JP2009116985A - Thin optical recording medium - Google Patents

Abstract

In a thin optical recording medium having two or more recording layers, it is necessary to improve a manufacturing process margin for low cost.
A thin optical recording medium having a high reflectivity metal layer 4 having a mirror surface at a position corresponding to at least a region where information is recorded or reproduced on the recording layer 2 is formed further back than the recording layer 2. When recording or reproduction is performed by injecting the beam 6 from the substrate 1 side through the lens, the beam of the PC substrate 1 is incident from the recording surface S0 that is farthest from the surface on which the beam of the PC substrate 1 is incident. When the distance to the surface is BLD, the thickness of the T0 spacer layer between the high reflectivity metal layer 4 and the S0 recording layer in front thereof is T0D, and the thickness of the PC substrate 1 is SD, SD = (BLD− 2T0D). As a result, the price of the thin optical recording medium can be reduced as compared with the prior art.
[Selection] Figure 3

Description

  The present invention relates to a thin optical recording medium and the like, and more particularly, to a thin optical recording medium that has substantially the same recording capacity but is cheaper than the conventional one.

  With the recent development of multimedia, an optical recording medium such as an optical disk has attracted attention as an information recording medium suitable for distributing a large amount of data and for long-term storage. Data recording and reproduction with respect to the optical recording medium are performed using laser light. The objective lens narrows the laser light to the diffraction limit and forms a light spot on the information layer of the optical recording medium. The diameter of the light spot at this time is represented by approximately λ / NA where λ is the wavelength of the laser beam and NA is the numerical aperture of the objective lens. That is, the diameter of the light spot is a value determined by the wavelength of the laser light and the numerical aperture of the objective lens.

  The resolution of recording / reproduction is determined by the diameter of the light spot, and the smaller the diameter, the higher the resolution of recording / reproduction. Therefore, in order to meet the demand for an increase in the capacity of the optical recording medium, reducing the diameter of the light spot is a direct and most effective means. As described above, since the diameter of the light spot is approximately represented by λ / NA, in order to reduce the light spot diameter, it is only necessary to shorten the laser wavelength and increase the numerical aperture of the objective lens. . For example, while the DVD laser wavelength λ is 650 nm or 635 nm and the numerical aperture NA of the objective lens is 0.6, in the next generation optical recording medium, the wavelength λ is about 400 nm and the numerical aperture NA is larger than 0.6. By doing so, the diameter of the light spot is reduced to increase the density. As an example of a next-generation optical recording medium, Blu-ray Disc achieves high density with a wavelength λ of 405 nm and a numerical aperture NA of 0.85.

  However, when the wavelength of the light source is further shortened, there is a problem that the transmittance of the optical element such as an objective lens and the optical recording medium substrate is rapidly reduced. Furthermore, when the numerical aperture of the objective lens is further increased, there is a problem that the lens working distance becomes extremely short.

  Therefore, in order to meet the demand for further increase in the capacity of the optical recording medium, an optical recording medium in which a plurality of recording layers are stacked in addition to the increase in density by reducing the diameter of the light spot has been proposed. On the other hand, as a different concept, a technique for increasing the capacity per volume by reducing the thickness of the substrate of the optical recording medium is also attracting attention. As a specific example, in order to realize an optical information recording / reproducing system that reliably and stably records / reproduces on a thin optical recording medium having a thickness of 0.3 mm or less, a thin optical as shown in Patent Document 1 is used. There is a method of holding a recording medium on a turntable.

JP 2006-344291 A

  Multi-layer manufacturing processes are more complex than single-layer manufacturing processes. Therefore, when the recording layer of the conventional thin optical recording medium is a multilayer, there is a problem that the price of the thin optical recording medium is increased due to the complexity of the multilayer manufacturing process.

  Also in the production of a multilayer thin optical recording medium, a thin optical recording medium is formed with a margin for each process. However, since the number of processes in a multi-layer process is larger than that in a single layer, manufacturing variations in each process are cumulatively accumulated, and various parameters of the thin optical recording medium that is finally completed deviate from the specified specifications. May end up. Therefore, there is a problem that the production yield of the thin optical recording medium is lowered, and as a result, the price per thin optical recording medium is increased. Examples of the predetermined specifications include optical characteristics and recording / reproducing characteristics of each recording layer, absolute film thickness and uniformity of the spacer layer and the cover layer, and eccentric amounts of each recording layer in the radial direction.

  FIG. 9 shows the structure of a conventional thin two-layer optical recording medium. In a thin two-layer optical recording medium, an L1 recording layer 101 is formed on a polycarbonate (PC) substrate 100 having a thickness of about 75 μm and having uneven portions formed by a nanoimprint method. The L1 recording layer 101 has a configuration in which at least both sides of the recording film are sandwiched between dielectric layers, and a semi-transparent metal reflective layer is provided on the back side of the L1 recording layer 101. Further, a T0 spacer layer 102 is provided on the L1 recording layer 101, and an L0 recording layer 103 is further formed on the T0 spacer layer 102. The L0 recording layer 103 has a configuration in which at least both sides of the recording film are sandwiched between dielectric layers, and a metal reflection layer that totally reflects is provided on the back side of the L0 recording layer 103. The T0 spacer layer is formed by a 2P method using an ultraviolet curable resin or a sheet-like nanoprint method, and has a thickness of about 25 μm in this embodiment. The protective layer 104 having a thickness of about 25 μm is provided on the side opposite to the substrate 100.

  During recording or reproduction, a beam 105 is incident from the PC substrate 100 side. In the case of a recording layer having a concavo-convex portion as shown in FIG. 9, the case where recording is performed on the recording surface (the convex portion in this case) on the near side with respect to the incident direction of the beam is called on-groove recording, The case where recording is performed on the recording surface (here, the concave portion) is referred to as in-groove recording. In the prior art, on-groove recording is performed.

