JPH05217212A - Information recording medium - Google Patents

Abstract

PURPOSE:To improve the sticking property of a protective layer to a reflecting layer, to enhance the mechanical strength of the protective layer and to increase the number of repetitions of overwriting. CONSTITUTION:A first protective layer 2, a recording layer 3, a second protective layer 4, a reflecting layer 5 and a third protective layer 6 are successively laminated on a substrate 1 for an optical disk to form a phase change optical disk. In this case, the first and second protective layers 2, 4 are especially made of a mixture of ZnS.SiOx (2.0>x>1.0) with Y2O3. Since this Y2O3 can be allowed to act as a binder, the above-mentioned purpose can be attained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an information recording medium such as an optical disk used for recording and reproducing information.

[0002]

2. Description of the Related Art As an optical disk as an information recording medium used for recording and reproducing information, a CD-only for reproducing information is used.
A ROM, a magneto-optical disk capable of recording and reproducing information, a phase-change optical disk, and the like are known, and these information recording media are applicable to storage devices of various computers.

Here, in a phase-change type optical disk (hereinafter referred to as a phase-change optical disk), which is particularly in the spotlight recently, a chalcogenide material is used as a recording layer (phase-change recording layer) used for recording and reproducing information. The recording and reproducing of information is performed by utilizing the phase change of the crystalline layer and the non-crystalline layer of the chalcogenide recording layer. Such a phase change optical disk is described in detail in "Rewritable Optical Disk Material" by Masahiro Okuda, published by Industrial Research Institute, Inc. on May 20, 1989.

FIG. 3 is a cross-sectional view showing the structure of a conventional phase change optical disc, in which a first dielectric protective layer 12, a phase change recording layer 13, a second dielectric protective layer 14 are provided on an optical disc substrate 11.
Reflective layer 15 and third protective layer 1 made of metal or alloy
6 are sequentially laminated.

Here, the optical disk substrate 11 is made of a material that is transparent and has little change over time, such as acrylic resin such as polymethylmethacrylate (PMMA), polycarbonate resin, epoxy resin, styrene resin, or glass. In this, continuous grooves, sample servo marks, preformat marks, etc. are formed according to the recording format.

The recording layer 13 is made of a phase-change material whose state changes when irradiated with a light beam. Examples of such phase change materials include GeTe-based and T-based materials.
eSe system, GeSbSe system, TeOx system, InSe system,
A chalcogenide-based amorphous semiconductor material such as GeSbTe-based or a compound semiconductor material such as InSb-based, GaSb-based, InSbTe-based can be formed by a vacuum deposition method, a sputtering method, or the like. As the layer thickness of the recording layer 13, a range of several nm to several μm is practically used.

The first and second protective layers 12 and 14 are arranged so as to sandwich the recording layer 13, and play a role of preventing the recording layer 13 from scattering or having holes due to irradiation of the recording beam. have. Recording layer 1 for recording
It also has a role of controlling the heat diffusion of heating and cooling of No. 3. As the first and second protective layers 12 and 14, for example, SiO
₂ , SiO, AlN, Al ₂ O ₃ , ZrO ₂ , Ti
O ₂ , Ta ₂ O ₃ , ZnS, Si, Ge, or the like can be used and can be formed by a vacuum evaporation method, a sputtering method, or the like. The layer thickness of these protective layers 12 and 14 is practically used from several nm to several μm.

The reflective layer 15 has a role of optically enhancing (strengthening) an optical change of the recording layer 13 to increase a reproduction signal and cooling the recording layer 13. As the reflective layer 15, for example, Au, Al, Cu, Ni-C
It can be formed by a vacuum evaporation method, a sputtering method, or the like using a metal or an alloy such as an r alloy. Reflective layer 1
The layer thickness of 5 is practically several nm to several μm.

