JP4112239B2 - Multilayer recording medium and method for manufacturing multilayer recording medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to multilayer recording, and relates to a structure of a multilayer recording medium capable of being a large-capacity optical recording medium and an information recording / reproducing system using the multilayer recording medium.
[0002]
[Prior art]
There is a need for a recording system that is large in capacity and easy to handle as part of a computer system or as part of a home entertainment device. In this application, there is an optical media characterized by ease of handling and compatibility with high-speed, large-capacity hard disks, and development competition is intensifying.
[0003]
The optical disk having the largest capacity, which is currently in widespread use, is the DVD. The DVD has a standard having two recording layers as a recording medium having a plurality of recording layers, and is used for recording movies and the like. . In this system, a two-layer disc having pits transferred by a stamper is bonded after depositing an Al film as a reflective layer. In this material system, the reflectivity per layer is high, and when the number of layers is increased, the number of layers increases and the S / N of the readout signal rapidly deteriorates.
[0004]
On the other hand, there is a report of a multi-layer disc in which the reflectance per layer is lowered to an appropriately low value with good reproducibility. That is, Japanese Patent No. 3066677 discloses an interface reflection (about 3.5%) between a disk (n = 1.492 for acrylic) and air (n = 1) by providing an air gap between disk layers. It is disclosed that the number of layers can be increased to about 10 layers.
[0005]
[Problems to be solved by the invention]
However, in the case of Japanese Patent No. 3066677, the number of layers is about 10 at most, and the range of application is limited to a read-only ROM system.
[0006]
However, in recent years, the capacity of a general hard disk exceeds 10 GB and is about to reach 100 GB. However, the storage capacity of an optical disk is only about 20 GB in a single layer even in a system using a blue-violet laser that is regarded as the next generation. Under such circumstances, there is a demand for an increase in the capacity of the optical disk that does not impair the ease of handling, which is the merit of the optical disk, and the securing of distribution.
[0007]
Accordingly, the present invention has been made to solve the above-described problems, and has a large capacity that can make a large number of recording layers in a multilayer structure and can be applied to a recordable medium as compared with Japanese Patent No. 3066677. An object of the present invention is to provide a multilayer recording medium structure and an information recording / reproducing system.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, in the first aspect of the present invention, a multilayer recording medium including two or more recording layers,
Each recording layer and a layer made of a material having a different refractive index from the material of each recording layer are laminated to form a heterogeneous material interface,
In one layer constituting the heterogeneous material interface, a dye material that can be recorded by light or heat is dispersed,
The interface reflection at the different materials interface to a reading of the recorded information, the most important feature Rukoto used in at least one of the read focus information and tracking information.
[0011]
In the second aspect of the present invention, a multilayer recording medium according to claim 1,
The main feature is that the reflectance of the interface between the different materials is less than 3%.
[0012]
In the invention of claim 3, wherein, a multilayer recording medium according to claim 1 or 2,
The main feature is that the material of the other layer constituting the interface between the different materials is a fluorine-containing polymer.
[0014]
According to a fourth aspect of the present invention, there is provided a method for producing a multilayer recording medium according to the third aspect ,
The other layer provided with grooves on one side or both sides is formed by injection molding a polymer containing fluorine,
The one layer is formed by spin-coating a polymer containing the coloring material on the surface provided with the groove ,
A main feature is a method for producing a multilayer recording medium, in which a plurality of composites composed of the one layer and the other layer are laminated via a thermal polymerization resin .
[0017]
DETAILED DESCRIPTION OF THE INVENTION
In an optical disc, information is recorded as the presence or absence of pits formed on a recording layer. In order to read out the presence / absence of pits as a change in the intensity of reflected light, the reflected light from the reflective layer deposited on the recording layer is used to read it indirectly. The merit in this case is that the intensity of the return light of the laser is large and a high S / N can be easily obtained due to the high reflectivity of the metal deposited film.
[0018]
However, when a metal vapor-deposited film is used as the reflective layer, the reflectance per layer is large and the transmission loss is large, so that the amount of laser light reaching the lower layer is greatly attenuated when it is multilayered.
