JP2005267832A - Optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical recording medium for high speed recording equivalent to 3-10×(10 m/s-36 m/s) DVD in which recording sensitivity is remarkably improved without degradation in overwriting characteristics or preservation reliability. <P>SOLUTION: (1) The optical recording medium includes, on a transparent substrate, at least a first protection layer, a high speed rewritable phase change recording layer in which the maximum linear velocity for recording is between 10.0-36.0 m/s, a second protection layer, and a reflective layer with thermal conductivity of 300 W/m K or more, and having a low thermal conductivity layer with film thickness of 1-6 nm consisting of the low thermal conductivity material with 7 W/m K or less between the second protection layer and the reflective layer. (2) The optical recording medium described in (1) has a thermal expansion coefficient of the low thermal conductivity layer of ≤10×10<SP>-6</SP>/°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a rewritable optical recording medium.

In recent years, a recording medium capable of recording and reproducing a large amount of data at a high density and at a high speed has been demanded as the amount of information increases. Phase change optical recording media that record and reproduce information by irradiating a light beam, especially phase change optical discs, are excellent in signal quality and capable of high density, and are easy to perform one-beam overwrite (repetitive recording). It is a recording medium with excellent high-speed accessibility.
Such a phase change optical disk generally has a reversible phase of at least a first protective layer, an amorphous phase, and a crystalline phase on a light-transmitting substrate on which a concave guide groove for guiding laser beam scanning is formed. A phase change recording layer that changes, a second protective layer, and a reflective layer made of metal are provided in this order, and a resin protective layer is further provided on the reflective layer. In the case of a bonded optical disk, the above structure is used for one or both, and the structure is bonded via an adhesive layer.

The signal recording / reproducing method of the phase change optical recording medium is as follows.
The optical recording medium is rotated at a constant linear velocity or a constant rotational speed (angular velocity) by means such as a motor, and the phase-change recording layer of the medium is irradiated with a focused laser beam whose intensity is modulated. At this time, the phase change recording layer changes in phase state between crystal and amorphous depending on the laser light irradiation condition, and a pattern formed as a difference between the phase states becomes a signal pattern. Reproduction is performed by detecting a difference in reflectance caused by a difference in phase state.
The intensity modulation of the focused laser beam is performed between three output levels. At this time, the highest output level (hereinafter referred to as recording power) is used for melting the phase change recording layer. An intermediate output level (hereinafter referred to as erasing power) is used to heat the phase change recording layer to a temperature just below the melting point and higher than the crystallization temperature. The lowest level is used to control the heating or cooling of the phase change recording layer.
The phase change recording layer melted by the laser beam of the recording power becomes amorphous or microcrystalline by the subsequent rapid cooling, and the reflectance is lowered, and becomes a recording mark (amorphous mark). Further, the laser beam with erasing power is all crystalline and can be erased. Thus, by modulating the intensity of the laser light between the three output levels, crystal regions and amorphous regions are alternately formed on the phase change recording layer, and information is stored.

In order to realize high speed recording, it is necessary to use a phase change material having a high crystallization speed for the phase change recording layer. Such a phase change material has a high crystallization speed and a high erase ratio at high speed recording, so that Ge—Te, Ge—Te—Se, In—Sb, Ga—Sb, Ge—Sb—Te, Ag-In-Sb-Te and the like are attracting attention.
However, it is not sufficient to realize high-speed recording only by increasing the crystallization speed of the phase-change recording layer material, and there is a problem of “recording sensitivity” as another big problem. For example, although a Ga—Sb phase change material known as a recording material for high speed recording has been reported to have an extremely high crystallization rate (Non-patent Document 1), the melting point in the eutectic composition is 630 ° C. Since it is relatively high, it becomes difficult to form a mark and a problem of insufficient sensitivity arises. Even if the laser light power during recording is increased to compensate for the lack of sensitivity, the rapid cooling structure necessary for mark formation is difficult to be realized, and sufficient recording characteristics cannot be obtained. As a result, the overwrite characteristics also deteriorate.

The following is mentioned as a well-known technique relevant to this invention.
In Patent Document 1, an adhesive layer containing an oxide is provided between the protective layer and the reflective layer and / or between the protective layer and the recording layer, and the oxide is Al ₂ O ₃ , GeO ₂ , SiO _2. An optical recording medium that is at least one selected from Ta ₂ O ₅ , TiO _2, and Y ₂ O ₃ is disclosed.
In Patent Document 2, a first protective layer, a recording layer, a second protective layer, a third protective layer, and a reflective layer are sequentially formed on a transparent substrate, and MgO, Al _{2 is} used as a material having a high Young's modulus for the third protective layer. An optical information recording medium using O ₃ , BeO, ZrO ₂ , ThO ₂ , UO ₂ , SiC, TiC, ZrC, AlN, Si ₃ N ₄ , MoSi ₂ , or the like alone, and SiO ₂ , Ta ₂ O _5. Optical using oxides such as TiO ₂ , nitrides such as Si ₃ N ₄ and AlN, sulfides such as SmS and SrS, and fluorides such as MgF ₂ singly or mixed with a material having a high Young's modulus An information recording medium is disclosed.

Patent Document 3 has a layer having both a thermal conductivity control function and a light absorption correction function, and the constituent elements of this layer are Ti, V, Cr, Fe, Ni, Zn, Zr, Nb, Mo, Rh. An optical recording medium that is at least one selected from W, Ir, Pt, and Te is disclosed.
Patent Document 4 discloses a light in which an absorption amount correction layer containing any of Ti, Cr, Fe, Ni, Zn, Zr, Nb, Mo, W, and Si is provided between the second protective layer and the reflective layer. A recording medium is disclosed.
In Patent Document 5, a lower protective layer / phase change recording layer / multilayer upper protective layer / a reflective heat-radiating layer mainly composed of silver is provided on a substrate, and an upper protective layer in contact with the reflective heat-dissipating layer is AlN. , SiNx, SiAlN, TiN, at least one nitride selected from the group consisting of BN and TaN, _{or, Al 2 O 3, MgO,} SiO, SiO 2, TiO 2, B 2 O 3, CeO 2, CaO An optical disc made of at least one oxide selected from the group consisting of Ta ₂ O ₅ , ZnO, In ₂ O ₃ and SnO ₂ is disclosed.

Patent Document 6 discloses a phase change optical disc in which a base protective layer, a recording layer, an upper transparent protective layer, an interference layer for controlling a difference in absorption between a mark portion and an erasure portion of a recording layer, and a reflective layer are sequentially formed on a substrate. The interference layer is made of one or more materials selected from Si, SiO ₂ , Ge, MgF ₂ , Al ₂ O ₃ , In ₂ O ₃ , and ZrO ₂ , and the reflective film is selected from Al, Au, Cu, and Ag. There has been disclosed a phase change type optical disc made of a metal.
Patent Document 7 discloses an optical recording medium in which a lower dielectric protective layer, a recording layer, an upper dielectric protective layer, and a reflective heat dissipation layer are sequentially laminated on a transparent substrate, and has a composition as a material of the upper dielectric protective layer ( ZrO ₂ ) 100-x (SiO ₂ ) x (0 <x <60 mol%) is disclosed.
Patent Document 8 has at least a first thin film layer (protective layer), a phase change optical recording material layer, a second thin film layer (protective layer), and a reflective layer on a transparent substrate, and Zr oxidation is performed as the second thin film layer. An optical recording medium using a material whose main component is an object is disclosed.

