JPH08115535A - Optical recording medium - Google Patents

Abstract

(57) An object of the present invention is to provide an optical recording medium which is excellent in erasing characteristics and jitter characteristics, and is excellent in durability against repeated overwriting. Information can be recorded, erased, and reproduced by irradiating a recording layer formed on a substrate with light.
In an optical recording medium in which information is recorded and erased by a phase change between an amorphous phase and a crystalline phase, the optical recording medium is a transparent substrate / first dielectric layer / recording layer / second dielectric layer / light. An optical recording medium having a laminated body of absorption layers as a constituent member and having a second dielectric layer having a film thickness of 1 nm or more and less than 30 nm.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention is
The present invention relates to an optical information recording medium capable of recording, erasing and reproducing information.

In particular, the present invention relates to a rewritable phase-change type optical recording medium such as an optical disk, an optical card, an optical tape having a recording information erasing / rewriting function and capable of recording an information signal at high speed and high density. It is a thing.

[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 it 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 below the melting point of the recording layer and above the crystallization temperature to crystallize the recording mark in an amorphous state, and the original unrecorded state. Return to the state.

As a material for the recording layer of these rewritable phase change optical recording media, alloys such as Ge ₂ Sb ₂ Te ₅ (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 high speed overwriting with a circular single beam is possible only by modulating the irradiation power. In an optical recording medium using these recording layers, a dielectric layer having heat resistance and translucency is usually provided on both surfaces of the recording layer to prevent deformation and opening of the recording layer during recording. Further, a metal reflective layer such as a light-reflective metal such as 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 and to cool the recording layer. Is known to facilitate the formation of recording marks in an amorphous state and improve erasing characteristics and repetitive characteristics.

In particular, the dielectric layer between the recording layer and the reflection layer is 5
The "quick cooling structure" in which the thickness is thinner than 0 nm is superior to the "slow cooling structure" in which the dielectric layer is thickened to about 200 nm in that the change in recording characteristics due to repeated rewriting is small and the erasing power margin is wide. It is known that (T.Ohota et al, Japanese Journal of Applie
d Physics, Vol28 (1989) Suppl.28-3 pp123-128) The above-mentioned problems in the conventional rewritable phase change optical recording medium are as follows.

That is, the conventional disk structure has a problem that the shape and formation position of the newly overwritten recording mark are modulated by the signal before overwriting, and the erasing rate and the jitter characteristic are limited. In particular, when high density technology such as miniaturization of the light spot using a short wavelength laser is applied to increase the density with pit position recording,
Alternatively, when the mark length recording is adopted instead of the conventional pit position recording and the high density recording technology is applied as in the case of the pit position recording, or when the recording is performed at a high linear velocity, the above problems become more serious. Will be.

As one of the causes of this problem, since the difference in reflectance between the recorded amorphous recording mark and the crystalline state is large, the amount of light absorbed in the amorphous state of the recording layer is higher than that in the crystalline state. It is conceivable that the recording mark portion is heated faster during recording. In other words, there is a difference in the temperature rise state during recording depending on whether the portion before overwriting is a crystal or an amorphous mark, and as a result, the shape and formation position of the newly overwritten recording mark are overwritten. It is considered that the cause is that the previous signal undergoes modulation and limits the erasure rate and jitter characteristics. Particularly, in the conventional normal quenching structure, as described above, a layer having a high thermal conductivity and a high reflectance such as an Al alloy is provided adjacent to the dielectric layer on the side opposite to the light beam incident direction. Durability and good recording characteristics were obtained, but when a layer with high reflectance was provided in this way, the amount of light absorption in the amorphous state of the recording layer was considerably larger than the amount of light absorption in the crystalline state, It is difficult to solve the above problems.

Further, in order to increase the recording density, it is said that the amplitude of the reproduction signal becomes small due to the restriction of the optical resolution in the region where the space between the recording marks is made smaller than the size (λ / NA) of the irradiating light beam. This is also considered to be one of the causes of this issue. Especially, when newly overwriting the recording with the light beam size (λ / NA) or less irradiating the space between the recording marks, the shape and position of the newly overwritten recording marks are modulated and erased. It is considered that the rate and jitter characteristics are limited.

In order to solve such a problem, the following techniques are known as means for solving the problem that the light absorption amount in the amorphous state becomes higher than the light absorption amount in the crystalline state. That is, as in Japanese Unexamined Patent Publication No. 5-159360, a Ti layer having a thickness of about 50 nm is formed as a light absorbing layer after a second dielectric layer having a thickness of 220 nm, and the light absorbing layer is further increased by absorption of light. A technique is known in which a relatively thick Al alloy having a thickness of about 50 nm is formed as a heat dissipation layer in order to reduce the thermal load due to temperature.

[0013]

However, in the above structure, the second dielectric layer has a large thickness of 220 nm, which is a so-called slow cooling structure, so that the cooling degree of the recording layer is low.
Therefore, the recording characteristics are largely deteriorated due to repeated rewriting, and the thermal interference between marks greatly deteriorates the characteristics such as jitter, which is not suitable for high density recording. Further, there is a problem that a sufficient carrier-to-noise ratio (C / N) cannot be obtained in the low linear velocity region.

An object of the present invention is to improve the erasing property of a conventional optical recording medium having a rapid cooling structure, which exhibits excellent properties such as the rewriting repetitive property described above. To provide a recording medium.

Another object of the present invention is to provide an optical recording medium having excellent durability against repeated overwriting.

