JPH08180459A - Optical information recording medium - Google Patents

Abstract

PURPOSE: To obtain an optical recording medium with which many times of repetitive recording and erasing are possible by constituting a dielectric layer of a mixture composed of respective specific contents of a chalcogen compd., zinc oxide and magnesium fluoride or calcium fluoride. CONSTITUTION: Powders of ZnS, ZnO and MgF2 are adjusted and mixed to 20 to 20 to 60 by mol ratio as a dielectric layer material and are molded by a hot press method to obtain a composite sintered target. A four-layered structure consisting of a dielectric layer/recording layer/dielectric layer/reflection layer respectively having prescribed thickness is formed on a polycarbonate resin substrate. At this time, the dielectric layer is formed to have the film density of >=80 deg. of the theoretical density by high-frequency sputtering. Many times of repetitive recording and erasing are executable by forming the optical recording medium in such a manner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical information recording medium capable of recording, erasing and reproducing information at high speed and high density by irradiation with laser light or the like.

[0002]

2. Description of the Related Art In recent years, an optical disk using a laser beam has been developed as a recording medium that meets the demands for increasing the amount of information and increasing the recording and reproducing density and speed. Optical disks are classified into a write-once type that allows recording only once and a rewritable type that allows recording / erasing as many times as desired.

Examples of the rewritable optical disk include a magneto-optical recording medium utilizing a magneto-optical effect and a phase change medium utilizing a reversible change in crystal state. The phase change medium is
Recording / erasing is possible by changing the power of the laser beam without the need for an external magnetic field. Further, there is an advantage that it is possible to perform one-beam overwriting in which erasing and re-recording are simultaneously performed with a single beam.

In the one-beam overwritable phase change recording method, it is general that the recording film is made amorphous to form a recording bit and is crystallized to erase. A chalcogen-based alloy thin film is often used as a recording layer material used in such a phase change recording method.

For example, Ge-Te system, Ge-Te-Sb
System, In-Sb-Te system, Ge-Sn-Te system alloy thin film, and the like. A write-once type phase change medium can be realized by using almost the same material and layer structure as the rewritable type. In this case, since there is no reversibility, information can be recorded and stored for a longer period of time, and in principle, it can be stored almost permanently.

When the phase change medium is used as the write-once type, unlike the perforated type, a bulge called a rim does not occur around the bit, so that the signal quality is excellent, and since an air gap is not required above the recording layer, it has an air sandwich structure. It has the advantage of not having to. Generally, in a rewritable phase change recording medium, two different laser light powers are used to realize different crystal states.

This method will be described by taking as an example the case of performing recording / erasing in an erased / initial state in which an amorphous bit and crystallized. Crystallization is performed by heating the recording layer to a temperature sufficiently higher than the crystallization temperature of the recording layer and lower than the melting point. In this case, the cooling layer is sandwiched between dielectric layers or a long elliptical beam is used in the moving direction of the beam so that the crystallization is sufficiently slow.

On the other hand, the amorphization is performed by heating the recording layer to a temperature higher than the melting point and quenching it. in this case,
The dielectric layer also has a function as a heat dissipation layer for obtaining a sufficient cooling rate (supercooling rate). In addition, in order to prevent deformation of the recording layer due to melting and volume change in the heating / cooling process, thermal damage to the plastic substrate, and deterioration of the recording layer due to moisture as described above, A protective layer consisting of a body layer is important.

The protective layer material is such that it is optically transparent to laser light, has a high melting point / softening point / decomposition temperature, is easy to form, and has suitable thermal conductivity. Selected from the perspective. Examples of the protective layer having sufficient heat resistance and mechanical strength include a dielectric thin film such as metal oxide or nitride.

Since the dielectric thin film and the plastic substrate differ greatly in the coefficient of thermal expansion and elastic properties, they may be peeled off from the substrate to cause pinholes and cracks during repeated recording and erasing. Further, the plastic substrate is liable to warp due to humidity, which may also cause peeling of the protective film.

On the other hand, ZnS is used as a new dielectric protective layer.
It has been proposed that the main component is, and SiO ₂ or Y ₂ O ₃ is mixed. These composite compound protective films are superior in adhesion to chalcogenide alloy thin films such as GeTeSb, which are often used as recording layers, as compared with pure oxide or nitride dielectric films. Therefore, in addition to durability against repeated overwriting, film peeling in the accelerated test is small and the reliability of the phase change medium is further improved.

[0012]

However, the composite compound does not always exhibit good properties when simply mixed. Depending on the composition range and the physical properties of the composite film, the reliability may be lowered rather than the case where individual pure compounds are used.

Conventionally, many proposals have been made for protective films in which oxides, nitrides, fluorides, carbides, etc. are mixed with ZnS, ZnSe, etc., which are compounds containing chalcogenide elements, but some of them have been proposed. Only the optimum composition range is described, and even if a mixture having that composition is used, it is not always possible to obtain properties superior to those of the original protective layer composed of pure compound alone.

