JPH09237435A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain the reducing of a crosstalk amount and a cross erasure without providing a special optical system and a signal processing circuit by making the reflectance of the crystallization state of a mirror part to be within a prescribed range. SOLUTION: An optical recording medium is constituted so that a recording sensitivity is high, the contrast of a signal is high and also the reflectance of the crystallization state of the mirror part is larger than 15% and is not larger than 35%. When the reflectance of the crystallization state of the mirror part is larger than 35%, the irradiating power of a light performing a recording and an erasing becomes insufficient and the recording becomes difficult in a high-speed revolution and the crosstalk from the recorded part of adjacent tracks is increased. Moreover, when the reflectance of the crystallization part is not larger 15%, since the difference of reflectances between the recorded mark and a non-crystallization part is small, the signal contrast at the time of reproducing becomes small. Here, the mirror part where grooves and pre-pits are not formed is called the mirror face part. Further, it is desirable that the reflectance of the non-crystallization part of the mirror part is not larger than 10%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to
The present invention relates to an optical information recording medium capable of recording, erasing, and reproducing information. Particularly, the present invention has a rewritable phase change type optical disk, optical card, optical tape or the like which has a function of erasing and rewriting recorded information on both the land surface and the groove surface, and can record information signals at high speed and high density. The present invention relates to an optical recording medium.

[0002]

2. Description of the Related Art The technology of the conventional rewritable phase change optical recording medium is as follows. These optical recording media have a recording layer whose main component is an alloy of Te, Ge and Sb. 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 melt the recording layer. The melted portion is quenched by thermal diffusion and solidified to form an amorphous recording mark. The light reflectance of this recording mark is lower than that of the crystalline state and can be reproduced optically 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 higher 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.

[0004] These optical recording media having a Te alloy as a recording layer have a high crystallization speed, and high-speed overwriting with a circular beam is possible only by modulating the irradiation power (T. Ohta et al, Proc. .Int.Symp.on Optical Memor
y 1989 p49-50). An optical disk is an example of such a rewritable phase change optical recording medium, and a groove and a land and a groove are formed on a substrate of the optical disk in advance. In a current general optical disc, a laser beam is focused only on one of a land and a groove to record and reproduce a signal.

In order to increase the recording capacity of such an optical disk, conventionally, the width of the land or groove is narrowed to close the track interval. However, if the track spacing is narrowed, the diffraction angle of the reflected light due to the groove becomes large, so that there is a problem that the tracking error signal for accurately causing the focused spot to follow the track is lowered. Further, when the width of the land or the groove is reduced, the width of the recording pit is also reduced, which causes a problem that the amplitude of the reproduced signal is reduced. On the other hand, a technique of recording a signal on both the land and groove tracks in order to increase the recording capacity is known (Japanese Patent Publication No. 63-57859). However, if signals are recorded on both the land and groove tracks, (i)
The signal leakage from adjacent tracks (crosstalk) increases and the reproduction signal deteriorates, increasing the error rate. (Ii)
There is a problem that the reproduction signal amplitude difference between the land and the groove becomes large, making it difficult to detect data. (Iii) When recording, erase the recorded marks of the adjacent tracks that have already been recorded (cross erase). was there.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the conventional optical recording medium, and to make the track pitch wider than the conventional one in the recording method using both the land and groove tracks. The crosstalk amount can be reduced without providing a special optical system or a signal processing circuit for reducing the crosstalk amount, and the reproduction signal amplitude of the land and the groove can be made almost the same, and further the cross erase can be reduced. An optical recording medium is provided.

Another object of the present invention is to provide an optical recording medium having high recording sensitivity and excellent recording characteristics such as carrier-to-noise ratio and erasing rate. Still another object of the present invention is to provide an optical recording medium which has excellent oxidation resistance and resistance to moist heat, and has a long service life that does not cause defects even during long-term storage.

[0008]

The present invention provides at least an optical recording medium in which recording and erasing of information are performed by a phase change between an amorphous phase and a crystalline phase, and recording is performed on both lands and grooves. Has a recording layer, a dielectric layer, and a reflective layer,
The reflectivity in the crystalline state of the mirror part is higher than 15%,
% Or less, the present invention relates to an optical recording medium.

