JP4326532B2 - Multilayer optical recording medium - Google Patents

Description

  The present invention relates to an optical recording medium and the like, and more particularly to a multilayer optical recording medium in which a plurality of information recording layers are stacked.

  Conventionally, CDs and DVDs are widely used as optical recording media. The recording capacity required for this type of optical recording medium has been increasing year by year, and various proposals have been made to meet the demand. For example, in a read-only optical recording medium such as a DVD-Video or a DVD-ROM, an information recording layer having a two-layer structure with an increased recording capacity has been put into practical use.

  As in the DVD shown in FIG. 9, pits are formed on each of the two substrates to form an information recording layer, and the two substrates are bonded with a spacer layer interposed therebetween with the information recording layer facing each other. An optical recording medium having a different structure has been put into practical use.

  As shown in FIG. 10, a hybrid structure DVD in which one information recording layer is formatted in the DVD format and the other information recording layer is formatted in the CD format has been put into practical use. In this case, for the purpose of adapting to each standard, the information recording layer that is a DVD format is set to 0.6 mm from the light incident surface and has a capacity of 4.7 GB, and the information that becomes a CD format is used. The recording layer is set to 1.2 mm from the light incident surface and has a capacity of 0.7 GB. In order to reproduce the signal recorded on each information recording layer, two types of optical systems having different wavelengths and numerical apertures (NA) are required.

  In recent years, a new standard such as a Blu-ray disc has been proposed in order to further increase the recording capacity. In the Blu-ray disc, an information recording layer is laminated in the vicinity of 0.1 mm from the light incident surface, and 25 GB of information can be recorded on this information recording layer. For example, in the case of a two-layer Blu-ray disc, one information recording layer is formed at a position 0.075 mm from the light incident surface, and the other information recording layer is formed at a position 0.1 mm from the light incident surface.

  In a large-capacity optical recording medium, it is required to reduce the beam spot diameter of laser light used for data recording / reproduction. For this purpose, it is necessary to increase the numerical aperture (NA) of the objective lens for focusing the laser light and shorten the wavelength λ of the laser light.

However, when the numerical aperture of the objective lens is increased, there arises a problem that the tilt margin of the laser beam with respect to the optical recording medium, that is, the tolerance of the tilt angle error of the optical axis with respect to the optical recording medium becomes very small. On the other hand, when the distance from the light incident surface of the optical recording medium to the information recording layer is reduced, the tilt margin is increased. Therefore, in order to prevent the tilt margin from being reduced while increasing the numerical aperture of the objective lens, the distance from the light incident surface to the information recording layer (that is, the thickness of the light transmission layer) is reduced. Is effective. Therefore, in the Blu-ray disc, the thickness of the light transmission layer is set to about 100 μm.
Japanese Patent No. 3206748 Japanese Patent No. 3210549

  However, when the light transmission layer is set thin like a Blu-ray disc, there is a problem that the distance between the information recording layers when multilayered becomes small and the characteristics deteriorate. For example, in the case of multi-layering with respect to the Blu-ray Disc standard, a plurality of information recording layers are laminated in the vicinity of 0.1 mm from the light incident surface, so that there is a problem that reproduction characteristics are likely to deteriorate. there were.

  In particular, according to the study by the present inventors, when an information recording layer having three or more layers, particularly four or more layers is formed, the characteristics of the intermediate information recording layer disposed between the two information recording layers are markedly deteriorated. The problem of doing was revealed.

  The present invention has been made in view of the above problems, and an object of the present invention is to suppress the deterioration of the recording / reproducing characteristics even when the optical recording medium is multilayered and to rationally increase the recording capacity.

In order to achieve the above object, the present invention, which has been made by diligent research by the present researchers, includes a first surface side information recording layer closest to one surface and a second surface side information recording layer closest to the other surface. And an intermediate information recording layer disposed between the first and second surface side information recording layers, the recording capacity of the intermediate information recording layer being compared with the first surface side information recording layer The multilayer optical recording medium is characterized in that the recording capacity of the intermediate information recording layer is set smaller than that of the second surface side information recording layer .

  The first surface side information recording layer close to the surface has a factor that causes crosstalk in the reproduction signal because the other information recording layer is arranged on one side, but there is no other information recording layer on the surface side, Signal quality can be improved. On the other hand, since the information recording layer is arranged on both sides of the intermediate information recording layer, crosstalk is greatly increased. Therefore, if the recording capacity of the intermediate information recording layer is positively set as in the present invention, the influence of crosstalk in the intermediate information recording layer can be suppressed. Homogenization is achieved.

  Further, in the present invention, the one surface is a light incident surface, and the recording capacity of the first surface side information recording layer closest to the light incident surface side is larger than that of the second surface side information recording layer. It is preferable that it is set. When light is incident from the surface of the medium adjacent to the first surface side information recording layer, no crosstalk occurs between this surface and the first surface side information recording layer, so that the signal characteristics are relatively good. The second surface side information recording layer farthest from the same surface has all other information recording layers interposed between the surface and the signal characteristics of the second surface side information recording layer, which is worse than that of the first surface side information recording layer. easy. Accordingly, the signal quality of the second information recording layer is improved by reducing the recording capacity of the second information recording layer as in the present invention, so that the first surface side information recording layer and the second surface side information recording layer can be improved. Signal characteristics can be homogenized.

