JP3986702B2 - Optical recording medium and substrate for optical recording medium - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical recording medium in which grooves or pits are formed in areas other than the information area, and more particularly to an optical recording medium in which tracking is performed only in the grooves or pits provided in the information area and a substrate used therefor .
[0002]
[Prior art]
Optical discs such as MO (magneto-optical disc) and DVD (digital versatile disc) are used as information recording media capable of recording and reproducing a wide variety of information data such as video, audio and text. In an optical disc, information is recorded in an information area defined by a standard, and a tracking guide groove (groove) and pits as format information or recording information are usually formed in this information area. The range of the information area differs depending on the type of the optical disk. For example, in a DVD-ROM having a diameter of 120 mm and a recording capacity of 4.7 GB (gigabyte), the area from the radius R22.6 mm to R58.5 mm depends on the standard. It is a defined information area. An MO (ISO / IEC 15286) having a recording capacity of 130 mm in diameter and 5.2 GB in size has a radius of R29. An area from Omm to R62.5 mm is an information area defined by the standard.
[0003]
A region other than the information region (hereinafter referred to as a non-information region) is usually a mirror region in which no groove or pit is formed. For example, in the 130 mm size 5.2 GB MO, the inner circumference R27. Omm to R29. The region up to Omm is a mirror region (reflective zone) where grooves and pits are not formed. On the other hand, a recording medium in which grooves or pits are formed in this mirror area is known. For example, Japanese Patent Application Laid-Open No. 4-195932 discloses an optical disk substrate in which grooves or pits are formed on the entire surface of the information recording surface. By forming grooves or pits on the entire surface of the information recording surface, a stamper and a substrate are disclosed. The stress generated in the substrate is reduced by preventing uneven release at the time of release.
[0004]
Japanese Laid-Open Patent Publication No. 2-66749 discloses an optical disc in which a dummy pattern is formed on the outer peripheral portion and / or the inner peripheral portion other than the recording region in order to prevent molten resin molding sinks that occur during the cooling process of the injection molding method. Is disclosed.
[0005]
[Problems to be solved by the invention]
However, when an optical recording medium having a concavo-convex pattern in a non-information area as disclosed in Japanese Patent Laid-Open Nos. 4-195932 and 2-66749 is recorded or reproduced by a recording / reproducing apparatus, It was found that problems like That is, since a certain uneven pattern exists in the non-information area, the drive device for recording / reproducing detects the tracking signal from the non-information area, and there is a risk of tracking. If tracking is applied to a non-information area, the drive device side erroneously recognizes that area as an information area where information is recorded, and tries to execute recording or reproduction of information. An error occurs because the shape is not specified in. As described above, there is a problem that the recording / reproducing apparatus malfunctions with respect to the optical recording medium having the uneven pattern in the non-information area.
[0006]
The present invention has been made to solve the above-described problems of the prior art, and an object thereof is an optical recording medium in which a recording / reproducing apparatus does not cause a tracking malfunction due to a groove or a pit existing in a non-information area. And providing a substrate thereof.
[0007]
Another object of the present invention is to provide an optical recording medium having uniform optical characteristics over the radial direction of a disk-shaped substrate and having grooves or pits having a uniform shape in an information area, and a substrate suitable for the same.
[0008]
[Means for Solving the Problems]
According to the first aspect of the present invention, in an optical recording medium for recording or reproducing information by condensing and irradiating light having a wavelength λ with a lens having a numerical aperture NA to an information area where information is recorded,
The region other than the information region has at least one of a groove and a pit in a concentric or spiral shape, and a track pitch of a track defined by the groove or the pit is 0.5λ / NA or less. An optical recording medium is provided.
