JP2004199786A - Disk-shaped phase change optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a phase change type optical recording medium which is broad in margin to a speed of crystallization in its whole region, high in recording speed and highly durable in storage. <P>SOLUTION: On a substrate 1, a lower dielectric layer 2, a lower interface layer 3, a nuclei generating layer 4, a recording layer 5, an upper interface layer 6, an upper dielectric layer 7, an adjusting layer 8, and a heat releasing layer 9 are laminated in this order, and the outer surface of each layer is covered with a protecting layer 10. The film thickness of the nuclei generating layer 4 is gradually changed in the diameter direction. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a disk-shaped phase-change optical recording medium, and more particularly, to a means for making a crystallization speed margin of a recording layer uniform on the inner and outer circumferences.
[0002]
[Prior art]
With the advent of the multimedia era, information has been diversified and the amount of information handled by information equipment has become enormous. As a result, the recording media responsible for storing information has a much larger capacity and faster information recording. Is desired. Of the recording media, optical recording media have attracted special attention because of their high reliability, and various technologies for realizing a larger capacity than before, such as reducing the track pitch, have increased the recording density in the track width direction. Technology for increasing the recording density in the track direction by adopting the mark edge recording method, technology for eliminating the waste of the recording density over the entire medium by employing the ZCAV format, And the like, and a technique for recording information in both of them has been proposed.
[0003]
Among them, the disk-shaped phase-change type optical recording medium has been remarkably popularized for consumer use since information can be rewritten and is inexpensive, and particularly for home use video recording is rapidly expanding. In general, when a disc-shaped recording medium is used as a video recording medium, it is possible to provide a new function, such as “follow-up playback”, which is impossible when a tape-shaped recording medium is used as a video recording medium. However, along with this, a higher characteristic than that of a disk-shaped recording medium used merely for information recording is required. For example, in the case of "follow-up playback", it is necessary to play back the image while the video is being recorded, so it is necessary to switch between recording and playback at regular time intervals. Will need to be faster than ever.
[0004]
There are several means for increasing the recording speed of the disk-shaped recording medium. The ZCAV method is also a typical example, and it is possible to increase the linear velocity toward the outer periphery by keeping the rotation speed of the disk constant. Become. However, when the linear velocity increases, when a phase-change optical recording medium is used, it is necessary to increase the crystallization speed of the recording layer correspondingly. There are mainly two methods for increasing the crystallization speed of the phase change recording layer. One is a method of increasing the crystallization speed of the recording layer itself, and a technique of adding an element such as Sn to the recording layer has been conventionally proposed. The other one is a method of increasing the number of crystal nuclei serving as a crystal base and promoting crystallization of the recording layer. For example, an Sn-Te-based or Bi-Te-based alloy layer is provided on one or both sides of the recording layer. Conventionally, a technique to be added has been proposed (for example, see Patent Document 1).
[0005]
By the way, when any of the above-mentioned methods of increasing the crystallization speed is adopted, in the disk-shaped phase change type optical recording medium such as the ZCAV system in which the recording linear velocity is different between the inner peripheral portion and the outer peripheral portion of the disk, It is necessary to adjust the crystallization speed of the recording layer to an appropriate value at both the inner peripheral portion and the outer peripheral portion. That is, if the crystallization speed is too fast, the lower the linear velocity region in the inner circumference, the amorphous mark can not be formed unless the recording layer is quenched at a faster speed than the crystallization speed that is just faster, It becomes difficult to form an amorphous mark. Conversely, if the crystallization speed is too slow, the higher the linear velocity region on the outer periphery, the lower the temperature of the recording layer before the time required for crystallization elapses, so the recording layer is less likely to be crystallized, It is difficult to completely erase information. Adjusting the crystallization speed so as to simultaneously satisfy the crystallization speed of the recording layer at the highest linear velocity and the crystallization speed of the recording layer at the lowest linear velocity requires recording and reproducing information even in a conventional low linear velocity drive. This is an indispensable condition for maintaining compatibility that must be able to be performed.