  In the present invention, a light reflecting film is preferably formed in the vicinity of the second surface side information recording layer, and signal characteristics in the second surface side information recording layer can be improved.

  Furthermore, in the present invention, a plurality of the intermediate information recording layers can be provided. For example, even if the information recording layers including the first and second surface side information recording layers are arranged in four or more layers, the signal characteristics of the intermediate information recording layer can be improved.

  In the present invention, it is preferable that a distance between the first surface side information recording layer and the second surface side information recording layer is 0.100 mm or less. Even when the intermediate layer is further laminated in a narrow range of 0.100 mm or less, the signal characteristics of the intermediate information recording layer can be improved according to the present invention. In the present invention, it is preferable that the distance from the one surface to the first surface side information recording layer is 0.100 mm or less, and a plurality of information recording layers are laminated at positions deviated to the one medium surface side. In this case, the signal characteristics can be improved.

  In the present invention, the interval between the information recording layers is preferably set within 0.020 mm. For example, even if the interval between adjacent information recording layers is within 0.020 mm and a multi-layer structure of three or more layers is used, it is possible to avoid deteriorating the recording characteristics of the information recording layer. It can be compatible.

The present invention that achieves the above object is capable of reading information by a first information recording layer capable of reading information by reading light incident from a light incident surface and reading light incident from the light incident surface. The information can be read by the second information recording layer disposed farther from the light incident surface than the first information recording layer, and the reading light incident from the light incident surface, and the first and first information recording layers can be read. and an intermediate information recording layer disposed between and adjacent to the second information recording layer, the recording capacity of the intermediate information recording layer is set to be smaller as compared with the first information recording layer, the intermediate The multilayer optical recording medium is characterized in that a recording capacity of the information recording layer is set smaller than that of the second information recording layer .

  In the present invention, it is preferable that the recording capacity of the first information recording layer is set larger than that of the second information recording layer.

  Furthermore, in the above invention, it is preferable that a distance between the first information recording layer and the intermediate recording layer is 0.020 mm or less.

Further, the present invention that achieves the above object includes a substrate constituting one surface, a protective layer constituting the other surface, a first surface side information recording layer closest to the other surface, and the one surface. The closest second surface side information recording layer, an intermediate information recording layer disposed between the first and second surface side information recording layers, and a spacer layer provided to secure a predetermined gap between the information recording layers And the recording capacity of the intermediate information recording layer is set smaller than that of the first surface side information recording layer, and the recording capacity of the intermediate information recording layer is set to be the second surface side information recording layer. The multilayer optical recording medium is characterized by being set smaller than the layer.

  According to the above invention, it is possible to set a large recording capacity in the first surface side information recording layer and the second surface side information recording layer while securing a constant recording capacity in the intermediate information recording layer. The recording capacity of the entire optical recording medium can be increased. That is, while the information recording layer is multi-layered, the recording capacity of all the information recording layers is not intentionally unified, and the recording capacity of the intermediate information recording layer is individually reduced, thereby improving the overall signal characteristics and the recording capacity. We are trying to make both the increase of the above reasonably compatible.

  The recording capacity can be increased or decreased by increasing or decreasing the recording area or the recording density. Regarding the recording density, the linear recording density and track density of the information recording layer may be set as appropriate. Further, when recording information on these multilayer optical recording media using a recording / reproducing apparatus, the recording light / recording capacity / recording on the information recording layer is controlled by controlling the rotational speed of the recording light or the multilayer optical recording medium. The density is set appropriately.

  According to the present invention, in a multilayer optical recording medium, it is possible to achieve an excellent effect of stabilizing the quality of signal reproduction characteristics in the entire information recording layer and rationally increasing the recording capacity.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1A shows a multilayer optical recording medium 1 according to an embodiment of the present invention. This multilayer optical recording medium 1 is a disc-shaped medium having an outer shape of about 120 mm and a thickness of about 1.2 mm. 1B, the multilayer optical recording medium 1 includes a substrate 10, an L0 information recording layer 20, a first spacer layer 30, an L1 information recording layer 22, and a second spacer layer. 32, the L2 information recording layer 24, the third spacer layer 34, the L3 information recording layer 26, the cover layer 36, and the hard coat layer 38 are laminated in this order.

  The first to third spacer layers 30, 32, 34, the cover layer 36, and the hard coat layer 38 are all light transmissive and transmit laser light incident from the outside. As a result, if the laser beam Z incident from the light incident surface 38A of the hard coat layer 38 is used, information can be recorded / reproduced on all of the L0 to L3 information recording layers 20, 22, 24, 26, and 28. ing.

  The L3 information recording layer 26 is the first information recording layer most on one surface (light incident surface 38A) of the multilayer optical recording medium 1, and the L0 information recording layer 20 is the other surface (substrate 10). The L1 and L2 information recording layers 22 and 24 become intermediate information recording layers positioned between the first and second information recording layers. When recording / reproducing information to / from the L0 information recording layer 20, the L0 information recording layer 20 is irradiated with the laser beam Z through the L1 to L3 information recording layers 22, 24, and 26. Similarly, when information is recorded / reproduced with respect to the L1 information recording layer 22, the L1 information recording layer 22 is irradiated with the laser beam Z2 via the L2 and L3 information recording layers 24 and 26. When recording / reproducing information to / from the L2 information recording layer 24, the L2 information recording layer 24 is irradiated with laser light through the L3 information recording layer 26. When recording / reproducing information to / from the L3 information recording layer 26, the L3 information recording layer 26 is directly irradiated with the laser beam Z without passing through another information recording layer.

