JP3557761B2 - Magneto-optical disk - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magneto-optical disk, and more particularly to a magneto-optical disk on which address signals and the like are written by emboss pits.
[0002]
[Prior art]
In the magneto-optical recording method, the temperature of the magnetic thin film is partially raised beyond the Curie point or the temperature compensation point, the coercive force in this part is eliminated, and the direction of magnetization is reversed to the direction of the externally applied recording magnetic field. This is based on the basic principle, and is being put to practical use in an optical file system, an external storage device of a computer, or a recording device for audio and video information.
[0003]
As a magneto-optical disk used in the magneto-optical recording method, a recording magnetic layer (for example, a magnetic recording layer having an easy axis of magnetization in a direction perpendicular to the film surface on one main surface of a transparent substrate made of polycarbonate or the like and having a large magneto-optical effect) is used. A recording portion is formed by laminating a rare earth-transition metal alloy amorphous thin film), a reflective layer, and a dielectric layer. In order to prevent corrosion of the recording portion, the recording portion is made of an ultraviolet curable resin or the like. A device formed so as to cover a protective layer is known.
[0004]
In such a magneto-optical disk, a spiral or concentric track is set on the disk, and an information signal is written along the track. This track is allocated to a plurality of sectors having a fixed capacity. Each sector is provided with an address area indicating the physical address (address) of the sector on the disk at the beginning, and the area other than this area is a data area to which a user writes a data signal.
[0005]
Usually, tracks and address pits formed in the address area are formed as irregularities on a transparent substrate. That is, the track is engraved as a spiral or concentric continuous groove, and the address pit is engraved as a fine emboss pit.
[0006]
By the way, the method of arranging the sectors on the track is selected in accordance with the rotation speed control method of the disk.
[0007]
There are two types of disk rotation speed control methods: a method for keeping the disk angular velocity constant (CAV method) and a method for keeping the linear velocity constant (CLV method). The former method is the disk rotation speed. There is an advantage that control is easy.
[0008]
In the CAV method, when the recording frequency is constant, the number of bytes is the same for the outer track and the inner track, so that the number of sectors is also equal. In this case, the angular range occupied by one sector on the outer peripheral side and the inner peripheral side becomes equal, and the address areas added to the head of the sector are arranged in the radial direction.
[0009]
Here, in such a sector format, the physical sector length becomes shorter toward the inner circumference side, and the recording density in the sector becomes higher. Although there is room in space on the outer peripheral side, the number of bytes that can be recorded on the inner peripheral side is limited, and the recording density cannot be sufficiently increased. For this reason, the CAV method is disadvantageous for increasing the recording density of a disk.
[0010]
Therefore, a ZCAV system (Zone CAV system) has been proposed as a system for effectively utilizing the space on the outer peripheral side. In the ZCAV system, a track is divided into blocks (zoning) in the radial direction, and recording and reproduction are performed at a constant angular velocity and a constant recording frequency in a track group (zone) corresponding to one block. The angular velocity and the recording frequency of the disc are controlled so that the linear density becomes substantially constant between the zones. As described above, in the ZCAV system, since the line density is substantially constant in the zone on the outer circumference side and the inner circumference side, high-density recording can be achieved on the entire disk.
[0011]
[Problems to be solved by the invention]
By the way, in the ZCAV system, the angular range occupied by one sector in the zone is equal on the outer peripheral side and the inner peripheral side, and the address areas of the sectors are arranged in the radial direction. On the other hand, when the zones are viewed from each other, the length in the line direction of the sector group formed by arranging the sectors in the radial direction in the zone becomes substantially constant. In this case, since the angular range occupied by the sector group becomes wider toward the inner peripheral side, a positional relationship occurs in the address area between adjacent zones.
[0012]
Here, if the address areas are in such a positional relationship that the address areas are shifted, the influence of the address pits on the reproduction signal becomes a problem.
[0013]
That is, the address pits in the address area are formed as emboss pits on the transparent substrate. Around the pits, the flow of the resin is discontinuous due to the anchor effect of the pits at the time of molding the substrate, so that the stress in the substrate remains, resulting in abnormal birefringence.