In Patent Document 9, a light transmission layer, a lower protective layer, a recording layer, a first upper protective layer, a second upper protective layer, and a reflective heat dissipation layer are laminated in this order from the laser light incident side. A phase change type information recording medium in which the thermal conductivity of the layer is 10 mW / cmK or less is disclosed.
Patent Document 10 discloses an optical information recording medium having a recording film, a heat insulating film, and a reflective film on a transparent substrate, and the heat conductivity of the heat insulating film is 10 W / mK or less.
In Patent Document 11, a first protective layer, a recording layer, a second protective layer, a third protective layer containing at least 35 atomic% of Si, a reflective layer containing at least 95% Ag, and an overcoat layer are sequentially formed on a substrate. A laminated optical recording medium is disclosed.
However, in any of the above documents, the low thermal conductivity of 10 W / m · K or less between the second protective layer and the reflective layer having a thermal conductivity of 300 W / m · K or more as in the present invention. There is no description about the medium configuration having the rate layer and its effect. For example, as shown in a comparative example to be described later, the effect of the present invention cannot be obtained with a combination that does not satisfy the above conditions.

Japanese Patent Laid-Open No. 06-139615 Japanese Patent Laid-Open No. 07-307036 JP 09-223332 A JP 2000-339759 A JP 2000-331378 A Japanese Patent No. 2850754 JP 2002-260281 A JP 2003-91871 A JP 2002-288879 A JP 2000-182278 A European Patent Application No. 1343155 “Phase-Change optical data storage in GaSb”, Applied Optics, Vol. 26, no. 22115, November, 1987

  The present invention provides an optical recording medium for high-speed recording corresponding to DVD 3 to 10 times speed (10 m / s to 36 m / s), in which the recording sensitivity is drastically improved and there is no deterioration in overwrite characteristics or storage reliability. With the goal.

The above problems are solved by the following inventions 1) to 14) (hereinafter referred to as the present inventions 1 to 14).
1) On a transparent substrate, at least a first protective layer, a phase change recording layer having a maximum recording linear velocity of 10.0 to 36.0 m / s and rewritable at a high linear velocity, a second protective layer, heat A film having a reflective layer having a conductivity of 300 W / m · K or more, and having a thickness of 1 to 6 nm made of a low thermal conductivity material having a thermal conductivity of 7 W / m · K or less between the second protective layer and the reflective layer. An optical recording medium having a low thermal conductivity layer.
2) The optical recording medium according to 1), wherein the low thermal conductivity layer has a thermal expansion coefficient of 10 × 10 ⁻⁶ / ° C. or less.
3) The optical recording medium according to 1) or 2), wherein the low thermal conductivity material is an inorganic oxide.
4) The optical recording medium according to 3), wherein the inorganic oxide is an oxide or composite oxide of at least one element selected from Group IIa to IVa and Group IIb to IVb.
5) The optical recording medium according to any one of 1) to 4), wherein the melting point of the low thermal conductivity material is equal to or higher than the melting point of the phase change recording layer material.
6) The optical recording medium according to any one of 1) to 5), wherein the low thermal conductivity material is represented by the following composition formula.
(ZrO ₂ ) a (TiO ₂ ) b (SiO ₂ ) c (X1) d
[Wherein, a to d represent the ratio (mol%) of each oxide, and 50 ≦ a ≦ 100, 0 ≦ b <50, 0 ≦ c <30, 0 ≦ d <10 (a + b + c + d = 100). , X1 is at least one selected from rare earth oxides. ]
7) The optical recording medium according to any one of 1) to 6), wherein the low thermal conductivity material contains a metal and / or metalloid carbide and / or nitride.
8) The optical recording medium according to any one of 1) to 7), wherein the reflective layer is made of pure Ag or an alloy containing Ag as a main component.
9) The optical recording medium according to any one of 1) to 8), wherein the reflective layer has a thickness of 100 to 300 nm.
10) The optical recording medium according to any one of 1) to 9), wherein the phase change recording layer is made of an alloy containing at least Ga, Sb, Sn, and Ge.
11) The alloy contains at least one element selected from In, Te, Al, Zn, Mg, Tl, Pb, Bi, Cd, Hg, Se, C, N, Au, Ag, Cu, Mn, and a rare earth element. The optical recording medium according to 10), wherein the total content of these elements is 0.1 to 10 atomic%.
12) The optical recording medium according to any one of 1) to 11), wherein the phase change recording layer has a thickness of 6 to 20 nm.
13) The optical recording medium according to any one of 1) to 12), wherein the second protective layer comprises a mixture of ZnS and SiO ₂ .
14) A substrate having a meandering groove with a groove pitch of 0.74 ± 0.03 μm, a groove depth of 22 to 40 nm and a groove width of 0.2 to 0.4 μm, and a DVD of 3 to 10 times speed (10 m / s to 36 m / s). The optical recording medium according to any one of 1) to 13), wherein recording is possible at a recording linear velocity of

Hereinafter, the present invention will be described in detail.
The inventors have at least a first protective layer on a transparent substrate and a phase in which the maximum recording linear velocity is between 3 and 10 times DVD (10.0 to 36.0 m / s) and can be rewritten at a high linear velocity. In an optical recording medium having a change recording layer, a second protective layer, and a reflective layer having a thermal conductivity of 300 W / m · K or more, the thermal conductivity is 7 W / m · K or less between the second protective layer and the reflective layer. By providing a low thermal conductivity layer having a film thickness of 1 to 6 nm made of a low thermal conductivity material, the recording sensitivity is drastically improved. Further, the low thermal conductivity layer is not provided, and the same low thermal conductivity is provided in the second protective layer. The inventors have found that the overwrite characteristics and the storage reliability are further improved as compared with the case of using the material, and have completed the present invention. In addition, the thermal conductivity in this invention is taken as the measured value of the bulk in room temperature (usually around 20 degreeC).
In the present invention, the maximum recording linear velocity is 10.0 to 36.0 m / h by the “cooperative action” of the high thermal insulation effect (heat storage action) and high toughness by the low thermal conductivity layer and the rapid cooling action by the high thermal conductivity reflective layer. The recording sensitivity of the optical recording medium between s is improved. When a low thermal conductivity layer having a thermal conductivity of 7 W / m · K or less is provided, the temperature reached by the phase change recording layer at the time of recording becomes higher, so that the recording sensitivity is improved. Further, when used in combination with the high thermal conductivity reflective layer, the cooling gradient with respect to the temperature change is also increased, so that a rapid cooling structure necessary for mark formation is realized and good recording characteristics can be obtained.

