JPH05205313A - High-durability optical recording medium - Google Patents

Abstract

PURPOSE:To prevent the deterioration by the flow of a recording layer and the relaxation of a structure and to improve the number of rewriting times by alternately laminating heat responsive layers and heat nonsensitive layers changing in physical states. CONSTITUTION:A (ZnS)80(SiO2)20 having about 120nm thickness is formed as a lower protective layer 2 by magnetron sputtering using Ar on a polycarbonate substrate 1 provided with grooves for tracking and pits indicating addresses at the time of injection molding. The heat responsive layers 31 of a phase transition type consisting of Ge-Sb-Te and having about 1nm thickness and the heat nonsensitive layers 32 consisting of the (ZnS)80(SiO2)20 and having about 60nm thickness are alternately superposed about 20 times thereon. The heat responsive layers 31 are nearly in an amorphous state and the single layer thereof constitutes an island of about 15nm diameter. Further, the (ZnS)80(SiO2)20 is superposed as an upper protective layer 4 at about 210nm thereon and a reflection film 5 consisting of Al96Cu4 and having about 100nm thickness is provided, on which a UV curing resin film 6 is superposed. Finally, this disk is stuck by a hot melt adhesive to the similarly formed disk with the resin films 6 positioned on the inner side. The content of the Cu in the Al96Cu4 is selected at 1 to 45 atomic %.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical recording medium for recording by raising the temperature of the recording medium using light, and more particularly to a phase change of a recording layer between a crystalline state and an amorphous state. The present invention relates to a phase-change optical recording medium for performing recording by recording or a magneto-optical recording medium for recording information according to the direction of magnetization of a recording layer.

[0002]

2. Description of the Related Art A conventional phase change type optical recording medium is, for example, as shown in FIG. 8, a disc-shaped polycarbonate having a tracking groove and an address pit (neither shown) formed on the surface during injection molding. On the substrate 11, by magnetron sputtering using argon gas,
First, the lower protective layer 12 having a thickness of about 120 nm (Zn
S) ₈₀ (SiO ₂ ) ₂₀ film is formed and the thickness is about 30 nm.
Forming a phase change recording layer 13 of Ge-Sb-Te. Next, by magnetron sputtering, the upper protective layer 14 having a thickness of about 210 nm (ZnS) ₈₀ (S
An iO ₂ ) ₂₀ film is formed, and then an Al ₉₆ Cu ₄ film having a thickness of about 100 nm is formed as the metal reflection layer 15. Next, the ultraviolet curable resin 16 is applied and irradiated with ultraviolet rays to be cured. Finally another disk made in the same way,
The UV curable resin side is placed inside and the pieces are attached with a hot melt adhesive. When the Cu content of the Al ₉₆ Cu ₄ film is in the range of 1 to 45 atomic%, good characteristics are obtained, and it is also effective when the unevenness is not formed on the recording film.

Recording / reproducing of information on the disk thus formed is performed as follows. While rotating the disk, the laser light is focused by the lens in the recording head and irradiated onto the recording layer through the substrate, and the low power that raises the temperature of the recording layer to the temperature at which crystallization occurs and the recording layer close to the melting point Recording is performed by changing the temperature according to the information signal to be recorded between high power and high temperature. When irradiated with a low-power laser beam, the temperature of the recording layer is kept at a temperature at which crystallization occurs for a relatively long time, so that the recording layer is crystallized. On the other hand, when irradiated with a high-power laser beam, the temperature of the recording layer, which has risen to near the melting point, drops sharply, so that the recording layer does not crystallize but becomes amorphous. In such a recording method, the recorded information is rewritten to the newly recorded information even if the already recorded portion is performed. That is, it is possible to overwrite. After erasing by irradiation with a constant power, recording may be performed by power-modulated irradiation. Reproduction is performed by keeping the laser light at a level (reproduction power) at which recording is not performed and detecting the intensity of reflected light. This method is described, for example, in JP-A-62-259229.

