JPH11339314A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the degradation in jitter characteristics, the deterioration at the beginning ends and terminals of sectors, the degradation in contrast and the occurrence of a burst defect by providing the surface of a substrate as a recording medium for executing recording and erasing of information by irradiation with light with at least a first dielectric layer/recording layer/second dielectric layer/reflection layer moreover disposing a layer consisting of an oxide between the recording layer and the first dielectric layer. SOLUTION: The representative constitution of the component members of the optical recording medium is obtd. by laminating the first dielectric layer, the oxide recording layer, the second dielectric layer and the reflection layer in this order on the transparent substrate. The material of the first dielectric layer is substantially transparent to recording light wavelengths and the material having the refractive index larger than the refractive index of the transparent substrate and smaller than the refractive index of the recording layer is preferable. The film of the oxide is required to be disposed between the first dielectric layer and the recording layer. The degradation in the jitter characteristics may be improved by such disposition. The oxide of the element selected from a group 2A to a group 4B of a third period and from group 2A to a group 4B of a fourth period of the periodic table is used as the essential component of the oxide.

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.

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

[0003]

2. Description of the Related Art The technology of a conventional rewritable phase-change optical recording medium is as follows. These optical recording media have a recording layer mainly containing tellurium or the like, and at the time of recording, a focused laser light pulse is applied to the crystalline recording layer 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. At the time of erasing, the recording mark portion is irradiated with a laser beam and heated to a temperature lower than the melting point of the recording layer and higher than the crystallization temperature, whereby the amorphous recording mark is crystallized and returned to the original unrecorded 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 (NY)
amada et al. Proc.Int.Symp.on Optical Memory 1987 p
61-66) are known.

[0005] These optical recording media using a Te alloy as a recording layer have a high crystallization speed, and high-speed overwriting with a single circular beam is possible only by modulating the irradiation power. In an optical recording medium using these recording layers, usually, a heat-resistant and light-transmitting dielectric layer is provided on each side of the recording layer to prevent deformation and opening of the recording layer during recording. I'm preventing. Further, a technique is known in which a metal reflective layer such as light reflective Al is laminated on the dielectric layer on the opposite side to the light beam incident direction to improve the signal contrast during reproduction by an optical interference effect. I have.

The problems in the above-mentioned conventional rewritable phase-change optical recording medium are as follows.

That is, in the conventional configuration, if a disk on which a signal is already recorded is left for a long time and then overwritten (hereinafter, referred to as an overwrite shelf), jitter characteristics deteriorate and an error occurs. There was a problem. For this reason, there was a problem in the storage durability of the disk.

[0008] As higher densities and higher speeds are required, higher linear densities and higher linear velocities are also being studied for phase-change optical recording media. The problem of degradation occurs. This hinders stable recording and reproduction in mark length recording, and makes it difficult to achieve high density and high speed.

Further, in the conventional disk structure, the repetition of overwriting causes deterioration of jitter characteristics, deterioration of recording waveforms at the start and end ends of sector recording, and reduction of signal amplitude (contrast reduction). . It is considered that the change is caused by a change in the thickness of the recording layer due to mass transfer of the recording layer. In addition, burst defects may occur due to crack growth in the protective layer.

[0010]

