JP2014024199A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium which can achieve both high transmission and high recording sensitivity.SOLUTION: An optical recording medium includes a substrate, plural information signal layers, and a protective layer. At least one layer of the plural information signal layers has a recording layer including Pd, Bi and O.

Description

  The present technology relates to an optical recording medium. Specifically, the present invention relates to an optical recording medium including a plurality of information signal layers.

  In recent years, a Blu-ray Disc (BD) has been commercialized as a large-capacity optical recording medium. This large-capacity optical recording medium realizes a recording capacity of about 25 GB by setting the recording / reproducing optical wavelength to about 405 nm and the numerical aperture NA of the condenser lens of the recording / reproducing optical system to about 0.85.

  In this large-capacity optical recording medium, various studies have been made on recording materials for write-once optical recording media. Recording materials used for write-once optical information recording media include inorganic materials and organic dye materials. In conventional write-once optical information recording media, organic dye materials have been mainly studied as recording materials, but in recent large-capacity optical information recording media, inorganic materials have been widely studied as recording materials. As a large-capacity optical recording medium using an inorganic material as a recording material, an information recording capacity exceeding 100 GB per optical recording medium has been reported. Specifically, an optical recording medium including three or four information signal layers using an inorganic recording material has been put into practical use as BD-XL. As inorganic recording materials, metal oxides such as Te oxide and Pd oxide have been proposed (see, for example, Patent Documents 1 to 3).

JP 2008-112556 A JP 2011-194617 A JP 2012-64275 A

  In recent years, there is an increasing demand for further increasing the recording capacity by multilayering the recording layer of the optical recording medium. In order to meet this requirement, it is important to develop a recording material that can achieve both high transmittance and high recording sensitivity.

  Accordingly, an object of the present technology is to provide an optical recording medium that can achieve both high transmittance and high recording sensitivity.

In order to solve the above problems, the present technology
A substrate, a plurality of information signal layers, and a protective layer;
At least one of the plurality of information signal layers is an optical recording medium having a recording layer containing Pd, Bi and O.

  In the present technology, the thickness of the protective layer is not particularly limited, and the protective layer includes a substrate, a sheet, a coating layer, and the like. As a high-density optical recording medium, a thin light-transmitting layer such as a sheet or a coating layer is used as a protective layer, and information signals are recorded and reproduced by irradiating light from the light-transmitting layer side. What has is preferable. In this case, it is also possible to employ a substrate having opacity as the substrate. The light irradiation surface for recording or reproducing the information signal is appropriately set on at least one of the surface on the protective layer side and the substrate side according to the format of the optical recording medium.

  In the present technology, since the recording layer contains Pd, Bi, and O, the recording sensitivity can be improved while maintaining high transmittance. Therefore, a suitable recording layer can be obtained by applying to a multilayer optical recording medium.

  As described above, according to the present technology, an optical recording medium that can achieve both high transmittance and high recording sensitivity can be provided.

FIG. 1A is a perspective view illustrating an example of an appearance of an optical recording medium according to an embodiment of the present technology. FIG. 1B is a schematic cross-sectional view illustrating an example of the configuration of an optical recording medium according to an embodiment of the present technology. FIG. 2A is a schematic diagram illustrating a first configuration example of each information signal layer. FIG. 2B is a schematic diagram illustrating a second configuration example of each information signal layer. FIG. 3A is a schematic diagram illustrating a third configuration example of each information signal layer. FIG. 3B is a schematic diagram illustrating a fourth configuration example of each information signal layer. FIG. 4 is a schematic diagram showing the configuration of the disk drive type evaluation apparatus. FIG. 5 is a diagram showing evaluation results of transmission characteristics and optimum recording power of the optical discs of Examples 1 to 3 and Comparative Examples 1 to 4. FIG. 6 is a diagram showing evaluation results of the RF signal quality of the optical disks of Examples 1 to 3 and Comparative Example 1.

Embodiments of the present technology will be described in the following order.
1. Outline 2. 2. Configuration of optical recording medium 3. Recording principle of optical recording medium Manufacturing method of optical recording medium

[1. Overview]
In the above-described large-capacity write once optical recording medium, in order to further increase the capacity, it is required to develop a multilayer technology of five or more layers and a high-density recording / reproducing technology for information signals. In order to realize a write-once optical recording medium having five or more recording layers, it is necessary to further increase the light transmittance of the information signal layer per layer as compared to the four-layer write-once optical recording medium.

  Specifically, in a BD-XL write-once medium that is commercialized as a four-layer write-once optical recording medium, the light transmittance of the uppermost information signal layer is a laser beam (wavelength used for recording and reproducing information signals). 405 nm) is 80%. Here, the uppermost information signal layer means the information signal layer closest to the light irradiation surface that emits light for recording or reproducing the information signal layer. On the other hand, in the five-layer or six-layer optical recording medium, the light transmittance of the uppermost information signal layer is 85% to 90% with respect to the laser beam used for recording / reproducing the information signal.

  As described above, when the light transmittance of the information signal layer is increased, the light absorption rate of the information signal layer is decreased. Therefore, in order to secure the amount of energy absorption of the laser light necessary for information recording, the irradiation power of the laser light Need to be increased. However, since the output of the existing laser diode (LD) is limited, a recording material capable of recording information even if the irradiation power of the laser beam is low, that is, a highly sensitive recording material is desired as the recording material.

  Specifically, for example, when the light transmittance is raised from the conventional 80% to 85% or more, the light absorption rate is simply reduced by 5%. If the light reflectance is 5%, the light absorption rate is 15% when the light transmittance is 80%, whereas the light absorption rate is reduced to 10% when the light transmittance is 85%. Therefore, when the transmittance is increased from 80% to 85%, it is necessary to increase the recording power by 1.5 times, that is, by 50%. A highly sensitive recording material that can minimize the increase in recording power is desired.

