JP2000285510A - Phase transition type recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain good overwrite jitter by constituting the medium of a substrate, two or more layers of recording layers formed on the substrate which transit between a crystalline state and a noncrystalline state by irradiation of light, a multilayer interference layer formed on the entrance side for light of at least one of the recording layers, and a dielectric layer having high thermal conductivity formed on the opposite side of at least one recording layer to the entrance side for light. SOLUTION: The light beam entering a first substrate 1 is condensed to a first recording layer 3 to record, erase or reproduce information. A second recording layer 7 is formed at an enough distance from the first recording layer 3 so that the light is not condensed on the second recording layer 7 but the energy of the light beam is absorbed only by the first recording layer 3. Similarly, when the light is condensed on the second recording layer 7, recording, erasing or reproducing is performed only in the second recording layer 7. By forming the multilayered interference layer, changes in the reflectance between crystalline and noncrystalline phases due to the interference effect are increased, and the absorptivity ratio of crystalline/noncrystalline phases can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a phase change recording medium for recording and reproducing information by irradiating a laser beam.

[0002]

2. Description of the Related Art Optical disks have supported the rise of personal computers these days as large-capacity storage media having high capacity, high-speed access, and medium portability.

[0003] Above all, optical disks using phase-change optical recording have recently begun to be put to practical use, taking advantage of the simple recording principle. The principle of recording / reproducing is that the recording layer on the substrate is irradiated with a semiconductor laser to change the recording portion to amorphous. The reversibility changes from crystalline to crystalline, and at the time of reproduction, the change in the reflectance of the recorded portion is read as recorded information. That is, at the time of recording, a relatively high-output short-pulse laser beam is applied to the phase-change optical recording material to heat the recording portion to a temperature equal to or higher than the melting point, and then rapidly cooled to form an amorphous recording mark. At the time of erasing, the phase-change recording material is irradiated with a laser beam having a lower output and a longer pulse than at the time of recording, so that the material is maintained at a temperature higher than the crystallization temperature and lower than the melting point to crystallize.

As described above, in the phase change optical recording, since the change in the reflectance between amorphous and crystalline is read, the structure of the optical system is simple. Also, unlike a magneto-optical recording, it does not require a magnetic field, has an advantage that overwriting by light intensity modulation is easy, and a data transfer speed is high. Furthermore, CD-ROM
It is also excellent in compatibility with read-only discs such as.

[0005] In order to improve the recording density of a phase change optical disk, it has been considered to shorten the interval between recording marks, reduce the size of recording marks, and shorten the wavelength of a light source. Among them, land / groove (L / G) recording, mark length recording, and the like have been proposed to shorten the recording mark interval. L / G recording is expected to achieve approximately twice the density of the conventional method. The mark length recording method detects a change in the reflectance at the recording mark edge portion (a differential component of the reflectance), and can be expected to have about 1.5 times higher density than the conventional mark position recording. In addition to such a high-density recording technology, if a super-resolution technology proposed for a ROM medium or the like is used, the recording density of about 650 Mbps (bit / inch ² ) can be improved 10 to 20 times at present. It is expected that it is possible.

It is also considered that shortening the wavelength of the light source is effective for increasing the density. When squeezing a laser light source using an optical lens, the minimum spot depends on the wavelength of the light source, and the shorter the wavelength, the smaller the light spot can be. Therefore, the recording density increases in inverse proportion to the wavelength of the light source. be able to.

As described above, the phase change optical disk has the potential for high density, but there are still many problems to be solved in order to enable overwriting tens of thousands of times. While the above-described L / G recording is an indispensable technique for increasing the track density, problems such as cross-erase and crosstalk become more pronounced as the track spacing becomes narrower. Both problems are caused by the fact that the beam diameter (diameter of beam intensity e- ² : 0.92 μm) is larger than the track width. Cross erase is a phenomenon in which a light beam erases a part of a recording mark of an adjacent track while recording a target track, and is a serious problem that information to be stored is destroyed. In addition, crosstalk is a phenomenon in which a light beam reads information of an adjacent track while a target track is being reproduced, and causes a reproduction error. All of these phenomena are caused by the increase in track density, and must be solved in order to improve the recording density of the optical disk.