SUMMARY OF THE INVENTION An object of the present invention is to provide excellent overwrite shelf characteristics, good erasing characteristics even under conditions of high linear velocity and high linear density, and deterioration of jitter characteristics due to repeated overwriting. It is an object of the present invention to provide a rewritable phase-change optical recording medium with less deterioration such as start / end deterioration of a sector, deterioration of contrast, occurrence of a burst defect and the like.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to record, erase, and reproduce information by irradiating light, and to record and erase information between an amorphous phase and a crystalline phase. A reversible phase change takes place and at least a first
An optical recording medium comprising a dielectric layer / a recording layer / a second dielectric layer / a reflective layer, wherein an oxide layer is provided between the recording layer and the first dielectric layer. This is achieved by a recording medium.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The problem to be solved by the present invention is that the overwrite shelf causes the jitter characteristic to deteriorate because the erasing characteristic deteriorates. The cause of the deterioration of the erasing characteristics is considered to be that the state of the atomic arrangement changes when the recording mark (amorphous phase) is left for a long time, or that the dielectric layer and the recording layer react. Can be In addition, it is considered that the problem to be solved by the present invention due to repetitive overwriting, that is, the deterioration of the jitter characteristic, the deterioration of the start and end of the sector, and the decrease of the amplitude are caused by mass transfer of the recording layer material. .
Furthermore, in realizing higher linear velocity and higher density, the problem of deterioration of the erasing characteristics is considered to be caused by a reduction in the time during which the recording layer is maintained at a temperature higher than the crystallization temperature. .

The present inventors have conducted intensive experiments and found that the provision of an oxide layer between the first dielectric layer and the recording layer can improve the deterioration of jitter characteristics due to the overwrite shelf.

That is, a typical layer constitution of the constituent members of the optical recording medium of the present invention is that a first dielectric layer, an oxide layer, a recording layer, a second dielectric layer, and a reflective layer are laminated on a transparent substrate in this order. It was done. However, it is not limited to this.

The material of the first dielectric layer is preferably substantially transparent at the wavelength of the recording light, and has a refractive index larger than that of the transparent substrate and smaller than that of the recording layer. Specifically, a thin film of ZnS, Si, Ge,
Thin films of oxides of metals such as Ti, Zr, Ta, Nb,
A thin film of a nitride such as Si or Ge, a thin film of a carbide such as Zr or Hf, and a film of a mixture of these compounds are preferable because of high heat resistance. In particular, a film made of a mixture of ZnS and SiO ₂ is preferable because deterioration due to repeated overwriting hardly occurs. In particular, ZnS and SiO
The mixture of ₂ and carbon is preferable because the residual stress of the film is small, and the recording sensitivity, the carrier-to-noise ratio (C / N), the erasing rate, and the like are unlikely to be deteriorated even when recording and erasing are repeated. The thickness of the film is determined by optical conditions, but is preferably from 10 to 500 nm. If the thickness is larger than this, cracks and the like may occur. If the thickness is smaller than this, the substrate is easily damaged by heat due to repetition of overwriting, and the repetition characteristics deteriorate. A particularly preferred range of the film thickness is 50 nm or more and 200 nm or less.

In the present invention, it is necessary to provide an oxide film between the first dielectric layer and the recording layer described below.
By providing this, the deterioration of the jitter characteristic due to the overwrite shelf can be improved. This is because even if left for a long time, changes in the atomic arrangement in the amorphous state,
It is presumed that this may prevent the reaction between the dielectric layer and the recording layer.

As the oxide, 2 in the third period of the periodic table
Use is made mainly of an oxide of an element selected from Group A to Group 4B, Group 4A to Group 4B in the fourth period, Group 2A to Group 4B in the fifth period, Group 2A to Group 5B in the sixth period. it can. Here, the oxide means MgAl ₂ O ₄ or SrTiO ₃
And the like.

Among them, Hf, Zr, Cr, Al, S
m, Zn, Ni, Nb, Ta, Eu, Ca, Mn, M
g, Ce, Sr, Cd, La, Dy, V, Sn, Ba,
Co, Ce, W, Fe, Ti, Y, In, Si, Sc,
Cu oxide is preferred because of its high heat resistance. In particular, Zr, Cr, Al, Nb, Ti, M
g and Zn oxides are more preferred.

Among them, particularly preferred are those containing zirconium oxide as a main component and an oxide of an element belonging to Group 2A or 3A of the periodic table excluding beryllium. Among them, Mg, Ca, Y, Ce, Pr, Nd, Sm,
Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, L
Addition of an oxide of u is preferable from the viewpoint of stability, and oxides of Mg, Ca, Y, and Ce are more preferable from the viewpoint of cost. Their content is 2 mol% or more, 30
When the content is less than mol%, the film is strong and stable, which is preferable.