The cross-sectional structure of the conventional magneto-optical recording medium is, for example, the structure shown in FIG. Transparent substrate 21 such as glass provided with a guide groove for tracking
A dielectric layer (lower protective layer) 22 made of silicon nitride or the like is formed on the upper surface of about 9
Recording layer 2 made of magnetic material such as 0 nm and TbFeCo
3 is about 100 nm, and the upper protective layer 24 such as silicon nitride is about 2 nm.
The layers are stacked in the order of 00 nm. The dielectric layer 22 has a function of multiply-reflecting the laser light incident from the substrate 1 side therein and increasing the rotation (Kerr rotation) of the polarization plane generated in the magnetic layer 23. The protective layer 24 has a function of protecting the magnetic layer 23 from corrosion such as oxidation.

Next, the principle of recording / reproducing on such a recording medium will be described. The coercive force Hc of the magnetic layer 23 is large at room temperature and small near the Curie temperature. Therefore, when the temperature of the recording medium is raised by irradiating the laser beam while applying the recording magnetic field Hrec to the recording medium, the coercive force Hc becomes equal to the recording magnetic field Hrec when the recording temperature Tw is reached. The magnetization is oriented in the direction of the recording magnetic field Hrec to form a recording magnetic domain. During reproduction, the recording magnetic domain is irradiated with laser light (reproducing light), and the rotation of the polarization plane of the reflected light is detected to detect the presence or absence of the recording magnetic domain, and the shape and size thereof. When erasing, the direction of the recording magnetic field Hrec may be reversed. This method is described, for example, in Japanese Examined Patent Publication No. 57-34.
There is a description in the 588 publication.

[0006]

However, when recording (overwriting) was repeated many times using the recording medium shown in FIG. 8, the C / N ratio gradually decreased as shown in FIG. I knew I would come. This is because the temperature of the recording layer rises up to the melting point by repeating a large number of times and the molten recording layer gradually flows and changes in the composition and film thickness of the recording layer. It depends.

Also, when recording / erasing is repeatedly performed many times using the magneto-optical recording medium shown in FIG. 2, the C / N decreases with repetition. The cause is that the recording layer is exposed to high temperature repeatedly many times,
This is because the atomic arrangement of the magnetic layer gradually changes and the magnetic characteristics deteriorate.

Regarding these phenomena, the Institute of Electrical, Information and Communication Engineers Technical Report CPM 90-36, P. 49 (1990) and Japanese Journal of Applied Physics (Jpn.J.Appl.Phys.) Vol.28 (1989) Suppl.
28-3, pp. 61-66.

An object of the present invention is to provide a highly durable optical recording medium in which the C / N ratio does not decrease even when recording / erasing (overwriting) is repeated.

[0010]

In order to achieve the above object, the present invention uses the following means.

In an optical recording medium in which the temperature of the recording medium is raised by the irradiation of light and the resulting change in the physical state of the recording layer is used to record information, the recording layer is the recording medium. The heat responsive layer made of a material whose physical state changes due to the temperature rise and the heat insensitive layer made of a material whose physical state does not change are alternately laminated at least two layers. At this time, at least 2 atomic layers or more are required for the heat responsive layer to be able to change the physical state, and 10 atoms are required for making the diffusion (movement) of atoms in the thermal responsive layer insignificant. It should be no more than one layer. Therefore, the thickness of the thermal responsive layer 1 is 0.5 nm or more and 3 n or more.
It is preferably m or less. Further, even if the physical state of the heat responsive layer changes, the heat insensitive layer needs at least two atomic layers or more so that the heat insensitive layer cannot change the physical state. The thickness of one layer of the heat insensitive layer needs to be 0.5 nm or more. In order to suppress a marked decrease in recording sensitivity, it is preferable that the heat insensitive layer has a thickness of 100 nm or less.

This means is a phase change type recording medium in which the change in the physical state of the recording layer is a reversible change between an amorphous state and a crystalline state, and the change is a change in the direction or magnitude of magnetization. The effect is most remarkable when applied to a certain magneto-optical recording medium. The phase change recording medium is Ge-Sb-Te, Ge-Sb.
-Te-Co, In-Sb-Te, In-Te-Ag,
Ge-Te and the like are given as candidates for the above-mentioned thermoresponsive layer. The magneto-optical recording medium is composed of Tb, Dy, Gd, Nd,
A rare earth amorphous alloy or Pt-Co whose main component is at least one element selected from the group of Pr and Sm and at least one element selected from the group of Fe, Co, Nd, Pr and Sm. , Alloys such as Pd-Co, or superlattice films.

