JPH0916962A - Optical recording medium - Google Patents

Abstract

PURPOSE: To stabilize tracking and reduce crosstalk. CONSTITUTION: This optical recording medium can have information recorded, erased, or reproduced by irradiating the recording layer formed on the substrate with light and the recording and erasure of the information are performed by a phase change between an amorphous phase and a crystalline phase; and guide grooves for tracks are formed on the surface of the said substrate where the recording layer is formed and the recording is performed both at the guide grooves and between the guide grooves. Before this optical recording medium is actually used, recording marks are previously formed on all the tracks at the guide groove parts and between the guide grooves in the actual recording area.

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 by irradiating light.

In particular, the present invention relates to a rewritable phase change type optical recording medium such as an optical disc having a function of erasing and rewriting recorded information and capable of recording information signals at high speed and high density.

[0003]

2. Description of the Related Art The conventional techniques for rewritable phase change type optical recording media are as follows.

These optical recording media have a recording layer containing tellurium as a main component, and at the time of recording, a focused laser light pulse is irradiated to the recording layer in a crystalline state for a short time to partially cover the recording layer. To melt. The melted portion is rapidly cooled by thermal diffusion and solidified to form a recording mark in an amorphous state. The light reflectance of this recording mark is lower than that of the crystalline state and can be optically reproduced as a recording signal.

Further, at the time of erasing, the recording mark portion is irradiated with a laser beam and heated to a temperature not lower than the melting point of the recording layer and not lower than the crystallization temperature to crystallize the recording mark in an amorphous state, and the original unrecorded state. Return to.

As the material of the recording layer of these rewritable phase change optical recording media, alloys such as Ge2 Sb2 Te5 (N.Ya
mada et al, Proc. Int. Symp.on Optical Memory 1987 p
61-66) is known.

Optical recording media using these Te alloys as recording layers have a high crystallization rate, and use these recording layers capable of high-speed overwriting with one circular beam only by modulating the irradiation power. In an optical recording medium, a dielectric layer having heat resistance and translucency is usually provided on both surfaces of a recording layer to prevent deformation and opening of the recording layer during recording. Further, a metal reflective layer such as light-reflective Al is provided on the dielectric layer on the side opposite to the light beam incident direction to improve the signal contrast at the time of reproduction by an optical interference effect. There is known a technique which facilitates formation of a recording mark in a crystalline state and improves erasing characteristics and repetition characteristics. In particular, the "quench-cooling structure" in which the recording layer and the dielectric layer between the recording layer and the reflecting layer are each thinned to about 20 nm is more repetitive than the "slow-cooling structure" in which the dielectric layer is thickened to about 200 nm. Excellent in that the recording characteristics are not deteriorated and the erasing power has a wide power margin (T.Ohota et al, Japanese Jounal of App
lied Physics, Vol 28 (1989) Suppl. 28-3 pp123-12
8).

Recently, in order to achieve higher density recording, a recording method has been proposed in which recording is performed not only in the guide grooves of the optical disk but also between adjacent guide grooves, and the rewriting type of this method using the phase change method is proposed. An optical disk has been proposed (Japanese Patent Laid-Open No. 5-28275).

[0009]

However, the above-described optical recording medium (hereinafter referred to as a land / groove recording medium) for recording in both the guide groove (groove) and the groove (land) has the following problems. It was

In the land / groove recording medium, the distance between the recording tracks is about half that of the conventional one, so that a considerable part of the laser beam spot extends to the adjacent recording tracks. Therefore, when the recording mark is recorded on only one of the adjacent tracks, the intensity distribution of the reflected light at the time of recording / reproducing becomes asymmetrical, and in the push-pull method and the three-beam method, which are general tracking means. There is a problem that an offset is apt to occur in tracking and during recording and reproduction, and as a result, crosstalk and cross erase from adjacent tracks increase and recording performance is impaired.

An object of the present invention is to solve the above-mentioned problems of the conventional optical recording medium and to provide an excellent optical recording medium having a large capacity, stable recording and reproducing characteristics, and easy to manufacture. It is in. Another object of the present invention is to provide an optical recording medium having excellent recording durability.

