JPH04329184A - Optical information recording medium - Google Patents

Abstract

PURPOSE:To obtain a phase change-type optical recording medium capable of recording and regenerating information at high speed and high packing density and deleting information rapidly with excellent repeatability properties by providing an optical recording layer consisting of a blend of a phase change recording material which changes a phase between a crystal material and an amorphous material reversibly and an inorganic dielectric on a transparent substrate. CONSTITUTION:The subject optical information recording medium consists of an optical recording layer 3 provided on a transparent substrate 1, and records and deletes information through a reversible change of an optical constant by irradiation of the optical recording layer 3 with an energy beam. The optical recording layer is composed of a blend of a phase change recording material 7 which changes reversibly between a crystal material and an amorphous material such as Sb-Te-Ge. The content of the phase change recording material 7 in the optical recording layer 3 is 20 to 80% based on the capacity of the layer 3. Thus the migration of the materials in the optical recording layer due to the repeated process of recording and deletion is significantly reduced and the reliability of repeatedly recorded data is remarkably enhanced.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a novel optical information recording medium, and more specifically, it is capable of optically recording and reproducing information at high speed and high density using light, heat, etc. The present invention relates to an optical information recording medium that is erasable and has excellent repeatability.

0002

[Prior Art] Conventionally, various methods have been known for recording information in a recording layer by irradiation with an energy beam such as a laser beam. The method that utilizes the reversible phase change between It has the advantage of being able to record information, so-called overwriting.

As a recording material for such an overwritable phase-change optical information recording medium, an In-Se alloy ["
Applied Physics Letters (Appl.Phys.
s. Lett) Volume 50, Page 667 (1987
], In-Sb-Te alloy [Appl. Phys. Lett Vol. 50, p. 16 (1987)], Ge-Te-
Chalcogen alloys such as Sb alloy (Japanese Unexamined Patent Publication No. 62-53886) are mainly used.

[0004] Phase change optical information recording media using these chalcogen alloys as recording materials have various advantages such as increasing optical contrast and optical absorption, preventing deformation of the substrate due to heat during erasing records, and preventing oxidation of the optical recording layer. For the purpose of has been used.

However, in such conventional optical information recording media, when recording and erasing by overwriting are repeated, asymmetric thermal expansion and surface energy differences occur due to thermal history corresponding to the recording and erasing patterns. A phenomenon in which the substance of the optical recording layer moves along the track direction, that is, when the optical recording layer is formed as a layered continuous film, when the recording layer dissolves during recording,
When some mechanical or physical force is applied, the material forming the recording layer inevitably moves in a direction parallel to the disk surface, and as a result, recording and recording due to overwriting occur. If erasing is repeated, the substance of the optical recording layer is locally dispersed to the surrounding area, making recording and erasing impossible.

[0006]

SUMMARY OF THE INVENTION The present invention overcomes the drawbacks of such conventional phase change optical information recording media, and enables information to be recorded and reproduced at high speed and high density.
The purpose of this invention is to provide a phase change optical information recording medium that can be erased at high speed and has excellent repeatability in overwriting.

[0007]

[Means for Solving the Problems] As a result of intensive research to develop a phase change type optical information recording medium with excellent repetition characteristics in overwriting, the present inventors have discovered that a phase change recording material is used in the optical recording layer. It has been discovered that by using a mixture with an inorganic dielectric material, mass transfer in the optical recording layer can be prevented and the above object can be achieved, and the present invention has been completed based on this knowledge.

That is, the present invention provides an optical information recording method in which an optical recording layer is provided on a transparent substrate, and the optical constants of the optical recording layer are reversibly changed by irradiating the optical recording layer with an energy beam to record and erase information. Provided is an optical information recording medium, wherein the optical recording layer is made of a mixture of a phase change recording material whose phase changes reversibly between crystalline and amorphous states and an inorganic dielectric. It is something.

In the optical information recording medium of the present invention, an optical recording layer made of a mixture of a phase change recording material and an inorganic dielectric material is used. As a phase change recording material,
Materials that undergo a reversible phase change between crystalline and amorphous states, such as Sb-Te-Ge, In-Sb-Te, In-Se
-Tl, Ge-Te-Sn-Au, Sb-Te-Ge-
Preferably mentioned are alloys based on Te or Se, such as Pd.

[0010] Also, as an inorganic dielectric material, for example, SiO2
, SiO, Ta2O5, ZrO2, BeO, MgO, A
l2O3, CaO, Sc2O3, TiO2, MnO, C
oO, NiO, ZnO, MoO2, CeO2, Sm2O
Metal oxides such as 3, metal nitrides such as Si3N4, AlN, ZrN, metal sulfides such as ZnS, CdS, Mg
Preferred examples include metal fluorides such as F2. Each of these inorganic dielectrics may be used alone, or two
More than one species may be used in combination, and if desired, it may be used in combination with an organic material such as polyvinyl chloride, polyimide, or polyethylene.

