JPS62285257A - magneto-optical disk - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] 3. Detailed Description of the Invention [Summary] As a method for facilitating the formation of a tracking guide on which information is recorded, a magneto-optical recording layer is provided on a glass substrate, and then this recording is performed. A magneto-optical disk with a concentric reflective film on the layer.

[Industrial application field]

The present invention relates to the structure of a magneto-optical disk in which the position of a tracking guide is changed.

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 record and play without contact, and is not easily affected by dust. It is a memory with excellent features.

0Comparing the two, optical discs are write-once memories (write-once memory) that use low-melting point metals or non-metals as the recording medium and record information with or without holes.
ce Memory) is the mainstream, and rewritable memory (which utilizes the difference in reflectance between crystal-amorphous or crystal-crystal phase transitions) is the mainstream.
Erasable Memory) has also been developed, but its ratio is small.

On the other hand, magneto-optical disks have been developed as rewritable memories from the beginning, and magnetization reversal caused by temperature rise in a magnetic film irradiated with a laser is used to record and erase information, and the light reflected from the magnetic film is used to record and erase information. Alternatively, rotation of the polarization plane of transmitted light is used to read out information.

[Conventional technology]

Conventional magneto-optical disks are made of polymethyl methacrylate (abbreviated as PMMA) and polycarbonate (abbreviated as PC).

Rare earth-transition metal amorphous alloys such as terbium, iron,
Cobalt (Tbie/Go), gadolinium/terbium/iron (Gd-Tb-Fe), etc. are formed into a perpendicularly magnetized film using a vacuum pumping method or sputtering method, and then silicon oxide (Sin), etc. is formed on top of this. A disk substrate is manufactured with a protective film.

Next, a magneto-optical disk is fabricated by placing the perpendicularly magnetized film on the inside of these two disk substrates, placing spacer rings made of plastic or metal on the inner and outer peripheries, and fixing them with adhesive from above and below.

To record information on such a magneto-optical disk, a laser beam focused by a lens is irradiated from the transparent disk substrate side while a perpendicular magnetic field is applied, and the temperature of the irradiated part of the perpendicularly magnetized film increases. This is done by utilizing the fact that the magnetization reaches the Curie temperature and the magnetization reverses in the direction of the magnetic field.

Furthermore, erasing is performed by applying a magnetic field in the direction opposite to the direction of magnetization at the recording position, heating it by irradiating it with laser light, and reversing the magnetization to the original direction.

Now, the inventors have proposed a magneto-optical disk with a new structure in which a crystalline magnetic Garb-Soto layer is used as a recording medium in place of the conventional rare earth-transition metal based amorphous alloy layer.

Figure 2 shows this structure, in which a recording layer 2 made of crystalline garnet whose magnetization direction is perpendicular to the substrate surface is formed on a transparent and heat-resistant disk-shaped substrate 1, and a recording layer 2 made of crystalline garnet whose magnetization direction is perpendicular to the substrate surface is formed on top of a transparent and heat-resistant disk-shaped substrate 1.
This structure is provided with a reflective film 3 made of metal.

Here, the reason why the inventors propose a magneto-optical disk with a new structure is as follows: (1) Since garnet is an oxide, it does not deteriorate due to oxidation.

■ Since garnet is transparent, the Faraday effect can be used for readout.

Depends on things like that.

Here, the recording layer 2 made of garnet is made by heating and crystallizing amorphous garnet formed on the substrate by a method such as sputtering, and the crystallization temperature is as high as 550°C or higher. . Therefore, the materials that can be used for the substrate are limited, and there is a problem in that polymer materials cannot be used.

That is, conventional magneto-optical disks use glass as a substrate, coated with a photopolymer using a spin code method, and then use photolithography to coat the photopolymer to act as a guide during trunking. The pregroove was patterned.

Here, the pregroove is formed of concentric grooves having a groove width and a groove interval of about 1 μm, respectively, and a depth of about 0.1 μm, for example.

However, as mentioned above, the magneto-optical disk proposed by the inventors cannot use photopolymers because of the high-temperature crystallization process.

Therefore, the pregroove 4 was formed by directly covering the glass substrate with a photoresist and etching it using a hydrofluoric acid (IIF)-based treatment liquid.

However, the etching speed of glass is slow, and the pregroove pattern is extremely fine, resulting in poor pattern accuracy.
Improvements were needed to improve the quality of magneto-optical disks.

[Problem that the invention seeks to solve]

As mentioned above, in order to form the magneto-optical disk that the inventors have developed, it is necessary to form a pregroove pattern directly on the disk substrate made of glass using photolithography, but the accuracy of this pattern is limited. The challenge is to increase the yield.

[Means for solving problems]

The above problem can be solved by a magneto-optical disk having a configuration in which a recording layer is provided on a glass substrate and then a concentric reflective film is provided on the recording layer.

[Effect]

As a method of solving this problem, the present invention eliminates the need to form pregrooves directly on a glass substrate, and instead forms a recording layer 2 directly on a substrate I with a flat surface as shown in FIG. This problem is solved by patterning a reflective film 5 having a conventional pregroove width on top.

The reason for this structure is that the recording layer of the magneto-optical disk proposed by the inventors is transparent because it is made of garnet, and reading is performed using the Faraday effect, so the tracking guide is placed on the substrate 1. This is because the reflective film 5 does not need to be provided directly on top, and the reflective film 5 can serve as a two-stage reflective film for readout light and a tracking guide, as in the conventional case.

Note that as a tracking method for a magneto-optical disk configured according to the present invention, wobbling (Wobbling) is used as in the conventional method.
bling) detection method can be used.

That is, the laser beam is scanned while being wobbled along a reflective film formed in a concentric pattern, and automatically so that the difference in the amount of reflected light that occurs when it deviates from the reflective film 5 alternately to the left and right is equalized. All you have to do is track while making corrections.

〔Example〕

Thickness 111 made of glass (Ni2O) manufactured by Hoya Glass
A substrate 1 with a diameter of 3 inches is used, and bismuth-doped gallium garnet (BizYGa) is deposited on it using a sputtering method.
Fe, 012 (hereinafter abbreviated as garnet) is 0.5
It was formed to a thickness of μm, and was heat-treated in the air at 650° C. for 5 hours to crystallize it.

Thereafter, chromium (Cr) was applied on top of this using a sputtering method.
was formed to have a thickness of 0.1 μm, and a concentric reflective film 5 with a width of 2 μm and a pinch of 4 μm was formed using photolithography.

Since the tracking guide of the magneto-optical disk formed in this way is accurately patterned, the tracking accuracy is improved and the C/N (Carrier-level
el/No1se-1evel) is 30 for the conventional one.
dB, but by implementing the present invention, it was possible to improve it to 35 dB.

〔Effect of the invention〕

As described above, in the manufacturing process of magneto-optical disks with the configuration proposed by the inventors, the formation of pregrooves has been a bottleneck, but by implementing the present invention, the reflective film can be used as a tracking guide. This makes it possible to improve the characteristics.

side view, Figure 2 is a partial cross-sectional view of a conventional magneto-optical disk substrate. It is.

In the figure, 2 is a substrate, 2 is a recording layer, 3.5 is a reflective film, and 4 is a pregroove.

Claims (1)

[Claims] In a magneto-optical disk in which a magneto-optical recording layer is provided on a glass substrate provided with concentric pregrooves, and a reflective film is provided on the recording layer, the magneto-optical recording layer is provided on the glass substrate, and then A magneto-optical disk characterized in that a concentric reflective film is patterned on a recording layer.