The present invention also provides an optical recording medium in which recording and erasing of information are performed by a phase change between an amorphous phase and a crystalline phase, and recording is performed on both lands and grooves.
The present invention relates to an optical recording medium having at least a recording layer, a dielectric layer, and a reflective layer, wherein the mirror portion has an amorphous reflectance of 10% or less.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The following description will be made step by step. In the optical recording medium of the present invention, since the recording sensitivity is high, the signal contrast is high, and the crosstalk can be reduced, the reflectance of the mirror portion in the crystalline state is higher than 15% and lower than 35%. Need to be configured. When the reflectance of the mirror portion in the crystalline state is higher than 35%, the recording sensitivity becomes low, the irradiation power of the light for recording and erasing becomes insufficient, and it becomes difficult to record at high speed rotation. Crosstalk from the recording unit increases. When the reflectance of the crystal portion is 15% or less, the difference in reflectance between the recording mark and the amorphous portion is small, and the signal contrast during reproduction is small. In view of these points, the reflectivity of the mirror portion in the crystalline state is more than 15% and more preferably 30% or less.

Here, the mirror portion means a mirror surface portion on which no groove or prepit is formed. By measuring the reflectance of the mirror portion, the reflectance on the optical recording medium can be accurately measured without being affected by the grooves and prepits.

The reflectance of the mirror portion in the amorphous state is 10
% Or less is preferable. If the reflectivity of the mirror portion in the amorphous state is higher than 10%, the signals of the adjacent tracks are easily read during reproduction, crosstalk increases and the reproduction signal deteriorates, resulting in an error rate. To increase. Further, if the reflectance of the mirror portion in the amorphous state is 5% or more, the servo of the track on which the recording mark is formed is stable, so 5% or more and 10% or less are particularly preferable.

In the optical recording medium of the present invention, it is preferable to set the groove depth to an optical path length of ⅕ or more and ⅕ or less of the wavelength of the reproducing light from the viewpoint of reducing crosstalk. When the groove depth is an optical path length of less than 1/7 or more than 1/5 of the wavelength of the reproduction light, crosstalk becomes large and accurate reproduction becomes difficult.

In order to make the reproduction signal amplitudes of the land and the groove the same and reduce crosstalk, the phase difference between the reflected light in the amorphous state and the reflected light in the crystalline state is 2nπ−π /.
3 or more and 2nπ + π / 3 or less, or 2nπ + 2π
It is preferable that it is configured to be / 3 or more and 2nπ + 4π / 3 or less. If the phase difference is outside the above range, the amplitude difference between the land and the groove becomes large, and the crosstalk also becomes large. More preferably, the absolute value of the phase difference is 2
It is nπ−0.2π or more and 2nπ + 0.2π or less, or 2nπ + 0.8π or more and 2nπ + 1.2π or less. It is more preferable if it is 2nπ + 0.8π or more and 2nπ + 1.2π or less because the amplitude of the reproduction signal becomes particularly large. Here, the above n represents an integer.

The value of the refractive index of the first and second dielectric layers is preferably 1.5 to 2.4 from the viewpoint of obtaining a signal contrast during reproduction due to an optical interference effect. When the value of the refractive index is less than 1.5, the signal contrast during reproduction cannot be sufficiently obtained, and when the value of the refractive index is more than 2.4, the dependency of the reflectance on the film thickness of the dielectric becomes large. .

The thickness of the first dielectric layer is preferably 50 nm or more because it is usually difficult to peel it from the substrate or the recording layer and cracks and other defects are less likely to occur. Further, considering the manufacturing cost and the film thickness error at the time of manufacturing, it is usually preferable that the thickness is about 300 nm or less.

Any method can be used to control the reflectance, and for example, it can be controlled by the refractive index and the thickness of the first dielectric layer. When a transparent substrate such as polycarbonate or glass is used, the refractive index of the substrate is about 1.5 and the refractive index of the first dielectric layer is about 1.5 to 2.4. In order to set the reflectance of the crystal portion in the mirror portion to more than 15% and 35% or less and the reflectance of the amorphous portion in the mirror portion to 10% or less, the optical path lengths n1 and d1 of the first dielectric layer are as follows. It is preferably within the range represented by the formula.

Equation (6) (N / 4-0.1) λ≤n1.d1≤ (N / 4 + 0.
1) λ 1.5 ≤ n1 ≤ 2.4 (where n1 is the refractive index of the first dielectric layer, d1 is the thickness of the first dielectric layer (nm), and λ is the wavelength of light (nm). Represent
N represents 1 or 3. )

The thickness of the second dielectric layer is usually 1-250 n.
m is often used. The range of about 1 to 50 nm is preferable because the range of the erasing power with which a good erasing rate can be obtained is wide. More preferably, the optical path length n2.d2 of the second dielectric layer is within the range represented by the following formula.

Equation (7) λ (1/50) ≦ n2 · d2 ≦ λ (1/10) 1.5 ≦ n2 ≦ 2.4 (where n2 is the refractive index of the second dielectric layer, and d2 is The thickness (nm) and λ of the second dielectric layer represent the wavelength (nm) of light.) In the formula (7), n2 · d2 is smaller than λ (1/50), or λ (1/10) In the case of a large range, it becomes very difficult to obtain the contrast between the crystal part and the amorphous part. Further, when it is smaller than λ (1/50), repeated durability is deteriorated, so that it is preferably within the range represented by the above formula.

