JPH0240143A - Information recording medium - Google Patents

Abstract

PURPOSE:To improve sensitivity of the recording medium and to reduce jitters by providing an interlayer between the recording layer and the substrate, the interlayer comprising island-like areas of metal having high surface tension in a specific temperature range and areas enclosing the islands, essentially comprising metal of low melting point. CONSTITUTION:The recording medium has the recording layer 3 in which informations can be written/read by laser beam, provided on the substrate 1 through the interlayer 2. The interlayer 2 consists of island-like areas 4 which are continuous in the depth direction but discrete in the plane and the areas 5 enclosing the islands. The island-like area contains such a metal having high surface tension of >=600dyn/cm at a temperature range from the melting point to 300 deg.C higher than that. The inter-island area contains metal of low melting point at <=600 deg.C. In this structure, thermal energy due to laser irradiation is diffused in the plane, which reduces largely the thermal loss. Thus, sensitivity of the medium is improved and jitters can be reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of the Invention] The present invention relates to an information recording medium on which information can be written and/or read using a high energy density laser beam.

[Technical Background of the Invention] In recent years, information recording media that use high energy density beams such as laser light have been developed and put into practical use. This information recording medium is called an optical disk, and can be used as a video disk, an audio disk, a large-capacity still image file, and a large-capacity computer disk memory.

The basic structure of an optical disk is a disc-shaped transparent substrate made of plastic, glass, etc., and a Bi
, a recording layer made of metal or semimetal such as Sn, In, Te, etc. Note that the surface of the substrate on which the recording layer is provided is usually coated with an undercoat layer or an undercoat layer made of a polymeric material in order to improve the flatness of the substrate, improve the adhesion with the recording layer, or improve the sensitivity of the optical disc. An intermediate layer is provided.

Information is written on an optical disk by, for example, irradiating the optical disk with a laser beam.
The irradiated portion of the recording layer absorbs the light and locally increases in temperature, resulting in a physical or chemical change that changes its optical properties, thereby recording information. Information is also read from an optical disk by irradiating the optical disk with a laser beam, and the information is reproduced by detecting reflected or transmitted light depending on changes in the optical characteristics of the recording layer.

Recently, as a disk structure for protecting the recording layer, a recording layer is provided on at least one of the two disk-shaped substrates, and the recording layer is located inside the two disk-shaped substrates. Also, an air sandwich structure has been proposed in which a ring-shaped inner spacer and a ring-shaped outer spacer are joined to form a space. In optical discs with such a structure, the recording layer is not in direct contact with the outside air, and information is recorded and reproduced using laser light that passes through the substrate, so the recording layer is generally not susceptible to physical or chemical damage. There is no possibility that the recording or reproducing of information will be hindered by dust or dirt adhering to the surface.

Information recording media are extremely useful in various fields as described above, but it is desired that their recording sensitivity be as high as possible. It is also desired that the recorded information be read with as high precision as possible.

Conventionally, for the purpose of improving recording sensitivity or reading accuracy, a layer made of a mixture of metal and GeS (Japanese Patent Publication No. 58-33120
A layer made of a mixture of a metal and a metal fluoride such as MgF2 and a metal oxide such as MoO2 (Japanese Patent Publication No. 58-15319) is known. In addition, as a recording layer consisting of two layers, a lamination of a metallic thin layer and a non-metallic thin layer consisting of a PbO1 metal fluoride or an In-Ge-5 based lucogen compound (Japanese Patent Publication No. 5934519), a metallic thin layer, etc. Lamination of metal or non-metallic thin layers consisting of combinations of various recording materials
No. 2) is known. The lower metallic thin layer is mainly made of a single metal, or if a plurality of metals are used, it is an alloy thin layer.

However, in such a recording layer, pits may not be sufficiently formed on the recording layer even if laser light is irradiated during recording of information. This is because, although the output of the laser beam itself is sufficient to melt the recording layer, pits are difficult to open in the melted recording layer material, and the material remains solidified in the same position. For this reason, it was necessary to increase the output of the laser beam, and it was difficult to say that the sensitivity of the recording medium was sufficiently high. Further, the presence of such unformed or incomplete pits increases jitter and causes errors when reading information.

[Object of the Invention] Another object of the present invention is to provide an information recording medium with high recording sensitivity and low jitter.

Another object of the present invention is to provide an information recording medium with a high C/N during reproduction and with reduced reading errors.

