JPS60209947A - Optomagnetic recording medium - Google Patents

Abstract

PURPOSE:To increase considerably the rotating angle of the plane of polarization of a recording medium and to improve the S/N ratio of a reproduction signal by using silicon (Si) for the 1st and 2nd high-refractive index interference layers of an optomagnetic recording medium provided with the 1st high-refractive index interference layer, optomagnetic recording layer, the 2nd high refractive index interference layer and reflecting layer on a transparent substrate. CONSTITUTION:A high-refractive index interference layer 3, an optomagnetic recording layer 2, a high-refractive index interference layer 3' and a reflecting layer 5 are provided on a transparent substrate 4. Si (refractive index n=2.5) is used as the layers, 3, 3'. Laser light 6 to be used for recording, reproducing and erasing is made incident from the substrate 4 side to perform recording of information on the layer 2. The information is reproduced from the rotation of the plane of polarization based on the Kerr rotating angle and Faraday rotating angle by the reflected light from the layer 2 and the layer 5. The film thickness of the layer 2 is set to the thickness at which the transmission of part of the wavelength of the laser light for reproduction is made possible. Since the effective use of the Faraday effect generated in the stage of transmission is thereby made possible, the rotation of the plane of polarization in the stage of reproduction is increased.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of industrial application) The present invention relates to a magneto-optical recording medium that records, reproduces and erases information using laser light.

(Prior art and its problems) Magneto-optical recording media are rewritable optical disks with large capacity and
Because high-speed access is possible, it is considered a new memory that can replace current magnetic disk memories.

Among them, magneto-optical disks using magneto-optical recording media have attracted the most attention because of their rewritability, and have been actively researched and developed in recent years.

The configuration of a conventionally known magneto-optical recording medium is as shown in FIG. 1, in which glass, metal, or organic resin is used as a support substrate 1, and the support substrate 1 has magnetization in a direction perpendicular to the substrate. A magneto-optical recording layer 2 made of a perpendicularly magnetized film is formed. As the magneto-optical recording layer, MnB1.
MnCuB1. PtCo, MnAl! Crystals such as Ge, rare earths such as Gd, Tb, Dy, and Ho, and Fe, C
o.

Amorphous magnetic thin films prepared by mixing transition metals such as Ni in various compositions are known. Magneto-optical recording media have the advantages of replacing the above-mentioned magnetic disk memories, but on the other hand, the playback signal level The disadvantage is that the 87N ratio is low.

In particular, reproduction is performed using reflected light from a magneto-optical recording medium. The reason for the low 87N ratio was that the Kerr rotation angle of the beak was small.

As a conventional method of improving the S/N ratio of the reproduced signal,
Improvements to the recording layer, such as making the magneto-optical recording layer multi-component or adding other elements, and forming a high refractive index interference layer on the laser beam incidence surface of the recording medium to reduce reflected light and increase the Kerr rotation angle. An increasing Kerr rotation amplification method is used.

Regarding the latter Kerr rotation amplification method, as shown in FIG. However, in this medium, when the recording layer 2 is easily oxidized, the 8i0 used for the high refractive index interference layer 3 is known.
．． There is a drawback that the oxygen in 8i02 forms oxides on the surface of the recording layer 20, and the Kerr rotation angle of the recording layer decreases over time. In addition, small dust, chips, and dirt that adhere to the high refractive index interference layer 3 are present near the focal point of the laser beam focused on the recording layer, so they become a source of noise during signal reproduction. There are 0 drawbacks (objective of the invention) The present invention eliminates these conventional drawbacks, provides a recording layer that is easy to produce, has excellent corrosion resistance and oxidation resistance, and can ignore the effects of small dust and dirt. An object of the present invention is to provide a novel magneto-optical recording medium which has a function of amplifying the Kerr rotation angle and can obtain an excellent reproduced signal ratio of 87N. a high refractive index interference layer, a magneto-optical recording layer is provided on the first high refractive index dielectric layer, a second high refractive index interference layer is provided on the magneto-optical recording layer, and a high refractive index interference layer is provided on the first high refractive index dielectric layer; In the magneto-optical recording medium in which a reflective layer is provided on the high refractive index interference layer of the first. A magneto-optical recording medium characterized in that silicon (Si) is used as the second high refractive index interference layer is obtained.