  That is, in a large capacity write once optical recording medium having five or more information signal layers, in order to perform recording / reproduction of all information signal layers satisfactorily, high light transmittance and low optical recording energy Realization of a recording material having both characteristics is desired. Accordingly, as a result of intensive studies on the recording material having such characteristics, the inventors have found a recording material containing Pd, Bi and O.

[2. Configuration of optical recording medium]
[Structure of optical recording medium]
FIG. 1A is a perspective view illustrating an example of an appearance of an optical recording medium according to an embodiment of the present technology. The optical recording medium 10 has a disk shape with an opening (hereinafter referred to as a center hole) provided at the center. The shape of the optical recording medium 10 is not limited to this example, and may be a card shape.

  FIG. 1B is a schematic cross-sectional view illustrating an example of the configuration of an optical recording medium according to an embodiment of the present technology. This optical recording medium 10 is a so-called multi-layer write once optical recording medium, and as shown in FIG. 1B, an information signal layer L0, an intermediate layer S1, an information signal layer L1,..., An intermediate layer Sn, an information signal layer Ln and the light transmission layer 12 which is a protective layer have the structure laminated | stacked on one main surface of the board | substrate 11 in this order. In the following description, the information signal layers L0 to Ln are referred to as information signal layers L unless otherwise distinguished.

  In the optical recording medium 10 according to this embodiment, information signals are recorded or reproduced by irradiating the information signal layers L0 to Ln with laser light from the surface C on the light transmission layer 12 side. For example, laser light having a wavelength in the range of 400 nm or more and 410 nm or less is condensed by an objective lens having a numerical aperture in the range of 0.84 or more and 0.86 or less, and each information is received from the surface C side of the light transmission layer 12. Information signals are recorded or reproduced by irradiating the signal layers L0 to Ln. An example of such an optical recording medium 10 is a multilayer BD-R. Hereinafter, the surface C on which the information signal layers L0 to Ln are irradiated with laser light for recording or reproducing information signals is referred to as a light irradiation surface C.

  The thickness of the optical recording medium 10 is selected to be 1.2 mm, for example. The number of information signal layers L is preferably 3 or more, more preferably 5 or more, and even more preferably 5 or 6 layers. When the number of information signal layers L is three or more, the recording capacity of the information signal layer L per layer is set to 30 GB or more, for example.

  Hereinafter, the substrate 11, the information signal layers L0 to Ln, the intermediate layers S1 to Sn, and the light transmission layer 12 constituting the optical recording medium 10 will be described in order.

(substrate)
The substrate 11 has, for example, a disk shape with a center hole provided at the center. One main surface of the substrate 11 is an uneven surface, for example, and the information signal layer L0 is formed on the uneven surface. Hereinafter, of the concavo-convex surface, the concave portion is referred to as in-groove Gin, and the convex portion is referred to as on-groove Gon.

  Examples of the shapes of the in-groove Gin and the on-groove Gon include various shapes such as a spiral shape and a concentric circle shape. Further, the in-groove Gin and / or the on-groove Gon are wobbled (meandered), for example, for stabilizing the linear velocity and adding address information.

  The diameter (diameter) of the substrate 11 is selected to be 120 mm, for example. The thickness of the substrate 11 is selected in consideration of rigidity, preferably 0.3 mm or more and 1.3 mm or less, more preferably 0.6 mm or more and 1.3 mm or less, for example 1.1 mm. The diameter (diameter) of the center hole is selected to be 15 mm, for example.

  As a material of the substrate 11, for example, a plastic material or glass can be used, and it is preferable to use a plastic material from the viewpoint of cost. As the plastic material, for example, a polycarbonate resin, a polyolefin resin, an acrylic resin, or the like can be used.

(Information signal layer)
The information signal layers L0 to Ln include at least a recording layer capable of recording an information signal by laser light irradiation. Each of the information signal layers L0 to Ln has a recording capacity of 25 GB or more with respect to, for example, a laser beam wavelength of 405 nm and a condensing lens numerical aperture NA of 0.85. The information signal layer Ln closest to the light irradiation surface C preferably has a transmittance of 85% or more with respect to a laser beam for recording or reproducing an information signal. When the number of information signal layers L is 5 or 6, the information signal layers Ln−1,..., L0 on the back side of the information signal layer Ln (n = 5 or 6) A sufficient amount of laser light can be reached for recording or reproduction. Therefore, information signals can be recorded or reproduced satisfactorily for all the information signal layers L0 to Ln.

From the viewpoint of improving storage reliability, the information signal layers L0 to Ln preferably further include a protective layer on at least one surface of the recording layer, and more preferably include protective layers on both surfaces of the recording layer. The layer configuration of the information signal layers L0 to Ln may be the same in all layers, and the layer configuration is changed in accordance with characteristics (for example, optical characteristics and durability) required for the information signal layers L0 to Ln. However, from the viewpoint of productivity, it is preferable that all layers have the same layer configuration. The information signal layers L0 to Ln may be composed of only the recording layer.
Hereinafter, first to fourth configuration examples will be described as specific examples of the information signal layers L0 to Ln.

(First configuration example)
FIG. 2A is a schematic diagram illustrating a first configuration example of each information signal layer. As shown in FIG. 2A, the information signal layers L0 to Ln are configured only by the recording layer 21. With such a simple configuration, the cost of the optical recording medium 10 can be reduced and the productivity can be improved. Such an effect becomes more remarkable as the medium has a larger number of information signal layers L0 to Ln.