[Summary of the Invention] The present invention provides an information recording medium in which a recording layer in which information can be written and/or read by a laser via an intermediate layer is provided on a substrate. It consists of island-shaped parts that are continuous in the plane and discontinuous in the plane direction, and gaps between the islands, and the island-shaped parts have a melting point of 600 d within a temperature range of 300°C higher than the melting point.
The information recording medium contains a metal having a surface tension of yn/am or more, and the gaps between the islands are filled with a metal containing a low melting point metal having a melting point of 600° C. or less.

Incidentally, the term "island-like" in the present invention does not mean a specific shape, but means that the parts corresponding to each island-like part are mutually independent and in a discontinuous relationship. Therefore, the island portion can take any shape.

Further, the intermediate layer of the present invention plays the role of a recording layer,
Pits formed when information is recorded are formed not only in the recording layer but also in the intermediate layer.

2. Preferred embodiments of the information recording medium of the present invention are as follows.

1 The average base area of the island-shaped portion is 103 to 107
2. Information recording medium according to claim 2, characterized in that it falls within the scope of 2.

2. The information recording medium according to claim 1, wherein the average distance of the gaps between the islands is within the range of 1 to 200.

3゜The metal having a surface tension of 600 dyn/c++ or more is Ag, AfL, Cd, Cu, Ge, Au, M
The information recording medium according to claim 1, wherein the information recording medium is made of at least one metal selected from n, Pd, Pb and Zn.

4. The information recording medium according to claim 1, wherein the metal having a surface tension of 600 dyn/c or more is Au.

5. The information recording medium as claimed in claim 2, wherein the low melting point metal is at least one metal selected from In, Te, Sn, Pb and Bi.

6゜The 600 dyn/cm contained in the above intermediate layer
The content ratio of the metal having the above surface tension and the low melting point metal is 99.9:0.1 to 60.0740.0 by weight.
The above-mentioned information recording medium as claimed in the claims is characterized in that it falls within the scope of.

7. The information recording medium according to claim 1, wherein the intermediate layer has a layer thickness in a range of 50 to 300X.

8. The information recording medium, wherein the recording layer contains a low melting point metal and at least one metal compound selected from metal sulfides, metal fluorides, and metal oxides.

9. The information recording medium according to claim 5, wherein the recording layer is made of a mixture of In and GeS.

10. The information recording medium according to claim 1, wherein the thickness of the recording layer is within a range of 300 to 1000.

[Effects of the Invention] As a result of further research on information recording media, the present inventor found that metals having a surface tension of 600 dyn/cm or more (hereinafter referred to as high surface tension The sensitivity of the recording medium is increased by providing an intermediate layer between the substrate and the recording layer, which consists of island-like parts made of (also called metal) and gaps between the islands filled mainly with a low-melting point metal. , and that the jitter can be reduced, leading to the present invention.

In other words, in the present invention, the intermediate layer in contact with the substrate side (or the undercoat layer, if there is an undercoat layer) is not a uniform thin layer of metal like in the past, but an island-like layer as shown in the figure. The gap between the formed metals with high surface tension is filled with a metal having a low melting point in the form of streaks.

Because this metal with high surface tension exists discontinuously in the form of islands on the substrate side, it is recorded in a mixed state with other recording materials, rather than as a continuous layer layered in parallel in the surface direction. It is possible to significantly reduce heat loss due to the diffusion of thermal energy in the surface direction due to laser beam irradiation, compared to the presence in the layer. This further enhances the effect of facilitating pit formation due to the high surface tension of the high surface tension metal, and allows well-shaped pits to be easily formed in the recording layer and intermediate layer with low laser output. Therefore, jitter can also be reduced.

[Detailed Description of the Invention] The information recording medium of the present invention can be manufactured, for example, by the following method.

The substrate used in the present invention can be arbitrarily selected from various materials used as substrates for conventional information recording media. Optical properties, flatness, processability of the substrate,
In terms of ease of handling, stability over time, and manufacturing cost,
Examples of substrate materials include glass such as soda lime glass; acrylic resins such as cell cast polymethyl methacrylate and injection molded polymethyl methacrylate; vinyl chloride resins such as polyvinyl chloride and vinyl chloride copolymers; epoxy resins; and polycarbonate. can be mentioned.

Among these, polymethyl methacrylate, polycarbonate, epoxy resin, and glass are preferred from the viewpoint of dimensional stability, transparency, and flatness.

