JPH02122985A - Optical recording medium - Google Patents

Abstract

PURPOSE:To contrive higher reflectance and contrast by dispersing a high-reflectance element in a low melting point substance, and setting the concentration of the element higher on the base side on which a recording light is incident. CONSTITUTION:A recording film is provided in which a high-reflectance element having a reflectance for a recording light higher than the reflectance of a low melting point substance having a melting point of 500 deg.C or below is dispersed in the low melting point substance. The high-reflectance element is dispersed with such a concentration gradient that the concentration of the element is high at the surface of a recording film on the side of irradiation with the recording light (ordinarily, the base side), and is lowered along the depth direction of the recording film. As the highreflectance element, an element selected from Au, Ag, Cu, Al, In, Ni, Pt and the like, preferably Au, is used. The low-melting point substance layer is preferably a Te layer or a Te alloy layer comprising at least 10 atom % of Te. The desired concentration gradient may be obtained as follows. For instance, where the recording film is provided by vacuum deposition, a DC power applied to an evaporation source of the high-reflectance element is gradually reduced. Where the recording film is provided by sputtering, an electric power applied to a target of the high-reflectance element is gradually reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an optical recording medium on which information is recorded and reproduced by irradiation with a light beam (for example, a laser beam). In particular, the present invention relates to an optical recording medium in which information is recorded by irradiating a light beam to form pits with a low reflectance on a recording film with a high reflectance.

[Prior Art] Optical recording media that record and reproduce information using laser light have been developed through improvements in basic technologies such as semiconductor lasers, recording materials, and film-forming methods, and Omiya! Due to its ability to record, the path to practical use has been rapidly opened recently. Recording methods for the optical recording medium include (1) deforming the recording film to form bits or bubbles using thermal energy from laser beam irradiation, and (2) modifying optical properties such as reflectance of the recording film. There are ways to change it.

Conventional recording materials for optical recording media include those containing chalcogen-based elements such as Te, Se, and S as main components. For example, Te and Se can be placed on the surface of a plastic substrate.
A recording film containing Pb or the like as a main component is provided, and the recording film is locally melted and removed using a focused laser beam to form pits, thereby recording information, and during reproduction, the pits are removed. An optical recording medium is known that detects the presence or absence of a laser beam based on a difference in the reflected intensity of laser light.

Incidentally, in an optical recording medium using the above recording film made of an alloy containing chalcogen-based elements as a main component, the reflectance is about 40% due to the characteristics of the material. On the other hand, since a high reflectance is required for an optical recording medium that is read by a reproduction device of a reproduction-only optical recording medium such as a conopact disk, it is difficult to use the above-mentioned recording film containing a chalcogen-based element as a main component.

Therefore, in order to obtain an optical recording medium with a high reflectance (50% or more), Japanese Patent Application Laid-Open No. 191332/1983 proposes a method in which the refractive index is higher than the refractive index of the plastic substrate. A technique of interposing a transparent thin film layer has been disclosed.

In addition, optical recording media using recording films containing metals with high reflectivity such as Au and Ag are disclosed in Japanese Patent Application Laid-Open Nos. 194137-1982, 272191-1981, and 502139-1980.
It is shown in the number etc.

[Problem to be solved by the invention] However, in the technology related to JP-A-63-191332,
The material is not particularly limited as long as it satisfies the above conditions, but in order to obtain sufficient effects, the transparent thin film layer needs to be thick enough to form a reflective multi-interference film, and the film thickness cannot be controlled. It was extremely difficult.

The technology described in JP-A-61-194137 is
This is the recording method described in (2) above, in which a metal with a high anti-q ratio is used and a structural change is caused by thermal energy caused by laser beam irradiation. However, the recording method (2) requires a relatively high laser power during recording, and has the problem that the optical contrast is lower than that of the recording method (1) based on shape change. For this reason, although it has been proposed, the membrane structure becomes unsophisticated.

By the way, in mark length recording in which the edges of pits are read as a recording and reproducing method, it is required that the edges of recording pits have good stability (knotter value). However, in the conventional recording method using pit formation,
Since the recording film melts and spreads, the shape of the pit edge is less likely to become uneven, making it possible to obtain a good jitter value. It was difficult to

JP-A No. 61-272191 discloses an optical recording medium having a recording film mainly composed of In, metal sulfides, etc., and further containing metals such as Ag and U at different concentrations on the substrate side and the surface side. It is shown. However, it has been difficult to control the pit shape of this optical recording medium to obtain a good jitter value.

On the other hand, even with the technique disclosed in Japanese Patent Publication No. 59-502139, it is difficult to obtain a good jitter value.
Furthermore, since gelatin is used as a dispersion matrix, it has the disadvantage that the writing characteristics change due to adsorption.