The thickness of these oxide layers is determined from the fact that they are difficult to peel off from the first dielectric layer and the optical conditions.
It is preferably from 0.5 nm to 10 nm. The thickness is 10
If it is not less than nm, it is easy to peel off from the first dielectric layer. On the other hand, if the thickness is less than 0.5 nm, it is difficult to deposit the film to a uniform thickness, and the effect of providing the oxide may not be obtained. The thickness is particularly preferably 0.5 nm or more and 5 nm or less.

When forming an oxide layer by a sputtering method,
Sputtering may be performed from the target of the oxide itself.
At this time, oxygen may be mixed with the sputtering gas. Also,
Reactive sputtering may be performed from a target such as a metal, a metalloid, and a semiconductor.

The recording layer of the present invention is not particularly limited, but may be a Ge—Te alloy, an In—Se alloy, a Ge
-Sb-Te alloy, In-Sb-Te alloy, Pd-Ge
-Sb-Te alloy, Pt-Ge-Sb-Te alloy, Nb
-Ge-Sb-Te alloy, Ni-Ge-Sb-Te alloy, Co-Ge-Sb-Te alloy, Ag-In-Sb-
Te alloy, Ag-Ge-Sb-Te alloy, Ag-Pd-
Ge-Sb-Te alloy, Pd-Nb-Ge-Sb-Te
Alloys.

In particular, Ge-Sb-Te alloy, Pd-Ge-
Sb-Te alloy, Pt-Ge-Sb-Te alloy, Nb-
Ge-Sb-Te alloy, Pd-Nb-Ge-Sb-Te
Alloys are preferable because they have a short erasing time, can be repeatedly recorded and erased many times, and are excellent in recording characteristics such as C / N and erasing rate.

The thickness of the recording layer of the present invention is preferably from 5 nm to 40 nm. When the thickness of the recording layer is smaller than the above, the recording characteristics are significantly degraded due to repeated overwriting, and when the recording layer is thicker than the above, the recording layer is likely to move due to repeated overwriting. Jitter becomes worse. In particular, when mark length recording is adopted, the recording layer is more likely to move due to recording and erasing than when pit position recording is used.To prevent this, it is necessary to further increase the cooling of the recording layer during recording. The thickness of the recording layer is preferably from 10 nm to 35 nm, more preferably from 10 nm to 24 nm.
nm.

The material of the second dielectric layer of the present invention may be the same as that of the first dielectric layer,
Different materials may be used. Thickness is 3nm or more and 50n
m or less is preferable. If the thickness of the second dielectric layer is smaller than the above, defects such as cracks occur, and the durability of the second dielectric layer is undesirably reduced. Further, the thickness of the second dielectric layer is
If the thickness is larger than the above, the cooling degree of the recording layer becomes low, which is not preferable. The thickness of the second dielectric layer has a more direct effect on the cooling of the recording layer, and in order to obtain better erasure characteristics and repetition durability, and particularly to achieve good recording in the case of mark length recording. -In order to obtain erasing characteristics, 30 nm or less is more effective. Since it absorbs light and can be efficiently used as thermal energy for recording and erasing, it is also preferable to be formed from a non-transparent material. For example,
The mixture of ZnS, SiO _2, and carbon has low residual stress in the film, and hardly causes deterioration in recording sensitivity, carrier-to-noise ratio (C / N), erasure rate, and the like even when recording and erasing are repeated. preferable.

Examples of the material for the reflective layer include metals and alloys having light reflectivity, and mixtures of metals and metal compounds. Specifically, a metal having a high reflectivity, such as Al, Au, Ag, or Cu, an alloy containing the same as a main component, Al, S
Metal compounds such as nitrides, oxides, and chalcogenides such as i are preferable. Metals such as Al and Au and alloys containing these as main components are particularly preferable because of their high light reflectivity and high thermal conductivity. In particular, an alloy containing Al as a main component is preferable because the price of the material can be reduced. The thickness of the reflective layer is generally about 10 nm or more and 300 nm or less. The thickness is preferably 30 nm or more and 200 nm or less because the recording sensitivity is high and the reproduction signal intensity can be increased.

