JP2007118557A - Multi-layer phase changing type optical recording medium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a multi-layer phase changing type optical recording medium which simultaneously solves a plurality of problems such as high speed recording characteristics, reproduction light stability and storage stability. <P>SOLUTION: The optical recording medium has a plurality of information layers containing a phase changing recording layer capable of recording information by generating phase change with irradiation with a laser light, and each information layer other than the deepest side seen from the side of irradiation with the laser light comprises a lower protective layer, the phase changing recording layer, an upper protective layer, a reflective layer and a thermal diffusion layer. The phase changing recording layer comprises at least three elements, i.e., Ge, Sb and Te, and when the compositional ratios [atom%] of the elements are α, β and γ, the requirement of 2≤α≤20, 65≤β≤90 and 3≤γ≤30 are satisfied. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a multilayer phase change type having a plurality of information layers including a phase change recording layer which records and reproduces information by optically changing the recording layer material by irradiating a light beam, and which can be rewritten. The present invention relates to an optical recording medium.

A phase change type optical disc (phase change type optical recording medium) such as a CD-RW is generally provided with a recording layer made of a phase change material on a plastic substrate, on which a light absorption rate of the recording layer is improved and The structure is basically provided with a reflective layer having a thermal diffusion effect, and information is recorded and reproduced by irradiating a laser beam from the substrate surface side.
The phase change recording material changes phase between a crystalline state and an amorphous state by heating by laser light irradiation and subsequent cooling, becomes amorphous when rapidly cooled after rapid heating, and crystallizes when cooled slowly. The phase change optical recording medium applies this property to information recording and reproduction.
Furthermore, for the purpose of preventing oxidation, transpiration or deformation of the recording layer caused by heating by light irradiation, a lower protective layer (also referred to as a lower dielectric layer), a recording layer and a reflective layer are usually provided between the substrate and the recording layer. An upper protective layer (also referred to as an upper dielectric layer) is provided therebetween. Furthermore, these protective layers have a function of adjusting the optical characteristics of the recording medium by adjusting the thickness thereof, and the lower protective layer softens the substrate by heat during recording on the recording layer. It also has a function to prevent this.

  In recent years, as the amount of information handled by computers and the like has increased, the signal recording capacity of rewritable optical discs such as DVD-RAM, DVD-RW, and DVD + RW has increased, and the density of signal information has been increasing. The current recording capacity of CDs is about 650 MB, and DVDs are about 4.7 GB. However, it is expected that the demand for higher recording density will increase in the future. In addition, it is considered that an improvement in recording speed is required as the amount of information increases. Currently, DVD rewritable discs have been developed that are capable of 8 × speed recording with a single layer. As a method for increasing the recording density using such a phase change type optical recording medium, for example, the laser wavelength used is shortened to the blue region, or the numerical aperture NA of an objective lens used for a pickup for recording / reproducing is used. Has been proposed to reduce the spot size of the laser beam irradiated to the optical recording medium, and research and development have been carried out, and further practical use has been made.

As a method of improving the recording capacity by improving the optical recording medium itself, it is created by stacking at least two information layers consisting of a recording layer and a reflective layer on one side of the substrate and bonding these information layers with an ultraviolet curable resin or the like. Various two-layer phase change optical recording media have been proposed. The separation layer (referred to as an intermediate layer in the present invention) that is an adhesive portion between the information layers has a function of optically separating the two information layers, and the information layer as far as possible from the laser beam used for recording and reproduction is used. Therefore, it is made of a material that absorbs as little light as possible.
Many problems still exist with this two-layer phase change optical recording medium. For example, if the laser beam is not sufficiently transmitted through the information layer (first information layer) on the front side when viewed from the laser beam irradiation side, information is recorded on the recording layer of the information layer (second information layer) on the back side. Since recording and reproduction cannot be performed, the reflective layer constituting the first information layer must be an extremely thin translucent reflective layer.
Recording on the phase-change optical recording medium is performed by irradiating the phase-change recording material of the recording layer with laser light to rapidly cool it to change the crystal to amorphous to form a mark. Therefore, in the case of a very thin translucent reflective layer having a film thickness of about 10 nm provided in the first information layer of the multilayer phase change optical recording medium, the heat dissipation effect becomes extremely small and it is difficult to form an amorphous mark. Become.

SbTe eutectic recording materials, which are one of the materials commonly used for phase change optical recording media such as CD-RW and DVD + RW, have an excellent erasure ratio compared to GeSbTe compound recording materials. Since it is highly sensitive, it is known as being excellent in that the outline of the amorphous portion of the recording mark is clear. However, since the SbTe eutectic recording material has a higher crystallization speed than the GeSbTe compound-based recording material, it needs to be rapidly cooled in order to become amorphous, and requires a rapid cooling structure. It is. Further, when the amount of Sb increases to some extent, there arises a problem that the crystallization temperature of the material is lowered. For this reason, there are problems that the amorphous mark is recrystallized just by irradiating the reproduction light and the information cannot be read, and that the information storage state at room temperature is deteriorated.
The following is mentioned as well-known literature considered to be related to the present invention.
First, Patent Documents 1 to 3 disclose an optical recording medium using a GeSbTe ternary material for a recording layer, but there is no description regarding an optical recording medium including two or more recording layers.
Patent Documents 4 to 13 disclose multilayer phase change optical recording media using a material mainly composed of SbTe for the recording layer, but there is no description regarding the composition ratio of the GeSbTe ternary system.
Further, Patent Document 14 discloses a multilayer phase change optical recording medium, but there is no description about a GeSbTe ternary system.
Patent Documents 15 to 16 disclose a two-layer phase change optical recording medium provided with a recording layer mainly composed of Ge, Sb, and Te, but there is no description that limits the composition ratio.