(Second configuration example)
FIG. 2B is a schematic diagram illustrating a second configuration example of each information signal layer. As shown in FIG. 2B, the information signal layers L0 to Ln are adjacent to the recording layer 21 having the upper side surface (first main surface) and the lower side surface (second main surface), and the upper side surface of the recording layer 21. And a protective layer 22 provided. With such a configuration, the durability of the recording layer 21 can be improved as compared with the first configuration example described above. Here, the light irradiation surface C side of the optical recording medium 10 is referred to as the upper side, and the opposite side is referred to as the lower side.

(Third configuration example)
FIG. 3A is a schematic diagram illustrating a third configuration example of each information signal layer. As shown in FIG. 3A, the information signal layers L0 to Ln are different from the recording layer 21 having the upper side surface (first main surface) and the lower side surface (second main surface) and the first configuration example described above. And a protective layer 23 provided adjacent to the lower surface of the recording layer 21. With such a configuration, the durability of the recording layer 21 can be improved.

(Fourth configuration example)
FIG. 3B is a schematic diagram illustrating a fourth configuration example of each information signal layer. As shown in FIG. 3B, the information signal layers L0 to Ln are adjacent to the recording layer 21 having an upper side surface (first main surface) and a lower side surface (second main surface), and the lower side surface of the recording layer 21. And a protective layer 22 provided adjacent to the upper surface of the recording layer 21. By adopting such a configuration, it is possible to improve the durability of the recording layer 21 as compared to the first and second configuration examples described above.

  In the first to fourth configuration examples described above, the case where the layer configuration of the information signal layers L0 to Ln is the same layer configuration in all layers has been described as an example. However, the first to fourth configuration examples described above are described. It is also possible to use a combination of two or more of the layer configurations in the information signal layers L0 to Ln.

(Recording layer)
The recording layer 21 contains Pd, Bi, and O. Pd, Bi and O are present in the recording layer as Pd oxide and Bi oxide. Here, the oxide includes oxides in an oxygen deficient state and an oxygen excess state.

  The recording layer 21 preferably further contains at least one metal selected from the group consisting of Sn, Zn, Ge, Co, W, Cu, and Al. These metals are present in the recording layer as oxides. Here, the oxide includes oxides in an oxygen deficient state and an oxygen excess state.

  Note that all the recording layers 21 of the information signal layers L0 to Ln are not limited to the configuration including Pd, Bi, and O. A configuration in which at least one recording layer 21 among the information signal layers L0 to Ln includes Pd, Bi, and O may be adopted. More specifically, some of the recording layers 21 of the information signal layers L0 to Ln are recording layers containing Pd, Bi, and O, while the remaining recording layers 21 are conventionally known. A configuration that is a recording layer using the above recording material may be adopted. It is preferable to adopt a configuration in which the recording layers 21 of all the information signal layers L1 to Ln other than the information signal layer L0 farthest from the light irradiation surface C include Pd, Bi, and O. In particular, it is preferable to adopt a configuration in which the recording layer 21 of the information signal layer Ln closest to the light irradiation surface C includes Pd, Bi, and O.

  The ratio C (= (B / A) × 100) of the amount B of Bi element to the total amount A of metal elements contained in the recording layer 21 is preferably 0 at% <C ≦ 50 at%, more preferably 0 at% <C ≦. The 45 at% relationship is satisfied.

(Protective layer)
As a material for the protective layer 22 and the protective layer 23, it is preferable to use a dielectric material. This is because the durability of the recording layer 21 can be improved by the protective layer 12 and the protective layer 13 functioning as a gas barrier layer. Further, by suppressing the escape of oxygen and the intrusion of H ₂ O in the recording layer 21, changes in the film quality of the recording layer 21 (mainly detected as a decrease in reflectivity) can be suppressed, which is necessary for the recording layer 21. It is also possible to ensure a good film quality.

Specifically, as the material of the protective layer 22 and the protective layer 23, for example, at least one selected from the group consisting of oxides, nitrides, sulfides, carbides, and fluorides can be used. As materials for the protective layer 22 and the protective layer 23, for example, the same or different materials can be used. Examples of the oxide include one or more elements selected from the group consisting of In, Zn, Sn, Al, Si, Ge, Ti, V, Ga, Ta, Nb, Hf, Zr, Cr, Bi, and Mg. An oxide is mentioned. As the nitride, for example, a nitride of one or more elements selected from the group consisting of In, Sn, Ge, Cr, Si, Al, Nb, Mo, Ti, Nb, Mo, Ti, W, Ta, and Zn Preferably, a nitride of one or more elements selected from the group consisting of Si, Ge, and Ti is used. Examples of the sulfide include Zn sulfide. Examples of the carbide include carbides of one or more elements selected from the group consisting of In, Sn, Ge, Cr, Si, Al, Ti, Zr, Ta, and W, preferably a group consisting of Si, Ti, and W And carbides of one or more elements selected from the above. Examples of the fluoride include fluorides of one or more elements selected from the group consisting of Si, Al, Mg, Ca, and La. Examples of the mixture include ZnS—SiO ₂ , SiO ₂ —In ₂ O ₃ —ZrO ₂ (SIZ), SiO ₂ —Cr ₂ O ₃ —ZrO ₂ (SCZ), In ₂ O ₃ —SnO ₂ (ITO). ), In ₂ O ₃ —CeO ₂ (ICO), In ₂ O ₃ —Ga ₂ O ₃ (IGO), In ₂ O ₃ —Ga ₂ O ₃ —ZnO (IGZO), Sn ₂ O ₃ —Ta ₂ O ₅ (TTO), TiO ₂ —SiO ₂ , Al ₂ O ₃ —ZnO, Al ₂ O ₃ —BaO, and the like.

