JPH034974B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magneto-optical storage element that records, reproduces and erases information using laser light.

In recent years, research and development of optical memory devices that meet requirements for high density, large capacity, high speed access, etc. have been actively promoted. One example that has already been put into practical use is an optical disk device that reads information by forming a row of minute pits corresponding to information on an information storage disk and using the diffraction phenomenon when each pit is irradiated with a laser beam. 2. Description of the Related Art There is an optical disk device that forms a reflectance change partial sequence corresponding to information on a storage medium of a storage disk and reads information by utilizing changes in the amount of reflected light when each portion is irradiated with a laser beam.

However, these devices are either only for reproduction or only capable of reproduction and additional recording, and currently no device capable of erasing information has been put into practical use.

The present invention relates to improvements in magneto-optical storage elements that are expected to be used as memory elements in optical disk devices capable of reproducing, recording, and erasing information. One of the difficulties when using a magneto-optical storage element as a memory element is that the reproduction signal level is low. In particular, in the so-called Kerr effect reproduction method, in which a magneto-optical memory element is irradiated with a laser beam and information is reproduced using the reflected light, the signal-to-noise ratio (S/
It was difficult to increase N). To this end, conventional efforts have been made to increase the Kerr rotation angle by improving the magnetic material used as the storage medium or by forming a dielectric film of SiO or SiO ₂ on the storage medium.

As an example of the latter, for example, on a TbFe magnetic thin film
Kerr rotation angle is 0.15 by forming SiO film.
An example of an increase from 0.6 degrees to 0.6 degrees has been reported (IEEE Trans of Mag Vol−16 No.−5 1980
P1194). However, the SiO or SiO ₂ dielectric film described above cannot provide substantial protection against corrosion if there is a risk of corrosion in the magnetic material, and dust and dirt as small as 1 μm may adhere to the dielectric film. In this case, since the recorded bit diameter is about 1 μm, bit detection becomes impossible, and therefore it is not suitable for practical use to form the dielectric film of SiO or SiO ₂ described above. In order to prevent the above-mentioned corrosion and to take measures against dust and dirt, it is considered desirable to cover the magnetic material with glass or transparent resin having a thickness of about 0.5 to 2 mm. However, with this coating material, it is naturally difficult to increase the Kerr rotation angle, and it is also difficult to obtain the effect of increasing the S/N ratio.

In addition to the above-mentioned method, the applicant has proposed a method for improving the apparent Kerr rotation angle by forming a reflective film behind the recording medium in a magneto-optical storage element using the Kerr effect reproduction method (patent application No. 55−85695)
are doing.

The feature of this structure is that the laser light reflected on the surface of the magnetic thin film and the laser light transmitted through the magnetic thin film and then reflected on the reflective film are combined, compared to a structure without the above reflective film. The apparent Kerr rotation angle is improved. In this case, it has been confirmed that the increase rate of the Kerr rotation angle varies depending on the wavelength of the laser beam used, the type and thickness of the magnetic film, the thickness of the reflective film, etc. The applicant has also already proposed a magneto-optical storage element having the structure shown in FIG. 1 is a substrate such as glass, 2 is a GdTbFe amorphous thin film, 3 is a SiO ₂ transparent film, and 4 is a Cu metal film. It has been confirmed that in this structure, when the thickness of the SiO ₂ transparent film 3 is changed, the Kerr rotation angle changes greatly. In Figure 2, the wavelength of the laser beam is 632.8 nm, and the SiO ₂
FIG. 3 is a graph diagram showing how the Kerr rotation angle changes when the thickness of the transparent film 3 is changed.

Since the Kerr rotation angle without the SiO ₂ transparent film 3 and the Cu metal film 4 is 0.27°, the importance of the presence of the Cu metal film 4 can be seen. In addition, the Kerr rotation angle without the SiO ₂ transparent film 3 is at most 0.5° even if other conditions (magnetic material film thickness, reflective film thickness, etc.) are changed, so the film thickness of the SiO ₂ transparent film 3 is It can be seen that the Kerr rotation angle can be greatly increased by making appropriate adjustments.

In view of the above points, the present invention aims to provide a more practical structure in a magneto-optical memory element provided with a reflective film.