[0019]
On the other hand, the reflectance R in the case of using the interface reflection of different materials according to the configuration of the present invention is R = (n ₁ −n ₂ ) ^ when the refractive indexes of two materials, n ₁ and n ₂ are used. 2 / (n ₁ + n ₂ ) ^ 2. This means that a multilayer recording medium having a reflectance of less than several percent can be configured by forming an interface using a homogeneous material. Therefore, not only a multi-layer recording medium exceeding 10 layers can be configured, but also the transmission loss per layer is small, so the attenuation of the readout signal is small, and if the detection system has high sensitivity, it is not necessary to have a wide dynamic range. There is a merit (it is difficult to realize a detector that satisfies both).
[0020]
The dye material that can be recorded by light or heat in the present invention refers to a material in which the refractive index changes due to absorption of light or heat. Since this dye material is included in any one layer of the interface between different materials constituting the present invention, the portion irradiated with light or heat does not change the refractive index in the layer not containing the dye. There is a change in the refractive index in the portion including. Therefore, the interface reflectance is modulated depending on the presence or absence of light or heat irradiation. Information is recorded / reproduced by using this modulation of reflectance.
[0021]
Multilayer recording medium of the present invention, it is preferable to present portions of the color element is limited only to the surface. If it is evenly distributed throughout, it is possible to focus on either the front or back side, but since the modulation by the written information is continuous in the depth direction, worst case interference occurs. There is. Therefore, either one of the front and back interfaces will be used as the recording layer. If the dye is dispersed only on the surface, both interfaces will be available if there is a distance in the optically resolvable depth direction. It becomes possible to write information in
[0022]
In a multilayer recording medium exceeding 10 layers, in order to prevent a rapid decay of the underlying readout light quantity, the reflectivity at the interface, as indicated in claim 2, it is desirable that less than 3%.
[0023]
The polymer containing fluorine shown in claim 3 generally has a low refractive index. Therefore, a larger refractive index difference can be provided at the interface between the fluorine-containing polymer and a general polymer such as acrylic, polycarbonate, and polystyrene, and as a result, the amount of reflected light can be increased. The said structure can also be used for some multilayer recording media. For example, by using it for the lower recording layer, it is possible to compensate for a decrease in the amount of reflected light from the lower layer and achieve a flattened reflected light amount.
[0024]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0025]
Reference example 1
It shows an example of a multilayer recording medium in Reference Example 1. Reference Example 1, the reflectance of the interface constituting each recording layer of the multilayer recording medium of less than 3%, produced by the production method of filling an ultraviolet curable resin between layers. In addition, an example of information reading method from the multilayer recording medium.
[0026]
A method for manufacturing a multilayer recording medium will be described with reference to FIGS. In FIG. 1, the recording surface of the recording medium is enlarged, and an arbitrary shape can be adopted for the chucking portion of the disk.
(A) Prepare stampers 101 and 102 with lands, grooves and pits. In this embodiment, since recording surfaces are provided on both sides, pits are carved on both of the stampers 101 and 102, but a configuration with only one side can also be taken.
(B) The recording layer 103 is formed by injection molding using the stampers 101 and 102. Polycarbonate is used as the material for the recording layer 103, but other optical grade polymers can be used as long as the refractive index difference with the polymer filling the recording layer described later takes a desired value. In this embodiment, the recording layer is molded by injection molding, but other molding methods such as thermal polymerization in a stamper and ultraviolet curing can be employed.
(C) The recording layer 103 removed from the stamper was obtained.
(D) After the recording layer 103 is laminated on the support substrate 104 with the ultraviolet curable resin 105 interposed therebetween, the protective layer 106 is laminated and irradiated with ultraviolet rays to be solidified and integrated. The ultraviolet curable resin used is acrylic and has a refractive index difference of about 0.1 with respect to the polycarbonate recording layer 103, and the reflectance at the interface is about 0.1%. The multilayer recording medium of the present invention is not limited to three layers, and the material of the heterogeneous interface constituting the recording layer is not limited to the combination of polycarbonate and acrylic shown in Example 1, and the intended reflectance is A combination of different materials satisfying the refractive index difference that can be obtained can be employed.