The surface of the substrate on which the recording layer is provided has improved flatness,
An undercoat layer may be provided for the purpose of improving adhesive strength and preventing deterioration of the recording layer. Examples of materials for the undercoat layer include polymethyl methacrylate, acrylic acid/methacrylic acid copolymer, nitrocellulose, polyethylene,
Polymer substances such as polypropylene and polycarbonate; organic substances such as silane coupling agents; and inorganic oxides (Si02, A, 03, etc.), inorganic fluorides (MgF2)
Inorganic substances such as

When the substrate material is glass, in order to prevent adverse effects on the recording layer due to alkali metal ions and alkaline earth metal ions liberated from the substrate, wood-philic groups such as styrene/maleic anhydride copolymer and/or Preferably, a subbing layer consisting of a polymer having maleic anhydride groups is provided.

The undercoat layer can be formed by, for example, dissolving or dispersing the above-mentioned substance in a suitable solvent, and then applying this coating solution to the substrate surface by a coating method such as spin cording, dip coating, or extrusion coating.

Alternatively, a pre-groove layer or a pre-pit layer may be provided on the substrate (or undercoat layer) for the purpose of forming tracking grooves or unevenness representing information such as address signals. As a material for the pregroove layer, etc., a mixture of at least one monomer (or oligomer) of acrylic acid monoester, diester, triester, and tetraester and a photopolymerization initiator can be used.

The pre-groove layer is formed by first coating a mixture of the above acrylic ester and polymerization initiator on a precisely made matrix (stamper), then placing the substrate on top of this coating solution layer. The liquid layer is cured by irradiation with ultraviolet rays through the substrate 1 or the matrix, thereby fixing the substrate and the liquid phase. Next, by peeling the substrate from the mother mold, a substrate provided with a pregroove layer is obtained. The layer thickness of the pre-groove layer etc. is generally 0.05
~100 lm, preferably 0.1~50 lm
It is within the range of 7zm. Furthermore, when the substrate material is plastic, pregrooves or prepits may be provided directly on the substrate by injection molding, extrusion molding, or the like.

Next, on the substrate (or undercoat layer or pregroove layer), or if a pregroove etc. is provided directly on the substrate, an intermediate layer, which is a characteristic requirement of the present invention, is provided on the pregroove etc. directly on the substrate. provided.

The intermediate layer of the present invention is composed of island-shaped portions that are continuous in the depth direction and discontinuous in the surface direction, and gaps between the islands, and the island-shaped portions have a melting point that is 300° C. higher than the melting point. Contains a metal with a surface tension of 600 dyn/cm or more within a temperature range (metal with high surface tension), and the gap between the islands is filled with a metal containing a low melting point metal with a melting point of 600 ° C or less It is a layer.

The average base area of the island-like parts is within the range of 10' to 107 or 2, and the average distance between the gaps between these islands is 1.
It is preferably within the range of ~200X.

The structure of the intermediate layer is obtained by co-evaporation of the high surface tension metal and the low melting point metal. 600°C within the range of the above melting point and a temperature 300°C higher than the melting point.
Examples of metals having a surface tension of dyn/ctm or higher include Ag, A, Cd, Co, Cu, Ge, Ga, M
o, Ni, St, V, Au, Be, Cr, Fe, Mn,
Mention may be made of Nb, Pt, Pd, Rh, Pb, Ti and Zn. Preferably Ag, A-texture, Cd, Cu
, Ge, Au, Mn, Pd, Pb and Zn, more preferably An, Au and Zn. And the most preferred is Au.

The preferred low melting point metals include In, Te, Sn,
Examples include Pb and Bi. During co-evaporation, the metals with high surface tension have relatively high melting points, so there is almost no melt mixing with the metals with low melting points. The metal with a high melting point forms an island shape, and the metal with a low melting point fills the gap to form the intermediate layer. However, depending on the deposition conditions for codeposition, melt mixing of a metal with high surface tension and a metal with a low melting point may occur, albeit in a small amount, and it is better to mix the metal with a small amount to increase the melting point of the entire intermediate layer. Easy to go down. However, if the mixing amount is too large, the characteristic of the present invention, which is easy formation of pits, will be lost.

The content ratio of the metal having a surface tension of 600 dyn/cm or more within a temperature range 300° C. higher than the melting point and the low melting point metal contained in the intermediate layer mentioned above is 99.9:0 by weight. It is preferably within the range of 1 to 60.0:40.0, particularly preferably 99.9:0.1 to 8.
It is within the range of 5.0:15.0. The thickness of the intermediate layer is preferably within the range of 50 to 300X.