Next, a method for manufacturing the optical recording medium of the present invention will be described. As a method of forming a first dielectric layer, an oxide layer, a recording layer, a second dielectric layer, a reflective layer and the like on a substrate,
A method of forming a thin film in a vacuum, for example, a vacuum deposition method, an ion plating method, a sputtering method and the like can be mentioned. 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 deposited state with a quartz crystal film thickness meter or the like.

Further, after forming the reflective layer, a dielectric layer of ZnS, SiO ₂ , ZnS—SiO ₂ , or the like, or ultraviolet curing may be used after forming the reflective layer within a range that does not significantly impair the effects of the present invention. A protective layer such as a resin may be provided as necessary.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments. (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 film thickness during the formation of the recording layer, the dielectric layer, and the reflective layer was monitored with a quartz crystal film thickness meter. The thickness of each layer was measured by observing the cross section with a scanning or transmission electron microscope.

In the optical recording medium formed by sputtering, the recording layer on the entire surface of the disk was crystallized and initialized with a beam of a semiconductor laser having a wavelength of 830 nm before recording.

(Example 1) A random pattern of 8/16 modulation was formed on a groove by using an optical head having a numerical aperture of an objective lens of 0.6 and a wavelength of a semiconductor laser of 650 nm under a condition of a linear velocity of 6 m / sec. Recorded in the mark length record. At this time, the recording laser waveform used was a general multi-pulse. The window width at this time was 34 ns.
Recording power and erasing power were optimized for each disk.

Thickness 0.6 mm, diameter 12 cm, 1.48
μm pitch (land width 0.74 μm, groove width 0.7
Sputtering was performed while rotating a polycarbonate substrate having a spiral groove of 4 μm) at 30 revolutions per minute.

First, the inside of the vacuum vessel is evacuated to 1 × 10 ^-3 Pa, and then SiO 2 is evacuated in an Ar gas atmosphere of 2 × 10 ^-1 Pa.
_A first dielectric layer having a thickness of 95 nm was formed on the substrate by sputtering ZnS to which 20 mol% of ₂ was added. Next, Y ₂ O ₃
Was sputtered on a ZrO ₂ target containing 2.5 mol% of, to form an oxide layer of 2 nm. Then, Ge, Sb,
Sputtering an alloy target made of Te to a thickness of 20
A recording layer having a composition of Ge _17.1 Sb _27.6 Te _55.3 nm was obtained.
Further, as the second dielectric layer, the same ZnS.
Sputtering SiO ₂ to form 16 nm, and on this,
An AlHfPd alloy was sputtered to form a reflective layer having a thickness of 150 nm, and an optical recording medium of the present invention was obtained.

Recording was performed once on this disk, and the byte error rate measured at that time was 2.5 × 10 ⁻⁵ . Dry as recorded, 1 at 80 ° C
It was left for 00 hours. Thereafter, when the byte error rate of the same portion was measured, there was almost no change of 3.0 × 10 ⁻⁵ . Furthermore, when this portion was overwritten once, it was confirmed that the byte error rate was 4.1 × 10 ⁻⁵ and hardly changed. The jitter at this time was a good value of 9.2% of the window width.

Example 2 A disk similar to that of Example 1 was obtained except that an Al ₂ O ₃ target was sputtered to obtain an oxide layer. The measurement was performed in the same manner as in Example 1. First, recording was performed once on this disk, and the byte error rate at that time was measured to be 4.5 × 10 ⁻⁵ . The recorded state was dried and left at 80 ° C. for 100 hours. After that, when the byte error rate of the same portion was measured, it was almost unchanged at 3.4 × 10 ⁻⁵ . Furthermore, when this portion was overwritten once, it was confirmed that the byte error rate was 2.8 × 10 ^-5 and hardly changed. The jitter at this time was a good value of 9.8% of the window width.