  Furthermore, in this multilayer optical recording medium 1, the recording capacity of the L3 information recording layer 26 closest to the light incident surface 38A is set larger than that of the L1 and L2 information recording layers 22 and 24. Specifically, the recording capacity of the L3 information recording layer 26 is 25 GB, and the recording capacities of the L1 and L2 information recording layers 22 and 24 are set to 23 GB. Further, the recording capacity of the L0 information recording layer 20 closest to the front surface side of the substrate 10 is also set larger than that of the L1 and L2 information recording layers 22 and 24, and specifically, set to 24 GB. Therefore, when the L0 information recording layer 20 and the L3 information recording layer 26 are compared, the recording capacity of the L3 information recording layer 26 is set large.

  Thus, by setting the recording capacity in the order of L3 information recording layer 26 (light incident side information recording layer)> L0 information recording layer 20> L1, L2 information recording layers 22 and 24, information will be described as will be described later. It is possible to suppress variations in the signal quality of the recording layer.

  The substrate 10 is a disk-shaped member having a thickness of about 1.1 mm, and various materials such as glass, ceramics, and resin can be used as the material. Here, polycarbonate resin is used. In addition to the polycarbonate resin, an olefin resin, an acrylic resin, an epoxy resin, a polystyrene resin, a polyethylene resin, a polypropylene resin, a silicone resin, a fluorine resin, an ABS resin, a urethane resin, or the like can be used as the resin. Of these, polycarbonate resins and olefin resins are preferred because of their ease of processing and molding. Further, grooves, lands, pit rows, and the like are formed on the surface of the substrate 10 on the information recording layer side according to applications.

  The first to third spacer layers 30, 32, and 34 are stacked between the L0 to L3 information recording layers 20, 22, 24, and 26, and between the information recording layers 20, 22, 24, and 26, respectively. Has the function of separating. Grooves (lands), pit rows, and the like are formed on the light incident surface 38A side surface of each spacer layer 30, 32, 34. Various materials can be used for the first to third spacer layers 30, 32, and 34. However, as described above, in order to transmit the laser beam Z, it is necessary to use a light transmissive material. For example, it is also preferable to use an ultraviolet curable acrylic resin.

  In the multilayer optical recording medium 1, the thickness of the first spacer layer 30 is set to 17 μm, the thickness of the second spacer layer 32 is set to 20 μm, and the thickness of the third spacer layer 34 is set to 13 μm. Thus, even when the spacer layers 30, 32, and 34 are set to have a thickness of 20 μm or less and the L1 and L2 information recording layers 22 and 24 are very close to the outer information recording layers, Since the recording capacities of the L1 and L2 information recording layers 22 and 24 located in the middle are actively reduced with respect to the recording capacities of the closest L0 and L3 information recording layers 20 and 26, the deterioration of signal characteristics is suppressed. can do. Here, the thickness of the spacer layers 30, 32, and 34 is made different from each other to further reduce the interference of the reproduction signal. The thickness of the hard coat layer 38 is set to 2 μm, and the thickness of the cover layer 36 is set to 48 μm.

  As a result, in this multilayer optical recording medium 1, the distance from the light incident surface 38A to the L3 information recording layer 26 can be set within 100 μm, specifically about 50 μm. The distance from the light incident surface 38A to the L2 information recording layer 24 is about 63 μm, the distance from the light incident surface 38A to the L1 information recording layer 22 is about 83 μm, and the distance from the light incident surface 38A to the L0 information recording layer 20 is about It is set to 100 μm. The distance between the L3 information recording layer 26 and the L0 information recording layer 20 is also set within 100 μm, preferably within 50 μm (here, about 40 μm). It should be noted that the L0 information recording layer 20 disposed at a position of about 100 μm from the light incident surface 38A can be matched with the Blu-ray Disc standard.

  The L0 to L3 information recording layers 20, 22, 24, and 26 are layers that hold data. As a data holding form, there are a read-only type in which data is written in advance and cannot be rewritten, and a recording type in which a user can write, and any of them may be adopted. In addition, when the data holding form is a recording type, in detail, a write-once type in which data cannot be written again in an area where data has been written once, and data is erased and written again in an area in which data is written. There are possible rewritable types, and any of them may be used. In the information recording layers 20, 22, 24, and 26, the data holding modes can be different from each other.

  As shown in FIG. 2A, when the data holding form of the L0 to L3 information recording layers 20, 22, 24, and 26 is a read-only type, the substrate 10, the first to third spacer layers 30, 32, A spiral pit row 40 is formed on the surface side of 34, thereby holding information. In this case, a reflective film is formed on the L0 to L3 information recording layers 20, 22, 24, and 26. The laser beam Z at the time of reproduction is reflected by the reflection films of the L0 to L3 information recording layers 20, 22, 24, and 26, and this reflection is performed by the pit row 40 that is in contact with each information recording layer 20, 22, 24, and 26. The rate changes and data can be read based on this change. Since the L1, L2, and L3 information recording layers 22, 24, and 26 are also required to have high light transmittance, it is necessary to reduce the thickness of the reflective film. That is, the L1, L2, and L3 information recording layers 22, 24, and 26 need to have both light transmittance and light reflection characteristics.