[0016]

According to the present invention, information is recorded by irradiating a recording layer formed on a substrate with light.
In an optical recording medium that can be erased and reproduced, and information is recorded and erased by a phase change between an amorphous phase and a crystalline phase, the optical recording medium is a transparent substrate / first dielectric layer / recording layer. / Second dielectric layer / light absorption layer as a constituent member, and the film thickness of the second dielectric layer is 1 nm or more and less than 30 nm. This is the first invention.

Further, according to the present invention, the thickness of the recording layer is 10 nm.
As described above, the present invention relates to the optical recording medium of the first invention, which is 45 nm or less. This is a second invention.

In the present invention, the material of the light absorption layer is substantially Ti, Zr, Hf, Cr, Ta, Mo, Mn, W,
Nb, Rh, Ni, Fe, Pt, Os, Co, Zn, P
At least one metal selected from d, or an alloy or mixture thereof,
The present invention relates to an optical recording medium of the second invention.
This is a third invention.

The present invention also relates to the optical recording medium of the third invention, characterized in that the material of the light absorbing layer is substantially Ti or an alloy or mixture containing Ti as a main component. This is a fourth invention.

The present invention also relates to the optical recording medium of the third invention, characterized in that the material of the light absorbing layer is substantially Nb or an alloy or mixture containing Nb as a main component. This is the fifth invention.

The present invention also relates to the optical recording medium of the third invention, characterized in that the material of the light absorbing layer is substantially W or an alloy or mixture containing W as a main component. This is the sixth invention.

The present invention also relates to the optical recording medium of the third invention, characterized in that the material of the light absorbing layer is substantially Mo or an alloy or mixture containing Mo as a main component. This is the seventh invention.

Further, according to the present invention, the thickness of the light absorption layer is 1 nm.
The present invention relates to the optical recording medium of the first invention or the second invention, which is not less than 200 nm. This is referred to as an eighth invention.

Further, according to the present invention, the heat conductivity of the material of the light absorption layer in the bulk state is 10 W / m · K or more and 200 W / m · K or more.
The present invention relates to the optical recording medium of the first invention or the second invention, characterized in that: This is the ninth invention.

In the present invention, the real part of the refractive index of the material of the light absorption layer is 1.0 or more and 8.0 or less, and the imaginary part of the refractive index is 1.5.
The present invention relates to the optical recording medium of the first invention or the second invention, which is not less than 6.5. This is the first
0 invention.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION In the optical recording medium of the present invention, by providing a light absorbing layer, the light absorbing amount of the recording layer in the amorphous state is reduced so that the difference in the light absorbing amount from the crystalline state becomes small. Can be configured. As a result, the difference in temperature rise at the time of recording becomes small, and the disorder of the shape of the recording mark, the deviation of the forming position, etc. can be reduced, and the erasing characteristic and the jitter characteristic can be improved.

The light absorbing layer of the present invention has a light reflectivity of 40 to 85% and a light reflectance of 20 to 50% at a wavelength λ of light used for recording and reproduction.
It is composed of a metal material having a light absorbing property. This light absorption effect reduces the amount of light absorption of the amorphous recording layer.

The materials are Ti, Zr, Hf and C.
r, Ta, Mo, Mn, W, Nb, Rh, Ni, Fe,
At least one metal selected from Pt, Os, Co, Zn, and Pd, or an alloy or mixture thereof is preferable because it has excellent heat resistance, strength, and corrosion resistance. In particular, Ti, Nb, W, Mo, Zr, Cr, alloys or mixtures of at least two of these, or alloys or mixtures containing these as the main components are preferable. Among these, Ti,
Nb, W, Mo, or an alloy or mixture of at least two of these, or an alloy or mixture containing these as the main components is preferable because the optical constant is in an appropriate range. Further, in view of corrosion resistance and material cost, Ti, Nb, alloys or mixtures of at least two kinds thereof, or alloys or mixtures containing these as the main components are preferable.

The thickness of the light absorption layer is preferably 1 nm to 200 nm. If the thickness of the light absorption layer is thinner than the above, the effect of light absorption is small, which is not preferable. In addition, from the erasing characteristics, it is preferable that the cooling effect of the recording layer is high, but since this cooling effect depends on the heat dissipation capacity determined by the light absorption layer, if the thickness of the light absorption layer is thin, the cooling effect is insufficient. , The erasing property is significantly reduced. Furthermore, the cooling degree of the recording layer is lowered, and the merit of the rapid cooling structure is lost. From the effects of light absorption and cooling, the thickness of the light absorption layer is more preferably 25 nm to 200 nm. Further, if the thickness of the light absorption layer is thicker than the above, a large laser power is required to form a recording mark, which is not practical.

The heat conductivity of the material of the light absorption layer is 10
W / m · K to 200 W / m · K are preferable. When the thermal conductivity of the light absorbing layer is high, the light absorbing layer can also serve as an effect of releasing heat of the recording layer during recording and cooling it.
When the thermal conductivity of the light absorption layer is lower than the above, the cooling degree of the recording layer at the time of recording is low, and the merit of the rapid cooling structure is reduced. The effect of light absorption cannot be obtained, which is not preferable. More preferably 20 W / m · K to 200 W / m · K
Is.

Here, the thermal conductivity is defined by the value of the bulk state of the material forming the light absorption layer. Such values are described in, for example, Iwanami Shoten, Iwanami Physics and Chemistry Dictionary, Cr (90 W / mK), Ta (58 W / mK).
K), Mo (138 W / mK), W (178 W / mK)
K), Nb (54 W / mK), Ti (22 W / m
K), Rh (150 W / mK), Ni (91 W / mK)
K), Fe (80 W / mK), Pt (71 W / mK)
K), Os (88W / mK), Co (99W / mK)
K), Zn (62 W / mK), Pd (76 W / mK)
K) etc.