Example 3 A disk similar to that of Example 1 was obtained except that an Nb ₂ O ₅ target was sputtered to obtain an oxide layer. The measurement was performed in the same manner as in Example 1. As a result, the disk was recorded once, and the byte error rate at that time was 5.5 × 10 ⁻⁵ . The recorded state was dried and left at 80 ° C. for 100 hours. Thereafter, when the byte error rate of the same portion was measured, it was almost unchanged at 5.2 × 10 ⁻⁵ . Further, when this portion was overwritten once, it was confirmed that the byte error rate was 6.8 × 10 ^-5 and hardly changed. The jitter at this time was a favorable value of 10.2% of the window width.

Example 4 A disk similar to that of Example 1 was obtained except that an oxide layer was obtained by sputtering a TiO ₂ target. The measurement was performed in the same manner as in Example 1. First, recording was performed once on this disk, and the byte error rate at that time was measured to be 6.8 × 10 ⁻⁵ . The recorded state was dried and left at 80 ° C. for 100 hours.
After that, when the byte error rate of the same portion was measured, it was almost unchanged at 8.0 × 10 ⁻⁵ . Further, when this portion was overwritten once, it was confirmed that the byte error rate was almost unchanged at 8.8 × 10 ⁻⁵ . The jitter at this time was a good value of 10.4% of the window width.

Example 5 A disk similar to that of Example 1 was obtained except that an MgO target was sputtered to obtain an oxide layer. The measurement was performed in the same manner as in Example 1. First, recording was performed once on this disk, and the byte error rate at that time was measured to be 6.1 × 10 ⁻⁵ . The recorded state was dried and left at 80 ° C. for 100 hours. Thereafter, when the byte error rate of the same part was measured, it was 6.6 × 10 ^−5, and there was almost no change. Further, when this portion was overwritten once, it was confirmed that the byte error rate was 7.8 × 10 ^-5 and hardly changed. The jitter at this time was a favorable value of 10.0% of the window width.

Example 6 A disk similar to that of Example 1 was obtained except that an oxide layer was obtained by sputtering a ZnO target. The measurement was performed in the same manner as in Example 1. First, recording was performed once on this disk, and the byte error rate at that time was measured to be 5.1 × 10 ⁻⁵ . The recorded state was dried and left at 80 ° C. for 100 hours. Thereafter, when the byte error rate of the same portion was measured, it was 4.6 × 10 ^−5, and there was almost no change. Furthermore, when this portion was overwritten once, it was confirmed that the byte error rate was 5.8 × 10 ^-5 and hardly changed. The jitter at this time was a good value of 9.9% of the window width.

Example 7 Z containing 8 mol% of MgO
Other than sputtering the rO ₂ target to obtain an oxide layer,
A disk similar to that of Example 1 was obtained. The measurement was performed in the same manner as in Example 1. First, recording was performed once on this disk, and the byte error rate at that time was measured.
It was 0 ^-5 . The recorded state was dried and left at 80 ° C. for 100 hours. After that, when the byte error rate of the same portion was measured, it was 4.2 × 10 ^-5 and there was almost no change. Furthermore, when this part was overwritten once, the byte error rate was 3.9 × 10
It was confirmed that there was almost no change to ^-5 . The jitter at this time was a good value of 9.5% of the window width.

Example 8 A disk similar to that of Example 1 was obtained except that a Cr ₂ O ₃ target was sputtered to obtain an oxide layer. The measurement was performed in the same manner as in Example 1. First, recording was performed once on this disk, and the byte error rate at that time was measured to be 2.2 × 10 ⁻⁵ . The recorded state was dried and left at 80 ° C. for 100 hours. After that, when the byte error rate of the same portion was measured, it was 3.2 × 10 ^-5 and there was almost no change. Furthermore, when this portion was overwritten once, it was confirmed that the byte error rate was 3.1 × 10 ^-5 and hardly changed. The jitter at this time was a favorable value of 9.0% of the window width.