This is because the physical properties of the above-mentioned composite material are greatly different from those of the compounds constituting the composite material, and changes in the physical properties due to the manufacturing method and other factors were unpredictable. For example, a sputtering method is widely used for forming a protective layer made of the above-mentioned composite compound. However, the composite compound protection which is naturally obtained when the composite target is used and when the individual targets are simultaneously sputtered. The physical properties of the film are different.

It is a well-known fact that even in the same manufacturing method, the physical properties change due to the pressure during sputtering. In the presence of such variations in the physical properties of the protective film, how to find a composite protective film suitable for a phase change medium has been an issue.

[0016]

SUMMARY OF THE INVENTION An object of the present invention is to provide an optical information recording medium having at least a phase transition type optical recording layer and a dielectric layer on a substrate, wherein the dielectric layer has at least a chalcogen compound and zinc oxide. And an optical information recording medium containing magnesium fluoride or calcium fluoride.

Chalcogen means four elements of sulfur, selenium, tellurium and polonium. As a chalcogen compound,
It is preferably at least one selected from the group of ZnS, ZnSe and ZnTe, and preferably the content X (mol%) of the chalcogen compound, the content Y (mol%) of zinc oxide and the fluorination in the dielectric layer. The content Z (mol%) of magnesium or calcium fluoride is such that X / Y is 1/3 or more and 3 or less, and (X + Y) / Z is 1/4 or more and 1.5 or less.

The dielectric layer is preferably provided by using a composite sputtering target composed of a mixture of a plurality of compounds forming the dielectric. Next, the structure of the optical recording medium according to the present invention will be described. The optical recording medium of the present invention usually has at least a substrate / dielectric layer /
The substrate 1 has a structure of recording layer / dielectric layer / reflection layer.
A transparent resin such as polycarbonate, acrylic, or polyolefin, or glass can be used.

On the surface of the substrate, a dielectric satisfying the above characteristics is
Usually, the thickness is set to 100 to 5000Å. When the thickness of the dielectric layer is less than 100 Å, the effect of preventing the deformation of the substrate and the recording film is insufficient, and it tends not to serve as a protective layer. If it exceeds 5000 Å, the internal stress of the dielectric itself and the difference in elastic properties from the substrate become remarkable, and cracks are likely to occur.

In the present invention, a mixture of three or more different compounds is used in the dielectric layer. That is, it contains at least zinc oxide, a chalcogen compound, and magnesium fluoride or calcium fluoride. The chalcogen compound is preferably at least one selected from the group of ZnS, ZnSe and ZnTe, and preferably the content X (mol%) of the chalcogen compound and the content Y (mol of zinc oxide in the dielectric layer. %) And magnesium fluoride or calcium fluoride content Z (mol%) is such that X / Y is 1/3 or more and 3 or less, and (X + Y) / Z is 1/4 or more and 1.5 or less.

When the contents X, Y and Z of each compound are out of the above ranges, the effect of preventing the deformation of the substrate and the recording film is insufficient, and it cannot be said that it is suitable from the viewpoint of the protective effect. The dielectric layer contains the chalcogen compound, zinc oxide, and magnesium fluoride or calcium fluoride as the main component (50 mol%).
The above is preferable and 80 mol% or more), and other dielectrics may be mixed.

Other dielectrics include SiO ₂ , ZrO ₂ , B
Examples include aO and B ₂ O ₃ . When another dielectric is mixed in the dielectric layer, it is necessary that the heat resistance at 1000 ° C. or higher and the optical characteristics are maintained. The heat resistance of 1000 ° C. or higher means that the melting point is maintained at 1000 ° C. or higher and decomposition does not occur even when heated to 1000 ° C.

The optical characteristic means that the light absorption coefficient is 0.02 or less at a thickness of 500Å. The dielectric layer preferably has a film density of 80% or more of the theoretical density. Here, the theoretical density of the film is represented by the following formula, and is an integrated value obtained by multiplying the density of each constituent compound in the bulk state by the molar content of the constituent compound. Theoretical density = Σ {(density of constituent compound in bulk state) × (molar content of constituent compound)} By setting the density of the mixture dielectric layer in this way, durability against repeated recording and aging can be significantly improved. it can.

The film density can be controlled by adjusting the vacuum degree at the time of sputtering. To increase the film density, the vacuum degree is lowered (the argon gas pressure is lowered).
The degree of vacuum is usually 1 Pa or less, preferably 0.8 to 0.1 or less. The dielectric layer is preferably provided by using a composite sputtering target composed of a mixture of a plurality of compounds forming the film.

This is because the sputtering method is generally widely used in forming the dielectric layer made of the above compound, but the compound target is used in comparison with the simultaneous sputtering using the individual compound targets. In addition, the resulting composite compound protective film is excellent in uniformity of the constituent elements, and thus the properties as a protective film are also excellent, which is preferable.

The recording layer of the medium of the present invention is a phase change type recording layer, and the thickness thereof is preferably in the range of 100Å to 1000Å. If the thickness of the recording layer is less than 100Å, sufficient contrast cannot be obtained. Also, the crystallization speed tends to be slow, and it becomes difficult to erase the record in a short time. While 10
If it exceeds 00ÅA, it becomes difficult to obtain optical contrast, and cracks are likely to occur, which is not preferable.