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a magneto-optical memory element according to the present invention will be described in detail below with reference to the drawings.

FIG. 3 is a partial side cross-sectional view of one embodiment of the magneto-optic memory element according to the present invention. In the figure, 5 is a substrate made of glass, acrylic resin, etc., and the thickness of the substrate is about 0.5 to 2 mm. Reference numeral 6 denotes a rare earth-transition metal amorphous thin film having an axis of easy magnetization perpendicular to the film surface, which is formed on the substrate by sputtering, vapor deposition, or the like. The materials of this rare earth-transition metal amorphous thin film are GdTbFe, TbDyFe, TbFe, and GdTbDyFe.
And these materials contain some impurities such as Bi, Sn,
A material containing Co or the like may be used. 7 is MgF ₂ , SiO ₂ , SiO, formed on the above amorphous thin film;
These are transparent thin films of TiO ₂ , Si ₃₄ , Ta ₂ O ₅ or the like, and 8 is a stainless steel thin film. As this stainless steel thin film, 18-8 stainless steel SUS304 (JIS standard) was used. The stainless steel thin film 8 acts as a reflective film. A stainless steel thin film is preferable as a reflective film because it has excellent corrosion resistance. Furthermore, since the stainless steel thin film has a low thermal conductivity, when the amorphous thin film 6 is irradiated with a laser spot to perform photothermal magnetic recording, less heat escapes to the reflective film. Therefore, the power loss during photothermal magnetic recording is small and the recording speed can be improved.

However, when a GdTbFe amorphous thin film was used at a laser wavelength of 632.8 nm and a transparent thin film was not provided between the amorphous thin film and the stainless steel thin film, the Kerr rotation angle was at most 0.33°, which was difficult in practice. However, when SiO ₂ was provided as the transparent thin film with a thickness of 500 nm, the Kerr rotation angle increased to 0.57°. With this Kerr rotation angle, there is no problem in practical terms (S/N).

Here, in addition to the above-described configuration, a transparent dielectric film such as SiO, TiO ₂ or the like may be provided between the substrate 5 and the amorphous thin film 6. This film is provided because the substrate 1 made of resin such as acrylic or polycarbonate is susceptible to corrosion. In this case, the refractive index of the transparent dielectric film is larger than the refractive index of the substrate 5, and the film thickness of the transparent dielectric film is approximately equal to (1/4n+m)...where: incident laser wavelength, n: transparent refractive index of dielectric film, m: integer,
If so, the light incident from the substrate 5 interferes within the transparent dielectric film, thereby increasing the Kerr rotation angle and improving the S/N ratio.

Of course, it is also possible to form a guide track with an uneven shape on the substrate 5, or to form a double-sided structure in which the transparent thin film 7, the amorphous thin film 6, and the substrate 5 are formed on both sides of the stainless steel film 8.

According to the present invention described in detail above, since a stainless steel thin film is provided as a reflective film of a magneto-optical memory element, it has excellent corrosion resistance and has low thermal conductivity, so power loss during photothermal magnetic recording is small. It is something.

[Brief explanation of the drawing]

FIG. 1 is a partial side cross-sectional view of a conventional magneto-optical memory element, FIG. 2 is a characteristic graph, and FIG. 3 is a partial side cross-sectional view of an embodiment of the magneto-optical memory element according to the present invention. In the figure, 1, 5: substrate, 2, 6: amorphous thin film,
3, 7: Transparent film, 4: Reflective film, 8: Stainless steel thin film.

Claims (1)

[Scope of Claims] 1. A magneto-optical memory element characterized in that a rare earth transition metal alloy thin film, a transparent film, and a stainless steel thin film are formed in this order on a substrate. 2 The transparent film is made of SiO ₂ , SiO, MgF ₂ , TiO ₂ ,
2. The magneto-optical storage element according to claim 1, comprising at least one of Si ₃ N ₄ and Ta ₂ O ₅ . 3 The rare earth transition metal alloy thin film is made of GdTbFe,
TbDyFe, TbFe, GdTbDyFe or these
Claim 1, characterized in that it is made of any one of substances containing impurities such as Bi, Sn, and Co.
3. The magneto-optical memory element according to item 1 or 2.