Comparative Example 1 A disk similar to that of Example 1 was obtained except that the oxide layer was omitted. The error rate after one recording was 4.0 × 10 ⁻⁵ . As in the case of Example 1, it was dried and left at 80 ° C. for 100 hours. Thereafter, when the byte error rate of the same portion was measured, there was almost no change of 3.0 × 10 ⁻⁵ . However, when this portion was overwritten once, an error occurred and the byte error rate deteriorated so that the byte error rate could not be measured. The cause of the error was due to the deterioration of the jitter. At this time, the jitter was about 18% of the window width.

(Embodiment 9) Wavelength 638n of semiconductor laser
m, an optical disk evaluation device having an optical head with a numerical aperture of the objective lens of 0.6 (DDU manufactured by Pulstec Industrial Co., Ltd.)
-1000) on a recording track under the following conditions.

(Condition a) At a linear velocity of 6 m / sec, the recording frequency f
Recording was performed 10 times at 1 = 1.1 MHz (long recording mark), and overwriting was performed once at f2 = 4.9 MHz (short recording mark). The duty was 50% and the window width was 34.2 ns. The erasing ratio is the ratio of the carrier of the signal of the long recording mark before and after overwriting the short recording mark,
The ratio of the carrier of the short recording mark to the carrier of the long recording mark after overwriting was measured as the effective erasing rate using a spectrum analyzer under the condition of a bandwidth of 30 kHz.

(Condition b) At a linear velocity of 9 m / sec and a recording frequency f
Recording was performed 10 times at 3 = 2.4 MHz (long recording mark), and overwriting was performed once at f4 = 10.6 MHz (short recording mark). The duty was 50% and the window width was 15.6 ns. As in the case of (condition a),
The erasing rate and the effective erasing rate were measured.

In both cases (condition a) and (condition b), the lengths of the long recording mark and the short recording mark are 13 times and 3 times the window width, respectively, and the recording linear density in the case of (condition b) Is
It is about 1.5 times that in the case of (condition a). In addition, the recording power and the erasing power were optimized for each disk.

Next, a polycarbonate substrate having a guide groove with a thickness of 0.6 mm, a diameter of 12 cm, and a pitch of 1.2 μm (a land width of 0.6 μm) is rotated at 30 revolutions per minute.
m, groove width 0.6 μm), the following sputtering film formation was performed.

First, the inside of the vacuum vessel was evacuated to 1 × 10 ^-3 Pa, and then SiO 2 was introduced in an Ar gas atmosphere of 2 × 10 ^-1 Pa.
₂ is sputtered with ZnS to which 20 mol% is added,
An 80 nm-thick first dielectric layer was formed on the substrate. Next, an Al ₂ O ₃ target was sputtered to form an Al ₂ O ₃ layer with a thickness of 5 nm to form an oxide layer. Then, Ge, Sb,
An alloy target made of Te was sputtered to obtain a recording layer having a thickness of 20 nm. Further, as the second dielectric layer, the same ZnS.SiO ₂ as the first dielectric layer was sputtered to form a 16 nm layer, and an AlHfPd alloy was sputtered thereon to form a 150 nm thick reflective layer.
An optical recording medium of the present invention was obtained.

When the erasure rate under (condition a) was measured, it was 4
The effective erasing rate was 1 dB, and the effective erasing rate was 30 dB. Next, when the erasing rate under (condition b) was measured, the erasing rate was 39 dB, and the effective erasing rate was 28 dB. Under all the conditions, practically sufficient erasing characteristics were obtained.

Example 10 A disk was obtained in the same manner as in Example 9 except that TiO2 was formed to 5 nm as an oxide layer.
When measurement was performed in the same manner as in Example 9, the erasing rate and the effective erasing rate under (condition a) were 39 dB and 29 dB, respectively.
The erasing rate and the effective erasing rate under (condition b) are each 38 d.
B, 27 dB, and practically sufficient erase characteristics were obtained under any of the conditions.

