JPS6320744A - Magneto-optical disk - Google Patents

Abstract

PURPOSE:To prevent the deterioration of the data transfer speed and to improve the recording density by forming a protecting film having its thickness decreasing toward the outer circumference from the inner circumference of a disk substrate and laminating a magnetic thin film and a protecting film having the uniform thickness. CONSTITUTION:A protecting film 12 having its thickness decreasing continuously toward the outer circumference from the inner circumference of a disk substrate 11 is formed on this substrate 11 in an area used for recording and reproducing. Then a magnetic thin film 13 and a protecting film 14 having the uniform thickness are laminated on the film 12. The rise of temperature is suppressed in a reproduction mode and the reproduction of signals is possible with large reproduction power by making use of dispersion of heat owing to the thickness of the film 12 increasing toward the inner circumference of the disk 11. Thus the maximum signal output is obtained. While the dispersion of heat is suppressed owing to the thickness of the film 12 decreasing toward the outer circumference of the disk 11. Thus it is possible to prevent the deterioration of the recording sensitivity and to maintain the fast revolutions of a magneto- optical disk.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a magneto-optical disk used for recording information and characterized by a 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 is attracting particular attention, has recently been confirmed to have excellent characteristics as a digital memory.

By the way, due to constraints such as the Curie temperature, which is the main factor that determines recording sensitivity, the Kerr rotation angle, which determines the quality of the reproduced signal, and film fabrication at low temperatures, magneto-optical thin film materials are made of rare earth transition metal amorphous magnetic materials. is used. This rare earth transition metal includes at least one of Fe, Go, and Ni, as well as Gd and Tb.
, an alloy of one or more rare earth elements mainly consisting of Dy.

Specifically, TbFe, GdTbFe, TbF
eCo etc.

However, although these magnetic thin films have a larger force-rotation angle than other magnetic materials, the angle is 0.3 to 0.
．． 5 degrees, and a sufficient signal-to-noise ratio cannot be obtained. Specifically, when using a magneto-optical disk as a digital memory, the following problems arise. In other words, the length of the NFC area (domain) recorded on the disk is
If the optical beam spot diameter used for reproduction is sufficiently larger than the optical beam spot diameter, a sufficient signal-to-noise ratio can be obtained, but on the other hand, if the recorded domain length becomes about the same as the optical beam spot diameter, the signal-to-noise ratio deteriorates rapidly. . Therefore, the signal-to-noise ratio is poor, which limits high-density recording, and it is necessary to obtain an even larger signal-to-noise ratio to improve the recording density.

In order to eliminate such drawbacks, in the configuration of magneto-optical disks, SiO,
Systems using high refractive index dielectric thin films such as ZnS, 5i5N4, and MulN have been proposed. This rL utilizes multiple reflections caused by a dielectric thin film to increase the Kerr rotation angle. Therefore, the thickness of the dielectric thin film is set to λ/4n, where n is the refractive index and λ is the laser wavelength used for recording and reproduction.

However, magneto-optical disks using these dielectric thin films and having a magnetic structure increase Kerr rotation, but cause 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, in order to prevent the Kerr rotation angle from deteriorating due to high temperature f, the magnetic thin film must reduce the light intensity during reproduction. When the laser input power during reproduction is 0, the reflectance of the magneto-optical disk is R, and the Kerr rotation angle is θX, the signal-to-noise ratio S/N with respect to noise
1-j S/Noc jiisin2θ,---(1)
It is expressed as In the above-mentioned magneto-optical disk using a dielectric thin film and having a magnetic structure, as the Kerr rotation angle θ increases, K, Io +
This leads to a decrease in H, and a large S/N improvement cannot be obtained.

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 has been easily considered that by reducing the amount of optical energy absorption, the light intensity during reproduction can be increased and a large signal-to-noise ratio can be obtained (as disclosed in Japanese Patent Application Laid-open No. 56-74844).

By the way, there are two types of disk rotation methods: a constant angular velocity force type and a constant linear velocity force type. In general, disk drives for data files use a constant angular velocity force method due to the need for high-speed access. However, if the amount of optical energy absorption is deliberately reduced in order to obtain a large signal-to-noise ratio, this also results in a decrease in recording sensitivity, resulting in the following problems. In other words, when a disk is operated using a constant angular velocity force type, a high power laser is required for recording at the outer periphery of the disk where the linear velocity is extremely high. However, from the standpoint of device size and cost of the drive, it is essential to use a semiconductor laser, and as a result, the number of rotations of the disk is severely restricted, resulting in the problem that the necessary data transfer rate cannot be obtained.

In view of the above-mentioned problems, the present invention provides a structure in which a first protective layer, a magnetic thin film, and a second protective layer are formed in this order on a disk substrate.
An object of the present invention is to provide an excellent dimensional magnetic disk that obtains a large signal-to-noise ratio without impairing the data transfer rate.

Means for Solving the Problems To achieve this object, the magneto-optical disk of the present invention has at least an inner periphery on the substrate within the area used for recording and reproduction;
A first protective film whose thickness decreases as it goes from the edge to the outer circumference i'l is formed, and further a magnetic thin film and a second protective film are laminated to form a groove.

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 while rotating the disk at a constant angular velocity, the recording domain length becomes shorter at the inner periphery and 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, since the medium movement speed increases at the outer periphery, it is necessary to increase the light input power during recording and 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 imposes a limit on device design, and at the seven outer circumferences of the disk, recording sensitivity imposes a limit on device design.