The low thermal conductivity layer needs to be provided between the second protective layer and the high thermal conductivity reflective layer.
According to the study by the present inventors, the recording sensitivity is further improved when the low thermal conductivity layer is provided between the phase change recording layer and the reflective layer than when it is provided between the first protective layer and the recording layer. . This is because when the recording layer reaches a high temperature once due to the heat storage effect of the low thermal conductivity layer during recording, the temperature must be rapidly cooled to form an amorphous mark. This is because it is necessary to provide a low thermal conductivity layer adjacent to the reflective layer in order to perform the process of "" in a short time and continuously.
Furthermore, the second protective layer is provided on the phase change recording layer, and the low thermal conductivity layer is provided between the second protective layer and the reflective layer. The storage reliability is further improved as compared with the case where a low thermal conductivity layer is provided between the reflective layers. The reason is considered as follows.

That is, when the low thermal conductivity layer is used as the thermal conductivity adjusting layer as described above, it is preferable that the film thickness is small. When the film thickness is thick, it becomes difficult to adjust the thermal conductivity of the optical recording medium, and as the film thickness increases, the heat insulation becomes higher, so that the optical recording medium is heated too much and the overwrite characteristics deteriorate. Because. Therefore, the upper limit of the film thickness of the low thermal conductivity layer is 6 nm. However, if the film thickness is too thin, the function as the low thermal conductivity layer cannot be exhibited, and the film formation becomes difficult. A preferable film thickness range is 1 to 4 nm.
However, on the other hand, even if the film thickness is reduced and the thermal conductivity is controlled, it becomes difficult to adjust the optical characteristics of the optical recording medium, resulting in a problem that sufficient recording characteristics cannot be obtained. In addition, when a low thermal conductivity layer made of an oxide or a crystalline material is provided in contact with the phase change recording layer, the phase change recording layer is oxidized or crystallization is promoted, so that the storage reliability is deteriorated. Therefore, if a second protective layer made of a material that does not cause such a problem is provided between the phase change recording layer and the low thermal conductivity layer, the optical characteristics are adjusted, and the phase change recording layer is oxidized and crystallized. By preventing this, the recording characteristics and storage reliability can also be improved.

The thermal conductivity of the reflective layer must be 300 W / m · K or higher. This is because, as described above, the combination of the low thermal conductivity layer and the high thermal conductivity reflective layer increases the cooling gradient with respect to the temperature change during recording and sufficiently realizes the rapid cooling structure necessary for mark formation. . There is no particular upper limit on the thermal conductivity, but among the commonly used materials, Ag of about 430 W / m · K is the highest.
Conventionally, the reflective layer material constituting an optical recording medium is related to the viewpoint of “thermal conductivity” related to the adjustment of the cooling rate of heat generated during recording, and the improvement of the contrast of the reproduction signal using the interference effect. From the “optical” point of view, “a metal having high thermal conductivity / high reflectance” is desirable, and a simple substance of Au, Ag, Cu, Al or an alloy containing these metals as a main component has been used. However, among these, Al having a thermal conductivity of less than 300 W / m · K and about 240 W / m · K cannot realize the desired quenching condition.

The cooperative action by the combination of the low thermal conductivity layer and the high thermal conductivity reflecting layer as described above can be expected for an optical recording medium having a maximum recording linear velocity of 10.0 to 36.0 m / s. Such an optical recording medium is required to form a large amorphous mark during short pulse irradiation for high-speed recording, and a high recording laser power is required.
On the other hand, an optical recording medium for low-speed recording with a maximum recording linear velocity of less than 10.0 m / s does not require so high recording laser power, and if a low thermal conductivity layer is provided, the time during which heat stays is long. As a result, the conditions for amorphization are destroyed, and the recording characteristics are deteriorated. On the other hand, in an optical recording medium for high-speed recording with a maximum recording linear velocity exceeding 36.0 m / s, a higher recording laser power is required, but this is a recording linear velocity region in which appropriate amorphization conditions are difficult to be realized. Therefore, at present, an optical recording medium having good recording sensitivity and overwrite characteristics has not been obtained.

In addition, when a material whose coefficient of thermal expansion of the low thermal conductivity layer is 10 × 10 ⁻⁶ / ° C. or less is selected, the lower the thermal expansion, the smaller the expansion and contraction of the low thermal conductivity layer with respect to the change in heat, resulting in a heat change. Therefore, even when the high power laser is irradiated during recording and the low thermal conductivity layer reaches a high temperature, deterioration of the layer itself is suppressed, so that the overwrite characteristics can be further improved. There is no particular lower limit of the thermal expansion coefficient, but there is no material that can be used in the present invention and has a thermal expansion coefficient of “0”, that is, a material that does not thermally expand.
As a material constituting the low thermal conductivity layer, it is desirable to select an appropriate material from the following viewpoints (1) to (4), and an inorganic oxide is preferable.
(1) It is optically transparent to laser light and has sufficient stability (from the viewpoint of resistance to temperatures such as melting point, softening point, decomposition temperature)
(2) Sufficient mechanical strength [from the viewpoint of toughness and hardness (thermal expansion coefficient)]
(3) Good adhesion to the metal reflective layer (4) Easy formation Among them, an oxide or composite oxide of at least one element selected from Group IIa to IVa and Group IIb to IVb It is preferable because all the above conditions are satisfied. However, in the case of complex oxides, care must be taken because toughness and hardness may be lost if the difference in thermal expansion coefficient is large.

Furthermore, when the “sufficient stability” in (1) is emphasized, it is desirable to use a low thermal conductivity material having a melting point equal to or higher than that of the phase change recording layer material.
In order to realize high-speed recording, it is necessary to control the heating / rapid cooling of the phase change recording layer in a shorter time, and therefore the pulse width of the light emission pulse irradiated to the phase change recording layer becomes narrower. Therefore, a higher laser power is required during recording. This is because if the pulse width is widened, the time during which pulses necessary for cooling are not emitted is shortened, the area and length of the amorphous mark are reduced, and it becomes difficult to form a mark having a desired length. .
One of the phase change materials capable of high-speed recording at 3 to 10 times the speed of DVD is Ga-Sb alloy, but the melting point near the eutectic composition of Ga-Sb alloy is very high at 630 ° C. Is used, it is necessary to raise the temperature of the phase change recording layer to a high temperature of 630 ° C. or higher by the recording laser power. Therefore, it is necessary to select a material with excellent heat resistance having a melting point of 630 ° C. or higher for the low thermal conductivity layer. An oxide having a melting point of 800 ° C. or higher, more preferably 1000 ° C. or higher is preferable, and specific examples include ZrO ₂ (2720 ° C.), TiO ₂ (1840 ° C.), and SiO ₂ (1710 ° C.). However, it is not necessarily limited to these.