[0009]
FIG. 1 shows an example of an optical recording medium according to the present invention. A center hole for fixing the optical recording medium to the spindle of the recording / reproducing apparatus is formed at the center of the optical recording medium. In most areas of the optical recording medium, there is an information area 1 in which information is recorded, which is defined by a standard. The information area 1 is usually composed of a lead-in area, a data area, a lead-out area, etc., but these are not shown in FIG. The optical recording medium 10 of the present invention has grooves or pits in an area other than the information area 1 in which information is recorded, that is, an outer area 2 and an inner area 3 of the information area 1. The tracks defined by them are spiral or concentric so that the track pitch is 0.5λ / NA or less. Here, λ represents the wavelength of light, NA represents the numerical aperture of the lens, and λ / NA represents the diameter of the light spot. That is, in the present invention, a groove is formed so that two or more grooves are included in the light spot, or in the case of pits, two or more pits are included in the light spot in the track width direction. Form a pit. Thereby, even if the light spot scans the non-information area in which the pits and grooves are formed, tracking does not occur. The reason will be described below.
[0010]
As a method for detecting the tracking signal, a push-pull method will be described as an example with reference to FIG. FIG. 4 is a conceptual diagram of the push-pull method. When the laser beam 42 focused by the objective lens 41 is irradiated onto the disk 10, the guide grooves (grooves) 43 or pits formed on the disk 10 serve as the diffraction grating. As a result, 0th-order diffracted light and 1st-order diffracted light are generated. In the push-pull method, first-order diffracted light reflected and diffracted from a groove or pit existing in a light spot is received by a two-divided photodiode detector 44 arranged symmetrically with respect to the center in the track width direction to detect each light. A difference in output between the units 44a and 44b is detected. When the center of the light spot coincides with the center of the groove or pit, the output difference between the light detection units 44a and 44b becomes equal, and the tracking error signal is not detected. On the other hand, when the center of the light spot deviates from the center of the groove or pit in the track width direction, the light intensity distribution of the diffracted light changes and a tracking error signal is detected.
[0011]
In the optical recording medium of the present invention, as shown in FIG. 2, the track pitch of the grooves or pits in the non-information area is adjusted so that two or more grooves or pits are included in the light spot. As a result, in the non-information area, the first-order diffracted light from two or more grooves or pits in the light spot enters the two-divided photodiode detector. Therefore, even if the light spot is shifted in the track width direction, at least two grooves or pits are always included in the light spot, and the total sum of diffracted light detected by the detector is constant. Therefore, the tracking signal cannot be detected from the non-information area and tracking is not applied. That is, since the grooves or pits formed in the non-information area are below the light spot reproduction resolution, the drive device shows only the same reaction as when scanning the mirror area. Therefore, a non-information area is not mistaken for a data area.
[0012]
In the present invention, when pits are formed in the non-information area, in order to prevent the tracking signal from being detected from the formed pits, as shown on the right side of FIG. The total length of the pit length and the interval between adjacent pits in the track direction, that is, the length of the space defined by the pits (hereinafter referred to as the space length) is 0. It is preferable to configure so as to be 5λ / NA or less. As a result, since at least two or more pits are included in the light spot diameter and become less than the reproduction resolution, the drive device cannot perform tracking even if the tracking operation is performed in the non-information area.
[0013]
In the present invention, the pit length and the space length can be arbitrarily combined as long as the above conditions are satisfied. For example, either the pit or the space may be formed to be long, or may be formed to have the same length.
[0014]
Further, in FIG. 2 used in the above description, as an example of the groove formed in the non-information area, the land has a wider type than the groove. However, the present invention is not limited to this, and two or more in the light spot. As long as the groove is included, the groove may be wider than the land. Further, a land / groove type in which the land and the groove have the same width may be used. Further, in the non-information area, only a groove may be formed, or only a pit may be formed, or a groove and a pit may be mixed.
[0015]
According to the second aspect of the present invention, it is used for an optical recording medium for recording or reproducing information by converging and irradiating light having a wavelength λ with a lens having a numerical aperture NA to an information area where information is recorded. In an optical recording medium substrate,
The region other than the information region has at least one of a groove and a pit in a concentric or spiral shape, and a track pitch of a track defined by the groove or the pit is 0.5λ / NA or less. An optical recording medium substrate is provided.