Japanese Patent No. 3584634 Japanese Patent No. 3485040 Japanese Patent No. 3494044 JP 2004-259382 A JP 2004-110911 A JP 2003-296966 A JP 2003-242687 A JP-A-2005-004943 JP 2004-110913 A JP 2004-47038 A JP 2003-45085 A JP 2004-185744 A JP 2004-95092 A JP 2002-100071 A JP 2001-195777 A Japanese Patent No. 3250899

  An object of the present invention is to provide a multilayer phase change type optical recording medium that simultaneously solves a plurality of problems of high-speed recording characteristics, reproduction light stability, and storage stability.

The above problems are solved by the following inventions 1) to 6) (hereinafter referred to as the present inventions 1 to 6).
1) A plurality of information layers including a phase change recording layer capable of recording information by causing a phase change by laser light irradiation, and each information other than the innermost side when viewed from the laser light irradiation side. In an optical recording medium in which the layer is composed of at least a lower protective layer, a phase change recording layer, an upper protective layer, a reflective layer, and a heat diffusion layer, the phase change recording layer is composed of at least three elements of Ge, Sb, and Te. A multilayer phase change optical recording medium characterized by satisfying the following requirements when the respective composition ratios [atomic%] are α, β, and γ.
2 ≦ α ≦ 20
65 ≦ β ≦ 90
3 ≦ γ ≦ 30
2) The multilayer phase change optical recording medium according to 1), wherein the reflective layer of the information layer other than the innermost layer as viewed from the side irradiated with the laser light contains Cu as a main component.
3) The multilayer phase change type according to 1) or 2), wherein the upper protective layer of the information layer other than the innermost layer as viewed from the side irradiated with the laser light is mainly composed of an oxide of Sn. Optical recording medium.
4) The multilayer phase change optical recording medium according to any one of 1) to 3), wherein the thermal diffusion layer is mainly composed of an oxide of In.
5) The multilayer phase change optical recording medium according to 4), wherein the thermal diffusion layer contains an oxide of Zn.
6) The multilayer phase change optical recording medium according to 4), wherein the thermal diffusion layer contains an oxide of Sn.

Hereinafter, the present invention will be described in detail.
There are roughly two types of conventional recording layer material development. Namely, GeTe which is a write-once recording layer material, Sb ₂ Te ₃ which is an alloy of Sb and Te capable of reversibly phase change, and GeSbTe ternary born from the solid solution or eutectic composition of these two materials. A recording layer material made of an alloy is one flow. Another flow is an alloy of Sb and Te, but a recording layer material in which a trace element is added to SbTe whose eutectic composition of Sb and Sb ₂ Te ₃ is about 70%. It is.
In the optical recording medium having a two-layer recording layer, the information layer on the near side as viewed from the laser light irradiation side is required to have high transmittance in consideration of recording and reproduction of the information layer on the back side, For this purpose, it is required to make the recording layer thinner in parallel with efforts to reduce the absorption rate of the metal layer. As the thickness of the recording layer is reduced, the crystallization speed decreases, so it is advantageous to make the recording layer material itself have a high crystallization speed. Therefore, in the flow of the above material series, the latter SbTe eutectic composition in which the Sb content is about 70% is preferable.
However, according to a study by the present inventors, when the Sb amount is increased in order to increase the crystallization speed, that is, in order to increase the corresponding linear speed, the crystallization temperature is lowered and the storage is continued. It was found that the characteristics deteriorated.

In a two-layer phase change optical recording medium, when reproducing the information layer on the back side as viewed from the laser light irradiation side, the reflectance is low due to absorption by the information layer on the near side, and the amplitude of the reproduction signal is low. There is a problem of being small. Considering this, a higher reproducing light power is required than when reproducing with an optical recording medium having a single recording layer.
In the SbTe system, the amount of Sb may be increased in order to increase the crystallization speed, but this tends to lower the crystallization temperature. Therefore, when the SbTe system is used for the information layer on the front side, if a high reproduction light power is used, there arises a problem that the amorphous mark is recrystallized and cannot be reproduced. At the same time, lowering the crystallization temperature is not preferable because the storage state becomes unstable. Therefore, by adding the third element Ge to the SbTe system, the crystallization temperature is kept high. As a result, the amorphous mark is not recrystallized even when reproduced with high reproduction light power, and the storage state can be stabilized.
As described above, in the phase change recording layer used in the multilayer phase change optical recording medium, the phase change recording material has good recording characteristics, can be reproduced even with high reproduction light power, and can stabilize the storage state. What consists of three elements of GeSbTe is preferable.
Further, other materials may be added to the GeSbTe three-element system. As the additive element, Ag, In, or the like is preferable, and is used for improving storage characteristics. The total composition ratio of the additive elements is preferably 8 atomic% or less. If it exceeds 8 atomic%, the storage characteristics are good, but the crystallization speed of the recording layer is slow, and it becomes difficult to record at high speed. Further, it is not preferable because the stability of the recording state with respect to the reproduction light is deteriorated.