Meanwhile, in order to improve the storage capacity of a phase change optical disk, a technique of providing two recording layers has recently been proposed.
The technique described in ptical Memory 1998, pp. 144-145 (October, 1998) will be described. This disk, ZnS-SiO ₂ / GeSbTe7nm on the first substrate using a polycarbonate (PC)
/ Zn-SiO ₂ are sequentially laminated, and Al-Cr / ZnS-SiO ₂ / GeSbTe 10 nm / ZnS-SiO ₂ / Au 10 nm are sequentially laminated on the second substrate using PC. It has a structure in which the surfaces that have been bonded are bonded with a UV curable resin. On one disc
Since there are two GeSbTe recording layers, the storage capacity is dramatically improved as compared with the case where the number of recording layers is one.

However, in this disc, the jitter after 10 overwrites is at most less than 12%, and is far from a practical disc. The reason why good overwrite jitter cannot be obtained with this disc can be presumed to be due to the influence of cross erase.

[0010]

As described above, the phase change optical disk has a simple optical system structure and does not require a magnetic field unlike magneto-optical recording, so that overwriting is easy and the data transfer speed is high. It has the advantage of being fast, and has excellent compatibility with read-only discs such as CD-ROMs.However, as the track spacing becomes narrower, problems such as crosstalk and cross-erase become noticeable. Therefore, there is a problem that it is an obstacle in improving the areal recording density.

Although a technique of providing two recording layers in order to improve the storage capacity of a phase change optical disk has been proposed, there is a problem that even this disk cannot obtain good overwrite jitter due to the influence of cross erase. Was.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to provide a phase change recording medium capable of obtaining good overwrite jitter.

[0013]

(Means) In order to achieve the above object, the present invention provides, as a first aspect, a substrate,
Two or more recording layers formed on the substrate and transitioning between a crystalline state and an amorphous state by light irradiation, a multilayer interference layer formed on at least one light incident side of the recording layers, A phase change recording medium, comprising: a high thermal conductivity dielectric layer formed on at least one of the recording layers on the side opposite to the light incident side.

According to a second aspect of the present invention, there is provided a substrate, a first recording layer formed on the substrate and transitioning between a crystalline state and an amorphous state by light irradiation, and formed on the first recording layer. A high thermal conductivity dielectric layer, a separation layer formed on the high thermal conductivity dielectric layer, a multi-layer interference layer formed on the separation layer, and a multi-layer interference layer formed on the multi-layer interference layer and irradiated with light. A phase change recording medium comprising: a second recording layer that transitions between a crystalline state and an amorphous state.

First, preferred embodiments of the multilayer interference layer are listed below.

(1) The second recording layer is formed at the light incident side interface.

(2) It is composed of two or more dielectric layers.

(3) The extinction coefficient k of each dielectric layer is 0.5 or less with respect to the wavelength of the light source.

(4) The total average film thickness is 300 nm or less.

Next, preferred embodiments of the high thermal conductivity dielectric layer will be described below.

(1) The first recording layer is formed at the interface opposite to the light incident side.

(2) The thermal conductivity is at least 10 times the thermal conductivity of the multilayer interference layer.

(3) The average film thickness is in the range of 10 to 500 nm. (Operation) In the present invention, a multilayer interference layer is disposed on the light incident side of the recording layer, and a high thermal conductivity dielectric layer is provided on the opposite side of the recording layer from the light incident side.

By providing a multilayer interference layer, the change in reflectance between crystal and amorphous due to the interference effect is increased. Further, it becomes easy to design the absorption ratio Ac / Aa of crystal / amorphous to 1.0 or more. By increasing Ac / Aa to 1 or more, preferably about 1.4 or more, it is possible to suppress the heat absorption of the amorphous recording marks in the adjacent tracks from the laser beam, thereby reducing the cross erase. can do. Further, when Ac / Aa> 1, the film temperature at the time of melting can be equalized between the crystal part and the amorphous part in consideration of the latent heat of fusion, so that the overwrite jitter can be reduced.

Further, by providing the high thermal conductivity dielectric layer, the heat absorbed in the recording layer can be released through the high thermal conductivity dielectric layer. Thermal diffusion is suppressed, which also reduces cross erase and consequently reduces overwrite jitter. Further, since heat can be released, intersymbol interference is reduced.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail. In the following description, a phase change optical disk as a phase change recording medium will be described.