  As shown in FIG. 2B, when the data holding form of the L0 to L3 information recording layers 20, 22, 24 and 26 is a recording type, the substrate 10 and the first to third spacer layers 30 and 32 are used. , 34 is formed with a spiral groove 42 (land 44). In this case, on the L0 to L3 information recording layers 20, 22, 24, and 26, a recording film capable of forming the recording mark 46 by the energy of the laser beam Z is formed. The groove 42 serves as a guide track for the laser beam Z at the time of data recording. By modulating the energy intensity of the laser beam Z traveling along the groove 42, the information recording layer 20 on the groove 42, Recording marks 46 are formed at 22, 24 and 26. When the data holding mode is a write-once type, the recording mark 46 is formed irreversibly and cannot be erased. On the other hand, when the data holding mode is a rewritable type, the recording mark 46 is formed reversibly and can be erased and re-formed. This recording film also needs to have both light transmittance and light reflection characteristics. Although the case where the recording mark 46 is formed on the groove 42 is shown here, it may be formed on the land 44 or on both the groove 42 and the land 44.

  As described above, when the information recording layers 20, 22, 24, and 26 are formed in multiple layers, in order to make the laser beam Z having sufficient intensity reach the L0 information recording layer 20 farthest from the light incident surface 38A, It is necessary to improve the light transmission characteristics of the information recording layers 22, 24, and 26. According to the study by the present inventors, it is desirable to set the light transmittance of the L3 information recording layer 26 closest to the light incident surface 38A to about 80%.

  As already described, in the multilayer optical recording medium 1, the recording capacity of the L3 information recording layer 26 closest to the light incident surface 38A and the recording capacity of the L0 information recording layer 20 closest to the surface on the substrate 10 is intermediate between these. The recording capacities of the L1 and L2 information recording layers 22 and 24 positioned are positively reduced. Furthermore, in this embodiment, the recording capacity of the L0 information recording layer 20 farthest from the light incident surface 38A is set smaller than the recording capacity of the L3 information recording layer 26 close to the light incident surface 38A.

  The recording capacity of each information recording layer 20, 22, 24, 26 is determined by the combination of the size of the recording area (area) and the size of the recording density. In this embodiment, each information recording layer 20, 22 is recorded. , 24, and 26 have the same recording area (area), the capacity is changed by changing the recording density. Specifically, as shown in FIG. 2B, the recording density is set small by increasing the linear density of each recording mark 46, that is, the length T of the unit recording mark 46 in the spiral direction. In other words, by maximizing the length T in the spiral direction of the unit recording marks 46 (distance on the medium that can be assigned to 1 bit) of the L1 and L2 information recording layers 22 and 24, these information recording layers 22 and 24 are maximized. Recording capacity is minimized. In this embodiment, in order to change the length T of the recording mark 46 in the spiral direction, the linear velocity (that is, the rotational speed of the disc) when the laser beam Z travels in the groove is controlled. For example, when information equivalent to 25 GB is recorded on the L3 information recording layer 26, the recording linear velocity is set to 4.9 m / s, and information equivalent to 23 GB is recorded on the L1 and L2 information recording layers 22 and 24. The recording linear velocity is set to 5.3 m / s, and when recording information equivalent to 24 GB on the L0 information recording layer 20, the recording linear velocity is set to 5.1 m / s. In this way, if the rotational speed of the disk is changed, the linear density can be easily changed without changing the recording timing on the laser beam Z side.

  Although the case where the linear density is changed is shown here, the recording density can be reduced by increasing the helical pitch (interval) P of the spiral pit row 40 (or groove 43). Is possible. Although not specifically shown here, the recording density can be changed by changing the recording method.

  When reproducing the data of the multilayer optical recording medium 1 having this structure, the laser beam Z incident from the light incident surface 38A is focused on one of the L0 to L3 information recording layers 20, 22, 24, and 26. For example, as shown in FIG. 3A, when reproducing data recorded on the L3 information recording layer 26, the beam spot S of the laser beam Z3 is substantially minimized in the L3 information recording layer 26. The focus is controlled. Since the light reflection amount of the laser beam Z3 depends on the change in the light reflectance of the L3 information recording layer 26, it is possible to detect the presence or absence of a recording mark, and data is reproduced.

  Further, as shown in FIG. 3B, when reproducing data recorded on the L2 information recording layer 24, the beam spot of the laser beam Z2 is substantially minimized in the L2 information recording layer 24. The focus is controlled. Since the light reflection amount of the laser beam Z2 depends on the change in the light reflectance of the L2 information recording layer 24, it is possible to detect the presence / absence of a recording mark, and data is reproduced.

  As shown in FIG. 3C, when reproducing data recorded in the L1 information recording layer 22, the focus is set so that the beam spot of the laser beam Z1 is substantially minimized in the L1 information recording layer 22. Be controlled. Since the light reflection amount of the laser beam Z1 depends on the change in the light reflectance of the L1 information recording layer 22, it is possible to detect the presence or absence of a recording mark, and data is reproduced.

  As shown in FIG. 3D, when reproducing data recorded in the L0 information recording layer 20, the focus is set so that the beam spot of the laser beam Z0 is substantially minimized in the L0 information recording layer 20. Be controlled. Since the light reflection amount of the laser beam Z0 depends on the change in the light reflectance of the L0 information recording layer 20, it is possible to detect the presence or absence of a recording mark, and data is reproduced.