[0012]

According to the present invention, information can be recorded, erased, and reproduced by irradiating a recording layer formed on a substrate with light.
An optical recording medium that is performed by a phase change between an amorphous phase and a crystalline phase, and a track guide groove is formed on the surface of the substrate on which the recording layer is provided, and both the guide groove and the guide groove are formed. In the optical recording medium for recording on the portion of, the optical recording medium is characterized by forming recording marks in advance on the guide groove portion in the actual recording area and all tracks between the guide grooves before being actually used. is there.

In the present invention, in order to avoid the occurrence of the above-described track offset set which occurs when recording is performed on only one of the adjacent tracks, the guide groove portion and the guide groove portion in the actual recording area are provided before the actual use. It is important to form recording marks on all the tracks in advance. Here, “actual use” means, for example, use by a user, full-scale use, or repeated use. That is, in the present invention, for example, before being used by the user in advance, the manufacturer or the like previously forms recording marks on the guide groove portion in the recording area of the user and all tracks between the guide grooves. As a result, since all tracks in the recording area of the user are recorded when the user uses it, even if the user newly records (that is, corresponds to rewriting), tracking becomes unstable and a track offset set or the like occurs. Will disappear.

As a method of recording in advance on all tracks,
Although not particularly limited, the groove portion (or the groove portion)
It is preferable to record all the tracks of any one of the above, and then record all the tracks of the remaining inter-groove portions (or groove portions) because the recording mark is formed without causing the track offset.

The recording mark to be recorded here is not particularly limited, but the mark length and the mark-to-mark space are substantially equal to each other so that a DC offset does not occur during reproduction. It is preferable to record so that the spaces are substantially random. The recording system for recording marks may be either mark position recording or mark length recording.

The structure of the optical recording medium used in the present invention will be described below.

The layer structure of the phase change optical recording medium of the present invention is not particularly limited, but at least the transparent substrate / first dielectric layer /
It is preferable to use a laminated body of recording layer / second dielectric layer / reflection layer as a constituent member because good recording characteristics can be obtained.
However, the present invention is not limited to this, and another layer such as a resin layer such as an ultraviolet curable resin or an adhesive layer for laminating with another substrate may be provided on the reflective layer as long as the effect of the present invention is not impaired. Good.

As the material for the substrate of the phase change optical recording medium of the present invention, various transparent synthetic resins, transparent glass, etc. can be used. To avoid the effects of dust and scratches on the board,
It is preferable to use a transparent substrate and perform recording from the substrate side with a focused light beam. Examples of such a transparent substrate material include glass, polycarbonate, polymethyl methacrylate, polyolefin resin, epoxy resin, polyimide resin and the like. In particular, a polycarbonate resin and an amorphous polyolefin resin are preferable because they have a small optical birefringence, a small hygroscopicity, and easy molding.

The thickness of the substrate is not particularly limited, but 0.01 mm to 5 mm is practical. 0.01m
If it is less than m, it is easily affected by dust even when recording with an optical beam focused from the substrate side. If it exceeds 5 mm,
It becomes difficult to increase the numerical aperture of the objective lens, and the spot size of the irradiation light beam becomes large, so that it becomes difficult to increase the recording density. The substrate may be flexible or rigid. These substrates may be formed into a contact bonding structure, an air sandwich structure or the like by using two substrates after forming a recording layer and the like.

Further, the depth of the guide groove of the disk substrate is defined as follows: where the recording light wavelength is λ and the refractive index of the substrate is n.
By setting it to be not less than 0.15 (λ / n) and not more than 0.2 (λ / n), the optical from the adjacent recording mark at the time of reproducing the recording mark 1 is utilized by utilizing the optical phase difference with the adjacent track. It is preferable that a high track density can be realized by reducing the effective crosstalk, and at the same time, tracking can be easily and stably made by increasing the track cross signal.

