JP2000011450A - Optical information recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a phase transition type optical disk having excellent overwriting characteristics. SOLUTION: This phase-change type optical information recording medium DD is constituted by laminating a first dielectric protective layer 2, a recording layer 3 consisting of a phase transition material, a second dielectric protective layer 4 and a reflection layer 5 on a transparent substrate 1 and records information by subjecting the recording layer 3 to temp. elevation liquid phasing by irradiation with a writing laser beam from the disk surface 1a side, then causing a change in reflectivity by rapid non-crystallization. The second dielectric protective layer 4 of this recording medium consists of a mixture composed of a first component and a second component. This first component is ZnS and this second component is an oxide of at least one kind among Al2O3, Ta2O5, SiO2, ZrO2, TiO2, BeO, MgO, Y2O3 and HfO2. The mixture described above has a compsn. gradient approximately not contg. ZnS in approximately the central part (b) in the thickness direction (a) of the second dielectric protective layer 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change type optical information recording medium for recording and reproducing information by irradiating a laser beam, and more particularly to a high-performance optical recording medium having excellent repetition characteristics of recording, reproduction and erasing (overwrite characteristics). The present invention relates to an optical information recording medium suitable for density recording.

[0002]

2. Description of the Related Art As shown in FIG. 1, a structure of a phase change type optical disk D is such that a first dielectric protective layer 2 and a first dielectric protective layer 2 are formed on a transparent substrate 1 having a disk surface 1a to which a write or read laser beam is irradiated. This is an optical disc in which a recording layer 3, a second dielectric protective layer 4, a reflective layer 5, and a protective layer 6 made of a variable material are sequentially laminated. The optical disc uses a method of recording, reproducing, and erasing by utilizing the fact that the optical constant of the recording layer 3 reversibly changes between a crystalline state and an amorphous state. More specifically, the phase change material constituting the recording layer 3 is heated to a liquid phase by irradiating a writing laser beam.
Information is written (recorded) by being cooled rapidly and becoming amorphous to change the optical constant. This change in the optical constant of the recording layer 3 is obtained by irradiating the read laser beam.
By detecting the change in the reflectance of the recording layer 3,
Read (reproduce) information.

[0003] In this phase change optical disk D, the recording layer 3 is crystallized and made amorphous by changing the power of one laser beam between two levels. That is, by irradiating the recording layer 3 with a high-power laser beam that raises the melting point of the phase change material constituting the recording layer 3 or more,
The recording layer 3 absorbs the energy of the laser beam, turns into a molten liquid phase, and after being rapidly cooled, becomes in an amorphous state. Also,
When the recording layer 3 is irradiated with a low-power laser beam that reaches a temperature range between the crystallization temperature and the melting point, the irradiated portion, that is, the amorphous portion is in a crystalline state.

Conventionally, the reflection layer 5 of the phase change type optical disc D
Plays a role in increasing the cooling rate when changing the phase change material constituting the recording layer 3 from the crystalline state to the amorphous state via the molten state, and the second dielectric material on the recording layer 3 The body protection layer 4 functions as a heat insulating layer. Therefore, optimally setting the thickness and the thermal characteristics of the second dielectric protection layer 4 which is a heat insulating layer requires recording, reproduction, and reproduction of the phase change optical disc D.
This is extremely important in securing the erasing characteristics.

The recording layer 3 which is a phase change material layer includes:
GeSbTe-based chalcogenide-based material, InSb
Te-based, InSe-based, and the like are used, and are mainly formed by a sputtering method, an electron beam vacuum evaporation method, or a layered method combining these. The first and second dielectric protection layers 2 and 4 are formed of a mixture of ZnS and SiO2 by the same film formation method. However, in general, sputtering is widely used in consideration of productivity. The state of the recording layer 3 immediately after film formation is a kind of amorphous state. In order to perform recording on this recording layer 3 to form a recording part in an amorphous state, the entire recording layer 3 is in a crystalline state. Is performed. That is, recording is achieved by forming an amorphous portion in this crystalline state.

In the phase-change type optical disk D, the recording layer 3 is melted above the melting point and cooled during recording as described above. Therefore, the first and second dielectric protection layers 2 and 4 sandwiching the recording layer 3
Are subjected to thermal stress repeatedly during heat mode recording of heating, melting and cooling of the recording layer 3. For this reason,
The first and second dielectric protection layers 2 and 4 are made of Z in consideration of heat resistance.
nS-SiO2 is used.

