JPH09204700A - Magnetooptic recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a magnetooptic recording medium performing land-and- groove recording in which effective recording density is enhanced by suppressing the effect of crosserase and crosstalk. SOLUTION: The recording medium has a structure where the land width 20 and groove width 21 are large and the quantity of light reflected on the land part 16 and groove part 17 and arriving at a photodetector exceeds 80% of the quantity of light reflected on the flat part and arriving at the photodetector. The land width 20 is larger than the groove width 21.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium capable of high density recording in land & groove recording.

[0002]

2. Description of the Related Art In recent years, an optical disk having a high recording capacity has attracted attention as a recording medium for audio, video and data. In particular, rewritable phase change recording media and magneto-optical recording media have been actively researched. In both the phase change disk and the magneto-optical disk, in order to improve the recording density, development of a short wavelength semiconductor laser is desired.

However, in the present situation, it is considered that a considerable time is required until a blue semiconductor laser that stably oscillates continuously at room temperature is manufactured at low cost. Under such circumstances, a technique for improving recording density by using laser diodes of the same wavelength has been actively developed. As such a technique, land and groove recording, an optical super-resolution phenomenon, MSR in a magneto-optical recording medium, and the like have been proposed.

There are mark position recording and mark edge recording as recording methods for optical disks, but mark edge recording is suitable for high density recording. In phase change recording or magneto-optical recording using an optical modulation method, it is difficult to control the mark length because the shape of the recording mark depends on the temperature distribution and heat diffusion when the laser beam is irradiated. Therefore, when performing mark edge recording, it is necessary to devise to write by combining a plurality of laser pulses having different amplitudes and pulse widths. On the other hand, in magneto-optical recording using magnetic field modulation, since the reversal position of the recording mark corresponds to the reversal of the applied magnetic field, the mark edge can be easily controlled, which is advantageous for high-density recording.

As described above, in magneto-optical recording using the magnetic field modulation method, the linear recording density can be maximized when a laser pickup of the same wavelength is used.
Further, it is also considered to improve the recording density by shortening the track pitch, land and groove recording, and the like.

[0006]

By shortening the track pitch and performing land-groove recording, cross-erasure that erases information on an adjacent track when writing information, and the next information when reading information. The crosstalk that detects the signal component of is a problem. Further, the shortening of the track pitch reduces the lateral width of the recording mark, resulting in a reduction in the reproduction signal output.

As a method of reducing crosstalk, a method of optimizing the groove depth has been proposed, as disclosed in JP-A-5-62250. However, it is not easy to improve the increase in cross erase and the decrease in reproduction output.

In land and groove recording, when recording and reproducing are performed at the same track pitch and the same linear recording density as in land recording or groove recording, the recording density is simply doubled. It is an attractive technology. However, the current land record or groove record is
The land and groove occupy a large proportion of the track pitch, so if land and groove recording and reproducing are performed using the same wavelength laser with the same track pitch, the effects of crosstalk and cross erase and the reproduction output Is a problem. In particular, since the linear recording density is suppressed due to the decrease in the signal resolution accompanying the decrease in the reproduction output, the advantages of magneto-optical recording using the magnetic field modulation method cannot be fully exerted.

Therefore, an object of the present invention is to optimize the groove shape of a recording medium, reduce the effects of crosstalk and cross erase, and maximize the product of linear recording density and track density when performing land and groove recording. In order to provide a magneto-optical disk capable of high density recording.

[0010]

According to the present invention, when a groove and a land are alternately formed on a substrate and the groove width and the land width are increased to condense laser light on the land portion or the groove portion. A groove-shaped recording in which the amount of light reflected from the magneto-optical recording medium and reaching the optical detector has a value of 80% or more of the amount of light reflected and reaching the optical detector when condensed on a flat portion. Composed of medium.