Next, the layer configuration of an optical recording medium having two information layers including a phase change recording layer and the characteristics of each layer will be described with reference to FIG.
As defined in the present invention 1, when the Sb amount (β) is in the range of 65 ≦ β ≦ 90 (atomic%), stable recording and reproduction can be performed as a phase change recording material. If the Sb content is less than 65 atomic%, stable recording cannot be performed, and the recording layer is not suitable for high-speed recording as a multilayer phase change optical recording medium. If the Sb content exceeds 90 atomic%, the crystallization speed is improved, but the crystallization temperature starts to decrease, making it difficult to reproduce with high reproduction light power, and the storage state becomes unstable.

Te promotes amorphization and improves the crystallization temperature, but is effective. However, when only Te is combined with Sb alone, the crystallization speed can be adjusted by utilizing the action of promoting amorphization, but the crystallization temperature is not sufficiently increased, which improves the stability of the amorphous phase. Therefore, the recorded amorphous mark may be lost by long-term storage or high-temperature storage. On the other hand, when Te is used in combination with Ge, there is an advantage that the stability of the amorphous phase is ensured by Ge and the stability of the crystal phase is further improved. The crystal state is generally a highly stable state. However, in the case of a high-speed recording material as described here, since the crystallization proceeds at a high speed at the time of initialization or recording, the formed crystal state is not necessarily It's not stable. For this reason, when recording is performed again after long-term storage or after high-temperature storage, there arises a problem that recording characteristics and recording conditions are changed from those before storage. This is presumably because the crystal state changed due to storage compared to before storage. However, when Te is added, the deviation in recording characteristics and recording conditions due to such storage can be reduced.
The film thickness of the first recording layer is preferably in the range of 4 to 12 nm. If it is thinner than 4 nm, the reflectance becomes too low, the signal quality is lowered, and the repeated recording characteristics are also deteriorated. If it is thicker than 12 nm, the light transmittance decreases, which is not preferable.
The thickness of the second information layer is preferably in the range of 10 to 20 nm. If it is thinner than 10 nm, the repeated recording characteristics are deteriorated, and if it is thicker than 20 nm, the recording sensitivity is deteriorated.

In order to obtain the effect of reducing the deviation in recording characteristics and recording conditions before and after storage by improving the stability of the crystal in this way, it is desirable to add Te at 3 atomic% or more (3 ≦ γ). However, if the amount is too large, the crystallization speed becomes too slow, and high-speed repeated recording cannot be performed. When used in at least the first recording layer of the two-layer phase change optical recording medium, it is preferable that the amount of Te is within 30 atomic% (γ ≦ 30).
In addition, when the Ge amount (α) is in the range of 2 ≦ α ≦ 20 (atomic%), reproduction with high power is possible, and the storage state can be improved. If the amount of Ge is less than 2 atomic%, the effect of adding Ge does not appear and the storage state is not good. Further, when the Ge content is more than 20 atomic%, the crystallization temperature can be increased, so that the stability of the reproduction light and the storage characteristics are improved, but the recording sensitivity is deteriorated due to the high melting point of Ge itself. The trouble that it ends up occurs.
The film thickness of the first recording layer is preferably in the range of 4 to 12 nm. If it is thinner than 4 nm, the reflectivity becomes too low, the signal quality is lowered, and the repeated recording characteristics are poor. If it is thicker than 12 nm, the light transmittance decreases, which is not preferable. The film thickness of the second recording layer is preferably in the range of 10 to 20 nm. If it is thinner than 10 nm, the repeated recording characteristics are deteriorated, and if it is thicker than 20 nm, the recording sensitivity is deteriorated.

In the second aspect of the present invention, Cu is used as a main component of the reflective layer (heat radiation layer) of the information layer other than the innermost side when viewed from the side irradiated with the laser beam. Thereby, it is possible to improve the recording characteristics and the storage characteristics in the first recording layer. Here, the main component means that 98% by weight or more of Cu is contained. The reason why the first reflective layer (heat radiating layer) mainly composed of Cu is suitable will be described below.
As shown in FIG. 1, in a phase change type optical recording medium having two recording layers, it is necessary to transmit laser light for recording / reproduction as much as possible to the second information layer. Therefore, it is preferable to use a material that does not easily absorb and transmits laser light for the first reflective layer.
Therefore, the present inventors performed optical measurement at various wavelengths of 660 nm for various reflective layers. Here, data of A (absorbance), R (reflectance), and T (transmittance) were measured. As a measurement sample, a metal film having a thickness of 10 nm was formed on a 0.6 mm polycarbonate substrate. The result is shown in FIG. From this result, it is expected that Pt, Pd, and Ti are not preferable as the first reflective layer because they have low transmittance and high absorption.

