JPS63299986A - Optical recording medium and recording method using the same - Google Patents

Abstract

PURPOSE:To contrive a higher sensitivity and a simpler construction, by causing a metallic thin film provided on a transparent resin substrate having a minutely rugged surface to comprise a platinum group element and other metallic or semimetallic element and to have a specified crystallinity. CONSTITUTION:A minutely rugged structure at the surface of a transparent resin substrate can be easily obtained by using a metallic mold having a minutely rugged structure at the time of molding the substrate by a molding method, e.g., calendering, injection molding, injection compression molding, compression molding or a photopolymer process (2P-process). A metallic thin film consists of a composition which comprises a platinum group element as an essential constituent and other metallic or semimetallic element as an auxiliary constituent, and has a crystallinity of not more than 60% of the crystallinity of the platinum group element alone. The metallic thin film is preferably a thin film of an amorphous alloy. By lowering the crystallinity of the material constituting the metallic thin film, it is possible to achieve favorable conditions for use as a recording medium, provided with properties such as a higher sensitivity and a higher CNR. The metallic or semimetallic element is preferably, for example, a IVa group element.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an optical recording medium on which information is recorded and reproduced using laser light.

<Prior art> Optical recording media, which record and create information using laser light, have improved due to improvements in basic technologies such as semiconductor lasers, recording materials, and film-forming technology, as well as the ability to record large amounts of information.
Recently, the path to practical application has been rapidly opened. In order to perform recording with laser light, it is necessary to cause some kind of state change in the area irradiated with the laser light, and it is necessary to bring about an optical change as a result of this. A bubble (void) formation method, a bit formation (hole drilling) method, an amorphous-crystalline transition method, etc. have already been proposed.

For example, recording media using the void formation method are
340 and Japanese Patent Application Laid-Open No. 56-127937.

On the other hand, in the case of drilling-type recording media, it is difficult to improve the CNR of the reproduced signal because it is inevitable that some of the recording film will scatter or build up around the holes that are created. It had drawbacks. In addition, in the case of a phase transition type recording medium, since the time required for phase transition is long, the recording speed is slow (and also has the disadvantage that high power is required for recording).

Furthermore, although most of these drawbacks have been eliminated in the void-forming recording medium proposed in Japanese Patent Laid-Open No. 56-127937, it still has the drawback of low recording sensitivity.

On the other hand, the recording medium proposed in JP-A-56-65340 has a light reflecting layer between the substrate and the organic intermediate layer, which improves the efficiency of laser light utilization;
The thicknesses of the energy (light) absorption layer and the intermediate organic layer must be precisely set to predetermined values according to the wavelength of the laser light used. This has the disadvantage that the manufacturing process is complicated and the yield is poor.

Here, an optical recording medium in which a metal thin film is provided on a plastic substrate with a fine uneven structure on the surface has a higher efficiency when compared to a recording medium in which a metal thin film is provided on a plastic substrate with a flat surface. Since it absorbs well, it is possible to record with low power, and it has the feature of simplifying the structure. For example, the technology is disclosed in Japanese Patent Application Laid-open No. 135643/1983. However, it is difficult to reduce the burden on laser light. With the development of multifunctional drives, laser cards, etc., the demand for more sensitive optical recording media has increased.

<Problems to be Solved by the Invention> The purpose of the present invention is to solve the above-mentioned problems as a technical problem, and to provide a void-forming recording medium having a fine uneven structure, using two or more components as a light absorption layer. The present invention aims to provide an optical recording medium which has a sufficiently high recording sensitivity compared to conventional techniques and has a simple structure by using a composition thin film made of a metal or metalloid.

Means for Solving the Problems> The present invention is made by laminating a metal thin film on a transparent resin substrate having a fine uneven structure on its surface, which strongly absorbs laser light in a predetermined wavelength range and absorbs the laser light. In an optical recording medium on which data can be written by forming voids, the metal thin film contains a platinum group element and another metal or metalloid element, and the crystallinity is a platinum group element monometal as an essential component. The optical recording medium is characterized in that the crystallinity is 60% or less of the crystallinity of the optical recording medium.

The basic structure of the recording medium of the present invention is a structure in which a metal thin film is provided on a transparent resin substrate having a fine uneven structure on its surface. The basic structure is described, for example, in U.S. Pat. No. 4,616,23.
It is obtained by the method disclosed in the specification of No. 7 or the specification of JP-A-59-135643.

