JP2001184717A - Optical recording medium - Google Patents

Abstract

(57) [Problem] To provide a phase change optical recording medium capable of preventing mark edge distortion due to overwriting and performing high density recording. SOLUTION: A light absorbing layer, a first dielectric layer,
In a phase-change optical recording medium in which a recording layer, a second dielectric layer, and a reflective layer are sequentially laminated, the light absorption layer is composed of a semiconductor film, and the reflectance when the recording layer is in a crystalline phase is Rc, and when the recording layer is in an amorphous phase. Where Ra> Rc when the reflectance of Ra is Ra.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable method for recording and reproducing information by condensing and irradiating a laser beam onto an optical recording medium to cause a reversible phase change between a crystalline phase and an amorphous phase in a recording layer material. It relates to a possible phase change optical recording medium.

[0002]

2. Description of the Related Art In a conventional phase-change type optical recording medium, an optical disk in which the reflectance of an amorphous phase is smaller than the reflectance of a crystalline phase is used for reproduction using a difference in the amount of reflected light. Was lower than that of the amorphous phase. When mark edge recording is performed on a disc having such characteristics by overwriting, distortion of the mark edge occurs due to a difference in absorptance, which will be described later, and prevents high-density recording.

[0003] In order to solve this problem, there have been proposed various types of phase change type optical disks which have been subjected to absorption rate control. For example, Japanese Patent Application Laid-Open No. 8-63781 discloses that a transparent substrate / first protective layer (first dielectric layer) / recording layer / second protective layer (second dielectric layer) / reflective layer has an amorphous phase. The reflectance Ra of the recording mark and the reflectance of the crystalline phase are Rc,
When the absorptance of the amorphous phase recording mark is Aa and the absorptivity of the crystalline phase is Ac, Rc> Ra and Ac> Aa
There is disclosed a phase change type optical disk satisfying the above. According to this optical disc, it is described that mark edge distortion at the time of overwriting is improved, jitter is reduced, and high density recording is possible. However, this optical disc has a practical problem because the reflectance Ra of the amorphous phase is actually larger than the reflectance Rc of the crystalline phase (Rc <Ra). This will be described with reference to FIG.

FIG. 6 shows a phase change type optical recording medium in which a first dielectric layer, a recording layer, a second dielectric layer, a reflective layer, and an ultraviolet curable resin layer (protective layer) are sequentially laminated on a transparent substrate. According to the prior art, the film thickness of each layer is set so that the amorphous phase reflectance Ra of the recording layer is smaller than the crystalline phase reflectance Rc (Rc> Ra). However, in this optical recording medium, while a good reproduction signal is obtained due to the change in reflectance, most of the light is reflected by the reflective layer. Has a defect that the crystal phase is smaller in absorption rate than the amorphous phase (Ac <Aa).
For this reason, the thermal conductivity of the crystalline phase is generally higher than that of the amorphous phase, and the latent heat required for melting is also larger. Occurs. In addition, it is necessary to accurately form an edge shape in order to give information to a mark edge. In a recording film with insufficient absorptance control, an overwrite signal is modulated by a signal component before overwriting, and edge shape distortion occurs near a mark edge.

[0005] Further, Japanese Patent Application Laid-Open No. 8-96411 discloses that
A phase-change optical disk provided with a light-absorbing protective layer made of a mixture of a dielectric material and a metal, semimetal or semiconductor material is disclosed. Although the difference in the absorptivity between the crystalline phase and the amorphous phase was certainly improved by this disk, the degree of improvement was sometimes insufficient in some cases.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a recording method which can perform good recording repeatedly without the above-mentioned disadvantages and without the above-mentioned disadvantageous phenomena such as edge shape distortion. An object of the present invention is to provide a changeable optical recording medium.