Next, when Cu and Ag having a relatively high transmittance and a relatively low absorption rate were investigated by changing (changing) the film thickness, the results shown in FIGS. 3 (Cu) and 4 (Ag) were obtained. It was. That is, it was found that the change due to the film thickness was larger in Ag. This indicates that Cu is more excellent in the stability of the optical constant with respect to the film thickness when the film is formed. Furthermore, the measurement result of the spectral transmittance is shown in FIG. 5, and it was found that the transmittances of Ag and Cu intersect in the wavelength region of about 450 nm. Accordingly, Cu has higher transmittance in a wavelength region longer than the wavelength region of about 450 nm, and it is preferable to use Cu as the first reflective layer for laser light in the vicinity of 660 nm. I understand.
Further, for each recording medium using Cu, Ag, and Au for the first reflective layer, a 3T single pattern was recorded on the first recording layer at a wavelength of 660 nm, and the C / N was measured, as shown in FIG. As a result. That is, the highest C / N was obtained when Cu was used. Thus, it was found that Cu is preferable from the viewpoint of recording characteristics. Each plot is obtained by arranging a plurality of experimental data horizontally.
The second reflective layer need not be translucent like the first reflective layer.

The film thickness of the first reflective layer is preferably in the range of 6 to 12 nm. If the thickness is less than 6 nm, the reflectivity becomes too low, the signal quality is deteriorated, and the heat dissipation is deteriorated, so that the repeated recording characteristics are deteriorated. If it is thicker than 12 nm, the light transmittance decreases, which is not preferable.
The thickness of the second reflective layer is preferably in the range of 100 to 200 nm. If the thickness is less than 100 nm, sufficient heat dissipation cannot be obtained and the recording characteristics are repeatedly deteriorated. If the thickness is more than 200 nm, a wasteful film thickness is formed even though the heat dissipation does not change. Mechanical properties deteriorate.
The first reflective layer and the second reflective layer as described above are formed by various vapor phase growth methods such as vacuum vapor deposition, sputtering, plasma CVD, photo CVD, ion plating, electron beam vapor deposition, and the like. it can. Among these, the sputtering method is excellent in mass productivity and film quality.

In the third aspect of the present invention, Sn oxide is used as the main component of the upper protective layer of the information layer other than the innermost layer when viewed from the side irradiated with the laser beam. Here, the main component means that 50 mol% or more of Sn oxide is contained.
The material used for the upper protective layer in the single-layer phase change optical recording medium is preferably made of a material that is transparent, allows light to pass through, and has a higher melting point than the recording layer, and prevents deterioration and deterioration of the recording layer. In particular, ZnS—SiO ₂ is often used, and the mixing ratio in this case is ZnS: SiO ₂ = 80: 20 (molar ratio). Most preferred.
However, in the case of a multilayer phase change type optical recording medium, when recording on the first recording layer, the film thickness of the first reflective layer is so thin that heat dissipation becomes poor and recording becomes difficult. Therefore, it is better to use a material having as good a thermal conductivity as possible for the first upper protective layer. Therefore, it is preferable to use an oxide of Sn that has higher heat dissipation than ZnS—SiO ₂ . Further, the oxide of Sn may contain a metal-based oxide (for example, In oxide, Zn oxide, Ta oxide, Al oxide). By using the Sn oxide, it is easy to form an amorphous mark on the first recording layer even if the first reflective layer is relatively thin. Sn oxide, Ta oxide, and Al oxide are all materials that do not promote deterioration with respect to the reflective layer, and the respective composition ratios may be selected depending on the production process, cost, allowable production time, and the like. However, when there are many Sn oxides and Zn oxides, the power required for recording tends to increase in order to accelerate the crystallization speed of the recording layer. When the amount of Ta oxide is large, the film formation rate does not decrease, but it becomes difficult to obtain recording characteristics in the first information layer. When the amount of Al oxide is large, the deposition rate tends to decrease. When there are many In oxides, material cost becomes high.

As for the second upper protective layer, ZnS—SiO ₂ may be used as usual, or Sn oxide may be used. The reason is that when recording on the second recording layer, the second reflective layer can be formed sufficiently thick, so that sufficient heat dissipation is obtained.
The film thickness of the first upper protective layer is preferably in the range of 2 to 30 nm. If it is thinner than 2 nm, the reflectivity becomes too high and the modulation degree is lowered. If it is thicker than 30 nm, the light transmittance is lowered, which is not preferable, and heat is easily generated, so that the recording characteristics are deteriorated.
The film thickness of the second upper protective layer is preferably in the range of 3 to 30 nm. If it is thinner than 3 nm, the recording sensitivity is deteriorated, and if it is thicker than 30 nm, heat is easily generated and recording characteristics are deteriorated.

The first lower protective layer and the second lower protective layer are preferably made of a material that is transparent, allows light to pass through, and has a melting point higher than that of the recording layer, prevents deterioration and deterioration of the recording layer, and increases the adhesive strength with the recording layer. The metal oxide, nitride, sulfide, carbide, etc. are mainly used. Examples include metal oxides such as SiO, SiO ₂ , ZnO, SnO ₂ , Al ₂ O ₃ , TiO ₂ , In ₂ O ₃ , MgO, ZrO ₂ , Si ₃ N ₄ , AlN, TiN, BN, ZrN, etc. Examples thereof include nitrides, sulfides such as ZnS, In ₂ S ₃ , and TaS ₄ , carbides such as SiC, TaC, B ₄ C, WC, TiC, and ZrC, diamond-like carbon, and mixtures thereof. These materials can be used alone as a protective film, but they may be mixed with each other. Further, impurities may be included as necessary. For example, a mixture of ZnS and SiO _{2 or} a mixture of Ta ₂ O ₅ and SiO ₂ can be used. In particular, ZnS—SiO ₂ is often used. In this case, the mixing ratio is most preferably ZnS: SiO ₂ = 80: 20 (molar ratio). Since this material has a high refractive index n and an extinction coefficient k of almost zero, the light absorption efficiency of the recording layer can be increased, and since the thermal conductivity is small, the diffusion of heat generated by light absorption can be reduced. Since it can be moderately suppressed, the temperature of the recording layer can be raised to a melting temperature.