  On the other hand, when the viewpoint is changed, in the case of a recording layer having an uneven portion as shown in FIG. 9, there are two recording surfaces for actual recording with respect to one recording layer. A recording surface (convex portion) on the near side and a recording surface (concave portion) on the back side with respect to the beam incident direction.

  Therefore, as one method for reducing the number of manufacturing processes, there is a method using land / groove recording which is a conventional technique for recording both on-groove and in-groove. If this method is used, the number of recording layers required to realize the same recording capacity can be reduced to half that of the prior art, so that the complexity of the multilayer manufacturing process can be eliminated.

  However, when the beam is incident from the cover layer side and focused on the on-groove or in-groove as in the prior art, there is a problem that the degree of concentration of the beam differs due to the influence of the groove. According to the simulation using numerical calculation, it is known that the beam is concentrated in the groove in the on-groove recording, whereas the beam spreads to the outside of the groove in the in-groove recording. When the beam spreads outside the groove, there arises a problem that information on adjacent tracks is erased by the beam. In order to avoid this problem, it is necessary to increase the interval between adjacent tracks. As a result, even if the complexity of the multilayer manufacturing process can be eliminated, a high recording density cannot be achieved.

  On the other hand, a technique for improving the rigidity of a disk while securing a large recording capacity by bonding two optical recording media to a thin optical disk has been studied. However, when the conventional hot melt bonding method is used as the bonding technique, there is a high possibility that the substrate will be deformed by heat. Therefore, in the manufacturing process of the bonded disk, it is important that the substrate is not heated as much as possible. For example, an adhesion method using an ultraviolet curable resin is a bonding method with little heat applied to the substrate. However, since the ultraviolet rays used for bonding cannot pass through the reflective layer provided on the thin optical recording medium, it is difficult to completely bond the two thin optical recording media by the bonding method using the ultraviolet curable resin.

  An object of the present invention is to solve such problems in the prior art and to provide an inexpensive thin optical recording medium having a small number of manufacturing processes and a sufficient manufacturing margin when compared with a recording capacity almost the same as that of the prior art. .

  In order to solve such a problem, in the present invention, in a thin optical recording medium capable of recording or reproducing information by irradiation with a beam, the thin optical recording medium includes a thin substrate, a recording layer group, a spacer. A recording layer group having at least one recording layer, and each recording layer has a first recording area and a second recording area. The high reflectivity metal layer has a mirror surface at a location corresponding to at least a region where information is recorded or reproduced in the recording layer group, and the recording layer group is formed on the thin substrate. The high reflectivity metal layer is formed so as to be separated from the recording layer group by the spacer layer, and at the time of recording or reproducing information, a beam is incident from the thin substrate side, and the first recording area Against The beam transmitted through the thin substrate is condensed, while the second recording area is transmitted through the thin substrate, the one or more recording layers, and the spacer layer, and the high reflectivity. The beam reflected by the mirror surface of the metal layer is collected, and the beam of the thin substrate is incident from the second recording region that is optically farthest from the surface on which the beam of the thin substrate is incident. The first thin optical recording medium satisfying the relational expression SD ≦ (BLD-2T0D) is assumed, where BLD is the distance to the surface to be formed, T0D is the thickness of the spacer layer, and SD is the thickness of the thin substrate. Provided.

  In the first thin optical recording medium of the present invention, since information is recorded or reproduced in the first recording area and the second recording area constituting the recording layer, the conventional thin optical recording medium having two recording layers The recording layer can be made one while having the same recording capacity. That is, in producing the first thin optical recording medium of the present invention, the number of manufacturing processes can be reduced as compared with the prior art, and the final manufacturing margin can be widened. As a result, an inexpensive thin optical recording medium can be manufactured.

  Further, the first thin optical recording medium of the present invention satisfies the relational expression SD ≦ (BLD-2T0D). In the recording / reproducing apparatus using the first thin optical recording medium of the present invention, if the spherical aberration correcting mechanism is determined so as to be able to correct the BLD, spherical aberration correction is achieved while satisfying the above formula and avoiding interlayer crosstalk. The mechanism reliably corrects the spherical aberration on each recording surface. Therefore, if this relational expression is satisfied, correction of spherical aberration can be made reliably and easily. In particular, when the recording layer group consists of one recording layer, the relational expression SD = (BLD-2T0D) is satisfied.

  The BLD is preferably about 100 μm. This is because the spherical aberration correction mechanism used in the conventional Blu-ray Disc in which the wavelength λ is 405 nm and the numerical aperture NA is 0.85 can be used. Furthermore, the T0D is preferably 5 μm or more. This is to avoid interlayer crosstalk.

  In the first thin optical recording medium, a protective layer may be provided so as to be in contact with a surface opposite to the surface in contact with the spacer layer among the surfaces of the high reflectance metal layer. In this case, it is preferable that the thickness of the protective layer is substantially the same as T0. This is because it becomes easy to create the protective layer.

  Furthermore, in the present invention, in a thin optical recording medium capable of recording or reproducing information by irradiation with a beam, the thin optical recording medium includes two thin substrates, two recording layer groups, and two spacer layers. And at least one high reflectance metal layer, the recording layer group has at least one recording layer, and each recording layer has a first recording area and a second recording area. The high reflectivity metal layer has a mirror surface at least in a location corresponding to a region where information is recorded or reproduced in the recording layer group, and the recording layer is formed on one thin substrate of the thin substrates. One recording layer group in the group, one spacer layer in the spacer layer, the high reflectance metal layer, the other spacer layer in the spacer layer, and the other recording layer in the recording layer group Group and thin above A second thin optical recording medium is provided in which the other thin substrate of the substrates is sequentially formed, and the high reflectance metal layer is also used in the two recording layer groups at the time of recording or reproducing information.