The phase change optical disk according to the present invention has two or more recording layers on a substrate, and a multilayer interference layer is arranged on the light incident side of the interface of the recording layer. On the opposite side, a high thermal conductivity dielectric layer is provided. Each recording layer needs to be stacked at intervals equal to or more than the focal depth of light irradiation, and is preferably separated by 10 μm or more.

The optical disk of the present invention has, for example, a phase-change recording layer, a protective layer, a separation layer for separating the recording layer, and a reflection layer laminated on a substrate. The protective layer plays a role as an interference film for adjusting the optical characteristics of the medium as well as mechanically and chemically protecting the recording layer. The separation layer is 2
When recording / erasing / reproducing independently on the recording layers above
It is necessary to focus the light beam on each recording layer independently. The reflecting layer reflects the irradiated light beam to efficiently use light energy.

The substrate used in the present invention is typically polycarbonate (PC), but may also include polymethyl methacrylate (PMMA) and amorphous polyolefin.
(PO) can also be used.

As the material constituting the recording layer in the present invention, a material which reversibly transitions between a crystalline state and an amorphous state by light irradiation and has different optical characteristics between the two states is used. For example, Ge-Sb-Te, In-Sb-Te, Sn-Se-Te, Ge-Te-S
n, In-Se-Tl and the like. In addition, Co, P
Even if at least one or more of t, Pd, Au, Ag, Ir, Nb, Ta, V, W, Ti, Cr, Zr, etc. are added in trace amounts, good characteristics as a recording layer can be obtained. Further, a trace amount of a reducing gas such as nitrogen may be added. The material most typically used for the phase change type recording layer is Ge-Sb-Te.

Average thickness of the first recording layer closest to the light incident side
t ₁ is preferably 5 nm or more and 20 nm or less in order to secure the minimum necessary light absorption and the amount of light transmission to the second recording layer and thereafter. The average thickness t _n of the second recording layer after in order to maintain the same effect, it is preferable to satisfy the relation of t _n ≧ t _n-1.

As the protective layer in the present invention, for example, Zn
_{S, ZnO, SiO 2, SiO} , Al 2 O 3, Cu 2 O, CuO, TaO, Y 2 O 3, Zr
O ₂ , CaF ₂ , MgF ₂ , Si ₃ N ₄ and composites thereof can be used. The average thickness of the protective layer is preferably in the range of 20 to 200 nm for the purpose of ensuring the absorption rate of the recording layer and maximizing the contrast as an optical disk.

As the separation layer in the present invention, a light beam
Extinction, considering minimizing energy loss
Use a transparent material whose coefficient k is 0.1 or less with respect to the light source wavelength
Is desirable. For example, such a material
For example, resin materials such as ultraviolet (UV) curable resin, PMMA, PC, etc.
Or SiO_Two, Al_TwoO_Three, TaO, V_TwoO_Five, CaO, ZrO_Two, Pb
_TwoO _Three, SnO_Two, CoO, CuO, Cu_TwoO, AgO, ZnO, Fe_TwoO_ThreeOxidation of etc.
Things and Si_ThreeN_Four, SiON, nitride such as SiAlON, MgF_Two, CaF_TwoEtc.
Fluoride is suitable. The recording layer is above the depth of focus of the light beam
The average thickness of the separation layer must be 10μm or more to separate
Becomes Therefore, an advantageous coating in producing such a thick film
A mold resin material is more preferred. These materials can be used as needed.
Can be used as a mixture or
Wear. On the other hand, if the thickness is too thick, the transmission amount and the recording layer
50 μm or less due to undesirable depth of focus
Is preferred.

As the reflection layer in the present invention, for example, Al
Ti, TiN, Au, AlMo, AlCu, Ag, Cu, Pt, Pd, Ir and the like can be used. The average thickness of the reflective layer is preferably in the range of 20 to 200 nm from the viewpoint of securing the reflectivity and cooling rate.