The third protective layer 16 is arranged to prevent scratches and dust when handling the phase change optical disk, and is usually formed of an ultraviolet curable resin or the like. The protective layer 16 is formed, for example, by applying an ultraviolet curable resin on the surface of the reflective layer 15 by a spin coating method and irradiating it with ultraviolet rays to cure it. The layer thickness of the protective layer 16 is practically used in the range of several μm to several hundreds μm.

The operation of such a conventional phase change optical disk is performed as follows.

(1) Since the recording layer 13 formed by the vacuum vapor deposition method, the sputtering method or the like is amorphous, it is brought into a crystalline phase by heat annealing treatment or light beam irradiation. This is called initial (crystallization).

(2) A short-pulse, high-power recording pulse is applied to the recording layer of the crystalline phase, and this is melted and rapidly cooled to be amorphized to form a recording mark.

(3) A long-pulse, low-power erasing pulse is added to the recording mark in the amorphous phase to crystallize the recording mark to erase the recording mark.

Further, it is also considered to overwrite the recording power with the erasing power. Considering the use of this phase-change optical disk as an auxiliary storage device of a computer, it is possible to ensure the reliability that the number of overwrite repetitions, that is, the information recording / erasing characteristic can be 1 million times or more. Is needed in.

[0015]

By the way, in the conventional phase change optical disk, the adhesion between the protective layer and the reflective layer is not good, and the mechanical strength of the protective layer is not sufficient, so that repeated recording and erasing by overwriting can be performed. Since the protective layer and the reflective layer are easily peeled off or the protective film is destroyed, there is a problem in that the number of overwrite cycles is limited to about 1,000 to 10,000 times.

That is, when the phase-change optical disk is repeatedly overwritten, peeling occurs at the boundary between the protective layer and the reflective layer made of metal or alloy, which deteriorates the repetitive characteristics. This is because the adhesion between the protective layer and the reflective layer is not good, and since the protective layer is most subjected to heat stress, the mechanical strength also decreases.

The present invention has been made to solve the above problems, and improves the adhesion between the protective layer and the reflective layer and the mechanical strength of the protective layer to increase the number of overwrite repetitions. It is an object of the present invention to provide an information recording medium configured to do so.

[0018]

In order to achieve the above object, the present invention is an information recording medium having at least a recording layer capable of recording / reproducing information and a reflective layer for enhancing the optical change of the recording layer. Then, a protective layer made of a dielectric containing at least Zn, S, Si, Y, O is provided adjacent to the recording layer.

[0019]

Function At least Zn, S, Si, adjacent to the recording layer,
As a dielectric containing Y and O, for example, ZnS, SiOx
By providing a protective layer composed of a mixed layer of (2.0>x> 1.0) and Y ₂ O ₃ , Y ₂ O ₃ acts as a binder, so that the adhesion between the protective layer and the reflective layer is good. And the mechanical strength of the protective layer can be made sufficient. As a result, the number of times overwriting can be repeated can be increased to the extent that reliability can be ensured.

[0020]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 shows an embodiment of a phase change optical disc as an information recording medium of the present invention. The phase change optical disc of this embodiment has a first dielectric protective layer 2 and a phase change recording layer on an optical disc substrate 1. 3, a second dielectric protective layer 4, a reflective layer 5 made of a metal or an alloy, and a third protective layer 15 are sequentially laminated, and in particular, the second and third protective layers 2 and 4 are formed. As will be described later, ZnS, SiO ₂ and Y ₂ O
_It consists of ₃ mixed dielectric layers.

The optical disc substrate 1 is made of a material that is transparent and does not easily change with time, such as polymethylmethacrylate (PMM).
It is made of acrylic resin such as A), polycarbonate resin, epoxy resin, styrene resin, or glass. In this, continuous grooves, sample servo marks, preformat marks, etc. are formed according to the recording format.