[0007]

As described above, as described above,
In the phase-change type optical disc D, the recording layer 3 is melted and cooled to become amorphous by irradiation of a writing laser beam to form a recording mark, and the difference in reflectance between the recording mark and a portion other than the recording mark is determined by reading laser beam. Is detected as a signal by irradiation. Conventionally, the first and second dielectric protective films 2 and 4 sandwiching the recording layer 3 are made of ZnS and SiO2 having heat resistance.
Was used, and showed excellent recording and erasing characteristics.

However, when overwriting is repeatedly performed, the recording layer 3 is repeatedly melted and cooled.
The flow of the recording medium 3 itself was caused, and as a result, a phenomenon that the film thickness of the recording layer 3 fluctuated and the reflectivity was reduced occurred, and the signal amplitude was reduced. In addition, the repetition of melting and cooling causes the first and second dielectric protection films 2 and 4 to be thermally damaged and deformed, damaging the recording layer 3 and increasing jitter. For the above reasons, the phase change type optical disc D has a problem that the overwrite characteristics are repeatedly deteriorated.

[0009] The object of the present invention is to solve the above problems,
An object of the present invention is to provide a phase change type optical information recording medium having excellent repetitive overwrite characteristics.

[0010]

In order to solve the above-mentioned problems, the present invention provides an optical information recording medium having the following configuration.

A first dielectric protection layer 2, a recording layer 3 made of a phase-change material, a second dielectric protection layer 4, and a reflection layer 5 are laminated on a transparent substrate 1 (from the disk surface 1a side). In the phase-change type optical information recording medium DD which records information by changing the reflectance by changing the temperature of the recording layer 3 to a temperature-raising liquid phase by irradiating a writing laser beam and then rapidly amorphizing the same, The dielectric protective layer 4 is composed of a mixture of a first component and a second component, wherein the first component is ZnS, and the second component is Al2 O3, Ta2 O5, SiO2, Zr.
O2, TiO2, BeO, MgO, Y2 O3, HfO2
Wherein the mixture has a composition gradient substantially free of ZnS at a substantially central portion b in the thickness direction a of the second dielectric protection layer 4. Optical information recording medium.

[0012]

By increasing the mechanical strength of the second dielectric protection layer 4 having the above-described structure, the deformation of the second dielectric protection layer 4 caused by the repetition of melting and cooling of the recording layer 3 is suppressed. By improving the heat dissipation characteristics by increasing the conductivity, damage to the second dielectric protection layer 4 and further damage to the recording layer 3 itself due to damage to the second dielectric protection layer 4 are suppressed. It is possible to suppress a decrease in signal amplitude and an increase in jitter at the time of overwriting, and to achieve an improvement in repeated overwriting characteristics.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the optical information recording medium of the present invention will be described below with reference to FIGS. FIG. 2 is a diagram for explaining the composition gradient of the mixture constituting the second dielectric layer.

As shown in FIGS. 1 and 2, a phase change type optical information recording medium (optical disk) DD of the present invention comprises a transparent substrate 1 on which a first dielectric protection layer 2 and a phase change material are recorded. A layer 3, a second dielectric protection layer 4, and a reflection layer 5,
In a phase-change type optical disk in which information is recorded by changing the reflectance by changing the temperature of the recording layer 3 to a temperature-raising liquid phase by irradiating a writing laser beam from the disk surface 1a and then rapidly amorphizing the recording layer 3, The body protective layer 4 is composed of a mixture of a first component and a second component, the first component being ZnS, and the second component being Al2 O3, Ta2 O5, SiO2, Z
rO2, TiO2, BeO, MgO, Y2O3, HfO2
And the mixture is an optical disk having a composition gradient substantially free of ZnS at a substantially central portion b in the thickness direction a of the second dielectric protection layer 4.

The transparent substrate 1 has concentric or spiral grooves (grooves), and can be made of polycarbonate resin, polyolefin resin, acrylic resin, quartz, glass, or the like. The recording layer 3 is made of, for example, a chalcogenide-based material such as GeSbTe-based or InSbTe-based material.
A phase change material such as a system, an InSe system, an InSb system, and a GeTe system can be used, and a material having a composition in which a metal is added to these phase change materials can also be used.

The first and second dielectric protection layers 2 and 4 are mainly composed of ZnS as a first component, Al 2 O 3 and Ta 2 O 5.
, SiO2, ZrO2, TiO2, BeO, MgO,
A dielectric material containing a mixture containing at least one oxide of oxides such as Y2 O3 and HfO2 as a second component can be used. Desirably, a mixture of ZnS—SiO 2 is good. Further, as shown in FIG. 2, the second dielectric protective layer 4 has a composition ratio of the second component in the mixture described above,
The optical disc has a composition gradient substantially free of ZnS at a substantially central portion b in a film thickness direction (a thickness direction of the dielectric protection layer) a.