(Example 11) A disk was obtained in the same manner as in Example 9 except that ZrO ₂ was formed to 3 nm as an oxide layer.
When measurement was performed in the same manner as in Example 9, the erasing rate and the effective erasing rate under (condition a) were 38 dB and 26 dB, respectively.
The erasing rate and the effective erasing rate under (condition b) are each 35 d.
B and 23 dB, and practically sufficient erase characteristics were obtained under any of the conditions.

Example 12 A disk was obtained in the same manner as in Example 9 except that 3 nm of ZrO ₂ containing 2.5 mol% of Y ₂ O ₃ was formed as an oxide layer. When the measurement was performed in the same manner as in Example 9, the erasing rate under (condition a) and the effective erasing rate were 39 dB and 27 dB, respectively, the erasing rate under (condition b),
The effective erase rates were 36 dB and 25 dB, respectively, and practically sufficient erase characteristics were obtained under any of the conditions.

Comparative Example 2 A disk was obtained in the same manner as in Example 2 except that no oxide layer was provided. When the same measurement as in Example 8 was performed, the erasing rate and the effective erasing rate under (condition a) were 38 dB and 24 dB, respectively, and the erasing characteristics were good. However, the erasing rate and effective erasing rate under (condition b) were 28 dB and 14 dB, respectively, and the erasing characteristics were deteriorated under the conditions of high linear velocity and high linear density.

(Embodiment 13) A linear velocity of 6 m /
Under the condition of seconds, an 8/16 modulation random pattern was overwritten 100,000 times by mark length recording using an optical head having a numerical aperture of an objective lens of 0.6 and a wavelength of a semiconductor laser of 680 nm. At this time, a multi-pulse was used as the recording laser waveform. Also, the window width at this time is
34 ns. Recording power and erasing power were optimized for each disk.

At the time of overwriting, the start and end of writing of the data group (recording mark) were fixed to one point on the disk. The distance between the data write start portion and the data write end portion was 1 cm, and only this portion was overwritten.

The jitter was measured by a time interval analyzer. The deterioration distance (collapse of the waveform) at the beginning and end of the recording area, the decrease in the amplitude of the signal waveform, and the presence or absence of a burst defect were observed with an oscilloscope.

Thickness 0.6 mm, diameter 12 cm, 1.48
μm pitch (land width 0.74 μm, groove width 0.7
Sputtering was performed while rotating a polycarbonate substrate having a spiral groove of 4 μm) at 30 revolutions per minute.

First, the inside of the vacuum vessel was evacuated to 1 × 10 ^-3 Pa, and then SiO 2 was evacuated in an Ar gas atmosphere of 2 × 10 ^-1 Pa.
_A first dielectric layer having a thickness of 95 nm was formed on the substrate by sputtering ZnS to which ₂ mol% was added. This first
The Knoop hardness of ZnS.SiO ₂ which is a dielectric layer of
0 kgf / mm ² and Young's modulus are 90 GPa. Next, Al ₂ O ₃ (Knoop hardness: 2000 kgf / mm ² , Young's modulus: 460 GPa) was formed to a thickness of 10 nm as an oxide layer. Then G
An alloy target made of e, Sb, and Te was sputtered to obtain a recording layer having a thickness of 20 nm. Further, the same ZnS.SiO ₂ as the first dielectric layer is used as the second dielectric layer.
An AlHfPd alloy was sputtered thereon to form a reflective layer having a thickness of 150 nm, thereby obtaining the optical recording medium of the present invention.

Observation of the collapse of the waveforms at the data write start portion and the data write end portion after 100,000 times overwriting revealed that they were 5 μm and 10 μm, respectively, which were sufficiently small for practical use. Also, it was confirmed that the jitter in this portion was 11% of the window width and was sufficiently small for practical use.
The signal amplitude is about 90% of the amplitude after 10 overwrites
This is a practically acceptable level. Also, no burst defects occurred.

