JPS60124039A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To enable the information recording with change of optical characteristics by providing a substrate at the outside of the 1st or 2nd layer and forming the 2nd layer with a composite material obtained by dispersing a material which has high light absorbing performance and changes its optical characteristics with heat. CONSTITUTION:The 1st layer 1 is formed on a substrate (a) with a material which has a >=30% reflection factor with just a single layer to the recording light of a specific wavelength. Then the 2nd layer 2 into which a material having high light absorbing performance with high stability to the heat and changing its optical characteristics by heat is provided on the layer 1. The material of high light absorbing performance of the layer 2 absorbs the semiconductor laser irradiated, and the energy of the laser light is converted into the thermal energy to cause temperature rise. The layer 2 changes the reflection factor, the transmittance, the refractive index, etc. at the area irradiated by the laser light owing to a local temperature rise at said area. Then the information is recorded by the optical difference between the area irradiated by the laser light and the area where no laser light is irradiated.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Technical Field The present invention relates to an optical information recording medium suitable for application to optical video discs, electronic files, digital audio discs, and the like.

(2) Background Art Various optical information recording media have been proposed in which information is recorded and reproduced by irradiating a thin film layer formed on a substrate with a laser beam.

For example, there is a method in which a recording thin film layer is formed of a low melting point metal such as binumuth Bl or tellurium Te, and information is recorded by irradiating this with laser light to melt and evaporate it to form recording pits. However, in order to form recording pits in this recording form, a laser beam with high power is required, and there is also a drawback that the shapes of the formed recording pits are not uniform. As a result, there are disadvantages in that it tends to cause noise when recording is reproduced, and that a stable reproduced signal cannot be obtained, that is, it is difficult to achieve high-density recording.

(3) Disclosure of the Invention An object of the present invention is to provide an optical information recording medium that solves the above-mentioned drawbacks.

The present invention provides an optical information recording medium in which a second layer and a first layer are sequentially laminated from the write and read sides, and further includes a substrate outside at least the second layer or the first layer, - The first layer is made of a material that exhibits a reflectance of 30% or more when used as a single layer for recording light of a specific wavelength, and the second layer has high light absorption and is resistant to heating. It is composed of a composite material in which a material whose optical properties change mainly by heating is dispersed in a stable material, and information is recorded by changing the optical properties of the second layer. It is an optical information recording medium.

That is, the present invention avoids a recording form in which information is recorded by forming recording bits by melting or evaporating a recording thin film, and in the present invention, the optical characteristics of the recording thin film, for example, each relative phase,
Information is recorded by changes in transmittance, refractive index, etc., making it possible to reduce recording power and achieve high-density recording. Furthermore, since the recording layer is composed of a thermally stable material in which a material whose optical properties change upon heating is dispersed, deterioration of sensitivity can be prevented.

Furthermore, whereas until now optical properties could change only if materials had a large absorption of irradiated light, thermally stable materials with large light absorption can change optical properties. Since heat beams and energy can be effectively applied to materials whose optical properties change, the absorption of materials whose optical properties change may be small.

(4) Best Mode for Carrying Out the Invention The present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view showing one embodiment of the present invention.

In the figure, a substrate (a), for example, a glass substrate or an acrylic resin or other light-transmissive substrate, has a first layer made of a material that exhibits a reflectance of 30% or more when used as a single layer for recording light of a specific wavelength. A layer (1) is provided, and the layer (1) is made of a material that has high light absorption and is stable against heating. A second layer (2) is provided in which a variable material is dispersed.

The first layer (1) has a wavelength of recording light, for example, a wavelength of 820.
It is made of a material that exhibits a reflectance of 30% or more when used as a single layer with respect to nm semiconductor laser light. In addition, 3- It is desirable that the first layer (2) undergo no physical or chemical changes in the temperature range in which the optical properties of the second layer (2) change due to thermal energy.

For example, gold Au, silver Ag, copper Cu, aluminum Al.

Nickel N1. Titanium TI or an alloy thereof can be used, and the film thickness is preferably 20 to 500 nm.

The second layer (2) is made of a thermally stable material, such as Bj2S3, which has a high light absorption property for two continuous recording beams.
+ Bi2Te3 + St + CuInSe2 +
AgInSe2, Cu1nTe2+GeS,
sb,,s3. Among compounds such as CdSe and CdTe, there are materials whose optical properties change mainly by heating.
For example, Se, Te, As, Sb, Cd
, In, Get Sn, or a compound containing these, for example, As2S3°Sb2Se3. T
eSe2, TeaoGe4oSnH) + GeS
A composite material in which As2Te3, etc. are dispersed can be used. The thickness of the second layer (2) is preferably 10 to 500 nm. Further, the volume ratio (filling coefficient) of the material contained in the second layer (2) whose optical properties change mainly due to heating is preferably in the range of 0.1 to 0.95.

41 Information is recorded on the optical information recording medium according to the present invention as follows.

As shown in FIG. 1, a semiconductor laser with a wavelength of 820 nm and an output of OmW, for example, is irradiated from the side having the second layer (2). At this time, in the second layer (2), absorption mainly occurs due to the material with high light absorption as described above, and the energy of the laser beam is converted into thermal energy, causing a temperature rise. Further, the remaining laser light that is not absorbed passes through the second layer (2) and reaches the first layer (1). Since this first layer (1) has a high reflectance, the laser light that reaches the first layer (1) is reflected and reaches the second layer (2).

Furthermore, due to the interference effect of the thin film, the energy of the laser beam can be efficiently applied to the second layer (2). These energies cause a local temperature increase in the part of the second layer (2) irradiated with the laser beam, which changes the optical properties of that part, such as reflectance, transmittance, and refractive index. , an optical difference appears between the areas that are irradiated with the laser light and the areas that are not, and information is recorded.