[0016]
In the substrate of the present invention, grooves or pits are provided in an area other than the information area where information is recorded, that is, a non-information area, and an interval in the track width direction of the groove or pit, that is, a track pitch is 0.5λ / It is adjusted to be NA or less. For this reason, even when an optical recording medium is manufactured using the substrate of the present invention, tracking does not occur in the non-information area, and the non-information area is not mistaken for the data area. Further, since the substrate of the present invention is provided with grooves or pits in the non-information area, the following problems that occur when the substrate is manufactured can be solved.
[0017]
In the conventional substrate for optical recording media, the area other than the information area where information is recorded, that is, the non-information area is a mirror area where no groove or pit exists. For this reason, for example, in the exposure process when manufacturing an optical disc master, even if exposure is performed with the same exposure intensity in order to form uniform grooves and pits over the entire circumference in the area corresponding to the information area, the exposed master In the developing process for developing the groove, the flow of the developer changes at the boundary between the information area and the mirror area, so that a groove or pit having a desired shape may not be obtained. For this reason, uniform grooves or pits are hardly formed in the information area of the substrate manufactured based on the master.
[0018]
Also, when a substrate is manufactured by injection molding, the stamper loaded in the injection mold is provided with an information area in which grooves or pits are formed and a groove or pit formed in the same manner as the substrate to be molded. Since there is a mirror area that is not formed, the fluidity of the molten resin changes at the boundary between the information area and the mirror area when the molten resin is injected and filled into the mold, There has been a problem that the resin filling state varies between the outermost peripheral portion and the innermost peripheral portion. For this reason, the optical characteristic of the board | substrate shape | molded changes in an outermost periphery part and an innermost periphery part, and the retardation by birefringence arises.
[0019]
On the other hand, since the optical recording medium substrate of the present invention is provided with grooves or pits in the non-information area, it is developed at the boundary between the information area and the non-information area in the development process of the master for producing such a substrate. The flow of the liquid does not change and development can be performed satisfactorily. Therefore, uniform grooves or pits are formed in the information area of the substrate. Also, when the substrate is manufactured by injection molding, since the grooves or pits exist in the non-information area of the injection molding stamper in the same manner as the information area, the molten resin is formed at the outermost periphery and the innermost periphery. The molten resin can be filled while keeping the fluidity constant. Therefore, the substrate of the present invention has uniform optical characteristics from the outermost periphery to the innermost periphery.
[0020]
For the optical recording medium substrate of the present invention, any material having optical transparency can be used. For example, transparent resin materials such as polycarbonate, polymethyl methacrylate, polymethylpentene, and epoxy can be used. The substrate can be manufactured, for example, by injection molding the transparent resin material using an injection molding machine equipped with a stamper having grooves or pits concentrically or spirally in an area other than the information area. Not only the manufacturing method but also 2P (Photo-Polymerization) method may be used.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Examples of the optical recording medium of the present invention will be specifically described below with reference to the drawings. However, the present invention is not limited to this.
[0022]
[Example 1]
In Example 1, a DVD-ROM was manufactured as an example of an optical recording medium according to the present invention. The DVD-ROM has a disk shape with a diameter of 120 mm, and an area with a radius of 22.6 mm to 58.5 mm is an information area defined by the standard. FIG. 5 shows a schematic sectional view of the DVD-ROM. The DVD-ROM 100 includes laminated bodies 110 and 120 each of which is formed by sequentially laminating a light reflecting layer 22 and a protective layer 23 on a set of light transmissive substrates 21, and an adhesive layer 24 so that the protective layer 23 side is on the inside. Have a structure in which they are bonded together. A method for manufacturing the DVD-ROM 100 having such a structure will be described below.