The recording layer 3 is made of a phase-change material whose state changes when irradiated with a light beam. Examples of such phase change materials include GeTe-based and Te-based materials.
Se system, GeSbSe system, TeOx system, InSe system, G
It can be formed by a vacuum deposition method, a sputtering method, or the like using a chalconide-based amorphous semiconductor material such as eSbTe type or a compound semiconductor material such as InSb-based, GaSb-based, or InSbTe-based. The layer thickness of the recording layer 3 is preferably in the range of several nm to several μm for practical use.

The first and second protective layers 2 and 4 are arranged so as to sandwich the recording layer 3 and play a role of preventing the recording layer 3 from scattering or having holes due to the irradiation of the recording beam. have. Also, heating of the recording layer 3 during recording,
It also has the role of controlling the thermal diffusion of cooling. This protective layer 2, 4
For example, a mixed derivative of ZnS and SiO ₂ and Y ₂ O ₃ can be formed by a vacuum deposition method, a sputtering method, or the like. The thickness of the protective layers 2 and 4 is practically n
It is preferably m to several μm.

The reflective layer 5 has a role of optically enhancing (strengthening) an optical change of the recording layer 3 to increase a reproduction signal and cooling the recording layer 3. This reflective layer 5
For example, Au, Al, Cu, Ni-Cr alloy,
It can be formed by a vacuum evaporation method, a sputtering method, or the like using a metal or an alloy such as an Al—Ti alloy.
The layer thickness of the reflective layer 5 is preferably several nm to several μm for practical use.

The third protective layer 6 is arranged to prevent scratches and dust when handling the phase change optical disk, and is usually formed of an ultraviolet curable resin or the like. The protective layer 6 is formed, for example, by applying an ultraviolet curable resin to the surface of the reflective layer 5 by spin coating and irradiating it with ultraviolet rays to cure it. The layer thickness of the protective layer 6 is preferably in the range of several μm to several hundreds μm in practical use.

Next, experimental results of the phase change optical disk obtained in this embodiment and the conventional phase change optical disk will be described.

As the phase change optical disk according to this embodiment,
ZnS-SiO ₂ -Y ₂ O ₃ protective layer by a sputtering method on a polycarbonate substrate (the optical disc substrate 1) (first protective layer 2) of 180 nm, GeSbTe recording layer (recording layer 3) of 20nm, ZnS-SiO ₂ - Y ₂ O ₃
The protective layer (second protective layer 4) and the Al alloy reflective layer (reflective layer 5) were formed in that order of 20 nm and 150 nm, respectively.

Similarly, as a conventional phase change optical disk, a polycarbonate substrate (optical disk substrate 11) is used.
The ZnS-SiO ₂ protective layer (first protective layer 12) is 180 nm, the GeSbTe recording layer (recording layer 13) is 20 nm, the ZeS-SiO ₂ protective layer (second protective layer 14) is 20 nm by sputtering. It was formed by sequentially laminating an Al alloy reflective layer (reflective layer 15) to a thickness of 150 nm. It should be noted that in each of the optical discs, each reflection layer 5,
An ultraviolet curable resin was spin-coated on 15 and then cured by irradiation with ultraviolet rays to form third protective layers 6 and 16.

A linear velocity of 8 m / s and a recording pulse of 60 n are recorded on the initially crystallized tracks of the two types of phase change optical disks.
s, recording peak power 22 mW, recording bias power 1
Recording frequency 5.23MHz and 2.00M as 1mW
Hz was alternately overwritten, and the occurrence of burst was examined repeatedly.

As a result, in the conventional phase change optical disk,
A large number of bursts occurred after 100,000 repetitions. On the other hand, it was confirmed that the phase-change optical disk according to the present example generated few bursts even after 1 million repetitions. In addition, Zn that is the first and second protective layers 2 and 4
The range of x in S-SiOx-Y ₂ O ₃ is X = 1.
It was confirmed that similar stable results could be obtained by selecting 0, 1.5 and 2.0.

