JPH0294045A - Magneto-optical recording disk - Google Patents

Abstract

PURPOSE:To make the C/N and erasing power constant by widening the width of a recording track existing in an inner circumferential part of a substrate more than the width of a recording track existing in an outer circumferential part of the substrate and restricting the track widths of the innermost circumference and the outermost circumference within their changeable range. CONSTITUTION:The width of the recording track existing in the inner circumferential part of the substrate is constituted to be wider than the width of the recording track existing in the outer circumferential part of the substrate, and the changeable range of the recording track widths is regarded as 1.0<W1X/W0<5.0, where W1 is denoted as the track width of the innermost circumference on the disk and W0 as the track width of the outermost circumference. By this constitution, the C/N and variations of the required power for erasing on a magneto-optical recording disk to be used at a constant revolving speed can be compensated, so that the C/N and the required power for erasing can thus be kept constant.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a magneto-optical recording disk that records and reproduces information using heat and light such as a laser beam, particularly when used at a constant rotation speed. The present invention relates to a so-called CAV disc.

<Prior art> In a magneto-optical recording disk, the temperature of a recording layer having a predetermined composition is raised to around the Curie point by irradiation with laser light, etc., and information is recorded by applying a magnetic field from outside at this time. .

Information is recorded using optical modulation recording, which records using modulated light while applying a magnetic field of a certain intensity, or magnetic field modulation recording, which records using a modulated magnetic field while applying light of a certain intensity. Ru.

Information on a magneto-optical recording disk can be erased either by applying a magnetic field externally greater than the Hc of the recording layer (bulk erase), or by irradiating a laser beam or the like along the recording track. This is done by a line erasure method in which the temperature of the recording layer is increased by applying an external magnetic field of a strength necessary to reverse the magnetization of the recording layer.

Further, when recording is performed by magnetic field modulation, recording and erasing can be performed by a so-called override method in which erasing is performed by overwriting information without providing an independent erasing process.

As the recording layer of the magneto-optical recording disk, for example, GdF
Amorphous magnetic thin film layers of rare earth transition metals such as TbFeC, TbFeC, O, and GdFeCo are known. These are formed as a thin film on a transparent disk-shaped substrate by a method such as a vacuum evaporation method or a sputtering method, and are used as a magneto-optical recording disk.

In such a magneto-optical recording disk, recording tracks are provided on the surface of the substrate on which the recording layer is provided. The recording track has a width of about 1.6 μm and is provided as a convex portion or a concave portion in a circular shape such as a spiral shape or a concentric shape.

Recording is performed on the recording layer on this recording track.

<Problems to be Solved by the Invention> In a magneto-optical recording disk, the C/N ratio and the erasing power in the line erasure method depend on the linear velocity.

That is, as the linear velocity increases, the C/N ratio improves but the erasing power increases, and when the linear velocity becomes small (the erasing power decreases but the C/N ratio decreases).

Therefore, the so-called CA used at a constant rotation speed
In the case of a V-disc, the linear velocity is different between the outer circumference of the disk and the inner circumference of the disk, so the C/N ratio and erasing power are not constant. For this reason, it is not possible to obtain the same C/N ratio between the outer circumference and the inner circumference of the disk. Furthermore, it is necessary to apply the maximum erase power required, which leads to an increase in the size of the disk drive device.

On the other hand, magneto-optical recording disks have wide recording tracks (
Indeed, it is known that the C/N ratio improves.
et al., 9th Japanese Society of Applied Magnetics Academic Lecture Abstracts, 29p.
B-3 (1985)].

However, when performing line erasing, there is no mention of the relationship between erasing power and recording track width.

The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a magneto-optical recording disk in which the C/N ratio and erasing power change little between the outer circumference of the disk and the inner circumference of the disk.

〈Means for solving problems〉 These objects are achieved by the invention described below.

That is, the present invention includes the following (1) to (3).

(1) A magneto-optical recording disk having a circular recording track on a substrate, characterized in that the width of the recording track existing at the inner circumference of the substrate is wider than the width of the recording track existing at the outer circumference of the substrate. Magneto-optical recording disk.

