JPH02152029A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To raise the reflectance of CD-DRAW medium by constituting the first layer of a material selected from a group consisting of S and Se and the second layer of such a material that reacts with the material of the first layer to give a compound having different reflectance from that of the first layer. CONSTITUTION:The first layer consists of at least one material selected from a group consisting of S and Se. The second layer consists of such a material that reacts with the material of the first layer when irradiated with laser beam to produce a compd. having different reflectance from that of the first layer, namely, at least one metal element selected from a group consisting of Al, Au, Ag, Cu and Cr. These two layers constitute the recording layer of the CD-DRAW medium which is a after-write-type medium and read out with a reproducing device for a read-only medium. By this constitution, the recording layer has high reflectance before recording, and after being irradiated with a laser beam, the reflectance of the irradiated area decreases because the first and second layers chemically react to produce sulfide or selenide or a mixture of those.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to optical information recording media (media) such as optical discs that can record and reproduce information using laser light, and in particular, compact discs (CDs).
The present invention relates to an improvement of an optical information recording medium, such as a CD-DRAW type recording medium, on which recording can be reproduced and also recorded (written) using a reproduction-only optical disk reproducing apparatus called .

Background of the Invention Optical information recording media, such as optical discs and optical cards, use laser light with a diameter of about 1 micron to write and read bit information on a recording layer. They can be roughly divided into three types: dedicated media, write-once type so-called DRAW type media that can be written to and reproduced, and so-called E-DRAW type media that can be written to, erased and reproduced.

Although read-only media are widely used such as compact discs (CDs) or video discs, users cannot of course write information to the read-only media.

On the other hand, write-once recording media that record information by irreversibly changing the characteristics or shape of the recording layer by irradiation with laser light include low melting point metals such as Te and Bi;
Recording materials made of alloys or dispersions of these metals are widely used in still image filing systems and the like. However, this write-once type recording medium cannot be read by the above-mentioned read-only type medium reproducing apparatus. The basic reason for this is that even if the formats of both are the same, the reflectance of the recording layer is different, and the presence or absence of bits cannot be detected by the pickup of the playback device based on the amount of reflected light from the write-once recording medium. be.

However, if write-once media recorded by a write-once media recording device can be read by a playback device for playback-only media, which has a relatively simple structure, the uses of optical media will expand dramatically. In order to meet these needs,
Recently, a system called CD-DRAW, that is,
A method is being researched in which write-once media recorded by a write-once media recording device is read by a playback device for playback-only media.

BACKGROUND OF THE INVENTION This CD-DRAW media is basically the same as conventional write-once media, except that the format and reflectance are changed to those for CDs.

Changing the format can be easily done with a mask ring device, but changing the reflectance requires changing the recording material itself, and in order to obtain a sufficient playback signal with a compact disc player, Reflectance is required.

In addition to the above-mentioned requirements for reflectance, recording materials for CD-DRAW media are also required to have recording/reproducing characteristics that allow recording on a write-once recording device and reproducing on a CD player without deterioration.

However, there is currently no known recording material that satisfies a reflectance of 70 to 90% and has the above-mentioned recording/reproducing characteristics among write-once media. In other words, several CD-DRAW media that can be played back using commercially available compact disc players have already been proposed, but the CD-DRAW media that have been proposed so far have a reflectance of 50%.
Since the servo characteristics are only moderate, sufficient servo characteristics cannot be obtained.

Also, as a write-once (DRAW) type media, it has two recording layers.
It consists of a composite layer of layers, and the first layer is irradiated with a laser beam.
A method is known in which a reaction occurs between the layer and the second layer, thereby changing the reflectance (for example, a combination of 5b-3e/B 1-Te). However, the reflectance of this system is less than 50%.

From the above viewpoint, the present inventors completed the present invention as a result of conducting various experiments to develop a medium that has a high reflectance and is capable of recording information using laser light.

Therefore, an object of the present invention is to provide an improved CD-DRAW medium having a high reflectance and the recording/reproducing characteristics described above.

Means for Solving the Problems The optical information recording medium provided by the present invention is characterized in that the recording layer formed on a substrate is irradiated with a recording laser beam from the substrate side, thereby physically and/or chemically injecting the recording layer into the recording layer. The information is read by recording information by applying a physical and/or chemical change, and detecting the change in reflectance caused by this physical and/or chemical change using a reproducing laser beam incident from the substrate side. An optical information recording medium comprising: a first layer in which the recording layer is formed on a substrate;
It is composed of a composite layer with a second layer formed on the first layer, and the first layer is a thin film composed of at least one material selected from the group consisting of S and Se. The second layer is characterized in that it is a thin film made of a material that reacts with the material of the first layer to form a compound with a different reflectance when irradiated with a laser beam.