According to the present invention, the land width is made wider than the groove width so that the amount of light reflected from the land portion and reaching the photodetector is larger than the amount of light reflected from the groove and reaching. It is composed of a recording medium having a shape.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a recording / reproducing apparatus for a magneto-optical recording medium according to the present invention.
The light emitted from the laser diode 1 of FIG. 1 is focused on the magneto-optical disk 5 by the objective lens 4 via the collimator lens 2 and the polarization beam splitter 3. The magneto-optical disk 5 is rotated by a spindle motor 6. In the present invention, a laser having a wavelength of 680 nm and an objective lens having an NA of 0.55 is used.

The light reflected from the magneto-optical disk 5 is 1
After passing through the / 2 wavelength plate 7 and the polarization beam splitter 8, the light is focused on the four-division photodiode 11 for focus error detection through the cylindrical lens 9 and the condenser lens 10. The astigmatism method is used for focusing. The other light that has passed through the polarization beam splitter 8 is divided into two by the condensing lens 12.
It is focused on 3. The push-pull method is used for tracking. Tracking to the land portion and the groove portion is performed using the polarity of the slope of the zero-cross portion of the push-pull signal.

The signal writing is performed by a magnetic field modulation method using the magnetic head 14. Since it also has a structure that can emit laser light in pulses in synchronization with the modulating magnetic field,
Magnetic field modulation using pulse assist can also be performed. Further, although not shown in the figure, a magneto-optical signal is read using a photodiode via a half-wave plate and a polarization beam splitter for signal reproduction.

As shown in FIG. 2, the groove shape of the substrate is wider than that of a conventional typical groove & land recording substrate. Further, the width of the land portion can be made larger than the width of the groove portion.

In a magneto-optical recording medium in which lands and grooves are provided alternately, the groove width and the land width are increased to collect information on the land portion or groove portion for recording / reproducing information. Diffraction of laser light is suppressed. This increases the amount of light that is reflected by the land portion or the groove portion when the information is reproduced and reaches the photodetector, so that the effective figure of merit of the reproduction signal increases and the reproduction output increases. Further, due to the increase of the land width and the groove width, crosstalk and cross erase do not increase even if a large mark is recorded in the track width direction. Therefore, the reproduction output is increased by enlarging the width of the recording mark.

[0017]

EXAMPLES The present invention will be described in detail below with reference to comparative examples and examples.

Comparative Example 15 FIG. 2 is a schematic view showing a cross section of a substrate of a magneto-optical recording medium in a comparative example of the present invention.
The substrate used is injection molded polycarbonate. A land 16 and a groove 17 are spirally formed on the substrate 15 with a track pitch of 1.1 μm and a duty of 50%. The groove depth is set to about 60 nm so that the push-pull signal becomes maximum. A film having a four-layer structure of a dielectric layer / magnetic recording layer / dielectric layer / reflection layer is formed on this substrate by a sputtering method. For the magnetic recording layer, an amorphous alloy thin film made of a transition metal and a rare earth metal is used, which has a Curie temperature of about 200 ° C. and a coercive force at room temperature of about 8 k Oe and a good perpendicular magnetic anisotropy.

The recording / reproducing characteristics of this magneto-optical recording medium were evaluated using the recording / reproducing apparatus described above. The radial position and the number of revolutions were set so that the linear velocity during recording was 5 m / sec, the writing frequency was changed, and crosstalk, cross erase, and C / N were investigated. In addition, the jitter characteristic when recording and reproducing a 1-7 modulated random signal was also examined.

(Embodiment 1) In FIG.
The schematic diagram of the cross section of the board | substrate used in FIG. As the substrate, a polycarbonate injection-molded using a stamper is used. Alternatively, a substrate in which a groove is formed by a 2P method on a flat glass or plastic disk may be used. The track pitch is 2.0 μm, and the groove depth and the duty of the land groove are 60 n each as in the comparative example.
m and 50%.

The groove shape and surface roughness were measured using a scanning tunneling microscope. From the results of measuring the surface roughness, it was found that the groove portion had better smoothness than the land portion. Since the same result was obtained by observing the surface of the stamper used when manufacturing the substrate, it is considered that the surface properties of the land portion and the groove portion depend on the mastering process of the substrate. Therefore, by setting the width of the land portion larger than the width of the groove portion, the smoothness of the surface can be made substantially the same.