[0023]
Initially, the glass original disk used when producing the transparent substrate 21 was manufactured as follows. First, a polished flat glass substrate was prepared, and a photoresist sensitive to ultraviolet rays was uniformly applied on the glass substrate with a predetermined film thickness. Next, a glass substrate was placed on a turntable of a master exposure apparatus (not shown), and exposure was performed by irradiating the photoresist with laser light while rotating the glass substrate. At this time, the exposure was performed by turning on and off the laser beam so that the concave / convex pattern corresponding to the recording information and the tracking pre-pits was formed in the area corresponding to the information area. On the other hand, in the region corresponding to the non-information region, that is, the region on the outer peripheral side from the radius of 58.5 mm and the region on the inner peripheral side from the radius of 22.6 mm, the pits and spaces are alternately arranged and both have a constant length of 270 nm or less. The exposure was carried out with the laser beam turned on and off so that was formed. In addition, the exposure of the master disk in the radial direction was controlled so that the track pitch of the tracks defined by the pits was 540 nm or less. Next, the exposed photoresist was developed using a developer. Irregularities corresponding to pre-pits were formed in the photoresist on the glass substrate. Thus, a glass master having desired pre-pits in the information area and the non-information area was produced.
[0024]
Next, a nickel stamper was produced by performing nickel electroforming on the glass master. Then, the produced stamper was mounted on a mold of an injection molding machine, and a polycarbonate resin was injected and filled into the mold to produce a light transmissive substrate 1. The produced light-transmitting substrate 21 had pits for recording information and pits for tracking in a spiral shape in the information area. The interval between pits in the substrate radial direction, that is, the track pitch was 740 nm, and the shortest pit length was 400 nm. Also, in a non-standard area outside the radius of 58.5 mm and an area outside the radius of 22.6 mm, a pit row with a track pitch of 540 nm or less and a duty of 50% is spirally formed with a shortest pit length of 270 nm or less. Had.
[0025]
On the light transmissive substrate 21 having such pits, a light reflecting layer 22 made of aluminum was formed in a film thickness range of 35 nm to 50 nm using a sputtering apparatus (not shown). Next, a protective layer 23 made of an ultraviolet curable resin was formed on the reflective layer 22 within a thickness range of 6 μm to 10 μm. Thus, the laminate 10 having the light reflecting layer 22 and the protective layer 23 on the light transmissive substrate 21 was produced. Furthermore, a laminate 20 having the same laminate structure as that of the laminate 10 is prepared, and the laminates 10 and 20 are ultraviolet-curing cationic polymerization epoxy resin or ultraviolet-curing so that the protective layer 23 is a bonding surface. A DVD-ROM 100 was manufactured by bonding using an adhesive made of a type radical polymerization acrylic resin.
[0026]
The DVD-ROM 100 manufactured in this way can be played back using a DVD-ROM playback device (not shown). The optical system of the DVD-ROM reproducing apparatus has a reproducing light wavelength λ of 650 nm, a lens numerical aperture of 0.60, and a light spot size of 1080 nm. In the information area, the ratio of the track pitch to the light spot diameter was 68.5%, and the ratio of the shortest pit length to the light spot diameter was 37.0%. In the non-information area of the DVD-ROM, the track pitch of the pit row is 540 nm or less, and the pit length at a duty of 50% is 270 nm or less. It is never mistaken for data. On the other hand, since the pit in the information area has a track pitch of 740 nm and the total length of the shortest pit length and the shortest space length is 800 nm, the pit can be reproduced sufficiently distinguishing from the pit formed in the non-information area.
[0027]
[Example 2]
In this example, a 5.2 GB magneto-optical disk (ISO / IEC 15286) was produced as another example of the optical recording medium according to the present invention. Such a magneto-optical disk has a disk shape with a diameter of 130 mm, and an area from a radius of 29 mm to 62.5 mm is an information area defined by the standard. FIG. 6 shows a schematic cross-sectional view of the magneto-optical disk 200. The magneto-optical disk 200 has a structure in which a first dielectric layer 32, a recording layer 33, a second dielectric layer 34, a reflective layer 35, and a protective layer 36 are sequentially laminated on a light transmissive substrate 31. A method for manufacturing the magneto-optical disk 200 having such a structure will be described below.