Further, by setting the ratio (Wg / Wl) of the width Wg of the flat surface portion of the guide groove to the width Wl of the flat surface portion between the guide grooves to be 0.7 or more and 1.3 or less, the guide groove and the guide groove are formed. Facilitate recording and reproduction of the disc by making the recording characteristics such as the reproduction signal strength of the recording marks recorded in each of the intervals, the power of the laser light required for recording and erasing, and the erasing rate at the time of overwriting almost the same. Is preferred.

Further, the track pitch from the center of the groove portion to the center of the next inter-groove portion is 60, which is the diameter of the light beam when the diameter of the light beam used for recording is λ / NA (recording wavelength λ and numerical aperture NA). % Or more and 80% or less is preferable because crosstalk and cross erase are small and the track density can be increased.

The first and second dielectric layers are the substrate during recording,
The effect of protecting the substrate and recording layer from heat, such as preventing the recording layer from being deformed by heat and degrading the recording characteristics. The optical interference effect has the effect of improving the signal contrast during playback. It is preferable to provide them in layers.

As the dielectric layer, ZnS, Si
There are inorganic thin films such as O ₂ , silicon nitride, and aluminum oxide. In particular, a thin film of ZnS, Si, Ge, Al, Ti,
Thin films of oxides of metals such as Zr and Ta, thin films of nitrides such as Si and Al, thin films of carbides such as Ti, Zr and Hf, and films of mixtures of these compounds are preferable because of high heat resistance. . A mixture of carbon and fluoride such as MgF2 is also preferable because the residual stress of the film is small.

In particular, a mixed film of ZnS and SiO ₂ or
A mixed film of ZnS, SiO ₂ and carbon is preferable because deterioration of recording sensitivity, C / N, erasing rate, etc. does not easily occur even when recording and erasing are repeated, and a mixed film of ZnS, SiO ₂ and carbon is particularly preferable.

The thickness of the first and second dielectric layers is approximately 10 to 500 nm. The thickness of the first dielectric layer is preferably 50 to 400 nm because it is difficult to peel it off from the substrate or the recording layer, and defects such as cracks are hard to occur. The second dielectric layer preferably has a thickness of 5 to 40 nm because it has stable recording characteristics such as C / N and erasure rate and can be stably rewritten many times.

The recording layer of the present invention is not particularly limited, but a Pd-Ge-Sb-Te alloy, Nb-G is used.
e-Sb-Te alloy, Ni-Ge-Sb-Te alloy, G
e-Sb-Te alloy, Co-Ge-Sb-Te alloy, I
n-Sb-Te alloy, Ag-In-Sb-Te alloy, I
There are n-Se alloys and the like.

Since the recording can be rewritten many times, Pd-Ge-Sb-Te alloy, Nb-Ge-Sb-Te
Alloy, Ge-Sb-Te alloy, Co-Ge-Sb-Te
Alloys are preferred.

In particular, the composition represented by the following composition formula has a short erasing time, allows recording and erasing to be repeated many times, and has excellent recording characteristics such as C / N and erasing rate. Therefore, it is preferable.

Compositional formula M z (Sbx Te1-x) 1-yz (Ge0.5 Te0.5) y 0.35 ≦ x ≦ 0.5 0.2 ≦ y ≦ 0.5 0.0005 ≦ z ≦ 0 0.005 Here, M represents at least one metal selected from palladium, niobium, platinum, silver, gold, and cobalt. Further, x, y, z and the numbers represent the number of atoms of each element (the number of moles of each element).

The thickness of the recording layer of the present invention is not particularly limited, but is 10 to 100 nm. In particular, the recording and erasing sensitivity is high, and the recording and erasing can be performed many times, so that the thickness is preferably 10 nm or more and 40 nm or less.

Further, it is preferable to provide a reflective layer on the second dielectric layer. As the material, A having light reflectivity
Metals such as 1, Au, Ag, and Cu, and alloys thereof, and mixtures of metals with metal compounds such as metal oxides, metal nitrides, and metal carbides are preferable, and Al and A are particularly preferable.
Metals having a high reflectance such as u, Ag and Cu, and alloys containing 80 atomic% or more of these as a main component are preferable.