Further, it is preferable to have a four-layer structure of substrate / first dielectric layer / recording layer / second dielectric layer / reflection layer because a rapid cooling structure is easy and repeated durability is improved as a result.

The material of the recording layer of the present invention is a chalcogen compound containing Te as a main component which can be in at least two states of a crystalline state and an amorphous state. The recording layer of the present invention is not particularly limited, but Ge-Sb-Te alloy, Pd-Ge-Sb-Te alloy, Nb-Ge-Sb-
Te alloy, Pt-Ge-Sb-Te alloy, Au-Ge-
Sb-Te alloy, Ag-Ge-Sb-Te alloy, Ni-
Ge-Sb-Te alloy, Co-Ge-Sb-Te alloy,
Pd-Nb-Ge-Sb-Te alloy, In-Sb-Te
Alloy, Ag-In-Sb-Te alloy, In-Se alloy, and the like. Because the record can be rewritten many times,
Pd-Ge-Sb-Te alloy, Nb-Ge-Sb-Te
Alloy, Pd-Nb-Ge-Sb-Te alloy, Ni-Ge
-Sb-Te alloy, Ge-Sb-Te alloy, Co-Ge
-Sb-Te alloy is preferred. Especially Pd-Ge-Sb-
Te alloys and Pd-Nb-Ge-Sb-Te alloys are preferable because they have a short erasing time, can be repeatedly recorded and erased many times, and have excellent recording characteristics such as C / N and erasing rate. In particular, Pd-Nb-Ge-Sb-Te
The alloy is more preferable because it has excellent properties described above. Setting the recording layer according to the following formula or the like is preferable because the recording can be rewritten many times.

Formula (8) M _α (Sb _x Te _1-x ) _1-y-α (Ge _0.5 Te _0.5 )
_y 0.4 ≦ x ≦ 0.6 0.3 ≦ y ≦ 0.5 0 ≦ α ≦ 0.05 (where x, y, and α represent molar ratios; M is Pd, N
At least one of b, Pt, Au, Ag, Ni, and Co is included. Further, it is more preferable that the value of y is 0.3 or more and 0.4 or less since the repetition durability at the time of rewriting is high and the thermal stability in an amorphous state is high. The value of α is 0.001 or more.
A value of 01 or less is more preferable because the crystallization speed is high, the repetition durability is high, and the thermal stability in an amorphous state is high.

The thickness of the recording layer is 10 to 40 nm. If the thickness is less than 10 nm, the contrast between the crystalline state and the amorphous state cannot be sufficiently contrasted. Further, when the thickness of the recording layer is 40 nm or more, the thermal conductivity of the recording layer becomes large, resulting in poor cross erase.

In the optical recording medium of the present invention, if the width of the inclined portion of the groove groove is 0.2 μm or less, the groove groove becomes close to a rectangular shape, and heat at the time of recording at the inclined portion is cut off, and cross erase is performed. It is preferable because durability is improved. However,
When the width of the inclined portion of the groove groove is less than 0.05 μm,
When the substrate is molded, it becomes difficult to peel the substrate from the stamper.

The track pitch of the optical recording medium of the present invention is
λ / NA (λ is the recording / reproducing light wavelength, NA is the lens numerical aperture)
If it is less than this, cross erase cannot be avoided. Further, if it exceeds 1.5 · λ / NA, the track pitch becomes wide and does not make sense for high-density recording. Therefore, it is preferable to keep the track pitch within the range.
Further, the ratio of the land and groove flat portions to the track pitch is preferably 0.2 or more and 0.6 or less.
Outside this range, the width of the flat portion of the land and the groove is largely different, and as a result, the amplitude of the reproduction signal between the land and the groove is significantly different, or the width of the inclined portion of the groove groove is wide. It means impairing the above effects. Further, it is more preferably 0.3 or more and 0.5 or less.

The width of the recording mark in the land and groove portions is 1 / the width of the flat portion in the land and groove portions, respectively, since the reproduction signal amplitude is large as the width of the recording mark.
It is preferably two or more. Further, in order to prevent the cross erase from occurring due to the increased width of the mark, the recording marks of the land and the groove portion are the land,
It is preferable that the width is less than the width of the flat portion of the groove portion.