[0028]
Initially, the glass original disk used when producing the transparent substrate 31 was manufactured as follows. First, a polished flat glass substrate was prepared, and a photoresist that reacts with ultraviolet rays was uniformly applied to the glass substrate with a predetermined film thickness. Next, a glass substrate was placed on a turntable of a master exposure apparatus (not shown), and exposure was performed by irradiating the photoresist with laser light while rotating the glass substrate. At this time, in the area corresponding to the information area, exposure was performed by turning on and off the laser beam so that a concavo-convex pattern corresponding to prepits and tracking grooves as format information was formed. On the other hand, in the area on the outer periphery side of the area radius of 62.5 mm corresponding to the non-information area, exposure is performed by controlling the radial position of the master so that the track pitch of the tracks defined by the groove is 625 nm or less. It was. Next, the exposed photoresist was developed using a developer. Irregularities corresponding to prepits and grooves were formed in the photoresist on the glass substrate. Thus, a glass master having desired prepits and pregrooves in the information area and desired grooves in the non-information area was manufactured.
[0029]
Next, a nickel stamper was produced by performing nickel electroforming on the glass master. Then, the produced stamper was mounted on a mold of an injection molding machine, and a polycarbonate resin was injected and filled into the mold to produce a light transmissive substrate 1. The produced light-transmitting substrate 21 had prepits and tracking grooves as preformat information in a spiral shape with a track pitch of 850 nm in its information area. The shortest pit length of the prepit was 540 nm. In addition, a groove having a track pitch of 625 nm or less was spirally formed in a region (non-information region) on the outer peripheral side from a radius of 62.5 mm which is outside the standard.
[0030]
A first dielectric layer 32 made of SiN is formed on the light-transmitting substrate 31 with a thickness of 85 nm to 100 nm using a sputtering apparatus (not shown). ₂₃ Fe ₆₀ Co ₁₄ Nb ₃ The recording layer 33 made of Si was deposited in a thickness of 20 nm, the second dielectric layer 34 made of SiN was deposited in a thickness of 20 nm, and the light reflecting layer 35 made of Al (aluminum) was sequentially deposited in a thickness of 100 nm. Next, a protective layer 36 made of a UV-based protective resin was formed on the reflective layer 35 within a thickness range of 6 μm to 10 μm. Thus, the magneto-optical disk 200 having the laminated structure shown in FIG. 6 was manufactured.
[0031]
The obtained magneto-optical disk 200 can be reproduced using a magneto-optical disk reproducing apparatus (not shown). The optical system of the magneto-optical disk reproducing apparatus has a reproducing light wavelength λ of 685 nm, a lens numerical aperture of 0.55, and a light spot size of 1250 nm. In the information area of the magneto-optical disk 200, the ratio of the track pitch to the optical spot diameter is 68.0%, and the ratio of the shortest pit length to the optical spot diameter is 43.2%. In the non-information area of the magneto-optical disk 200, since the groove track pitch is 625 nm or less, there are two or more grooves in the light spot, and tracking is not applied, and the data is erroneously recognized as data. There is no.
[0032]
[Example 3]
Except for using a substrate in which the track pitch of tracks defined by grooves and prepits in the information area is 370 nm, the shortest pit length of prepits is 250 nm, and the track pitch of tracks defined by grooves in the non-information area is 360 nm or less. A high-density magneto-optical disk was manufactured in the same manner as in Example 2. Such a high-density magneto-optical disk can be reproduced using a reproducing apparatus (not shown) having an optical system having a reproducing light wavelength λ = 430 nm and a numerical aperture NA = 0.60 of the lens. Becomes 720 nm. In the information area of the high density magneto-optical disk, the ratio of the track pitch to the optical spot diameter is 51.4%, and the ratio of the shortest pit length to the optical spot diameter is 34.7%. In the non-information area of such a high-density magneto-optical disk, since the groove track pitch is 360 nm or less, two or more grooves are included in the light spot, and tracking is not performed in the non-information area.
[0033]
In addition, the table of FIG. 3 collectively shows various dimensions such as the track pitch of each optical recording medium manufactured in Examples 1 to 3 and the performance of the optical system of the reproducing apparatus used.