Particularly preferred as the low thermal conductivity material is an oxide or composite oxide having the composition defined in the sixth aspect of the present invention.
ZrO ₂ has particularly excellent toughness, extremely low thermal conductivity (κ≈2.0 W / m · K), and thermal expansion coefficient (α′≈9 × 10 ⁻⁶ / ° C.) is also close to that of metal. Is easy to combine, and further has the characteristics of enhancing the mechanical strength and chemical durability, so that it becomes the main constituent material of the present invention for the purpose of improving “recording sensitivity” and “overwrite characteristics”.
Like ZrO ₂ , TiO ₂ (κ≈6.5 W / m · K, α′≈7.6 × 10 ⁻⁶ / ° C.), which is known as a hard oxide, reduces the high temperature viscosity of the low thermal conductivity layer. Since it has the characteristic of improving the meltability, it contributes to the stabilization of the layer and the improvement of the durability.
Even if the material has a thermal conductivity exceeding 10 W / m · K, the properties of individual materials can be improved by selecting an appropriate combination so that the thermal conductivity of the composite oxide as a whole is 10 W / m · K or less. Various low thermal conductivity materials can be designed.

For example, SiO ₂ (κ≈1.6 W / m · K, α′≈0.5 × 10 ⁻⁶ / ° C.) having low thermal conductivity similar to ZrO ₂ is Al ₂ O ₃ (κ≈30 W / K). When combined with an intermediate oxide of m · K, α′≈6.5 × 10 ⁻⁶ / ° C., mechanical properties such as rigidity and heat resistance are improved.
When forming a complex oxide, it is desirable to use a material having a thermal expansion coefficient as close as possible. If the thermal expansion is wrongly controlled, stress may be generated and the structure may be destroyed. In the case of a composite oxide, if the thermal expansion coefficient is different, the stress is likely to be generated, and thus control is necessary.
The optical properties of TiO ₂ and SiO ₂ can be adjusted by adjusting the addition amount. Rare earth oxides typified by Y ₂ O ₃ (κ≈27 W / m · K) reduce the volume change with respect to the temperature of the material, so that the stability against the temperature change at the time of initialization and recording is improved, and the target It has a function of preventing cracks, and further has a function of improving durability and high-temperature meltability.

When ZrO ₂ is a main constituent material (50 mol% or more of the whole constituent material) and TiO ₂ , SiO ₂ , or rare earth oxide is added as a modifying component, the amount added is 50 mol% of the whole constituent material in TiO _2. Less than 30 mol% of the entire constituent material for SiO ₂ , and less than 10 mol% of the entire constituent material for rare earth oxides. If the added amount exceeds the above range, it becomes difficult to form a material having a thermal conductivity of 10 W / m · K or less.
When TiO ₂ and SiO ₂ are compared, SiO ₂ has a low refractive index, and if the mixing ratio is increased, the refractive index of the entire material may be lowered. Therefore, in order to suppress a decrease in the refractive index, it is desirable to mix TiO ₂ which is a high refractive index dielectric alone or to mix TiO ₂ and SiO ₂ together.
Moreover, the partially stabilized zirconia stabilized by adding several mol% of Y ₂ O ₃ , MgO, CaO, Nb ₂ O ₅ , Al ₂ O ₃ , rare earth oxide, etc. to ZrO ₂ has mechanical properties. In particular, it is more preferable because it prevents cracking of the target material used when producing the optical recording medium of the present invention, and further lowers the thermal conductivity as compared with ZrO ₂ alone.
As the rare earth oxide, Y ₂ O ₃ is particularly preferable, and if added in a small amount, it contributes to the improvement of the specific elastic modulus and the homogenization of the oxide layer, so the addition amount is less than 10 mol%.

Further, when the metal and / or metalloid carbide and / or nitride is contained in the low thermal conductivity material, the adhesion with the reflective layer can be improved. Specific examples of such materials include carbides and nitrides such as Si, Ge, Ti, Zr, Ta, Nb, Hf, Al, Y, Cr, W, Zn, In, Sn, and B. However, if the content exceeds 50 mol%, low thermal conductivity is not exhibited, which is not preferable. Although there is no particular lower limit of the amount, it is desirable to contain 1 mol% or more in order to exert the effect.
It is preferable to use pure Ag or an alloy containing Ag as a main component for the reflective layer. This is because Ag has a very high thermal conductivity of 427 W / m · K, and when used in combination with a low thermal conductivity layer, a rapid cooling structure suitable for forming an amorphous mark can be easily realized.
When pure Ag or an alloy containing Ag as a main component is used for the reflective layer, if a low thermal conductivity layer containing sulfur is provided in contact with the reflective layer, the reflective layer deteriorates due to the sulfurization reaction of Ag. Become. Therefore, in such a case, it is necessary to select a low thermal conductivity layer that does not contain sulfur.
The thickness of the reflective layer is preferably 100 to 300 nm. In order to sufficiently realize a desired quenching structure and expect sufficient cooperation with the low thermal conductivity layer, the thickness of the reflective layer needs to be at least 100 nm, and the upper limit is 300 nm from the viewpoint of productivity. .

As the recording material, a phase change material obtained by adding Sn and Ge to a Ga—Sb-based material having high-speed crystallization characteristics is preferable, and the maximum recording linear velocity is between 10.0 and 36.0 m / s. In this case, an optical recording medium having good recording characteristics and storage reliability can be provided.
Sb, which is the first main constituent element, can adjust the crystallization speed by changing the Sb ratio in the constituent material, and can increase the crystallization speed by increasing the ratio. It is a very good element essential for realization.
However, if an optical recording medium capable of high-speed recording corresponding to 36.0 m / s is realized with Sb alone, problems arise in overwrite characteristics and storage reliability. Therefore, Ga is essential as a second main constituent element that improves the crystallization speed without impairing the overwrite characteristics and storage reliability. Ga has the effect of increasing the crystallization temperature of the phase change material with a small addition amount, and is therefore an effective element for the stability of the mark.

Sn, the third main constituent element, has the effect of increasing the crystallization rate slowed by the addition of Ga, and at the same time has the effect of lowering the melting point, and adjusting the crystallization temperature increased by the addition of Ga. Can do. As a result, it is possible to improve the adverse effect of the initialization failure caused by the high crystallization temperature of the Ga—Sb-based material, and it is effective for improving the sensitivity of the optical recording medium, improving the reflectance, and reducing the initialization noise. It is a very excellent constituent element that comprehensively improves recording characteristics.
Ge, which is the fourth main constituent element, is indispensable as a constituent element because storage reliability is dramatically improved by addition of a small amount.
Among such phase change materials containing at least Ga, Sb, Sn and Ge, the composition formula is GaαSbβSnγGeδ, 2 ≦ α ≦ 20, 40 ≦ β ≦ 80, 5 ≦ γ ≦ 25, 2 ≦ δ ≦ 20 [ However, α, β, γ, and δ are composition ratios (atomic%) of each element, and α + β + γ + δ = 100 is preferable.
If Sn is less than 5 atomic%, the melting point becomes high and the sensitivity is deteriorated, and if Sn exceeds 25 atomic%, the crystallization speed becomes too fast and it becomes difficult to form an amorphous state. On the other hand, if Sb is less than 40 atomic%, the melting point becomes high and the recording sensitivity deteriorates. If Sb exceeds 80 atomic%, the storage reliability deteriorates, which is not preferable. Further, when Ga and Ge are less than 2 atomic%, the storage reliability is deteriorated, and when it exceeds 20 atomic%, the crystallization temperature becomes too high and initialization becomes difficult.

