JPH0969244A - Magneto-optical disk - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the occurrence of the decrease in cross-tank characteristics hard to occur even when a narrow track pitch is realized. SOLUTION: The depth D of a groove part 3 along a recording track 11 with a track pitch of Tp 1.2μm or less, which is formed on one main surface of a transparent substrate 1, on one surface 1a of which a recording layer 10 is formed, is set in the range of λ/8n<=D<=/5.6n, provided that the wavelength of the recording/reproducing light and the refractive index of the transparent substrate are set λ and n respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical disk having a so-called guide groove which is a groove portion along a recording track. More specifically, the present invention relates to a magneto-optical disk characterized by suppressing the deterioration of crosstalk characteristics by defining the depth of the guide groove when the track pitch is narrowed.

[0002]

2. Description of the Related Art In a magneto-optical recording system, the temperature of a magnetic thin film is partially raised above a Curie point or a temperature compensation point, and the coercive force in this portion is eliminated to magnetize the magnetic thin film in the direction of an externally applied recording magnetic field. It is based on the principle of reversing the direction of an image, and is being put to practical use in an optical file system, an external storage device of a computer, a recording device for audio and video information, and the like.

When information is recorded on a magneto-optical recording medium such as a magneto-optical recording medium, a magnetic thin film formed on a transparent substrate is irradiated with laser light or the like as described above. If the magnetic thin film is partially heated above the Curie point or the temperature compensation point and the coercive force of this part is extinguished and a recording magnetic field is applied by a magnetic head from the outside, the magnetic thin film is recorded with cooling. A recording mark whose magnetization direction is reversed in the direction of the magnetic field is formed, and information is recorded depending on the position of the recording mark.

Further, when reproducing information on the magneto-optical disk, the phenomenon that the polarization plane is rotated by the magneto-optical effect in the portion where the recording mark is formed is also irradiated with light such as laser light. The position of the recording mark is detected and the information is reproduced. The method of recording information by the position of the recording mark in this way is called a mark position recording method.

By the way, in recent years, a higher recording density has been required in the magneto-optical recording system, and in order to meet this demand, instead of the mark position recording system for recording information at the position of the recording mark, the magnetic head traveling direction is changed. A mark edge recording method has been proposed in which the length of the portion where the magnetic field is reversed in, that is, the length of the recording mark is recorded as information.

However, when the mark edge recording method is applied, not only the recording method is changed, but also the wavelength of the laser beam used is shortened and the track pitch is narrowed to effectively increase the recording density. I have to.

These recording marks are formed along recording tracks formed in a spiral shape on the magneto-optical disk, for example. Therefore, as a matter of course, the recording light is irradiated along the spiral recording track, the recording magnetic field is applied by the magnetic head to form the recording mark along the recording track, and the recording track is recorded. A reproducing light is emitted along the recording marks to reproduce the recording marks formed along the recording tracks.

At this time, in order to form a recording mark accurately on the recording track and reproduce it easily, a groove is formed on the transparent substrate along the recording track, and this groove is used. The position of the recording track is accurately detected so that the tracking can be performed accurately. The groove is referred to as a guide groove. Further, since the recording tracks are spiral, the grooves and the recording tracks are alternately arranged in the radial direction of the magneto-optical disk, in other words, the recording tracks are arranged between the grooves.

To detect the position of the recording track, for example, the guide groove of the transparent substrate is irradiated with recording / reproducing light such as laser light, and the light reflected and diffracted by the guide groove is directed to the center of the recording track. The light is received by two light receiving portions arranged symmetrically with respect to each other, and the push-pull method or the like is used to detect the position of the recording track by detecting the output difference between the light receiving portions. Get the tracking error signal. In addition, by detecting the position of the recording track,
It goes without saying that the correction is made when the tracking error has occurred.