(2) When the track width at the innermost circumference of the disk is Wl and the track width at the outermost circumference is Wo, 1.0<w+/wo
The magneto-optical recording disk according to (1) above, wherein <5.0.

(A3) The above (
2) The magneto-optical recording disk according to item 2).

Effect> The magneto-optical recording disk of the present invention is preferably used as a so-called CAV disk in which recording and reproduction are performed at a constant rotational speed.

In a CAV disk, the linear velocity of the recording surface gradually decreases from the outer circumference of the disk toward the inner circumference of the disk.

As mentioned above, as the linear velocity increases, the C/N ratio improves, but the power required for erasing increases, and as the linear velocity decreases, the power required for erasing decreases, but the C/N ratio decreases. .

That is, in a CAV disk, the C/N ratio gradually decreases from the outer circumference to the inner circumference, but the power required for erasing also gradually decreases.

On the other hand, as mentioned above, in magneto-optical recording disks,
The C/N ratio improves as the recording track width increases.
Furthermore, when performing so-called line erasing, the power required for erasing increases as the recording track width becomes wider.

In the present invention, in a CAV disk, the C/N ratio and the power required for erasing are different between the outer circumference and the inner circumference. This can be compensated for by configuring the area to be wider than that, and the C/N ratio and the power required for erasing can be kept almost constant.

<Specific Configuration> In the present invention, recording tracks are provided in a spiral shape or a circular shape such as a concentric circle shape on a disk-shaped substrate.

In the present invention, the width of the recording track existing on the inner circumference of the substrate is
The width of the recording track is wider than the width of the recording track existing on the outer periphery of the substrate.

When the magneto-optical recording disk of the present invention is used as a CAV disk that is used at a constant rotation speed, and when the recording track is provided in a spiral shape, the recording track width increases from the outer circumference of the disk to the inner circumference. Preferably, it is configured to increase gradually.

Further, when the recording tracks are provided concentrically, it is preferable that each track is spaced at a constant interval and that the track width gradually increases from the outer circumference toward the inner circumference.

In each of these cases, the rate of change in the recording track width can be determined theoretically or experimentally based on the track density, the beam diameter of the reproduction light, and the like.

Note that in the present invention, the track interval (track pitch) may be changed as well as the recording track width.

When the linear velocity changes, the C/N ratio and the power required for erasing change, but the rates of change of these two do not necessarily match. Further, even if the recording track width changes, the C/N ratio and the power required for erasing change, but the rates of change in both do not necessarily match. Therefore, for example, if the rate of change in the recording track width is determined so that the C/N ratio remains almost constant by canceling out the change in the C/N ratio due to the change in linear velocity, the power required for erasing becomes almost constant. Not necessarily.

Therefore, depending on the purpose, the rate of change in the recording track width may be determined so that either the C/N ratio or the power required for erasing remains approximately constant. Furthermore, the rate of change in the recording track width can be determined so that both the change in the C/N ratio and the change in the power required for erasing are within a permissible range.

In the present invention, the C/N ratio being substantially constant means that the difference in the C/N ratio between the outer circumference and the inner circumference of the disk falls within a certain range.

This range varies depending on the purpose, use, etc., but for example,
When a magneto-optical recording disk with a diameter of 150 mm is used with a user area having a radius of 30 to 60 mm and a CAV rotation speed of 1800 rpm, it is preferably within 4 dB, particularly within 2.5 dB, in consideration of ease of erasing.

In addition, the power required for erasing, that is, the minimum erasing power (
For example, there is an upper limit to the output power of the laser diode (minimum power at which the residual signal output ratio is less than 1.0 dB), and it is also necessary to allow for a variation in output power of about 10%. , within 1.0mW,
In particular, it is preferably within 0.8 mW.

In order to keep the C/N ratio between the outer circumference of the disk and the inner circumference of the disk and the amount of change in the power required for erasing within the above range, the range of change in the recording track width must be set so that the track width at the outermost circumference of the disk is Wo and the maximum If the inner track width is W+,
1. Oku w + / W o < 5, 0, especially 1
．． 3<w+/w.

<3. Preferably it is O.

Here, wo is preferably in the range of 0.5 to 1.6 μm.