Any transparent resin can be used as long as it has the property of causing thermal decomposition or thermal deformation in the substrate portion of the metal thin film layer irradiated with the recording laser beam. Examples of these materials include transparent resin materials with excellent transparency such as polyester resin, polyolefin resin, polyamide resin, polycarbonate resin, and polymethacrylic resin. The laser to be used is not particularly limited, but in order to make the drive device compact, a semiconductor laser is preferable, and a laser with a wavelength of 750 to 850 nI is preferable.
11 areas are used. In this case, the recording power is generally in the range of about 1 to 10 mW.

The fine irregularities on the surface of the transparent resin substrate are formed when the substrate is molded by a molding method such as calendaring, injection molding, injection compression molding, compression molding, or photopolymer method (2P method). This fine concave-convex structure, which can be easily obtained by using a molding die, has the property of strongly absorbing laser light in a predetermined wavelength range and facilitating writing with the laser light. The structure generally has a regular period measured transversely to the average surface level that is less than the wavelength of the recording laser beam and a depth of 0.01.
~1 μm, preferably 0.05 to 1 μm. When the lateral period exceeds the wavelength of the laser beam or the depth is less than 0.01 μm, the same level of recording power as a transparent resin substrate with a flat surface is required, and the effect of creating an uneven surface structure is required. is difficult to express. On the other hand, if the depth is greater than 1 μm, it is preferable in terms of efficiently absorbing recording laser light, but it becomes difficult to mold with good reproducibility and in a short time using the above-mentioned molding method.

The metal thin film used in the present invention is a composition (including alloys) containing a platinum group element as an essential component and other metals or metalloid elements as subcomponents, and the crystallinity is a platinum group element as an essential component. A material with a crystallinity lower than that of a single metal is used.

Examples of platinum group elements include platinum, ruthenium, rhodium, palladium, osmium, and iridium, among which platinum is particularly preferred. A metal thin film containing platinum as an essential component is highly malleable, so it is suitable for the recording method (void formation) of the present invention, and it is highly chemically stable and maintains the initial performance of the recording medium over a long period of time. It has the feature of being able to

Furthermore, the metal thin film layer (light absorption layer) used in the present invention is made by adding one or more suitable other metals or semimetals to the platinum group element, which is an essential component, and as a result, the platinum group element monometal, which is an essential component, is a composition with a degree of crystallinity lower than the degree of crystallinity;
Preferably, it is a thin film of an amorphous alloy. That is, by reducing the crystallinity of the material constituting the metal thin film, it is possible to achieve the desirable conditions for a recording medium, such as high sensitivity and high CNR, which are the objectives of the present invention. Although the mechanisms by which these effects occur are not necessarily clear, they are due to temperature effects specific to amorphous metals, such as the phenomenon of significant softening near the glass transition temperature, high ductility, high toughness, or a decrease in elastic modulus. It is assumed that. Furthermore, lowering the crystallinity also has the effect of reducing noise caused by crystal particles, which is advantageous in obtaining a high CNR.

It was also observed that the above effect becomes more pronounced as the degree of crystallinity decreases. A more preferable crystallinity of the metal thin film in the present invention is 30% or less of the crystallinity of the platinum group element single metal, and particularly, it is substantially amorphous.

As the metal or metalloid element added as a bipedal subcomponent, any element can be used as long as it has the ability to significantly reduce the crystallinity of platinum group elements when mixed. For example, IVa in the periodic table can be used. Preferred examples include elements of the group A. They are carbon (C), silicon (S i
), germanium (Ge), tin (Sn) or lead (P
b). Although the mixing ratio of the elements as subcomponents is determined as appropriate, in order to reduce the degree of crystallinity, it is preferable to select a composition near the eutectic point in each phase diagram.

A preferred composition of subcomponents when platinum is selected as the metal is as follows: Si, Ge, and Sn have an atomic percentage of 15
~35%, especially 20-30%. In a composition within this range, these subcomponents tend to form an amorphous structure with platinum.

The thickness of the metal thin film is not particularly limited, but it is preferably set so that the reflectance before recording when laser light is incident from the substrate side is in the range of 5 to 60%.