The shape of the intermediate layer will be explained with reference to FIGS. 1 and 2 of the accompanying drawings.

FIG. 1 is a partial cross-sectional view showing an example of the structure of an information recording medium of the present invention in which a substrate 1, an intermediate layer 2, and a recording layer 3 are laminated in this order. The intermediate layer 2 is made up of an island-like portion 4 containing a metal with high surface tension and a gap portion 5 containing a low-melting point metal filling the island-like portion 4 therebetween.

Further, FIG. 2 is a plan view showing an example of the island-shaped portion 4 of the intermediate layer and the gap portion 5 in the cut plane when the intermediate layer is cut parallel to the surface direction.

That is, in the present invention, the intermediate layer in contact with the substrate side (or the undercoat layer, if there is an undercoat layer) is not a uniform thin layer of metal as in the conventional case, but is formed in the form of an island as described above. The gap between the high surface tension metal is filled with a low melting point metal in the form of a stripe.

Since this metal with high surface tension exists discontinuously in the form of islands on the substrate side, it is recorded in a mixed state with other recording materials, rather than in a continuous layer stacked parallel to the surface direction. It is possible to significantly reduce heat loss due to the diffusion of thermal energy in the surface direction due to laser beam irradiation, compared to the presence in the layer. This further enhances the effect of facilitating pit formation due to the high surface tension of this high surface tension metal, making it possible to easily form well-shaped pits in the recording layer and intermediate layer with low laser power. Therefore, jitter can also be reduced.

The intermediate layer of the present invention has a form in which the interstices of the island-shaped metal with high surface tension are filled in stripes with a low-melting point metal, and the island-like portions are made of a metal with high surface tension. It is thought that it also contains a small amount of low melting point metal, and it is thought that the gap portion also contains a small amount of metal with high surface tension in addition to the low melting point metal. Therefore, the distribution state of such metals is also
Since the melting point of the entire intermediate layer is lowered, it is presumed that this contributes to the above-mentioned improvement in sensitivity.

In addition to these advantages, when manufacturing information recording media,
Since the reflectance of the substrate can be arbitrarily adjusted by changing the layer thickness of the intermediate layer, it is also easy to adjust the reflectance of laser light during reading.

The intermediate layer is formed of the material on the substrate by a method such as vapor deposition, sputtering, or ion blasting. The area of the island-shaped portions containing the metal with high surface tension forming the intermediate layer and the gap distance between the islands filled with the low-melting point metal can be controlled using the metal with high surface tension and the low-melting point metal as the evaporation material. This can be done by changing the mixing ratio with the metal, the substrate temperature, the degree of vacuum, the metal vapor deposition rate, etc. during the vapor deposition process. The mixing ratio of the metal with high surface tension and the metal with low melting point is 99.9:0 by weight as described above.
．． It is preferably within the range of 1 to 60.0:40.0, particularly preferably 99.920.1 to 85.0:15.
．． It is within the range of 0.

Also, the degree of vacuum is IXI O-3~IX10-6T
orr(7) range is preferred, particularly preferably I
It is in the range of 10-' to 1×10-5 Torr. Further, the deposition rate is preferably in the range of 0.1 to 10X/sec.

Materials for the recording layer include In, Te, Sn, Pb, and Bi.
Low melting point metals such as

The recording layer materials used in combination with the above metals include CrS, Cr25. Cr253. MoS2,
MnS, FeS, FeS2, CoS, Co25. ,,N
iS, Ni2S, PbS, Cu2S
, Ag 2S, ZnS, In2si, In252, G
e S x (0, 5<X≦2.0), SnS, 5n
Metal sulfides such as S2, As, , S3.5b2S, and Bi2S3; MgF2. Metal fluorides and M such as CaF2 and RhF3.

Mention may be made of metal oxides such as O2, In2O, In2O3, GeO and PbO. Preferably, it is a mixture of a low melting point metal and at least one metal compound selected from metal sulfides, metal fluorides, and metal oxides.

Particularly preferred is the case where the recording layer material is a combination of In and GeS.

The content of low melting point metal in the recording layer is generally 20 to 9
9% by weight, preferably in the range of 50-80% by weight. Further, the content of metal compounds such as metal sulfides, metal fluorides, and metal oxides is generally in the range of 1 to 80% by weight, preferably 20 to 50% by weight.

The recording layer is formed on the substrate using the above-mentioned materials by a method such as vapor deposition, sputtering, or ion blasting.