As an example of the aforementioned alloy, Al, Si, M
g, Cu, Pd, Ti, Hf, Zr, Ta, Cr, N
At least one element such as b or Mn is 5 atomic% in total
Below, more than 05 atom% added, or Au to C
at least 1 of r, Ag, Cu, Pd, Pt, Ni, etc.
For example, a total of 20 atomic% or less and 1 atomic% or more of seed elements may be added. In particular, an alloy containing Al as a main component is preferable because the cost of the material can be reduced.

In particular, since the Al alloy has good corrosion resistance, at least one metal selected from Ti, CrZr, and Hf is added to Al in a total amount of 5 atomic% or less and 0.5 atomic% or more. , Pd in an amount of 0.05 atomic% or more and 0.5 atomic% or less is preferable.

The thickness of the reflective layer is about 30 nm.
Not less than 300 nm. High recording sensitivity and excellent recording durability make it 100 nm or more and 200 n or more
m or less.

In particular, since the recording sensitivity is high, the single beam overwrite is possible at a high speed, the erasing rate is large, and the erasing characteristic is good, the main part of the optical recording medium can be constructed as follows. preferable.

That is, the dielectric layer is a mixed film of ZnS, SiO2, and carbon, the mixing ratio of SiO2 is 15 to 35 mol%, the carbon mixing ratio is 1 to 10 mol%, and the refractive index at the recording light wavelength is set. Is 2.0 to 2.3, the first dielectric layer has a thickness of 150 nm to 400 nm, the second dielectric layer has a thickness of 10 nm to 30 nm, and the recording layer has a thickness of 1 nm.
0 nm to 30 nm, reflective layer thickness 50 nm to 200 nm
It is preferable that the recording layer is composed of the Al alloy and the composition of the recording layer is in the range represented by the following formula.

Compositional formula M z (Sbx Te1-x) 1-yz (Ge0.5 Te0.5) y 0.35≤x≤0.5 0.2≤y≤0.5 0.0005≤z≤0 0.005 Here, M represents at least one metal selected from palladium, niobium, and platinum. Further, x, y, z and the numbers represent the number of atoms of each element (the number of moles of each element).

The light source used for recording on the optical recording medium of the present invention is a high-intensity light source such as laser light or strobe light. Particularly, the semiconductor laser light has a small light source, low power consumption, and modulation. It is preferable because it is easy.

Recording is performed by irradiating a laser beam pulse or the like to the crystalline recording layer to form an amorphous recording mark. Alternatively, a recording mark in a crystalline state may be formed on a recording layer in an amorphous state. Erasure can be performed by irradiating a laser beam to crystallize an amorphous recording mark or to amorphize a crystalline recording mark.

Since the recording speed can be increased and the recording layer is hardly deformed, it is preferable to form an amorphous recording mark at the time of recording and crystallize at the time of erasing.

Further, when forming the recording mark, the light intensity is high,
The one-beam overwrite in which the light is slightly weakened at the time of erasing and rewriting is performed by irradiating the light beam once is preferable because the rewriting time is shortened.

The recording layer is preferably preliminarily crystallized by irradiation with light such as a laser beam or a xenon flash lamp before actual recording.

[0044]

EXAMPLES The present invention will be described below based on examples. (Analysis and measurement method) The compositions of the reflective layer and the recording layer were confirmed by ICP emission analysis (manufactured by Seiko Denshi Kogyo KK).
The carrier-to-noise ratio and the erasing rate (difference in reproduced carrier signal intensity after recording and after erasing) were measured by a spectrum analyzer.

The film thickness during the formation of the recording layer, the dielectric layer and the reflective layer was monitored by a crystal oscillator film thickness meter. The thickness of each layer was measured by observing the cross section with a scanning or transmission electron microscope.

(Example 1) Thickness 0.6 mm, diameter 12c
A recording layer, a dielectric layer, and a reflective layer were formed by a high frequency sputtering method while rotating a polycarbonate substrate with a spiral groove having a pitch of m and 1.4 μm at 30 rpm.