The recorded information is read out by similarly irradiating the second layer (2) with a semiconductor laser and detecting the difference in optical properties in the second layer (2). At this time, the power of the semiconductor laser used for reading is sufficiently lower than that during recording, for example, 3 mW, and no recording is performed with this reading power.

The first layer (1) is preferably a material having a reflectance of 30%. This is to increase the contrast between areas where information is recorded and areas where information is not recorded, and the reflectance is 30.
This is because if it is below 50%, the S/N ratio will decrease.

In the example described above, the first layer is provided on 1- of the substrate (a), and the second layer (2) is further provided on the -L. A second layer (2) is provided to the
- can also be provided with a first layer (1). Figure 2 shows an example of the latter; in this case, the adhesive layer (
6) is used to bond another substrate (a'), and a sandwich structure is illustrated in which a recording medium is sandwiched between the substrates on both sides. Note that writing and reading of information using a laser beam is performed from the substrate (a) side as shown in FIG.

Next, specific examples of the optical information recording medium according to the present invention will be shown.

EXAMPLE A first layer (1) consisting of a thin Al film having a thickness of 100 nm was formed on the glass substrate a by a vapor deposition method using resistance heating, and on the second layer, a Mihara vapor deposition method using resistance heating was similarly applied. A second film with a thickness of approximately 150 nm was prepared by dispersing antimony selenium Sb2Se3 in cadmium selenium CdSe.
A layer (2) was formed. At this time, if the volume ratio (filling coefficient) of Sb2Se3 contained in the second layer (2) is q, then Q = 0.6. The second layer of this recording medium (
The reflectance from the side having 2) was 10% before heat treatment, and 37% after heat treatment at 200° C., that is, after recording with semiconductor laser light (wavelength 820 nm). It is possible to read information using this difference in reflectance before and after recording. next,
The above recording medium was manufactured on a disk-shaped glass substrate, and 1
After heat treatment at 50°C for 40 minutes, the substrate was heated to 180Orp.
Recording was performed using a semiconductor laser with a wavelength of 820 nm while rotating at 7 m. The laser power at that time is the medium surface]
- at 15 mW, the spot diameter was focused to 1.2 μm, and the recording frequency was 5 MT (z, 20% duty ratio. As a result, a good reproduced signal was obtained, and 30% of the band
The C/N was 51 dB at KHz. Furthermore, the rotational speed of this disk was lowered to 100 rpm, and a continuous oscillation laser spot with an output of 5 mW was used at the medium surface.
4- When the recorded bit portion described above was traced, it was confirmed that the recorded signal of 5 MHz described above had disappeared, and it was also observed with an optical microscope that the recorded bit had been erased. After repeating these recordings and deletions, 102
It was possible to repeat up to three times. An unrecorded medium prepared under the same conditions as in 1. was placed in an atmosphere of 45°C and 95% RH for 1 hour.
After leaving it for 0 days, we conducted a recording experiment in the same way.
The C/N of the recording/reproduction signal at 5 MHz was 46 dB.

In another embodiment, using a method similar to the above embodiment, a first layer (
1) and on top of this another material 8- a second layer (2) of the same filling factor (q = 0.6) for the same film thickness and material of varying optical properties.
As a comparative example, a first layer (1) of AI with the same thickness was formed on a glass substrate a, and then a second layer (1) with the same thickness was formed using only Sb2Se3.
The recording medium on which layer (2) was formed was tested in the same manner as in the above example.

The results are summarized in Table 1. In Table 1, the second layer A indicates a material that has high light absorption and is stable against heating, and B indicates a material whose optical properties change mainly by heating. In the example of the present invention, compared to the comparative example, the C/N of the recording/reproducing signal at 5 MHz was 45°C and 95°C.
%RH, and does not easily deteriorate even after being left in an atmosphere of %RH.
The number of times recording and erasing can be repeated has been improved.

As described above, compared to conventional information recording media, that is, a method in which pits are formed by melting, evaporation, etc. of a recording thin film, the optical information recording medium according to the present invention records information by changing optical characteristics. Therefore, it is possible to reduce recording power. Furthermore, since information recording does not depend on the formation of pits, non-uniformity in the shape of recording pits can be prevented and high-density recording can be achieved. Also, the second
Layer (2) is composed of a composite material in which a material whose optical properties change mainly by heating is dispersed in a material that has high light absorption and is physically and chemically stable. It can prevent deterioration due to humidity, etc., and has excellent long-term storage stability.

In addition, by creating a matrix structure in which a material with changing optical properties is dispersed in a physically and chemically stable material, stable recording is possible because metal flow is prevented, and reversible reactions are possible. is also possible.

Furthermore, until now, materials whose optical properties could change were limited to materials that had high absorption of irradiated light.11- However, by using materials that have high light absorption and are stable against heating, Since thermal energy can be effectively applied to a material whose optical properties change, the absorption of the material whose optical properties change may be small.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views of an embodiment of an optical information recording medium according to the present invention. a... Substrate a/... Bonded substrate. 1...First layer, 2...Second layer. 6... Adhesive layer. 12- Figure 2

Claims (1)

[Claims] An optical information recording medium in which a second layer and a first layer are sequentially laminated from the write and read sides, and further has a substrate outside at least the second layer or the first layer, The layer is made of a material that exhibits a reflectance of 30% or more when used as a single layer for recording light of a specific wavelength, and the second layer is made of a material that has high light absorption and is stable against heating. An optical information recording medium characterized in that it is mainly composed of a composite material in which a material whose optical properties change upon heating is dispersed, and information is recorded by the change in the optical properties of the second layer.