JPS626450A - Photomagnetic disk - Google Patents

Abstract

PURPOSE:To attain recording or erasing by the same laser power by forming a light absorbing film between a transparent substrate and a vertically magnetizing film and changing the film thickness of the absorbing film from the inner peripheral part to the outer peripheral part. CONSTITUTION:Irradiation time per unit area is reduced in accordance with a distance from the inner peripheral part to the outer peripheral part, so that the temperature rise of the vertically magnetizing film 3 is reduced. To compensate the reduction, the light absorbing film 2 is arranged under the film 3 and the film thickness is adjusted so that light absorption is low in the inner peripheral part and the value is increased in accordance with the distance from the inner peripheral part to the outer peripheral part. Consequently, the temperature rise of the film 3 is held at a fixed value, matched with its linear speed. Thus, the recording or erasing can be attained by the same laser power.

Description

[Detailed Description of the Invention] [Summary] As a method for recording and erasing with the same power on the inner and outer circumferential parts of a magneto-optical disk, which rotate at different linear velocities, the method uses A magneto-optical disk with a light-absorbing film whose thickness changes toward the other direction.

[Industrial application field]

The present invention relates to a structure of a magneto-optical disk that enables recording and erasing with uniform laser power over the entire area of the disk.

A magneto-optical disk is a memory that uses laser light to record high-density information. Like an optical disk, it has a large storage capacity, can perform contactless recording and playback, and is unaffected by dust. It is a memory with unique characteristics.

In other words, the laser beam can be narrowed down to a small spot with a diameter of 1 μm or less using a lens.
The area required for recording bit information is only about 1 μm2.

Therefore, compared to the magnetic disk or magnetic tape, which requires an area of several tens to hundreds of micrometers to record one bit of information, only a few grooves are required, and therefore large-capacity recording is possible.

In addition, when narrowing down with a lens, the beam diameter becomes about 1 fl on the substrate surface of the magneto-optical disk, so even if there is dust with a size of several tens of μII+2 on the substrate surface, recording and
This can be done with almost no effect on playback.

Magneto-optical disks and optical disks that use laser light as a light source have excellent properties, but when comparing the two, optical disks use a low-melting point metal as a recording medium, and information is recorded and reproduced using holes (bits). ) Read only memory (Read 0nly Memo)
ry) is the main one and has already been put into practical use.

On the other hand, magneto-optical disks are rewritable memory (!!ra
It is being developed as SABL (Memory), and magnetization reversal due to temperature rise of a magnetized film irradiated with a laser is used to record and erase information, and rotation of the polarization plane of reflected or transmitted light from the magnetized film is used. is used to produce a series of lights.

Here, a perpendicular magnetization film is used as the magnetization film because the perpendicular magnetization film is more stable and enables high-density recording when the recording nodes of 1 and O are adjacent to each other.

[Conventional technology]

As mentioned earlier, a magneto-optical disk projects a laser beam focused to a diameter of 1 μm or less onto a perpendicularly magnetized film, which is a recording medium, and the irradiated area is partially heated to a temperature near or below the Curie temperature. Recording and erasing is performed by utilizing the temperature rising to the above temperature.

Here, if the rotational speed of the disk is constant, there is a problem that the temperature of the irradiated area will differ even if irradiated with the same laser power because the linear velocity is different between the outer and inner periphery of the magneto-optical disk. .

That is, as the linear velocity increases from the inner circumference to the outer circumference, the temperature rise becomes smaller.

Therefore, it is necessary to devise ways to perform recording and erasing while keeping the laser power constant and the rotational speed constant.

However, at present, magneto-optical disks have not been put into practical use.
A clear processing method has not yet been determined, and experimentally a method has been adopted in which the laser power is continuously varied depending on the position where information is recorded or erased.

[Problem that the invention seeks to solve]

As mentioned above, in a magneto-optical disk, the linear velocity differs between the inner and outer peripheries during rotation of the disk substrate, so when the rotational speed of the disk substrate is kept constant and the laser power is kept constant, The problem is how to harmonize it.

[Means for solving problems]

The above problem occurs in magneto-optical disks in which a perpendicularly magnetized film is formed on a transparent substrate, and the perpendicularly magnetized film is irradiated with a laser beam to record, reproduce, and erase information. This problem can be solved by a magneto-optical disk characterized in that a light absorbing film is provided on the periphery, and the thickness of the absorbing film is changed from the inner periphery toward the outer periphery.

[Effect]

Information is recorded and erased on a magneto-optical disk by irradiating a perpendicularly magnetized film with a laser while applying a magnetic field, heating it to a Curie temperature, and changing the magnetization of the perpendicularly magnetized film in the direction of the magnetic field. However, in this case, the temperature rise of the perpendicularly magnetized film is proportional to the irradiation time when the laser irradiation intensity is kept constant.