In the optical disk of the present invention, in addition to the recording layer, the protective layer, the separation layer for separating the recording layer, and the reflection layer, one or more interference layers are arranged on the light incident side of each recording layer interface. . At this time, two or more multilayer interference layers are provided on the light incident side of at least one interface of the first and second recording layers. In particular, when the first recording layer has a so-called H-to-L polarity in which the reflectance of an unrecorded crystal part is high and the reflectance of an amorphous recording part is low, the second and subsequent recording layers are H to L
It is necessary to have a polarity of L to H, which is the opposite polarity to that of the second recording layer, because it is effective to provide a multilayer interference layer on the light incident side after the second recording layer. It is preferable to provide a multilayer interference layer at the light incident side interface.
The reason why the first recording layer has the polarity of H to L is that focus control cannot be performed unless the reflectance of the unrecorded portion is at least 5% or more.

The interference layer is composed of one or more dielectric layers. In order for the recording layer to efficiently absorb light, the extinction coefficient k of each dielectric layer is preferably 0.5 or less. The dielectric layer is ZnS, ZnO, SiO ₂ , SiO, Al ₂ O ₃ , Cu ₂ O, CuO, TaO, Y _{2
O 3, ZrO 2, CaF 2} , MgF 2, Si 3 N 4 and the like of these composites are preferred for reasons such as an internal stress of the thin film can be finely adjusted.

Here, in order to configure a multilayer interference layer using two or more dielectric layers, and to maximize the difference in reflectance between a recorded portion and an unrecorded portion, that is, the optical contrast as a disc, each dielectric layer must be It is desirable that the refractive index n of the layer is 1.5 or less and 1.7 or more. Since the refractive index of the thin film is significantly different depending on the film forming method, the above-mentioned constraint is an actual measured value of the thin film measured by ellipsometry or the like.

Although the thickness of each layer of the interference layer may be infinitely varied depending on the optical design, in order to secure the amount of light transmitted to the recording layer, the total average thickness of the interference layer is one layer, two layers or more. In any case, it is desirable that the thickness be 300 nm or less.

In the case of a multilayer interference layer, the polarity of L to H and the polarity of H to
The polarity of L can be arbitrarily designed. Furthermore, it is desirable that these dielectric layers have a large surface energy in order to promote the two-dimensional growth of the recording layer directly laminated thereon. Although the surface energy of a solid substance is specific to the substance, in the case of a thin film, it depends largely on the film formation conditions. Therefore, it is preferable to select a condition that appropriately increases the surface energy.

Each layer constituting the multilayer interference layer preferably has a different dielectric constant from an adjacent layer in the multilayer interference layer. If adjacent layers have different dielectric constants, a semiconductor layer, a metal layer, or the like can be used in addition to the dielectric layer. Since the dielectric constant is a physical quantity containing the refractive index n and the extinction coefficient k, the refractive index n
Only the extinction coefficient k, the refractive index n
And the extinction coefficient k may be different.

When Ge—Sb—Te is used for the recording layer, ZnS—SiO ₂ having a relatively large refractive index n is generally used for the interference layer. Therefore, the multilayer interference layer is composed of three layers, the first layer,
The third layer is preferably used ZnS-SiO _2. In this case, it is preferable to use a material in which n is smaller than ZnS—SiO ₂ for the second layer sandwiched between the first layer and the third layer, in consideration of a range of material selection, a margin of optical design, and the like. In the second layer
With SiO _2, and most preferred for mixing of the material is reduced at the interface between the ZnS-SiO _2.

As the difference between n of the first, third and second layers increases, the optical contrast of the medium increases. Also, a material that gives an excessive internal stress to the recording layer should be avoided. For example, when the amount of SiO2 in ZnS-SiO2 is increased, the hardness is increased, so that deformation of the recording layer due to overwriting cannot be tolerated, which is not preferable.

By providing such a multilayer interference layer, the change in reflectance between crystal and amorphous due to the interference effect increases. Further, it becomes easy to design the absorption ratio Ac / Aa of crystal / amorphous to 1.0 or more. By increasing Ac / Aa to 1 or more, preferably about 1.4 or more, it is possible to suppress the heat absorption of the amorphous recording marks in the adjacent tracks from the laser beam, thereby reducing the cross erase. can do. Further, when Ac / Aa> 1, the film temperature at the time of melting can be equalized between the crystal part and the amorphous part in consideration of the latent heat of fusion, so that the overwrite jitter can be reduced. In addition, since the recording layer having a large surface energy promotes the two-dimensional growth of the recording layer formed thereon, a recording layer having excellent two-dimensional continuity and high repetitive recording performance can be formed.