The film thickness of the first lower protective layer is preferably in the range of 40 to 80 nm. If it is thinner than 40 nm, the repeated recording durability deteriorates and the recording characteristics deteriorate. If it is thicker than 80 nm, the light transmittance decreases, which is not preferable.
The thickness of the second lower protective layer is preferably in the range of 110 to 160 nm. If the thickness is less than 110 nm, the reflectance is lowered and the reproduction signal quality is deteriorated. When it is thicker than 160 nm, the mechanical properties of the recording medium itself are deteriorated.
The first and second upper protective layers and the first and second lower protective layers as described above are formed by various vapor deposition methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating. Or by electron beam evaporation. Among these, the sputtering method is excellent in mass productivity and film quality.

In the present invention 4, an oxide of In is used as the main component of the thermal diffusion layer. Here, the main component means that 90 mol% or more of In oxide is contained. As the thermal diffusion layer, it is desirable that the thermal conductivity be high in order to quench the first recording layer irradiated with the laser beam. It is also desirable that the absorption rate at the laser wavelength is small so that the second information layer on the back side can be recorded and reproduced.
Therefore, it preferably contains at least one of nitride, oxide, sulfide, carbide, and fluoride. Examples thereof include AlN, Al ₂ O ₃ , SiC, SiN, IZO (indium oxide-zinc oxide), ITO (indium oxide-tin oxide), DLC (diamond-like carbon), and BN. Among them, IZO (corresponding to the present invention 5) and ITO (corresponding to the present invention 6) are considered most preferable.

First, it is preferable that 1 to 10% by weight of tin oxide contained in ITO (indium oxide-tin oxide) is contained. If it is out of this range, the thermal conductivity and transmittance will decrease. Further, other elements may be added for the purpose of improving storage stability. These elements can be added within a range that does not affect the optical properties, and are preferably contained in an amount of 0.1 to 5% by weight. If it is less than 0.1% by weight, the effect cannot be obtained. On the other hand, when the amount is more than 5% by weight, the light absorption increases and the transmittance decreases. In addition, at the wavelength of the laser beam used for recording / reproducing information, the absorption coefficient is preferably 1.0 or less, and more preferably 0.5 or less. If the absorption coefficient is larger than 1.0, the absorption rate in the first information layer increases, and recording / reproduction of the second information layer becomes difficult.
In addition, when IZO (indium oxide-zinc oxide) is used instead of ITO (indium oxide-tin oxide), the internal stress in the optical recording medium is reduced, so that a very small change in film thickness hardly occurs. preferable.
The thickness of the thermal diffusion layer is preferably in the range of 40 to 80 nm. If it is thinner than 40 nm, the heat dissipation becomes poor and the repeated recording characteristics deteriorate. If it is thicker than 80 nm, the light transmittance decreases, which is not preferable.
The thermal diffusion layer as described above can be formed by various vapor phase growth methods such as vacuum vapor deposition, sputtering, plasma CVD, photo CVD, ion plating, electron beam vapor deposition and the like. Among these, the sputtering method is excellent in mass productivity and film quality.

The first substrate needs to sufficiently transmit light irradiated for recording / reproduction, and those conventionally known in the technical field are applied. As the material, glass, ceramics, or resin is usually used, and resin is particularly preferable in terms of moldability and cost.
Examples of the resin include polycarbonate resin, acrylic resin, epoxy resin, polystyrene resin, acrylonitrile-styrene copolymer resin, polyethylene resin, polypropylene resin, silicon resin, fluorine resin, ABS resin, and urethane resin. Acrylic resins such as polycarbonate resin and polymethyl methacrylate (PMMA), which are excellent in terms of moldability, optical characteristics, and cost, are preferable.
On the surface on which the information layer on the first substrate is formed, a spiral or concentric groove for tracking the laser beam is formed as necessary, and a concave / convex pattern usually referred to as a groove portion or a land portion is formed. This is usually formed by an injection molding method or a photopolymer method. The thickness of the first substrate is preferably about 10 to 600 μm.
As the material of the second substrate, the same material as that of the first substrate may be used, but a material opaque to the recording / reproducing light may be used, and the material and groove shape may be different from those of the first substrate. Good. The thickness of the second substrate is not particularly limited, but it is preferable to select the thickness of the second substrate so that the total thickness with the first substrate is 1.2 mm.

The intermediate layer preferably has low light absorption at the wavelength of light irradiated for recording / reproduction, and the material is preferably a resin in terms of moldability and cost, and is an ultraviolet curable (UV) resin, slow-acting. Resins, thermoplastic resins, and the like can be used.
The second substrate and the intermediate layer may be provided with uneven patterns such as grooves and guide grooves formed by an injection molding method or a photopolymer method, similar to the first substrate.
The intermediate layer is a layer that enables the pickup to discriminate between the first information layer and the second information layer and perform optical separation when recording / reproducing, and the thickness is preferably 10 to 70 μm. If the thickness is less than 10 μm, crosstalk between information layers occurs. On the other hand, when the thickness is larger than 70 μm, spherical aberration occurs when recording / reproducing the second recording layer, and recording / reproduction tends to be difficult.