Further, in order to obtain a large light absorption effect, it is necessary that the optical constant of the light absorption layer is in an appropriate range, and the real part of the refractive index of the material of the light absorption layer at the wavelength of the light used. 1.0-8.0, the imaginary part of the refractive index is 1.5-
It is preferably 6.5. In order to obtain a larger light absorption effect, the real part of the refractive index of the light absorption layer is 2.0 to
It is preferable that the refractive index is 6.0 and the imaginary part of the refractive index is 2.0 to 5.5.

Here, the optical constant of the material forming the light absorption layer is, for example, Academic Press, Inc., Edward D. Pali.
k (Editor), “Handbock of Optical constants of Sol
idsII ”, the film-like optical constants used in the optical recording medium of the present invention are measured, for example, as follows. When the optical recording medium is a rewritable phase change optical disk, an adhesive tape It is possible to use a sample obtained by peeling off the layer formed by using the like, or a sample in which a thin film made of the material used for the light absorption layer is formed on quartz glass. It is possible to perform measurement by using the light having the same wavelength as the wavelength of the light for recording, erasing, and reproducing by the standard ellipso method with such a device.

Measuring device: Nikon phase difference measuring device NPDM-1000 Spectrometer: M-70 Light source: Halogen lamp Detector surface: Si-Ge Polarizer, Analyzer: Gram-Thomson Analyzer rotation speed: 2 times Angle: 45 degrees to 80 degrees, 2 degree pitch The first and second dielectric layers of the present invention include a substrate, which prevents the substrate, the recording layer, etc. from being deformed by heat during recording to deteriorate the recording characteristics. The effect of protecting the recording layer from heat,
The optical interference effect has the effect of improving the signal contrast during reproduction.

For this dielectric layer, ZnS, Si
O ₂ , silicon nitride, aluminum oxide, ZnC, Zn
There are inorganic thin films such as metal sulfides such as Se, metal oxides, metal nitrides, metal carbides, metal selenides and mixtures thereof. Especially ZnS thin film, Si, Ge, Al,
Thin films of oxides of metals such as Ti, Zr, Ta, Si, A
A thin film of a nitride such as l, a thin film of a carbide such as Ti, Zr, and Hf and a film of a mixture of these compounds are preferable because of high heat resistance. In addition to these, carbon and MgF ₂
Mixtures of such fluorides are also preferable because the residual stress of the film is small. Especially mixed film of ZnS and SiO ₂ or a mixed film of ZnS and SiO ₂ and carbon are recorded, even by the repetition of erasing, preferably since the recording sensitivity, C / N, hardly occurs deterioration, such as the erasure rate, in particular Z
A mixed film of nS, SiO ₂ and carbon is preferable.

The thickness of the first dielectric layer is approximately 10-50.
It is 0 nm. The thickness is preferably 50 to 400 nm because it is difficult to peel from the substrate or the recording layer and defects such as cracks are hard to occur. In particular, since the difference in the amount of light absorption between the amorphous state and the crystalline state of the recording layer can be reduced, the thickness of the first dielectric layer is preferably set to satisfy the following equation.

Nλ / 4−0.2λ ≦ nd1 ≦ Nλ / 4 + 0.2λ where N is an integer selected from 1, 3, and 5, where λ is the wavelength used for recording and n is the first The refractive index (real part) of the dielectric layer, d1, is the thickness of the first dielectric layer.

The material of the second dielectric layer of the present invention may be the same as the material listed as the material of the first dielectric layer, or may be a different material.

The thickness of the second dielectric layer is 1 nm or more and 30 n.
Less than m is required. If the thickness of the second dielectric layer is smaller than the above value, defects such as cracks are generated, and the durability against repetition is reduced, which is not preferable. Further, if the thickness of the second dielectric layer is thicker than the above, the degree of cooling of the recording layer at the time of recording becomes low, which is not preferable. Considering the cooling degree of the recording layer at the time of recording / erasing and that the light absorption amount in the amorphous state does not become larger than the light absorption amount in the crystalline state, the thickness is preferably less than 20 nm. The thickness is more preferably less than 10 nm, and less than 5 nm is more effective when a material having a relatively low thermal conductivity is used as the light absorbing layer. When the thickness of the second dielectric layer is large, for example, a technique using W containing 5 at% or more of Au as a reflective layer is known (Japanese Patent Laid-Open Publication No. Hei.
No. 178051), in this case, a recording layer having a thickness of 30 nm is formed after a first dielectric layer having a thickness of 100 nm, and then a second dielectric layer having a thickness of 30 nm is formed, and a thicker layer is formed as a reflective layer. W containing 5 at% or more of Au of 50 nm in thickness is formed, and the effect of the amount of light absorption is small with respect to the laser light of the wavelength of 680 nm or 780 nm, and the cooling rate is low. Remarkably bad.

