JPH0553019B2 - - 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. As materials for this optical recording medium, chalcogen elements such as Te or compounds thereof are used (Japanese Patent Publication No. 47-26897). In particular, tellurium selenium alloys are often used (Japanese Patent Publication No. 54-41902, Japanese Patent Publication No. 57-7919, Japanese Patent 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 (phys.stat. sol.7.189.1964)).

Conventionally, optical recording media have 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, polymethylpentene, acrylic, and epoxy resins, and glass are used. The recording layer 21 is usually
Tellurium selenium alloys of 200 Å to 1000 Å thick have been used.

(Problems to be Solved by the Invention) However, it is not easy to control the composition of the tellurium selenium alloy, which poses a problem in mass production. In addition, an optical recording medium that has a small ratio of the second high frequency to the recording carrier (2ndH/C), is highly sensitive, does not change its optical characteristics even under high temperature and high humidity, and does not have cracks around the pit. I couldn't get it.

An object of the present invention is to provide a truly practical optical recording medium that is easy to mass produce, has good weather resistance, high sensitivity, and 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 has at least three layers: a selenium layer, a tellurium layer, and a selenium layer. , and the total thickness of the three layers is less than 200 Å.

The present inventors have developed a substrate 1 as shown in FIG.
A recording layer is formed by laminating selenium layer 2, tellurium layer 3, and selenium layer 4 on top, and the thickness of the above three layers is 200 Å.
By making it less than 2ndH, it has excellent mass productivity and
It was discovered that an optical recording medium having a small carbon content, high sensitivity, and high weather resistance was obtained, and the present invention was developed.

(Example 1) Examples of the present invention will be described below. Inner diameter 15
A polycarbonate resin disk substrate with a guide groove having a diameter of 130 mm, an outer diameter of 130 mm, and a thickness of 1.2 mm was placed in a vacuum evaporation apparatus and evacuated to 4×10 ^-6 Torr or less. As evaporation sources, Te was placed in the first resistance heating boat, and Se was placed in the second resistance heating boat. First, Se
25 Å thick evaporation, then 125 Å thick evaporation of Te, and finally
Se was deposited to a thickness of 25 Å. After annealing this optical disk for 1 hour in a nitrogen atmosphere at 80°C,
When the reflectance of the substrate incident at 8300 Å was measured, it was 25%. AlGaAs semiconductor laser light with a wavelength of 8300 Å is incident through the substrate and focused to approximately 1.5 μmφ, medium linear velocity is 5.6 m/sec, and recording frequency is 0.625 MHz.
(Duty 50%) and played back at 0.7mW. The recording power at which 2ndH/C shows the minimum value is
3.5mW, 2ndH/C at that time is -36dB,
The carrier to noise ratio (C/N) was good at 55 dB. 25Å thick Se, 250Å for comparison
For optical disks made of thick Te and 25 Å thick Se, the substrate incidence reflectance after annealing is 41%, and the recording power at which 2ndH/C shows the minimum value is 4.5 mW, and 2ndH/C at that time is -32 dB. , and the C/N was 54 dB. The reason why the C/N of the comparison disk is low despite its large reflectance is because the unrecorded noise is worse at -64 dB for the comparison disk compared to -67 dB for the disk of this example. This is due to the fact that it is easy to change. From this point of view as well, it is desirable that the film thickness be thinner. In addition, by making the film thickness less than 200 Å as in the disk of this embodiment, the reflectance is less than 30%, which makes it possible to reduce the change in medium reflectance before and after recording, thereby reducing the instability of the focus and tracking servos. Does not occur. Next, the disk of this example was placed in a high temperature and high humidity environment of 70°C and 80% for 490°C.
After storage for a period of time, the above characteristics were examined, but there were no changes, confirming that the optical recording medium had excellent weather resistance. This is thought to be because the film is thin, less than 200 Å, so stress within the film is small and no cracks occur. In the case of a tellurium selenium alloy recording film, when the film thickness is less than 200 Å, pinpoles and the like occur in the above-mentioned high temperature and high humidity test and the recording and reproducing characteristics deteriorate, but this does not occur with the three-layer structure of the present invention.

(Example) In the same manner as in Example 1, only the Te layer thickness was set to 100 Å. The substrate incidence reflectance after annealing was 22%. When evaluated in the same manner as in Example 1, the recording power was 3.5 mW, the C/N was 51 dB, and the 2ndH/C was -
It was good at 37dB, and there was no change in the above characteristics even in a high temperature and high humidity test at 77°C and 80%.

The thickness of the upper and lower Se layers is preferably in the range of 5 to 50 Å from the viewpoint of weather resistance.

(Effects of the Invention) As is clear from the above embodiments, the present invention provides high sensitivity, good signal quality, and stable servo.
Moreover, it is possible to obtain an optical recording medium that does not produce cracks or pinholes even under high temperature and high humidity, and since there is no need to control the composition, it can be mass produced, and since the film thickness can be thin, the manufacturing cost is low, making it truly practical. An optical recording medium can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view showing an example of the optical recording medium of the present invention, and FIG. 2 is a schematic cross-sectional view of a conventional optical recording medium. In the figure, 1 is a substrate, 2 and 4 are selenium layers, 3 is a tellurium layer, 21 is a recording layer, and 22 is a pit.

Claims (1)

[Claims] 1. In an optical recording medium that records and reads information using laser light, a selenium layer, a tellurium layer,
has at least three layers with a selenium layer, and the above three
An optical recording medium characterized in that the total thickness of the layers is less than 200 Å.