Considering that the refractive index of ordinary solids or liquids is in the range of 1 to 5, at least the optical film thickness of the recording layer necessary for producing an appropriate change in the reflected light is irradiated during reproduction. Wavelength of light (500-830nm)
Is about 10%. That is, the total thickness of the recording layer needs to be at least 10 nm or more. Further, in order to prevent a decrease in recording sensitivity, the total film thickness of the recording layer is preferably 200 nm or less.

Further, the heat insensitive layer is preferably made of an optically transparent material so as not to unnecessarily reduce the amount of reproducing light.

The heat-insensitive layer is made of oxide, nitride,
Composed of sulfides or mixtures thereof, or
It is preferably composed of a refractory metal. For example, ZnS,
CdS, In ₂ S ₃ , ZnSe, CdSe, In ₂ Se ₃ ,
SiO ₂ , SiO, AlSiN ₂ , TiO ₂ , ZrO ₂ , A
l ₂ SiN ₃ , AlSi ₂ N ₃ , Si-Al-O-N, Y ₂
O ₃ , Si ₃ N ₄ , Ta ₂ O ₅ , AlN, Cu ₂ O and SiC
A material mainly composed of a material having a composition close to at least one selected from the group consisting of Si, Ti, N
It is preferable to be composed of i, Cr, Al, Pt, Pd and an alloy of two or more kinds thereof, or an oxide, a nitride, a sulfide and a mixture thereof. Among them, S
i ₃ N ₄ and ZnS—SiO ₂ are particularly preferable because they have excellent optical transparency. Among refractory metals, Ti, Si,
Pt and the like are particularly good. Ti has excellent durability and Pt
Has an advantage that a large reproduction output can be obtained because of high reflectance.

When a magneto-optical recording material such as TbFeCo or GdTbFeCo is used as the heat responsive layer, it is convenient in manufacturing to use a nitride or an oxide of the magneto-optical recording material as the heat insensitive layer. Since the optical constants of the heat-responsive layer and the heat-insensitive layer are close to each other, the magneto-optical effect is increased.

The upper protective layer or the lower protective layer is Z
nS, CdS, In ₂ S ₃ , ZnSe, CdSe, In ₂
Se ₃ , SiO ₂ , SiO, TiO ₂ , ZrO ₂ , Ta
₂ O ₅ , Y ₂ O ₃ , Si ₃ N ₄ , AlN, Cu ₂ O, AlSi
_{N 2, Al 2 SiN 3,} AlSi 2 N 3, Si-Al-O-N
It is preferable that the main component is a material having a composition close to at least one selected from the group consisting of SiC and SiC, or a mixture thereof. Of these, Si
_{3 N 4, Al 2 O 3} , ZnS and Al-Si-N-based material is particularly preferred. Moreover, its thermal conductivity is 1 W / mK or more 6
It is preferably 0 W / m · K or less.

[0018]

The principle of the present invention will be described below with reference to FIGS. Generally, when a film is formed by a method such as sputtering, an island-shaped film is formed in the initial stage of film formation. The film thickness at the initial stage is about 0.5 nm or more and 3 nm or more.
The range is as follows. Utilizing this fact, the thermal response layer 31
When a film is formed, as shown in FIG. 4, a recording film (thermal response layer) is formed.
There is a portion where is formed and a portion where is not formed. After that, when the heat insensitive layer 32 is laminated, as shown in FIG.
The recording film (heat-responsive layer) is surrounded by the heat-insensitive layer.
Therefore, the heat responsive layer in that portion cannot flow to another place even if melting is repeated.
Therefore, even if rewriting is repeated, there is no concern that the composition or film thickness of the recording layer will change, unlike in the conventional medium, and therefore no erasure will occur. Therefore, it is possible to obtain a highly durable optical recording medium in which the C / N does not change even when the recording is repeated many times.