[0014]
When the address areas are arranged in the radial direction, the address pits in the address area and the magneto-optical signal (MO signal) in the data area are not adjacent to each other. Therefore, the birefringence abnormality around the address pit hardly affects the reproduction signal obtained from the data area.
[0015]
However, if the address areas are not arranged in the radial direction and have a shifted positional relationship, the address pits of the address area may be adjacent to the MO signal of the data area. In such a case, a problem arises in that the birefringence abnormality around the address pit affects the MO signal and gives spike noise to the reproduced waveform.
[0016]
Therefore, the present invention has been proposed in view of such a conventional situation. In the case where the birefringence abnormality around the embossed pit is suppressed to be small and the ZCAV method is adopted, a good reproduction signal can be obtained from the data area. It is an object to provide a magneto-optical disk .
[0017]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides a transparent substrate in which land portions and groove portions are alternately formed concentrically, and embossed pits indicating addresses are formed in the groove portions in which data areas are formed. And a recording section including a recording magnetic layer having a magneto-optical effect formed on the surface of the transparent substrate on which the land section and the groove section are formed, and a light for recording and reproducing data by the ZCAV method. In the magnetic disk, when the depth of the embossed pit formed in the groove portion from the bottom surface of the groove portion is λ / 3.3n to λ where the reading laser wavelength is λ and the refractive index of the substrate is n. characterized in that it is formed by the range of lambda / 2.7 N.
[0018]
When the depth of the embossed pit formed on the substrate is within the above range, the internal stress around the embossed pit is reduced, and the abnormal birefringence is suppressed. Therefore, even when the emboss pits and the data signal recorded on the recording section are adjacent to each other on the disk, the data signal can be reproduced well.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of an optical disk according to the present invention will be described.
[0020]
The optical disk of this embodiment is a magneto-optical disk to which the ZCAV system is applied. First, the recording format of the magneto-optical disk will be described with reference to FIGS.
[0021]
In this magneto-optical disk, a plurality of concentric tracks are set on the disk surface, and the plurality of tracks are divided into blocks in the radial direction. As shown in FIG. 1, the track groups divided into blocks are alternately made into data fields 10 and buffer fields 11. Here, one data field and の of the buffer fields on both sides of the data field correspond to one zone 12.
[0022]
The data field 10 is an area in which an information signal is recorded on a recording magnetic layer by a user. Each track in the data field 10 is allocated to a plurality of sectors 13 having a fixed capacity. In each of the sectors 13, an address area 14 representing a physical address (address) of the sector 13 on the disk is provided at a head portion, and the other area is a data area 15 in which a data signal is written by a user. You.
[0023]
The sector 13 is arranged so that the number of sectors per track in the zone 12 is equal, that is, the angular range occupied by the sector 13 is equal between the outer track and the inner track. When they are viewed from each other, the length in the line direction of the sector group formed by arranging the sectors 13 in the radial direction in the zone 12 is set to be substantially constant. Therefore, the address areas 14 provided at the head of the sector 13 are arranged in the radial direction in the zone 12, but the adjacent zones 12 have a positional relationship shifted to the address area 14 as shown in FIG. Has occurred. That is, in this format, adjacent zones 14 have areas in which address areas 14 and data areas 15 are arranged in the radial direction. FIG. 2 shows the arrangement of the address areas 15 on the entire disk.
[0024]
A magneto-optical disk in which such a recording format is set has a configuration in which a recording section 2 is laminated on one main surface of a substrate 1 as shown in FIG.
[0025]
The substrate 1 is a disk-shaped transparent substrate having a thickness of about several mm, and a guide groove (groove) 3 is formed on the surface on the side where the recording unit 2 is provided, corresponding to the track of the recording format described above. Also, minute emboss pits 4 are formed in correspondence with the address pits in the address area.
[0026]
Here, in this magneto-optical disk, the depth d of the embossed pits 4 is in the range of λ / 3.3n to λ / 2.7n when the reading laser wavelength is λ and the refractive index of the substrate is n. It has been.