The thicknesses of the recording layer and the dielectric layer are set so that the absorption efficiency of laser light is good and the amplitude of the recording signal, that is, the contrast between the recorded state and the unrecorded state is large, in consideration of the interference effect associated with the multilayer structure. To be chosen. For the recording layer, a ternary compound such as GeSbTe or InSbTe is selected as an overwritable material.

0.1 to 10 atomic% of these ternary compounds
Sn, In, Pb, As, Se, Si, Bi, Au,
Crystallization rate by adding one or more elements from Ti, Cu, Ag, Pt, Pd, Co, Ni, etc.
It is also effective to improve optical constants and oxidation resistance. An optical reflection layer and a hard coat layer for preventing thermal deformation are provided on the protective layer. The optical reflection layer is preferably a substance having a high reflectance, and Au, Ag, Cu, Al or the like is used.

This reflective layer has the effect of promoting the diffusion of the thermal energy absorbed by the recording layer, and therefore Ta, Ti, Cr, Mo, Mg, V, Nb, Zr for controlling thermal conductivity and the like.
Etc. may be added in a small amount. The recording layer, the dielectric layer, and the reflective layer are formed by a sputtering method or the like. It is desirable to perform film formation by an in-line apparatus in which the target for recording film, the target for protective film, and the target for reflective layer material, if necessary, are installed in the same vacuum chamber in order to prevent oxidation and contamination between the layers. It is also excellent in terms of productivity.

[0030]

The present invention will be described in detail with reference to the following examples. Example 1 As a dielectric layer material, ZnS, ZnO, and MgF ₂ powders were adjusted and mixed in a molar ratio of 20:20:60,
A composite sintered body target obtained by the hot pressing method was obtained.

An electric layer / recording layer / dielectric layer / reflection layer was provided on a polycarbonate resin substrate to prepare a recording medium having a four-layer structure. The thickness of each layer is as follows: lower dielectric layer 1000Å, recording layer 300Å, upper dielectric layer 300Å, reflective layer 1000
Å The composition of the recording layer is Ge _(22.2) Sb _(22.2) Te
_{(55.6 )} .

An Al alloy was used for the reflective layer. The dielectric layer is A
A film was formed by high frequency (13.56 MHz) sputtering with an r gas pressure of 0.7 Pa. Film density is 3.3g / cc
And was 84% of the theoretical density. The recording layer and the reflective layer were formed by DC sputtering under Ar gas pressure of 0.7 Pa.

Further, an ultraviolet curable resin having a thickness of about 4 μm was provided. This disk was further initialized by using an Ar ion laser, that is, the recording layer was crystallized, and the dynamic characteristics of the disk were evaluated under the following conditions. 4MHz, duty 50% while rotating at a linear velocity of 10m / s
The pulsed light was used to repeatedly overwrite with a recording power of 18 mW and a base power of 9.5 mW, and the C / N ratio was measured each time a predetermined number of times was reached. As a result, as shown in FIG. 1, the number of repetitions was 10,000 and the decrease in C / N was about 3 dB as compared with the 10th repetition.

Comparative Example 1 ZnS and MgF ₂ as protective layer materials in Example 1
A disk was prepared in the same manner as above except that it was used at a molar ratio of 20:80, and the same dynamic characteristics were evaluated.
The result is 100 times and 10 times as shown in FIG.
The decrease in C / N was about 13 dB compared with the first time. The film density was 3.0 g / cc, which was 88% of the theoretical density.

Example 2 A disk was prepared in the same manner as in Example 1 except that 10 mol% of ZrO ₂ was mixed with the protective layer material, and the same dynamic characteristics were evaluated. The results were almost the same as in Example 1.

[0036]

By using the optical recording medium of the present invention, repeated recording and erasing can be performed many times, and it is very effective for practical use of this type of repetitive recording and erasing medium.

[Brief description of drawings]

FIG. 1 is a graph showing changes in C / N in an example.

FIG. 2 is a graph showing changes in C / N in a comparative example.

[Explanation of symbols]

 1 Graph of Example 1 2 Graph of Comparative Example 1

Claims (5)

[Claims] 1. A phase transition type optical recording layer on a substrate,
An optical information recording medium having a dielectric layer, wherein the dielectric layer contains at least a chalcogen compound, zinc oxide, and magnesium fluoride or calcium fluoride. 2. The optical information recording medium according to claim 1, wherein the chalcogen compound is at least one selected from the group consisting of ZnS, ZnSe and ZnTe. 3. The content X (mol%) of a chalcogen compound, the content Y (mol%) of zinc oxide and the content Z (mo) of magnesium fluoride or calcium fluoride in a dielectric layer.
1%), X / Y is 1/3 or more and 3 or less, and (X + Y) / Z is 1/4 or more and 1.5 or less.
The optical information recording medium as described in 1. 4. The optical information recording medium according to claim 1, wherein the film density of the dielectric layer is 80% or more of the theoretical density. 5. The optical information recording device according to claim 1, wherein the dielectric layer is a film formed by sputtering from a target made of a mixture of a plurality of compounds constituting the dielectric. Medium.