Therefore, the irradiation time per unit area decreases as you go from the inner circumference to the outer circumference.Therefore, as a method of compensating for the decrease in the temperature rise of the perpendicularly magnetized film, the present invention provides a light absorbing film under the perpendicularly magnetized film. By adjusting the thickness of this film so that light absorption is small in the inner circumference and increases toward the outer circumference, the temperature rise of the perpendicularly magnetized film can be matched to the linear velocity and maintained at a constant value. It is something.

In other words, if a thin film with a refractive index of nl is provided in contact with a plane, and light is incident on it through a medium with a refractive index of n2, the light will be reflected at the interface between the plane and the thin film, and the light will be reflected at the interface between the thin film and the medium. In this case, the condition for maximum absorption of light is n + t = 1/4 (2N + 1) n
2 λ (1) The condition for minimizing light absorption is n 2 t = 1/4 ・2 N nz λ .
...(2) However, there is a relationship between L and the thickness of the thin film N, which are positive integers.

Therefore, the present invention is designed to increase light absorption from the inner circumferential portion to the outer circumferential portion in accordance with the irradiation linear velocity of the laser beam.

〔Example〕

FIG. 1 is a cross-sectional view of a magneto-optical disk embodying the present invention.
Zinc sulfide (ZnS) with a refractive index of 2.4 is placed on a transparent substrate 1 made of polymethyl methacrylate (PMMA).
A light absorbing film 2 consisting of
．． 0 terbium-iron-cobalt (Tb Fe Co)
A perpendicular magnetization film 3 is provided, and the light absorbing layer M2 is formed with a different thickness from the inner circumferential portion to the outer circumferential portion.

Moreover, silicon oxide (Sin) is further formed on this perpendicular magnetization film 3.
A protective film 4 made of, for example, is provided.

As shown in the figure, such a transparent substrate 1 has the part where the perpendicularly magnetized film 2 is formed on the inside, spacer rings 5 made of plastic or metal are placed on the inner and outer peripheries, and a disk substrate such as PMMA is laminated from above. A magnetic disk is formed.

The light absorption film made of ZnS used in the present invention has light absorption characteristics as shown in FIG. 2 for laser light having a wavelength of 830n++.

That is, ZnS films with varying thicknesses were formed on PMMAO, and the light absorption characteristics of the films were investigated by irradiating a laser through the PMMA, and the reciprocal of the reflectance was used as a measure of the amount of light absorption.

In other words, the maximum absorption occurs when the film thickness is around 800 mm and around 1800 mm, but in the case of the example, using the former condition, Zn was
The film thickness of S was adjusted.

Here, as a method for adjusting the film thickness, when forming ZnS on a disk substrate by vacuum evaporation, a mask 7 having an opening 6 as shown in FIG. The substrate to be deposited (transparent substrate 1 in this case)
It was formed by rotating and vapor depositing.

Next, on the ZnS light absorption film 2 formed in this way, Te, Fe, and Co are deposited by a two-part deposition method to a thickness of approximately 1.
A perpendicularly magnetized film 3 made of Te Fe Co with a thickness of about 1,000 yen is formed thereon, and an SiO protective film 4 with a thickness of about 1,000 yen is further formed thereon.
A magneto-optical disk was then formed using a conventional method for packaging.

Information was then recorded with a laser power of 2 m<->, but the recording was performed under uniform conditions, and no difference was observed in the readout intensity.

〔Effect of the invention〕

As described above, by providing a light absorption film with an adjusted thickness, the present invention enables recording or recording with the same laser power even though the linear velocity differs between the inner and outer circumferential parts of the magneto-optical disk substrate. The operation mechanism of the magneto-optical disk can be simplified by implementing the present invention.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a magneto-optical disk embodying the present invention, FIG. 2 is a diagram showing the absorption characteristics of a light-absorbing film, and FIG. 3 is a plan view of a vapor deposition mask. In the figure, 1 is a transparent substrate, 2 is a light absorption film, 3 is a perpendicular magnetization film, 6 is an opening, and 7 is a mask.

Claims (1)

[Claims] In a magneto-optical disk, a perpendicularly magnetized film (3) is formed on a transparent substrate (1), and information is recorded, reproduced, and erased by irradiating the perpendicularly magnetized film (3) with a laser beam. ) and a perpendicularly magnetized film (3), a light absorption film (2) is provided between the light absorption film (2) and the thickness of the light absorption film (2) is changed from the inner circumference toward the outer circumference. magnetic disk.