The phase change recording layer further includes at least one selected from In, Te, Al, Zn, Mg, Tl, Pb, Bi, Cd, Hg, Se, C, N, Au, Ag, Cu, Mn, and rare earth elements. It is preferable to contain these elements. The total content of these elements is preferably from 0.1 to 10 atomic%, more preferably from 0.5 to 8 atomic%.
In has an effect of improving initialization failure in a high-speed recording material. However, excessive addition of In causes deterioration of the reproduction light and causes a decrease in reflectivity. Tl, Pb, Bi, Al, Mg, Cd, Hg, Mn, or a rare earth element has an effect of increasing the crystallization rate, and among these elements, Bi that easily takes the same valence as Sb is more preferable. However, if the addition amount is too large, it causes deterioration of reproduction light and initial jitter, so that the composition range must be 10 atomic% or less.
Storage reliability can also be improved by adding Te, Al, Zn, Se, C, N, Se, Au, Ag, and Cu in addition to Ge. Of these, Al and Se further promote high-speed crystallization, and Se is effective in improving recording sensitivity. Au, Ag, and Cu are effective elements that have excellent storage reliability and improve the initialization failure of high-speed recording materials. However, Au, Ag, and Cu also have the property of reducing the crystallization speed and hindering high-speed recording characteristics. Therefore, the upper limit of the total addition amount of Au, Ag, and Cu is preferably 10 atomic%. On the other hand, if the amount is too small, the effect of addition becomes unclear, so the lower limit of the added amount of Au, Ag and Cu is preferably 0.1 atomic%.

Further, it has been found that Mn and rare earth elements have the same effect as In. In particular, Mn is an additive element having excellent storage reliability that does not require much increase in the Ge addition amount. The optimum Mn addition amount is 1 to 10 atomic%. This is because if it is less than 1 atomic%, the effect of increasing the crystallization speed does not appear, and if it exceeds 10 atomic%, the reflectance in an unrecorded state (crystalline state) becomes too low.
As described above, by appropriately combining the Ga—Sb—Sn—Ge material and the additive element, even in high speed recording in which the maximum recording linear velocity is between 10.0 and 36.0 m / s, it is favorable. An optical recording medium having recording characteristics and storage reliability can be designed.
The thickness of the phase change recording layer is preferably 6 to 20 nm. If the thickness is smaller than 6 nm, the deterioration of the overwrite characteristic becomes remarkable. If the thickness is larger than 20 nm, the phase change recording layer is easily moved by the overwrite, and the increase in jitter becomes severe. Further, in order to improve the erasing characteristics by reducing the difference in absorption between the crystal and the amorphous as much as possible, the thickness of the phase change recording layer is preferably thin, and more preferably 8 to 17 nm.

It is preferable to use a mixture of ZnS and SiO ₂ for the first protective layer and the second protective layer that supplements the optical adjustment. This material is not only suitable for correcting the optical properties of the disc that need to be adjusted by providing a low thermal conductivity layer, but also protects against excellent heat resistance, low thermal conductivity, and chemical stability This is particularly preferable because it is suitable as a layer, has a small residual stress in the film, and does not easily deteriorate characteristics such as recording sensitivity and erasing ratio even when recording / erasing is repeated.
Although the optimal range is selected from the thermal and optical conditions, the thickness of the first protective layer is preferably 40 to 200 nm, more preferably 40 to 90 nm.
The film thickness of the second protective layer is 0.5 to 20 nm. If the thickness is less than 0.5 nm, defects such as cracks are caused and the durability of the overwrite is lowered, and the recording sensitivity is deteriorated. On the other hand, if the thickness exceeds 20 nm, the cooling rate of the phase change recording layer becomes slow, so that it becomes difficult to form a mark and the mark area becomes small. Since the second protective layer has a direct influence on cooling of the phase change recording layer, it is preferably 2 nm or more in order to obtain good erasing characteristics and overwrite durability. The optimum range is 2-8 nm.

Invention 15 uses a substrate having meandering grooves with a groove pitch of 0.74 ± 0.03 μm, a groove depth of 22 to 40 nm, and a groove width of 0.2 to 0.4 μm as the substrates of Inventions 1 to 13. It is. Thus, it is possible to provide a DVD + RW medium capable of high-speed recording at 3 × speed or higher (specifically, DVD 3 to 10 × speed) in conformity with the current DVD + RW medium standard. The purpose of meandering the groove is to access a specific unrecorded track or to rotate the substrate at a constant linear velocity.
FIG. 1 shows a schematic sectional view of an example of the optical recording medium of the present invention. On the upper surface of the transparent substrate 1 provided with a laser light guide groove, a first protective layer 2, a phase change recording layer 3 that reversibly changes between crystalline and amorphous, a second protective layer 8, and a low thermal conductivity. This is an example having a layer structure in which a layer 4, a reflective layer 5, and a resin protective layer 6 are provided, and finally a similar bonding substrate 7 is bonded.
FIG. 2 is a schematic sectional view of a conventional optical recording medium excluding the second protective layer 8 from FIG.

  According to the present invention, the recording sensitivity is drastically improved by the “cooperative action” of the high heat storage action and high toughness by the low thermal conductivity layer and the rapid cooling action by the high thermal conductivity reflective layer, and the overwriting characteristics and the storage reliability are improved. It is possible to provide an optical recording medium in which the maximum recording linear velocity is between 10.0 and 36.0 m / s without any deterioration in properties.

EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited at all by these Examples, the initialization apparatus used, etc. The materials used for the low thermal conductivity layers of Examples 1 to 18 are materials that satisfy κ ≦ 7 W / m · K and α ′ ≦ 10 × 10 ⁻⁶ / ° C. Moreover, the evaluation results of Examples and Comparative Examples are collectively shown in Tables 1 and 2.