The recording layer of the present invention is not particularly limited, but Pd-Ge-Sb-Te alloy, Nb-G.
e-Sb-Te alloy, Pd-Nb-Ge-Sb-Te alloy, Pt-Ge-Sb-Te alloy, Ge-Sb-Te alloy, Co-Ge-Sb-Te alloy, In-Sb-Te alloy, Ag-In-Sb-Te alloy, In-Se alloy and the like are available. Since it is possible to rewrite many times, P
d-Ge-Sb-Te alloy, Nb-Ge-Sb-Te alloy, Pd-Nb-Ge-Sb-Te alloy, Ge-Sb-
Te alloys are preferred. In particular, Pd-Ge-Sb-Te alloy, Nb-Ge-Sb-Te alloy, Pd-Nb-Ge-
The Sb-Te alloy and the Pt-Ge-Sb-Te alloy are preferable because the erasing time is short, the recording and erasing can be repeated many times, and the recording characteristics such as C / N and erasing rate are excellent.

The thickness of the recording layer is 10 nm to 45 n.
m is preferred. If the recording layer is thinner than the above,
The recording characteristics are remarkably deteriorated due to repeated rewriting, and when the recording layer is thicker than the above, the recording layer is likely to move due to recording and erasing, resulting in poor jitter.

Conventionally, when recording on an optical recording medium such as a rewritable phase change type optical disk, recording is performed by irradiating a laser light pulse having a recording power level with a fixed time width according to the position of a mark to be recorded. ing. Therefore, for example, when recording is performed by the pit position recording method, recording marks of substantially constant size and area are recorded on the recording track in correspondence with the modulation code.

When the recording is rewritten by overwriting, the difference in the light absorption amount between the amorphous portion and the crystalline portion described above is set so that the amplitude of the reproduction signal of the previously recorded recording mark is reduced. The unevenness of the temperature rise due to the difference in the thermal conductivity and the difference in the thermal conductivity are reduced, and the distortion of the reproduced waveform can be reduced as the erasing characteristic of the previously recorded mark is improved.

Further, in the recording area where the price of the recording mark is equal to or smaller than the size of the irradiated light beam (λ / NA), the amplitude of the reproduced waveform becomes small due to the restriction of the optical resolution. The signal amplitude becomes extremely small, making it difficult to detect normal data.

In view of this point, in the case of pit position recording, it is possible to utilize the thermal interference between marks within the range where the jitter characteristic is not deteriorated, and the thicker the recording layer is within the above range. On the other hand, from the viewpoint of the amount of light absorption, the thinner the thickness of the recording layer, the smaller the amount of light absorption of the recording layer in the amorphous state, and the smaller the difference from the amount of light absorption in the crystalline state. Since the light absorption in the crystalline state can be made higher than the light absorption in the recording layer in the amorphous state, the thickness of the recording layer is preferably 18 nm to 45 nm in consideration of the both. More preferably, it is 26 nm to 45 nm.

On the other hand, when the mark length recording is adopted, the recording layer is likely to move due to recording and erasing as compared with the case of the pit position recording, and in order to prevent this, cooling of the recording layer at the time of recording is further increased. It is necessary that the thickness of the recording layer is thinner within the above range, preferably 10 nm.
˜35 nm, more preferably 15 nm to 30 nm.

Since the recording sensitivity is high, the one-beam overwriting is possible at a high speed, the erasing rate is large, and the erasing characteristic is good, it is preferable to configure the main part of the optical recording medium as follows.

That is, for the recording layer, an alloy containing at least three elements of Ge, Sb, and Te as constituent elements is used, the thickness of the first dielectric layer is d1, and the refractive index of the first dielectric layer (real part). Is an integer selected from n, 1, 3, and 5 is N, the laser wavelength used for recording is λ, and the thickness of the recording layer is d.
r, the thickness of the second dielectric layer is d2, and the thickness of the light absorption layer is dh
Then, it is preferable to set the layer thickness so as to satisfy the following equation.

Nλ / 4−0.2λ ≦ nd1 ≦ Nλ / 4 + 0.2λ 10 ≦ dr ≦ 45 (unit nm) 1 ≦ d2 <30 (unit nm) 1 ≦ dh ≦ 200 (unit nm) In particular, the dielectric layer Is a mixed film containing at least ZnS and SiO ₂ as constituent materials, and the mixing ratio of SiO ₂ is 15 to 35.
It is more preferable that the content is mol% and the composition of the recording layer is in the range represented by the following formula.

M _z (Sb _x Te _1-x ) _1-yz (Ge _0.5 Te _0.5 ) _y 0.35 ≦ x ≦ 0.5 0.2 ≦ y ≦ 0.5 0.0005 ≦ z ≦ 0.01 Here, M is at least one metal selected from palladium, niobium, platinum, silver, gold, and cobalt. Sb represents antimony, Te represents tellurium, and Ge represents germanium. In addition, x, y, z, and numbers represent the number of atoms of each element (the number of moles of each element).

As the material of the substrate of the present invention, various transparent synthetic resins, transparent glass and the like can be used. In order to avoid the influence of dust and scratches on the substrate, it is preferable to use a transparent substrate and perform recording from the substrate side with a focused light beam.As such a transparent substrate material, glass, polycarbonate, polymethyl methacrylate, Examples thereof include polyolefin resin, epoxy resin and polyimide resin. 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. 0.01 m
If it is less than m, even when recording with a light beam focused from the substrate side, it is easily affected by dust, and if it is 5 mm or more,
It becomes difficult to increase the numerical aperture of the objective lens, and the irradiation light beam spot size becomes large, which makes it difficult to increase the recording density.

The substrate may be flexible or rigid. The flexible substrate is used in the form of tape, sheet or card. The rigid board is used in the form of a card or disk. In addition, these substrates, after forming the recording layer,
An air sandwich structure, an air incident structure, and a close-bonding structure may be used by using two substrates.

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 is capable of downsizing, low power consumption, and modulation. Is preferable because it is easy.