If it exceeds this range or is too low, tracking will not be sufficient during recording or reproduction, making stable recording difficult. On the other hand, if it is too high, the recording laser beam cannot be absorbed sufficiently, and either no recording is possible or high power is required for recording, which is not preferable. In order for the metal thin film layer to have such a reflectance, there are differences depending on the blended elements, but generally 5.
The film thickness is ~20 Or+m.

It is very difficult to measure the degree of crystallinity in such thin films. However, in recent years, with the development of X-ray diffraction measurement technology, it has become possible to obtain very clear diffraction peaks even from thin film samples of several tens of nanometers. The degree of Note that the degree of crystallinity in a thin film depends on the thickness of the film. Therefore, the crystallinity of the metal thin film and platinum group single metal defined in the present invention is based on values measured at the same film thickness.

Furthermore, in the case of a void-forming recording medium, it has been known for a long time that the film thickness should be made as thin as possible in order to promote high sensitivity. However, if it is too thin beyond a certain range, phenomena such as irregular holes being formed during laser irradiation and voids formed collapsing over time are observed, which has an adverse effect on CNH. However, when a low-crystallinity metal film, more preferably an amorphous thin film, is used as in the present invention, the film hardness increases significantly, and the film thickness can be made thinner while maintaining void strength. .

The metal thin film layer as shown above can be formed by a sputtering method, a vacuum evaporation method, or an ion blasting method, and the film forming method is not particularly limited.

When the optical recording medium manufactured as described above is irradiated with laser light, the fine uneven structure on the surface strongly absorbs the laser light, causing gas generation due to local decomposition of the transparent resin substrate, and permanent deformation of the metal thin film. A permanent record can be made by creating a void that is recognized as a

The recording medium of the present invention can be protected by any protective layer. Further, the shape of the recording medium may be circular, rectangular, etc., or may be disk-shaped, card-shaped, etc.

<Example> The present invention will be explained in more detail with reference to Examples below.

[Example 1, Comparative Example A] Regular period measured in the lateral direction with respect to the average display level is 0.3 μm1 Its depth is Q, thickness 1.2n+n+1 with unevenness of 1 μm, inner diameter 15mn+, outer diameter 130mm
A transparent resin disc made of polycarbonate was molded by injection molding. Next, on this disk, a Pt target support Si
Using a target, the atomic ratio is 7:3 considering the sputtering rate.
A voltage was applied so as to give a thin film with a thickness of 12 nm by sputtering, and an optical recording medium was obtained. When the crystallinity of this film was measured by X-ray diffraction, no diffraction peak was observed, confirming that the metal thin film was amorphous. Furthermore, in this optical recording medium, the reflectance when laser light is incident from the substrate side is 7%.
Since the absorption rate was 56% and sufficient focusing and tracking were performed to enable recording at a wavelength of 830 nm, recording was performed while successively changing the recording power from 1 to lomW and the CNR was measured. The results are shown in Figure 1.

As Comparative Example A, PT was applied to the polycarbonate transparent resin disk having the above-mentioned fine irregularities by a sputter link method.
An optical recording medium was produced by forming a film to a thickness of 12 nm using only TUTAT. This platinum thin film has a 2θ of 39 by X-ray diffraction method.
．． A clear diffraction peak was observed at 5 degrees. As in Example 1, recording was performed while successively changing the recording power, and the CNR was measured. The results are shown in FIG. 1 together with Examples.

As is clear from FIG. 1, in Example 1 based on the present invention, the CNR rises rapidly at low power compared to Comparative Example A, which has a metal thin film layer made only of platinum. Furthermore, high-sensitivity recording was possible.

As an example, electron micrographs are shown in FIG. 2 (Example 1) and FIG. 3 (Comparative Example A) to confirm the shape of bubbles when writing was performed at a recording power of 7 mW. From the diagram reading, the shape of the bubble is clear in the case of the example, and the high CN
It is presumed that the cause of H is attributable to the shape of the bubble.

[Examples 2 to 4, Comparative Example Day] Films were formed with the composition and film thickness shown in Table 1 according to Example 1, except that Sn, C, Ge, and Pd were used as targets instead of Si. An optical recording medium having a predetermined metal thin film layer was obtained. When the same measurements as in Example 1 were carried out on these, it was found that based on the present invention
The same effect as the example shown in the figure was obtained. However, in Comparative Example B, which is not based on the present invention, only the same level of sensitivity as Comparative Example A was obtained.