When the position of the recording track is detected by the push-pull method as described above, since the light diffraction phenomenon is utilized as described above, the tracking error signal of the best signal level is obtained. In order to take out the light, it is desirable that D = λ / 8n, where λ is the wavelength of the recording / reproducing light, n is the refractive index of the transparent substrate, and D is the depth of the guide groove.

[0011]

By the way, in the above-mentioned mark edge recording method, although the high recording density is achieved, the crosstalk characteristics are likely to be deteriorated.
This is because at the time of information recording, the heat of the recording light applied to the first recording track diffuses also to the adjacent second recording track, and the information of the first recording track reaches the second recording track. This is because if the mark is recorded, the mark edge recording method, which requires the length accuracy of the recording mark more than the mark position recording method, is strongly affected.

Further, in the mark edge recording system, the track pitch is also narrowed in order to increase the recording density, and from this fact, the signal of the first recording track is adjacent to the second recording track. Is easily recorded in
It is easily affected, and crosstalk characteristics are unlikely to deteriorate.

Therefore, the present invention has been proposed in view of the conventional circumstances, and corresponds to the mark edge recording system, and the crosstalk characteristic is deteriorated even if the track pitch is narrowed to 1.2 μm or less. An object is to provide a hard magneto-optical disk.

[0014]

As a result of intensive studies made by the present inventors in order to achieve the above object, as a result of deepening the depth of the guide groove formed along the recording track, It is possible to prevent the heat generated by the recording light applied to the first recording track from diffusing to the adjacent second recording track, which can suppress the deterioration of the crosstalk characteristics. I found it.

That is, according to the present invention, the track pitch is 1.
The wavelength of the recording / reproducing light of a magneto-optical disk having a recording layer formed on the main surface of a transparent substrate having a groove along the recording track of 2 μm or less on one main surface is λ, and the refractive index of the transparent substrate is When the depth is n, the groove depth D is λ / 8n ≦ D
It is characterized in that the range is ≦ λ / 5.6n.

If the depth D of the grooves is deeper than the above range, the grooves are located between the grooves when the shape of the grooves is, for example, a generally U-shaped cross section that widens toward the opening side. The width of the recording track, which will be different, becomes too narrow, resulting in a decrease in output.

If the depth D of the groove is smaller than the above range, the signal level of the tracking error signal by the push-pull method will be lowered. It should be noted that even if the depth D of the groove portion is made deeper than λ / 8n, the signal level lowers, but the degree is small, and in the above range, the deterioration of the crosstalk characteristic is sufficiently prevented. It is useful.

That is, in the magneto-optical disk of the present invention, even if the track pitch is narrowed to 1.2 μm or less, the depth D of the groove portion formed along the recording track is determined by the wavelength of the recording / reproducing light. When λ and the refractive index of the transparent substrate are n, the range is set to λ / 8n ≦ D ≦ λ / 5.6n, and the depth is deep. Transmission is hindered and deterioration of crosstalk characteristics is suppressed.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Specific embodiments of the present invention will be described in detail below with reference to the drawings.

A magneto-optical disk to which the present invention is applied is shown in FIG.
As shown in, the recording layer 10 mainly composed of a recording film and a protective film is laminated on the transparent substrate 1. However, in FIG. 1, a part thereof is cut away.

Next, FIG. 2 shows an enlarged view of the magneto-optical disk of this example. A recording track portion 2 corresponding to a spiral recording track and a guide groove 3 are formed along the main surface 1a of the transparent substrate 1, and the guide groove 3 is formed in the radial direction of the magneto-optical disk. 3 and recording track portions 2 are formed alternately.

On the main surface 1a of the transparent substrate 1, a first
The dielectric film 4, the recording magnetic film 5, the second dielectric film 6, and the reflective film 7 are sequentially laminated to form a recording film 8 and a protective film 9, which are formed as a recording layer 10. Each membrane is
Since it is formed along the shape of the one main surface 1a of the transparent substrate 1, the portion corresponding to the recording track portion 2 of the recording magnetic film 5 becomes the recording track 11. It goes without saying that the guide groove 3 is formed along the recording track 11.