A magneto-optical recording medium was manufactured by forming a film having the same structure as that of the comparative example on the substrate manufactured as described above by a sputtering method. The recording / reproducing characteristics of this magneto-optical recording medium were evaluated using the recording / reproducing apparatus described above. So that the linear velocity during recording is 5 m / sec,
The radial position and the number of revolutions were set, the writing frequency was changed, and crosstalk, cross erase, and C / N were investigated. In addition, the jitter characteristic when recording and reproducing a 1-7 modulated random signal was also examined.

(Embodiment 2) Reference numeral 19 in FIG.
The schematic diagram of the cross section of the board | substrate used in FIG. As the substrate, a polycarbonate injection-molded using a stamper is used. Alternatively, a substrate in which a groove is formed by a 2P method on a flat glass or plastic disk may be used. The track pitch was 2.0 μm, and the land width 20 and the groove width 21 were set to 6: 4. The groove depth was 60 nm, which is the same as in the comparative example. A film having the same structure as that of the comparative example was formed on this substrate by a sputtering method. The recording / reproducing characteristics of this magneto-optical recording medium were evaluated using the recording / reproducing apparatus described above. The radial position and the number of rotations were set so that the linear velocity during recording was 5 m / sec, the writing frequency was changed, and crosstalk, cross erase, and C / N were investigated. In addition, the jitter characteristic when recording and reproducing a 1-7 modulated random signal was also examined.

Table 1 shows the measurement results of crosstalk, cross erase and C / N. Crosstalk amount is 5
Data of two consecutive lands or grooves are erased by using a constant magnetic field and laser light, then a mark with a mark length of 0.8 μm is recorded on the central land or groove by the magnetic field modulation method, and the carrier level C After measuring _C , the adjacent lands or grooves on both sides were read, and the higher one of the measured carrier levels was taken as C _M, and crosstalk C _CR = C _M −C _C was obtained.
The crosstalk was measured for each of the land and the groove, and the one having the larger value including the sign is shown in Table 1. C _C
The writing power of C was measured by measuring the writing power dependence of C _C and set to the power P _{S at} which the value saturates.

The cross erase amount is obtained by first erasing the data of three adjacent land or groove areas, recording a mark having a mark length of 0.8 μm on the central land or groove under the same conditions as the crosstalk, and determining the carrier level C
After measuring _A , data on the adjacent lands or grooves on both sides are erased with a laser beam having a constant magnetic field and intensity P _S , and then the carrier level C _B of the central land or groove is measured again. The cross erase C _E = C _B −C _A was obtained. The cross erase was measured for each of the land and the groove, and the one with the smaller value including the sign is shown in Table 1.

C / N is a duty ratio of a mark having a mark length of 0.45 μm for a land portion and a groove portion.
The measurement was performed by recording / reproducing in%. Table 1 shows the smaller value of the C / N measured for the land portion and the groove portion.

Table 2 shows the ratio of the amount of light reflected from the land portion and the groove portion and reaching the optical detector to the mirror portion. In the comparative example, the light reflected from the land portion and the groove portion is greatly affected by diffraction as compared with the mirror portion, so that the amount of light reaching the detector is small. On the other hand, in Example 1 and Example 2, the land width and the groove width are large with respect to the beam waist of the focused laser light, so that the amount of light reaching the detector is large. In particular, in the second embodiment, the land width is wider than the groove width, so that the amount of light reaching the detector from the land portion is larger than that in the groove portion.

[0028]

[Table 1]

[0029]

[Table 2]

In Table 3, the writing frequency is changed and
The following shows the shortest recording mark length and the recording density at which the jitter value becomes 10% or less when recording / reproducing a 1-7 modulated random signal. In the comparative example, the condition that the jitter value was 10% or less was not obtained. In Example 1, the resolution of the signal when the land portion was read was worse than that of the groove portion. In the groove portion, a jitter of 10% or less was obtained even at 0.47 μm. In the second embodiment, the difference between the land portion and the groove portion is
Hardly ever seen.