That is, Y ₂ is added to the ZnS-SiO ₂ mixed layer.
By adding O ₃ , Y ₂ O ₃ becomes ZnS and SiO ₂
By functioning as a binder, the adhesion between the protective layers 2 and 4 and the reflective layer 5 is improved, and the mechanical strength of the protective layers 2 and 4 can be made sufficient.

In each of the protective layers 2 and 4, if only ZnS is used, it tends to be crystallized and thus lacks in durability. Therefore, a mixture of this with SiO ₂ is used. However, when mixing approximately 20 mol% or more of SiO _2, although crystallization of ZnS can be prevented, the mechanical strength of the protective layer is not sufficient, usually a SiO ₂ 20 m
For example, (ZnS) ₈₀ (SiO ₂ ) ₂₀ mixed up to ol%
What is composed of a mixed film of mol is used as a protective film.

Here, Y ₂ O ₃ has the property that when mixed with other components, it forms a complex oxide thereof and the mechanical strength of the mixed film can be improved.

The present invention has been made by paying attention to this property, and by mixing YO with the component of Zn-S-Si-O, a dielectric film of Zn-S-Si-YO is obtained. Is formed to be used as a protective film.

When a mixed film is used as the protective film, its refractive index becomes a problem, but the above (ZnS) ₈₀ (SiO ₂ ) ₂₀
The refractive index of the mol mixed film is 2.18. On the other hand, Y ₂
The refractive index of O ₃ is 1.92. Therefore, since the two values are close to each other, even if a small amount of Y ₂ O ₃ is mixed with ZnS-SiO ₂ , the change in the refractive index of the obtained mixed film can be suppressed to a small value, and the mixed film of ZnS-SiO ₂ can be suppressed. The mechanical strength can be improved without significantly changing the optical properties of the.

[0037] FIG. 2 shows the change in the refractive index of the _{(ZnS-SiO 2 -Y 2 O} 3) mixed film in the case of changing the mixing ratio of Y ₂ O _3. The mixing ratio of Y ₂ O ₃ is 20mo
By controlling the ratio to be 1% or less, the change in the refractive index is almost 0.
Since it can be suppressed to about 05% or less, 20
It is desirable to select less than mol%. If the mixing ratio of Y ₂ O ₃ is selected to be 20 mol% or more, the physical properties of the Y ₂ O ₃ change and cracks are likely to occur, which is not desirable.

When Y ₂ O ₃ is mixed in an amount of 20 mol% or less, Y ₂ O ₃ acts as a binder and sufficient mechanical strength can be obtained. Further, since the boundary surface is also flatter, the adhesion with the reflective layer 5 is improved.

Not limited to the structure of this embodiment, the protective layers 2 and 4 may be arranged on the upper side or both sides of the reflective layer 5. Furthermore, the protective layers 4 and 6 can be omitted in some cases. It is also possible to use two surfaces by laminating two optical disks with the surface having the recording layer 2 inside.

Further, the present invention is not limited to the phase change optical disc, but can be similarly applied to a magneto-optical disc, a CD-ROM and the like.

[0041]

As described above, according to the present invention, by using a protective layer made of a specific component, the adhesion between the protective layer and the reflective layer is improved and the mechanical strength of the protective layer is improved. Since this is done, it is possible to provide an information recording medium capable of increasing the number of overwrite repetitions.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a phase change optical disc as an information recording medium of the present invention.

FIG. 2 is a characteristic showing a change in refractive index of a protective film containing Y ₂ O ₃ used in this example.

FIG. 3 is a cross-sectional view showing a conventional phase change optical disc.

[Explanation of symbols]

 1 optical disk substrate 2, 4, 6 protective layer 3 recording layer 5 reflective layer

Claims (1)

[Claims] 1. An information recording medium having at least a recording layer capable of recording and reproducing information and a reflective layer for enhancing optical change of the recording layer, wherein at least Zn, S, Si adjacent to the recording layer. , Y, O containing a protective layer made of a dielectric material.