  FIG. 4 shows the situation of crosstalk when data recorded in these L0 to L3 information recording layers 20, 22, 24, and 26 is reproduced. As shown in FIG. 4A, when reproducing data from the L3 information recording layer 26, a part of the laser beam Z3 passes through the L3 information recording layer 26 and is reflected by the lower L2 information recording layer 24. Therefore, the reproduction signal of the L3 information recording layer 26 interferes with the reproduction signal of the L2 information recording layer 24. On the other hand, since only the hard coat layer 38 and the cover layer 36 exist between the L3 information recording layer 26 and the light incident surface 38A, there is almost no interference therebetween. As a result, the L3 information recording layer 26 can obtain relatively good signal characteristics.

  As shown in FIG. 4B, when reproducing the data of the L2 information recording layer 24, a part of the laser beam Z2 is reflected by the L3 information recording layer 26 on the upper layer side, and the other part is recorded in the L2 information recording layer. The light passes through the layer 24 and is reflected by the lower L1 information recording layer 22. As a result, the reproduction signal of the L2 information recording layer 24 interferes with the reproduction signals of the adjacent L1 and L3 information recording layers 22 and 26, so that the signal is likely to deteriorate. As shown in FIG. 4 (C), when the data of the L1 information recording layer 22 is reproduced, since the data is sandwiched between the L0 information recording layer 20 and the L2 information recording layer 24, the reproduction signal is similarly likely to interfere. become.

  As shown in FIG. 4D, when reproducing the data of the L0 information recording layer 20, a part of the laser beam Z0 is reflected by the L1 information recording layer 22 on the upper layer side. The signal interferes with the reproduction signal of the L1 information recording layer 22. On the other hand, since there is no data interference factor on the substrate 10 side in the L0 information recording layer 20, there is no signal interference on the substrate 10 side. As a result, the L0 information recording layer 20 can obtain relatively good signal characteristics. In particular, since the L0 information recording layer 20 has a plurality of information recording layers on the light incident surface side, a high reflectance is required. In this case, by laminating a light reflecting film on the substrate side 10, the light reflectance of the laser light Z0 can be further increased. It is also possible to reduce the influence of the reflected light of the L1 information recording layer 22 and improve the reproduction signal characteristics.

  As a result, in the multilayer optical recording medium, the influence of crosstalk tends to increase in the intermediate information recording layers (L1, L2 information recording layers 22 and 24) sandwiched between the two information recording layers. It can be seen that in the information recording layers close to (L0, L3 information recording layers 20, 26), deterioration of signal quality is suppressed.

  Therefore, in the multilayer optical recording medium 1 of the present embodiment, the recording capacities of the L1 and L2 information recording layers 22 and 24 located in the middle of the recording capacities of the L0 and L3 information recording layers 20 and 26 closest to the medium surface are set. We are actively reducing it. Decreasing the recording capacity results in an increase in the length of the recording mark (or pit) or an increase in the spiral pitch of the groove (or pit row), and the influence of the crosstalk of the reproduction signal. Can be substantially reduced. Accordingly, the bit error rate of the reproduction signal is reduced and the reproduction error in each information recording layer 22 and 24 can be easily corrected. Therefore, the reproduction characteristics of the L0 and L3 information recording layers 20 and 26 can be improved. In addition, a plurality of intermediate information recording layers can be formed even when the distance from the light incident surface 38A is within a range of 100 μm, and the information recording layer in the vicinity of 100 μm is adapted to the Blu-ray Disc standard while Further multilayering can be realized on the incident surface 38A side.

  Furthermore, in this multilayer optical recording medium 1, since the distance between the L3 information recording layer 26 closest to the light incident surface 38A and the L0 information recording layer 20 farthest from the light incident surface 38A is set within 100 μm, Multiple layers of three layers or more are realized within a very narrow range. In the present embodiment, by setting the thickness of the spacer layers 30, 32, and 34 to 20 μm or less, the multilayering of four or more layers within the range of 100 μm is realized. Note that the L0 information recording layer 20 whose signal quality is likely to deteriorate somewhat due to the influence of the plurality of information recording layers 22, 24, 26 arranged on the light incident surface 38 A side also has a recording capacity with respect to the L3 information recording layer 26. By reducing it, it is possible to obtain signal quality substantially the same as that of the L3 information recording layer 26.

  [Reference analysis]

  First, in order to clarify the basic signal characteristics of the information recording layer itself, only one information recording layer having the same composition and thickness as those of the L0 to L3 information recording layers 20, 22, 24, and 26 in Examples described later is provided. Four analytical disks were formed and coated with a 100 μm cover layer thereon. FIG. 5 shows the result of evaluating the jitter when the random signals recorded on the four discs are reproduced. The L0 to L3 information recording layers 20, 22, 24, and 26 have an evaluation value of 6.1% to 6.5% in the single layer state, and the information recording layers 20, 22, 24, and 26 themselves have a difference in signal characteristics. You can see that there is no.