The optical disk of the present invention has a high thermal conductivity dielectric layer on the recording layer interface on the side opposite to the light incident side, in addition to the above-described multilayer interference layer. In particular, when the reflective layer is not provided on the first recording layer, the heat absorbed by the first recording layer is suddenly released, so that a high thermal conductivity dielectric is provided at the interface opposite to the light incident side of the first recording layer. It is preferred to provide a layer.

As the high thermal conductivity dielectric layer, AlN, TiN, Ge
N, HfN, ZrN, TaN, VN, Si 3 N 4, BN, Al 2 O 3, CaO, MgO,
NiO, TiO, C, HfC, NbC, TaC, TiC, ZrC, and their composites are preferable from the viewpoint that a high thermal conductivity can be obtained.

The high thermal conductivity dielectric layer may be composed of two or more layers.

The thermal conductivity of the high thermal conductivity dielectric layer is relatively higher than that of the multilayer interference layer, and the ratio is preferably 10 or more in order to suppress in-plane thermal diffusion in the recording layer. . More specifically, the thermal conductivity is preferably 20 W / m / K or more. However, considering heat absorption to the recording layer, 10
It is preferably 0 W / m / K or less.

The average thickness of the high thermal conductivity dielectric layer is preferably 10 nm or more and 500 nm or less. At least 10 nm is required to function as a heat radiation layer, and it is required to be 500 nm or less to ensure the amount of light transmitted to the recording layer.

By providing a high thermal conductivity dielectric layer,
Since the heat absorbed by the recording layer can be released through the high thermal conductivity dielectric layer, the heat diffusion to the amorphous recording mark of the adjacent track is suppressed, and thus the cross erase is reduced, As a result, overwrite jitter is reduced. Further, since heat can be released, intersymbol interference is reduced.

FIG. 1 shows an example of the layer structure of the optical disk according to the present invention, and a recording / reproducing method will be described. FIG.
1 is a schematic sectional view of an optical disc according to one embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes a first substrate using a PC. On the first substrate 1, a dielectric layer 2 as an interference layer, a first recording layer 3, a high thermal conductivity dielectric layer 4, a separation layer 5, dielectric layers 6-1, 6-2, 6-3 as multilayer interference layers, second recording layer 7, dielectric layer
8, a reflective layer 9, and a second substrate 10 using a PC are sequentially laminated. The dielectric layer 2 may be a multilayer interference layer, and the dielectric layer 8 may be a high thermal conductivity dielectric layer.

The light beam incident from the first substrate 1 side is the first
The light is focused on the recording layer 3 to perform recording, erasing, and reproduction. At this time,
Since the first recording layer 3 and the second recording layer 7 have a sufficient space, they are not converged on the second recording layer 7 and the energy of the light beam is absorbed only by the first recording layer 3. When light is focused on the second recording layer 7, recording, erasing, and reproduction are performed only on the second recording layer 7 for the same reason.

At the time of recording, the recording layer is irradiated with a relatively high-power, short-pulse laser beam to heat the recording portion to a temperature equal to or higher than the melting point, and then rapidly cooled to form an amorphous recording mark. At the time of erasing, the phase-change recording material is irradiated with a laser beam having a lower output and a longer pulse than at the time of recording, so that the material is maintained at a temperature higher than the crystallization temperature and lower than the melting point to crystallize. At the time of reproduction, reproduction is performed by irradiating a laser beam with a lower output than irradiation at the time of erasing.

Each layer of the phase change optical disk shown in the present invention can be formed by a general physical vapor deposition method. It can be formed by any film forming method such as RF / DC sputtering, electron beam evaporation, resistance heating evaporation, molecular beam epitaxy (MBE), etc. In controlling the thermal conductivity and the optical constants of the dielectric layers located above and below the recording layer, a certain degree of control can be performed even in the film forming process. For example, when a nitride layer is formed by RF sputtering, films having different thermal conductivity and optical constant can be obtained by appropriately changing RF output, sputtering gas pressure, nitrogen addition amount, and the like. After film formation,
When the surface morphology is modified by bias sputtering the surface of each layer, the thermal conductivity can be changed to some extent.