(Middle layer)
The intermediate layers S1 to Sn serve to separate the information signal layers L0 to Ln with a sufficient physical and optical distance, and an uneven surface is provided on the surface thereof. The uneven surface forms, for example, concentric or spiral grooves (in-groove Gin and on-groove Gon). The thickness of the intermediate layers S1 to Sn is preferably set to 9 μm to 50 μm. Although the material of intermediate | middle layer S1-Sn is not specifically limited, If illustrated, photocurable resin or a thermosetting resin will be mentioned. As the photocurable resin, an ultraviolet curable resin is preferably used. Moreover, since the intermediate layers S1 to Sn serve as an optical path of a laser beam for recording or reproducing information signals to the inner layer, it is preferable that the intermediate layers S1 to Sn have sufficiently high light transmittance.

(Light transmission layer)
The light transmission layer 12 is a resin layer formed by curing a resin material, for example. The resin material for the resin layer is not particularly limited, and examples thereof include a photocurable resin or a thermosetting resin. For example, an ultraviolet curable resin is preferably used as the photocurable resin. Further, the light transmissive layer 12 may be constituted by a light transmissive sheet having an annular shape and an adhesive layer for bonding the light transmissive sheet to the substrate 11. The light-transmitting sheet is preferably made of a material having a low absorption ability with respect to laser light used for recording and reproduction, specifically, a material having a transmittance of 90 percent or more. As a material for the light transmissive sheet, for example, a polycarbonate resin material, a polyolefin-based resin (for example, ZEONEX (registered trademark)), or the like can be used. As the material for the adhesive layer, for example, an ultraviolet curable resin, a pressure sensitive adhesive (PSA), or the like can be used.

  The thickness of the light transmission layer 12 is preferably selected from the range of 10 μm or more and 177 μm or less, for example, 100 μm. By combining such a thin light transmission layer 12 and an objective lens having a high NA (numerical aperture) of, for example, about 0.85, high-density recording can be realized.

(Hard coat layer)
Although not shown in the drawing, the recording / reproduction quality of the information signal may be caused on the surface (laser irradiation surface) of the light transmission layer 12 due to, for example, protection against mechanical impacts and scratches, and adhesion of dust and fingerprints when handling by the user. You may further provide the hard-coat layer for protecting. The hard coat layer may be made of a mixture of fine silica gel powder to improve the mechanical strength, or an ultraviolet curable resin such as a solvent type or a solventless type. In order to have mechanical strength and water repellency or oil repellency, the thickness is preferably about 1 μm to several μm.

[3. Recording principle of optical recording medium]
In the optical recording medium 10 having the above-described configuration, an information signal is recorded as follows.
For example, when the recording layer 21 is irradiated with laser light having a central wavelength of about 405 nm, PdO contained in the recording layer 21 is decomposed into Pd and O ₂ , PdO ₂ is decomposed into PdO and O ₂ , and O ₂ is generated. The area swells structurally. Thereby, recording marks having different reflectances from the surroundings are formed.
When the composition ratio of Bi and Pd is adjusted, for example, when the amount of Bi is increased and the amount of Pd is decreased, the recording sensitivity increases (that is, the recording power increases even though the transmittance and the light absorption amount do not change). Tend to decrease). The principle that the recording sensitivity changes in this way is estimated as follows.
The recording material contains a plurality of metal oxides, and oxygen atoms are scrambled and pressed between metal atoms. It is considered that by adding Bi ₂ O ₃ , oxygen is supplied to PdO and PdO ₂ is easily generated. It is presumed that the increase in PdO ₂ having a high light absorption capability supplements the light absorption capability of the recording layer 21 and suppresses the decrease in the light absorption amount as the recording layer 21 even if the Pd amount decreases.
Although the light absorption ability of the recording layer 21 does not change as the amount of Bi increases, the point that the recording sensitivity increases (that is, the recording power decreases) is related to the thermal conductivity of Bi ₂ O _3. It is thought that. Since Bi and its compounds have very low thermal conductivity, increasing the amount of Bi ₂ O ₃ added makes it easy for the recording layer 21 to generate heat. Therefore, when the amount of Bi ₂ O ₃ added is increased, the temperature of the recording layer 21 can be easily increased by laser light irradiation during recording, so that the recording power can be lowered.

[4. Manufacturing method of optical recording medium]
Next, an example of a method for manufacturing an optical recording medium according to an embodiment of the present technology will be described.

(Substrate molding process)
First, the substrate 11 having an uneven surface formed on one main surface is formed by transferring the shape of the mastering master. As a method for molding the substrate 11, for example, an injection molding (injection) method, a photopolymer method (2P method: Photo Polymerization), or the like can be used.

(Information signal layer formation process)
Next, the information signal layer L0 is formed on the substrate 11 by, for example, sputtering. The specific formation process of the information signal layer L0 differs depending on the configuration of the information signal layer L0.
Hereinafter, a process of forming the information signal layer L0 when the above-described fourth configuration example (see FIG. 3B) is adopted as the configuration of the information signal layer L0 will be specifically described.

(Protective layer deposition process)
First, the substrate 11 is transferred into a vacuum chamber provided with a target for forming a protective layer, and the inside of the vacuum chamber is evacuated to a predetermined pressure. Thereafter, the target is sputtered while introducing a process gas such as Ar gas or O ₂ gas into the vacuum chamber, and the protective layer 23 is formed on the substrate 11. As the sputtering method, for example, a radio frequency (RF) sputtering method or a direct current (DC) sputtering method can be used, and a direct current sputtering method is particularly preferable. This is because the direct current sputtering method is cheaper and has a higher film formation rate than the high frequency sputtering method, and thus can reduce manufacturing costs and improve productivity.