This invention was made in view of the above problem, and information is written by strongly absorbing light in a predetermined wavelength range, deforming and removing the recording film formed on the substrate by the tip, and forming pits. The object of the present invention is to provide an optical recording medium that has high reflectance, high contrast, good recording and reproduction characteristics, and exhibits a good Notter value.

[Means for Solving the Problems] In order to achieve the above object, the optical recording medium of claim (1) of this application includes a layer of a low melting point material having a melting point of 5 [10° C. or less] that is resistant to recording light. A recording film is formed by dispersing a high reflectance element whose reflectance is higher than that of the low melting point substance, and the concentration of the high reflectance element is determined by the concentration of the high reflectance element on the surface of the recording film on the side irradiated with the recording light (usually the substrate...II ) is high and is dispersed with a concentration gradient that decreases toward the depth of the recording film.

Here, the concentration of the high reflectance element is 7 on the substrate side surface.
It is preferable that the number of atoms is 0% or more.

Then, as the film thickness increases from the weir plate side to the recording film surface side, the above concentration decreases rapidly, and the above concentration is O at about 1/2 of the total film force on the recording film surface side. It's good to have one. Note that the concentration in this application refers to ESCA
This is a value obtained as a result of analyzing the composition of the recording film in the depth direction using a method.

The high reflectance elements mentioned above include Au, 8g, Cu, and AI.
, In, Ni, Pt, etc. are used.

The melting point of the low melting point substance is preferably 500°C or less,
If the temperature is higher than that, the writing sensitivity will decrease. Examples of low melting point substances include fluorescent metal layers such as Te5Se, Te5Se, etc.
-Se or an alloy layer of these and Bi, a layer of a polymer compound such as polypropylene, polyethylene terephthalate, etc.

The low melting point substance is preferably a Te-based alloy layer containing 10% or more of Te in terms of atomic percent. A recording film containing Te is preferably used because pits can be easily formed therein. In particular, it is preferable to use an alloy layer consisting of Te and Se as the low-melting point material layer, which contains 60% or more of Te in terms of atomic percent, since high recording sensitivity can be obtained.

The high reflectance element may be the Au element described in claim (3).

The Au element has low adhesion to synthetic resin substrates, etc., and dispersing the Au element is preferable because high recording sensitivity can be obtained.

In the optical recording medium according to claim (4) of this application, an intermediate layer containing fluorocarbon is formed on a substrate, and the recording film is laminated on the intermediate layer. By providing the above-mentioned fluorocarbon intermediate layer, it is possible to achieve uniform recording pit shapes and high sensitivity during recording. The content of F in the fluorocarbon layer obtained from the analysis using the ES CA method is F'/(F+C)XIQO.
It is sufficient if the atomic number percent h<40% or more and 65% or less. If F exceeds this range and is too small, the effect of making the recording pits uniform and increasing the sensitivity during recording will be weakened.On the other hand, if it is too large, the adhesion between the intermediate layer and the recording film will deteriorate and the recording A problem arises in that the film tends to peel off.

In the optical recording medium of the present invention, when the fluorocarbon intermediate layer is provided, the adhesion between the fluorocarbon layer and the recording layer made of a Te-Se alloy in which Au elements are dispersed is low. When you do this, a bubble (
Since the recording layer is made of a low-melting point material, pits are likely to form, so pits are formed that look like the tops of bubbles have been blown off.

In an optical recording medium, the reflectance before recording when a laser beam is incident is usually in the range of 5 to 60%.

If the reflectance is too low, tracking cannot be performed sufficiently during recording and reproduction, making stable recording and reproduction difficult. On the other hand, if it is too high, it will not be able to absorb enough light and recording will not be possible at all, or high power will be required for recording. It is particularly desirable to set the reflectance before recording in the range of 10 to 50%. In order for the recording film layer to have such a reflectance, it generally has a film thickness of 5 to 200 nm, although it varies depending on the element composition.

In the present invention, the method for forming the recording film is not particularly limited, and may be performed by sputtering, vacuum evaporation, or existing film forming methods for ion blating substrates. Then, when forming a film using the vacuum evaporation method, the DC power applied to the evaporation source of the element with a fixed plate q= is gradually reduced, or when using the sputtering method, the power applied to the target of the high reflectance element is gradually reduced. A desired concentration gradient can be obtained by, for example, making the concentration smaller.

Furthermore, the fluorocarbon intermediate layer can be formed using a sputtering method or the like. The appropriate thickness of the fluorocarbon layer is 5 to 1100 nm.

Any substrate can be used as long as it is transparent enough to transmit laser light. For example, glass, polyester resin, polyolefin resin, polyamide resin,
Substrate materials with excellent transparency such as polycarbonate resin and polymethacrylic resin can be used. A recording film may be formed on the transparent substrate or by laminating an intermediate layer, and an arbitrary opaque member may be bonded onto this recording film. Further, an arbitrary transparent protective layer can be formed on the recording film. The shape of the substrate may be circular, rectangular, etc., or may be disk-shaped, card-shaped, etc.

