method, an ion plating method, an ion beam deposition method, etc. may also be used.

As the substrate, commonly used materials such as synthetic resins such as polycarbonate, polyolefin, polymethylpentene, acrylic epoxy resin, and glass are used.

[Function] By interposing the fluoride layer between the substrate and the tellurium-selenium-nitrogen layer, pits are prevented from expanding significantly, and an excellent optical recording medium can be obtained. This is considered to be because the difference in surface energy depending on the presence or absence of the tellurium-selenium-nitrogen layer changes due to the formation of the fluoride layer.

[Example] Examples of the present invention will be described below.

Magnesium fluoride was formed to a thickness of about 50 Å on a polycarbonate resin disk substrate with an inner diameter of 15 mm, an outer diameter of 130 mm, and a thickness of 1.2 mm, which had been annealed at 100°C for 2 hours.Subsequently, a tellurium-selenium alloy target was coated with argon and nitrogen gas. By magnetron sputtering with a mixed gas, a tellurium-selenium-nitrogen layer with a tellurium-selenium-nitrogen ratio of 90:4:6 at a thickness of about 240 Å was formed with a ratio of tellurium, selenium, and nitrogen in atomic percent. After annealing this optical disk in a nitrogen atmosphere at 95° C. for 1 hour, the substrate incident reflectance at a wavelength of 8300 Å was measured and found to be 34%. Semiconductor laser light with a wavelength of 8300 Å is incident through the substrate to form a 1.6 μm diameter on the recording layer.
Medium linear velocity 5.6m/sec, recording frequency
3.777MHz, recording pulse width 70nsec, recording power
Recording was performed under 6.5mW conditions and playback was performed at 0.7mW. Carrier to noise ratio (C/
N) was good at 50 dB. This optical disk
After storing for 60 hours in a high temperature and high humidity environment of 70°C and 80%, the above characteristics were examined, but there were no changes, confirming that the optical recording medium had excellent weather resistance.

Compared to an optical disc without a magnesium fluoride layer for comparison, the recording power range in which a C/N of 45 dB or more can be obtained is approximately twice as large.
It was confirmed that there is a large margin for fluctuations in recording power. Also, the tracking and focus servos did not become unstable.

[Effects of the Invention] As explained above, the optical recording medium of the present invention has good weather resistance, high sensitivity, and good signal quality.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view showing one embodiment of the optical recording medium of the present invention, and FIG. 2 is a partial sectional view showing a conventional optical recording medium. DESCRIPTION OF SYMBOLS 1... Substrate, 2... Fluoride layer, 3... Tellurium-selenium-nitrogen layer, 21... Recording layer, 22... Pit.

Claims (1)

[Scope of Claims] 1. An optical recording medium comprising a substrate and a recording layer formed on the substrate, a portion of which is selectively removed by laser light to record information, wherein the recording layer is a layer formed on the substrate side containing magnesium chloride or a fluoride of a rare earth element as a main component; and a layer containing tellurium, selenium, and nitrogen as main components adjacent to this layer and formed on the outside of the substrate. An optical recording medium comprising at least the following. 2. The optical recording medium according to claim 1, wherein the rare earth element fluoride is cerium fluoride or lanthanum fluoride.