The material of the second layer is preferably at least one metal element selected from the group consisting of AI, Au, Ag, Cu, and Cr.

Function The present invention is characterized by having two recording layers, the first layer being a thin film made of Se or S, or a mixture thereof, and the second layer being a thin film made of Se or S or a mixture thereof.
The advantage is that the layer is a thin film composed of a metal element that has a high reflectance and that easily forms sulfides or selenides.

By adopting the above structure of the present invention, the reflectance is high before recording, but the irradiation area where the laser is irradiated has a first reflectance.
The layer and the second layer chemically react to form sulfide or selenide or a mixture thereof, resulting in a decrease in reflectance at the irradiated site. Therefore, this change in reflectance can be used to record information, and by optically detecting it, the information can be read out.

The substrate used in the present invention is generally disk-shaped, but may also be card- or drum-shaped. As the substrate material, a transparent material made of glass, polycarbonate, polymethyl methacrylate, or other plastic is used.

The first layer of S, Se, or a mixture thereof in the present invention can be formed by a physical vapor deposition method such as a vacuum evaporation method or a sputtering method. The thickness of this first layer varies depending on the optical properties of the second layer thin film, but
Generally, the film thickness range for obtaining a good CN ratio and recording sensitivity is 10 to 300, more preferably 30 to 100.
It's a person. If the film thickness is less than 10 Å, sufficient contrast in reflectance cannot be obtained, and if it is more than 300 Å, a large laser writing power is required, making it impossible to write with a semiconductor laser.

AI and Au react with the first layer to form sulfide or selenide by laser irradiation in the present invention.

The second layer made of at least one element selected from Ag, Cu, and Cr can also be formed by a physical vapor deposition method such as a vacuum evaporation method or a sputtering method, similarly to the first layer. The thickness of the second layer varies depending on the materials forming the first and second layers and the thickness of the first layer, but is generally 300 Å to 300 Å.
2000 people, more preferably 500 Å to 200
It is 08. If the film thickness is less than 300 Å, a sufficient reflectance cannot be obtained, and if it exceeds 2,000 people, the heat of the laser is lost through thermal conduction, resulting in a loss of writing power.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

Example 1 Diameter: 130 mm, thickness: 1. 1 by RF sputtering method on a spiral grooved substrate made of hn+n polycarbonate resin.
A Se film was formed to a thickness of 1,000 nm, and then an Ag film was formed to a thickness of 1,000 nm by DC sputtering.

While rotating this disk at 30 rpm, an 830 nm semiconductor laser was used at a position of 90 mm in diameter at a frequency of 750 kHz and a duty ratio (d
uty) A 50% repetition signal was written while changing the laser output, and the CN ratio was measured.

Additionally, the reflectance of this disk was measured with a laser having the same characteristics as used above.

The measurement results of the obtained CN ratio and reflectance are shown in Table 1.

Examples 2-5 The same operations as in Example 1 were repeated. However, Example 2~
In Example 5, after forming the same first layer as in Example 1, Ag
Instead of each metal element (AI, [l'u
, Au, (:r) was deposited to a thickness of 1000.

The same evaluation as in Example 1 was performed on each of the obtained discs. The results are summarized in Table 1.

Example 6 The same operations as in Example 1 were repeated. However, in Example 6, instead of Se in the first layer of Example 1, S was formed into a film with a thickness of 100A using a vacuum evaporation method.

The obtained disc was evaluated in the same manner as in Example 1. The results are shown in Table 1.

Claims (4)

[Claims] (1) Recording information by physically and/or chemically changing the recording layer by irradiating the recording layer formed on the substrate with a recording laser beam from the substrate side;
An optical information recording medium in which the above information is read by detecting a change in reflectance caused by this physical and/or chemical change with a reproduction laser beam incident from the substrate side, In an optical information recording medium in which the layer is constituted by a composite layer of a first layer formed on a substrate and a second layer formed on this first layer, the first layer comprises S and A thin film made of at least one material selected from the group consisting of Se, wherein the second layer is a compound that reacts with the material of the first layer and has a different reflectance when irradiated with a laser beam. An optical information recording medium characterized in that it is a thin film made of a material that forms. (2) The material of the second layer is at least one metal element selected from the group consisting of Al, Au, Ag, Cu, and Cr.
The optical information recording medium described in . (3) The optical information recording medium according to any one of claims 1 to 3, wherein the first layer has a thickness of 10 to 300 Å. (4) The optical information recording medium according to any one of claims 1 to 4, wherein the second layer has a thickness of 300 Å to 2000 Å.