[0006]
Therefore, in order to adjust the crystallization speed of the recording layer to an optimum value corresponding to the recording linear velocity over the entire recording area, the crystallization speed of the recording layer in the radial direction of the disk is adjusted to a value corresponding to the recording linear velocity. It is most preferable to sequentially change the crystallization speed, but conventionally, it is difficult to adjust the crystallization speed, and the crystallization speed of the recording layer required at the innermost periphery and the recording speed required at the outermost periphery are difficult. A method has been adopted in which the crystallization speed of the recording layer is set to a constant value that satisfies both the crystallization speeds of the layers.
[0007]
[Patent Document 1]
JP-A-11-167722 [0008]
[Problems to be solved by the invention]
However, if the crystallization speed of the recording layer is adjusted to be compatible with a wide linear velocity region, a problem arises in that the storage life of the medium is shortened in the inner and outer peripheral regions where the crystallization speed margin is small. For example, if a phase-change optical recording medium on which information is recorded at a high linear velocity is stored in a high-temperature, high-humidity environment, and then information is recorded again at a high linear velocity, the information is correctly rewritten. A problem arises that it is not possible. Such inconvenience occurs because the crystallization speed of the recording layer is reduced by storage, and as a result, the crystallization speed is insufficient in a region where the margin is small, and information cannot be completely erased at a high linear velocity.
[0009]
The present invention has been made in order to solve the deficiencies of the related art, and an object thereof is to increase a margin of a crystallization speed of a recording layer over the entire recording area, to achieve a high recording speed and a long storage life. An object of the present invention is to provide a long phase change optical recording medium.
[0010]
[Means for Solving the Problems]
The present invention, in order to solve the above problems, a disk-shaped phase-change optical recording medium in which a nucleation layer for increasing the crystallization speed of the recording layer is added to one or both sides of the recording layer, The thickness of the nucleation layer is gradually changed in the diameter direction of the recording layer.
[0011]
According to the study of the present inventor, the crystallization rate of the recording layer of the nucleation layer made of a Bi—Te alloy increases as the thickness of the nucleation layer increases. Therefore, by gradually changing the thickness of the nucleation layer in the diameter direction of the recording layer, the crystallization speed of each part of the recording layer can be adjusted to an optimum value corresponding to the recording linear velocity. The recording speed can also be improved for a phase-change optical recording medium in which the recording linear velocity increases in the outer peripheral region, such as the disk-shaped phase-change optical recording medium described above. In addition, since the margin of the crystallization rate can be increased for each part of the recording layer, even if the crystallization rate decreases due to storage in a high-temperature and high-humidity environment, the crystallization rate can have a margin, and information can be provided. Since the rewriting can be performed accurately, the storage life of the phase change optical recording medium can be improved. In the case where the nucleation layer is formed of a material in which the crystallization speed of the recording layer decreases as the film thickness increases, the thickness of the nucleation layer may be increased toward the inner periphery.
[0012]
Further, according to the present invention, in the disk-shaped phase-change optical recording medium having the above-described configuration, recording and reproduction of information with respect to the recording layer are performed at a constant medium rotation speed.
[0013]
As described above, the thickness of the nucleation layer is gradually changed in the diameter direction of the recording layer in the disk-shaped phase change type optical recording medium in which the recording and the reproduction of the information on the recording layer are performed at a constant medium rotation speed. In addition, since the margin of the crystallization speed of the recording layer can be increased in both the inner peripheral region and the outer peripheral region, it is possible to simultaneously increase the recording speed and extend the storage life.
[0014]
Further, according to the present invention, in the disk-shaped phase-change optical recording medium having the above-mentioned configuration, the nucleation layer has a larger thickness in an outer peripheral region of the recording layer.
[0015]
As described above, in a phase-change optical recording medium in which the recording linear velocity increases in the outer peripheral region, the crystallization speed of the recording layer needs to be increased in the outer peripheral region. In the case of forming a nucleation layer having a higher speed, the crystallization rate in the outer peripheral region of the recording layer can be increased by increasing the thickness of the nucleation layer in the outer peripheral region of the recording layer, and the recording speed can be reduced. Higher speed and longer storage life can be achieved.