  [Comparative example]

  Next, as a comparative example, the L0 to L3 information recording layers 20, 22, 24, and 26 are formed in a single medium in the same manner as in the examples described later to create a multilayer optical recording medium, and these information recording layers Random signals were recorded and reproduced with the same recording capacity (25 GB) / recording density for 20, 22, 24, and 26. The result of evaluating the jitter of the reproduced signal is shown in FIG. The signal characteristics of the L0 information recording layer 20 and the L3 information recording layer 26 are not so deteriorated as compared with the single layer, but 7.0% for the L1 and L2 information recording layers 22 and 24 located in the middle. It can be seen that the signal characteristics deteriorate significantly. The L1 and L2 information recording layers 22 and 24 are considered to be caused by crosstalk between adjacent information recording layers at a distance of 20 μm or less on both sides.

  [Example 1]

  Based on the above result, the Example at the time of actually manufacturing the multilayer optical recording medium 1 is shown concretely. In addition, this invention is not limited to these Examples at all.

  [Create sample media]

  First, the substrate 10 was manufactured by an injection molding method. A spiral groove having a track pitch of 0.32 μm was formed on the surface of the substrate 10. A polycarbonate resin was used as the material of the substrate 10 and the thickness was set to 1.1 mm and the diameter was 120 mm.

  Next, this substrate 10 was set in a sputtering apparatus, and the L0 information recording layer 20 having a thickness of 48 nm was formed on the surface on the side where the grooves were formed. Specifically, the composition of the L0 information recording layer 20 is bismuth (Bi), oxygen (O), and germanium (Ge), and the composition ratio (atm%) is Bi: O: Ge = 29: 70: 1. Set to.

  Next, the substrate 10 on which the L0 information recording layer 20 was formed was set in a spin coater, and an acrylic ultraviolet curable resin was dropped while being rotated, and this was spin coated. Thereafter, a light transmissive stamper having a spiral groove pattern was pressed against the surface of the spin-coated resin, and the resin was cured by irradiating the resin with ultraviolet rays through the light transmissive stamper. After curing, the light transmissive stamper was peeled off to complete a first spacer layer 30 having a spiral groove (track pitch is 0.32 μm) and a thickness of 17 μm.

  Next, the L1 information recording layer 22 was formed on the first spacer layer 30 by the same method as the L0 information recording layer 20. The composition ratio (atm%) of bismuth (Bi), oxygen (O), and germanium (Ge) was set to Bi: O: Ge = 25: 71: 4, and the thickness was 62 nm.

  Further, a second spacer layer 32 was formed on the L1 information recording layer 22 by the same method as that for the first spacer layer 30. The thickness of the second spacer layer 32 was set to 20 μm. Next, on the second spacer layer 32, the thickness is 68 nm, and the composition ratio (atm%) of bismuth (Bi), oxygen (O), and germanium (Ge) is set to Bi: O: Ge = 25: 68: 7. The L2 information recording layer 24 is formed, and a third spacer layer 34 having a thickness of 13 μm is formed thereon. Further, on the third spacer layer 34, a thickness of 73 nm, bismuth (Bi), oxygen (O ), The L3 information recording layer 26 in which the composition ratio (atm%) of germanium (Ge) was set to Bi: O: Ge = 23: 68: 9 was formed.

  Then, the substrate 10 on which the L3 information recording layer 26 is formed is set in a spin coater, and an acrylic ultraviolet curable resin is dropped while rotating, and the cover layer 36 having a thickness of 48 μm is completed by irradiating it with ultraviolet rays. It was.

  Further, an ultraviolet / electron beam curable hard coating agent is applied onto the cover layer 36 by a spin coating method, and then heated in the atmosphere for 3 minutes to remove the diluting solvent inside the coating, and the uncured hard coating material layer Formed. A surface material solution was applied to the uncured hard coat material layer by a spin coat method. This surface material solution was prepared by adding perfluoropolyether diacrylate (0.33 parts by weight, molecular weight: about 2000) and 3-perfluorooctyl-2-hydroxypropyl to a fluorinated solvent (99.5 parts by weight). It is prepared by adding acrylate (0.17 parts by weight). Thereafter, the hard coat material layer was dried at 60 ° C. for 3 minutes and further irradiated with an electron beam under a nitrogen stream to simultaneously cure the hard coat material layer and the surface material solution, thereby completing the hard coat layer 38. In addition, about the irradiation of an electron beam, the electron beam irradiation apparatus Curetron (made by Nissin High Voltage Co., Ltd.) was used, the electron beam acceleration voltage was 200 kV, and the irradiation dose was 5 Mrad. The oxygen concentration in the irradiation atmosphere was 80 ppm. In this way, a multilayer optical recording medium 1 was obtained.

  [Evaluation of sample media]

  Random sample data was recorded on the L0 to L3 information recording layers 20, 22, 24, and 26 of the multilayer optical recording medium 1. At this time, the L0 information recording layer 20 and the L3 information recording layer 26 perform recording with the recording capacity set to 25 GB, and the recording capacities for the L1 and L2 information recording layers 22 and 24 are set to 23 GB and 23 GB. Recorded. Considering the unit recording marks, the recording marks of the L1 and L2 information recording layers 22 and 24 are longer than the recording marks of the L0 and L3 information recording layers 20 and 26.