[0027]
Next, a method for reading information from the multilayer recording medium will be described with reference to FIG. The readout light emitted from the semiconductor laser 209 is converted into parallel light by the coupling lens 208, and then passes through an optical isolator composed of a polarization beam splitter (PBS) 204 and a quarter wavelength plate 203 and is converted into circularly polarized light. A part of the readout light condensed by the condensing lens 202 on the different kind of interface constituting one of the recording surfaces of the multilayer recording medium 201 is reflected by the refractive index (in the case of the reference example 1, approximately 0. 0). 1%). This reflected light has an optical rotation direction reversed, is converted into linearly polarized light in a polarization direction perpendicular to the readout light by the quarter wavelength plate 203, reflected by the PBS 204, passes through the condensing lens 205 and the cylindrical lens 206, and is then converted into four. Guided to a split avalanche photodiode (4D-APD) 207. Focus and track control is performed by a signal detected with high sensitivity by the 4D-APD 207, and a recorded signal is reproduced. Oite the method of reading information from the multilayer recording medium, by using a highly sensitive 4D-APD in the detection system, it is possible to detect the recording signals with high sensitivity, large capacity by multi-layering is It becomes possible. The information reading method described with reference to FIG. 2 is an example of the information reading method from the multilayer recording medium , and it goes without saying that other configurations can be adopted. Further, the form of the medium is not limited to the disk, and may take other forms such as a card form.
[0028]
Example 1
Example 1 shows a multilayer recording medium which is an example of an example of the present invention. Example 1 is a multilayer recording medium in which the reflectance of each recording layer satisfies less than 3% . In addition, an example of a method of reading information from the multilayer recording medium. A method for manufacturing a multilayer recording medium will be described with reference to FIGS. In FIG. 3, the recording surface of the recording medium is enlarged, and any shape can be adopted for the chucking portion of the disk.
(A) A stamper 301 inscribed with lands and grooves and a stamper 302 for forming a back surface that transmits ultraviolet rays are prepared. In this embodiment, since a recording surface is provided on one side, lands and grooves are carved only on the stamper 301. However, when used as a ROM, a configuration in which lands, grooves and pits are formed on both sides can be used.
(B) An ultraviolet curable resin is filled between the stampers 301 and 302 and cured with ultraviolet rays to form the medium 303. The medium 303 is made of an acrylic UV curable resin, but other optical grade polymers can be used as long as the refractive index difference with the polymer filling the recording layer described later takes a desired value. It is. In addition to molding with an ultraviolet curable resin, other molding methods such as thermal polymerization in a stamper and ultraviolet curing can be employed.
(C) A recording layer 304 made of a polymer film containing a dye was formed by spin coating on the medium 303 removed from the stamper. The polymer forming the recording layer is a polycarbonate resin, and focusing and tracking are controlled by interface reflection due to a difference in refractive index with the medium 303.
(D) After the composite of the recording layer 304 and the medium 303 is laminated on the support substrate 307 via the thermal polymerization resin 306, the protective layer 305 is laminated and solidified and integrated by thermal polymerization. The multilayer recording medium of the present invention is not limited to three layers, and the material of the heterogeneous interface that constitutes the recording layer is not limited to the combination of polycarbonate and acrylic shown in Example 2, but has an intended reflectance. A combination of different materials satisfying the refractive index difference that can be obtained can be employed.
[0029]
Next, a method for writing information from the multilayer recording medium will be described with reference to FIG. The readout light emitted from the semiconductor laser 409 is converted into parallel light by the coupling lens 408, then passes through an optical isolator composed of a polarization beam splitter (PBS) 404 and a quarter wavelength plate 403, and is converted into circularly polarized light. A part of the readout light condensed by the condenser lens 402 on the different kind of interface constituting one of the recording surfaces of the multilayer recording medium 401 is reflected by the difference in refractive index (in the case of the first embodiment, about 0.1. 1%). This reflected light has an optical rotation direction reversed, is converted into linearly polarized light having a polarization direction perpendicular to the readout light by the quarter wavelength plate 403, reflected by the PBS 404, and passes through the condenser lens 405 and the cylindrical lens 406, The light is guided to a quadrant avalanche photodiode (4D-APD) 407. Focus and track control are performed by a signal detected with high sensitivity by the 4D-APD 407. At the time of tracking, the output by the reading laser is controlled to be negligible, and at the time of writing, the output of the semiconductor laser is modulated according to the writing information to form a recording pit. The refractive index changes due to the exposure of the dye, and as a result, the reflected light is modulated according to the recording pits. In the method of reading information from the multilayer recording medium, it is possible to detect the recording signal with high sensitivity by using a highly sensitive 4D-APD in the detection system, and to electrically modulate the reflected light based on the writing information. It can be detected as a signal. As described above, the capacity can be increased by increasing the number of writable recording media. The information reading method described with reference to FIG. 4 is an example of a method for reading information from the multilayer recording medium , and it goes without saying that other configurations can be adopted. Further, the form of the medium is not limited to the disk, and may take other forms such as a card form.