(Recording layer deposition process)
Next, the substrate 11 is transferred into a vacuum chamber provided with a target for forming a recording layer, and the inside of the vacuum chamber is evacuated until a predetermined pressure is reached. Thereafter, while introducing a process gas such as Ar gas or O ₂ gas into the vacuum chamber, the target is sputtered to form the recording layer 21 on the protective layer 23.

By forming the recording layer 21 by sputtering while performing oxygen assist, the metal forms a stable oxide. For example, Pd forms PdO as Pd oxide and PdO ₂ which is unstable and absorbs light.

  As the target for forming the recording layer, it is preferable to use a complex oxide target containing Pd and Bi. Pd and Bi are present in the composite oxide target, for example, as Pd oxide and Bi oxide. Here, the oxide includes oxides in an oxygen deficient state and an oxygen excess state.

  It is preferable that the composite oxide target further includes at least one metal selected from the group consisting of Sn, Zn, Ge, Co, W, Cu, and Al. These metals are present in the composite oxide target as oxides. Here, the oxide includes oxides in an oxygen deficient state and an oxygen excess state.

  The target for forming the recording layer is not limited to the above example, and the recording layer 21 may be formed by a co-sputtering method by preparing respective targets for Pd and Bi. When the recording layer 21 further includes at least one metal selected from the group consisting of Sn, Zn, Ge, Co, W, Cu, and Al, a target for each of these metals is further prepared, and co-sputtering is performed. The recording layer 21 may be formed by a technique.

(Protective layer deposition process)
Next, the substrate 11 is transferred into a vacuum chamber provided with a target for forming a protective layer, and the inside of the vacuum chamber is evacuated to a predetermined pressure. Thereafter, the target is sputtered while introducing a process gas such as Ar gas or O ₂ gas into the vacuum chamber, and the protective layer 22 is formed on the recording layer 21. As the sputtering method, for example, a radio frequency (RF) sputtering method or a direct current (DC) sputtering method can be used, and a direct current sputtering method is particularly preferable. This is because the direct current sputtering method is cheaper and has a higher film formation rate than the high frequency sputtering method, and thus can reduce manufacturing costs and improve productivity.
Thus, the information signal layer L0 is formed on the substrate 11.

(Intermediate layer formation process)
Next, an ultraviolet curable resin is uniformly applied on the information signal layer L0 by, for example, a spin coating method. Thereafter, the concave / convex pattern of the stamper is pressed against the ultraviolet curable resin uniformly applied on the information signal layer L0, and the ultraviolet curable resin is irradiated with ultraviolet rays to be cured, and then the stamper is peeled off. Thereby, the uneven pattern of the stamper is transferred to the ultraviolet curable resin, and for example, an intermediate layer S1 provided with in-groove Gin and on-groove Gon is formed on the information signal layer L0.

(Information signal layer and intermediate layer formation process)
Next, in the same manner as the formation process of the information signal layer L0 and the intermediate layer S1, the information signal layer L1, the intermediate layer S2, the information signal layer L2,. The signal layer Ln is laminated on the intermediate layer S1 in this order.

(Light transmission layer forming process)
Next, a photosensitive resin such as an ultraviolet curable resin (UV resin) is applied on the information signal layer Ln by, for example, spin coating, and then the photosensitive resin is irradiated with light such as ultraviolet rays to be cured. Thereby, the light transmission layer 12 is formed on the information signal layer Ln.
Through the above steps, the target optical recording medium 10 is obtained.

(effect)
According to this embodiment, the recording material of the recording layer 21 contains Pd, Bi, and O, and Pd and Bi are present in the recording layer as oxides (including an oxygen deficient state and an oxygen excess state). This makes it possible to provide a write-once information signal layer L that achieves both high light transmittance and the ability to record information signals with low optical recording energy. The information signal layer L can be used to provide a multilayer write-once type optical recording medium. The information signal layer L is particularly suitable for application to a write-once optical recording medium having five or more layers.

  When a large capacity write-once optical recording medium having five or more information signal layers L is manufactured using the recording layer 21 containing Pd, Bi, and O, information can be obtained using a drive device that can be assumed at present. It is possible to record and reproduce signals without difficulty.

  Hereinafter, the present technology will be specifically described by way of examples. However, the present technology is not limited only to these examples.

In this embodiment, the recording material is PdO _x + M (M is a metal oxide containing at least one selected from the group consisting of Sn, Zn, Ge, Co, W, Cu and Al), and Bi ₂ I was used to was added O _3. Then, the effect of Bi ₂ O ₃ addition to the recording material was examined by comparing the recording / reproducing signal characteristics of the optical disks produced using this recording material.

(Evaluation equipment)
In this embodiment, the evaluation of the disk such as the recording / reproducing signal was performed using a BD disk drive type evaluation apparatus. In this embodiment, verification of the effect of adding Bi oxide in the recording material is the key, so an optical disc having only one information recording layer (so-called single-layer disc) was adopted as the optical disc.

  FIG. 4 shows the configuration of the disk drive type evaluation apparatus. Hereinafter, with reference to FIG. 4, an operation and a procedure until the optical disk 20 to be evaluated is mounted on the disk drive type evaluation apparatus and signal evaluation is performed will be described.

  First, the optical disk 20 is attached to the spindle motor unit 31 and rotated. Next, the recording / reproducing optical system 32 causes the laser diode 41 to emit light, and the laser light LB enters the mirror 44 via the collimator lens 42 and the beam splitter 43. The laser beam LB reflected by the mirror 44 is incident on the recording layer of the optical disc 20 through the objective lens 45 while being condensed.