In the case of a magneto-optical recording medium, the recording layer (heat responsive layer) is not melted as described above, but since the heat responsive layer is surrounded by the heat insensitive layer, it is Atoms are less likely to move, and as a result, there is no fear that the C / N ratio will decrease even if rewriting is repeated many times.

At this time, the heat insensitive layer is preferably made of a refractory metal or ceramics whose characteristics do not change due to the heat of laser light (recording light) irradiation. Particularly, when the heat-insensitive layer is optically transparent, unnecessary light absorption by the heat-insensitive layer does not occur, which is advantageous because the amount of reproduction light is large. Further, refractory metal is more advantageous because it tends to form islands during sputtering.

[0021]

【Example】

<Embodiment 1> As shown in FIG. 1, a magnetron using an argon gas was formed on a disc-shaped polycarbonate substrate 1 on the surface of which grooves for tracking and pits (not shown) for indicating addresses were formed during injection molding. First, the lower protective layer 2 having a thickness of about 120 n is formed by sputtering.
m (ZnS) ₈₀ (SiO ₂ ) ₂₀ film was formed. On top of that, a phase change type thermal response layer 31 made of Ge-Sb-Te having a thickness of about 1 nm and a heat insensitive layer 32 made of (ZnS) ₈₀ (SiO ₂ ) ₂₀ having a thickness of about 2 nm are alternately provided. By stacking 20 times, a recording layer 3 having a total film thickness of about 60 nm was formed. The heat responsive layer 31 is in a substantially amorphous state, and a single layer has an average diameter of about 1
It has an island shape of 5 nm.

After that, as shown in FIG. 1, a (ZnS) ₈₀ (SiO ₂ ) ₂₀ film having a thickness of about 210 nm, which is the upper protective layer 4, is further formed by magnetron sputtering, and then a metal reflective layer 5 is formed. Al ₉₆ C of about 100 nm
A u ₄ film was formed. Next, the ultraviolet curable resin 6 was applied and irradiated with ultraviolet rays to be cured. Finally, another disk prepared in the same manner was pasted with a hot-melt adhesive with the UV-curable resin side inside. Good characteristics are obtained when the Cu content of the Al ₉₆ Cu ₄ film is in the range of 1 to 45 atom%. When the cross section of this recording medium is observed by a transmission electron microscope, this heat responsive layer is in a substantially amorphous state and has an island shape with an average diameter of about 15 nm. Therefore, as shown in FIG. 5, it was found that the heat responsive layer 31 had a structure surrounded by the heat insensitive layer 32. Therefore, it has been found that an effect of preventing the melted thermoresponsive layer 31 from flowing can be expected.

Recording / reproduction of information on the disk thus formed was performed as follows. One disc
The semiconductor laser (wavelength 780n is rotated at 800 rpm.
The light of m) was kept at a level (1 mW) at which recording was not performed, was condensed by the lens in the recording head, and was irradiated to one recording layer 3 through the substrate. By detecting the reflected light, automatic focusing was performed so that the focus was on the recording layer 3, and tracking was performed so that the center of the light spot was always aligned with the center of the tracking groove.

Next, the laser power is changed to 6 m for crystallization.
Recording was performed by changing between W and 15 mW at which a change into a state close to an amorphous state occurs according to an information signal to be recorded. As the recording signal, a signal having a constant frequency or a digital data signal is used here. It is considered that the recorded portion is near the amorphous state as the recording point. In such a recording method, the recorded information is rewritten to the newly recorded information even if the already recorded portion is performed. Of course, after erasing by irradiation with constant power, recording may be performed by irradiation with power modulation.

The reading was performed as follows. Rotate the disc at 1800 rpm and perform 1mW while tracking and auto-focusing the same as during recording.
The intensity of the reflected light was detected with the laser light of, and a reproduction signal was obtained.
This reproduced signal was put into a spectrum analyzer, and the ratio between the recorded constant frequency information signal (carrier wave) and noise was determined.

A conventional disc (FIG. 8) in which the recording layer 13 has a film thickness of 30 nm and a disc of this embodiment (FIG. 1) are prepared.
Overwrite many times (record rewriting by overwriting)
The increase in the reproduced signal noise at that time was as shown in Table 1.