[0016]
Further, according to the present invention, in the disk-shaped phase-change optical recording medium having the above-mentioned structure, the nucleation layer is made of a Bi-Te alloy or a Sn-Te alloy.
[0017]
Bi-Te alloys or Sn-Te alloys have excellent properties as nucleation layer materials. Therefore, when the nucleation layer is made of a Bi-Te alloy or a Sn-Te alloy, the crystallization speed of the recording layer can be increased, and the recording speed can be increased and the storage life can be extended. it can.
[0018]
Further, according to the present invention, in the disk-shaped phase-change optical recording medium having the above configuration, the recording layer and the nucleation layer are formed by a sputtering method.
[0019]
As described above, when the recording layer and the nucleation layer are formed by the sputtering method, these layers can be formed continuously, so that the film formation process is simplified, and the low cost of the disk-shaped phase-change optical recording medium as a product is achieved. Can be achieved.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 shows an example of a cross-sectional structure of a phase-change optical recording medium according to the present invention.
[0021]
As is clear from this figure, the phase change type optical recording medium of this example has a lower dielectric layer 2, a lower interface layer 3, a nucleation layer 4, a recording layer 5, an upper interface layer 6, The dielectric layer 7, the adjustment layer 8, and the heat radiation layer 9 are laminated in this order, and the outer surface of each layer is covered with a protective layer 10.
[0022]
The substrate 1 is formed into a disk of a predetermined size by injection molding a resin material such as polycarbonate, polymethyl methacrylate, or polyolefin, and has a recording track of information formed in a spiral or concentric shape on one surface. Can be
[0023]
The lower dielectric layer 2 and the upper dielectric layer 7 are for preventing the substrate 1 and the recording layer 5 from being damaged by heat during recording, and include zinc sulfide, silicon oxide, and silicon nitride. It is formed of an inorganic dielectric material such as aluminum oxide and a mixture or a laminate of these inorganic dielectric materials.
[0024]
The lower interface layer 3 functions as a barrier layer for preventing diffusion of atoms from the lower dielectric layer 2 to the recording layer 5, and the upper interface layer 6 functions as a diffusion of atoms from the upper dielectric layer 7 to the recording layer 5. Which functions as a barrier layer for preventing metal oxides, oxides and nitrides of metals such as Si, Ge, Ti, Zr, Ta, Nb, Hf, Al, Y, Cr, W, Zn, In, and Sn. And so on.
[0025]
The recording layer 5 is formed of a phase-change material, such as a GeSbTe alloy, which is reversibly changed between a crystalline state and an amorphous state by performing appropriate heating and cooling. When a GeSbTe alloy is used for the recording layer 5, a GeSnSbTe alloy to which an appropriate amount of Sn is added can be used in order to increase the recording speed and the erasing speed.
[0026]
The nucleation layer 4 is for promoting crystallization of the recording layer 5, and can be formed of a Bi-Te alloy, a Sn-Te alloy, or the like. As illustrated in FIG. 2, the nucleation layer 4 has a thickness that gradually changes in the diameter direction of the recording layer 5 so that the crystallization speed of the recording layer 5 increases as the recording linear velocity increases. Formed. In the example of FIG. 2A, the nucleation layer 4 is formed to be thicker in a region where the recording linear velocity is higher, but the nucleus in which the crystallization speed of the recording layer 5 is lower as the film thickness is larger. When the generation layer 4 is used, as illustrated in FIG. 2B, the nucleation layer 4 is formed to have a smaller thickness as the recording linear velocity increases. Further, in the example of FIG. 2A, the film thickness of the nucleation layer 4 uniformly increases according to the recording linear velocity. However, the gist of the present invention is not limited to this. As illustrated in FIG. 2C, the thickness of the nucleation layer 4 can be changed stepwise according to the recording linear velocity. Further, in FIG. 1, the nucleation layer 4 is formed only on one side of the recording layer 5, but it is of course possible to form it on both sides of the recording layer 5.