The two-layer phase change optical recording medium of the present invention is usually produced through a film formation process, an initialization process, and an adhesion process.
In the film forming step, the first information layer is formed on the surface of the first substrate of FIG. 1 on which the groove is provided, and the second information layer is formed on the surface of the second substrate on which the groove is provided. The first information layer and the second information layer can be formed by various vapor deposition methods such as vacuum deposition, sputtering, plasma CVD, photo CVD, ion plating, and electron beam deposition. Among them, the sputtering method is excellent in mass productivity and film quality. In the sputtering method, film formation is generally performed while flowing an inert gas such as argon. At this time, reactive sputtering may be performed while oxygen, nitrogen, or the like is mixed.
In the initialization step, the entire surface is initialized by irradiating the first information layer and the second information layer with energy light such as laser light, that is, the recording layer is crystallized. If there is a possibility that the film may float due to laser light energy during the initialization process, before the initialization process, spin coat UV resin or the like on the first information layer and the second information layer, It may be cured by irradiating with ultraviolet rays, and an overcoat may be applied. Moreover, after performing the contact | adherence process previously, you may initialize a 1st information layer and a 2nd information layer from the 1st board | substrate side.
In the adhesion process, the first substrate and the second substrate are bonded to each other through the intermediate layer while the first information layer and the second information layer face each other. For example, UV resin is applied to any one of the film surfaces, the film surfaces are faced to each other, both substrates are pressed and adhered, and the resin is cured by irradiating ultraviolet rays.

  ADVANTAGE OF THE INVENTION According to this invention, the multilayer phase change type | mold optical recording medium which solved simultaneously the several subject of a high-speed recording characteristic, reproduction light stability, and storage stability can be provided.

  EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further more concretely, this invention is not limited by these Examples.

Example 1
ZnS (80 mol%)-SiO ₂ (20 mol%) is formed on a first substrate made of a polycarbonate resin having a diameter of 12 cm and a thickness of 0.6 mm and having a tracking guide unevenness on one side with a track pitch of 0.74 μm. ), A first lower protective layer having a thickness of 60 nm, a first recording layer having a thickness of 8 nm, made of Ge ₅ Sb ₈₆ Te ₉ , In ₂ O ₃ (9.2 mol%)-ZnO (27.5 mol%). A first upper protective layer with a thickness of 12.5 nm made of -SnO ₂ (53.3 mol%)-Ta ₂ O ₅ (10 mol%), a first reflective (heat dissipation) layer with a thickness of 8 nm made of Cu, In _A first information diffusion layer was formed by sputtering in an Ar gas atmosphere in the order of a 60 nm-thickness first thermal diffusion layer made of ₂ O ₃ (90 mol%)-ZnO (10 mol%).
Further, a substrate similar to the first substrate is used as the second substrate, and a second reflective (heat radiation) layer made of Ag having a thickness of 140 nm, SnO ₂ (80 mol%)-Ta ₂ O ₅ (4 mol) is formed on the second substrate. %)-Al ₂ O ₃ (16 mol%) 11 nm thick second upper protective layer, Ag _0.2 In _3.5 Sb _71.4 Te _21.4 Ge _3.5 thick 14 nm thick The second recording layer and the second lower protective layer having a thickness of 120 nm made of ZnS (80 mol%)-SiO ₂ (20 mol%) are formed in this order by sputtering in an Ar gas atmosphere, and the second information layer is formed. Next, the first information layer and the second information layer were irradiated with laser light from the first substrate side and the second information layer film side, respectively, and an initialization process was performed. Initialization was performed by condensing the laser beam emitted from the semiconductor laser (emission wavelength 810 ± 10 nm) with an optical pickup (NA = 0.55). The initialization condition of the first recording layer is that the first substrate provided with the first information layer is rotated by CLV (constant linear velocity) mode, the linear velocity is 3 m / s, the feed amount is 36 μm / rotation, the radial position is 23 mm to 58 mm, The initialization power was 700 mW. The initialization condition of the second recording layer is that the second substrate provided with the second information layer is rotated in the CLV (constant linear velocity) mode, the linear velocity is 2 m / s, the feed amount is 36 μm / rotation, the radial position is 23 mm to 58 mm, The initialization power was 660 mW.
Next, an ultraviolet curable resin is applied on the film surface side of the first information layer, the second information layer surface side of the second substrate is bonded and spin-coated, and ultraviolet rays are irradiated from the first substrate side to be cured. A two-layer phase change optical recording medium having two information layers shown in FIG. 1 as an intermediate layer having a thickness of 40 μm was prepared.
The sputtering apparatus is an 8-channel single wafer sputtering apparatus manufactured by Balzers.

(Examples 2-18, Comparative Examples 1-6)
Each of the two-layer phase change optical recording media of Examples 2 to 12 and Comparative Examples 1 to 6 is the same as Example 1 except that the material of the first recording layer is changed to that of the composition shown in Table 1. Created.
Further, except that the material of the first recording layer was changed to the composition shown in Table 1, and the first thermal diffusion layer was changed to In ₂ O ₃ (90 mol%)-SnO ₂ (10 mol%), In the same manner as in Example 1, each two-layer phase change optical recording medium of Examples 13 to 18 was prepared.