As the material of the substrate of the present invention, various general transparent synthetic resins, transparent glass and the like can be used. In order to avoid the effects 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,
Examples thereof include polycarbonate, polymethyl methacrylate, 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 preferably within the range represented by the following formula. ◎ Equation (9) 0.01 ≦ (NA) ³ · d ≦ 0.2 where NA is the numerical aperture of the objective lens and d is the substrate thickness (m
m).

Since the coma aberration is proportional to the product of the cube of NA and the substrate thickness d, if the value of the above equation is larger than 0.2, the disc tilt is apt to be influenced, resulting in the recording density. When the value of the above equation is less than 0.01, the image is easily affected by dust or scratches even when recording with a light beam focused from the substrate side.

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

In the present invention, the dielectric layer has an effect of protecting the substrate and the recording layer from heat, such as preventing the substrate and the recording layer from being deformed by heat during recording and deteriorating the recording characteristics, and an optical interference effect. This has the effect of improving the signal contrast during reproduction. As the dielectric layer, Zn
Inorganic thin films such as S, SiO ₂ , silicon nitride, and aluminum oxide can be used. Especially ZnS thin film, Si, G
e, Al, Ti, Zr, Ta, and other metal oxide thin films, Si, Al, and other nitride thin films, Ti, Zr, and Hf.
Thin films of carbides such as and films of these compounds are preferable because they have high heat resistance. The refractive index of these thin films is 1.5 or more and 2.4 or less. Further, a mixture of carbon and a fluoride such as MgF ₂ is also preferably used because the residual stress of the film is small. Especially Zn
A mixed film of S and SiO ₂ or a mixed film of ZnS, SiO ₂ and carbon can be used for recording sensitivity, carrier-to-noise ratio (C / N) and erasing rate (after recording and after erasing) by repeating recording and erasing. This is preferable because deterioration such as difference in reproduced carrier signal strength is unlikely to occur. The composition ratio of the chalcogen compound, the oxide and the carbon is not particularly limited, but in view of the large effect of reducing the internal stress of the dielectric layer, SiO ₂ 15
It is more preferable that the content is ˜35 mol% and carbon is 1 to 15 mol%.

As the material of the reflective layer, a metal such as Al or Au having light reflectivity, containing Ti or C as a main component, is used.
Examples include alloys containing additional elements such as r and Hf, and metals such as Al and Au mixed with metal compounds such as metal nitrides such as Al and Si, metal oxides and metal chalcogenides. Metals such as Al and Au and alloys containing these as the main components have high light reflectivity and high thermal conductivity, and can quickly diffuse the heat during recording, and as a result, cross erase can be reduced. Is preferred.
Examples of the above alloys include Al, Si, Mg, Cu and P.
At least one element such as d, Ti, Cr, Hf, Ta, Nb, and Mn added in a total amount of 5 atomic% or less and 1 atomic% or more, or Au, Cr, Ag, Cu, Pd,
Examples thereof include those in which at least one element such as Pt or Ni is added in a total amount of 1 atom% or more and 20 atom% or less.
In particular, Al or an alloy containing Al as a main component is preferable because the price of the material is low. Above all, Al, Ti, Cr, Ta, Hf, Zr,
An alloy in which at least one metal selected from Mn and Pd is added in a total amount of 0.5 atom% or more and 5 atom% or less is preferable. Furthermore, since the corrosion resistance is good and the occurrence of hillocks is unlikely to occur, the total amount of additive elements is 0.5
Al-Hf-Pd alloy, Al-Hf alloy, Al-Ti alloy, Al-Ti-H containing at least 3 atomic%
f alloy, Al-Cr alloy, Al-Ta alloy, Al-Ti
It is preferable to be composed of any one of a -Cr alloy and an Al-Si-Mn alloy containing Al as a main component. These A
Among the alloys, Al- having the composition represented by the following formula:
Hf-Pd alloy has particularly excellent thermal stability,
By repeating recording and erasing a large number of times, it is possible to reduce deterioration of recording characteristics.

Pd _j Hf _k Al _1-jk 0.001 <j <0.01 0.005 <k <0.1 where j and k are the number of atoms of each element (the number of moles of each element)
Represents

The thickness of the above-mentioned reflective layer is about 10 nm or more and 200 nm regardless of which alloy is used.
Hereafter, it is more preferably 50 to 200 nm.

Examples of the light source used for recording on the optical recording medium of the present invention include high-intensity light sources such as laser light and strobe light. Particularly, the semiconductor laser light can be miniaturized and has low power consumption. It is preferable because it can be easily modulated.

Recording is performed by irradiating a crystalline recording layer with a laser light pulse or the like 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 during recording and crystallize during erasing. Further, the light intensity is high at the time of forming the recording mark and slightly weak at the time of erasing, and rewriting is performed by irradiating the light beam once.
Beam overwrite is preferable because it takes less time to rewrite.