Example 14 The same measurement as in Example 13 was performed using the disk of Example 1.

Observation of the waveform collapse at the data write start portion and the write end portion after 100,000 times overwriting revealed that they were 8 μm and 5 μm, respectively, which were sufficiently small for practical use. Also, it was confirmed that the jitter in this portion was 10% of the window width and was sufficiently small for practical use. The amplitude of the signal is about 90% of the amplitude after 10 overwrites, which is a level that does not cause any practical problem. Also, no burst defects occurred.

Example 14 Using the disk of Example 7, the same measurement as in Example 13 was performed.

Observation of the waveform collapse at the data write start portion and the data write end portion after 100,000 times overwriting revealed that they were 4 μm and 10 μm, respectively, which were sufficiently small for practical use. Also, it was confirmed that the jitter in this portion was 11% of the window width and was sufficiently small for practical use.
The signal amplitude is about 85% of the amplitude after 10 overwrites
This is a practically acceptable level. Also, no burst defects occurred.

Example 15 The same measurement as in Example 13 was performed using the disk of Example 8.

Observation of the collapse of the waveform at the start of data writing and the end of data writing after overwriting 100,000 times revealed that they were 10 μm and 3 μm, respectively, which were sufficiently small for practical use. Also, it was confirmed that the jitter in this portion was 10% of the window width and was sufficiently small for practical use.
The signal amplitude is about 90% of the amplitude after 10 overwrites
This is a practically acceptable level. Also, no burst defects occurred.

Comparative Example 3 A disk similar to that of Example 1 was obtained except that the oxide layer was omitted. When the same measurement as in Example 13 was performed, the jitter after overwriting 100,000 times was as large as 15% of the window width. Further, when the waveform collapse at the start of writing and at the end of writing was observed, each was 200 μm. , 50 μm, and it was found that accurate data reproduction was difficult. Further, the amplitude of the signal was 75% of the amplitude after overwriting 10 times, and the contrast was low.

[0067]

According to the optical recording medium of the present invention, the following effects can be obtained. (1) Even if recording / erasing is performed many times, the decrease in signal amplitude is small. (2) Good jitter characteristics can be obtained even if recording / erasing is performed many times. (3) Burst defects do not occur even if recording / erasing is performed many times. (4) Good storage durability. (5) It can be easily manufactured by a sputtering method.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Toshio Nonaka 1-1-1, Sonoyama, Otsu-shi, Shiga Pref.

Claims (6)

[Claims] The present invention enables recording, erasing, and reproducing of information by irradiating light. Recording and erasing of information are performed by a reversible phase change between an amorphous phase and a crystalline phase. An optical recording medium comprising at least a first dielectric layer, a recording layer, a second dielectric layer, and a reflective layer in this order,
An optical recording medium characterized in that a layer made of an oxide is provided at least between a recording layer and a first dielectric layer. 2. The thickness of the oxide layer is 0.5 nm.
2. The optical recording medium according to claim 1, wherein said optical recording medium has a thickness of 10 nm or less. 3. A layer made of an oxide is made of a 2A group to a 4B group in the third period of the periodic table, a 2A group to a 4B group in the fourth period,
5th period from 2A group to 4B group, 6th period from 2A group to 5
2. An oxide comprising an oxide of an element selected from Group B as a main component.
The optical recording medium according to the above. 4. The optical recording medium according to claim 1, wherein the layer made of an oxide contains zirconium oxide as a main component. 5. A layer made of an oxide containing zirconium oxide as a main component and an oxide of an element belonging to Group 2A or 3A of the periodic table excluding beryllium in an amount of 2 mol% or more and 30 mol or more.
The optical recording medium according to claim 1, wherein the content is 1%. 6. The method according to claim 1, wherein the first dielectric layer or the second dielectric layer is Z
_2. The optical recording medium according to claim 1, comprising nS and SiO2.