  FIG. 7 shows the result of evaluating the jitter of the reproduction signal of the multilayer optical recording medium 1 on which data has been recorded. In this multilayer optical recording medium 1, the L0 information recording layer 20 has a jitter of 6.4%, the L1 information recording layer 22 has a jitter of 6.3%, the L2 information recording layer 24 has a jitter of 6.3%, and an L3 information recording medium. It can be seen that the jitter of the layer 26 is 6.7%, and the reproduced signal is homogenized in a high quality state in all of the L0 to L3 information recording layers 20, 22, 24, and 26. Further, when analyzed in relation to the L0, L1, and L2 information recording layers 20, 22, and 24, in [Comparative Example], the jitter of the L1 and L2 information recording layers 22 and 24 located in the middle is 7.7 and 7.4%. Although the recording capacities of the L1 and L2 information recording layers 22 and 24 (23 GB and 23 GB) are made smaller than the recording capacities (25 GB) of the L0 information recording layer 20, L1 and L2 It can be seen that the jitter of the information recording layers 22 and 24 can be improved.

  These recording capacities need only be set by controlling the rotational speed of the multilayer optical recording medium 1 by the recording / reproducing device, so that no special development burden is imposed on the recording / reproducing device, thereby reducing development costs. You can also In the multilayer optical recording medium 1, three or more information recording layers, preferably four or more information recording layers can be stacked within an extremely narrow range of about 100 μm from the light incident surface 38A. (Pickup) can be shared between these information recording layers, and the manufacturing cost of the recording / reproducing apparatus can be reduced.

  [Example 2]

  Next, using the same sample medium as the multilayer optical recording medium 1 shown in Example 1, 24 GB (recording linear velocity 5.1 m / s) is used for the L0 information recording layer 20, and 25 GB (recording linear velocity) is used for the L3 information recording layer 26. 4.9 m / s), sample data was recorded on the L1 and L2 information recording layers 22 and 24 with a recording capacity of 23 GB (recording linear velocity 5.3 m / s).

  FIG. 8 shows the result of evaluating the jitter of the reproduction signal of the multilayer optical recording medium 1. In this multilayer optical recording medium 1, the recording capacity of the L0 information recording layer 20 farthest from the light incident surface 38A is set smaller than that of the L3 information recording layer 26 closest to the light incident surface 38A. The jitter of the L0 information recording layer 20 is reduced to 6.2%. That is, in the L0 information recording layer 20, the laser light from the light incident surface 38A side is weakened by the reflection of all the other information recording layers 22, 24, and 26. Although the characteristics are likely to deteriorate, by doing so, the signal quality of the L0 information recording layer 26 is individually improved, and the signal characteristics of the L0 to L3 information recording layers 20, 22, 24, and 26 are further homogenized. It will be. Although not particularly shown here, it is also preferable to further improve the reflectance of the reproduction light of the L0 information recording layer 20 by separately forming a light reflecting film in the vicinity of the L0 information recording layer 20.

  As described above, in the present embodiment, the information recording layer closest to the surface of the multilayer optical recording medium 1 is shown only when the recording capacity is reduced to the intermediate information recording layer, but the present invention is not limited thereto. An intermediate information recording layer is appropriately selected from the three or more information recording layers excluding the surface side, and the recording capacity of the intermediate information recording layer is set to first and second information recording layers adjacent to both outer sides of the intermediate recording layer. The recording capacity may be set smaller than the recording capacity. By doing so, it becomes possible to individually improve the signal reproduction characteristics of the intermediate information recording layer.

  For example, when the user carries the multilayer optical recording medium 1 or inserts it into a recording / reproducing device, foreign matter 50 such as fingerprints and dust adheres to the light incident surface 38A. The foreign matter 50 may deteriorate the reproduction signal characteristics of the multilayer optical recording medium 1. Accordingly, it is conceivable to set the recording capacity on the L3 information recording layer 26 side small in order to cope with the deterioration of signal characteristics due to disturbance in advance. In such a case, in consideration of the special circumstances of the L3 information recording layer 26, the recording capacity of the L1 information recording layer 22 is set smaller than the recording capacity of the L2 information recording layer 24, and the L1 information recording layer 26 is set. It is also possible to individually improve the signal characteristics of the layer 22.

  Further, in the present embodiment, only when the recording capacities of a plurality of information recording layers arranged therebetween are set smaller than the recording capacities of the information recording layers closest to both outer surfaces of the multilayer optical recording medium. Although shown, the invention is not so limited. In the case where there are a plurality of information recording layers located in the middle, the present invention includes the case where the recording capacity of one of the information recording layers is set smaller than the recording capacity of the information recording layer closest to the outer surface. Yes.

  In the present embodiment, the information recording layer of the multilayer optical recording medium is shown as being only four layers, but the present invention is not limited to this and may be three layers or five layers or more. In the present embodiment, all four information recording layers are shown to be stacked within 100 μm from the light incident surface. However, the present invention is not limited to this, and the information recording layers are stacked in a place of 100 μm or more. May be. It is also preferable that a part of the information recording layer in the multilayer is laminated at a place of 100 μm or more.

  In this embodiment, the interval between adjacent information recording layers, that is, the thickness of the spacer layer is shown only when it is set to 0.020 nm or less, but the present invention is not limited to this. For example, the thickness of some spacer layers may be 0.020 nm or less, and the thickness of other spacer layers may be larger than 0.020 nm. In the present invention, it is not always necessary to set the interval between all the information recording layers to 0.020 nm or less.