[0027]
There are several methods for making the film thickness different between the inner and outer circumferences. In the case of a film forming method using a sputtering method, the film thickness is adjusted by appropriately selecting the size of the target, or the film thickness is controlled by the power of discharge. A method of adjusting the difference or providing a film thickness adjusting plate or a mask between the target and the substrate for adjusting the film thickness can be used. In the method using this mask, when the inner circumference is to be thinned, the mask may be centered on the inner circumference of the substrate, and when the outer circumference is thinned, the mask may be centered on the outer circumference of the substrate. . In addition, when a self-revolution type sputtering apparatus is used, the difference between the inner and outer circumferences of the film thickness can be controlled by changing the number of revolutions of the substrate in the self-revolution. For example, according to an experiment separately performed by the inventor of the present invention, when a self-revolving sputtering apparatus is used, when a ZnS film is formed on a substrate having a diameter of 120 mm at a discharge power of 600 W, the ZnS film has a thickness of 30 nm in the middle circumference. When the film is formed in the discharge time, when the rotation speed of the carrier used for the film formation is 50 rpm, the inner circumference is 30.2 nm and the outer circumference is 29.7 nm. When the rotation speed of the carrier is 80 rpm, The inner diameter was 30.6 nm, and the outer diameter was 29.6 nm.
[0028]
The adjustment layer 8 corrects the difference in light absorptance between the amorphous portion and the crystal portion of the recording layer 5 and suppresses waveform distortion after rewriting. For example, the adjustment layer 8 is mainly composed of Ge such as GeCr. Is formed with a Ge alloy to which an appropriate amount of the above-mentioned element is added.
[0029]
The heat radiation layer 9 is for increasing the heating temperature of the recording layer 5 and the reflectance of the reproduction light, and has a high thermal conductivity and a metal material having a high reflectance with respect to a laser wavelength range to be used. It is formed with an alloy material. As the heat radiation layer material, Al, Ag, or an alloy containing Al or Ag as a main component is preferably used because it is relatively inexpensive, has high thermal conductivity and reflectance, and has excellent chemical stability.
[0030]
The protective layer 10 is formed of an ultraviolet curable resin.
[0031]
The lower dielectric layer 2, the lower interface layer 3, the nucleation layer 4, the recording layer 5, the upper interface layer 6, the upper dielectric layer 7, the adjustment layer 8, and the heat radiation layer 9 have a plurality of spack chambers, The film is formed using a sputtering apparatus having a small distribution and high reproducibility. The protective layer 10 is formed using a spin coater.
[0032]
In the disk-shaped phase-change type optical recording medium according to the present embodiment, since the thickness of the nucleation layer 4 is gradually changed in the diameter direction of the recording layer 5, the crystallization speed of each part of the recording layer is reduced by the recording linear velocity. The recording speed can be improved for a phase-change optical recording medium in which the recording linear velocity becomes higher in the outer peripheral area, such as a ZCAV-type disc-type phase-change optical recording medium. it can. In addition, since the margin of the crystallization rate can be increased for each part of the recording layer, even if the crystallization rate decreases due to storage in a high-temperature and high-humidity environment, the crystallization rate can have a margin, and information can be provided. Since the rewriting can be performed accurately, the storage life of the phase change optical recording medium can be improved.
[0033]
Hereinafter, the effects of the present invention will be clarified by giving more specific examples of the phase-change optical recording medium according to the present invention.