First, the inside of the vacuum chamber was evacuated to 1 × 10 ^-5 Pa, and then SiO 2 in an Ar gas atmosphere of 2 × 10 ^-1 Pa.
ZnS added with 20 mol% of ₂ was sputtered to form a first dielectric layer having a film thickness of 100 nm on the substrate. A recording layer was formed. Further, a second dielectric layer of the same material as the first dielectric layer is formed to a thickness of 20 nm, and an Al98.1Hf1.7 Pd0.2 alloy is sputtered on this to form a film with a thickness of 1
A 50 nm reflective layer was formed.

After the disk was taken out of the vacuum container, an acrylic UV curable resin (SD-101 manufactured by Dainippon Ink and Chemicals, Inc.) was spin-coated on the reflective layer and cured by UV irradiation to give a film thickness of 10 μm. A resin layer was formed to obtain the optical recording medium of the present invention. Further, a double-sided disk was prepared by laminating a disk of the same type as the disk formed in the same manner with a hot melt adhesive (XW30 manufactured by Toagosei Kagaku Kogyo Co., Ltd.).

This optical recording medium was irradiated with a semiconductor laser beam having a wavelength of 820 nm to crystallize and initialize the recording layer on the entire surface of the disk.

Next, a linear velocity of 9 m / s was obtained by a drive device (using a push-pull tracking system) having an optical head with a semiconductor laser wavelength of 680 nm and a numerical aperture of 0.6.
s, a recording power of 12 mW, and an erasing power of 4.5 mW, the continuous 50 tracks of this optical disk were previously recorded at a recording frequency of 3 MHz in the order of 25 tracks in the guide groove portion and 25 tracks between the guide grooves, and the optical recording of the present invention The medium was obtained.

Then, a signal of 4 MHz was recorded on the track of the guide groove portion of this recorded area, and a signal of 5 MHz was recorded on the track between the guide grooves by overwriting one track each. Here, for recording, a track to be recorded was randomly selected from 50 tracks each time, recording was performed only on unrecorded tracks, and recording was performed on all 50 tracks.

Next, the recorded track was reproduced, and the crosstalk from the adjacent track was measured. As a result, the crosstalk on any track was -30 dB, which was a very small and good value.

(Comparative Example) Using an optical disk having the same structure as in Example 1, the same crosstalk measurement was performed without recording at 3 MHz in advance.

Depending on the track to be reproduced, there is a large variation of crosstalk of -30 dB, while there is a good track of -15 dB.

[0055]

According to the present invention, since the recording marks are formed in advance on the optical recording medium of the land / groove recording system, the following effects can be obtained. (1) Tracking was stable and crosstalk could be reduced. (2) Stable tracking can be performed even with the push-pull tracking method.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Futoshi Okuyama 1-1-1, Sonoyama, Otsu City, Shiga Prefecture Toray Co., Ltd. Shiga Plant

Claims (3)

[Claims] 1. Information can be recorded, erased, and reproduced by irradiating a recording layer formed on a substrate with light, and the recording and erasing of information is performed in a phase between an amorphous phase and a crystalline phase. In an optical recording medium which is performed by a change, a guide groove of a track is formed on the surface of the substrate on which the recording layer is provided, and an optical recording medium which performs recording in both the guide groove and the guide groove is provided. The optical recording medium is characterized in that the recording marks are formed in advance on the guide groove portion in the actual recording area and all the tracks between the guide grooves before being actually used. 2. An optical recording medium comprising at least a transparent substrate / first
The optical recording medium according to claim 1, wherein a laminated body of dielectric layer / recording layer / second dielectric layer / reflection layer is used as a constituent member. 3. The optical recording medium according to claim 2, wherein the composition of the recording layer is represented by the following composition formula. Composition formula M z (Sbx Te1-x) 1-yz (Ge0.5 Te0.5) y 0.35 ≦ x ≦ 0.5 0.2 ≦ y ≦ 0.5 0.0005 ≦ z ≦ 0.005 here Here, M represents at least one metal selected from palladium, niobium, platinum, silver, gold and cobalt. Further, x, y, z and the numbers represent the number of atoms of each element (the number of moles of each element).