The recording layer may be a single layer or a multilayer, but its layer thickness is generally from 300 to 15 mm in terms of optical density required for optical information recording.
00X, preferably 300-1000X.

Note that the surface of the substrate opposite to the side on which the recording layer is provided is coated with an inorganic substance such as silicon dioxide, tin oxide, or magnesium fluoride in order to improve scratch resistance and moisture resistance.
A thin film made of a polymeric substance such as a thermoplastic resin or a photocurable resin may be provided by a method such as vacuum deposition, sputtering, or coating.

In this way, an information recording medium having a basic configuration in which the substrate and the recording layer are laminated in this order can be manufactured.

Note that a bonded type recording medium can be manufactured by bonding two substrates having the above structure using an adhesive or the like.

Furthermore, an air sandwich type recording medium can be manufactured by joining two disk-shaped substrates, at least one of which has the above configuration, via a ring-shaped outer spacer and an inner spacer. can.

Next, Examples and Comparative Examples of the present invention will be described.

[Example 1] Au and Pb were deposited on a disc-shaped polycarbonate substrate (outer diameter: 130 mm, inner diameter: 15 mm, thickness: 1, 2 mm) at a substrate temperature of 40°C, a deposition rate of 4X/sec, and a vacuum degree of 1O- Co-evaporation was carried out under the condition of 5 Torr, and Au and P were
b formed an intermediate layer with a weight ratio of 90:10. In the obtained intermediate layer, the average base area of the island-like portions 4 shown in FIGS. 1 and 2 was 10'λ2, and the average distance of MH5 of the island-like portions was 50. On the intermediate layer, Further, In and GeS were co-deposited under the same conditions as above to form a recording layer consisting of In and GeS at 60%
It was formed with a layer thickness of 0. At this time, the weight ratio of In and GeS in the recording layer was 66.7=33.3.

In this way, an information recording medium consisting of a substrate, an intermediate layer, and a recording layer was manufactured in this order.

[Example 2J The same procedure as in Example 1 was carried out except that the recording layer materials in Example 1 were changed to Te and Se, and the composition of Te and Se in the obtained recording layer was 80:20 by weight. An information recording medium was manufactured.

Comparative Example 11 An information recording medium was manufactured in the same manner as in Example I except that the intermediate layer material was changed to only Au.

[Comparative Example 2] An information recording medium was manufactured in the same manner as in Example 2 except that the intermediate layer material was changed to only Au.

[Evaluation of information recording media] (1) For each information recording medium obtained in the sensitivity test,
Binary information was recorded at a linear velocity of 1.3 m/sec, and the laser output at which the ratio of the output level of carrier to noise (C/N ratio) was maximized was measured.

(2) The information recording medium on which the jitter information was recorded was played back on a commercially available CD player (manufactured by YAMAHA ■). The time from rise to fall and time from fall to rise of a binary signal, such as a reproduced signal, was measured many times for each signal length, and the standard deviation thereof was determined.

The results obtained are shown in Table 1.

Table 1 Sensitivity (mW) Jitter (ns) Example 1 Example 2 Comparative Example 1 13 28 Comparative Example 2
11 31 As is clear from the results shown in Table 1, the information recording medium of the present invention (Examples 1 and 2)
) was able to obtain a high C/N ratio with low recording power and had excellent recording sensitivity. Additionally, the jitter value was extremely small, reducing reading errors.

On the other hand, information recording media for comparison (Comparative Examples 1 and 2)
required high recording power and had poor recording sensitivity. Furthermore, the jitter value is large, and reading errors are likely to occur.

[Brief explanation of the drawing]

FIG. 1 is a partial cross-sectional view showing an example of the configuration of an information recording medium of the present invention. FIG. 2 is a plan view showing an example of the island-like structure of the intermediate layer of the present invention. l2 Substrate 2: Intermediate layer 3: Recording layer 4: Island-shaped portion containing Au

Claims (1)

[Claims] 1. An information recording medium in which a recording layer on which information can be written and/or read by a laser is provided on a substrate via an intermediate layer, wherein the intermediate layer is continuous in the depth direction and discontinuous in the surface direction. 600 dyn/cm within the range of the melting point and a temperature 300°C higher than the melting point.
What is claimed is: 1. An information recording medium comprising a metal having a surface tension of 600° C. or more, and wherein the gaps between the islands are filled with a metal containing a low melting point metal having a melting point of 600° C. or lower.