[0027]

[Table 1]

The recording layer 3 comprises a heat responsive layer 31 and a heat insensitive layer 32.
It can be seen that the characteristics of rewriting many times were significantly improved by forming the layers by the alternate stacking.

Results of evaluation of the recording medium having the recording layer 3 formed by changing the diameter of the island region of the heat responsive layer 31 by changing the forming condition of the heat responsive layer 31. A range in which the average diameter of the island-shaped region is 2 nm or more and 100 nm or less, and the distance between the island-shaped regions and the island-shaped regions (the average value of the distance between the centers of two adjacent island-shaped regions, the same applies hereinafter) is 4 nm or more and 200 nm or less. However, the bit error rate after rewriting a million times was less than 1 per 10 ⁵ bits. Moreover, the average diameter of the island region is 3n.
In the range of m or more and 50 nm or less and the average value of the interval between island-like regions of 5 nm or more and 100 nm or less, the bit error rate after rewriting 1 million times was 1 or less per 2 × 10 ⁵ bits. The erasing ratio upon overwriting (reduction rate of the signal level of the previously written signal) was also improved from 30 dB in the conventional disk to 33 dB or more in this embodiment.

The heat-responsive layer 31 has a thickness of 8 nm per layer and is a layered film having a substantially layered structure rather than an island-shaped structure.
Even if the thickness of 2 was set to 16 nm and the alternating lamination was performed 3 times, there was almost no change in the noise level after rewriting 1 million times. This is because when the film thickness is small, the heat insensitive layer 3 is a continuous film.
This is because it is difficult to flow near the interface with 2 and it is difficult to flow as a whole.

Further, the (ZnS) ₈₀ (Si
Some or all of O ₂ ) ₂₀ is ZnS, CdS, In ₂ S ₃ , Z
nSe, CdSe, In ₂ Se ₃ , SiO ₂ , SiO, TiO
₂ , ZrO ₂ , Ta ₂ O ₅ , Y ₂ O ₃ , Si ₃ N ₄ , AlN, C
u ₂ O, AlSiN ₂ , Al ₂ SiN ₃ , AlSi ₂ N ₃ , S
Similar results can be obtained by substituting a material having a composition close to at least one selected from the group consisting of i-Al-O-N and SiC as a main component. Of these, A
l ₂ O ₃ and Al-Si-N-based material is particularly preferred.

The thermal conductivity of the thin film containing oxide or sulfide as the main component of the lower protective layer 2 in this embodiment is 1 W / m · K.
It is preferably 60 W / m · K or less.

The product of the refractive index and the average film thickness (refractive index 5.1 of the portion where the recording film exists) of the recording layer 3 in a state close to amorphous is 100 nm or more and 600 nm or less, and the upper protective layer. The carrier-to-noise ratio of the reproduced signal was 46 dB or more in the range where the product of the refractive index and the film thickness of No. 4 was 50 nm or more and 600 nm or less. The thickness of the upper protective layer 4 is 150 nm or more and 300 n
The C / N ratio was 48 dB or more in the range of m or less. The materials that can be used for the lower protective layer can also be used for the upper protective layer. The product of the refractive index and the average film thickness of the crystalline portion of the recording layer 3 may be within the above range. When the upper protective layer was not formed, the recording sensitivity was reduced by about 50%, but there was no significant change in other characteristics and it was usable. Further, even when at least one of the lower protective layer and the reflective layer is not formed, the number of rewritable times was reduced by about one digit, but it was usable.

As shown in FIG. 6, a guide groove is formed on the surface of the ultraviolet curable resin layer 8 formed on the glass substrate 7, and a recording layer similar to the disc of FIG. A similar effect was obtained even if the metal reflective layer was composed of an Al-Cu film) and was used without being bonded to another disk. In this case, it is preferable to further form the organic protective film 9 on the uppermost part. However, in these cases, the laser light was made incident from the side opposite to the substrate.