In the optical recording layer made of the mixture of the phase change recording material and the inorganic dielectric, the volume ratio occupied by the recording material (hereinafter referred to as filling factor) is preferably in the range of 20 to 80%. If this ratio is less than 20%, the difference in the attenuation coefficient K of the recording layer before and after recording is small, and the resulting optical information recording medium may have insufficient optical modulation degree (contrast). There is a possibility that the object of the present invention cannot be fully achieved because the mass transfer of the recording material cannot be suppressed.

[0012] There are no particular restrictions on the method of forming this optical recording layer, and any method conventionally used for forming thin films, such as sputtering, vacuum evaporation, CVD, or spin coating, can be used. However, among these methods, sputtering methods, such as co-sputtering of an inorganic dielectric and a phase change recording material, or sputtering using a mixed target thereof, are preferable.

The layer structure of the optical information recording medium of the present invention differs depending on the intended use, but it is also possible to use one in which only a single optical recording layer is provided on a transparent substrate. However, when actually used as a disc, it is necessary to increase the optical properties, particularly the degree of optical modulation (contrast), so it is desirable to have a structure in which protective layers are provided on both sides of the optical recording layer. In this case, the thicknesses of the optical recording layer and the protective layer may be determined as appropriate, taking into account interference effects, optical properties, thermal properties, and the like.

Furthermore, a reflective layer made of metal or the like may be provided on the top for the purpose of improving optical characteristics. It is desirable to provide an ultraviolet curing resin layer, such as urethane-based, acrylic-based, silicone-based, or polyester-based resin, on the reflective layer in order to protect and strengthen the film.

[0015] As the material of the protective layer, for example, SiO
2. Metal oxides such as SiO, Ta2O5, ZrO2,
Examples include metal nitrides such as Si3N4 and AlN, metal sulfides such as ZnS, metal fluorides such as MgF2, and mixtures thereof, as well as organic materials such as polyvinyl chloride, polyimide, and polyethylene.

[0016] Also, as a material for the reflective layer, for example, Al
, Cr, Ni, Au, Ti, and alloys thereof.

There are no particular restrictions on the transparent substrate used in the optical information recording medium of the present invention, and those conventionally used as substrates for optical discs can be used.
Polycarbonate, glass, and the like are preferred because they have good optical properties, high mechanical strength, and excellent dimensional stability.

FIG. 1 is a cross-sectional view showing an example of the layer structure of the optical information recording medium of the present invention, in which a transparent substrate 1 is provided with a lower protective layer 2 made of a mixture of a recording material and an inorganic dielectric material. It shows a structure in which an optical recording layer 3, an upper protective layer 4, a reflective layer 5, and an ultraviolet curing resin layer 6 are sequentially laminated.

[0019]

[Operation] By forming the optical recording layer using a mixture of a recording material and an inorganic dielectric, the optical recording layer can be roughly divided into the following two forms. One of them is (1) Figure 2
As shown in FIG. 2, a large number of clusters or fine particles of the recording material 7 are dispersed in the inorganic dielectric material 8. This often occurs when the filling rate is small.

The other case is (2) which occurs when the filling ratio is large, and as shown in FIG. state.

As an intermediate between these, (3) for example, as shown in FIG. 4, there may be a form in which the gaps between the recording materials 7 arranged in an amoeba-like manner are filled with an inorganic dielectric material 8.

In the embodiment (1) above, even if the optical recording layer is heated to a temperature higher than the melting point of the recording material, it melts only in minute regions that are separated from each other, so that no mass transfer of the recording material occurs. Furthermore, in the above embodiments (2) and (3), although the melted portions are connected, the inorganic dielectric material that is dispersed or in the gaps acts as resistance to the flow of the recording material, causing mass transfer of the recording material. is hindered.

[0023]

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

Example 1 On a polycarbonate disk substrate with a thickness of 1.2 mm,
Each layer was formed according to the procedure shown below. FIG. 5 shows an outline of the sputtering apparatus used.

First, using a target made of ZnS,
A protective layer with a thickness of 100 nm was formed by RF sputtering, and then on this protective layer, an Sb-Te-Ge alloy as a phase change recording material and ZnS as an inorganic dielectric were co-sputtered (both were sputtered). A rate ratio of 1:1) was used to form an optical recording layer with a thickness of 120 nm.

Next, on this optical recording layer, a protective layer made of ZnS with a thickness of 150 nm was formed in the same manner as described above, and then a reflective layer of Al alloy with a thickness of 100 nm was formed on this. The optical information recording medium of the present invention was prepared by applying an ultraviolet curable resin thereon to a thickness of 5 nm by spin coating and curing it with ultraviolet rays (layer structure A).

For comparison, a conventionally used optical information recording medium having a continuous optical recording layer was coated with ZnS one by one from the substrate side using the same film forming apparatus and method as described above.
50 nm thick, a 20 nm thick Sb-Te-Ge alloy layer, a 20 nm thick ZnS layer, a 100 nm thick Al alloy reflective layer, and a 5 μm thick ultraviolet curing resin layer were prepared (layer structure B).