[0034]
【Example】
On the surface of the polycarbonate substrate 1 having a diameter of 120 mm and a thickness of 0.6 mm on which a preformat pattern is formed, ZnS—SiO ₂ (a mixture of ZnS and SiO ₂ ) having a thickness of 140 nm as a lower dielectric layer 2, a lower interface layer Numeral 3 is Cr ₂ O _{3 having} a thickness of 6 nm, nucleation layer 4 is Bi ₂ Te ₃ having an innermost peripheral portion of 2 nm and outermost peripheral portion is 6 nm, and recording layer 5 is 10 nm thick. GeSbTe, Cr ₂ O _{3 with} a thickness of 2 nm as the upper interface layer 6, ZnS—SiO _{2 with} a thickness of 40 nm as the upper dielectric layer 7, GeCr with a thickness of 15 nm as the adjustment layer 8, and film thickness as the heat dissipation layer 9 After sputtering AlTi of 100 nm in this order, a protective layer 10 made of an ultraviolet curable resin is formed so as to cover the outer surface of the heat radiation layer 9, and has a sectional structure shown in FIG. To prepare a disc-shaped phase-change optical recording medium. After that, the recording layer 5 was irradiated with an initialization laser, and the entire surface of the recording layer 5 was subjected to initial crystallization.
[0035]
On one surface of the polycarbonate substrate 1, a spiral pre-groove having a track pitch of 0.615 μm and a groove depth of 65 nm and having grooves and lands connected alternately and continuously was formed as a preformat pattern. The information recording area includes a lead-in area formed by emboss (pit), a rewritable lead-in area, a data area divided into 35 zones, and a rewritable lead-out area. did. The groove and the land are both divided into sectors, and each sector includes a header area, a mirror area, and a recording area of 2018 bytes. Each header area includes a header 1 to a header 4 and exists between the groove and the land. As viewed from the land track, the header 1 area and the header 2 area are closer to the outer circumference, and the header 3 area and the header 4 area are closer to the inner circumference. Are located in
[0036]
A semiconductor laser (wavelength: 655 nm, numerical aperture: 0.6), a waveform generator for generating a recording pulse, a laser driver, and a waveform equivalent circuit are used as an information recording device for recording on the phase change optical recording medium. And an information recording device including a binarization circuit. This information recording apparatus can record information by a mark edge recording method in which the shortest mark is 0.42 μm using 8-16 modulation.
[0037]
In this embodiment, in order to show as accurately as possible the effect of the film thickness of the nucleation layer 4 on the crystallization rate, two types of phase-change optical recording media having different film thicknesses of the nucleation layer 4 were separately manufactured. evaluated. This is to eliminate as much as possible the effects of slight differences in the groove shape or land shape between the inner circumference and the outer circumference and the effects of mechanical properties even within the same substrate. Care was taken to keep the same conditions, and a film was formed to have a desired film thickness at a radius of 53.8 mm. The measurement was performed on a track having a radius of 53.8 mm, and the rotation speed of the disk was adjusted so that the linear velocities in the track became 8.2 m / s and 20.5 m / s, respectively. The linear velocities of 8.2 m / s and 20.5 m / s are roughly equivalent to the innermost recording linear velocity and the outermost recording linear velocity of the ZCAV type disk-shaped phase change optical recording medium driven to rotate at 3246 rpm. Equivalent to.
[0038]
As a method of measuring the crystallization rate, a differential scanning calorimeter (DSC) or the like is generally used. However, in this embodiment, it is necessary to know the crystallization rate of the recording layer 5 in the state of the medium. However, the accuracy is slightly reduced, but the measurement is performed according to the following procedure. At this time, the reproduction power Pr was 1 mW, and a groove was selected as a measurement point.
[0039]
a. The optimum recording level Pwl and the optimum erasing level Pw2 in the single pulse overwrite multipulse are obtained.
b. The 11T signal is recorded over several tracks with the obtained Pwl and Pw2 (frequency 2.65 MHz).
c. One track is selected from the recording tracks, and the carrier level C0 is read by a spectrum analyzer.
d. DC erase of recorded information at a certain power Pe without using multi-pulses.
e. The carrier level Cl of the erased track is read, and the difference from C0 is set as the erase ratio ΔCl = Co−C1 for one-time erase.
f. The operations of c, d, and e are repeated by changing the values of the track and Pe.
g. The second DC erasure is performed on the track selected in c with the same Pe.
h. The carrier level C2 of the track after the second DC erasing is read, and the difference from C0 is set as an erasing ratio ΔC2 = C0−C2 of the second erasing i. The operations of g and h are repeated by changing the value of the track and Pe.
j. The difference between the two erasure ratios for each Pe is ΔC = ΔC2−ΔCl.