Example 2 A disk was formed in the same manner as in Example 1, except that a Tb-Fe-Co magneto-optical recording film having a film thickness of about 1.5 nm was used as the heat responsive layer 31, and the heat insensitive layer was used. 32
For this, a Pt film with a thickness of about 1.5 nm was used. As shown in FIG. 7, a 60 nm SiN film is formed as the lower protective layer 2 on the polycarbonate substrate 1, and the T of the heat responsive layer 31 is formed thereon.
The total thickness of the recording film 3 is 30 nm by alternately laminating the b-Fe-Co magneto-optical recording film 3 nm and the Pt film 3 nm of the heat insensitive layer 32.
It was formed by a sputtering method using argon gas. Next, a 20 nm SiN film was laminated as the upper protective layer 4, and a 50 nm AlTi alloy was laminated as the metal reflective layer 5.

In this embodiment, a magnetic field coil placed between the magneto-optical head and the disk on the opposite side of the magneto-optical head is used to modulate the laser power between 1 mW and 8 mW in accordance with the information signal for recording. Recording was performed by a pit edge method in which 1s of digital information corresponded to both ends of a point.
The reading was performed by utilizing the rotation of the polarization plane due to the Kerr effect. In this disc, since heat conduction in the lateral direction can be prevented, there are effects such as improvement of recording sensitivity, prevention of erasure of adjacent tracks, and improvement of shape of recording point. Further, since the structural relaxation of the amorphous state due to heat is suppressed, the C / N after rewriting 10 million times did not change from that before rewriting.

In this embodiment, the heat responsive layer 31 includes Gd-Tb-Fe-Co and Gd-Dy- in addition to those of this embodiment.
Fe-Co, Tb-Dy-Fe-Co, Nd-Dy-F
The same effect can be obtained by using e-Co or Nd-Tb-Fe-Co. Of these, the former two are characterized by a relatively large car rotation angle and a large reproduction output. The last two have excellent reproduction characteristics in the short wavelength region.
Regarding the perpendicular magnetic anisotropy, Tb-Fe-Co of this example is the most excellent. Further, in order to improve the corrosion resistance, elements such as Nb, Ti, Al, Cr, Ni and V may be added to the above composition in the range of 10 atomic% or less.

As the heat insensitive layer 32, a nitride film or an oxide film in which oxygen or nitrogen is mixed in the same composition as the heat responsive layer 31 may be used instead of Pt in this embodiment. These are produced by mixing nitrogen gas or oxygen gas in the sputtering gas. In this case, since the thermal conductivity is smaller than that of Pt, it is particularly excellent in improving the sensitivity and suppressing the spread of heat to the adjacent tracks. In addition, ZnS, Cd
S, In ₂ S ₃ , ZnSe, CdSe, In ₂ Se ₃ , Si
O ₂ , SiO, TiO ₂ , ZrO ₂ , Ta ₂ O ₅ , Y ₂ O ₃ ,
Si ₃ N ₄ , AlN, Cu ₂ O, AlSiN ₂ , Al ₂ SiN
Similar results can be obtained by substituting a material having a composition close to at least one selected from the group consisting of ₃ , AlSi ₂ N ₃ , Si-Al-O-N, and SiC as the main component.
Since these are optically transparent, they have excellent reproduction characteristics. Of these, Si ₃ N ₄ and AlN-based materials are particularly preferable. The Pt of this embodiment has the effect of improving the reproduction characteristics in the short wavelength region by exchange coupling with the magnetic layer. Further, this Pt may be replaced with a refractory metal such as Ti or V.

Since these heat-insensitive layers have an antioxidant effect, the upper protective layer 4 and the lower protective layer 3 can be omitted.

The heat responsive layer 31 and the heat insensitive layer 32 are also provided.
The same effect can be obtained even if the composition modulation film is formed by mixing two layers in the vicinity of the interface with and. In this case, the method for laminating the recording layer is such that when the substrate is manufactured by using a rotary sputtering apparatus while moving the substrate away from or near the target, the recording layer has a portion close to the target composition and a portion mixed with a large amount of residual gas such as nitrogen. It will be laminated alternately.

The method of the present invention can also be applied to a magneto-optical overwrite film or a super-resolution reproducing film having two or more recording layers.
In this case, the effect can be obtained by applying the method of the present invention to at least one of the two recording layers, which requires the most thermal stability, to form an alternating laminated film of a heat responsive layer and a heat insensitive layer. .. Of course, the method of the present invention may be applied to all layers.