[0030]
Example 2
Example 2 shows a multilayer recording medium which is an example of an example of the present invention. Example 2 is a multilayer recording medium in which one material constituting the heterogeneous interface is a polymer containing fluorine, and the reflectance of each recording layer is less than 3% . A method for manufacturing a multilayer recording medium will be described with reference to FIGS. In FIG. 5, the recording surface of the recording medium is enlarged, and an arbitrary shape can be adopted for the chucking portion and the like of the disc.
(A) A stamper 501 carved with lands and grooves and a stamper 502 without grooves forming the back surface are prepared. In this embodiment, since a recording surface is provided on one side, lands and grooves are carved only on the stamper 501, but when used as a ROM, a configuration in which lands, grooves, and pits are formed on both sides can be taken.
(B) Teflon (registered trademark) AF (for example, refractive index 1.35), which is a kind of fluorine-containing polymer, is injected between the stampers 501 and 502 to mold the medium 503. As the material of the medium 503, other optical grade polymers can be used as long as the refractive index difference with a polymer filling a recording layer described later takes a desired value. In the present embodiment, the recording layer of the medium 503 is formed by injection molding. However, other forming methods such as thermal polymerization in a stamper and ultraviolet curing can be employed.
(C) On the medium 503 removed from the stamper, a recording layer 504 made of a polymer film containing a dye was formed by spin coating. The polymer forming the recording layer is a polycarbonate resin, and focusing and tracking are controlled by interface reflection due to a difference in refractive index with the medium 503. In this case, the difference in refractive index between the two is about 0.25, which is about 2.5 times the combination of polycarbonate and acrylic. Further, the reflectance is about 0.7%, which is about 7 times.
(D) After the composite of the recording layer 504 and the medium 503 is laminated on the support substrate 507 via the thermal polymerization resin 506, the protective layer 505 is laminated and solidified and integrated by thermal polymerization. The multilayer recording medium of the present invention is not limited to three layers, and the material of the heterogeneous interface constituting the recording layer is not limited to the combination of polycarbonate and Teflon (registered trademark) AF shown in Example 3, A combination of different materials satisfying the refractive index difference capable of obtaining the intended reflectance can be employed.
[0031]
The multilayer recording medium created in this embodiment can record and reproduce information by the same principle and system as the multilayer recording medium of the first embodiment. The multilayer recording medium described with reference to FIG. 5 is an example of the embodiment of the present invention, and it goes without saying that other configurations can be adopted. Further, the form of the medium is not limited to the disk, and may take other forms such as a card form.
[0032]
【The invention's effect】
As described above, the present invention according to claim 1 is a multilayer recording medium having at least two recording layers, wherein the recording medium is formed of a laminated structure of different materials having different refractive indexes, and Since the multilayer recording medium is characterized in that the interface reflection is used to read out the recording information or at least one of the reading out of the focus information and the tracking information, the reflection of the medium is achieved due to the stable property in the medium called the refractive index of the material As a result, it is possible to easily obtain a recording medium having a uniform reflectance of the recording layer in the layer and the medium, and to obtain a large-capacity multilayer recording medium capable of reading the recording information stably. In addition, a wider reflectance can be set than when a solid-gas interface is used as the heterogeneous interface. On the other hand, when a metal-based reflective layer having a high reflectance is used in the first place, a higher transmittance is required to read the lower recording layer as the number of recording layers constituting the medium increases. For this reason, it is difficult to suppress variations in the recording surface or each layer in the medium and between the media, for example, it is necessary to uniformly form a reflective film having a thickness around the wavelength of light.
[0033]
The present invention according to claim 1 is a multilayer recording medium characterized in that a dye material that can be recorded by light or heat is dispersed in any one of the layers constituting the interface of different materials in addition to the above configuration . In addition to the above merits, information can be written after the medium is created by dispersing a dye material that can be recorded by light or heat in the recording layer. As the media of the present invention, both media that can be recorded only once and media that can repeat recording and erasing can be created by selecting a material according to the application.