[Example 1]
A first protective layer 2, a phase change recording layer 3, a second protective layer 8, a low thermal conductivity layer 4, and a reflective layer 5 are formed in this order on the substrate 1 by a sputtering method, and a spin coat method is formed thereon. A resin protective layer 6 was formed, and finally a bonding substrate 7 was bonded to produce and initialize an optical recording medium having the layer structure shown in FIG.
As the substrate 1, a substrate with a guide groove made of polycarbonate having a diameter of 12 cm and a thickness of 0.6 mm and having a track pitch of 0.74 μm was used.
For the first protective layer 2, ZnS—SiO ₂ (80:20 mol%) having a thickness of 60 nm was used.
For the phase change recording layer 3, Ga ₁₂ Sb ₈₈ with a thickness of 16 nm was used.
For the second protective layer 8, ZnS—SiO ₂ (80:20 mol%) (κ≈8.6 W / m · K) having a thickness of 7 nm was used.
The low thermal conductivity layer 4 is made of 4 nm thick ZrO ₂ (containing 3 mol% Y ₂ O ₃ ) (κ≈5.1 W / m · K, α′≈9.5 × 10 ⁻⁶ / ° C.). Using.
The reflective layer 5 was made of Ag (κ≈430 W / m · K) having a thickness of 140 nm.
An ultraviolet curable resin (SD318 manufactured by Dainippon Ink & Chemicals, Inc.) was used for the resin protective layer 6.
As the bonding substrate 7, a polycarbonate substrate having a diameter of 12 cm and a thickness of 0.6 mm was used.
Initialization is performed by using an initialization device “PCR DISK INITIALIZER” manufactured by Hitachi Computer Equipment Co., Ltd., rotating the optical recording medium at a constant linear velocity, and supplying a laser beam with a power density of 10 to 20 mW / μm ² in a radial direction. Irradiation was carried out while moving by the feed amount.
Next, the C / N ratio, recording sensitivity, and storage reliability of this optical recording medium were evaluated.
Evaluation was performed using an optical disk evaluation apparatus (DDU-1000 manufactured by Pulse Tech Co., Ltd.) having a pickup with a wavelength of 660 nm and NA of 0.65, a recording linear velocity of 28 m / s (equivalent to 8 times the speed of DVD), and a linear density of 0.267 μm / bit. The evaluation was performed by evaluating the C / N ratio when the 3T single pattern was overwritten 10 times and 1000 times by the EFM + modulation method. In addition, “storage reliability” for evaluating the recording characteristics again after leaving the optical recording medium in a thermostat bath at 80 ° C. and 85% RH for 300 hours was also evaluated.
The evaluation criteria are as follows.
Regarding the recording characteristics, when realizing a rewritable optical disk system, the C / N ratio is required to be at least 45 dB or more, and if it is 50 dB or more, preferably 55 dB or more, a more stable system can be realized. It is said that.
Regarding the storage reliability, the recording characteristics (shelf characteristics) when the same recording is performed after the optical recording medium after initialization is left in a constant temperature bath at 80 ° C. and 85% RH for 300 hours are evaluated. “−” Was assigned to the sample of.
Regarding the recording sensitivity, the disk having an optimum recording power of 34 mW or less was indicated by “◯”, the disk exceeding 34 mW but 36 mW or less was indicated by “Δ”, and the disk recording exceeding 36 mW was indicated by “X”.

[Example 2]
Except that the material of the low thermal conductivity layer 4 was changed to ZrO ₂ (including 3 mol% Y ₂ O ₃ ) -20 mol% TiO ₂ (κ≈2.0 W / m · K), the same as in Example 1. Thus, an optical recording medium was prepared and initialized, and then evaluated.

[Example 3]
Except that the material of the low thermal conductivity layer 4 is changed to ZrO ₂ (including 3 mol% Y ₂ O ₃ ) -10 mol% SiO ₂ (κ≈3.5 W / m · K), the same as in Example 1. Thus, an optical recording medium was prepared and initialized, and then evaluated.

[Example 4]
Example 1 except that the material of the low thermal conductivity layer 4 was changed to ZrO ₂ (including 3 mol% Y ₂ O ₃ ) -20 mol% Al ₂ O ₃ (κ≈3.5 W / m · K). An optical recording medium was prepared and initialized in the same manner as described above, and then evaluated.

[Example 5]
An optical recording medium was produced and initialized in the same manner as in Example 1 except that the thickness of the low thermal conductivity layer 4 was changed to 1 nm and evaluated.

[Example 6]
Except that the thickness of the low thermal conductivity layer 4 was changed to 2 nm, an optical recording medium was prepared and initialized in the same manner as in Example 1, and then evaluated.

[Example 7]
An optical recording medium was prepared and initialized in the same manner as in Example 1 except that the thickness of the low thermal conductivity layer 4 was changed to 6 nm and evaluated.

[Example 8]
An optical recording medium was fabricated in the same manner as in Example 1 except that the material of the phase change recording layer 3 was changed to Ga ₁₂ Sb ₈₀ Sn ₈ .
Compared to Example 1, in this example, a recording layer was used in which Sn was added to reduce the Sb ratio in the recording layer material, instead of increasing the crystallization speed and improving recording sensitivity.
When this optical recording medium was initialized and evaluated in the same manner, a high C / N ratio was obtained at a recording linear velocity of 28 m / s, and there was almost no deterioration even after an environmental test at 80 ° C. and 85% RH. I understand. In addition, a uniform and high reflectance optical recording medium can be obtained with a lower initialization power than in Example 1, and the addition of Sn can further increase the crystallization speed. Recording at a speed of 35 m / s (10 times the speed of DVD) was also good.

[Example 9]
An optical recording medium was produced in the same manner as in Example 1 except that the material of the phase change recording layer 3 was changed to Ge ₁₂ Sb ₈₀ Sn ₈ .
Compared to Example 1, in this example, Ga in the recording layer material is replaced with Ge which is effective in storage reliability, and the Sb ratio is further lowered, and instead the crystallization speed is increased and the recording sensitivity is improved. Also, a recording layer added with Sn, which is also effective, was used.
When this optical recording medium was initialized and evaluated in the same manner, it was possible to realize uniform and high reflectivity initialization with a lower initialization power than in Example 1, and a high recording linear velocity of 28 m / s. It was found that a C / N ratio was obtained. Furthermore, even when left under an environmental test at 80 ° C. and 85% RH for 500 hours, the characteristics hardly deteriorated and the storage reliability was very high.

[Example 10]
An optical recording medium was produced in the same manner as in Example 1 except that the material of the phase change recording layer 3 was changed to Ga ₉ Sb ₈₃ Sn ₅ Ge ₃ .
Compared to Example 1, in this example, a part of Ga in the recording layer material is replaced with Ge which is effective in improving the storage reliability, and the Sb ratio is further lowered, and instead the crystallization speed is increased. In addition, a recording layer added with Sn, which is effective in improving recording sensitivity, was used.
When this optical recording medium was initialized and evaluated in the same manner, a very high C / N ratio was obtained at a recording linear velocity of 28 m / s, and it was allowed to stand for 500 hours under an environmental test at 80 ° C. and 85% RH. However, it was also found that the characteristics were hardly deteriorated and the storage reliability was very high.

[Example 11]
An optical recording medium was produced in the same manner as in Example 1 except that the material of the phase change recording layer 3 was changed to Ga ₁₂ Sb ₈₀ Mn ₈ .
Compared to Example 1, in this example, a recording layer was used in which Mn was added, which lowers the Sb ratio in the recording layer material, increases the crystallization speed, and improves the storage reliability.
When this optical recording medium was initialized and evaluated in the same manner, a high C / N ratio was obtained at a recording linear velocity of 28 m / s, and the characteristics were maintained even when left in an environment of 80 ° C. and 85% RH for 500 hours. Almost no deterioration and very high storage reliability.
Further, by adding Mn, the crystallization speed can be increased without impairing the storage reliability, and recording at a recording linear speed of 35 m / s (10 times the speed of DVD) was also good.

