JPS6381091A - Optical recording medium - Google Patents

Abstract

PURPOSE:To provide an optical recording medium having favorable weatherability and signal quality together with high sensitivity and being stable, by providing a crystalline recording layer comprising tellurium, tellurium nitride and selenium as main constituents. CONSTITUTION:A recording layer 21 is provided on a base 1, and recording laser light is focused on the recording layer 21 through the base 1, whereby a pit 22 is formed. A guide groove or grooves are provided for ensuring accurate recording through formation of such pits 22 in a concentric or spiral pattern at regular intervals. When light is incident on the groove, the width of which is about the diameter of a laser beam, the light is diffracted, so that the spatial distribution of the intensity of the diffracted light is changed as the center of the beam is deviated from the groove. A servo system is arranged to detect the change and cause the laser beam to be incident on the center of the groove. With selenium incorporated in the recording layer, the melting point of the whole system of the layer is lowered, and with the layer made to be crystalline, formation of a small hole in the beginning stage of formation of the pit takes place at a relatively low temperature, resulting in a higher sensitivity. Weatherability is enhanced through interactions of tellurium, tellurium nitride and selenium, and since the recording layer is crystalline, a favorable signal quality can be stably obtained.

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. As materials for this optical recording medium, chalcogen elements such as Te and compounds thereof are used (for example, Japanese Patent Publication No. 47-26897).

(Problems to be Solved by the Invention) However, none of these media fully satisfies all of the requirements of weather resistance, sensitivity, and signal quality.

An object of the present invention is to provide a stable optical recording medium with sufficiently good weather resistance, high sensitivity, and sufficiently good signal quality.

(Means for Solving the Problems) The optical recording medium of the present invention is an optical recording medium in which information is recorded and read by laser light, and includes a crystalline recording layer containing tellurium, tellurium nitride, and selenium as main components. It is characterized by having.

(effect) The optical recording medium has a structure as shown in FIG.

That is, the recording layer 21 is provided on 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. As the substrate 1, synthetic resins such as polycarbonate, polyolefin, polymethylpentene, acrylic, and epoxy resins, and glass are used.

Guide grooves are provided on the substrate so that pits are recorded concentrically or spirally at regular intervals with high accuracy. 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 0.3 to 1.311 m,
The depth of the groove is set within the range of 1112 to 174 wavelengths of the laser used. A servo system is similarly configured for condensing light. Information is read by irradiating a laser beam with a weaker power than during recording so as to pass over the pits, and detecting changes in reflectance due to the presence or absence of pits.

Various materials can be used for the recording layer 21. Among them, tellurium has relatively good recording and reproducing properties. However, it could not be put to practical use because of severe oxidative deterioration in high-temperature environments. Also, the sensitivity was somewhat insufficient.

As one solution to the lack of sensitivity, it has been proposed to include nitrogen in the tellurium film so that nitrogen is liberated during heating and increases the sensitivity (Japanese Patent Laid-Open No. 57-58250). The present inventors repeated this example, fabricated an optical recording medium, and evaluated the recording and reproducing characteristics, and found that the semiconductor laser wavelength (approximately 8
300A), the sensitivity was insufficient because there was almost no absorption. In addition, since nitrogen is easily liberated, the storage stability in high-temperature environments was not sufficient. Furthermore, instead of forming a film by sputtering in nitrogen gas as proposed above, it has also been proposed to form a film by sputtering in a mixed gas of argon and nitrogen (Applied Physics Letters). Appl, Phys, Lett, 4
5, 202.1984)). However, this still did not provide sufficient recording sensitivity. By making the recording layer a crystalline material whose main components are tellurium, tellurium nitride, and selenium, the present inventors have achieved an optical recording medium with high sensitivity and good weather resistance, while also achieving good and stable signal quality. This discovery led to the present invention. The reason why this recording layer has high sensitivity, good weather resistance, good signal quality, and stability is not clear, but it is because the melting point of the entire system is lowered by adding selenium, and the layer is made crystalline. It seems that the sensitivity has increased because the formation of small holes, which is the initial stage of pore formation, occurs at a relatively low temperature, and the interaction between tellurium, tellurium nitride, and selenium works favorably, resulting in improved weather resistance. It is thought that the interaction between tellurium, tellurium nitride, and selenium and the fact that it is crystalline work favorably, resulting in good and stable signal quality.