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

A method of forming an amorphous recording mark at the time of recording and crystallizing at the time of erasing is preferable since the recording speed can be increased and the deformation of the recording layer hardly occurs.

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.

Next, a method for manufacturing the optical recording medium of the present invention will be described.

As a method for forming the dielectric layer, the recording layer, and the light absorption layer on the substrate, there are known known methods for forming a thin film in vacuum, such as a vacuum deposition method, an ion plating method and a sputtering method. In particular, the sputtering method is preferable because the composition and the film thickness can be easily controlled.

The thickness of the recording layer or the like to be formed can be easily controlled by monitoring the deposition state with a well-known technique such as a crystal oscillator film thickness meter.

The recording layer or the like may be formed with the substrate fixed, or moved or rotated. Since the in-plane uniformity of the film thickness is excellent, it is preferable to rotate the substrate, and it is more preferable to combine the revolution.

In addition, within a range that does not significantly impair the effects of the present invention, after forming a reflective layer or the like, a dielectric layer such as ZnS, SiO ₂ , ZnS-SiO ₂ or ultraviolet curing for preventing scratches and deformation. A protective layer of resin or the like may be provided if necessary. Furthermore, a hub or the like may be provided on the substrate as needed. Further, after forming the reflective layer or the like, or after further forming the above-mentioned resin protective layer, the two substrates may be opposed to each other and bonded with an adhesive.

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

[0064]

EXAMPLES The present invention will be described below based on examples.

(Analysis / Measurement Method) The compositions of the dielectric layer, recording layer and light absorbing layer were confirmed by ICP emission analysis (manufactured by Seiko Denshi Kogyo KK). The C / N and 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 light absorption 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 electron microscope or a transmission electron microscope.

Example 1 By a high frequency sputtering method while rotating a polycarbonate substrate with a spiral groove having a thickness of 0.6 mm, a diameter of 8.6 cm and a pitch of 1.0 μm at 30 rpm.
A recording layer, a dielectric layer and a light absorption layer were formed.

First, the inside of the vacuum chamber was evacuated to 1 × 10 ^-3 Pa, and then SiO 2 in an Ar gas atmosphere of 2 × 10 ^-1 Pa.
ZnS containing 20 mol% of ₂ was sputtered to form a 230 nm-thick first dielectric layer on the substrate. continue,
A ternary alloy target composed of Ge, Sb, and Te is sputtered to have a composition of Ge _0.24 Sb _0.23 Te _{0.53 and} a film thickness of 20 nm
Was formed. Further, a second dielectric layer made of the same material as the first dielectric layer was formed to a thickness of 5 nm, and an Nb target was sputtered on the second dielectric layer to form a light absorption layer having a thickness of 60 nm. The bulk state thermal conductivity of the material of the light absorption layer is 54 W /
m · K. After the disk was taken out from 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 form a resin layer with a film thickness of 10 μm. An optical recording medium of the present invention was obtained by the formation. Further, a double-sided disc was prepared by laminating the same type of disc 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.

The above-mentioned "Handbook of Optical Co
According to "nstants of Solids II", the optical constants of Nb, which is the material of the light absorption layer, at a wavelength of 680 nm were 2.7 for the real part of the refractive index and 2.9 for the imaginary part of the refractive index.

The amounts of light absorption in the amorphous state and the crystalline state of this disk were 53% and 63%, respectively, at the light wavelength of 680 nm as a result of calculation from the refractive index and thickness of each layer. The amount was larger than that in the amorphous state. The reflectance of the crystalline state calculated from the calculation is 21%
It is confirmed that this calculation result is appropriate since it is almost the same as the actually measured value of the disk.

Thereafter, this disk was rotated at a rotation speed of 3600r.
Rotate at pm, track the radius of 39 mm, the numerical aperture of the objective lens is 0.6, the wavelength of the semiconductor laser is 680 nm
Using the optical head of the above, at a frequency of 5.73 MHz (pulse width of 20 ns), a peak power of 8 to 15 mW and a bottom power of 3 to 8 mW were used to perform overwriting recording 100 times with a semiconductor laser beam, and then a reproducing power was obtained. 1.
Bandwidth 30kHz by irradiating 2mW semiconductor laser light
C / N was measured under the conditions of.

Further, this portion is irradiated with the semiconductor laser beam modulated at 15.3 MHz (pulse width 20 ns) in the same manner as above, and one-beam overwriting is performed.
The erase rate of the pre-recorded signal of 73 MHz was measured. With a peak power of 10 to 15 mW, a C / N of 49 dB or more is obtained,
Moreover, an erasing rate of 18 dB or more was obtained at a bottom power of 5.5 to 6.5 mW. In addition, the jitter value (σ) of the pit position when overwriting with a bottom power of 6 mW is
It was 6.2 ns.

Further, under the conditions of peak power of 12.0 mW, bottom power of 6.0 mW and frequency of 15.3 MHz,
After repeating the one-beam overwrite operation 10,000 times, the same measurement was performed, but the changes in C / N and erase rate were
Almost no deterioration was observed within 3 dB.

Example 2 The composition of the recording layer of Example 1 was changed to the composition Ge _0.19 Sb _0.28 Te.
A disk having the same structure as in Example 1 _{except for 0.53} was prepared. When the C / N, the erasing rate and the jitter were measured in the same manner as in Example 1, almost the same characteristics as in Example 1 were obtained.

Further, in the same manner as in Example 1, the one-beam overwrite was repeated 10,000 times and the same measurement was performed. However, as in Example 1, changes in C / N and erasing rate were all 3 dB. Almost no deterioration was observed within.