[Example 12]
An optical recording medium was fabricated and initialized in the same manner as in Example 1 except that the phase change recording layer 3 was changed to Ga ₄ Sb ₇₁ Sn ₁₈ Ge ₇ having a thickness of 14 nm and the thickness of the reflective layer 5 was changed to 200 nm. And then evaluated.

[Example 13]
An optical recording medium was prepared and initialized in the same manner as in Example 12 except that the material of the low thermal conductivity layer 4 was changed to ZrO ₂ (including 3 mol% Y ₂ O ₃ ) -20 mol% TiO ₂ . Later, it was evaluated.

[Example 14]
An optical recording medium was prepared and initialized in the same manner as in Example 12 except that the material of the low thermal conductivity layer 4 was changed to ZrO ₂ (including 3 mol% Y ₂ O ₃ ) -10 mol% SiO ₂ . Later, it was evaluated.

[Example 15]
An optical recording medium was prepared in the same manner as in Example 12 except that the material of the low thermal conductivity layer 4 was changed to ZrO ₂ (including 3 mol% Y ₂ O ₃ ) -20 mol% Al ₂ O _3. And then evaluated.

[Example 16]
An optical recording medium was obtained in the same manner as in Example 12 except that the material of the low thermal conductivity layer 4 was changed to ZrO ₂ (including 3 mol% Y ₂ O ₃ ) -20 mol% TiO ₂ and 10 mol% SiO _2. Was evaluated after evaluation.

  In Examples 12 to 15, the film thickness of the phase change recording layer is 2 nm thinner and the film thickness of the reflective layer is 60 nm thicker than those of Examples 1 to 4. According to these embodiments, the storage reliability (especially shelf characteristics) of the optical recording medium is improved by reducing the film thickness of the phase change recording layer, and after overwriting 1000 times by increasing the film thickness of the reflective layer. It was confirmed that the C / N ratio was further improved. In Example 16, it was also confirmed that the C / N ratio after 1000 overwrites was further improved without deteriorating the recording sensitivity and recording characteristics as compared with Example 13.

[Example 17]
Except that the material of the low thermal conductivity layer 4 was changed to ZrO ₂ (including 3 mol% Y ₂ O ₃ ) -50 mol% TiO ₂ (κ≈1.7 W / m · K), the same as in Example 12. Thus, an optical recording medium was prepared and initialized, and then evaluated.
In this example, compared with Example 13, the C / N ratio after 1000 times of overwriting slightly decreased, but good recording characteristics exceeding 60 dB were obtained.

[Example 18]
An optical recording medium was prepared and initialized in the same manner as in Example 12 except that the material of the low thermal conductivity layer 4 was changed to TiO ₂ (κ≈6.5 W / m · K) and evaluated.
In this example, compared with Example 13, the C / N ratio after 1000 times of overwriting decreased, but good recording characteristics exceeding 50 dB were obtained.

[Comparative Example 1]
An optical recording medium was produced in the same manner as in Example 1 except that the material of the low thermal conductivity layer 4 was changed to Si ₃ N ₄ .
Si ₃ N _{4 has} a thermal conductivity of about 25 W / m · K, a thermal expansion coefficient of 3.2 × 10 ⁻⁶ / ° C., and a thermal conductivity outside the scope of the present invention.
After initializing this optical recording medium, it was evaluated in the same way. The object of the present invention is “cooperation of high heat storage and toughness by the low thermal conductivity layer and rapid cooling by the high thermal conductivity reflective layer”. Was not effectively exhibited, and a decrease in recording sensitivity was confirmed. In realizing high-speed recording, the current recording power is about 30 mW or more for the purpose of increasing the degree of modulation when the phase change material having a high crystallization speed exemplified in the present invention is used for the recording layer. It is necessary. For this reason, when the recording sensitivity is lowered, a higher output recording power is required, so that the practicality becomes poor and the optical recording medium itself is also damaged.

[Comparative Example 2]
An optical recording medium was produced in the same manner as in Example 1 except that the material of the low thermal conductivity layer 4 was changed to Al ₂ O ₃ .
Al ₂ O _{3 has} a thermal conductivity of about 30 W / m · K, a thermal expansion coefficient of 6.5 × 10 ⁻⁶ / ° C., and a thermal conductivity outside the scope of the present invention.
When this optical recording medium was initialized and evaluated in the same manner, as in Comparative Example 1, the objective of the present invention was “high heat storage action and high toughness by the low thermal conductivity layer and rapid cooling by the high thermal conductivity reflective layer. The “cooperation of action” was not effectively exhibited, and a decrease in recording sensitivity was confirmed.

[Comparative Example 3]
An optical recording medium was produced in the same manner as in Example 1 except that the material of the low thermal conductivity layer 4 was changed to CaO.
The thermal conductivity of CaO is approximately 14.4 W / m · K, the thermal expansion coefficient is 13.6 × 10 ⁻⁶ / ° C., and the thermal conductivity (and the thermal expansion coefficient in the present invention 2) is out of the scope of the present invention. It is a material.
When this optical recording medium was initialized and evaluated in the same manner, as in Comparative Example 1, the objective of the present invention was “high heat storage action and high toughness by the low thermal conductivity layer and rapid cooling by the high thermal conductivity reflective layer. "Cooperation of action" was not effectively exhibited, and the recording sensitivity was lowered and the overwrite characteristics were deteriorated.

[Comparative Example 4]
An optical recording medium was produced in the same manner as in Example 1 except that the material of the reflective layer was changed to Al.
The thermal conductivity of Al is about 240 W / m · K, which is lower than that of Ag of about 430 W / m · K. Therefore, it is expected that the quenching effect required for the reflective layer is weakened.
When this optical recording medium was initialized and evaluated in the same manner, the recording sensitivity was poor as in Comparative Example 1, and a sufficient C / N ratio was not obtained.

[Comparative Example 5]
The second protective layer 8 was changed to ZrO ₂ (containing 3 mol% Y ₂ O ₃ ) having a thickness of 4 nm, and the low thermal conductivity layer 4 was changed to ZnS—SiO ₂ (80:20 mol%) having a thickness of 7 nm. Except for this point, the optical recording medium was prepared and initialized in the same manner as in Example 1, and then evaluated. As a result, there was no tendency to improve the recording sensitivity, and the C / N ratio after 1000 overwrites deteriorated. In addition, the recording characteristics after storage have also deteriorated compared to immediately after initialization.

[Comparative Example 6]
Except that the thickness of the low thermal conductivity layer 4 was changed to 0.5 nm, the optical recording medium was prepared and initialized in the same manner as in Example 1 and evaluated. As a result, sufficient recording characteristics were not obtained. In addition, significant deterioration of the overwrite characteristics was confirmed.