  In the second thin optical recording medium of the present invention, the high reflectance metal layer is also used in the recording layer group on one side. For this reason, since the entire thickness of the thin optical recording medium can be reduced, an inexpensive thin optical recording medium can be produced.

  In the second thin optical recording medium of the present invention, one recording layer group of the recording layer groups is formed on one thin substrate of the thin substrates, and further, the one recording layer group The high reflectance metal layer is formed so as to be separated by one spacer layer, and the other recording layer group of the recording layer groups is formed on the other thin substrate of the thin substrates. The thin optical recording medium includes a surface of the high reflectivity metal layer formed on the one thin substrate and a surface of the other recording layer group formed on the other thin substrate, and the other spacer layer. It can create by bonding together and forming.

  The other spacer layer in the second thin optical recording medium of the present invention is preferably used as an adhesive layer made of an ultraviolet curable resin. This is because the adhesive layer can be used as a spacer layer without providing a separate adhesive layer.

  In the second thin optical recording medium of the present invention, the beam of the one thin substrate is optically transmitted from the second recording region that is optically farthest from the surface on which the beam of the one thin substrate is incident. When the distance to the incident surface is BLda, the thickness of the spacer layer is T0Da, and the thickness of the one thin substrate is SDa, the relational expression SDa ≦ (BLDA-2T0Da) is satisfied. .

  Further, in the second thin optical recording medium of the present invention, the second thin substrate is optically separated from the second recording region optically farthest from the surface on which the beam of the other thin substrate is incident. When the distance to the beam incident surface is BLDb, the thickness of the adhesive layer is T0Db, and the thickness of the other thin substrate is SDb, the relational expression SDb ≦ (BLDb−2T0Db) is satisfied. And

  In the recording / reproducing apparatus using the second thin optical recording medium of the present invention, as long as the spherical aberration correction mechanism is determined to be able to correct the BLDA and the BLDb, while satisfying the above formula, the interlayer crosstalk is avoided. The spherical aberration correction mechanism surely corrects the spherical aberration on each recording surface.

  In the first and second thin optical recording media of the present invention, the thin substrate has a thickness of about 75 μm.

  By using such a substrate, a thin optical recording medium can be realized while ensuring sufficient rigidity of the substrate.

  In the first and second thin optical recording media of the present invention, the recording layer has a concave portion and a convex portion that form irregularities on a surface substantially perpendicular to the beam traveling direction, and the first recording is formed on the convex portion. An area is formed, and the second recording area is formed in the concave portion.

  By forming in this way, the first recording area and the second recording area are realized by the concave and convex portions formed in the recording layer.

  Thus, according to the present invention, although the number of manufacturing processes can be reduced as compared with the conventional method, almost the same recording capacity can be achieved as compared with the conventional method, so that an inexpensive thin optical recording medium is provided.

The best mode for carrying out the present invention will be described below in detail with reference to the drawings.
Example 1
FIG. 1 is a sectional view showing the structure of a thin optical recording medium in this embodiment. Although the recording layer is one layer, there are two recording surfaces on which recording is actually performed. A recording surface (convex portion) on the near side and a recording surface (concave portion) on the back side with respect to the beam incident direction.

  The L0 recording layer 2 was formed by sputtering on a polycarbonate (PC) substrate 1 having a thickness of about 75 μm. In the area of the PC substrate 1 where information is recorded or reproduced, at least uneven portions are formed by the nanoimprint method. The L0 recording layer 2 has a configuration in which at least both sides of the recording film are sandwiched between dielectric layers. Next, a T0 spacer layer 3 having a thickness of about 10 μm was formed on the L0 recording layer 2, and a high reflectivity metal layer 4 was formed thereon with a thickness of about 100 nm by sputtering. In the thin optical recording medium of the present invention, the surface of the high reflectivity metal layer 4 is a mirror surface having no concave and convex grooves and pit rows at least in a place corresponding to a region where information is recorded or reproduced on the recording layer. Is a feature.

  In this embodiment, the surface of the T0 spacer layer 3 corresponding to the area where information is recorded or reproduced on the L0 recording layer 2 is a mirror surface. Finally, an ultraviolet curable resin is applied on the high reflectivity metal layer 4 and then cured to form a protective layer 5 of about 10 μm to complete a thin optical recording medium. In addition, when using a sheet-like resin sheet for both the T0 spacer layer 3 and the protective layer 5, the same thickness is preferable.

  During recording or reproduction, a beam 6 is incident from the PC substrate 1 side. In order to reduce the influence of interlayer crosstalk, the distance between the high reflectivity metal layer 4 and the L0 recording layer 2 is preferably at least 5 μm or more (the thickness of the T0 spacer layer 3 is 5 μm or more).

  As the high reflectivity metal layer 4 used in this embodiment, a metal made of a material that reflects 90% or more of the incident beam at the mirror surface at the wavelength of the beam 6 is used (reflectance of 90% or more). For example, a metal such as silver or aluminum or an alloy containing them.

The recording film can be the phase change recording film used in the prior art, but in order to obtain a high transmittance, a nitride-based or oxide-based material may be used as required. In addition, in order to optimize the reflectance and absorptance on each recording surface, the film thickness of the recording film and the dielectric layer (ZnS—SiO ₂ or the like) is optimized, and if necessary, the film is in contact with the dielectric layer. The metal reflective layer may be formed thin. In the drawings, the L0 recording layer is indicated as L0, the recording surface S0 as S0, the recording surface S1 as S1, the high reflectivity metal layer as R, the T0 spacer layer as T0, and the protective layer as PL.