[0040]
The fact that the crystallization rate is high means that the erasure is easy in one erasure, and that ΔCl becomes a value close to ΔC2, that is, ΔC approaches zero. Therefore, the measurement of ΔC is equivalent to the measurement of the crystallization rate, and it can be shown that the smaller the ΔC, the higher the crystallization rate.
[0041]
The samples used for the measurement had two nucleation layer thicknesses of 2 nm and 6 nm. For each disk, the recording linear velocity was 8.2 m / s and 20.5 m / s on a track having a radius of 53.8 mm. The erase ratio ΔCl, erase ratio ΔC2, and erase ratio difference ΔC were measured. The results are shown in FIGS.
[0042]
As is clear from these figures, in the region of Pe ≦ 5 mW, ΔC is smaller when the nucleation layer 4 is thicker (6 nm), and is smaller than when the nucleation layer 4 is thinner (2 nm). This indicates that the crystallization rate is high. In FIG. 6, it seems that ΔC is larger at Pe = 5.5 mW when the film thickness of the nucleation layer 4 is thicker. This is because the temperature of the recording layer 5 is higher in the recording state than in the erased state. This is because it has approached, and such a region in which both ΔCl and ΔC2 have decreased may be ignored. Specifically, when the thickness of the nucleation layer 4 is 2 nm, Pe ≧ 5 mW at 8.2 m / s, Pe ≧ 5.5 mW at 8.2 m / s, and the thickness of the nucleation layer 4 is 6 nm. In the case of, Pe ≧ 4.5 mW at 8.2 m / s and Pe ≧ 5.5 mW at 20.5 m / s may be ignored.
[0043]
As described above, in the phase-change optical recording medium in which the Bi ₂ Te ₃ nucleation layer is added to the interface of the GeSbTe recording layer on the substrate side, by increasing the thickness of the nucleation layer, the erasing ratio of one-time erasure can be improved. It was found that the erasing ratio difference ΔC between ΔCl and the erasing ratio ΔC2 of the two-time erasing was small, and the crystallization speed could be increased. Therefore, if the film thickness of the nucleation layer 4 is gradually changed in the diameter direction on the same substrate and the outer periphery where the linear velocity becomes faster in the ZCAV system in which the rotation speed of the medium is constant, the maximum linear velocity becomes higher. It is possible to obtain an accurate crystallization rate that is acceptable in the entire medium including both the outermost circumference and the innermost circumference with the lowest linear velocity. Furthermore, with the increase in the crystallization speed of the recording layer, even when the recording mark is overwritten after storage, the mark recorded before storage can be sufficiently erased, and the storage of the phase change optical recording medium can be performed. Lifespan can also be improved.
[0044]
Although the embodiments of the phase-change optical recording medium according to the present invention have been described above, the gist of the present invention is not limited to this, and other than the film thickness distribution of the nucleation layer 4 may be appropriately adjusted as necessary. Can be changed.
[0045]
For example, in the above-described embodiment, the nucleation layer 4 is formed of Bi ₂ Te ₃ , but the gist of the present invention is not limited to this, and the number of crystal nuclei serving as the base of the crystal is determined. Any substance that has the effect of accelerating the crystallization of the recording layer 5 can be used as the nucleation layer forming material.
[0046]
In the above embodiment, the shortest mark length is 0.42 μm and the track pitch is 0.615 μm. However, the same effect can be obtained even if the track pitch is narrower or the shortest mark length is shorter.
[0047]
Further, in the above embodiment, the substrate 1 on which the land group type preformat pattern is formed is used. However, the same effect can be obtained with a substrate for land recording or group recording.