Example 3 The composition of the recording layer of Example 1 was changed to Nb _0.005 Ge _0.175 Sb.
A disk having the same structure as in Example 1 _except that it was _0.26 Te _0.56 was produced. When the C / N and the erasing rate were measured in the same manner as in Example 1, the peak power was 10 to 15
A C / N of 49 dB or more was obtained at mW, and an erasing rate of 20 dB or more was obtained at a bottom power of 5 to 7 mW. The jitter value (σ) of the pit position at the time of overwriting with a bottom power of 6 mW was 5.0 ns.

Further, in the same manner as in Example 1, the one-beam overwrite was repeated 10,000 times and the same measurement was carried out. However, as in Example 1, changes in C / N and erasing rate were both 2 dB. Almost no deterioration was observed within.

Example 4 The composition of the recording layer of Example 1 was changed to Pd _0.002 Nb _0.003 Ge.
A disk having the same structure as in Example 1 was prepared _{except that 0.175} Sb _0.26 Te _0.56 was used. When the C / N, erasure rate and jitter were measured in the same manner as in Example 1, almost the same characteristics as in Example 3 were obtained.

Further, in the same manner as in Example 1, the one-beam overwrite was repeated 10,000 times and the same measurement was carried out. However, as in Example 1, changes in C / N and erasing rate were both 2 dB. Almost no deterioration was observed within.

Example 5 A substrate made of polycarbonate with a spiral groove having a thickness of 1.2 mm, a diameter of 13 cm and a pitch of 1.6 μm was used.
A recording layer and a dielectric layer having the same composition as in Example 4 were formed by the same method, and the light absorption layer was formed by sputtering a W target.

The film thicknesses of the first dielectric layer, the recording layer, the second dielectric layer and the light absorption layer are 230 nm, 20 nm and 10 respectively.
nm and 50 nm.

The above-mentioned "Handbook of Optical Co."
According to "nstants of Solids II", the optical constants of W, which is the material of the light absorption layer, at a wavelength of 680 nm were 3.8 for the real part of the refractive index and 2.9 for the imaginary part of the refractive index.

The amounts of light absorption in the amorphous state and the crystalline state of this disk were calculated from the thickness and refractive index of each layer, and as a result, at a light wavelength of 680 nm, 53% and 62%, respectively.
It was larger than that in the crystalline state and that in the amorphous state. The reflectance obtained from the calculation was 20%, which was almost the same as the value actually measured on the disk, which confirmed that this calculation was valid.

After that, when the C / N and the erasing rate were measured in the same manner as in Example 1, the peak power was 9 to 15 mW.
C / N of 50 dB or more is obtained with a bottom power of 5
An erasing rate of 20 dB or more was obtained at ˜7 mW. The jitter value (σ) of the pit position at the time of overwriting with a bottom power of 6 mW was 4.2 ns.

Further, under the conditions of a peak power of 12 mW, a bottom power of 6 mW, and a frequency of 15.3 MHz, one beam overwrite was repeated 10,000 times, and the same measurement was performed. The change was within 2 dB, and almost no deterioration was observed.

Example 6 Using the same substrate as in Example 1, a dielectric layer having the same composition as in Example 1 was formed by the same method, and the composition of the recording layer was Nb.
_0.005 Ge _0.175 Sb _0.26 Te _0.56 and the light absorption layer is N
b target was sputtered and formed. The thickness of this disc is 230 nm, 30 nm, 10 nm and 60 n for the first dielectric layer, the recording layer, the second dielectric layer and the light absorption layer, respectively.
It was m.

The amounts of light absorption in the amorphous state and the crystalline state of this disk were 63% and 64% at the light wavelength of 680 nm, respectively, as a result of calculation from the refractive index and the thickness of each layer. The amount was almost the same as that in the amorphous state. The reflectance of the crystalline state calculated from the calculation is 27.
%, Which is in agreement with the actual measured value of the disk, confirming that this calculation result is appropriate.

After that, when the C / N and the erasing rate were measured in the same manner as in Example 1, the peak power was 13 to 15 m.
A C / N of 50 dB or more was obtained at W, and an erasing rate of 20 dB or more was obtained at a bottom power of 4 to 6 mW. Also,
The jitter value (σ) of the pit position at the time of overwrite with a bottom power of 5 mW was 3.6 ns.

Further, under the conditions of a peak power of 13 mW, a bottom power of 5 mW, and a frequency of 15.3 MHz, one beam overwriting was repeated 10,000 times, and the same measurement was performed. The change was within 2 dB, and almost no deterioration was observed.

Example 7 Using the same substrate as in Example 1, a dielectric layer having the same composition as in Example 1 was formed by the same method, and the composition of the recording layer was Nb.
_0.005 Ge _0.175 Sb _0.26 Te _0.56 with light absorption layer of W
The target was sputtered and formed. The bulk state thermal conductivity of the material of the light absorption layer is 178 W / m · K. The thickness of this disc is 230 nm, 30 nm, 5 n for the first dielectric layer, the recording layer, the second dielectric layer, and the light absorption layer, respectively.
m and 40 nm.

The amounts of light absorption in the amorphous state and the crystalline state of this disk were 59% and 63%, respectively, at the light wavelength of 680 nm as a result of calculation from the refractive index and the thickness of each layer. The amount was larger than that in the amorphous state. The reflectance of the crystalline state calculated from the calculation is 25%
Since this is in agreement with the value actually measured on the disk, it was confirmed that the result of this calculation was appropriate.