  As shown in FIG. 1, the thin optical recording medium of the present invention has two recording surfaces (S0 and S1) as in the conventional case, and therefore has almost the same recording capacity as the conventional thin double-layer optical recording medium. However, since only one recording layer is required, the thickness of the spacer layer can be reduced. In addition, since only one recording layer is required in this embodiment, the eccentricity between the recording layers, which is necessary for the conventional thin two-layer optical recording medium, is not required. Therefore, the price of the optical recording medium can be reduced as compared with the conventional case.

  Further, when the film configuration is such that the amount of absorbed light is the same on both recording surfaces, the detected light amount is inevitably smaller on the S0 recording surface than on the S1 recording surface. Therefore, in this embodiment, the width of the S0 recording surface is made wider than the width of the S1 recording surface. Specifically, the detected light amount is adjusted by shifting the groove width ratio of the L0 recording layer 2 from 50% with respect to the track pitch.

  In this embodiment, the designation of the recording surface of each recording layer is defined as follows. That is, the beam 6 is incident from the PC substrate 1 side, and as the recording surface in the L0 recording layer 2, the recording surface which is the on-groove on the front side is S1, and the recording surface which is the in-groove on the back side is S0. .

  Next, an example of the manufacturing process of the thin optical recording medium in the present embodiment will be described with reference to FIG. First, as shown in FIG. 2A, an L0 recording layer 2 was formed on a polycarbonate (PC) substrate 1 having a thickness of about 100 μm by sputtering. On the substrate 1, at least in a region where information is recorded or reproduced, a concavo-convex portion is formed in advance by a nanoimprint method. The L0 recording layer 2 has a configuration in which at least both sides of the recording film are sandwiched between dielectric layers. Then, an ultraviolet curable resin to be the T0 spacer layer 3 is applied on the L0 recording layer 2, and at least in a region where information is recorded or reproduced, the transparent stamper 7 which is a flat portion having no concave and convex grooves and pit rows is pressed. Hit it. Then, as shown in FIG. 2C, the ultraviolet curable resin is appropriately exposed to ultraviolet rays by the ultraviolet exposure machine 8 through the transparent stamper 7 and then peeled off. Further, as shown in FIG. 2D, a high reflectance metal layer 4 is formed on the surface of the T0 spacer layer 3 by sputtering. Thereby, at least in the area where information is recorded or reproduced, the surface of the high reflectivity metal layer 4 becomes a mirror surface which is not an uneven groove or pit row. Finally, a protective layer 5 is formed on the high reflectance metal layer 4 to complete a thin optical recording medium used in this embodiment as shown in FIG.

  As described above, the thin optical recording medium of the present invention requires a smaller number of manufacturing processes than the conventional recording layer double-layer disc, so that the cumulative amount of manufacturing variation in each process is reduced. As a result, the various parameters of the final thin optical recording medium are less likely to deviate from the predetermined specifications, so that an inexpensive thin optical recording medium can be manufactured.

  The focused state of the beam on each recording surface is as follows. As shown in FIG. 3A, the beam 6 incident from the PC substrate 1 side is focused on the recording surface S1 onto the recording surface S1, which is the recording surface on the front side of the recording layer. On the other hand, as shown in FIG. 3B, the recording surface S0, which is the recording surface on the back side of the recording layer, is reflected by the high reflectivity metal layer 4 on the recording surface S0. Condensed to S0. Therefore, the condensing direction of the beams is opposite in the recording surfaces S0 and S1. As a result, on-groove recording is performed on all recording surfaces (S0 and S1).

  By the way, the beam of the PC substrate 1 is incident from the second recording area (in the present embodiment, the inner recording surface) that is optically farthest from the surface on which the beam of the PC substrate 1 is incident. When the distance to the target surface is BLD, the thickness of the spacer layer between the high reflectivity metal layer 4 and the L0 recording layer 2 in front of it is T0D, and the thickness of the substrate is SD, SD ≦ (BLD-2T0D) is satisfied. ing. Further, the second recording area optically present on the innermost side when viewed from the surface of the PC board 1 is the second recording area where the beam incident from the PC board 1 side is reflected by the high reflectance metal layer. Considering focusing on the recording area, it means the second recording area having the longest distance from the surface of the PC board 1 to the second recording area among the plurality of second recording areas.

  In the case where there is one recording layer as in this embodiment, SD = (BLD-2T0D).

The value of BLD is a number that changes depending on the beam wavelength, the NA of the objective lens, the tilt margin, and the spherical aberration correction margin, but the beam wavelength (405 nm) of the semiconductor laser used in this example and the objective lens (NA 0.85). The thickness was about 100 μm. Thereby, the spherical aberration correction mechanism used in the conventional Blu-ray Disc in which the wavelength λ is 405 nm and the numerical aperture NA is 0.85 can be used. T0D is preferably 5 μm or more from the viewpoint of preventing interlayer crosstalk. Therefore, in this embodiment,
SD = (100 μm−2T0D) where T0D ≧ 5 μm
Holds. This makes it possible to reliably correct spherical aberration on each recording surface.

  Further, the thickness of the protective layer 5 is preferably about the same as the thickness of the T0 spacer layer 3. This is because formation is easy.

  FIG. 4 shows a schematic configuration of a recording / reproducing apparatus for recording / reproducing information on / from a thin optical recording medium according to an embodiment of the present invention. In FIG. 4, the recording / reproducing apparatus includes a thin optical recording medium 9, a turntable 10 for controlling the attitude of the thin optical recording medium 9 during rotation, and a constant between the turntable 10 and the thin optical recording medium 9. A spacer 11 for forming a gap, a spindle 12 for rotating the thin optical recording medium 9 and the turntable 10, a clamp 13 for stabilizing chucking, and an optical pickup 14 for recording / reproducing. And at least.

  Further, the recording / reproducing apparatus of the present embodiment includes an interface unit 15 for inputting / outputting recording / reproducing signals, a signal for encoding a signal for recording, and a signal for decoding the reproduced signal read by the optical pickup A processing unit 16; a focus / tracking servo circuit 17 that generates a focus / tracking servo signal; an optical head access mechanism 18 that operates the optical pickup 14 in accordance with the servo signal from the focus / tracking servo circuit 17; And a rotation control circuit 19 for controlling the rotation speed.

