JPS6040542A - Optical memory medium - Google Patents

Abstract

PURPOSE:To obtain an optical memory medium which permits rewriting and reading out with high efficiency when a laser light beam is made incident to a photomagnetic film by forming the photomagnetic film which is made substantially thick to increase the effect of Krr rotation, a thin transparent material film and an extremely thin metallic film in this order on a base. CONSTITUTION:A photomagnetic film 22 consisting of, for example, Tb23Fe77 is formed to about 600Angstrom thickness on a transparent base body 1 consisting of glass, etc. and thereafter a thin transparent SiO2 film 23 and an extremely thin metallic film 24 of extremely thin Al, etc. are formed thereon. An optical memory medium which permits recording, reproducing and erasing of information when a laser light beam 6 is made incident thereto from the film 24 side is thus obtd. An equally good result is also obtd. by forming the film 32, the film 33 and the film 34 in this order on the base plate 1 and making the beam 6 of laser light 4 incident thereto from the plate 1 side. The films 22, 34 are thus made thick and the Kerr rotating angle is increased by the interfering effect of the films 23, 33 and the films 24, 32 to prevent oxidation deterioration of the films 22, 34, by which the optical memory medium having a long life and excellent recording and reproducing efficiency is obtd.

Description

Detailed Description of the Invention (Technical Substances) The present invention relates to a rewritable optical memory medium suitable for various uses such as image files, document files, and digital data memories, and in particular, to a rewritable optical memory medium suitable for various uses such as image files, document files, and digital data memories. It is related to media configuration.

(Prior art) Information is recorded using the magneto-optical recording method by irradiating a recording medium such as a crystalline MnB1 thin film, an amorphous Gdco thin film, or a TbFe thin film with a focused laser beam to locally raise the temperature. At the same time, a magnetic field is applied from the outside and the magnetization of the local area is directed in the direction of the applied magnetic field.

The magnetic Kerr effect, which is an interaction between light and magnetism, is used to read out the recorded magnetization direction using a laser beam and reproduce information.

The Kerr effect of magneto-optical materials currently discovered is generally small, with a Kerr rotation angle of about o30 in most cases, and even MnB1, which has a relatively large Kerr rotation angle, has a
Not enough.

Therefore, media configurations that emphasize this Kerr rotation angle (generally referred to as Kerr enhancement) are being researched.

An example of the structure of a conventional optical memory medium for car enhancement is shown in FIGS. 1 and 2.

In the configuration shown in FIG. 1, a magneto-optical film λ (for example, M
nB1 film) and an interference layer 3 (for example, a SiO film) are laminated in this order.

When a focused laser beam obtained by focusing the laser beam l by a lens j is made incident on the interference layer 3, the chance that the laser beam 6 is reflected at the interface between the magneto-optical film and the interference layer 3 is due to interference. As the layer 3 increases compared to the case without it, the angle of rotation of the plane of polarization of the light emitted from such a medium increases.

In such a configuration, factors that can maximize the total effect include the thickness of the interference layer and the refractive index of the interference layer.

The configuration shown in FIG.
(e.g. SiO film) and metal film/3 (e.g. Au film)
are stacked in this order.

A focused laser beam 6 obtained by focusing laser optomagnetic light with a lens j passes through the magneto-optical film (at this time, due to the Faraday effect (the plane of polarization rotates), it is confined in the transparent thin film 12, The Kerr effect at the interface between the transparent thin film /2 and the magneto-optical film // and the Faraday effect when passing through the magneto-optical film // are superimposed, and the rotation angle of the plane of polarization of the reflected light emitted from the medium is Increased.

In the configuration shown in FIG. 1, as mentioned above, it is necessary for the interference layer λ to have a large refractive index in order to further increase the enhancement effect.
It is difficult to form a thin film of the above), and in most cases, a SiO film (refractive index of 2) is used.