Table 1 [Reference Example A] A polycarbonate transparent resin disc with a smooth surface and a thickness of 1 mm or 2 mm, an inner diameter of 15 mm, and an outer diameter of 130 mm was molded by injection molding. Next, using a Pt target and an S1 target, a voltage was applied on this disk so that the atomic ratio was 7:3 considering the sputtering rate, a thin film with a thickness of 12 nm was formed by sputtering, and an optical recording medium was formed. I got it. Here, when the crystallinity of this film was measured by the X-ray diffraction method described in the text, no diffraction peak was observed, confirming that the metal thin film was amorphous. In addition, in this optical recording medium, when the laser beam is incident from the substrate side, the reflectance is 12%, the absorption rate is 64%, and the wavelength is 83%.
At 0 nm, focusing and tracking for recording and reacquisition could be performed sufficiently, so recording was performed while successively changing the recording power from 1 to 10 mW, and the CNR was measured. The results are shown in Figure 1. A comparison with Example 1 confirmed that a significant increase in sensitivity was achieved by using a substrate having a fine uneven structure on its surface.

<Effects of the Invention> According to the present invention, in an optical recording medium comprising a metal thin film layer provided on a substrate, the metal thin film layer contains platinum group as an essential component and one or more metals or metalloid elements are added. By using a composition which is formed by the following methods and whose crystallinity is smaller than that of a platinum group single metal, it is possible to obtain an optical recording medium that is chemically stable and capable of high-sensitivity recording.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the relationship between the recording power and CNR measured for the optical recording media obtained in Example 1, Comparative Example A, and Reference Example A, and FIG. 2 and 3 are the recording media of the present invention. 3 is an electron micrograph showing the recording state of a recording medium of a comparative example. Patent applicant: Rira Reclare Plasmon Data Systems KX Company Representative: Patent attorney Ken Honda CNR (dB) g2D laser power (IW) Figure 2

Claims (1)

[Claims] 1) A metal thin film is laminated on a transparent resin substrate having a fine uneven structure on the surface, absorbs laser light in a predetermined wavelength range, and forms voids with the laser light. In an optical recording medium on which data can be written, the metal thin film contains a platinum group element and another metal or metalloid element, and the crystallinity is 60% higher than that of the platinum group element monometal as an essential component. % or less. 2) The transparent resin substrate has regular irregularities such that the regular period measured in a transverse direction with respect to the average surface level is less than the wavelength of the recording laser and the depth is 0.01 to 1 μm. The optical recording medium according to claim 1, having a structure. 3) The optical recording medium according to claim 1, wherein the reflectance before recording when irradiated with laser light from the transparent resin substrate side is in the range of 5 to 60%. 4) The optical recording medium according to claim 1, in which the fine irregularities on the surface of the transparent resin substrate are formed by a plastic duplication method such as a calendering method, injection molding, injection compression molding, compression molding, or a photopolymer method (2P method). 5) The optical recording medium according to claim 1, wherein the platinum group element is platinum, ruthenium, rhodium, palladium, osmium, or iridium. 6) The optical recording medium according to claim 5, wherein the platinum group element is platinum. 7) The optical recording medium according to claim 6, wherein the other metal or metalloid element is carbon, silicon, germanium, tin or lead. 8) The optical recording medium according to claim 7, wherein the metal thin film has a crystallization rate of 30% or less. 9) Claim 7 in which the metal thin film is amorphous
Optical recording medium described in Section 1. 10) The optical recording medium according to any one of claims 1 to 9, wherein the metal thin film has a thickness in the range of 5 nm to 200 nm. 11) The optical recording medium according to claim 1, wherein the metal layer is protected by a protective layer. 12) The optical recording medium according to claim 1, wherein the transparent resin material is a thermoplastic resin. 13) The optical recording medium according to claim 11, wherein the thermoplastic resin is a polyester resin, a polyolefin resin, a polyamide resin, a polycarbonate resin, or a polymethacrylic resin. 14) A recording method using the optical recording medium described above and performing permanent recording by irradiating the transparent resin substrate with a laser beam to generate gas due to local decomposition of the transparent resin substrate and forming voids. 15) A recording medium in which recording is performed by forming a void (bubble) using the above optical recording medium.