  In the optical pickup 14, a semiconductor laser serving as a laser light source, a photodetector for detecting reflected light, an objective lens, and a laser beam are irradiated onto the thin optical recording medium by the objective lens, and the reflected beam is applied to the photodetector. An optical system for guiding is formed. In this embodiment, a high-power semiconductor laser having a wavelength of 405 nm is used, and the NA of the objective lens is 0.85. Furthermore, a mechanism for correcting the spherical aberration of the beam is also provided. In this embodiment, a spherical aberration correction plate using a liquid crystal element is used.

  In this embodiment, a turntable 10 made of transparent glass having a thickness of 0.5 mm is used, and a recording / reproducing beam is recorded through the turntable 10 via the PC substrate 1 of the thin optical recording medium 9. The layer was irradiated. However, the PC board 1 side is set far from the turntable 10 (the positional relationship between the PC board 1 and the protective layer 5 is reversed in FIG. 1), and the turntable 10 is relocated to the upper side in FIG. The recording layer may be irradiated with the beam through the PC substrate 1 without passing through.

  When the spindle 12 starts to rotate, an air flow is generated in the space between the thin optical recording medium 9 and the turntable 10 starting from the space formed by the spacer 11. This air constantly moves from the inner periphery to the outer periphery by centrifugal force. Thereby, the local air biting phenomenon can be completely removed. The distance between the thin optical recording medium 9 formed by the spacer 11 and the turntable 10 is usually preferably 0.01 to 0.5 mm. In this embodiment, it is 0.1 mm.

  Even in a thin two-layer optical recording medium, the recording medium manufacturing method, the light condensing state at the time of recording or reproduction, and the like are the same as in this embodiment. In short, although there are two recording layers, there are four recording surfaces on which recording is actually performed, and a recording capacity almost the same as that of a conventional thin four-layer optical recording medium can be realized. In this case, the total number of recording layer preparation processes is two, the number of spacer layer formation processes is two, and the number of cover layer formation processes is one, for a total of five processes. The number of each process can be reduced by double the spacer layer formation by 0.67 times. As a result, the number of processes can be greatly reduced as compared with the conventional case, so that the final manufacturing margin can be widened and the yield of thin optical recording media can be improved.

  Furthermore, since the total thickness of the surface of the cover layer and the surface of the substrate is reduced, the material cost can be reduced.

That is, as a result of the above effects of the present invention, it is possible to reduce the price of a thin optical recording medium. The same applies to a thin multilayer optical recording medium having a multilayer recording layer composed of two or more recording layers.
(Example 2)
FIG. 5 shows a structural sectional view of the type in which the thin optical recording medium in this embodiment is bonded. There are two recording layers on both sides, but there are four recording surfaces on which recording is actually performed. This is because each recording layer has a recording surface (convex portion) on the near side and a recording surface (concave portion) on the back side with respect to the incident direction of the beam. In the following, description will be given mainly taking one side as an example.

  An L0a recording layer 22a is formed on a polycarbonate substrate 21a having a concavo-convex portion and a thickness of about 90 μm. The L0a recording layer 22a has a configuration in which at least both sides of the recording film are sandwiched between dielectric layers. A high reflectivity metal layer 24 is formed on the L0a recording layer 22a with a T0a spacer layer 23a therebetween at about 100 nm. At least in the area where information is recorded or reproduced, the feature of this embodiment is that the surface of the high reflectivity metal layer 24 is a mirror surface having no concave and convex grooves and pit rows. In order to reduce the influence of interlayer crosstalk, the distance between the high reflectivity metal layer 24 and the L0a recording layer 22a is preferably at least 5 μm or more (the thickness of the T0a spacer layer 23a is 5 μm or more).

  Then, another thin optical recording medium having the same structure is bonded so as to share the high reflectivity metal layer 24. In this case, the adhesive layer at the time of double-sided bonding can be used as the T0b spacer layer, and the high reflectivity metal layer 24 is also used in a single-sided thin optical recording medium. Therefore, the entire thickness of the thin optical recording medium can be reduced.

  At the time of recording or reproduction, a beam 25a having a wavelength of 405 nm collected by the objective lens is made incident from the substrate 21a side. Further, as the high reflectivity metal layer 24 used in the present embodiment, a metal made of a material capable of reflecting 90% or more of the incident beam at the mirror surface at the wavelength of the beam 25a is used (reflectivity). 90% or more). For example, a metal such as silver or aluminum or an alloy containing them. Further, since a high transmittance is required for the recording film, a nitride-based material or an oxide-based material is properly used as necessary.

In addition, in order to optimize the reflectance and the absorptance on each recording surface, the film thickness of the recording film and the dielectric layer (ZnS—SiO ₂ or the like) is optimized. If necessary, the metal reflective layer may be thinly formed in contact with the dielectric layer. In this example, the recording surface of each recording layer was defined as follows. That is, the beam 25a is incident from the substrate 21a side, and as the recording surface in the L0a recording layer 22a, the recording surface which is the front on-groove is S1a, and the recording surface which is the in-groove on the back side is S0a. In the drawings, the L0a recording layer is L0a, the L0b recording layer is L0b, the recording surface S0a is S0a, the recording surface S0b is S0b, the recording surface S1a is S1a, the recording surface S1b is S1b, and the T0a spacer layer is T0a. , T0b spacer layer is denoted as T0b, and high reflectivity metal layer is denoted as R.