[0027]
The upper limit λ / 2.7n of the pit depth is set from the viewpoint of suppressing the abnormal birefringence around the address pit and reducing noise caused by the abnormal birefringence affecting the MO signal adjacent to the address pit. You.
[0028]
First, FIG. 4 shows the relationship between the depth of an address pit and the byte error rate of a reproduced signal obtained from a data area. As described above, the byte error rate increases as the depth of the pit increases, and can be reduced by reducing the depth of the pit.
[0029]
Here, the correction limit of the error correction code (ECR) of the magneto-optical recording / reproducing system is a byte error rate of 10 ⁻³ or less, and the reason that the byte error rate is suppressed to such a range is that the pit depth is λ. /2.7n or less. That is, in order to obtain a good reproduction signal from the data area, the depth of the address pit formed on the substrate needs to be λ / 2.7n or less.
[0030]
However, the depth of the address pit also affects its signal strength. From the viewpoint of light wave interference, the signal intensity becomes highest when the pit depth is λ / 4n. If the signal strength of the address pit becomes too large, the signal leaks into the tracking error signal, and tracking or the number of cross tracks cannot be accurately detected.
[0031]
To show this, FIG. 5 shows the relationship between the depth of the address pit and the amount of leakage of the signal into the tracking error signal.
[0032]
Here, the amount of leakage into the tracking error signal was examined by detecting a track cross signal obtained when the reproduction light spot was scanned across the track. When the reproduction light spot is scanned across the track, a reproduction waveform having an amplitude corresponding to the number of grooves and lands over which the reproduction light spot straddles is obtained as shown in FIG. The leakage of address pits is observed as spike-like noise superimposed on the reproduced waveform. The ratio B / A × 100 (%) of the noise magnitude B to the amplitude A of the reproduced waveform is the leakage amount of the tracking error signal of the address signal.
[0033]
As shown in FIG. 5, the amount of leakage into the tracking error signal increases as the pit depth approaches λ / 4n. In order to keep the amount of leakage into the tracking error signal within a practical range (40% or less), the depth of the address pit needs to be λ / 3.3n or more.
[0034]
From the above results, the depth of the address pit should be λ / 3.3n to λ in order to suppress the noise on the reproduction signal due to the birefringence abnormality around the address pit and the leakage of the address signal into the tracking error signal. /2.7n, so that a high-quality reproduced signal can be obtained from the data area without sacrificing access reliability by setting the depth of the address pits to this range. become.
[0035]
In this magneto-optical disk, the depth of the address pits 4 is regulated as described above. As the material of the transparent substrate 1 on which the pits are formed, any of those commonly used in magneto-optical disks can be used. . Specifically, glass and the like are used in addition to plastic materials such as acrylic resin, polycarbonate resin, polyolefin resin, and epoxy resin. In the former case, the guide grooves 3 and the embossed pits 4 are formed in an uneven shape by injection molding, and in the latter case, by a photopolymer method (2P method).
[0036]
Of these, substrates commonly used in magneto-optical disks are polycarbonate, polymethyl methacrylate, glass, and the like, and the refractive index n of these substrates is about 1.59 at a wavelength of 680 nm. In the case where reproduction is performed on a magneto-optical disk using such a substrate with reading light having a wavelength of 680 nm, the depth of the address pit may be 0.130 to 0.158 μm.
[0037]
A recording unit is formed on such a transparent substrate.
[0038]
As shown in FIG. 3, the recording section 2 has a four-layer structure including, for example, a recording magnetic layer 5, dielectric layers 6, 7, and a reflective layer 8, and a first dielectric layer 6, a recording magnetic layer Layer 5, second dielectric layer 7, and reflective layer 8 are stacked in this order.
[0039]
Of these, as the first dielectric layer 6 and the second dielectric layer 7, oxides or nitrides can be used, but oxygen in the dielectric layers may adversely affect the recording magnetic layer. For this reason, nitride is more preferable, and silicon nitride, aluminum nitride, or the like is preferable as a substance that does not transmit oxygen and moisture and that can sufficiently transmit the used laser beam.