[0031]

[Table 3]

Further, the jitter characteristic of a 1-7 modulated random signal with a shortest mark length of 0.45 μm was measured on a magneto-optical disk with a track pitch of 1.7 μm and a land width and a groove width of 6: 5. The following values were obtained. The amount of light reaching the photodetector from the land portion and the groove portion of this magneto-optical disk was about 82% of that of the flat portion.

[0033]

According to the present invention, in the land-and-groove recording using the magneto-optical recording medium, the land width and the groove width are both increased, and the amount of light reflected from the land portion and the groove portion to reach the photodetector. By increasing
It is possible to improve the effective figure of merit. As a result, the linear recording density can be improved because the reproduction output is high even if the recording mark length is shortened. actually,
The total recording density is determined by the reduction of the recording density due to the increase of the land width and the groove width and the linear recording density. When land-and-groove recording is performed with a short track pitch, the reproduction output is reduced due to the shortening of the land width and the groove width. Therefore, when attempting to increase the linear recording density, the signal resolution is extremely reduced. Also, since the effects of crosstalk and cross erase are large,
Writing conditions such as recording power are severely restricted.

The land width and the groove width are set so that the light quantity reflected from the land and the groove and reaching the photodetector becomes 80% or more of the light quantity from the flat portion having neither the land nor the groove. Although the pitch is increased, the total recording density can be increased by improving the linear recording density. By sufficiently widening the land width and groove width, the effects of crosstalk and cross erase are reduced.

Further, by making the land width larger than the groove width, it is possible to reduce the influence of noise in the land portion due to the mastering process. As a result, the overall recording density can be improved by adjusting the balance of the recording characteristics of the land portion and the groove portion.

The technique of the present invention can be effectively used even if a short wavelength laser such as a blue semiconductor laser is used. In particular, in an amorphous alloy thin film made of a rare earth transition metal having a good perpendicular magnetic anisotropy such as the current TbFeCo, a reduction in Kerr rotation angle due to a shorter wavelength of a light source leads to a reduction in reproduction output. However, if the track pitch is easily reduced, the linear recording density cannot be improved. Even if a blue semiconductor is used, high density recording can be realized by performing land groove recording according to the present invention and setting the linear recording density and track pitch.

According to the embodiment of the present invention, when the upper limit of the jitter value is set to 10%, the wavelength of 680 nm and the NA of the objective lens are set in a magneto-optical disk having a size of 3.5 inches.
= 0.55, a recording capacity of 1.3 GB on one side can be easily realized without using a special method such as MSR.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a recording / reproducing apparatus for a magneto-optical recording medium used in the present invention.

FIG. 2 is a schematic view showing a cross section of a magneto-optical recording medium used in the present invention.

[Explanation of symbols]

 1. Laser diode 2. 2. Collimator lens 3. Polarization beam splitter Objective lens 5. Magneto-optical disk 6. Spindle motor 7.1 / 2 wave plate 8. Polarizing beam splitter 9. Cylindrical lens 10. Condensing lens 11.4 split photodiode 12. Condensing lens 13.2-division photodiode 14. Magnetic head 15. Comparative example substrate cross section 16. Land 17. Groove 18. Example 1 Substrate cross section 19. Example 2 Substrate cross section 20. Land width 21. Groove width

Claims (2)

[Claims] 1. In a magneto-optical recording medium in which grooves and lands are alternately formed on a substrate, the amount of light reflected and reaching a photodetector when laser light is focused on the grooves or lands is Groove of magneto-optical recording medium,
A magneto-optical recording medium having a value of 80% or more of the amount of light that is reflected and reaches the photodetector when condensed on a flat portion where lands and pits are not formed. 2. The light according to claim 1, wherein the amount of light reflected from the land part and reaching the photodetector is larger than the amount of light reflected from the groove part and reaching the photodetector. Magnetic recording medium.