  As shown in FIG. 5, since the thin optical recording medium of the present invention has four recording surfaces (S0a, S1a, S0b, S1b), the recording capacity is almost the same as that of a conventional thin optical recording medium having four layers in total. Have However, since only one recording layer per side is required, the number of recording layer manufacturing processes, the number of spacer layer forming processes, and the number of bonding processes can be greatly reduced. In other words, the final manufacturing margin can be widened by significantly reducing the number of processes compared to the conventional method. Furthermore, since the total thickness is reduced, the material cost can be reduced, resulting in a thin both sides. The price of the optical recording medium can be reduced.

  Further, in this embodiment, since there is only one recording layer on one side, it is not necessary to make an eccentricity between the recording layers, which is necessary in the conventional two layers. Also from this point of view, it is possible to further reduce the price of the optical recording medium as compared with the conventional case.

  In addition, when the film configuration is such that the absorbed light amount is the same on both recording surfaces, the detected light amount on the recording surface S0a is inevitably smaller than that on the recording surface S1a. Therefore, in this embodiment, the width of the recording surface S0a is made wider than the width of the recording surface S1a. Specifically, the groove width ratio of the L0a recording layer is shifted from 50% with respect to the track pitch.

  Next, an example of a manufacturing process for manufacturing a bonded-type thin optical recording medium in this embodiment will be described with reference to FIG.

  First, an L0a recording layer 22a was formed by sputtering on a polycarbonate (PC) substrate 21a having an uneven portion on the surface and having a thickness of about 90 μm. Then, an ultraviolet curable resin serving as the T0a spacer layer 23a is applied thereon, and at least in a region where information is recorded or reproduced, a transparent stamper 26 whose surface is a mirror surface with no concave and convex grooves and pit rows is pressed ( FIG. 6 (A)). Then, UV light is appropriately exposed to the T0a spacer layer 23a by the ultraviolet exposure machine 27 through the transparent stamper 26, and the mirror portion of the transparent stamper 26 is transferred to the T0a spacer layer 23a (FIG. 6B). After peeling off the transparent stamper 26, a high reflectivity metal layer 24 is formed on the surface of the T0a spacer layer 23a by sputtering (FIG. 6C). Subsequently, an ultraviolet curable resin serving as the T0b spacer layer 23b is applied on the high-reflectance metal layer 24, and the L0b recording layer 22b is formed on the surface. At least in the region where information is recorded or reproduced, the surface is uneven. A transparent PC board 21b having a thickness of about 90 μm is pressed against it (FIG. 6D). Then, ultraviolet rays are appropriately exposed to the T0b spacer layer 23b by the ultraviolet exposure machine 28 through the transparent PC substrate 21b to bond them together (FIG. 6E). Through these processes, the thin optical recording medium used in this embodiment is completed (FIG. 6F).

  As described above, the thin optical recording medium of the present invention requires a smaller number of manufacturing processes than the conventional double-layer thin optical recording medium, and therefore, the cumulative amount of manufacturing variation in each process. Becomes smaller. As a result, the various parameters of the thin optical recording medium finally produced are less likely to deviate from the predetermined specifications, so that an inexpensive recording medium can be produced. In addition, as a method for forming the concavo-convex portion on the surface of the PC substrate, a hot embossing method, a nanoimprint method, a 2P method, or the like may be used as necessary.

  Furthermore, in the thin optical recording medium of the present invention, since an adhesive method using an ultraviolet curable resin can be used, the warpage of the substrate due to heat at the time of double-sided bonding, which has been a problem in the prior art, is eliminated.

  FIG. 7 is a diagram for explaining a beam condensing state on each recording surface in a thin type optical recording medium of the pasted type. First, the beam 25a incident from the substrate 21a side is condensed on the recording surface S1a on the near side of the L0a recording layer 22a. On the other hand, on the recording surface S0a on the back side of the L0a recording layer 22a, the beam 25a incident from the substrate 21a side is reflected by the high reflectivity metal layer 24 and condensed on the recording surface S0a. Therefore, the direction of focusing on the recording surface S0a is opposite to the direction of the beam 25a incident from the PC substrate 21a side.

  In this case, on-groove recording can be realized on all recording surfaces (S0a and S1a). Therefore, it is possible to solve the problem of the spread of the focused beam that occurs during conventional in-groove recording.

  Therefore, according to the present invention, the complexity of the multi-layer manufacturing process can be eliminated, and even when recording is performed on all recording surfaces (S0a and S1a), the problem of the spread of the condensed beam does not occur. Therefore, a high recording density can be achieved. Similarly, the beam 25b is irradiated in the same manner on the opposite L0b recording layer 22b. The same applies to the double-sided thin optical recording medium in other layers.

  In this embodiment, the distance from the recording surface S0a, which is the farthest optically viewed from the surface on which the beam of the PC substrate 21a is incident, to the surface on which the beam of the PC substrate 21a is incident is represented by BLDA, which is a high reflectance. When the thickness of the spacer layer between the metal layer 24 and the L0a recording layer 22a is T0Da, and the thickness of the PC substrate 21a is SDa, SDa ≦ (BLDA-2T0Da) is satisfied. When there is a single recording layer as in this embodiment, SDa = (BLDa-2T0Da).

  The value of BLDa is a number that varies depending on the beam wavelength, the NA of the objective lens, the tilt margin, and the spherical aberration correction margin, but the beam wavelength (405 nm) of the semiconductor laser used in this example and the objective lens (NA 0.85). The thickness was about 100 μm. This is because the conventional spherical aberration correction mechanism used in the Blu-ray Disc in which the wavelength λ is 405 nm, the numerical aperture NA is 0.85, and the substrate thickness is about 100 μm can be used. T0Da is preferably 5 μm or more from the viewpoint of preventing interlayer crosstalk. Therefore, in this embodiment, SDa = (100 μm−2T0Da) holds. However, T0Da ≧ 5 μm. This makes it possible to reliably correct spherical aberration even when recording or reproducing on each recording surface.