[0035]
According to a second aspect of the invention, in addition to the configuration, since a multilayer recording medium, wherein the reflectivity of the interface constituting each recording layer is less than 3%, low even reflectance per, The high transmittance avoids the problem that the amount of reflected light from the lower layer, which becomes a problem when a large number of recording layers are stacked, can be avoided, and a high S / N read signal can be obtained from all the recording layers. it can. In addition, even when using a highly sensitive detection system, there is no extreme level difference in the signal intensity from the upper layer and lower layer of the readout signal, and all signals can be photoelectrically converted with one detection system. Cost reduction is possible.
[0036]
According to a third aspect of the present invention, there is provided a multilayer recording medium characterized in that, in addition to the above structure, one of the materials constituting the heterogeneous interface is a polymer containing fluorine. The refractive index of the fluorine-containing polymer is lower than that of the polymer before adding fluorine. Therefore, it is possible to increase the difference in refractive index that forms the heterogeneous interface, and the control range of the reflectance at the interface is expanded. As the fluorine-containing polymer, acrylic or epoxy ultraviolet curable resins can be selected from materials for injection molding, and various methods for producing multilayer recording media are possible.
[0037]
According to a fourth aspect of the present invention , in the multilayer recording medium according to the third aspect , a layer made of a fluorine-containing polymer having grooves and pits on one or both sides is formed by injection molding, and the polymer layer is formed into a multilayer laminated Runode be filled with different resins interlayer, fluorine it is possible to take a medium structure by taking advantage of transparency of the resin containing, also, the property is a low refractive index of a resin that contains fluorine alive, A wide range of reflectivity can be set.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a process according to a first embodiment of the present invention.
FIG. 2 is a schematic diagram of an optical system according to a first embodiment of the present invention.
FIG. 3 is an explanatory diagram of a process according to a second embodiment of the present invention.
FIG. 4 is a schematic diagram of an optical system according to a second embodiment of the present invention.
FIG. 5 is a process conceptual diagram according to the third embodiment of the present invention;
[Explanation of symbols]
101: Stamper 102: Stamper 103: Recording layer 104: Support substrate 105: UV curable resin 106: Protective layer 201: Multi-layer recording medium 202: Condensing lens 203: 1/4 wavelength plate 204: Polarizing beam splitter (PBS)
205: condenser lens 206: cylindrical lens 207: four-divided avalanche photodiode (4D-APD)
208: coupling lens 209: semiconductor laser 301: stamper 302: stamper 303: medium 304: recording layer 305: protective layer 306: thermal polymerization resin 307: support substrate 401: multilayer recording medium 402: condenser lens 403: 1/4 Wave plate 404: polarization beam splitter (PBS)
405: condenser lens 406: cylindrical lens 407: four-divided avalanche photodiode (4D-APD)
408: Coupling lens 409: Semiconductor laser 501: Stamper 502: Stamper 503: Medium 504: Recording layer 505: Protective layer 506: Thermopolymer resin 507: Support substrate

Claims (4)

A multilayer recording medium including two or more recording layers,
Each recording layer and a layer made of a material having a different refractive index from the material of each recording layer are laminated to form a heterogeneous material interface,
In one layer constituting the heterogeneous material interface, a dye material that can be recorded by light or heat is dispersed,
The interface reflection at the different materials interface, multi-layer recording medium to the reading of the recorded information, wherein Rukoto used in at least one of the read focus information and tracking information. A multilayer recording medium according to claim 1,
A multilayer recording medium, wherein a reflectance of the interface between the different materials is less than 3%. A multilayer recording medium according to claim 1 or 2,
A multilayer recording medium, wherein the material of the other layer constituting the different material interface is a fluorine-containing polymer. A method for producing a multilayer recording medium according to claim 3 ,
The other layer provided with grooves on one side or both sides is formed by injection molding a polymer containing fluorine,
The one layer is formed by spin-coating a polymer containing the coloring material on the surface provided with the groove ,
A method for producing a multilayer recording medium, comprising: laminating a plurality of composites composed of the one layer and the other layer with a thermopolymer resin interposed therebetween .

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