Next, a method of manufacturing the optical recording medium of the present invention will be described. Examples of the method for forming the reflective layer and the recording layer on the substrate include a general thin film forming method in vacuum, such as a vacuum vapor 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 to be formed can be easily controlled by monitoring the deposition state with a crystal oscillator film thickness meter which is a general technique.

The recording layer and the like may be formed either with the substrate fixed, or with the substrate moved or rotated. The substrate is preferably rotated on its own because of excellent in-plane uniformity of the film thickness, and more preferably combined with revolution.

A preferred layer structure of the optical recording medium of the present invention is: transparent substrate / first dielectric layer / recording layer / second dielectric layer /
One in which a reflective layer is laminated in this order is exemplified. However, the present invention is not limited to this, and a dielectric layer such as ZnS or SiO ₂ or an ultraviolet curable layer may be formed after the formation of a reflective layer or the like to prevent scratches and deformation, as long as the effects of the present invention are not significantly impaired. A resin protective layer such as a resin can be provided as necessary. Light enters from the transparent substrate side. After the formation of the reflective layer or the like, or after the formation of the above-mentioned resin protective layer, the two substrates may be bonded to each other with an adhesive.

The recording layer is preferably crystallized by irradiation with laser light, light from a xenon flash lamp, or the like before actually recording.

[0042]

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 Instruments Inc.).
The carrier-to-noise ratio and erasing rate (difference in reproduced carrier signal intensity after recording and after erasing), crosstalk, and cross-erase are the drive device used for recording, or an optical head equivalent to this (laser wavelength, objective lens It measured by the spectrum analyzer using the drive which has (NA).

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.

The reflectance of the mirror section is measured by measuring the mirror section on the disk with a spectrophotometer, or a drive unit used for recording, or an optical head equivalent to this (laser wavelength, NA of objective lens). Was measured by observing the reflection level of the reproduction light of the mirror portion in the prepit with an oscilloscope.

(Example 1) Thickness 0.6 mm, groove depth 72
nm, diameter 12 cm, 1.4 μm pitch (land flat part 0.55 μm, groove flat part 0.55 μm, guide groove slope part 0.15 μm), while rotating the substrate made of polycarbonate with spiral groove at 30 rpm, The recording layer, the dielectric layer, and the reflective layer were formed by the sputtering method.

First, the inside of the vacuum vessel was evacuated to 1 × 10 ^-3 Pa, and then SiO 2 in an atmosphere of 2 × 10 ^-1 Pa of zero Ar gas.
ZnS containing 20 mol% of ₂ was sputtered to form a 100-nm-thick first dielectric layer on the substrate. continue,
An alloy target composed of Pd, Nb, Ge, Sb, and Te is sputtered to form a composition Nb _0.45 Pd _0.05 Ge _19.0 Sb.
A recording layer having a thickness of 25 nm of _25.5 Te _55.0 was formed. A second dielectric layer having a thickness of 15 nm was formed in the same manner as the first dielectric layer, and an Al _98.1 Hf _1.7 Pd _0.2 alloy was sputtered thereon to form a reflective layer having a thickness of 150 nm.

After the disk was taken out of the vacuum container, an acrylic ultraviolet curable resin was spin-coated on the reflective layer and irradiated with ultraviolet rays to be cured to form a resin layer having a thickness of 10 μm to form an optical recording medium of the present invention. Got Further, a disk prepared in the same manner was laminated with a hot melt adhesive to prepare a double-sided disk. This optical recording medium has a wavelength of 830n.
The recording layer on the entire surface of the disk was crystallized and initialized by the beam of the semiconductor laser of m.

When the reflectance of the crystal part and the amorphous part was measured by the mirror part, the reflectance was 27% in the crystal part and 8% in the amorphous part. Further, when the phase difference between the reflected light of the reproduction light of the crystal part and the amorphous part was calculated from the refractive index and the film thickness of each layer, the phase difference was 0.1π ((phase of the reflected light of the amorphous part)-
(The phase of the reflected light of the crystal part)).

Next, the numerical aperture of the objective lens was 0.6, and the linear velocity of each of the land and the groove was 4.4 m / sec.
Using an optical head with a wavelength of 680 nm of a semiconductor laser,
In edge recording, a recording mark equivalent to 2Tw of 1-7RLLC (Tw is a window width) (frequency 4.2 MHz during reproduction)
z) can be formed using general pulse splitting,
A semiconductor laser modulated to each of a peak power of 7 to 15 mW and a bottom power of 2 to 6 mW was used to perform overwriting recording 100 times, and then a semiconductor laser having a reproduction power of 1.2 mW was irradiated to C / C under a condition of a bandwidth of 30 kHz. N was measured. Furthermore, this part is 7Tw (1.2MHz),
A semiconductor laser modulated in the same manner as above was irradiated, one-beam overwriting was performed, and the erasing rate of 2 Tw at this time was measured.