  Next, the objective lens 45 is moved up and down in a direction (optical axis direction) perpendicular to the light irradiation surface of the optical disc 20 so that the focal point of the laser beam LB crosses the recording layer of the optical disc 20. At this time, the laser beam LB reflected by the recording layer of the optical disc 20 returns along the path that has traveled, and a part or all of the laser beam LB is reflected by the beam splitter 43 of the recording / reproducing optical system 32, so that the condensing lens. The light then enters the photodetector 47 via 46. The light received by the photodetector 47 is converted into an electrical signal and supplied to the signal analyzer 34. The signal analyzer 34 generates a focus servo error signal, a tracking servo error signal, an RF signal, and the like based on the electrical signal supplied from the photodetector 47, and performs servo control based on these generated signals. For example, in the focus servo control, a focus error signal is used to control the laser beam so that the laser beam is always focused on the recording layer using the focus error signal. Also, control is performed using the tracking error signal so that the focal point of the laser beam comes on the convex portion (groove) of the guide groove on the recording layer. The processing so far is ready for information recording. If an information signal has already been recorded on the optical disc, the information signal can be read (reproduced) from the optical disc 20.

Information signals are recorded on the optical disc 20 as follows. The signal generator 33 controls the laser emission of the laser diode 41 based on the information signal recorded on the optical disc 20. As a result, the emission waveform of the laser beam LB emitted from the laser diode 41 is controlled and irradiated onto the recording layer of the optical disc 20. The recording layer irradiated with the laser beam LB is changed by this laser energy. In the recording layer of this embodiment, PdO ₂ is decomposed by laser energy and PdO and O ₂ are generated, causing a change in the refractive index of the recording layer and physical volume expansion. The output of the laser diode 41 is selected so that the laser beam LB supplies the recording layer with sufficient energy for this change to occur.

  The reproduction of the information signal with respect to the optical disc 20 is performed as follows. Information signal reproduction is sufficiently low in power so that the recording layer of the optical disk 20 does not change even when the same layer is reproduced one million times by laser light irradiation, and the recorded information signal can be read with sufficient S / N. Performed with power. The laser beam set in this way is called reproduction light, and the laser power at that time is called reproduction power. The reproduction light applied to the recording layer of the optical disc 20 is detected by the photodetector 47 by going back through the recording / reproducing optical system. The optical disc 20 is an optical disc designed so that the amount of return light from the recording portion is lower than the amount of return light from the unrecorded portion, and the amount of return light from the recording portion is higher than the amount of return light from the unrecorded portion. There are optical discs designed to be. The former recording method is called a High to Low recording method, and the latter recording method is called a Low to High recording method.

The optical disk 20 of this embodiment is a medium of a high to low recording system, and this recording system is adopted in CD, DVD and BD. The light detected by the photodetector 47 is converted into an electric signal and supplied to the signal analysis device 34, and the signal quality is evaluated by the signal analysis device 34. Examples of the evaluation function include the following already established in the optical disc technology.
i-MLSE, modulation degree, SER (error rate), asymmetry, etc. i-MLSE and SER indicate the quality of information extracted from the RF signal. Also in this example, signal quality was evaluated using these evaluation functions.

(Evaluation method of signal characteristics)
In this example, the recording / reproduction signal evaluation of the optical disk was performed as follows using the above-described evaluation apparatus for BD. The information recording density was equivalent to 32 GB per information recording layer, which is 1.28 times BD: 25 GB, and five continuous tracks were recorded by double speed recording (7.69 m / s), and the signal of the center track was measured. For evaluation of signal quality, an index called i-MLSE used in BD-XL was used. The wavelength of the recording laser beam in the evaluation apparatus is 405 nm, and the numerical aperture NA of the condenser lens is 0.85. The recording power at which i-MLSE was the best was determined as the optimum recording power Pwo.

Example 1
First, a polycarbonate substrate having a thickness of 1.1 mm was formed by injection molding. An uneven surface having in-grooves and on-grooves was formed on the polycarbonate substrate. Next, an information signal layer was formed by sequentially laminating a dielectric layer, a recording layer, and a dielectric layer on the uneven surface of the polycarbonate substrate by sputtering. The information signal layer was designed to correspond to the L5 layer.

Specifically, the configuration of each layer of the information signal layer is as follows.
Dielectric layer (light transmission layer side)
Material: ITO, thickness: 20nm
Recording layer Material: Cu—Zn—Pd—W—Bi—O composite oxide (Cu: Zn: Pd: W: Bi = 6.7: 30.2: 4.7: 38.8: 21.9 ( Atomic ratio (unit: at%), thickness: 45 nm
Dielectric layer (substrate side)
Material: ITO, thickness: 10 nm

The recording layer was formed as follows. A film was formed by co-sputtering a Pd oxide target, a Bi oxide target, a Cu target, a Zn target, and a W target in a mixed gas atmosphere of Ar gas and O ₂ gas. However, the atomic ratio of Cu, Zn, Pd, W, Bi in the recording layer is Cu: Zn: Pd: W: Bi = 6.7: 30.2: 4.7: 38.8: 21.9. The input power of each target was adjusted so that Further, the flow rate ratio of Ar gas and O ₂ gas was adjusted so that a mixed gas atmosphere having a high oxygen concentration was obtained.
The specific recording layer deposition conditions are shown below.
Ar gas flow rate: 10-15 sccm
O ₂ gas flow rate: 15 to 24 sccm
Input power: 50-400W

Next, an ultraviolet curable resin was uniformly applied onto the dielectric layer by spin coating, and the light transmissive layer having a thickness of 100 μm was formed by irradiating the resin with ultraviolet rays to be cured.
Thus, the target optical disk was obtained.

(Example 2)
Except that the film formation conditions were adjusted so that the composition of the recording layer was Cu: Zn: Pd: W: Bi = 5.1: 26.1: 3.6: 31.6: 33.6 in atomic ratio. In the same manner as in Example 1, an optical disk was obtained.