[0040]
Further, the recording magnetic layer 5 is an amorphous magnetic thin film having an easy magnetization direction in a direction perpendicular to the film surface, has excellent magneto-optical characteristics, has a large coercive force at room temperature, and It is desirable to have a Curie point around 200 ° C. Examples of the recording material satisfying such conditions include a rare earth-transition metal alloy amorphous thin film and the like, and a TbFeCo-based amorphous thin film is particularly preferable. An additional element such as Cr may be added to the recording magnetic layer for the purpose of improving corrosion resistance.
[0041]
The reflection layer 8 is preferably made of a high-reflectance film that reflects laser light at 70% or more at the boundary with the second dielectric layer, and is preferably a nonmagnetic metal vapor-deposited film. It is desirable that this reflective layer be a good conductor thermally, and aluminum is suitable in consideration of availability and ease of film formation.
[0042]
Further, a protective layer may be formed on the recording section 2. This protective layer is for isolating the recording unit from water and oxygen in the atmosphere, and an ultraviolet curable resin such as an acrylic ultraviolet curable resin is used.
[0043]
Information is recorded and reproduced on the magneto-optical disk having such a configuration by the ZCAV method. That is, in the zone, recording and reproduction are performed by the constant angular velocity and the constant recording frequency, that is, the CAV method, and when the zones are viewed from each other, the angular velocity and the recording frequency are controlled so that the linear density becomes substantially constant between the zones. Here, in this magneto-optical disk, since the depth of the address pit is within a predetermined range, a target sector can be accessed accurately, and a reproduced signal with small noise can be obtained from the data area. Properties can be obtained.
[0045]
【The invention's effect】
As described above, according to the present invention, in a magneto-optical disk on which data is recorded and reproduced by the ZCAV method, the depth from the bottom surface of the groove portion of the emboss pit indicating the address formed in the groove portion forming the data area is described. Is formed in the range of λ / 3.3n to λ / 2.7n, where λ is the reading laser wavelength and n is the refractive index of the substrate. noise is suppressed, leakage of the address tracking error signal of the embossed pit signal is reduced. Therefore, even in the case of adopting a format such as the ZCAV system in which an area where the data recorded in the embossed pits and the data recorded in the recording section are adjacent to each other is formed on the disk, a high-quality reproduced signal can sacrifice access reliability. Obtained without doing.
[Brief description of the drawings]
FIG. 1 is a schematic diagram for explaining a format of an optical disc to which the present invention is applied.
FIG. 2 is a schematic diagram showing an arrangement of address areas of the optical disc.
FIG. 3 is a cross-sectional view showing one configuration example of an optical disc to which the present invention is applied.
FIG. 4 is a characteristic diagram showing a relationship between a depth of an emboss pit and a byte error rate.
FIG. 5 is a characteristic diagram showing the relationship between the depth of an emboss pit and the amount of leakage into a tracking error signal.
FIG. 6 is a schematic diagram for explaining an amount of leakage into a tracking error signal.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Recording part 3 Guide groove 4 Address pit 10 Data field 11 Buffer field 12 Zone 13 Sector 14 Address area

Claims (2)

The land portion and the groove portion are alternately formed concentrically, and a transparent substrate in which emboss pits indicating an address are formed in the groove portion forming the data area, and the land portion and the groove portion of the transparent substrate are formed. A recording portion including a recording magnetic layer having a magneto-optical effect formed on the formed surface side, and a magneto-optical disk in which data is recorded and reproduced by the ZCAV method.
The depth of the embossed pits formed in the groove portion from the bottom surface of the groove portion is λ / 3.3n to λ / 2.3 when the reading laser wavelength is λ and the refractive index of the substrate is n. A magneto-optical disk formed to have a range of 7n. 2. The magneto-optical disk according to claim 1, wherein a read laser wavelength used for reading data recorded in the data area is approximately 680 nm.

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