JPH04133791A - Optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a recording layer which is highly moisture-proof and superbly sensitive by specifying the average composition of a recording layer in its film thickness direction to a specific range excepting areas near a substrate side surface and/or its opposite side surface, and increasing the Sb sensity compared to that of the other part of the recording layer. CONSTITUTION:The crystallization of areas near the substrate side surface and/or the opposite side surface of a Sbalpha Sx-AyBz recording layer is made easy by increasing the density of Sb near said areas and the enhancement of recording sensitivity is made possible by increasing a crystallization speed as a whole. The recommended thickness of the surface layer is 10% or lower or 100Angstrom or lower of the whole thickness of the recording layer. The recording layer is formed using vacuum evaporation or sputtering technique. It is recommended that coevaporation based on vapor sources under vacuum condition be performed from a viewpoint of composition control. In sputtering process, an alloy target of specified composition, or a composite target consisting of alloy chips combined in mosaic style at an area proportion complying with each composition can be used. The recommended thickness of the recording layer is 300 to 2000Angstrom .

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical recording medium, and in particular to a phase change type optical recording medium.

[Prior Art] Many types of phase-change optical recording media have been proposed, and many of them have compositions containing Te as a main component.

The oldest one is Te-G in Special Publication No. 47-26897.
Optical recording media of e type, As-T e-G e type, and Te-0 type are disclosed.

Optical recording using phase change does not involve deformation of the recording film, so it has the advantage of being able to produce double-sided discs made by directly bonding two discs together, or single-disc discs in which a protective layer is provided directly on the recording film. Taking a single-plate disk as an example, the layer structure of the disk is as shown in Figure 1, with a dielectric layer on the substrate,
It has become common to have a structure in which a recording layer and a dielectric layer are sequentially laminated. This is to prevent the recording layer from deforming due to repeated recording and erasing by sandwiching the recording layer between strong dielectric materials. Since this dielectric layer also serves as a moisture prevention layer, the disk also has good moisture resistance.

By the way, among the reversible phase changes between amorphous and crystal,
Since the change from the amorphous phase to the crystalline phase is highly sensitive, it is possible to create a high-sensitivity write-once disk by utilizing only this change. In this case, there is no need for dielectric sandwiching, and in order to create a low-cost write-once disk, for example, the second
As shown in the figure, a configuration in which a recording layer is provided directly on a resin molded substrate is desirable. In this case, since there is no moisture prevention layer, the moisture resistance of the recording layer itself is important.

Now, many of the various phase change materials that have been proposed so far have Te as a main component. Te has a large absorption in the semiconductor laser wavelength range, and an amorphous phase is easily formed, so it is suitable for a phase change recording material. However, since the crystallization temperature of Te alone is too low, it becomes an amorphous phase or is unstable at room temperature. Therefore, combinations with various elements have been attempted, and materials with very excellent recording and reproducing properties have been obtained (Japanese Patent Laid-Open No. 63225934). However, Te
Because of its poor moisture resistance, although a disk configuration as shown in FIG. 1 can be used, there is a problem in that reliability cannot be ensured with a low-cost configuration as shown in FIG.

In order to solve these problems, the present inventors have already proposed a phase change optical recording material that is mainly composed of Sb and Cu and has excellent moisture resistance. This material also has excellent recording sensitivity,
Linear speed 11 Jm/see.

Sufficient recording is possible under the conditions of a recording power of 5a+W and a recording signal frequency of 3.7 MHz. However, for example, video recording requires a linear velocity of 20 m/sec or more and a recording signal frequency of 10 m/sec.
Considering that high output semiconductor lasers corresponding to MHz are required and are expensive, it is necessary to further increase the sensitivity of the recording medium.

[Problem to be solved by the invention] The present invention is based on Sb Cuα, which has excellent moisture resistance, as disclosed in the earlier application.
The object of the present invention is to improve the X AB type recording medium and improve the z degree of the recording layer.

[Means for Solving the Problems] Similar to Te, Sb has large absorption in the semiconductor laser wavelength range, and an amorphous phase is easily formed. However, when used alone, the amorphous phase is unstable and crystallization easily occurs. Therefore, it is necessary to stabilize the amorphous phase by adding elements. As a result of various studies taking these matters into consideration, we came up with the invention of the Sb S A B based recording α x y z material of the previous application. Similar to the previous application, the present invention is also based on the premise that a so-called as-depo amorphous phase is left in an unrecorded state and recording marks of a crystalline phase are formed by laser beam irradiation.

The crystallization process can be broadly divided into a crystal nucleation process and a crystal growth process. Naturally, nucleation is followed by crystal growth. If crystal nuclei are generated in a part of the recording layer earlier than originally expected, crystal growth will be accelerated accordingly, making crystallization easier as a whole.

The Sb S A B system of the previous application has sufficient amorphous stabilization to the extent that nucleation does not occur under normal storage conditions α XYZ , but if the Sb concentration is increased, the amorphous becomes unstable. become. In other words, it becomes easier to crystallize.

Therefore, the present inventors investigated Sb S A B near the substrate side interface of the recording layer α x y z and/or near the interface on the opposite side.
Increasing the concentration of b facilitates crystallization of that portion and increases the crystallization speed of the recording layer as a whole, thereby making it possible to improve recording sensitivity.