Each of the two-layer phase change optical recording media of Examples 1 to 18 and Comparative Examples 1 to 6 was evaluated. The results are summarized in Table 1.
As an evaluation device, DVDtester LM330A manufactured by Shiba Soku Co., Ltd. is used, the laser wavelength irradiated when recording on the recording layer is 660 nm, and the recording linear velocity when recording on the first recording layer is as shown in Table 1. The numerical aperture NA of the objective lens is 0.65. The reproducing light power was 1.4 mW.
Evaluation was performed by repeatedly recording 10 times on 3 adjacent tracks of the recording layer, and reproducing the middle track. The recording method used was a 1T periodic recording strategy, and the characteristic evaluation was data-to-clock jitter (DC jitter) when marks and spaces of 3T to 11T and 14T were randomly recorded. The DC jitter represents the time lag between the boundary and the clock when the reflectance level of the mark and space is binarized at the slice level. The lower this value, the better the recording characteristics. A DC jitter of 10% or less is a pass criterion. Note that the pulse width of the recording strategy when recording information on the second recording layer was 0.4T.
In addition, an experiment was conducted to confirm the storage stability. The storage condition was that the phase change optical recording medium was stored for 100 hours in an environment of 80 ° C. and 85%. As a result of measuring the jitter of the recording layer after 100 hours, the increase amount is suppressed to 1% or less compared to the jitter before storage, and the case where the increase amount is suppressed to 1.5% or less. The case where it exceeded 5% was set as x.

  Examples 19 to 24 below demonstrate the effects of further experiments on the multilayer phase change optical recording medium of the first invention. Note that the pulse width of the recording strategy when recording information on the second recording layer was 0.4T.

Example 19
ZnS (80 mol%)-SiO ₂ (20 mol%) is formed on a first substrate made of a polycarbonate resin having a diameter of 12 cm and a thickness of 0.6 mm and having a tracking guide irregularity with a continuous groove having a track pitch of 0.74 μm on one side. ), A first lower protective layer having a thickness of 60 nm, a first recording layer having a thickness of 8 nm, made of Ag _0.6 In _5.5 Sb _71.4 Te ₁₉ Ge _3.5 , and In ₂ O ₃ (9.2). Mol 1) -ZnO (27.5 mol%)-SnO ₂ (53.3 mol%)-Ta ₂ O ₅ (10 mol%) 12.5 nm thick first upper protective layer, Mo A 10 nm-thick first reflective (heat dissipation) layer made of Cu containing 1 wt% and a 60 nm-thick first heat diffusion layer made of In ₂ O ₃ (90 mol%)-ZnO (10 mol%) in this order. Sputtering in Ar gas atmosphere Deposited by ring method to form a first information layer.
Further, a substrate similar to the first substrate is used as the second substrate, and a second reflective (heat radiation) layer made of Ag having a thickness of 140 nm, SnO ₂ (80 mol%)-Ta ₂ O ₅ (4 mol) is formed on the second substrate. %)-Al ₂ O ₃ (16 mol%) and a second upper protective layer having a film thickness of 11 nm, and second film having a film thickness of 15 nm made of Ag _0.6 In _5.5 Sb _71.4 Te ₁₉ Ge _3.5 . A recording layer and a 140 nm-thick second lower protective layer made of ZnS (80 mol%)-SiO ₂ (20 mol%) were formed in this order by sputtering in an Ar gas atmosphere to form a second information layer. .
Next, the first information layer and the second information layer were irradiated with laser light from the first substrate side and the second information layer film surface side, respectively, and an initialization process was performed. Initialization was performed by condensing the laser beam emitted from the semiconductor laser (emission wavelength 810 ± 10 nm) with an optical pickup (NA = 0.55). The initialization condition of the first recording layer is that the first substrate provided with the first information layer is rotated by CLV (constant linear velocity) mode, the linear velocity is 3 m / s, the feed amount is 36 μm / rotation, the radial position is 23 mm to 58 mm, The initialization power was 620 mW. The initialization condition of the second recording layer is that the second substrate provided with the second information layer is rotated in the CLV (constant linear velocity) mode, the linear velocity is 2 m / s, the feed amount is 36 μm / rotation, the radial position is 23 mm to 58 mm, The initialization power was 660 mW.
Next, an ultraviolet curable resin is applied on the film surface side of the first information layer, the second information layer surface side of the second substrate is bonded and spin-coated, and ultraviolet rays are irradiated from the first substrate side to be cured. A two-layer phase change optical recording medium having two information layers shown in FIG. 1 as an intermediate layer having a thickness of 40 μm was prepared.
The sputtering apparatus is an 8-channel single wafer sputtering apparatus manufactured by Balzers.

For the two-layer phase change optical recording medium, ODU-1000 manufactured by Pulstec Co., Ltd. was used as a recording device, recording linear velocity 15.3 m / s, recording power Pp = 30 mW, erasing power Pe = 6 mW, bias power Pb Recording was performed at a setting of 0.1 mW. The width of the multipulse was 0.3T.
When recording was repeated 100 times on the same track for each of the first and second recording layers, the DC jitter of the first recording layer was 9.2%, and the DC jitter of the second recording layer was 8.1%. Met. Further, when recording was repeated 1000 times, the DC jitter of the first recording layer was 9.8%, and the DC jitter of the second recording layer was 8.9%, which was good.