Then, the C / N and the erasing rate were measured in the same manner as in Example 1. The peak power was 12 to 15 m.
A C / N of 50 dB or more was obtained at W, and an erasing rate of 20 dB or more was obtained at a bottom power of 4 to 6 mW. Also,
The jitter value (σ) of the pit position at the time of overwrite with a bottom power of 5 mW was 3.6 ns.

Further, under the conditions of a peak power of 12 mW, a bottom power of 5 mW, and a frequency of 15.3 MHz, one beam overwriting was repeated 10,000 times, and the same measurement was performed. The change was within 2 dB, and almost no deterioration was observed.

Example 8 Using the same substrate as in Example 1, a dielectric layer having the same composition as in Example 1 was formed by the same method, and the composition of the recording layer was Nb.
_0.005 Ge _0.175 Sb _0.26 Te _0.56 and the light absorption layer is M
o A target was sputtered to form. The bulk state thermal conductivity of the material of the light absorption layer is 138 W / m · K. The thickness of this disc is 70 nm, 35 nm, 5 n for the first dielectric layer, the recording layer, the second dielectric layer, and the light absorption layer, respectively.
m and 40 nm.

The above-mentioned "Handbook of Optical Co."
According to "nstants of Solids II", the optical constants of Mo, which is the material of the light absorption layer, at a wavelength of 680 nm were 3.8 for the real part of the refractive index and 3.6 for the imaginary part of the refractive index.

The amounts of light absorption in the amorphous state and the crystalline state of this disk were 65% and 66% at the light wavelength of 680 nm as a result of calculation from the refractive index and the thickness of each layer. The amount was almost the same as that in the amorphous state. The reflectance of the crystalline state calculated from the calculation is 27.
%, Which is in agreement with the actual measured value of the disk, confirming that this calculation result is appropriate.

After that, when the C / N and the erasing rate were measured in the same manner as in Example 1, the peak power was 11 to 14 m.
A C / N of 50 dB or more was obtained at W, and an erasing rate of 20 dB or more was obtained at a bottom power of 3 to 5 mW. Also,
The jitter value (σ) of the pit position at the time of overwrite with a bottom power of 4 mW was 3.4 ns.

Further, under the conditions of a peak power of 11 mW, a bottom power of 4 mW, and a frequency of 15.3 MHz, one beam overwriting was repeated 10,000 times, and the same measurement was performed. The change was within 2 dB, and almost no deterioration was observed.

Example 9 A substrate similar to that of Example 1 was used, a dielectric layer having the same composition as that of Example 1 was formed by the same method, and the composition of the recording layer was Nb.
_0.005 Ge _0.175 Sb _0.26 Te _0.56 and the light absorption layer is T
The i target was formed by sputtering. The bulk state thermal conductivity of the material of the light absorption layer is 22 W / m · K. The film thickness of this disc is 210 nm, 30 nm, 3 n for the first dielectric layer, the recording layer, the second dielectric layer, and the light absorption layer, respectively.
m and 70 nm.

The amounts of light absorption in the amorphous state and the crystalline state of this disk were 59% and 61% at the light wavelength of 680 nm as a result of calculation from the refractive index and the thickness of each layer. The amount was almost the same as that in the amorphous state. The reflectance of the crystalline state obtained from the calculation is 25
%, Which is in agreement with the actual measured value of the disk, confirming that this calculation result is appropriate.

Then, the C / N and the erasing rate were measured in the same manner as in Example 1. The peak power was 13 to 15 m.
A C / N of 50 dB or more was obtained at W, and an erasing rate of 21 dB or more was obtained at a bottom power of 4 to 6.5 mW. Further, the jitter value (σ) of the pit position at the time of overwriting with a bottom power of 5 mW was 3.1 ns.

Further, under the conditions of peak power of 13 mW, bottom power of 5 mW, and frequency of 15.3 MHz, one beam overwriting was repeated 10,000 times, and the same measurement was performed. The change was within 2 dB, and almost no deterioration was observed.

Example 10 The composition of the recording layer of Example 9 was changed to Pd _0.002 Nb _0.003 Ge.
A disk having the same structure as in Example 9 was prepared _{except that 0.175} Sb _0.26 Te _0.56 was used.

Then, this disk was rotated at a rotation speed of 3000r.
Rotate at pm, track the radius of 39 mm, the numerical aperture of the objective lens is 0.6, the wavelength of the semiconductor laser is 680 nm
Using the optical head of the above, at a frequency of 4.78 MHz (pulse width of 20 ns), a semiconductor laser beam modulated to each condition of a peak power of 8 to 15 mW and a bottom power of 3 to 8 mW was used to perform overwriting recording 100 times, and then reproduction power was obtained. 1.
Bandwidth 30kHz by irradiating 2mW semiconductor laser light
C / N was measured under the conditions of.

Further, this portion is irradiated with the semiconductor laser light modulated at 12.8 MHz (pulse width 20 ns) in the same manner as above, and one-beam overwriting is performed.
The erase rate of the pre-recorded signal of 78 MHz was measured. C / N of 50 dB or more is obtained at a peak power of 12 to 15 mW,
Moreover, an erasing rate of 21 dB or more was obtained at a bottom power of 3.5 to 6 mW. Also, the jitter value (σ) of the pit position at the time of overwriting with a bottom power of 5 mW is 3.3 ns.
Met.

Further, under the conditions of peak power 13.0 mW, bottom power 5.0 mW and frequency 12.8 MHz,
After repeating the one-beam overwrite operation 10,000 times, the same measurement was performed, but the changes in C / N and erase rate were
Almost no deterioration was observed within 2 dB.