  Furthermore, in the present embodiment, the density of the information in the line direction (longitudinal direction of the groove) is reduced to reduce the information recording capacity. However, the present invention is not limited to this, and other methods are used. May adjust the recording capacity. Further, the recording area of the information recording layer closest to the light incident surface can be reduced. Note that the multilayer optical recording medium of the present invention is not limited to the above-described embodiment, and it is needless to say that various modifications can be made without departing from the gist of the present invention.

  According to the present invention, in various multilayer optical recording media in which data is held, it is possible to rationally improve the signal characteristics of an information recording layer disposed in the middle, and to increase the overall recording capacity. .

1 is a perspective view and an enlarged sectional view showing a multilayer optical recording medium according to an example of an embodiment of the present invention. An enlarged perspective view showing a data holding form in the information recording layer of the multilayer optical recording medium Sectional drawing which shows the state which reproduces | regenerates each information recording layer of the multilayer optical recording medium Sectional view showing a state in which crosstalk occurs due to transmission / reflection of laser light of the multilayer optical recording medium Chart showing the results of analyzing the signal characteristics of the information recording layer itself used in the multilayer optical recording medium Chart showing results of analyzing signal characteristics of multilayer optical recording medium as comparative example FIG. 3 is a chart showing the results of analyzing the signal characteristics of the multilayer optical recording medium of Example 1. FIG. FIG. 5 is a chart showing the results of analyzing the signal characteristics of the multilayer optical recording medium of Example 2. Sectional view schematically showing the structure of a conventional DVD Sectional view schematically showing the structure of a conventional hybrid DVD

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Multi-layer optical recording medium 10 ... Substrate 20 ... L0 information recording layer 22 ... L1 information recording layer 24 ... L2 information recording layer 26 ... L3 information recording layer 30 ... First 1 spacer layer 32 ... 2nd spacer layer 34 ... 3rd spacer layer 36 ... cover layer 38 ... hard coat layer 38A ... light incident surface

Claims (13)

A first surface-side information recording layer closest to one surface;
A second surface side information recording layer closest to the other surface;
An intermediate information recording layer disposed between the first and second surface side information recording layers,
The recording capacity of the intermediate information recording layer is set smaller than that of the first surface side information recording layer ,
A multilayer optical recording medium , wherein a recording capacity of the intermediate information recording layer is set smaller than that of the second surface side information recording layer . A first surface-side information recording layer closest to one surface;
A second surface side information recording layer closest to the other surface;
An intermediate information recording layer disposed between the first and second surface side information recording layers,
The one surface is a light incident surface, and the recording capacity of the first surface side information recording layer closest to the light incident surface side is set larger than that of the second surface side information recording layer,
A multilayer optical recording medium, wherein a recording capacity of the intermediate information recording layer is set smaller than that of the first surface side information recording layer. The one surface is a light incident surface, and the recording capacity of the first surface side information recording layer closest to the light incident surface side is set larger than that of the second surface side information recording layer. The multilayer optical recording medium according to claim 1 .   4. The multilayer optical recording medium according to claim 1, wherein a light reflecting film is formed in the vicinity of the second surface side information recording layer.   The multilayer optical recording medium according to claim 1, comprising a plurality of the intermediate information recording layers.   6. The multilayer optical recording medium according to claim 1, wherein a distance between the first surface side information recording layer and the second surface side information recording layer is within 0.100 mm.   7. The multilayer optical recording medium according to claim 1, wherein a distance from the one surface to the first surface side information recording layer is 0.100 mm or less.   The multilayer optical recording medium according to any one of claims 1 to 7, wherein a distance between adjacent information recording layers is within 0.020 mm. A first information recording layer capable of reading information by reading light incident from a light incident surface;
A second information recording layer that is capable of reading information by reading light incident from the light incident surface and is disposed farther from the light incident surface than the first information recording layer;
An intermediate information recording layer capable of reading information by reading light incident from the light incident surface, and disposed adjacent to the first and second information recording layers,
A recording capacity of the intermediate information recording layer is set to be smaller than that of the first information recording layer ;
A multilayer optical recording medium , wherein a recording capacity of the intermediate information recording layer is set smaller than that of the second information recording layer . A first information recording layer capable of reading information by reading light incident from a light incident surface;
A second information recording layer that is capable of reading information by reading light incident from the light incident surface and is disposed farther from the light incident surface than the first information recording layer;
An intermediate information recording layer capable of reading information by reading light incident from the light incident surface, and disposed adjacent to the first and second information recording layers,
The recording capacity of the intermediate information recording layer is set smaller than that of the first information recording layer,
A multilayer optical recording medium, wherein a recording capacity of the first information recording layer is set larger than that of the second information recording layer. The multilayer optical recording medium according to claim 9 , wherein a recording capacity of the first information recording layer is set larger than that of the second information recording layer.   12. The multilayer optical recording medium according to claim 9, wherein a distance between the first information recording layer and the intermediate recording layer is within 0.020 mm. A substrate constituting one surface, a protective layer constituting the other surface, a first surface side information recording layer closest to the other surface, and a second surface side information recording layer closest to the one surface; An intermediate information recording layer disposed between the first and second front side information recording layers, and a spacer layer provided to ensure a predetermined gap between the information recording layers,
The recording capacity of the intermediate information recording layer is set smaller than that of the first surface side information recording layer ,
A multilayer optical recording medium , wherein a recording capacity of the intermediate information recording layer is set smaller than that of the second surface side information recording layer .

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