The optical disk having two recording layers according to the present invention can be manufactured, for example, by the following procedure. An interference layer, a first recording layer, and a high thermal conductivity dielectric layer are formed in this order on a resin substrate having an L / G shape by any of the methods described above. A reflective layer, a dielectric layer, a second recording layer, and a multilayer interference layer are formed in this order on a resin substrate also having a land / groove shape. A UV curable resin is applied as an adhesive layer on the former high thermal conductivity dielectric layer, and the latter is adhered to the multilayer interference layer side.

Although the embodiment of the present invention has been described with reference to a phase change optical disk as an example, the present invention is not limited to a phase change optical disk, and various types of optical recording cards, optical recording tapes and the like can be used. Applicable to a change recording medium.

Finally, a recording / reproducing apparatus using an optical disk as in the present invention will be described.

A laser beam is irradiated from the first recording layer side, and this laser beam is focused on one of the recording layers by an optical system, and recording / reproducing is performed only on the focused layer.
Data recording is performed by modulating the laser beam intensity by the operation of the recording system, and data reproduction is performed by extracting from the reflected light of the optical disk by the operation of the reproduction system. In addition, the apparatus is also provided with a servo system. The servo system performs the rotation control of the motor for rotating the disk and the position control of the optical system, thereby selecting the recording layer and the track and performing the following operation. A controller is also provided to manage all of these device operations.

[0059]

Embodiments of the present invention will be described below. (Embodiment 1) FIG. 2A is a schematic sectional view of a phase change optical disc according to Embodiment 1 of the present invention. Hereinafter, this disc will be described along the manufacturing process. First, using a PC with a thickness of 0.575 mm in a film forming apparatus evacuated to 5 × 10 ^-4 (Pa) or less.
RF power 1 kW to ZnS (80) -SiO ₂ (20) target on substrate 11
Was applied to form a dielectric layer 12 as an interference layer having an average thickness of 90 nm using ZnS-SiO ₂ , and subsequently applying a RF power of 50 W to a Ge ₂₅ Sb ₂₃ Te ₅₂ target to apply Ge ₂₅ Sb ₂₃ Te. the first recording layer 13 having an average thickness of 10nm using _52, AlN target RF power 400W
Was applied in a (Ar + 10% N ₂ ) gas atmosphere, and a high thermal conductive dielectric layer 14 having an average film thickness of 40 nm using AlN was sequentially formed.
On the other hand, a DC power of 1 kW was applied to an AlTi target on a second substrate 22 using a PC having a thickness of 0.6 mm and a reflective layer 21 having an average film thickness of 100 nm using AlTi.
Apply 30W in a (Ar + 10% N ₂ ) gas atmosphere by applying 00W and form TaN
A high thermal conductive dielectric layer 20 having an average film thickness of 30 nm is sequentially formed by using GaN, and subsequently, RF power of 50 W is applied to a Ge ₂ Sb ₂ Te ₅ target to form a film, and an average film using Ge ₂ Sb ₂ Te ₅ is formed. A second recording layer 18 having a thickness of 20 nm was formed. _{Then, ZnS (80) -SiO 2 (} 20) Average thickness 70nm that by applying RF power 1kW using ZnS-SiO ₂ in the target
Apply 800 W RF power to the dielectric layer 18 of the SiO ₂ target
The dielectric layer 17 having an average thickness of 100nm using SiO _2, ZnS (80) -Si
An RF power of 1 kW was applied to an O ₂ (20) target to sequentially form a dielectric layer 16 having an average film thickness of 70 nm using SiO ₂ . Dielectric 16,1
7, 18 are multilayer interference layers. After a UV curable resin is applied on the high thermal conductive dielectric layer 14 of the first substrate 11 by a spinner, the UV curable resin and the side of the multilayer interference layers 16, 17, 18 of the second substrate 22 are bonded to each other to form an average film of the UV curable resin. Adjust the thickness to about 50 (m) and cure,
The phase change optical disk according to Example 1 was completed as the separation layer 15 using a UV curable resin. The obtained disk is referred to as disk A. Comparative Example 1 A disk of Comparative Example 1 was manufactured in substantially the same manner as in the example. FIG. 2 (b) shows a schematic sectional view thereof. Comparative Example 1 is different from Example 1 in that a normal dielectric layer 3 using ZnS-SiO2 instead of the high thermal conductivity dielectric layers 14 and 20 is used.
The point that 4,38 is used, instead of the multilayer interference layers 16,17,18, Au
The point is that the layer 36 is used.