Incidentally, FIG. 2 shows an example in which a pit 12 such as an address pit of a magneto-optical disk is formed in a part of the recording track portion 2.

In the magneto-optical disk of this example, the pitch of the recording tracks 11 shown by Tp in the figure, that is, the track pitch is 1.2 μm or less, and the depth of the guide groove 3 shown by D in the figure is recorded and reproduced. When the wavelength of light is λ and the refractive index of the transparent substrate is n, λ / 8n ≦ D ≦ λ / 5.6n
The range is set to.

In the magneto-optical disk of the present example, the constituent material usually used in this type of magneto-optical disk can be used, and the transparent substrate 1 is made of, for example, polycarbonate, amorphous polyolefin or glass. Etc., the first and second dielectric films 4 and 6 may be made of, for example, Si ₃ N ₄ , and the recording magnetic film 5 may be made of, for example, a TbFeCo alloy. May be made of, for example, aluminum or the like, and the protective film 9 may be made of, for example, an ultraviolet curable resin or the like.

The transparent substrate 1 having the above-mentioned shape may be manufactured by means of injection molding method, 2P method or the like which is usually used for manufacturing a magneto-optical disk of this kind, and each film is also made of this kind of magneto-optical disk. It may be formed by means of vapor deposition, sputtering or the like which is usually used for manufacturing disks.

When information is recorded on the magneto-optical disk of this example, a recording magnetic field is applied by a magnetic head while irradiating recording light such as laser light along a recording track, and the length in the magnetic head traveling direction is changed. A recording mark serving as information is formed and recorded by the mark edge recording method. At this time, the guide groove 3 is also irradiated with recording light such as laser light to accurately detect the position of the recording track 11 by, for example, the push-pull method, and perform correct tracking based on the tracking error signal to record a recording mark. The track 11 is properly formed.

When reproducing information on the magneto-optical disk, reproducing light such as laser light is irradiated along the recording track, and the length of the recording mark is detected by the magneto-optical effect to reproduce the information. . Also at this time, the guide groove 3 is irradiated with reproduction light such as laser light to accurately detect the position of the recording track 11 by, for example, the push-pull method, and perform correct tracking based on the tracking error signal.
The length of the recording mark can be easily detected.

In the magneto-optical disk of this example, even if the track pitch is narrowed to 1.2 μm or less, the depth D of the guide groove, which is a groove formed along the recording track, is set to When the wavelength is λ and the refractive index of the transparent substrate is n, the range of λ / 8n ≦ D ≦ λ / 5.6n is set, and the depth is deep. It is possible to prevent the transfer of heat between the adjacent recording tracks, prevent the information of the first recording track from being recorded on the adjacent second recording track, and suppress the deterioration of the crosstalk characteristics.

In this type of magneto-optical disk, the guide groove 3 is generally formed in a substantially U-shaped cross-section that widens toward the opening side, and the depth D of the guide groove 3 is large.
Is deeper than the above range, the width of the recording track portion 2 located between the guide grooves 3 becomes narrow, and the track width of the recording track 11 becomes too narrow accordingly, which causes a decrease in output. In the magneto-optical disk described above, such inconvenience does not occur.

Further, if the depth D of the guide groove 3 is smaller than the above range, the signal level of the tracking error signal by the push-pull method will be lowered. It should be noted that even if the depth D of the guide groove 3 is made deeper than λ / 8n, the signal level drops, but the degree of the drop is small, and in the magneto-optical disk of this example, the signal level of the tracking error signal is reduced. Is sufficiently secured, the recording mark is accurately formed on the recording track, recording is performed, and the reproduction thereof is easily performed.

Although an example of the magneto-optical disk in which the recording tracks are formed in a spiral shape has been described here, the present invention has a plurality of recording tracks formed adjacent to each other and has a guide groove between them. It goes without saying that it can be applied to any magneto-optical disk.