Track width W. If it is less than the above range, the power required for erasing will be reduced, but the C/N ratio will be insufficient. Furthermore, the strength of the tracking signal also decreases.

Note that for a disk with a diameter of 300 mm or less, the amount of change in the C/N ratio and the power required for erasing can always be within the above range based on the relationship of W + /W o.

In such a case, it is preferable that the track width becomes wider in proportion to the disk radius, but depending on the case, it can take various forms such as increasing stepwise.

Such a recording track may be provided in a convex shape,
It may be provided in a concave shape.

The height or depth of the recording track is usually between 20 and 110 mm.
It is about 0n.

Also, the interval (pitch) between recording tracks is usually 1.0
It is about ~30 μm.

Although the above description has been made of a CAV disk in which the reproduction rotation speed of all parts of the recording track is constant, the present invention is not limited to such a disk, but can also be applied to a CAV disk in which the reproduction rotation speed is different in some parts of the disk, For example, it can be suitably used for a CAV disc in which the reproduction rotation speed is different between the outer circumference and the inner circumference. In this case as well, the track width and its rate of change can be determined theoretically or experimentally.

The substrate on which the recording tracks described above are provided is made of glass or a resin such as acrylic resin, polycarbonate resin, polyolefin resin, epoxy resin, or polymethylpentene resin, and is transparent to recording or reproduction light. Good to have.

In order to form recording tracks on the substrate, known methods such as injection molding and 2P method may be used.

In addition, the dimensions of the board are usually about 50 to 300 mm in outer diameter,
The thickness is approximately 0.5 to 3 mm. Note that when a protective plate is provided opposite to the substrate, the material of the protective plate may be the same as the material of the substrate. Furthermore, since the recording/reproducing light enters from the substrate side, the protection plate does not need to be transparent.

There are no particular limitations on the recording layer of the magneto-optical recording disk of the present invention, but rare earth metals such as Gd, Tb, and Dy, and preferably Fe.
It is preferable that an amorphous film is formed of an alloy of transition metals such as , Co, etc. by sputtering, vapor deposition, or the like.

In such a recording layer, information is magnetically recorded using a modulated heat beam or a modulated magnetic field, and the recorded information is reproduced by magneto-optical conversion.

The thickness of such a recording layer is usually 10 to 11000 nm.
That's about it.

This kind of recording layer has a small amount on the top or bottom (on the one hand,
Preferably, a protective layer is formed.

When the protective layer is composed of an inorganic thin film of about 30 to 300 nm made of various oxides, carbides, nitrides, sulfides, or mixtures thereof, corrosion resistance is improved.

In addition, there is a gap of 30 to 150 between the protective layer and the recording layer on the incident side of the recording/reproducing light (the disk main surface 111 side in the present invention).
When a layer of various dielectric materials with a thickness of about nm is formed as an intermediate layer, the C/N ratio is improved.

Furthermore, it is preferable to provide a protective coat on the laminate consisting of the protective layer, intermediate layer, and recording layer.

The protective coat is preferably provided not only on the entire surface of the laminate, that is, on the top surface of the laminate, but also on the inner and outer side surfaces. This improves corrosion resistance.

Although various organic substances may be used as the protective coating material, it is preferable to use a radiation-curable compound having an acrylic double bond that is cured with radiation such as electron beams or ultraviolet rays.

The thickness of such a protective coat is generally between 1 and 150 μm.
degree.

The substrate having the laminate and the protective plate may be bonded together using a known adhesive such as a hot melt adhesive, a thermosetting adhesive, or an anaerobic adhesive.

Note that the present invention is suitable not only for a single-sided recording type magneto-optical recording disk in which a substrate and a protective layer are bonded together, but also for a double-sided recording type magneto-optical recording disk in which two of the above-mentioned substrates each having a recording layer are bonded together. Applicable to

<Example> Hereinafter, the present invention will be explained in further detail by giving specific examples of the present invention.

[Example 1] A spiral recording track with a diameter of 130 mm
A polycarbonate substrate with a thickness of 1.2 mm was used.

The recording track width is the innermost track width w+1.
1 μm, outermost track width W.