[0034]
As mentioned above, although the optical recording medium of this invention was demonstrated by Examples 1-3, it cannot be overemphasized that this invention is not limited to the said Example, and those deformation | transformation and improvement are included. For example, in the first embodiment, pits are formed in the non-information area. However, grooves can be formed instead of pits, and pits and grooves can be mixed. In the second and third embodiments, the groove is formed in the non-information area. However, the present invention is not limited to this, and a pit may be formed instead of the groove, or the groove and the pit may be mixed.
[0035]
【The invention's effect】
In the optical recording medium of the present invention, at least one of a groove and a pit is provided in a non-information area different from the information area defined by the standard, and the track pitch of the groove and the pit is set to be equal to or less than half of the light spot diameter. It is adjusting. Therefore, the drive device side cannot perform tracking in the non-information area, and the non-information area is not erroneously recognized as an information area in which information is recorded.
[0036]
Further, since the optical recording medium substrate of the present invention is provided with grooves or pits in at least one non-information area of the outer peripheral area and the inner peripheral area with respect to the information area, when manufacturing such a substrate, When developing the master to be used, the flow of the developer becomes good at the boundary between the information area and the non-information area, and uniform pits or grooves can be formed in the entire information area. In addition, when the substrate is manufactured by injection molding, the flow of the molten resin is suppressed from changing in the boundary portion between the information area and the non-information area in the mold, so that the innermost peripheral portion extends to the outermost peripheral portion. A substrate having uniform optical characteristics can be obtained. Also, since the track pitch of the grooves or pits formed in the non-information area is adjusted to be less than half of the light spot diameter, even if an optical recording medium is manufactured using such a substrate, There is no tracking.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining an information area and a non-information area of an optical recording medium according to the present invention.
FIG. 2 is a diagram showing a state where grooves or pits formed in a non-information area of an optical recording medium according to the present invention are included in an optical spot.
FIG. 3 shows the relationship between the types of optical recording media according to the present invention and the optical system of a reproducing apparatus that reproduces each optical recording medium, and the dimension data of grooves or pits in the information area and non-information area of each optical recording medium. FIG.
FIG. 4 is a conceptual diagram of a tracking signal detection method in the push-pull method.
FIG. 5 is a diagram schematically showing a cross-sectional structure of a DVD-ROM according to the present invention.
FIG. 6 is a diagram schematically showing a cross-sectional structure of a magneto-optical disk according to the present invention.
[Explanation of symbols]
1 Information area
2 Non-information area on the outer circumference
3 Non-information area on the inner circumference
10 Optical recording media
41 Objective lens
42 Laser light
43 Groove
44 Two-segment photodiode detector
44a, 44b Photodetector
100 DVD-ROM
200 magneto-optical disk

Claims (5)

In an optical recording medium for recording or reproducing information by converging and irradiating light having a wavelength λ with a lens having a numerical aperture NA to an information area where information is recorded,
A region other than the information region has at least one of a groove and a pit in a concentric or spiral shape, and a track pitch of a track defined by the groove or the pit is 0.5λ / NA or less. Optical recording medium. 2. The optical recording medium according to claim 1, wherein the total length of the pit length of the pits and the interval between adjacent pits in the track direction is 0.5λ / NA or less. 3. The optical recording medium according to claim 1, wherein the wavelength λ is in a range of 390 nm to 780 nm, and the numerical aperture NA is in a range of 0.55 to 0.90. In an optical recording medium substrate used for an optical recording medium for recording or reproducing information by condensing and irradiating light having a wavelength λ with a lens having a numerical aperture NA to an information area where information is recorded,
A region other than the information region has at least one of a groove and a pit in a concentric or spiral shape, and a track pitch of a track defined by the groove or the pit is 0.5λ / NA or less. Optical recording medium substrate. 5. The optical recording medium substrate according to claim 4, wherein the total length of the pit length of the pits and the interval between adjacent pits in the track direction is 0.5λ / NA or less.

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