[Comparative Example 7]
Except that the thickness of the low thermal conductivity layer 4 was changed to 7 nm, the optical recording medium was prepared and initialized in the same manner as in Example 1 and evaluated. As a result, sufficient recording characteristics were not obtained. The “cooperative action of the high heat storage action and toughness by the low thermal conductivity layer and the rapid cooling action by the high thermal conductivity reflective layer”, which is the object of the present invention, was not exhibited effectively, and the overwrite characteristics were not improved.

[Comparative Example 8]
Except that the second protective layer 8 was not provided, the optical recording medium was prepared and initialized in the same manner as in Example 1, and then evaluated. As a result, the C was obtained when left in an environment of 80 ° C. and 85% RH for 500 hours. The / N ratio was 45 dB, and it was found that the storage reliability was significantly deteriorated as compared with Example 1.

[Comparative Example 9]
An optical recording medium was prepared in the same manner as in Example 1 except that the material of the low thermal conductivity layer was changed to ZnS—SiO ₂ (80:20 mol%) (κ≈8.6 W / m · K). As a result of evaluation, the recording sensitivity was not improved, and the C / N ratio after 1000 overwrites was deteriorated. This comparative example is an example using a material having a low thermal conductivity layer of κ≈8.6 W / m · K, but the material of the second protective layer is also ZnS—SiO ₂ (80:20 mol%). Therefore, as a result, it can be regarded as an example in which only the second protective layer having a thickness of 11 nm is provided without providing the low thermal conductivity layer.

In each of Examples 1 to 18, a high C / N ratio of 55 dB or more was obtained after 10 times of overwriting, and a favorable result of 50 dB or more was obtained in the evaluation of the C / N ratio after 1000 times of overwriting.
In addition, it was confirmed that the deterioration was small even after leaving in a thermostatic bath at 80 ° C. and 85% RH for 300 hours, and it had good storage reliability.
Further, in Examples 2 to 4 and 13 to 16, the phase change recording layer is effectively deteriorated due to the excellent heat resistance and high hardness of SiO ₂ , TiO ₂ , and Al ₂ O ₃ contained in the low thermal conductivity layer. It was confirmed that there was no deterioration even after 1000 times of overwriting.

Also, in FIG. 3, for the optical recording media of Examples 1 and 12 and Comparative Examples 1, 2, 4, and 9, the thermal diffusion inside the phase change recording layer was performed using the commercially available thermal calculation software TEMPROFILE 5.0 (* Note). The result of calculating the state of is shown.
In TEMPFILE, a multilayer film on a flat substrate is used as a model, a plane parallel to the substrate is defined as an XY plane, and a direction perpendicular to the substrate is defined as a Z-axis direction. Each layer is defined by a film thickness, a complex refractive index, a specific heat, and a thermal conductivity. Irradiation light is perpendicularly incident from the substrate side toward the positive direction of the Z axis.
As input data, the complex refractive index of each layer is the value when λ = 660 nm, the specific heat and thermal conductivity are general bulk values (document values) of 0 ° C to 200 ° C, and the pulse waveform of the irradiation light is rotated. A waveform was input assuming that a laser beam having a symmetric Gaussian profile records a minimum mark (3T single pattern; 3T mark) in DVD 8 × recording.
(*note)
Professor of University of Arizona, USA Developed by Mansuripur, MM Research, Inc. From the thermal calculation results shown in FIG. 3, the temperature rise inside the phase change recording layer is higher in Examples 1 and 12 than in the comparative example, and the sensitivity is improved. In addition, despite the high heat reaching temperature, the time for cooling to a low temperature is almost the same as that of the comparative example, so it can be seen that the structure has a rapid cooling effect and is more suitable for the formation of amorphous marks. .

1 is a schematic cross-sectional view showing an example of an optical recording medium of the present invention. FIG. 3 is a schematic cross-sectional view of a conventional optical recording medium excluding a second protective layer 8 from FIG. 1. The figure which shows the result of having calculated the mode of the thermal diffusion inside a phase change recording layer using commercially available thermal calculation software about the optical disk of Examples 1, 12 and Comparative Examples 1, 2, 4, and 9. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 1st protective layer 3 Phase change recording layer 4 Low thermal conductivity layer 5 Reflective layer 6 Resin protective layer 7 Substrate for bonding 8 Second protective layer

Claims (14)

  On a transparent substrate, at least a first protective layer, a phase change recording layer having a maximum recording linear velocity of 10.0 to 36.0 m / s and capable of being rewritten at a high linear velocity, a second protective layer, thermal conductivity Has a reflective layer of 300 W / m · K or more, and a low heat with a film thickness of 1 to 6 nm made of a low thermal conductivity material having a thermal conductivity of 7 W / m · K or less between the second protective layer and the reflective layer. An optical recording medium comprising a conductivity layer. The optical recording medium according to claim 1, wherein the low thermal conductivity layer has a thermal expansion coefficient of 10 × 10 ⁻⁶ / ° C. or less.   3. The optical recording medium according to claim 1, wherein the low thermal conductivity material is an inorganic oxide.   4. The optical recording medium according to claim 3, wherein the inorganic oxide is an oxide or composite oxide of at least one element selected from Group IIa to IVa and Group IIb to IVb.   The optical recording medium according to claim 1, wherein the melting point of the low thermal conductivity material is equal to or higher than the melting point of the phase change recording layer material. The optical recording medium according to any one of claims 1 to 5, wherein the low thermal conductivity material is represented by the following composition formula.
(ZrO ₂ ) a (TiO ₂ ) b (SiO ₂ ) c (X1) d
[Wherein, a to d represent the ratio (mol%) of each oxide, and 50 ≦ a ≦ 100, 0 ≦ b <50, 0 ≦ c <30, 0 ≦ d <10 (a + b + c + d = 100). , X1 is at least one selected from rare earth oxides. ]   The optical recording medium according to claim 1, wherein the low thermal conductivity material contains a metal and / or metalloid carbide and / or nitride.   8. The optical recording medium according to claim 1, wherein the reflective layer is made of pure Ag or an alloy containing Ag as a main component.   The optical recording medium according to claim 1, wherein the reflective layer has a thickness of 100 to 300 nm.   The optical recording medium according to claim 1, wherein the phase change recording layer is made of an alloy containing at least Ga, Sb, Sn, and Ge.   The alloy contains at least one element selected from In, Te, Al, Zn, Mg, Tl, Pb, Bi, Cd, Hg, Se, C, N, Au, Ag, Cu, Mn, and a rare earth element. 11. The optical recording medium according to claim 10, wherein the total content of these elements is 0.1 to 10 atomic%.   The optical recording medium according to claim 1, wherein the phase change recording layer has a thickness of 6 to 20 nm. The optical recording medium according to claim 1, wherein the second protective layer is made of a mixture of ZnS and SiO ₂ . A substrate having a meandering groove with a groove pitch of 0.74 ± 0.03 μm, a groove depth of 22 to 40 nm, and a groove width of 0.2 to 0.4 μm, and a DVD of 3 to 10 times speed (10 m / s to 36 m / s) 14. The optical recording medium according to claim 1, wherein recording is possible at a recording linear velocity.

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