[0033]

EXAMPLES Hereinafter, specific examples of the present invention will be described based on experimental results. That is, magneto-optical disk samples each having a recording layer formed on a transparent substrate in which the track pitch is 1.2 μm or less and the depth of the guide groove is changed are prepared, and the crosstalk characteristics of these samples are investigated. The relationship of crosstalk characteristics was investigated.

As the transparent substrate, a polycarbonate substrate having a thickness of 1.2 mm and a refractive index n of 1.5 is used. The track pitch is 1.2 μm or less on one main surface of the substrate and the recording track portion is guided. A groove having alternating grooves was prepared. The guide groove has a substantially U-shaped cross section that widens toward the opening side, and its depth D is the wavelength λ of the recording / reproducing light (here, 680 nm) and the refractive index n of the transparent substrate (here). And 1.5)), λ /
Transparent substrate samples 1 to 5 were prepared by changing the thickness in the range of 14n to λ / 5.6n. When the depth of the guide groove of each of the transparent substrate samples 1 to 5 was measured by an atomic force microscope,
Λ / 14n, λ / 10n, λ / 8n, λ /
The values were 7.4n and λ / 5.6n.

Then, on the recording track portion and the guide groove forming surface of the transparent substrate samples 1 to 5, a Si ₃ N ₄ film having a thickness of 110 nm ± 10% as a first dielectric film and a thickness of 20 nm as a recording magnetic film were formed. ± 10% TbFeCo alloy magnetic film, 30 nm thick Si as the second dielectric film ± 10%
_{A 3} N ₄ film and an aluminum film having a thickness of 40 to 120 nm as a reflective film are sequentially laminated to form a recording film, and a protective film is further laminated thereon to form a recording layer. Samples 1 to 5 were used.

Next, these magneto-optical disk samples 1 to 5
On the other hand, the recording linear velocity was set to 9.4 m / s, laser light having a wavelength of 680 nm was emitted as recording light with an output of 6 mW, and a recording magnetic field was applied, and the length in the magnetic head traveling direction was about 2.7 μm. A single signal having the following recording marks was recorded for one track. The laser light of the above wavelength is a rectangular pulse having a time of 93% with respect to the length of the recording mark.

At this time, the width of the actual recording mark is expected to be slightly wider at the end of writing than at the beginning of writing due to the accumulation of heat during recording, and the above rectangular pulse is practically optimal for recording. It cannot be said that it is a light emission pattern, but it can be said that it is a light emission pattern suitable for determining the quality of the crosstalk characteristics.

Subsequently, after the single signal is recorded on the predetermined recording track as described above, the reproduction output on this recording track and the reproduction on the recording track adjacent to this recording track where nothing is recorded originally. The output was measured and the relative ratio of these was taken as the crosstalk value.

Further, the recording was carried out by changing the output of the laser light when recording a single signal on the magneto-optical disk samples 1 to 5, and the crosstalk value was similarly investigated.

The results are summarized in FIG. In the figure, the horizontal axis indicates the laser light output, the vertical axis indicates the crosstalk value, and Δ in the figure indicates the result of the magneto-optical disk sample 1.
In the figure, ∇ shows the result of the magneto-optical disk sample 2, ○ in the figure shows the result of the magneto-optical disk sample 3, x in the figure shows the result of the magneto-optical disk sample 4, and □ in the figure shows the magneto-optical disk sample. The result of 5 is shown.

In this type of magneto-optical disk, it is considered practically desirable that such a crosstalk value is smaller than -26 dB. From the result of FIG. 3, the depth of the guide groove is λ / 8n. It was confirmed that this condition was satisfied in the deeper magneto-optical disk samples 1 to 3.