In this project, the first C') protective film is formed with a thickness of 1 degree as it goes toward the inner periphery, thereby utilizing thermal diffusion to suppress the temperature rise of 1 degree during regeneration, and This enables signal reproduction using the reproduction power and maximizes the signal output, which limits device design.The first protective film becomes thinner toward the outer periphery to prevent heat diffusion and prevent recording. This prevents a decrease in sensitivity and maintains high speed rotation of the disk.

Compared to conventional magneto-optical disks, this improves recording density without reducing data transfer speed.
This increases the recording capacity of a single disc.

EXAMPLE Hereinafter, an example of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing the correspondence between the structure of a magneto-optical disk and the thickness distribution of a first protective film according to an embodiment of the present invention. In FIG. 1, 11 is a plastic or glass substrate, 12 is a first protective thin film, 13 is a magnetic thin film, and 14 is a second protective film. A first protective film 12 is formed on a disk-shaped substrate 11 so that the film thickness decreases continuously from the inner circumference to the outer circumference of the substrate. On this first protective film 12, a magnetic thin film 13 having a uniform thickness and a second protective film 14 are laminated in this order.

The magneto-optical disk of this embodiment has a diameter of 130Wtttφ and a radius of 30M to 60! ff is recorded and reproduced. The thickness of the first protective film 12 at the inner circumferential portion of the area used for recording and reproduction is 200 OA, and the film thickness at the outermost circumferential portion is 500 Å.

Next, a method for manufacturing the magneto-optical disk of this example will be described. FIG. 2 shows a configuration diagram of the first protective film manufacturing apparatus.

In FIG. 2, 21 is a substrate holder, 22 is a substrate made of plastic or glass, 23 is Mg0x,
An evaporation source for evaporating 5iOy, and 24 a film thickness correction plate. First, a first protective film, Mg0x, 5i, is deposited using an evaporation apparatus equipped with an electron beam evaporation source shown in FIG.
Oy (o<x<1, O(Y<2) is formed into a film.

After first evacuation to 2 x 10 Torr, Mg0 is removed from the evaporation source 23 while rotating the substrate 22 with a diameter of 13QM'lφ mounted on the substrate holder 21 at 6 Orpm.
x, S process 07 is deposited. At this time, in order to obtain a desired film thickness distribution, a film thickness correction plate 24 is placed between the evaporation source 23 and the substrate 22. On top of that, a magnetic thin film of GdTbFe with a thickness of 800 nm is applied using a vapor deposition device or a sputtering device
The second protective film Mg0x, 5iOy was
form.

Mg0x is produced by a film forming apparatus having these configurations.

By forming a film of 5iOy, a protective film having the film thickness distribution shown in FIG. 1 can be obtained. Note that the film forming speed is 1oA/sec on the inner circumference due to the effect of the film thickness correction plate 24.

The outer circumference is 0.2 mm/sea or less.

Next, FIG. 3 shows the recording and reproducing characteristics of the magneto-optical disk of this example. FIG. 3A shows a characteristic diagram of the present implementation, and FIG. 3A shows a characteristic diagram of the conventional configuration. The record is 3000 r
4.5 MHz while rotating the disk at pH 1.
The signal was recorded. Therefore, the recording domain length is 0.8 μm at the innermost circumference, which is shorter than the conventional 1.0 μm, and 2.0 μm at the outermost circumference.

In the conventional structure, the signal-to-noise ratio (C/N) at the innermost circumference is 6.
0.0 (iB), but in this example, the signal-to-noise ratio (C/N) was 5 without causing a decrease in recording sensitivity at the outer periphery.
2.0 dB can be obtained.

In FIG. 3, the solid line A indicates the recording laser power, and the dotted line B indicates the signal-to-noise ratio.

In this example, the first protective film is Mg0x, 5iO
Although it is set to y, 5102 may also be used. In the case of 5i02, the film thickness at the inner peripheral portion is 300OA. Further, in this embodiment, (1, dTbFe is used as the magnetic film), but other magneto-optical magnetic materials may be used.

Further, in this embodiment, plastic, resin, or glass was used as the substrate, but a substrate made of metal or the like may be used.

Effects of the Invention In the present invention, a first protective film whose film thickness decreases from the inner circumference to the outer circumference is formed on a substrate, and a magnetic thin film and a second protection film are laminated thereon. This improves the signal-to-noise ratio at the inner periphery by 2 dB without causing a decrease in recording sensitivity at the outer periphery. As a result, the shortest recording domain length can be shortened from 1 μm to 0.8 μm. The recording capacity per sheet can be increased by 25%.

[Brief explanation of drawings]

Figure 1 is a correspondence diagram between the structure and film thickness distribution of a magneto-optical disk in an embodiment of the present invention, and Figure 2: Configuration of a protective film tabulation device for realizing a magneto-optical disk written by Kasamoto. 3 are recording and reproducing characteristics diagrams in one embodiment of the invention. 11... Substrate, 12... First protective thin film, 13... Magnetic thin film, 14... Second
protective thin film, 21-...substrate holder, 22...
... Substrate, 23 ... Mountain/evaporation source, 24 ... Film thickness correction plate. Name of agent: Patent attorney Toshio Nakao and one other person. TS “To ° Gui - Fuji)

Claims (1)

[Claims] A first protective thin film, a magnetic thin film, and a second protective thin film are laminated in this order on a disk-shaped substrate that is rotated at a constant angular velocity, and the first protective thin film is used at least for recording and reproduction. What is claimed is: 1. A magneto-optical disk having a film thickness that decreases from an inner circumferential portion to an outer circumferential portion.