(Example 3)
Except that the film formation conditions were adjusted so that the composition of the recording layer was Cu: Zn: Pd: W: Bi = 3.4: 22.2: 2.4: 27.8: 45.1 in atomic ratio. In the same manner as in Example 1, an optical disk was obtained.

(Comparative Example 1)
As a material for the recording layer, a composite oxide of Cu—Zn—Pd—W—O was used, and the composition ratio in terms of atomic ratio was Cu: Zn: Pd: W = 11.5: 36.5: 8.0: 46. An optical disk was obtained in the same manner as in Example 1 except that the film formation conditions were adjusted to be 0.9.

(Comparative Example 2)
Similar to Comparative Example 1 except that the film formation conditions were adjusted so that the composition of the recording layer was Cu: Zn: Pd: W = 12.3: 35.8: 8.5: 43.3 in atomic ratio. An optical disc was obtained.

(Comparative Example 3)
The same as Comparative Example 1 except that the film formation conditions were adjusted so that the composition of the recording layer was Cu: Zn: Pd: W = 13.6: 34.8: 9.4: 44.9 in atomic ratio. An optical disc was obtained.

(Comparative Example 4)
The same as Comparative Example 1 except that the film formation conditions were adjusted so that the composition of the recording layer was Cu: Zn: Pd: W = 15.4: 33.4: 10.7: 40.5 in atomic ratio. An optical disc was obtained.

Table 1 shows the compositions (atomic ratios of constituent elements) of the recording materials of the optical disks of Examples 1 to 3 and Comparative Examples 1 to 4.

(Evaluation of optical disc)
The following evaluation was performed on the optical disks of Examples 1 to 3 and Comparative Examples 1 to 4 obtained as described above.

(Evaluation of transmission characteristics)
The light transmittance was determined using a spectrophotometer. Specifically, the light transmittance of the information signal layer was obtained by numerical analysis from the measured value of the ellipsometer. The result is shown in FIG.
The measurement conditions are shown below.
Spectrophotometer: JAWoollam W-VASE
Measurement wavelength: 405 nm

(Evaluation of optimum recording power Pwo)
The recording power at which i-MLSE was the best was obtained, and this recording power was determined as the optimum recording power Pwo. The result is shown in FIG.

(Evaluation of RF signal quality)
Information recording is performed by changing the recording power proportionally with respect to the optimum recording power, and numerically expressed using i-MLSE as a specification used for RF signal quality evaluation, and a change in the i-MLSE value with respect to the recording power is plotted. A so-called power margin evaluation was performed. The evaluation results are shown in FIG. The recording conditions are the conditions described in the above “Signal characteristic evaluation method”. In addition, as an evaluation result of the optical disk in which Bi ₂ O ₃ is not added to the recording layer, the comparative example 1 of the comparative examples 1 to 4 is shown as a representative.

(Evaluation results)
FIG. 5 shows the evaluation results of the transmittance and optimum recording power of the optical disks of Examples 1 to 3 and Comparative Examples 1 to 4. In FIG. 5, the data surrounded by the frame line “Recording layer: Bi ₂ O ₃ added” relates to the evaluation results regarding the optical discs of Examples 1 to 3. Further, the data surrounded by the frame line “Recording layer: Bi ₂ O ₃ non-added” in FIG. 5 relates to the evaluation results regarding the optical disks of Comparative Examples 1 to 4. Note that the ratio C (= (B / A) × 100) [at% (atomic%)] of the amount B of Pd element with respect to the total amount A of metal elements contained in the recording material, with the transmittance and optimum recording power as the vertical axis. Is on the horizontal axis. That is, the horizontal axis corresponds to the numerical value of Pd in the composition ratio of Table 1.

The following can be understood from FIG.
In the recording layer without addition of Bi ₂ O ₃ , the transmittance increases and the recording power Pwo tends to increase (that is, the recording sensitivity deteriorates) as the Pd element content decreases. Transmittance recording power at 20mW is inferred from the approximate straight line L _T of the approximate straight line L _P and the transmittance of the recording power to be about 88%. Therefore, in the recording layer without addition of Bi ₂ O ₃ , if the recording power Pwo is Pwo ≦ 20 mW, the transmittance T is estimated to be T ≦ 88%.

The above tendency can be explained as follows. The oxide recording material of Pd—Cu—W—Zn—O is a composite oxide material composed of PdO, PdO ₂ , CuO, WO ₃ , and ZnO. Among these materials, main materials that play a role of absorbing light with respect to light having a wavelength of 405 nm are PdO ₂ and CuO, and other materials are substantially transparent to light with a wavelength of 405 nm. That is, when the absolute amount of PdO ₂ or CuO in the recording material decreases, the light absorption in the recording layer decreases, the light transmittance increases, and the recording power required for recording the information signal increases.

In contrast, in the recording layer of Bi ₂ O ₃ added, with increasing Bi ₂ O ₃ (i.e. with decreasing the content of Pd element), although the transmittance is substantially constant without change On the other hand, the recording power tends to be low (that is, the recording sensitivity is improved). When the ratio C of the amount B of Bi element to the total amount A of metal elements contained in the recording material is 45 at%, a transmittance of 89% can be obtained at a recording power of 17 mW.

From the above, it can be seen that recording power can be reduced while maintaining high light transmittance by adding Bi ₂ O ₃ to the recording layer.