Example 11 Using a polycarbonate substrate with a spiral groove having a thickness of 0.6 mm, a diameter of 12 cm, and a pitch of 1.4 μm,
A dielectric layer having the same composition as in Example 1 was formed by the same method, and the composition of the recording layer was Pd _0.001 Nb _0.003 Ge _0.176 S.
b _0.26 Te _0.56 , and the light absorption layer was formed by sputtering a Ti target. The thickness of this disc is 210 for each of the first dielectric layer, the recording layer, the second dielectric layer, and the light absorption layer.
nm, 15 nm, 5 nm and 70 nm.

The light absorption amounts in the amorphous state and the crystalline state of this disk were calculated from the thickness refractive index of each layer, and were 46% and 59%, respectively, at the light wavelength of 680 nm. Was larger than that in the amorphous state. The reflectance obtained from the calculation was 21%, which was almost the same as the value actually measured on the disk, which confirmed that this calculation was valid.

Thereafter, under the condition of a linear velocity of 4.4 m / sec, the numerical aperture of the objective lens is 0.6 and the wavelength of the semiconductor laser is 680.
1-7 RL with edge recording using an nm optical head
In order to form a recording mark (frequency 4.2 MHz at the time of reproduction) corresponding to LC 1.33T, the peak power is 7 to
After overwriting recording 100 times with a semiconductor laser light modulated to each condition of 15 mW and a bottom power of 2 to 6 mW, the semiconductor laser light having a reproduction power of 1.2 mW was irradiated to measure the C / N under the condition of a bandwidth of 30 kHz. .

Further, this portion is changed to 4.66T (1.2M
Of the semiconductor laser light modulated in the same manner as above, and one-beam overwriting was performed.
The erasure rate of T and the jitter at the edge of the end portion of the reproduction signal of the recording mark were measured. A practically sufficient C / N of 50 dB or more was obtained at a peak power of 9 mW or more, and a practically sufficient erasing rate of 20 dB or more was obtained at a bottom power of 3 to 5 mW. The jitter value (σ) at the time of overwriting with a bottom power of 4 mW was 3.5 ns.

Further, after repeating the one-beam overwrite operation 10,000 times under the condition of the frequency 4.2 MHz with the semiconductor laser modulated under the conditions of the peak power of 10 mW and the bottom power of 4.5 mW, the same measurement was carried out. But,
The changes in C / N and erasing rate were all within 2 dB, and almost no deterioration was observed.

Comparative Example 1 The second dielectric layer of the optical recording medium of Example 5 had a thickness of 35 nm,
A disk having the same structure as in Example 5 except that the thickness of the first dielectric layer was 270 nm was produced.

The amounts of light absorption in the amorphous state and the crystalline state of this disk were calculated as 64% and 59% at the light wavelength of 680 nm as a result of calculation from the refractive index and thickness of each layer. Was smaller than that in the amorphous state. The calculated reflectance of the crystalline state is 27%, which is in agreement with the measured value of the disk.
It was confirmed that this calculation result was appropriate.

When measured in the same manner as in Example 5, the maximum erasing rate was 18 dB and the jitter was 8.5 ns, which was inferior to Example 5.

[0116]

According to the present invention, the following effects are obtained. (1) Good erasing rate and jitter characteristics. (2) Even if recording and erasing are repeated a large number of times, the operation is stable and there is almost no deterioration of characteristics or occurrence of defects. (3) It can be easily manufactured by the sputtering method.

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

Claims (10)

[Claims] 1. Information can be recorded, erased, and reproduced by irradiating a recording layer formed on a substrate with light.
In an optical recording medium in which information is recorded and erased by a phase change between an amorphous phase and a crystalline phase, the optical recording medium is a transparent substrate / first dielectric layer / recording layer / second dielectric layer / light. An optical recording medium having a laminated body of absorption layers as a constituent member and having a second dielectric layer having a film thickness of 1 nm or more and less than 30 nm. 2. The optical recording medium according to claim 1, wherein the recording layer has a thickness of 10 nm or more and 45 nm or less. 3. The material of the light absorption layer is substantially Ti, Zr,
Hf, Cr, Ta, Mo, Mn, W, Nb, Rh, N
The optical recording medium according to claim 1 or 2, which is at least one metal selected from i, Fe, Pt, Os, Co, Zn, and Pd, or an alloy or mixture thereof. 4. The optical recording medium according to claim 3, wherein the material of the light absorbing layer is substantially Ti or an alloy or mixture containing Ti as a main component. 5. The optical recording medium according to claim 3, wherein the material of the light absorbing layer is substantially Nb or an alloy or mixture containing Nb as a main component. 6. The material of the light absorption layer is substantially W or W.
The optical recording medium according to claim 3, wherein the optical recording medium is composed of an alloy or a mixture containing as a main component. 7. The optical recording medium according to claim 3, wherein the material of the light absorbing layer is substantially Mo or an alloy or mixture containing Mo as a main component. 8. The optical recording medium according to claim 1, wherein the thickness of the light absorption layer is 1 nm or more and 200 nm or less. 9. The optical recording medium according to claim 1, wherein the material for the light absorption layer has a bulk state thermal conductivity of 10 W / m · K or more and 200 W / m · K or less. 10. The real part of the refractive index of the material of the light absorbing layer is 1.0.
3. The optical recording medium according to claim 1, wherein the optical recording medium has a refractive index of not less than 8.0 and an imaginary part of a refractive index of not less than 1.5 and not more than 6.5.