0.6μm, Wl /wo =l, 8, track depth 6
0 nm, and the track spacing was 1.6 μm.

The recording track width was changed linearly with respect to the disk radius, and the rate of change was 0.017 μm/mm.

On this substrate, a protective layer made of glass was formed to a thickness of 40 nm by high-frequency magnetron sputtering, and on this protective layer, an intermediate layer made of S L N x was formed to a thickness of 80 nm by high-frequency magnetron sputtering. .

Next, a TbFe11:o recording layer was formed on the intermediate layer by sputtering to a thickness of 80 nm.

Furthermore, a protective layer having the same composition as the protective layer was formed on the recording layer to a thickness of 1100 nm by high-frequency magnetron sputtering,
A protective coat was provided on this protective layer. The protective coat was formed by applying a coating composition containing a polyfunctional oligoester acrylate and a photosensitizer onto the protective layer using a spinner coat, and then irradiating it with ultraviolet rays for 15 seconds to crosslink and cure it. .

The thickness of the protective coat was 5 μm.

In this way, magneto-optical recording disk sample No. 1 was produced.

The following measurements were performed on this sample No. 1.

(1) C/N ratio Disc rotation speed 1800 rpm Frequency 3.7MHz Recording power 2.0-6.0mW Playback power 1.5mW RB W 3 0 k Hz V　B　W　1　0　0　Hz Measured at

FIG. 1 shows the relationship between the distance of the recording track from the center of the disk (disk radius) and the C/N ratio.

In addition, the optical system is N=830 nm, N, A=0.52,
A PIN differential type is used, and the magnetic field strength during recording is 300.
It was set to 0e.

(2) Minimum erasing power The minimum erasing power required for erasing at an erasing magnetic field strength of 4000e (the minimum power at which the residual signal output ratio is less than 1.0 dB) was measured.

Note that the optical system used was the same as in the C/N ratio measurement.

FIG. 2 shows the relationship between the distance of the recording track from the center of the disk (disc radius) and the minimum erasing power.

[Comparative Example 1] A magneto-optical recording disk having a recording track width of 0.8 μm and a constant width on the inner and outer circumferences was prepared in the same manner as in Example 1 and designated as Sample No. 2.

The same measurements as above were performed on this sample.

The results are also shown in Figures 1 and 2.

[Example 2] As the recording track width, the innermost track width W+2.
0 μm, outermost track width W.

0.8 μm, w+ /wo =2.5, track depth 60 nm, and track spacing was 2.6 μm at the outermost circumference and 1.4 μm at the innermost circumference.

Both the recording track width and the recording track spacing were changed linearly with respect to the disk radius, and the rate of change in the recording track width was 0.040 μm/mm, and the rate of change in the recording track spacing was 0.040 μm/mm.

Except for this, magneto-optical recording disk sample No. 3 was prepared in the same manner as in Example 1, and the same measurements as in Example 1 were performed.

The results are also shown in FIGS. 1 and 2.

The effects of the present invention are clear from the results shown in FIGS. 1 and 2.

Note that for both samples No. 1 and 2, sufficient tracking signal strength was obtained.

<Effect> According to the configuration of the present invention, the C/N in the CAM disk is
Fluctuations in the ratio and the power required for erasure can be compensated for, and the C/N ratio and the power required for erasure can be kept approximately constant.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the distance of the recording track from the center of the disk (disk radius) and the C/N ratio. FIG. 2 is a graph showing the relationship between the distance of the recording track from the center of the disk (disc radius) and the minimum erasing power.

Claims (1)

[Scope of Claims] (1) In a magneto-optical recording disk having a circular recording track on a substrate, the width of the recording track existing at the inner circumference of the substrate is the width of the recording track existing at the outer circumference of the substrate. A magneto-optical recording disk that is characterized by being wider. (2) The magneto-optical recording disk according to claim 1, wherein 1.0<w_I/w_O<5.0, where w_I is the track width at the innermost circumference of the disk and w_O is the track width at the outermost circumference of the disk. (3) Claim 2 where 1.3<w_I/w_O<3.0.
The magneto-optical recording disk described in .