  Although the above has described the PC board 21a side, the same applies to the PC board 21b side. In other words, in this embodiment, the distance from the recording surface S0b that is optically viewed from the surface on which the beam of the PC substrate 21b is incident to the surface on which the beam of the PC substrate 21b is incident is BLDb, When the thickness of the spacer layer of the reflectance metal layer 24 and the L0b recording layer 22b is T0Db and the thickness of the PC substrate 21b is SDb, SDb ≦ (BLDb−2T0Db) is satisfied. When there is one recording layer as in this embodiment, SDb = (BLDb-2T0Db).

  FIG. 8 shows a schematic configuration of a recording / reproducing apparatus for carrying out recording / reproduction on a thin optical recording medium of a type in which bonding is performed according to an embodiment of the present invention. In this figure, a case where different beams are irradiated from both sides of the thin optical recording medium 29 and recording / reproducing both sides simultaneously is described as an example.

  The recording / reproducing apparatus forms a certain gap between the thin optical recording medium 29, the turntable 30 for controlling the posture of the thin optical recording medium 29 during rotation, and the turntable 30 and the thin optical recording medium 29. At least a spacer 31 for rotating, a spindle 32 for rotating the thin optical recording medium 29 and the turntable 30, a clamp 33 for stabilizing chucking, and an optical pickup 34a for recording / reproducing. ing.

  For recording / reproduction to / from the recording layer on the PC substrate 21a side of the thin optical recording medium 29, an interface unit 35 for inputting / outputting a recording / reproducing signal, a signal for recording are encoded, and The signal processing unit 36 for decoding the reproduction signal read by the optical pickup, the focus / tracking servo circuit 37a for generating the focus / tracking servo signal, and the optical pickup 34a according to the servo signal from the focus / tracking servo circuit 37a At least a rotation control circuit 39 for controlling the rotation speed of the spindle 32.

  Further, a focus / tracking servo circuit 37b for generating a focus / tracking servo signal and a servo signal from the focus / tracking servo circuit 37b are used for recording / reproducing on the recording layer on the PC substrate 21b side of the thin optical recording medium 29. And at least an optical head access mechanism 38b for operating the optical pickup 34b.

  In addition, in the optical pickups 34a and 34b, a semiconductor laser serving as a laser light source, a photodetector for detecting reflected light, an objective lens, and a laser beam are irradiated onto the thin optical recording medium by the objective lens, and the reflected beam is applied to the optical pickup 34a and 34b. An optical system for leading to the photodetector is formed. In this embodiment, the optical pickup 34a is equipped with a high-power semiconductor laser having a wavelength of 405 nm and an objective lens having an NA of 0.65, and the optical pickup 34b is equipped with a high-power semiconductor laser having a wavelength of 405 nm and an objective lens having an NA of 0.85. Is installed. Furthermore, both optical pickups are provided with a mechanism for correcting the spherical aberration of the beam. Here, a spherical aberration correction plate using a liquid crystal element was used.

  Further, when the spindle 32 starts to rotate, an air flow is generated in the space between the thin optical recording medium 29 and the turntable 30 starting from the space formed by the spacer 31. This air constantly moves from the inner periphery to the outer periphery by centrifugal force. Thereby, the local air biting phenomenon can be completely removed. The distance between the thin optical recording medium 29 formed by the spacer 31 and the turntable 30 is usually preferably 0.01 to 0.5 mm. In this embodiment, it is 0.1 mm.

  In this embodiment, a turntable 30 made of transparent glass having a thickness of 0.5 mm is used. When recording / reproducing the recording layer on the PC substrate 21a side of the thin optical recording medium 29, the recording layer is irradiated with laser through the turntable 30. Therefore, the recording track pitch of the recording layer on the PC substrate 21a side is set larger than the recording track pitch of the recording layer on the PC substrate 21b side. As a result, the recording capacity of the recording layer on the PC substrate 21a side is smaller.

  However, a thin optical recording medium having the same recording capacity on both sides may be used to perform recording / reproduction using only the optical pickup 34b. In this case, when the recording / reproducing on one side of the thin optical recording medium is completed, it is necessary to remove the thin optical recording medium from the recording / reproducing apparatus, turn it over, and reset the thin optical recording medium.

  Note that the manufacturing method of the recording medium, the light condensing state during recording or reproduction, and the like are the same as in this embodiment even in a type in which a thin optical recording medium having two layers of single-sided recording layers is bonded. In short, there are four recording layers on both sides, but there are eight recording surfaces on which recording is actually performed, and the recording capacity is almost the same as that of a conventional thin optical recording medium having eight layers on both sides. The final manufacturing margin is broadened by drastically reducing, and furthermore, the total cost between the surface of the cover layer and the surface of the substrate is reduced, so that the material cost is reduced, resulting in the low price of the thin optical recording medium. Can be realized. The same applies to other thin multilayer optical recording media.

  As described above, according to the present invention, it is possible to reduce the warpage of the substrate due to the heat at the time of double-sided bonding, and it is possible to obtain a thin optical recording medium that is less expensive than the conventional optical recording medium, although it has almost the same recording capacity as the conventional one. realizable.