In addition, in the configuration shown in FIG. 2, the magneto-optical film l/ is extremely thin, so it deteriorates due to oxidation.
The drawback was that the information recording and reproducing functions were lost after a few days. In addition, since the magneto-optical film// is extremely thin, pinholes are likely to occur, resulting in many information defects, ie, dropouts, and a high error rate.

(Purpose) The present invention was made in view of the drawbacks of these conventional magneto-optical media, and its purpose is to provide a sufficiently thick magneto-optical film,
To provide a rewritable optical memory medium which is composed of a transparent film and an interference layer that is a combination of an ultra-thin metal film, has a large car-enhancement effect, reproduces signals with high efficiency, and has excellent safety. It is in.

(Structure of the Invention) In order to achieve this object, the present invention includes a seventh layer made of a magneto-optical material, a second (1) layer made of a transparent material, and a layer made of a metal material with a film thickness of 70 to 200 layers. A certain third layer is arranged in this order, and the structure is such that a laser beam can be incident on the first layer to record, reproduce, and erase information.

In a preferred embodiment of the present invention, the seventh layer, the first layer, and the third layer are arranged in this order on a flat substrate, and a laser beam is applied to the first layer from the third layer side. can be input.

In another preferred embodiment of the present invention, the third layer, the second layer, and the first layer are arranged in this order on a flattened transparent substrate, and the first layer is arranged from the transparent substrate side to the first layer. Allows laser light to enter.

Here, a protective layer made of a transparent material may be disposed on the surface on the side where the laser beam is incident. (Example) The present invention will be described in detail below with reference to the drawings.

FIG. 3 is a diagram showing the first embodiment of the optical memory medium of the present invention, where / is the diameter Δ, the thickness is /, the glass substrate processed to be flat is 2 mm, and n is the magneto-optical material. , for example Tb2. B is a transparent thin film made of a transparent material such as 5j-0, and 2II is an extremely thin metal film made of a metal material such as Al.

The Tb-Fe film, which is the magneto-optical film n, was fabricated by a high frequency magnetron sputtering method using a composite target, and the film thickness was approximately 100 mm. Subsequently, a Sin film as the transparent thin film n and one film as the ultra-thin metal film 2 were laminated by vacuum evaporation, with film thicknesses of 330 mm and 30 λ, respectively.

The main factors that determine the enhancement effect of the car rotation angle are:
This is the thickness of the transparent thin film n. In determining the film thickness of the Sin film as the transparent thin film n, 330 people, the film thickness of the Sin film was changed and the Kerr rotation angle was measured. A comparison with the case without the membrane is shown in FIG. Here, the measurement light was made incident from the ultra-thin metal film 2 side.

As is clear from Fig. 9, when an Al film (50 people) is loaded (curve A), the Kerr rotation angle is
In the case of the aluminum film, the maximum value is shown as 〆, and when no Al film is loaded (curve B), compared to the conventional configuration shown in Fig. 1, the maximum value is approximately ≈S times larger. Obtained.

Five in the configuration of the present invention! The ultra-thin metal film 2 is required to be semitransparent. That is, the focused laser beam 6 as the incident light passes through the ultra-thin metal film A/2 and passes through the transparent thin film n.
After reaching the magneto-optical film n, it is necessary to enhance the Kerr rotation angle by multiple and repeated reflections within the transparent thin film n.

Therefore, the film thickness of the two AI ultra-thin metal films is /θ~,
200 is preferred; film thicknesses outside this range reduce the enhancement effect. - In the first embodiment described above, an Al film was used, but metal films other than AI, such as Ag
, Au, Ou, Or, etc., the same thing as above applies.

Furthermore, the thickness of the Tb-Fe film, which is a magneto-optical film, needs to be so thick that it is not transparent.Moreover, in order to prevent deterioration due to acid, the film thickness should be set at SOOÅ or more. preferable.

Regarding the optical disk medium shown in the first embodiment above,
As a result of evaluating the reproduction S/N and reproduction S/M over time using an information recording/reproduction test device using a laser diode, the S/N was 1 to II codB.

