JPS63124250A - Optical magnetic recording disk - Google Patents

Abstract

PURPOSE:To improve a S/N in an inner peripheral part and to increase a storage capacity without deteriorating a recording sensitivity in an outer peripheral part by laminating in order of a protective film, a magnetic body film and a thermal diffusion film on a substrate, and reducing the film thickness of the thermal diffusion film from the inner peripheral part to the outer peripheral part. CONSTITUTION:A magnetic thin film 3 is laminated on the substrate 1 formed by plastic through a protective layer 2, and furthermore, the thermal diffusion film 5 whose film thickness decreases from the inner part to the outer part of the disk is formed through a dielectric 4. The optical magnetic disk has a diameter of 130mmphi, and a radius from 30mm to 60mm is used for recording and reproduction. The film thickness of the thermal diffusion film 5 in the inmost peripheral part is 500Angstrom , and below 50Angstrom in an outermost peripheral part. Thus, the S/N in the inner peripheral part can be improved by about 2dB over, and a shortest domain length can be shortened from mum to 0.8mum, whereby the storage capacity per disk can be increased by 25%.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magneto-optical recording disk used for recording information, which has an improved thin film structure.

BACKGROUND OF THE INVENTION In recent years, as the information society has progressed, there has been a strong desire to put rewritable large-capacity magneto-optical disks into practical use. Among these, magneto-optical memory, which has attracted particular attention, has recently been confirmed to have excellent characteristics as a digital memory.

By the way, magneto-optical thin film materials are limited to rare earth transition metal amorphous magnetic materials due to constraints such as the Chierly temperature, which is the main factor that determines recording sensitivity, the Kerr rotation angle, which determines the quality of reproduced signals, and film production at low temperatures. is used. This rare earth transition metal contains at least one of Fe, Go, and Ni, and G(1,T
b. It is composed of an alloy of one or more rare earth elements, mainly Dy.

Specifically, TbFe, G4TbFe, TbFeCo, etc. are used.

However, although these magnetic thin films have a large Bekar rotation angle compared to other magnetic materials, the angle is 0.3 to 0.
．． 6 degrees, and a sufficient signal-to-noise ratio cannot be obtained. Specifically, when using a magneto-optical disk as a digital memory, the following problem arises: In other words, the length of the domain recorded on the disk is sufficiently larger than the optical beam spot diameter used for recording and reproduction. On the other hand, when the recorded domain length becomes approximately the same as the optical beam spot diameter, the signal-to-noise ratio deteriorates rapidly. Therefore, the signal-to-noise ratio limits high-density recording, and it is desired to obtain an even larger signal-to-noise ratio.

In order to eliminate such drawbacks, in the structure of magneto-optical disks, 3io, zn are conventionally used between the substrate and the magnetic thin film.
A method using a high refractive index dielectric thin film such as s, 5isNasmuIN, etc. has been devised. This is intended to increase the Kerr rotation angle by utilizing multiple reflections caused by a dielectric thin film. Therefore, the thickness of the dielectric thin film is such that its refractive index is n,
When the laser wavelength used for recording and reproduction is λ, λ/
At 0, which is set to 4n, magneto-optical disks structured using these dielectric films suffer from a decrease in reflectance and an increase in optical energy absorption rate. Therefore, although an improvement in recording sensitivity can be expected, similar energy absorption occurs during reproduction as well. However, since the Kerr rotation angle of magnetic thin films deteriorates due to high temperatures, it is necessary to reduce the light intensity during reproduction. When the laser input power during reproduction is Io, the reflectance of the magneto-optical disk is R, and the Kerr rotation angle is θ, the signal-to-noise ratio S/N with respect to sirot noise is S/N cx:55in2θk...・・・・・・(1
). In the magneto-optical disk having the structure using the dielectric film described above, as the Kerr rotation angle Ok increases, so does the process. ,R
Problems to be Solved by the Invention In magneto-optical disks, the limit of high-density recording is determined by the signal-to-noise ratio as described above. Therefore, it is easy to think that by reducing the amount of optical energy absorption, it is possible to increase the optical intensity during reproduction and obtain a large signal-to-noise ratio (
For example, Japanese Patent Application Laid-Open No. 56-74844). By the way, disk rotation methods include a constant angular velocity method and a constant linear velocity method.