Cross-sectional view of the structure of a thin optical recording medium in Example 1 Manufacturing process explanatory drawing of the thin optical recording medium in Example 1 Explanatory drawing of the beam condensing state in each recording surface of the thin optical recording medium in Example 1 1 is a schematic configuration diagram of a recording / reproducing apparatus in Embodiment 1. Structural sectional view of a thin optical recording medium in Example 2 Manufacturing process explanatory drawing of the thin optical recording medium in Example 2 Explanatory drawing of the beam condensing state in each recording surface of the thin optical recording medium in Example 2 Schematic configuration diagram of a recording / reproducing apparatus in Embodiment 2 Cross-sectional view of structure of optical recording medium in conventional example

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,100 Polycarbonate substrate 2, 103 L0 recording layer 3, 102 T0 spacer layer 4 High reflectivity metal layer 5, 104 Protective layer 6, 105 Beam 7 Transparent stamper 8 Ultraviolet exposure machine 9 Thin optical recording medium 10 Turntable 11 Spacer 12 Spindle 13 Clamp 14 Optical pickup 15 Interface unit 16 Signal processing unit 17 Focus / tracking servo circuit 18 Optical head access mechanism 19 Rotation control circuits 21a and 21b Polycarbonate substrates 22a and 22b Recording layers 23a and 23b Spacer layer 24 High reflectivity metal layer 25a 25b Beam 26 Transparent stamper 27, 28 Ultraviolet exposure machine 29 Thin optical recording medium 30 Turntable 31 Spacer 32 Spindle 33 Clamp 34a, 34b Optical pickup 35 Interface section 36 Signal processor 37a, 37b Focus / tracking servo circuit 38a, 38b Optical head access mechanism 39 Rotation control circuit 101 L1 recording layer L0a, L0b, L1a, L1b Recording layer S0a, S0b, S1a, S1b Recording surface T0a, T0b Spacer layer PL Protective layer R High reflectivity metal layer

Claims (12)

In a thin optical recording medium capable of recording or reproducing information by being irradiated with a beam,
The thin optical recording medium has at least a thin substrate, a recording layer group, a spacer layer, and a high reflectance metal layer,
The recording layer group has at least one recording layer, and each recording layer has a first recording area and a second recording area,
The high reflectivity metal layer has a mirror surface at a location corresponding to an area where information is recorded or reproduced in at least the recording layer group,
The recording layer group is formed on the thin substrate, and further, the high reflectance metal layer is formed so as to be separated from the recording layer group by the spacer layer,
When recording or reproducing information, a beam is incident from the thin substrate side,
For the first recording area, the beam transmitted through the thin substrate is focused, while for the second recording area, the thin substrate, the one or more recording layers, and the spacer. The beam that has passed through the layer and reflected by the mirror surface of the high reflectivity metal layer is collected,
The distance from the second recording region that is optically farthest to the surface on which the beam of the thin substrate is incident to the surface on which the beam of the thin substrate is incident is defined as BLD, and the thickness of the spacer layer A thin optical recording medium satisfying a relational expression SD ≦ (BLD-2T0D), where T0D is the thickness and SD is the thickness of the thin substrate.   2. The thin optical recording medium according to claim 1, wherein when the recording layer group is composed of one recording layer, the relational expression SD = (BLD-2T0D) is satisfied.   2. The thin optical recording medium according to claim 1, wherein the BLD is about 100 [mu] m.   2. The thin optical recording medium according to claim 1, wherein the T0D is 5 [mu] m or more.   2. The thin optical recording medium according to claim 1, wherein a protective layer is provided so as to be in contact with a surface opposite to the surface in contact with the spacer layer among the surfaces of the high reflectance metal layer, and the thickness of the protective layer is the T0. A thin optical recording medium characterized by substantially the same as the above. In a thin optical recording medium capable of recording or reproducing information by being irradiated with a beam,
The thin optical recording medium has at least two thin substrates, two recording layer groups, two spacer layers, and one high reflectance metal layer,
The recording layer group has at least one recording layer, and each recording layer has a first recording area and a second recording area,
The high reflectivity metal layer has a mirror surface at a location corresponding to an area where information is recorded or reproduced in at least the recording layer group,
On one thin substrate of the thin substrates, one of the recording layer groups, one spacer layer of the spacer layers, the high reflectivity metal layer, and the other of the spacer layers Spacer layer, the other recording layer group of the recording layer group, and the other thin substrate of the thin substrate are sequentially formed,
A thin optical recording medium, wherein the high reflectance metal layer is also used in the two recording layer groups at the time of recording or reproducing information. The thin optical recording medium according to claim 6,
One recording layer group of the recording layer groups is formed on one thin substrate of the thin substrates, and further, separated from the one recording layer group by one spacer layer. A highly reflective metal layer is formed,
On the other thin substrate of the thin substrates, the other recording layer group of the recording layer groups is formed,
The thin optical recording medium includes a surface of the high reflectivity metal layer formed on the one thin substrate and a surface of the other recording layer group formed on the other thin substrate, the spacer of the other A thin optical recording medium characterized by being formed by laminating using layers.   8. The thin optical recording medium according to claim 7, wherein the other spacer layer is used as an adhesive layer made of an ultraviolet curable resin.   7. The thin optical recording medium according to claim 6, wherein the beam of the one thin substrate is incident from the second recording region that is optically farthest from the surface on which the beam of the one thin substrate is incident. The thin film is characterized in that the relational expression SDa ≦ (BLLa−2T0Da) is satisfied, where BLDi is the distance to the surface to be processed, T0Da is the thickness of the spacer layer, and SDa is the thickness of the one thin substrate. Optical recording medium.   7. The thin optical recording medium according to claim 6, wherein the beam of the other thin substrate is incident from the second recording region that is optically farthest from the surface on which the beam of the other thin substrate is incident. The thin film is characterized by satisfying the relational expression SDb ≦ (BLDb−2T0Db), where BLDb is the distance to the surface to be bonded, T0Db is the thickness of the adhesive layer, and SDb is the thickness of the other thin substrate. Optical recording medium.   7. The thin optical recording medium according to claim 1, wherein the thin substrate has a thickness of about 75 [mu] m. The thin optical recording medium according to claim 1 or 6, wherein the recording layer group has a concave portion and a convex portion that form concave and convex portions on a surface substantially perpendicular to the traveling direction of the beam,
A thin optical recording medium, wherein the first recording area is formed in the convex part, and the second recording area is formed in the concave part.

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