The substrate may have irregularities such as guide grooves for tracking and the like.

Although the wavelength of the laser beam used for recording etc. is not particularly limited, a wavelength of 1oooon+a or less is suitable for use. Therefore, with current semiconductor lasers, the wavelength is 75
Those in the 0 to 850 nm region are effectively used.

In this case, the recording power is generally 1 to 15 my
A range of degrees is used.

[Example code] Hereinafter, the present invention will be explained in more detail with reference to Examples.

(Example 1) Conditions for forming a film consisting of a fluorocarbon intermediate layer and Te-3e on a polycarbonate transparent disk having a group portion as a recording portion and a land portion as a track guide groove are shown below. The inside of the chamber was evacuated to 5×1 CI@Torr, then Ar gas was introduced, and the gas pressure was reduced to 5
It was set to X to 'Toor. The target is polytetrafluoroethylene tercerato, Te. S
An alloy target having a Q + u composition (atomic ratio) and an Au target were used. First, a high m r< tar was applied to the polytetrafluoroethylene target to form a fluorocarbon desert of 2 hm above I7 and f2. Furthermore, when the composition of L fluorocarbon thin film formed under the same conditions was analyzed by ESCA method, l? The fruit-bearing insect is P/(F-C)
F atom 1jl represented by X100 percent is 5
It was 7%. After forming the above fluorocarbon intermediate layer, high frequency power was applied to the Te-Se alloy target, and Au
By applying DC power to each target, Te-S
Au elements were dispersed in the e layer to obtain an f-co recording film (film thickness: 5
0nm). Here, the thin film formed under the conditions of gradually reducing the DC power applied to the Au target was subjected to ESC.
When the concentration distribution of the Au element in the depth direction was measured using the A method, the concentration of the Au element on the substrate side surface was 90 atomic percent, and then the concentration decreased rapidly in the direction of the film thickness. The Au elemental variation was 0% at half the thickness.

The optical disk produced by the above method had a high reflectance, and the reflectance measured from the substrate side using light with a wavelength of 780 nm was 71% at a portion of the disk mirror. EFM change F on the above disk at a linear velocity of 1.4 m/s and a writing power of 9 mW!
When recording, the CNR was 55 dB.

The notter was 25 ns, and very good recording and reproducing characteristics could be obtained. This optical disc could be played on a commercially available CD player. Further, a PET film was attached to the recording film 1 using a urethane adhesive to form a protective layer. Although this optical disk required lomW of writing power, other characteristics did not change in particular. Note that the recording pits of the optical disc of this invention are SE
When observed by M, the top of the bubble was blown off to form a caldera-shaped pit, and the shape of the bit edge was stable (uniform).

By the way, Tea. An optical disc having a recording film with se + 5 pbs (atomic ratio) was created, and E FM modulation recording was performed in the same manner as described above, but the notter value was 60 ns.
This was not as good as that of this example. Also, when the disk surface is observed by SEM, the Vl of the recording pit
, r-nirims created during bit formation were observed around the edges.

(Examples 2 to 4) In Example I, an optical recording medium was prepared by changing the type of low melting material and high reflectance element, or without providing a fluorocarbon layer, and by the same method as in Example 1. Good characteristics were obtained in all examples.

Blank Table below) Effects of the Invention As explained above, the optical recording medium of claim (1) of this application has a high reflectance element dispersed in a low melting point substance and is irradiated with recording light. On the substrate side, since the high reflectance element has a high density, an optical recording medium having high reflectance and high contrast can be obtained.

In the above optical recording medium, the low melting point material layer is
High recording sensitivity can be obtained by using Te or a Te-based alloy as described in 2) and Au as described in claim (3) as the high reflectance element.

Furthermore, when a fluorocarbon intermediate layer is provided as in claim (4), the color of the recording pits becomes uniform, and the knotter value becomes good.

Patent applicant RiRashi Co., Ltd.

Claims (4)

[Claims] (1) In an optical recording medium that has a substrate and a recording film, and records information by deforming the recording film by irradiating the recording film with recording light, the recording film has a melting point of 500°C. A high reflectance element having a higher reflectance to the recording light than the low melting point substance is dispersed in the low melting point material layer, and the concentration of the high reflectance element is lower than the irradiation of the recording light. An optical recording medium characterized in that the surface of the recording film on the side is high and the concentration is distributed with a concentration gradient that decreases toward the depth of the recording film. (2) The optical recording medium according to claim 1, wherein the low melting point material layer is a Te layer or a Te-based alloy layer containing 10% or more of Te in atomic percent. (3) The optical recording medium according to claim 1 or 2, wherein the high reflectance element is an Au element. (4) The optical recording medium according to any one of claims 1 to 3, wherein an intermediate layer containing fluorocarbon is formed on the substrate, and the recording film is laminated on the intermediate layer.