These two types of optical information recording media were repeatedly irradiated with a laser beam having a wavelength of 830 nm to evaluate their characteristics in a stationary state. The evaluation was performed by arbitrarily changing the emission time of the laser beam from 20 nsec to 60 μsec and the power of the laser beam within the range of 1 mW to 20 mW. The results of this evaluation are shown in FIG. Among the curves in FIG. 6, the upper curve corresponds to the reflectance in the crystalline state, that is, the erased state, and the lower curve corresponds to the reflectance in the amorphous state, that is, the recorded state. The difference between the two is the signal-to-noise ratio (C
/N ratio). As can be seen from FIG. 6, in both layer structures, there is no change in the reflectance in the recorded state and the reflectance in the erased state up to 106 times.

Next, an optical information recording medium having a similar two-layer structure was created on a polycarbonate disk substrate on which grooves with a diameter of 130 mm, a thickness of 1.2 mm, and a pitch of 1.6 μm were previously provided. We performed dynamic measurements while rotating these. The linear velocity was approximately 7.5 m/s, the recording frequency was 3.7 MHz, and the recording pulse width was 90 nsec.
Repeated overwriting. The recording power and erasing power were 19 mW and 7 mW, respectively.

FIGS. 7 and 8 show the results of the conventional optical information recording medium and the optical information recording medium of the present invention, respectively. As can be seen from these figures, in the optical information recording medium of the conventional structure, from 105 repetitions onwards, the reproduction signal amplitude decreases and noise increases, corresponding to changes in film thickness due to mass transfer in the optical recording layer. The C/N ratio (signal-to-noise ratio) begins to decline, whereas the optical information recording medium of the present invention has no change in the C/N ratio until 106 times, and its repetition characteristics are improved by more than 10 times compared to those with a conventional structure. are doing.

Example 2 An experiment similar to Example 1 was conducted with different recording layers. The recording layer is formed using an inorganic dielectric (ZnS) and a phase change recording material (
This was done by RF sputtering of a mixed target with Sb-Te-Ge alloy).

As an optical information recording medium, in order from the substrate side, ZnS is 180 nm thick, the recording layer (mixed layer of Sb-Te-Ge alloy and ZnS) is 160 nm thick, ZnS is 24 nm thick,
The reflective layer of Al alloy is 100 nm thick, and the ultraviolet curing resin layer is 5 nm thick.
A layer was prepared in which layers were sequentially stacked to a thickness of μm. In this experiment, almost the same results as in Example 1 were obtained.

[0033]

Effects of the Invention The optical information recording medium of the present invention uses a mixture of a phase change recording material and an inorganic dielectric material in the optical recording layer, and the material movement in the optical recording layer due to repeated recording and erasing is prevented. The reliability of recorded data is significantly higher than that of conventional structures.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an example of the layer structure of the optical information recording medium of the present invention.

FIG. 2 is a schematic diagram showing one example of the form of the optical recording layer in the optical information recording medium of the present invention.

FIG. 3 is a schematic diagram showing different examples of the configuration of the optical recording layer in the optical information recording medium of the present invention.

FIG. 4 is a schematic diagram showing examples of different forms of the optical recording layer in the optical information recording medium of the present invention.

FIG. 5 is an explanatory diagram of a sputtering apparatus used in an example of the present invention.

FIG. 6 is a graph showing the evaluation results of static repetition characteristics in Example 1.

FIG. 7 is a graph showing the evaluation results of the dynamic repetition characteristics of the optical information recording medium with the conventional structure in Example 1.

FIG. 8 is a graph showing the evaluation results of the dynamic repetition characteristics of the optical information recording medium of the present invention in Example 1.

[Explanation of symbols]

1 Transparent substrate 2 Lower protective layer 3 Optical recording layer 4 Upper protective layer 5 Reflective layer 6 Ultraviolet curing resin layer 7 Phase change recording material 8 Inorganic dielectric 9 Board holder 10 Bell jar

Claims (3)

[Claims] 1. An optical information recording medium in which an optical recording layer is provided on a transparent substrate, and the optical constants of the optical recording layer are reversibly changed by irradiating the optical recording layer with an energy beam to erase information. 1. An optical information recording medium, wherein the recording layer is made of a mixture of a phase change recording material whose phase changes reversibly between crystalline and amorphous states and an inorganic dielectric. 2. The optical information recording medium according to claim 1, wherein the optical recording layer contains a phase change recording material in a proportion of 20 to 80% based on capacity. [Claim 3] The inorganic dielectric is SiO2, SiO, Ta.
2O5, ZrO2, BeO, MgO, Al2O3, Ca
O, SC2O3, TiO2, MnO, CoO, NiO,
Metal oxides consisting of ZnO, MoO2, CeO2 and Sm2O3, metal nitrides consisting of Si3N4, AlN and ZrN, metal sulfides consisting of ZnS and CdS and M
The optical information recording medium according to claim 1 or 2, wherein the optical information recording medium is at least one selected from metal fluorides of gF2.