The specific layer structure was as follows. First
In order from the substrate 11, ZnS-SiO ₂ 90 nm dielectric layer 32 / Ge ₂₅ Sb ₂₃
Te ₅₂ 10 nm first recording layer 33 / ZnS-SiO ₂ 40 nm dielectric layer 34 / U
V cured resin 50 μm separation layer 35 / Au 10 nm Au layer 36 / Ge ₂ Sb ₂ Te ₅ 2
0 nm second recording layer 37 / ZnS-SiO ₂ 30 nm dielectric layer 38 / AlTi100
nm reflective layer 39 / second substrate 22. This disk is called disk B.

The discs obtained in Example 1 and Comparative Example 1 were subjected to comparative evaluation. In all the examples after this example, the disk characteristics were examined under the evaluation conditions shown in Table 1 below.

[Table 1] FIG. 3 shows jitter characteristics when a random pattern is overwritten on five consecutive tracks on the first recording layer of these discs. FIG. 3 shows the dependence of the random jitter on the erasing power, with the horizontal axis representing the erasing power and the vertical axis representing the random jitter.

As shown in FIG. 3, the disk according to the present invention
A shows a good jitter characteristic of about 8% in the range of 4.5 to 6.5 mW in the first recording layer, while disk B shows 10%
Staying back and forth. In the disk B, since the heat conduction between the tracks is not properly controlled, it is considered that the jitter is increased mainly due to the influence of the cross erase.

Next, FIG. 4 shows the overwrite characteristics of the first recording layer of both disks. In FIG. 4, the horizontal axis represents the number of overwrites, and the vertical axis represents random jitter.

[0064] As shown in FIG. 4, the disk A is hardly changed jitter up to 10 ⁵ times, an increase in jitter is observed in the disk B is 10 ³ times or more.

As described above, the phase change optical disk according to this embodiment is
Has good cross-erase and good overwrite characteristics
It was clear that (Embodiment 2) A 0.58 mm thick P
On the C substrate, SiO_Two60nm, ZnS (80) -SiO _Two(20) 100nm, Ge_TwoSb_Two
Te_FiveAfter stacking in order of 8nm, TaC, the other thickness 0.6mmPC
Au30nm, GeN40, Ge on the substrate₂₀Sb_{twenty four}Te₅₆25nm, TiO_Two60n
m, SiO_Two100nm, ZnS (80) -SiO_Two(20) Laminated in order of 70nm
The substrates are bonded together with a UV curable resin 40 (m
A disk according to Example 2 was manufactured.

The jitter characteristics were examined using the average thickness of the TaC film on the first recording layer as a parameter. FIG. 5 shows a change in the 5-track random jitter of the first recording layer with respect to the average thickness of TaC, wherein the horizontal axis represents the average thickness of TaC and the vertical axis represents the jitter.

As shown in FIG. 5, the average thickness of TaC is 35 to 4
About 8% jitter is obtained up to 5nm. The increase in jitter at other film thicknesses is considered to be caused by improper control of the heat conduction in the recording layer surface, indicating that this film thickness is appropriate for suppressing cross-erase.

As described above, it was found that the phase change optical disk according to the present embodiment was effective in reducing the cross erase. (Embodiment 3) In the same manner as in Embodiment 1, a 0.57 mm thick P
On a C substrate, Si ₃ N ₄ 120 nm, SiO ₂ 30 nm, ZnS (80) -SiO ₂ (20) 1
After laminating in the order of 00 nm, Ge ₂₁ Sb ₂₄ Te ₅₅ 10 nm, AlN 30 nm,
TiN 50 nm, ZrN, Ge ₂ Sb ₂ T
_{e 5 18nm, TiO 2 60nm,} SiO 2 100nm, ZnS (80) -SiO 2 (20) 70nm
Were laminated on the film surface with a UV-curable resin 60 (m) therebetween to produce a disk according to Example 3.

The jitter characteristic was examined using the thickness of the ZrN film on the second recording layer as a parameter. FIG. 6 shows the change of the 5-track random jitter of the second recording layer with respect to the average thickness of ZrN, where the horizontal axis represents the average thickness of ZrN and the vertical axis represents the jitter.

As shown in FIG. 6, the average thickness of ZrN is 40 to 5
A jitter of 8% or less is obtained toward 0 nm. The increase in jitter at other film thicknesses is considered to be caused by improper control of the heat conduction in the recording layer surface, indicating that this film thickness is appropriate for suppressing cross-erase.