[0048]
Further, in the above-described embodiment, the substrate 1 in which the recording area is divided into 35 zones in the radial direction is used. However, the same effect can be obtained even if the number of zones is further increased or decreased, or the zones are not divided. There is.
[0049]
In the above embodiment, a semiconductor laser having a wavelength of 655 nm is used. However, a similar result can be obtained by using a laser having a longer wavelength, for example, a laser having a wavelength of around 780 nm or 830 nm. Conversely, a similar result can be obtained by using a short-wavelength laser, for example, one near or below 405 nm.
[0050]
In the above embodiment, the objective lens having a numerical aperture of 0.6 is used. However, the same result can be obtained by using an objective lens having a numerical aperture of 0.45 to 0.7. In addition, the same result can be obtained by combining two or more lenses and using an objective lens having a numerical aperture of 0.7 or more. In particular, by using a lens having a numerical aperture of 0.85 and a laser having a wavelength of 405 nm in combination, higher-speed and higher-density recording becomes possible. Further, the same effect can be obtained in near-field recording using evanescent light by SIL by setting the effective numerical aperture to 1 or more in combination with SIL (Solid Immersion Lens) or the like.
[0051]
【The invention's effect】
As described above, according to the present invention, since the thickness of the nucleation layer is gradually changed in the diameter direction of the recording layer, the crystallization speed of each part of the recording layer is set to an optimal value according to the recording linear velocity. The recording speed can be improved for a phase-change optical recording medium in which the recording linear velocity increases in the outer peripheral region, such as a ZCAV-type disc-shaped phase-change optical recording medium. In addition, since the margin of the crystallization rate can be increased for each part of the recording layer, even if the crystallization rate decreases due to storage in a high-temperature and high-humidity environment, the crystallization rate can have a margin, and information can be provided. Since the rewriting can be performed accurately, the storage life of the phase change optical recording medium can be improved.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating a film structure of a phase change recording medium according to an embodiment.
FIG. 2 is a graph illustrating a film thickness distribution of a nucleation layer.
FIG. 3 is a graph showing a change in an erase ratio ΔCl for a single erase operation and a change in an erase ratio ΔC2 for a double erase operation with respect to a DC erase power Pe of a medium having a nucleation layer thickness of 2 nm.
FIG. 4 is a graph showing a change in an erasing ratio difference ΔC with respect to a DC erasing power Pe of a medium having a nucleation layer thickness of 2 nm.
FIG. 5 is a graph showing a change in the erase ratio ΔC1 of single erase and the erase ratio ΔC2 of double erase with respect to the DC erase power Pe of a medium having a nucleation layer thickness of 6 nm.
FIG. 6 is a graph showing a change in an erase ratio difference ΔC with respect to a DC erase power Pe of a medium having a nucleation layer thickness of 6 nm.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Substrate 2 Lower dielectric layer 3 Lower interface layer 4 Nucleation layer 5 Recording layer 6 Upper interface layer 7 Upper dielectric layer 8 Adjustment layer 9 Heat dissipation layer 10 Protective layer

Claims (5)

In a disc-shaped phase-change optical recording medium in which a nucleation layer for increasing the crystallization speed of the recording layer is added to one or both sides of the recording layer, the film thickness of the nucleation layer is adjusted to the thickness of the recording layer. A disk-shaped phase-change optical recording medium characterized by being gradually changed in a diameter direction. 2. The disk-shaped phase-change type optical recording medium according to claim 1, wherein recording and reproduction of information on and from the recording layer are performed at a constant medium rotation speed. 3. The disk-shaped phase-change optical recording medium according to claim 1, wherein the thickness of the nucleation layer increases as the outer peripheral area of the recording layer increases. The disk-shaped phase-change optical recording medium according to any one of claims 1 to 3, wherein the nucleation layer is made of a Bi-Te alloy or a Sn-Te alloy. The disk-shaped phase-change optical recording medium according to any one of claims 1 to 4, wherein the recording layer and the nucleation layer are formed by a sputtering method.

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