FIG. 6 shows the evaluation results of the RF signal quality of the optical disks of Examples 1 to 3 and Comparative Example 1. From this result, the following can be understood.
i-MLSE bottom value, when added to Bi ₂ O ₃ in the recording layer shows good values in comparison with the case without the addition of Bi ₂ O _3. From this, it is understood that Bi ₂ O ₃ is preferably added to the recording layer from the viewpoint of signal quality.
The i-MLSE bottom value is a better value than the case where the ratio C is 0 at% even when the ratio C of the amount B of Bi element to the total amount A of metal elements contained in the recording material is 45 at%. Show. Such an effect of improving the i-MLSE value is presumed to be obtained when the ratio C of the amount B of Bi element to the total amount A of metal elements contained in the recording material is about 50 at%.
From the above, the ratio C (= (B / A) × 100) [at% (atomic%)] of the amount B of Pd element to the total amount A of metal elements contained in the recording material is preferably 0 at% <C ≦ 50 at. %, More preferably in the range of 0 at% <C ≦ 45 at%.

  In the above-described embodiments, examples in which the present technology is applied to an optical disc having a single recording layer have been described. However, it is easily assumed that the present technology can be applied to an optical disc having a plurality of recording layers. it can. Specifically, for example, it can be easily estimated that a five-layer disc can be realized by laminating the above-described recording layer on a four-layer write-once disc of BD-XL.

  As mentioned above, although embodiment of this technique was described concretely, this technique is not limited to the above-mentioned embodiment, Various deformation | transformation based on the technical idea of this technique is possible.

  For example, the configurations, methods, processes, shapes, materials, numerical values, and the like given in the above-described embodiments are merely examples, and different configurations, methods, processes, shapes, materials, numerical values, and the like are used as necessary. Also good.

  The configurations, methods, processes, shapes, materials, numerical values, and the like of the above-described embodiments can be combined with each other without departing from the gist of the present technology.

  In the above-described embodiment, a plurality of information signal layers and a light transmission layer are stacked in this order on the substrate, and laser light is irradiated to the plurality of information signal layers from the light transmission layer side. Thus, the case where the present technology is applied to an optical recording medium on which information signals are recorded or reproduced has been described as an example, but the present technology is not limited to this example. For example, a plurality of information signal layers and a protective layer are stacked in this order on a substrate, and information signals can be recorded or reproduced by irradiating a plurality of information signal layers with laser light from the substrate side. An optical recording medium to be used, or a structure in which a plurality of information signal layers are provided between two substrates, and information is obtained by irradiating a plurality of information signal layers with laser light from one substrate side. The present technology can also be applied to an optical recording medium on which a signal is recorded or reproduced.

  In the above-described embodiment, the present technology is applied to an optical recording medium having a plurality of information signal layers. However, the present technology is not limited to this example, and an optical signal having a single information signal layer is used. It is also possible to apply the present technology to a recording medium.

  Further, a part of the information signal layers of the multilayer information signal layer may be a write-once information signal layer, and the remaining information signal layers may be information signal layers other than the write-once information signal layer. In this case, the present technology is applied to the recording layer of the write-once information signal layer. Further, the present technology can also be applied to an optical recording medium in which a recording area such as a read-only pit is partially provided.

The present technology can also employ the following configurations.
(1)
A substrate, a plurality of information signal layers, and a protective layer;
An optical recording medium in which at least one of the plurality of information signal layers has a recording layer containing Pd, Bi and O.
(2)
The optical recording medium according to (1), wherein the Pd, Bi, and O are contained in the recording layer as Pd oxide and Bi oxide.
(3)
The optical recording medium according to any one of (1) to (2), wherein the recording layer further includes at least one selected from the group consisting of Sn, Zn, Ge, Co, W, Cu, and Al.
(4)
The ratio C (= (B / A) × 100) of the amount B of Bi element to the total amount A of metal elements contained in the recording layer satisfies the relationship of 0 at% <C ≦ 50 at% (1) to (3) The optical recording medium according to any one of the above.
(5)
A light irradiation surface for irradiating light for recording or reproducing an information signal;
The optical recording medium according to any one of (1) to (4), wherein the information signal layer closest to the light irradiation surface has a transmittance of 85% or more with respect to the light.
(6)
The optical recording medium according to any one of (1) to (5), wherein the information signal layer further includes a protective layer provided on at least one of the surfaces of the recording layer.
(7)
The optical recording medium according to (6), wherein the protective layer includes a dielectric material.
(8)
The optical recording medium according to any one of (1) to (7), wherein light for recording or reproducing an information signal is applied to the protective layer side.

DESCRIPTION OF SYMBOLS 11 Substrate 12 Light transmission layer 10 Optical recording medium 21 Recording layer 22, 23 Dielectric layer L, L0-Ln Information signal layer S1-Sn Intermediate layer Gin In-groove Gon-on-groove C Light irradiation surface

Claims (8)

A substrate, a plurality of information signal layers, and a protective layer;
An optical recording medium in which at least one of the plurality of information signal layers has a recording layer containing Pd, Bi and O.   The optical recording medium according to claim 1, wherein the Pd, Bi, and O are contained in the recording layer as Pd oxide and Bi oxide.   The optical recording medium according to claim 1, wherein the recording layer further includes at least one selected from the group consisting of Sn, Zn, Ge, Co, W, Cu, and Al.   2. The light according to claim 1, wherein a ratio C (= (B / A) × 100) of an amount B of Bi element to a total amount A of metal elements contained in the recording layer satisfies a relationship of 0 at% <C ≦ 50 at%. recoding media. A light irradiation surface for irradiating light for recording or reproducing an information signal;
The optical recording medium according to claim 1, wherein the information signal layer closest to the light irradiation surface has a transmittance of 85% or more with respect to the light.   The optical recording medium according to claim 1, wherein the information signal layer further includes a protective layer provided on at least one of the surfaces of the recording layer.   The optical recording medium according to claim 6, wherein the protective layer includes a dielectric material.   The optical recording medium according to claim 1, wherein light for recording or reproducing an information signal is applied to the protective layer side.

Images