(Example) Examples of the present invention will be described below.

A tellurium selenium alloy target was magnetron sputtered with a mixed gas of argon and nitrogen onto 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 that had been annealed at 100°C for 2 hours. A storage film was formed and then stored for 12 hours in an environment with a temperature of 85° C. and a relative humidity of 90% to produce an optical recording medium. Analysis of the recording film produced in this manner revealed that the recording layer contained tellurium, tellurium nitride, and selenium, and the ratio of tellurium, nitrogen, and selenium atoms was approximately 90:5:5. The layer was polycrystalline. When the reflectance of this optical disk was measured when it was incident on the substrate at a wavelength of 5 aooA, it was about 29%.

Semiconductor laser light with a wavelength of 8300 A is incident through the substrate and focused onto the recording layer to a medium diameter of 1.6 pm, and the medium linear velocity is set to 5.
Recording was performed under the conditions of 65 m1 sec, recording frequency of 3.77 MHz, recording pulse width of 70 nsec, and recording power of 6.0 mW, and reproduction was performed at 0.7 mW. The carrier-to-noise ratio (C/N) with a bandwidth of 30 KHz was as good as 48 dB. This value was sufficiently stable for practical use even against fluctuations in recording power caused by changing the recording/reproducing device. After this optical disc was stored in a high temperature and high humidity environment of 85°090% for 60 hours, the above characteristics were examined, but there was no change, and it was confirmed that the optical recording medium had excellent weather resistance.

The thickness of the layer mainly composed of tellurium, tellurium nitride, and selenium is desirably in the range of 100 to 1000 from the viewpoint of recording and reproducing characteristics, and the selenium content is 2% or more and less than 40% in atomic percent. The content of tellurium nitride is desirably within the range of 2% or more in terms of the number of nitrogen atoms from the viewpoint of recording/reproducing characteristics and weather resistance.

In the layer whose main components are tellurium, tellurium nitride, and selenium,
When at least one element selected from the group of lead, tin, germanium, antimony, indium, gallium, zinc, bismuth, aluminum, copper, silver, magnesium, tantalum, gold, palladium, and cobalt is added, the shape of the pits can be changed. It may be well arranged. However, the amount added is preferably less than 20% in atomic percent.

Tellurium and nitride If at least one layer of oxide, nitride, fluoride, carbide, sulfide, or boride is formed between the layer containing tellurium and selenium as main components and the substrate, it will be effective against fluctuations in recording power. The margin increases, and tracking and focus servos may become more stable.

(Effects of the Invention) As is clear from the above examples, the present invention provides a stable optical recording medium with sufficiently good weather resistance, high sensitivity, and sufficiently good signal quality.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an example of an optical recording medium. In the figure, 1 is a substrate, 21 is a recording layer, and 22 is a pitch 1
Illustration procedure amendment (spontaneous) 62.11.27 Showa 1988 Patent Application No. 22765
No. 2 No. 2, Name of the invention Optical recording medium 3, Person making the amendment Relationship to the case Applicant 5-33-1 Shiba, Minato-ku, Tokyo (423) NEC Corporation Representative Tadahiro Sekimoto - Agent 5, Amendment (1) Contents of amendment in Column 6 of Detailed Description of the Invention of the Specification (1) The following sentence should be inserted after the 11th line of page 7 of the specification. “Examples of tellurium, selenium, and lead alloys are explained below.

Claims (1)

[Claims] An optical recording medium for recording and reading information using a laser beam, characterized by having a crystalline recording layer containing tellurium, tellurium nitride, and selenium as main components.