The reflective layer 5 is made of a metal film having a good reflectivity of an irradiation laser beam, for example, containing Al as a main component, Cu, Cr,
A mixture with a metal such as Ni, Ti, Mo, W, or
Au or the like can be used. As the protective layer 6, a thermosetting or ultraviolet curable resin can be used on the reflective layer 5.

The production of the phase-change optical disk DD having the above-described configuration will be described in detail with reference to specific examples.

Thickness 1.2 mm, track pitch 1.6 μ
A phase-change optical disk DD is formed by sequentially laminating a first dielectric protection layer 2, a recording layer 3, a second dielectric protection layer 4, and a reflection layer 5 on a polycarbonate disk transparent substrate 1 having m continuous grooves. did.

First, using a target (composition ratio: 80:20, mol%) composed of two components of ZnS and SiO 2, R
The first dielectric protection layer 2 having a thickness of 100 nm was formed by the F sputtering method. Next, on the first dielectric protection layer 2,
A GeSbTe-based alloy was deposited to a thickness of 20 nm by a DC sputtering method as a phase change material constituting the recording layer 3. next,
A target (composition ratio: 80:20, mol%) composed of two components of ZnS and SiO2 and a SiO2 target were prepared, and a second dielectric protective layer 4 having a composition gradient of 20 nm was formed by RF sputtering.

That is, in the present embodiment, the second dielectric protection layer 4
An SiO2 layer was formed substantially at the center b in the thickness direction a, and ZnS-SiO2 layers having a composition gradient were formed on both sides thereof (shown in FIG. 2). As a formation method, at the start and end of the formation of the second dielectric protection layer 4, the RF input power of the SiO2 target becomes 0, and only the SiO2 layer is constant at almost the center b in the thickness direction a of the layer. The film is formed by appropriately controlling the RF input power so that the film is formed.

Further, on the second dielectric protection layer 4, A
A reflective layer 5 of 1 alloy was formed to a thickness of 150 nm. Finally, an ultraviolet curable resin is applied on the reflective layer 5 by spin coating.
Protective layer 6 was formed by applying a coating of 10 μm to 10 μm and curing with ultraviolet rays. Immediately after film formation, the recording layer 3 was in a kind of amorphous state, and thus was subjected to an initialization process for changing to a crystalline state. Through the above process, a phase-change optical disk DD was manufactured.

The phase-change optical disk DD manufactured as described above was rotated, and dynamic measurement and evaluation were performed. The wavelength of the irradiation laser light is 685 nm, the numerical aperture NA of the objective lens is 0.60, the linear velocity is 6.0 m / s, and the recording power is 11.0 m.
W and an erasing power of 4.5 mW, and a random signal of 8-16 modulation was recorded. The reproduction power was 1.0 mW. After repeated recording and erasing, the jitter (σ) of the 3T signal (T: channel clock period), which is the shortest mark, was measured after repeated recording and erasing, and the state of change due to the number of overwrites was observed. As a result, the phase-change optical disk DD manufactured in this example exhibited excellent characteristics in which the increase in jitter was remarkably small as compared with the related art even when the number of overwrites exceeded 105 times.

[0024]

According to the present invention, the second dielectric protective layer is composed of a mixture of ZnS and an oxide having a composition gradient, and contains ZnS in the center of the second dielectric protective layer in the thickness direction. With a configuration having an oxide layer which is not used, overwrite characteristics can be repeatedly improved, and as a result, a phase-change optical disc having high reliability can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a structure of a phase change optical disk.

FIG. 2 is a diagram for explaining a composition gradient of a mixture constituting a second dielectric layer.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 First dielectric protection layer 3 Recording layer 4 Second dielectric protection layer 5 Reflective layer a Thickness direction of dielectric protection layer b Central part D, DD Phase change optical disk

Claims (1)

[Claims] A first dielectric protective layer, a recording layer made of a phase change material, a second dielectric protective layer, and a reflective layer are laminated on a transparent substrate, and the recording layer is irradiated with a writing laser beam. In a phase-change optical information recording medium that records information by changing the reflectance by rapidly cooling and amorphizing after liquid-phase heating, the second dielectric protective layer includes a first component and a second component. Wherein the first component is ZnS and the second component is Al2 O3, Ta2 O5, SiO2, ZrO2, T
at least one oxide of iO2, BeO, MgO, Y2O3, and HfO2, and the mixture is substantially free of ZnS in a substantially central portion in a thickness direction of the second dielectric protection layer. An optical information recording medium having a composition gradient.