As described above, it was found that the phase change optical disk according to the present embodiment was effective in reducing the cross erase.

[0072]

As described in detail above, according to the present invention, by using a multilayer interference layer and a high thermal conductivity layer together,
It is possible to provide a phase change recording medium capable of obtaining good overwrite jitter.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a phase-change optical disc according to an embodiment of the present invention.

FIG. 2 is a schematic sectional view of a phase-change optical disc according to Example 1 of the present invention and Comparative Example 1.

FIG. 3 is a characteristic diagram showing random jitter characteristics of the phase-change optical disks according to Example 1 of the present invention and Comparative Example 1.

FIG. 4 is a characteristic diagram showing overwrite characteristics of the phase-change optical disks according to Example 1 of the present invention and Comparative Example 1.

FIG. 5 is a characteristic diagram showing the dependency of the random jitter characteristic on the TaC film thickness in the phase-change optical disc according to the second embodiment of the present invention.

FIG. 6 is a characteristic diagram showing a ZrN film thickness dependency of a random jitter characteristic in the phase change optical disc according to the third embodiment of the present invention.

[Explanation of symbols]

1． First substrate 2. Dielectric layer 3. First recording layer 4. 4. High thermal conductivity dielectric layer Separation layer 6. Multilayer interference layer 7. Second recording layer 8. Dielectric layer 9. Reflective layer 10. Second substrate 11. First PC board 12. ZnS-SiO ₂ dielectric layer 13. Ge ₂₅ Sb ₂₃ Te ₅₂ First recording layer 14. AlN high thermal conductivity dielectric layer 15. UV curable resin separation layer 16. ZnS-SiO ₂ dielectric layer 17. SiO ₂ dielectric layer 18. ZnS-SiO ₂ dielectric layer 19. Ge ₂ Sb ₂ Te _5- layer second recording layer 20. TaN high thermal conductivity dielectric layer 21. AlTi reflective layer 22. Second substrate 32. ZnS-SiO ₂ dielectric layer 33. Ge ₂₅ Sb ₂₃ Te ₅₂ First recording layer 34. ZnS-SiO ₂ dielectric layer 35. UV curable resin separation layer 36. Au layer 37. Ge ₂ Sb ₂ Te ₅ second recording layer 38. ZnS-SiO ₂ dielectric layer 39. AlTi reflective layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat 参考 (Reference) G11B 7/24 541 G11B 7/24 541B (72) Inventor Katsutaro Ichihara No. 1 F-term in Toshiba R & D Center (Reference) 5D029 JB05 LB01 LB07 LB11 LC01 LC03 LC17 MA09 MA27 RA01 RA04 RA18 RA19 RA45 RA49

Claims (7)

[Claims] 1. A substrate, at least two recording layers formed on the substrate and transitioning between a crystalline state and an amorphous state by light irradiation, and formed on at least one light incident side of the recording layer. A phase change recording medium, comprising: a multi-layered interference layer formed; and a high thermal conductivity dielectric layer formed on a side of at least one of the recording layers opposite to a light incident side. 2. A substrate, a first recording layer formed on the substrate and transitioning between a crystalline state and an amorphous state by light irradiation, and a high thermal conductivity dielectric formed on the first recording layer A layer, a separation layer formed on the high thermal conductivity dielectric layer, a multilayer interference layer formed on the separation layer, and a crystalline state and amorphous state formed on the multilayer interference layer by light irradiation. And a second recording layer that transitions between states. 3. The phase change recording medium according to claim 1, wherein said multilayer interference layer is composed of two or more dielectric layers. 4. The phase change recording medium according to claim 3, wherein the extinction coefficient k of the dielectric layer is 0.5 or less with respect to the wavelength of the light source. 5. The phase change recording medium according to claim 1, wherein a total average thickness of said multilayer interference layer is 300 nm or less. 6. The phase change recording medium according to claim 1, wherein the thermal conductivity of the high thermal conductivity dielectric layer is at least 10 times the thermal conductivity of the multilayer interference layer. 7. The high thermal conductivity dielectric layer having an average thickness of 10
Claims 1 and 2, characterized in the range of ~ 500 nm.
7. The phase change recording medium according to item 6.