That is, the structure of the present invention is an optical recording medium as described in the claims.

For convenience, the portion near the interface will be referred to as an interface layer, and the thickness of the interface layer is preferably 10% or less of the total thickness of the recording layer and 100 Å or less. Due to this thinness, the influence of the interface layer on the optical properties (reflectance, transmittance) of the recording layer can be ignored regardless of whether the interface layer is crystallized or not. Therefore, the interfacial layer may crystallize under normal storage conditions or may be in an amorphous phase or unstable to the extent that it is already crystallized due to the softness of the as-depo. The crystal grains in the interface layer serve as crystallization nuclei for the amorphous phase in other parts of the recording layer. Since the amorphous phase in areas other than the interface layer is sufficiently stabilized, crystal growth does not occur unless irradiated with laser light, and storage stability is sufficiently ensured.

The recording layer can be formed by vacuum deposition, sputtering, or the like. In vacuum deposition, co-deposition from a plurality of sources is desirable from the viewpoint of composition control. Further, in sputtering, an alloy target having a desired composition may be used, or a composite target may be used in which chips of each element are combined in a mosaic shape at an area ratio according to each composition. The thickness of the recording layer is 100 to 3000K, preferably 300 to 2000K. Formation of the interface layer is possible by controlling the deposition rate of each element in vacuum evaporation, but in the case of sputtering, Sb? It is practical to prepare a separate target with a high degree of a to form the interfacial layer.

As the substrate material, transparent resin such as polycarbonate, PMMA, polyolefin, epoxy, or glass can be used. Guide grooves for tracking, guide bits, and preformats such as address signals may be formed on the surface of the substrate.

A protective layer can be appropriately provided on the recording layer, and examples of the material include 5iO1Si02, TiO2, Si3N4.
, inorganic compounds such as ZnS, polycarbonate, acrylic, polyamide, epoxy, polyolefin, and other resin materials can be used. Acrylic and epoxy ultraviolet curing resins are also suitable examples of materials. Each of the above materials may be used alone, or a plurality of them may be mixed or stacked. The thickness of the protective layer is not particularly limited, and may be appropriately selected depending on the purpose, such as increasing the thickness if scratch resistance is important.

Furthermore, it goes without saying that an undercoat layer may be provided between the substrate and the recording layer if necessary.

[Example] Hereinafter, the present invention will be specifically explained with reference to Examples.

Example 1 First, an Sb layer was formed as an interfacial layer to a thickness of about 80 mm by vacuum evaporation on a polycarbonate injection molded substrate with a tracking guide groove, and then 5t) yos +
A recording layer of sSn+5 was provided to a thickness of about 1i00 L. Further, an epoxy ultraviolet curable resin protective layer having a thickness of about 5 μm was provided thereon to prepare a recording medium.

Attach this medium to an optical disk tester and use a laser beam with a wavelength of 7
80rv, N, A, 0.5 linear velocity 20m/sec.

Recording signal frequency: 10 MHz, recording optical power: 7 mW.

Recording and reproduction were performed under the conditions of reproduction optical power 0.5a+W, and the C
/N (bandwidth 30kHz) was measured.

Furthermore, after storing this medium in an environment of 60° C. and 90% RH for 30 days, the C/N was measured again under the above conditions.

Example 2 An optical recording medium was produced under the same conditions as in Example 1 except that S b 90 Sn 1a was used as the interface layer, and a test was conducted under the same conditions.

Example 3 An optical recording medium was produced under the same conditions as in Example 1, except that Sbgos 5 St+5 was used as the interface layer, and tested under the same conditions.

Example 4 Sb6. An optical recording medium was produced under the same conditions as in Example 1, except that S +2Sn+2AU++ and 5bs5Aυ15 were used as the interface layer, and tested under the same conditions.

Comparative Example 1 No interface layer was provided in Example 1, and 5b7oS+5Sn
++; Optical recording medium with approximately 900 recording layers.

Comparative Example 2 No interface layer was provided in Example 4, and 5b6sS +23
An optical recording medium with approximately 900 n12AIJ+1 recording layers.

The test results for each of the above Examples and Comparative Examples are shown in Table 1 below.

Table 1 [Effects of the Invention] As explained above, the recording layer of the present invention has excellent moisture resistance,
Moreover, it is highly sensitive.

[Brief explanation of drawings]

FIGS. 1 and 2 are schematic cross-sectional views showing the structure of a specific example of a phase-change optical recording medium. 1.3... Dielectric layer, 2... Recording layer, 4... Substrate, 5... Ultraviolet curing resin layer.

Claims (1)

[Claims] (1) Average composition in the film thickness direction of the recording layer (atomic %) excluding the vicinity of the interface on the substrate side of the recording layer and/or the vicinity of the interface on the opposite side
is represented by the following general formula, and the concentration of Sb near the substrate-side interface and/or near the interface on the opposite side thereof is higher than in other parts of the recording layer. General formula Sb_αS_xA_yB_z However, 60≦α≦90 5≦x≦30 5≦y≦30 0≦z≦20 α+x+y+z=100 A: Any element selected from group IIb or group IVb elements, B: IVa, Va, Group VIa elements and platinum group elements (Ru,
represents any element selected from Rh, Pd, Os, Ir, Pt), Ag, and Au.