Generally, data file disk drives use a constant angular velocity method due to the need for high-speed access. Therefore, if the amount of optical energy absorbed is reduced in order to obtain a large signal-to-noise ratio, the recording sensitivity will also be reduced at the same time, resulting in the following problems. In other words, in the constant angular velocity method, a high power laser is required for recording at the outer periphery of the disk where the linear velocity increases. However, the use of a semiconductor laser is indispensable in terms of the device size and cost of the drive, and as a result, the number of rotations of the disk is severely restricted, resulting in the problem that the required data transfer rate cannot be obtained.

In view of the above-mentioned problems, the present invention provides an excellent magneto-optical recording disk that provides a higher signal-to-noise ratio than conventional disks without impairing the data transfer rate.

Means for Solving the Problems To achieve this objective, the magneto-optical disk of the present invention includes:
A heat diffusion layer is provided on the opposite side of the magnetic film from the laser beam input surface, and the thickness of the layer decreases from the inner circumference toward the outer circumference.The heat diffusion layer is formed by vacuum evaporation or Although the film is formed by a known method such as sputtering, a desired film thickness distribution can be obtained by using a film thickness correction plate provided between the evaporation source or the target and the substrate. Alternatively, the desired film thickness distribution can be obtained by appropriately setting the position of the evaporation source or the discharge area on the target.

Function Generally, in a magneto-optical disk, as the length of the recording domain becomes shorter, the reproduced signal becomes smaller.

When recording is performed without rotating the disk at a constant angular velocity, the recording domain length is not short at the inner periphery, but becomes longer at the outer periphery. The shortest recording domain length is determined because a sufficient signal-to-noise ratio can be obtained when the shortest pulse width is recorded at the innermost circumference. On the other hand, the media movement speed increases at the outer periphery during recording.

It is necessary to increase the optical input power during erasing.

In other words, the number of rotations of the disk is determined based on the recording sensitivity constraint that sufficient recording can be performed with the maximum input power that can be used with a semiconductor laser.

Therefore, at the inner circumference of the disk, the magnitude of the signal output limits the device design, and at the outer circumference of the disk, the recording sensitivity limits the device design.

Therefore, the present invention utilizes thermal diffusion to suppress the temperature rise during reproduction by making the thickness of the heat diffusion layer in the inner circumference thicker than that in the outer circumference, thereby making it possible to reproduce signals with large reproduction power, and to improve device design. This is to obtain the maximum signal output that gives the limit.

At the same time, by reducing the thickness of the heat diffusion layer at the outer periphery, heat diffusion is prevented, recording sensitivity is prevented from decreasing, and high speed rotation of the disk is maintained.

With this configuration, compared to conventional magneto-optical recording disks, the recording density is improved and the storage capacity per disk is increased without causing a decrease in data transfer speed.

EXAMPLE Hereinafter, an example of the present invention will be described in detail with reference to the drawings. FIG. 1 is a correspondence diagram showing the correspondence between the structure of a magneto-optical recording disk according to an embodiment of the present invention and the thickness distribution of its heat diffusion layer. In FIG. 1, a magnetic thin film 3 is laminated on a disk-shaped substrate 1 made of plastic with a protective film 2 in between. Further, a thermal diffusion film 6 is formed with the dielectric film 4 interposed therebetween, the thickness of which decreases from the inner circumference to the outer circumference of the disk. Note that the structure of a magneto-optical disk requires an additional protective layer to prevent oxidation of the magneto-optical thin film.
Since it is not a main component of the present invention, it will be omitted here.