Peak power of 9 mW for both land and groove
With the above, practically sufficient C / N of 50 dB or more was obtained, and the difference between the C / N of land and groove at each peak power was 1 d.
Below B, there was almost no change. As for the erasing rate, the bottom power is 3 to 5 mW for both land and groove.
As a result, an erasing rate of 20 dB or more, which is practically sufficient, and a maximum of 30 dB was obtained.

Next, the difference between the signal strength recorded in the groove (or land) and the reproduction signal of the land (or groove) next to the recorded track in which the signal is not written is defined as the crosstalk amount and measured. .

After overwriting recording 100 times with a semiconductor laser modulated to each condition of a peak power of 9 to 15 mW with a frequency of 4.2 MHz and a bottom power of 4.5 mW on a land, a reproducing power of 1.2 mW was formed on an adjacent groove. When irradiated with a semiconductor laser and measured under the condition of a bandwidth of 30 kHz, a practically sufficient crosstalk of -30 to -27 dB was obtained. Also, under the same conditions for the groove, 1
After the overwrite recording was performed 00 times, the crosstalk of the adjacent land was measured, and the same characteristics as those of the groove were obtained.

Further, with a semiconductor laser in which a groove (or land) is modulated with a peak power of 10 mW and a bottom power of 4.5 mW, a C / N when a signal having a frequency of 4.2 MHz is overwritten 100 times, After overwriting the land (or groove) which is the adjacent track with a signal of 1.2 MHz frequency by the semiconductor laser similarly modulated, the C / N with the previously recorded groove (or land) is compared. When this reduction amount is defined as the cross erase amount and measured, it is 1 dB.
There was little change below.

An optical recording medium having the same structure as the above was prepared, and the peak power was 10 mW and the bottom power was 4.5.
When a recording mark corresponding to 8 Tw (1.1 MHz) was recorded under the condition of mW and observed with a transmission electron microscope, the width of both the land and the groove was 0.46 μm, which was 84% of the flat portion of the land and the groove. Met.

Furthermore, after the optical recording medium was left in an environment of 80 ° C. and 80% relative humidity for 1000 hours, the recorded portion was reproduced, but the change in C / N was less than 2 dB, and there was almost no change.

(Example 2) The thickness of the first dielectric layer is 85n.
m, the thickness of the recording layer is 22 nm, and the thickness of the second dielectric layer is 1
An optical recording medium was produced in the same manner as in Example 1 except that the thickness of the reflective layer was 0 nm and the thickness of the reflective layer was 100 nm.

When the reflectivity of the crystal part and the amorphous part was measured by the mirror part, the reflectivity was 21% in the crystal part and 6% in the amorphous part. Further, when the phase difference between the reflected light of the reproduction light of the crystal part and the amorphous part is calculated from the refractive index and the film thickness of each layer, the phase difference is π ((phase of the reflected light of the amorphous part)-(of the crystal part The phase of reflected light)).

Under the condition that the linear velocity is 5.8 m / sec for both the land and the groove of this disc, the numerical aperture of the objective lens is 0.
6. Using an optical head with a wavelength of 680 nm of a semiconductor laser, it is possible to form a recording mark (frequency of 4.7 MHz during reproduction) corresponding to the shortest mark (3 Tw) of 8/16 (EFM plus) modulation method by edge recording. C / N was measured in the same manner as in Example 1 using pulse division. Furthermore, this frequency is 1.3MHz (11Tw) at the time of reproduction,
Irradiation was performed with a semiconductor laser modulated in the same manner as above, one-beam overwriting was performed, and an erasing rate of 3 Tw was measured.

Peak power of land and groove 9.
50 dB or more, practically sufficient at 0 mW or more, 57 dB maximum
Of C / N was obtained. At each peak power, the C / N difference between the land and the groove was less than 1 dB, and there was almost no difference.
Regarding the erasing rate, the same value as in Example 1 was obtained at a peak power of 10.5 mW.

The crosstalk was measured at a recording frequency of 4.
The same measurement as in Example 1 was performed except that the peak power was 7 MHz and the peak power was 10.5 mW. As a result, a sufficiently small crosstalk of −30 dB to −27 dB similar to that of Example 1 was obtained.

The cross erase was measured in the same manner as in Example 1 except that the recording track recording frequency was 4.7 MHz, the adjacent track recording frequency was 1.3 MHz, and the peak power was 10.5 mW. Then 1d
A sufficiently small cross erase less than B was obtained.