Although the disk-shaped information recording member has been described in the above embodiments, the present invention can be applied to other-shaped information recording members such as a tape and a card.

[0043]

The present invention has an effect of significantly improving the number of rewritable times because the flow of the recording layer can be almost completely prevented for the phase change optical disk. In addition, since the size of the crystal grain is limited, it is possible to reduce the remaining unerased due to the difference in the size of the crystal grain in each part. Furthermore, since crystallization occurs at least partially when unevenness is formed on the surface of the recording layer, there is an effect that the initial crystallization of the recording layer, which is conventionally required after the disc is manufactured, is not necessary or is simplified. There is. Further, for a magneto-optical disk, since the structural relaxation of the recording layer in the amorphous state is suppressed, it has an effect of significantly improving the number of rewritable times. Further, since in-plane heat conduction is prevented, there is an effect that the fidelity of the reproduced signal is improved and the recording sensitivity is improved. In addition, the corrosion resistance of the recording layer is improved.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a laminated structure of a recording medium according to an embodiment of the present invention.

FIG. 2 is a sectional view showing an example of a laminated structure of a conventional optical recording medium.

FIG. 3 is a characteristic diagram of a conventional optical recording medium.

FIG. 4 is a perspective view showing the manufacturing principle of the optical recording medium of the present invention.

FIG. 5 is a perspective view showing the manufacturing principle of the optical recording medium of the present invention.

FIG. 6 is a sectional view showing a laminated structure of a recording medium according to another embodiment of the invention.

FIG. 7 is a sectional view showing a laminated structure of a recording medium according to another embodiment of the present invention.

FIG. 8 is a sectional view showing an example of a laminated structure of a conventional optical recording medium.

[Explanation of symbols]

1 ... Substrate, 2 ... Lower protective layer, 3 ... Recording layer, 31 ... Thermally responsive layer, 32 ... Heat insensitive layer, 4 ... Upper protective layer, 5 ... Metal reflective layer, 6 ... UV curable resin layer.

Front page continuation (72) Motoyasu Terao, 1-280 Higashi Koigokubo, Kokubunji, Tokyo, Central Research Laboratory, Hitachi, Ltd. (72) Masahiro Ojima, 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi Central Research Laboratory, Ltd.

Claims (13)

[Claims] 1. An optical recording medium for recording information by raising the temperature of a recording medium by irradiation of light and utilizing the resulting change in the physical state of the recording layer on the recording medium, wherein the recording layer comprises: An optical recording medium, wherein at least two layers of a heat responsive layer made of a material whose physical state changes and a heat insensitive layer made of a material whose physical state does not change are alternately laminated. 2. The optical recording medium according to claim 1, wherein the thickness of the heat-responsive layer 1 layer is 0.5 nm or more and 3 nm or less. 3. The optical recording medium according to claim 1, wherein the thickness of the heat-insensitive layer is 0.5 nm or more and 100 nm or less. 4. The optical recording medium according to claim 1, wherein the change in the physical state of the recording layer is reversible. 5. The optical recording medium according to claim 1, 2, 3 or 4, wherein the total film thickness of the recording layer is 10 nm or more and 200 nm or more. 6. The method according to claim 1, 2, 3, 4 or 5.
An optical recording medium, wherein the heat-insensitive layer is made of an optically transparent material. 7. The optical recording medium according to claim 1, 2, 3, 4, 5 or 6, wherein the change in the physical state of the recording layer is a phase change between an amorphous state and a crystalline state. 8. The optical recording medium according to claim 1, 2, 3, 4, 5 or 6, wherein the change in the physical state of the recording layer is a change in the direction or magnitude of the magnetization of the recording layer. 9. The optical recording medium according to claim 7, wherein the phase change is a change between an amorphous state and a crystalline state. 10. The optical recording medium according to claim 8, wherein the recording layer is a magneto-optical recording material. 11. The optical recording medium according to claim 1, wherein the heat insensitive layer is an oxide, a nitride, a sulfide or a mixture thereof. 12. The optical recording medium according to claim 1, wherein the heat insensitive layer is a refractory metal. 13. An optical recording medium according to claim 1, wherein a protective layer is provided on the lower part, the upper part or both of the recording layer.