The magneto-optical disk of this embodiment has a diameter of 130++ mφ, and the radius from 30 mI to 60 mm is used for recording and reproduction. The thickness of the heat diffusion film at the innermost part of the usage area is 5.
00 people, and the film thickness at the outermost periphery is less than 5.08. Further, the film thickness continuously changes from the innermost circumferential portion to the outermost circumferential portion of the usage area.

Next, a method for manufacturing the magneto-optical disk of this example will be described.

First, 1000° of SiO was deposited on the substrate 12 in which the grooves were formed by ordinary vacuum evaporation, and then 80° of GdTbFe was deposited by ordinary RF sputtering.

I formed it. Next, 200 layers of 2MgSiO2 were formed as a dielectric thin film, and then palladium was formed as a heat diffusion layer. FIG. 2 shows the configuration of the palladium layer manufacturing apparatus.

A vapor deposition apparatus equipped with an electron beam evaporation source is used to form the thermal diffusion layer. First, after evacuation to 2×10 Torr, Pd is evaporated from the evaporation source 13 while rotating the plastic substrate 12 with a diameter of 1 sotmφ mounted on the substrate holder 11 at 6° rpm. At this time, in order to obtain a desired film thickness distribution, a film thickness correction plate 14 is disposed between the evaporation source and the substrate. A dielectric film having a film thickness distribution as shown in FIG. Furthermore, due to the effect of the film thickness correction plate 14, the film formation speed is 5 persons/s a a on the inner circumference and O, S on/s on the outer circumference.
It is below sec.

Next, FIG. 3 shows the recording and reproducing characteristics of the magneto-optical disk constructed according to the present invention. For comparison, a magneto-optical disk with a conventional structure is also shown. Figure 3 shows the characteristics of this embodiment, and Figure 3 shows the conventional characteristics. Recording was performed while rotating the disc at 3000 rpm.4.
A 5 MHz signal was recorded. Therefore, the recording domain length is 1.0 μm at the innermost circumference and 2.0 μm at the outermost circumference.

In the conventional structure, the signal-to-noise ratio (C/N) at the innermost circumference is 5.
0.0 (IB), but in this example, the signal-to-noise ratio (C/N) f52 was achieved without causing a decrease in recording sensitivity in the outer peripheral area.
．． odB can be obtained.

In FIG. 3, the solid line indicates the recording power, and the dotted line B indicates the signal-to-noise ratio, and the same applies to the following figures.

Next, a second embodiment of the present invention will be described.

A magneto-optical disk similar to that of the first example was prepared except that the material of the heat diffusion layer was changed to Cu, and the recording laser power and reproduction signal-to-noise ratio were measured.

FIG. 4 is a characteristic diagram thereof. The recording and reproducing conditions were the same as in the first embodiment, with a disk rotation speed of 3 oo'orpm.

The recording and reproducing frequency was 4.5 MHz.

In the conventional structure, the signal-to-noise ratio (C/N') at the innermost circumference was 50.0 (IB), but in the second embodiment of the present invention, the signal-to-noise ratio (C/N') at the innermost circumference was 50.0 (IB). A signal-to-noise ratio (C/N) ts 2.5 a+a can be obtained.

Next, a third embodiment of the present invention will be described.

In this example, a magneto-optical disk similar to that of the second example was prepared except that the material of the protective film was changed to ZnS, and the recording laser power and reproduction signal-to-noise ratio were measured.

FIG. 5 is a characteristic diagram thereof.

The recording and reproducing conditions were the same as in the embodiment shown in FIG. 1, with a disk rotation speed of sooorpm and a recording and reproducing frequency of 4.5 MHz.

In the conventional structure, the signal-to-noise ratio (C/N) at the innermost circumference is 50.
．． 0 (IB), but in the third embodiment according to the present invention, a signal-to-noise ratio (07N) of 52.0 dB can be obtained without causing a decrease in recording sensitivity in the outer peripheral area.