[0007]

According to the present invention, first, a light absorbing layer, a first dielectric layer, a recording layer, a second dielectric layer, and a reflective layer are sequentially laminated on a transparent substrate. In a phase-change optical recording medium in which a recording layer receives a laser beam and undergoes a reversible phase change between a crystalline phase and an amorphous phase to record or erase information, the light absorbing layer comprises a semiconductor film, In addition, an optical recording medium is provided, wherein Ra> Rc, where Rc is the reflectance when the recording layer is in a crystalline phase and Ra is the reflectance when the recording layer is in an amorphous phase. Secondly, the first optical recording medium is provided, wherein the light absorption layer is made of a semiconductor film of Si or Ge. Third, the first or second optical recording medium is provided, wherein the recording layer is made of a material containing Ag, In, Sb, and Te as main components. Fourth, the first and second
The ZnS-SiO ₂ as a dielectric layer, Ag as the recording layer, In, a material mainly composed of Sn and Te, that the Si as the light-absorbing layer, using Al-Ti respectively as the reflective layer The above-mentioned first optical recording medium is provided. Fifth, the thickness of the light absorbing layer Si is 1
0 to 25 nm, the first dielectric layer ZnS—SiO _{2 has} a thickness of 130 to 180 nm, and the second dielectric layer ZnS—S
iO _{2 having} a thickness of 20 to 30 nm, and the recording layer AgInS
The fourth optical recording medium is provided, wherein the film thickness of nTe is 10 to 25 nm.

The optical recording medium of the present invention has a five-layer structure in which a light absorbing layer made of a semiconductor film is provided on a substrate in order to control the absorption of the recording layer. By making it larger than that, the absorption rate of the crystalline phase is made larger than the absorption rate of the amorphous phase, thereby preventing mark edge distortion and realizing high density recording.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. FIG. 1 is a schematic sectional view showing a layer structure of a phase change type optical recording medium of the present invention, in which a light absorbing layer 2, a first dielectric layer 3, a recording layer 4, and a second dielectric layer 5 are provided on a transparent substrate 1. The reflective layer 6 is formed sequentially by sputtering. An ultraviolet curable resin layer 7 is spin-coated on the reflective layer as a protective layer.

As the transparent substrate 1, a plastic substrate such as acrylic or polycarbonate (PC) or a glass substrate is used. The first dielectric layer, the second dielectric layer consists of a mixture of ZnS and SiO ₂ ZnS-Si
Materials such as O ₂ , ZnS, SiO ₂ , TiO ₂ , AlN, and Si ₂ N ₂ are used.

The recording layer is made of AgInSbTe, G
eSbTe system, InSbTe system, InSe system, InTe
System, TeOx-GeSn system, TeSeSn system, SbSe
Chalcogenide-based materials such as Bi-based and BiSeGe-based are used.

As the reflection layer, a material having high thermal conductivity such as a metal is used in order to simultaneously provide a heat radiation function. For example, Al, an Al-Ti alloy, Au, Ag, Cu, and a metal material composed of these alloys are mentioned.

An ultra-thin semiconductor film is used as the light absorbing layer. If the film thickness is not reduced, the light use efficiency is deteriorated. Further, Si, Ge, or the like is used as the material of the ultra-thin semiconductor film.

The phase change type optical recording medium which can be used in the present invention is as follows.
Although not limited to the above-mentioned materials, the above-described structure and material are preferable because recording / reproducing and overwriting characteristics are improved.

FIGS. 2 to 4 show examples of the reflectivity of the crystalline phase and the amorphous phase of the optical recording medium using the above-mentioned layer structure.
In the figure, the reflectance of the multilayer film is calculated by using a generally known matrix method, and the horizontal axis represents the thickness of the first dielectric layer. In the figure, the reflectance of the crystalline phase where the recording layer is in the unrecorded state is indicated by Rc, and the reflectance of the amorphous phase which is the recording mark is indicated by Ra. Wavelength is λ
= 635 nm.