(Example 20)
The same recording apparatus was used for the same two-layer phase change optical recording medium as in Example 19, recording linear velocity 9.2 m / s, recording power Pp = 28 mW, erasing power Pe = 5.5 mW, bias power Pb = Recording was performed at a setting of 0.1 mW. The width of the multipulse was 0.2T.
When each of the first and second recording layers was recorded 100 times on the same track, the DC jitter of the first recording layer was 8.6%, and the DC jitter of the second recording layer was 8.2%. Met. Further, when recording was repeated 1000 times, the DC jitter of the first recording layer was 9.8%, and the DC jitter of the second recording layer was 8.7%, which was good.

(Example 21)
The same recording apparatus was used for the same two-layer phase change optical recording medium as in Example 19, recording linear velocity 8.4 m / s, recording power Pp = 26 mW, erasing power Pe = 5.4 mW, bias power Pb = Recording was performed at a setting of 0.1 mW. The width of the multipulse was 0.2T.
When recording was repeated 100 times on the same track for each of the first and second recording layers, the DC jitter of the first recording layer was 8.3%, and the DC jitter of the second recording layer was 8.2%. Met. Further, when recording was repeated 1000 times, the DC jitter of the first recording layer was 8.8%, and the DC jitter of the second recording layer was 8.7%, which was good.

(Example 22)
The same recording apparatus was used for the same two-layer phase change optical recording medium as in Example 19, recording linear velocity 7.7 m / s, recording power Pp = 24 mW, erasing power Pe = 5.2 mW, bias power Pb = Recording was performed at a setting of 0.1 mW. The width of the multipulse was 0.15T.
When recording was repeated 100 times on the same track for each of the first and second recording layers, the DC jitter of the first recording layer was 8.5% and the DC jitter of the second recording layer was 8.0%. Met. Further, when recording was repeated 1000 times, the DC jitter of the first recording layer was 9.1%, and the DC jitter of the second recording layer was 8.8%, which was good.

(Example 23)
A two-layer phase change optical recording medium was prepared in the same manner as in Example 19 except that the first recording layer and the second recording layer were changed to Ag _0.5 In ₂ Sb ₆₉ Te ₂₅ Ge _3.5 . Using the same recording apparatus as in Example 19, recording was performed at a recording linear velocity of 9.2 m / s, recording power Pp = 26 mW, erasing power Pe = 5.9 mW, and bias power Pb = 0.1 mW. The width of the multipulse was 0.23T.
When recording was repeated 100 times on the same track for each of the first and second recording layers, the DC jitter of the first recording layer was 8.3%, and the DC jitter of the second recording layer was 8.0%. Met. Further, when recording was repeated 1000 times, the DC jitter of the first recording layer was 9.9%, and the DC jitter of the second recording layer was 8.4%, which was good.

(Example 24)
The same recording apparatus was used for the same two-layer phase change optical recording medium as in Example 23, recording linear velocity 7.7 m / s, recording power Pp = 23 mW, erasing power Pe = 5.7 mW, bias power Pb = Recording was performed at a setting of 0.1 mW. The width of the multipulse was 0.18T.
When recording was repeated 100 times on the same track for each of the first and second recording layers, the DC jitter of the first recording layer was 8.2%, and the DC jitter of the second recording layer was 8.1%. Met. Furthermore, when recording was repeated 1000 times, the DC jitter of the first recording layer was 9.5%, and the DC jitter of the second recording layer was 8.3%, which was good.

The figure showing the layer structure of the two-layer phase change type optical recording medium. The figure showing the absorptivity, reflectance, and transmittance of the reflective layer material. The figure showing the film thickness dependence of the absorptivity, reflectance, and transmittance of Cu at 660 nm. The figure showing the film thickness dependence of the absorptivity, reflectance, and transmittance of Ag at 660 nm. The figure showing the wavelength dependence of the transmittance | permeability of Cu and Ag. The figure showing the recording characteristic of the 1st recording layer in case the 1st reflective layer is Cu, Ag, and Au.

Explanation of symbols

A Absorbance R Reflectance T Transmittance

Claims (6)

A plurality of information layers including a phase change recording layer capable of recording information by causing a phase change by laser light irradiation are provided, and each information layer other than the innermost side is viewed from the laser light irradiation side. In an optical recording medium composed of at least a lower protective layer, a phase change recording layer, an upper protective layer, a reflective layer, and a heat diffusion layer, the phase change recording layer is composed of at least three elements of Ge, Sb, and Te, A multilayer phase change optical recording medium, wherein the following requirements are satisfied when the composition ratio [atomic%] is α, β, γ:
2 ≦ α ≦ 20
65 ≦ β ≦ 90
3 ≦ γ ≦ 30   2. The multilayer phase change optical recording medium according to claim 1, wherein the reflective layer of the information layer other than the backmost layer as viewed from the side irradiated with the laser light contains Cu as a main component.   3. The multilayer phase change optical recording according to claim 1, wherein the upper protective layer of the information layer other than the innermost layer when viewed from the side irradiated with the laser light contains Sn oxide as a main component. Medium.   The multilayer phase change optical recording medium according to any one of claims 1 to 3, wherein the thermal diffusion layer contains an oxide of In as a main component.   5. The multilayer phase change optical recording medium according to claim 4, wherein the thermal diffusion layer contains an oxide of Zn. 5. The multilayer phase change optical recording medium according to claim 4, wherein the thermal diffusion layer contains an oxide of Sn.

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