Next, a fourth embodiment of the present invention will be described.

In this example, a dielectric film is not provided between the magnetic thin film and the heat diffusion layer, and the film thickness of the heat diffusion layer is set to 2.
000 people, except that the outer circumference was less than 20 Å.
A magneto-optical disk similar to that in Example was prepared, and the recording laser power and reproduction signal-to-noise ratio were measured. FIG. 6 is a characteristic diagram thereof. The recording and reproducing conditions are the same as in the first embodiment.
Disk rotation speed 300 rpm, recording/playback frequency 4
．． It was performed at 5MHz.

In the conventional structure, the signal-to-noise ratio (C/N) at the innermost circumference is 5.
However, in the fourth example according to the present invention, a signal-to-noise ratio (C/N) of 62.0 dB can be obtained without causing a decrease in recording sensitivity in the outer peripheral area.

As described above, according to each embodiment of the present invention, by decreasing the film thickness of the heat diffusion film from the inner circumferential portion toward the outer circumferential portion, it is possible to prevent the recording sensitivity from decreasing in the outer circumferential portion. The signal-to-noise ratio at the periphery can be improved by about 2 dB or more, and the shortest domain length can be shortened from 1 μm to 0.8 μm. This reduces the storage capacity per disk by 26%.
can be increased.

Although plastic was used for the substrate in this example,
It is effective for any substrate such as glass and metal.

In this example, the dielectric film is made of sio and ZnS.

SiNx was used. However, although the dielectric film is naturally required to be optically transparent, the higher the refractive index and the higher the thermal conductivity, the greater the effect.
io, Muro N, BIG! LH, G63N4゜Goo
According to the present invention, great effects can be obtained even if dielectric films such as the following are used.

Effects of the Invention The present invention has a protective film, a magnetic film, and a heat diffusion film laminated on a substrate, and the thickness of the heat diffusion film decreases from the inner periphery toward the outer periphery. It is possible to improve the signal-to-noise ratio in the inner circumference without causing a decrease in recording sensitivity, and as a result, it is possible to shorten the shortest domain length. Therefore, as a result, the storage capacity per disk can be increased.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the correspondence between the structure and film thickness distribution of a magneto-optical disk in the first embodiment of the present invention, and FIG. 2 shows the configuration of a magneto-optical disk thermal diffusion layer manufacturing apparatus for realizing the present invention. A schematic side view, FIG. 3 is a characteristic diagram of the magneto-optical disk in the first embodiment of the present invention, FIG. 4 is a characteristic diagram in the second embodiment of the present invention, and FIG. 6 is a characteristic diagram in the third embodiment. Characteristic diagram,
FIG. 6 is a characteristic diagram in the fourth embodiment. 1.12...Substrate, 2...Protective film, 3
...Magnetic film, 4...Dielectric film, 6.
...Thermal diffusion film, 11...Substrate holder, 1
3...P (1 evaporation source, 14... film thickness correction plate. Name of agent: Patent attorney Toshio Nakao and 1 other person 7-
Eleven boards? - Protective film 3 - Magnetic film 4 - Dielectric film S - Expansion Figure 1 @ Distance from Raft Nakayu R (Way m) Outer III Inner circumference Inner circumference Outer shoulder 11 - - Base bare holder I2- Substrate 13- Pd total source 4- Membrane R, corrected provisional 2nd mouth Figure 3 (σ) Distance from the middle of the disk (b) Figure 4 Figure 5 From inside the disk distance (mm)

Claims (1)

[Claims] A heat diffusion layer is provided on the magneto-optical thin film directly or via a dielectric layer on the opposite surface of the light input surface during recording and reproduction.
A magneto-optical recording disk, characterized in that the heat diffusion layer is configured such that the film thickness decreases continuously from the inner circumference toward the outer circumference within the region used for recording and reproduction.