(Example 3) 8 mol% of carbon was added to the first and second dielectric layers to obtain ((ZnS) ₈₀ (SiO ₂ ) ₂₀ ) ₉₂ C ₈
An optical recording medium similar to that in Example 1 was manufactured except for the above.

When the reflectivity of the crystal part and the amorphous part was measured by the mirror part, the reflectivity was 27% in the crystal part and 8% in the amorphous part. Further, when the phase difference between the reflected light of the reproduction light of the crystal part and the amorphous part was calculated from the refractive index and the film thickness of each layer, the phase difference was 0.1π ((phase of the reflected light of the amorphous part)-
(The phase of the reflected light of the crystal part)).

In the same manner as in Example 1, C / N, erasing rate, cross erase and cross talk were measured. Peak power of 9 mW or more for both land and groove, 50 dB for practical use
The above C / N was obtained, and the difference in C / N between the land and the groove was less than 1 dB at each peak power, and there was almost no difference. As for the erasing rate, a land power of 3 to 5 mW for both the land and the groove was 20 dB or more, which was practically sufficient, and a maximum erasing rate of 30 dB was obtained. Crosstalk is also -30
A sufficiently small cross talk of dB to -27 dB was obtained, and a sufficiently small cross erase of less than 1 dB was also obtained.

(Comparative Example 1) The first of the optical recording media of Example 1
An optical recording medium having the same structure as in Example 1 except that the thickness of the dielectric layer was 320 nm was prepared, and the peak power and the bottom power when measuring C / N and crosstalk were changed. The same measurement as in Example 1 was performed.

When the reflectance of the crystal part and the amorphous part was measured at the mirror part, the reflectance was 38% in the crystal part and 18% in the amorphous part. Further, when the phase difference between the reflected light of the reproduction light of the crystal part and the amorphous part was calculated from the refractive index and the film thickness of each layer, the phase difference was 0.1π ((phase of the reflected light of the amorphous part)-
(The phase of the reflected light of the crystal part)).

The peak power of 10 to 15 mW and the bottom power of 4 to 8 mW were modulated, and the same measurement as in Example 1 was carried out. As a result, in the land, the peak power of 11 mW or more gave a practically sufficient C / N of 50 dB or more. With the bottom power of 4 to 8 mW, a practically sufficient erasing rate of 20 dB or more and a maximum of 30 dB was obtained, and the groove had the same characteristics.

The peak power of 10 to 15 mW and the bottom power of 4 to 8 mW were used for modulation, and the same measurement as in Example 1 was carried out. As a result, a peak power of 11 mW or more and a practically sufficient C / N of 50 dB or more were obtained. With the bottom power of 4 to 8 mW, a practically sufficient erasing rate of 20 dB or more and a maximum of 30 dB was obtained, and the groove had the same characteristics.

The cross erase was measured in the same manner as in Example 1 except that the peak power was 12 mW and the bottom power was 5.5 mW, and there was almost no change within 1 dB.

However, when the bottom power in the land was set to 5.5 mW and the peak power was modulated to each condition of 11 to 15 mW, and the crosstalk was measured in the same manner as in Example 1, it was as large as −18 to −15 dB and was normal. It was difficult to reproduce the data. Similar values were obtained with the groove. From this, it has been clarified that in the above-mentioned layer structure, since the reflectance is high, the crosstalk becomes large and it is difficult to record a signal on both the land and groove tracks.

Comparative Example 2 An optical recording medium similar to Comparative Example 1 was prepared except that the thickness of the first dielectric layer in Comparative Example 1 was changed to 305 nm.

When the reflectance of the crystal part and the amorphous part was measured by the mirror part, the reflectance was 37% in the crystal part and 14% in the amorphous part. Further, the phase difference of the reflected light of the reproduction light of the crystal part and the amorphous part was calculated from the refractive index and the film thickness of each layer, and the phase difference was 0.1π.

Regarding C / N, erasing rate and cross erase, the same results as in Comparative Example 1 were obtained.

When crosstalk was measured in the same manner as in Comparative Example 1, it was as large as −18 to −23 dB, and it was at a level at which normal data reproduction was difficult.

[0075]

According to the optical recording medium of the present invention, the following effects can be obtained. (1) Crosstalk in the land / groove recording method can be reduced. (2) In the land / groove recording method, the recording characteristics of the land and the groove can be matched. (3) Cross erase in the land / groove recording method can be reduced. (4) Can be easily manufactured by sputtering.