The embodiment of FIGS. 2A, 2B and 2C is as follows.
The AgInSbTe as the material of the recording layer, the Si semiconductor material as the light-absorbing layer of very thin, the first and second dielectric layers are a ZnS-SiO _2, which is a mixture of ZnS and SiO _2, the reflective layer is Al-Ti Using a polycarbonate resin as the transparent substrate and changing the thickness of the semiconductor film of Si to reflectivity R
c and Ra were calculated. In the figure, the first dielectric layer is represented by the symbol UL, and the second dielectric layer is represented by the symbol TL. The thickness of the recording layer AgInSbTe is 17 nm, and the second dielectric layer Zn
The film thickness of the S-SiO ₂ is 20 nm, the film thickness of the reflective layer Al-Ti and 120 nm, 10n the thickness of the Si in FIGS. 2 (a)
m, 16 nm in FIG. 2 (b), and 25 nm in FIG. 2 (c), a layer configuration in which the reflectance Rc of the crystalline phase and the reflectance Ra of the amorphous phase satisfy the relational expression Ra> Rc. Has been realized. In particular, when the film thickness of Si is 10 nm to 25 n
When it is in the range of m, the reflectance difference Ra-Rc becomes large, so that a good reproduced signal can be obtained.

FIGS. 3A, 3B and 3C show the crystal phase when the thickness of the recording layer is changed by setting the thickness of the semiconductor film Si to 10 nm and the thickness of the TL to 30 nm. It is an example of the reflectance of the amorphous phase. FIG. 3A shows the recording layer A.
The reflectivity of a layer configuration having a thickness of gInSbTe of 10 nm
FIG. 3B shows the reflectance of the recording layer AgInSbTe having a thickness of 17 nm, and FIG. 3C shows the recording layer AgInSbTe.
The film thickness of SbTe shows a reflectance of 25 nm.

FIGS. 4A and 4B show the crystal layer and the recording layer AgInSbTe when the thickness of the semiconductor layer Si is 10 nm and the thickness of the recording layer AgInSbTe are 10 nm and 25 nm, respectively. It is an example showing the reflectance of the amorphous phase.

3 and 4, the reflectance Ra of the amorphous phase and the reflectance Rc of the crystalline phase are both Ra>
It can be confirmed that a layer configuration satisfying the relationship of Rc exists. The thickness range of the recording layer AgInSbTe is 1
25nm from 0nm is, as the thickness range of ZnS-SiO _2, which is a TL 30 nm from 20nm is a UL. The range of the thickness of ZnS—SiO ₂ is particularly preferably 130 nm to 180 nm. It goes without saying that there is a layer configuration satisfying Ra> Rc other than the above range as the thickness range of each layer.

[0020]

EXAMPLES Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

Example 1 On a polycarbonate substrate provided with a guide groove, a thickness of 10 n
a light absorbing layer made of semiconductor Si having a thickness of 1 m on the light absorbing layer.
The first dielectric layer made of ZnS-SiO ₂ of 60 nm, a recording layer made of AgInSbTe with a thickness of 13nm on the first dielectric layer, a thickness of 25nm on the recording layer ZnS-SiO ₂
A second dielectric layer made of, and having a thickness of 120 n on the second dielectric layer
m, a reflective layer made of Al-Ti is sequentially formed by a sputtering method, and then the surface of the reflective layer is spin-coated with an ultraviolet curable resin, and then initialized using a high-power laser to perform a phase change optical recording medium. It was created.

The optical disk prepared in this manner is moved at a linear velocity of 6 m /
s to overwrite a 30 MHz signal on the track. The optical system at this time has a wavelength λ = 635 nm,
With the objective lens NA = 0.6, the laser power was set to 6 mW for erasing power and 12 mW for recording power. The recording waveform at that time is shown in FIG. From the obtained reproduced signal, the reflectance of the amorphous phase recording mark was 20%, the reflectance of the crystalline phase was 10%, and a value of the reflectance difference Ra-Rc = 10% was obtained. Further, as the reproduction signal jitter at the time of overwriting, σ
/ Tw <90% was obtained, and good overwrite jitter characteristics were realized.