This is about 7 (E of iB,
/N will improve. Furthermore, this S/N value shows no deterioration at all even after 90 days have passed since the medium of the first embodiment described above was produced, and is more stable than the conventional medium shown in FIG. It was confirmed that it is excellent.

A second embodiment of the invention is shown in FIG. Here, it is a disk-shaped glass substrate with a diameter of 3θ and a thickness of 8.2 mm.
It was a gate. 32 is a glass substrate/an ultra-thin metal film according to A) placed on top, and its thickness was 30. 33 is a transparent thin film of Sin disposed on the ultra-thin metal film 32;
Approximately 200 people participated. 3G is a Gd,..., Oo, film as a magneto-optical thin film disposed on the transparent film 33-F;
The thickness of the film was 100 people. The above three-layer films were successively laminated and formed on a glass substrate in the same sputtering apparatus.

Regarding the optical disc medium thus obtained, (9) S/N was measured using an information recording/reproducing test device using a laser diode, as in the case of the first embodiment. However, in this case, the laser beam 6 was made incident from the substrate side. In this example, a S/N value of 110 dB was obtained. As for the change in S/'H over time, no deterioration was observed even 90 days after the disk medium was manufactured, as in the case of the first example.

In addition, a transparent protective film of 30 μm 11 is formed on the light-receiving surface of the medium of the first and second embodiments described above by coating and curing a transparent material, such as an ultraviolet-curable acrylic resin. Due to this, S due to fingerprints etc.
It is also possible to adopt a structure that prevents a decrease in /N.

(Effects) As explained above, according to the present invention, by forming an optical disk medium by laminating an interference layer consisting of an ultra-thin metal film and a transparent film on a sufficiently thick magneto-optical film, The magneto-optical Kerr rotation angle is increased and its effect is greater than that of the conventional one, and as a result (/θ) there is an advantage that the S/N can be improved. Furthermore, since the film thickness of the magneto-optical film is sufficiently thick, there is a practical advantage that the deterioration of S/N over time due to oxidative deterioration is greatly improved.

[Brief explanation of drawings]

1 and 2 are cross-sectional views showing an example of the structure of a conventional optical memory medium, FIG. 3 is a cross-sectional view showing a first embodiment of the optical memory medium of the present invention, and FIG. 9 is a detailed explanation of the present invention. FIG. 3 is a cross-sectional view showing the λth embodiment of the optical memory medium of the present invention. /...Substrate, C...Magneto-optical film, 3...Interference layer, D...Laser light, S...Lens, 6...Focused laser light, l/...Magneto-optical film , /2...Transparent thin film, /3...Metal film, n...Magneto-optical film (first layer), B...Transparent thin film (second layer), 21...Ultra-thin metal film (3rd layer), 32... Ultra-thin metal film (7th layer), 33... Transparent film (2nd layer), 3Il... Magneto-optical film (31st layer). Patent Applicant Nippon Telegraph and Telephone Public Corporation Figure 1 Figure 2 Figure 3 Go to 11-71 Figure 4 SiO (J, +m)

Claims (1)

[Scope of Claims] A first layer made of a magneto-optical material, a second layer made of a transparent material, and a third layer made of a metal material and having a film thickness of 10-200A are arranged in this order, An optical memory medium characterized in that a laser beam can be incident on a layer to record, reproduce, and erase information. 2. In the optical memory medium according to claim 1, the first layer, the first layer, and the third layer are arranged in this order on a flat substrate, and the third layer side An optical memory medium, wherein a laser beam can be incident on the first layer. 5) In the optical memory medium according to claim 1, the third layer, the second layer, and the first layer are arranged in this order on a flat transparent substrate, and the transparent A photomagnetic medium, characterized in that a laser beam can be incident on the layer/layer from the substrate side. 4) In the original memory medium according to any one of claims 1 to 5, a protective layer made of a transparent material is disposed on the surface on the side where the laser beam is incident. Features of optical memory media.