Claims (15)

[Claims] 1. An optical recording medium in which information is recorded and erased by a phase change between an amorphous phase and a crystalline phase, and recording is performed on both a land and a groove, at least a recording layer,
An optical recording medium having a dielectric layer and a reflective layer, wherein the mirror portion has a reflectance in a crystalline state of more than 15% and 35% or less. 2. An optical recording medium in which recording and erasing of information are performed by a phase change between an amorphous phase and a crystalline phase, and recording is performed on both a land and a groove, at least a recording layer,
An optical recording medium having a dielectric layer and a reflective layer, wherein the reflectance of the mirror portion in an amorphous state is 10% or less. 3. An optical recording medium in which recording and erasing of information are performed by a phase change between an amorphous phase and a crystalline phase, and recording is performed on both a land and a groove, at least a recording layer,
It has a dielectric layer and a reflection layer, and the reflectance of the mirror portion in the amorphous state is 10% or less, and the reflectance of the mirror portion in the crystalline state is 15% or less.
%, And 35% or less. 4. The phase difference between the reflected light of the amorphous phase and the reflected light of the crystalline phase is 2nπ−π / 3 or more and 2nπ + π / 3 or less, and any one of claims 1 to 3 is characterized. An optical recording medium according to item 1. Here, n is an integer. 5. The phase difference between the reflected light of the amorphous phase and the reflected light of the crystalline phase is not less than 2nπ + 2π / 3 and not more than 2nπ + 4π / 3, in any one of claims 1 to 3. The optical recording medium described. Here, n is an integer. 6. The groove depth of the groove is 1/7 of the wavelength of the reproduction light.
The optical recording medium according to any one of claims 1 to 3, wherein the optical path length is 1/5 or less. 7. An optical recording medium is formed by laminating a substrate / a first dielectric layer / a recording layer / a second dielectric layer / a reflective layer in this order,
The refractive index and the film thickness of the first dielectric layer and the second dielectric layer are within the ranges represented by the following formulas (1) and (2), respectively. 3. The optical recording medium according to any one of 3 above. Formula (1) 1.5 ≤ n1 ≤ 2.4 50 ≤ d1 ≤ 300 Formula (2) 1.5 ≤ n2 ≤ 2.4 1 ≤ d2 ≤ 50 where n1 and n2 are the first dielectric layer and the Refractive indices d1 and d2 of the second dielectric layer are film thicknesses (nm) of the first dielectric layer and the second dielectric layer. 8. The optical recording medium according to claim 1, wherein the recording layer contains at least Sb or Te. 9. The composition of the recording layer is a three-element alloy of Ge, Sb, and Te or three elements of Ge, Sb, and Te, and Pd and N.
It is an alloy with at least one metal selected from b, Pt, Au, Ag, Ni, and Co, and has a recording layer thickness of 10 n.
The optical recording medium according to any one of claims 1 to 3, wherein the optical recording medium has a thickness of m or more and 40 nm or less. 10. The optical recording according to claim 1, wherein the composition of the recording layer is represented by the following formula (3), and the composition of the reflective layer is made of an Al alloy. Medium. Formula (3) M _α (Sb _x Te _1-x ) _1-y-α (Ge _0.5 Te _0.5 )
_y 0.4 ≤ x ≤ 0.6 0.3 ≤ y ≤ 0.5 0 ≤ α ≤ 0.05 (where x, y and α are molar ratios, M is Pd, N
It represents at least one selected from b, Pt, Au, Ag, Ni and Co. ) 11. The optical recording medium according to claim 1, wherein the track pitch, the land flat portion width, and the groove flat portion width are represented by the following equations. Formula (4) Tp = a · λ / NA 1 ≦ a ≦ 1.5 Tg = Tp · b 0.2 ≦ b ≦ 0.6 Tl = Tp · b 0.2 ≦ b ≦ 0.6 where Tp Is the track pitch (μm), NA is the numerical aperture of the lens, λ is the reproduction wavelength (μm), Tg is the width of the groove flat portion (μm), and Tl is the width of the land flat portion (μm). 12. A land and a groove are substantially made up of a flat portion and an inclined portion, and the width of the inclined portion is 0.05 μm or more.
The optical recording medium according to any one of claims 1 to 3, wherein the optical recording medium has a thickness of 2 µm or less. 13. The width of the mark recorded on the land is 1/2 or more and less than 1 of the flat portion of the land, or the width of the mark recorded on the groove is 1/2 or more and less than 1 of the flat portion of the groove. The optical recording medium according to any one of claims 1 to 3, wherein 14. The optical recording medium according to claim 1, wherein the thickness of the substrate is represented by the following formula (5). Formula (5) 0.01 ≦ (NA) ³ · d ≦ 0.2 (where NA is the numerical aperture of the lens, d is the substrate thickness (m
m). ) 15. The optical recording medium according to claim 1, wherein the dielectric layer contains at least ZnS, SiO ₂ and carbon.