Further, from the results of FIG. 3, when the laser light output at the time of recording becomes large, the width of the recording mark widens, so that heat is easily transferred to the adjacent track, the crosstalk value becomes high, and the crosstalk value becomes high. It can be seen that the talk characteristics deteriorate overall. However, the depth of the guide groove is λ /
In the magneto-optical disk samples 1 to 3 deeper than 8n, the degree of deterioration is relatively small and the depth of the guide groove is λ /
In the magneto-optical disk sample 1 of 5.6n,
It was confirmed that there was almost no deterioration, and it was confirmed that there was a wide margin for the laser light output during recording.

Therefore, from the above, as in the magneto-optical disk of the present invention, the track pitch is 1.2 μm or less, and the depth D of the guide groove which is a groove portion along the recording track is equal to that of the recording / reproducing light. In a magneto-optical disk having a wavelength λ and a refractive index n of a transparent substrate within a range of λ / 8n ≦ D ≦ λ / 5.6n, even if the track pitch is narrowed to 1.2 μm or less, crosstalk will occur. It was confirmed that the deterioration of the characteristics was suppressed and the crosstalk characteristics that were practically preferable were secured.

Further, by defining the depth of the guide groove as in the magneto-optical disk of the present invention, the degree of deterioration of the crosstalk characteristic is small even if the laser light output during recording is increased, and the crosstalk characteristic is reduced. It was confirmed that the decrease in

Next, when the depth D of the guide groove was made deeper than λ / 8n, the degree of decrease in the signal level of the tracking error signal by the push-pull method was investigated.
As a result, it was found that even in the case of λ / 5.6n, the reduction was suppressed to about 20%.

Therefore, by defining the depth of the guide groove as in the magneto-optical disk of the present invention, the signal level of the tracking error signal can be sufficiently secured and the recording mark can be accurately formed on the recording track. It was confirmed that the recording was done and the reproduction could be done easily.

Further, a magneto-optical disk was manufactured with the depth D of the guide groove being deeper than λ / 5.6n, λ / 5.0n, and a single signal was recorded in the same manner as described above. When reproduced, the reproduction output is 1 as compared with the magneto-optical disk sample 1 in which the depth D of the guide groove is λ / 5.6n.
It was confirmed that the value decreased by more than dB. This is because the guide groove has a substantially U-shaped cross section that widens toward the opening side. Therefore, if the depth D of the guide groove is deeper than the above range, the track width of the recording track becomes too narrow. it is conceivable that.

Accordingly, it was confirmed that it is preferable that the depth D of the guide groove is shallower than λ / 5.6n.

[0049]

As is apparent from the above description, in the magneto-optical disk of the present invention, the track pitch is 1.
Even if the track pitch is narrowed to 2 μm or less, the depth D of the groove formed along the recording track is λ / 8n ≦, where λ is the wavelength of the recording / reproducing light and n is the refractive index of the transparent substrate.
Since the range of D ≦ λ / 5.6n is set to be deep, the guide groove prevents transfer of heat due to recording light between adjacent recording tracks, and suppresses deterioration of crosstalk characteristics.

[Brief description of drawings]

FIG. 1 is a partially cutaway perspective view of a magneto-optical disk to which the present invention is applied.

FIG. 2 is an enlarged sectional view of an essential part schematically showing a magneto-optical disk to which the present invention is applied.

FIG. 3 is a characteristic diagram showing the relationship between laser light output and crosstalk value in each magneto-optical disk sample.

[Explanation of symbols]

 1 transparent substrate 2 recording track section 3 guide groove 10 recording layer 11 recording track

Claims (1)

[Claims] 1. A magneto-optical disk having a recording layer formed on the main surface of a transparent substrate having a groove portion along one of the recording tracks formed on one main surface, wherein the track pitch is 1.2 μm or less, and recording is performed. A magneto-optical disk, wherein λ / 8n ≦ D ≦ λ / 5.6n, where λ is the wavelength of the reproducing light, n is the refractive index of the transparent substrate, and D is the depth of the groove.