[0023]

According to the optical recording medium of the first and second aspects, a light absorbing layer made of a semiconductor film is provided on a transparent substrate, and the reflectance Ra of the amorphous phase is made larger than the reflectance Rc of the crystalline phase. Effectively, the absorptance of the crystalline phase is set to be higher than the absorptivity of the amorphous phase, and the absorptance control functions to prevent the mark edge distortion at the time of overwriting, thereby realizing high density recording.

The optical recording medium according to claim 3 is characterized in that A
Since a material containing g, In, Sb, and Te as main components is used, high-density recording with excellent erasing characteristics is realized.

According to a fourth aspect of the present invention, in the optical recording medium, ZnS—SiO ₂ is used as the first and second dielectric layers, and Ag and I are used as the recording layers.
Since a material mainly composed of n, Sb, and Te is used, and a light absorption layer is made of Si and a reflection layer is made of Al-Ti, a larger reflectance difference Ra-Rc is realized, and the absorption rate control is effectively performed. And high-density recording is realized.

In the optical recording medium according to the fifth aspect, since the material of each layer is specified and the thickness of each layer is appropriately set, high-density recording excellent in recording / reproducing characteristics and overwriting characteristics is realized. You.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view illustrating a layer configuration of an example of a phase-change optical recording medium according to the present invention.

FIGS. 2A to 2C are diagrams showing reflectance and absorptance characteristics of an embodiment of the phase-change optical recording medium of the present invention.

FIGS. 3A to 3C are diagrams showing the reflectance and absorptance characteristics of another embodiment of the phase-change optical recording medium of the present invention.

FIGS. 4A and 4B are diagrams showing reflectance and absorptance characteristics of another embodiment of the phase-change optical recording medium of the present invention.

FIG. 5 is a diagram illustrating signals at the time of overwriting in the embodiment of the present invention.

FIG. 6 is a diagram illustrating a layer configuration of an example of a conventional phase change optical recording medium.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Light absorption layer 3 First dielectric layer 4 Recording layer 5 Second dielectric layer 6 Reflective layer 7 Ultraviolet curing resin layer

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Hajime Yonehara 1-3-6 Nakamagome, Ota-ku, Tokyo F-term in Ricoh Co., Ltd. (Reference) 5D029 JA01 JC02 LA14 LA15 LA17 LB01 LB03 LB07 MA02 MA03 MA13 MA14

Claims (5)

[Claims] A light absorbing layer, a first dielectric layer,
A recording layer, a second dielectric layer, and a reflective layer are sequentially laminated, and the recording layer is irradiated with a laser beam to cause a reversible phase change between a crystalline phase and an amorphous phase to record or erase information. In the variable-type optical recording medium, when the light absorbing layer is made of a semiconductor film and the recording layer is in a crystalline phase and the reflectance is Rc, and when the recording layer is in an amorphous phase is Ra, Ra> Rc. An optical recording medium characterized by the above-mentioned. 2. The optical recording medium according to claim 1, wherein said light absorbing layer is made of a semiconductor film of Si or Ge. 3. The recording layer is made of Ag, In, Sb and Te.
2. A material mainly composed of:
Or the optical recording medium according to 2. 4. The first and second dielectric layers are made of ZnS.
-SiO ₂ as the recording layer, a material containing Ag, In, Sn and Te as main components, and the light absorbing layer as Si.
The optical recording medium according to claim 1, wherein Al-Ti is used as the reflection layer. 5. The light absorption layer Si has a thickness of 10 to 25 n.
m, the thickness of the first dielectric layer ZnS—SiO ₂ is 130
The optical recording medium according to claim 4, wherein the thickness of the second dielectric layer ZnS-SiO2 is ₂₀ to 30 nm, and the thickness of the recording layer AgInSnTe is 10 to 25 nm.