(Detailed explanation of the structure) The present invention solves the problems of the prior art by adopting the above-mentioned structure.Firstly, by using a transparent substrate as a medium support substrate, it is possible to record, reproduce and erase multiple signals. A method can be adopted in which laser light is made incident on the recording layer from the substrate side. According to this method, the laser beam is not focused on the surface of the substrate, so small dust, particles, etc. that adhere to the surface of the transparent substrate, etc.
Dirt has almost no effect on recording, reproducing, and erasing performance.

The feature of the present invention is the use of silicon (8i) as a high refractive index interference layer.
．． 0 or 8i, which has a larger refractive index than 5iO1 and therefore has a larger Kerr rotation angle amplification effect, has a semiconductor laser wavelength of 7.
It is also advantageous as an interference layer that there is no absorption in the wavelength range of 80 to 830 nm.0 When changes such as oxidation occur on the surface of the recording layer,
The Kerr rotation angle, which is easily affected by the surface condition of the recording layer, decreases, deteriorating the medium properties, but since Si is not an oxide and is chemically stable, oxides are formed at the interface between the interference layer and the recording layer. It will not be done.

The magneto-optical recording layer is set to have a thickness that allows a portion of laser light used for recording, reproduction, and erasing to pass through. Regenerate it with this.
The laser light has a large polarization plane rotation due to the Kerr rotation that it receives on the surface of the recording layer, and the Faraday rotation that it receives when it passes through the recording layer, passes through the interference layer, is reflected by the reflection layer, and passes through the interference layer and the recording layer again. reflected. At this time, the thickness of the interference layer used between the recording layer and the reflective layer is set to be 1/2 of the wavelength of the laser light in the interference layer.The magneto-optical recording layer is a high refractive index interference layer made of Si. Since the silicon layer is sandwiched between layers, it is resistant to air and moisture intrusion from the substrate side or the reflective layer side (the Si layer also serves as a protective layer).

(Embodiment) FIG. 3 is a cross-sectional view of an embodiment of a magneto-optical recording medium to which the present invention is applied.
Furthermore, it has a magneto-optical recording layer 2, a high refractive index interference layer 31, and a reflective layer 5. The transparent substrate 4 may be made of glass, organic resin (polymethylmetalliflate, polycarbonate,
◇High refractive index interference layer 3,
8i (refractive index n=2.5) is used as 3'. 8i has a higher refractive index than 8i0.8i02. As the magneto-optical recording layer 2, MnB1. MnCuB1. Pico
, MnAl! Crystals such as Ge or Gd, Tb,
As the reflective layer 5, an amorphous magnetic thin film made of various compositions of rare earth elements such as Dy and Ho and transition metals such as Fe, Co, and Ni is used.

Metals such as Cu, Cr, Ag, and Au are used.

A laser beam 6 used for recording, reproduction, and erasing enters from the side of the transparent substrate 4 and records information on the recording layer 2, and the Kerr rotation angle and the 7Alade rotation angle are determined by the reflected light from the recording layer 2 and the reflective layer 5. Regenerate information from the rotation of the plane of polarization based on . By setting the film thickness of the recording layer 2 to a thickness that allows a portion of the wavelength of the reproduction laser light to pass through, the Faraday effect that occurs during transmission can be effectively utilized, and the rotation of the plane of polarization during reproduction can be effectively utilized. For example, in a structure in which a magneto-optical recording layer is formed on a transparent substrate to a thickness of 200X, a Si interference layer is provided on top of the layer, and a reflective layer is further formed on top of the magneto-optical recording layer, the semiconductor laser wavelength (λ=83
0 am ), the rotation of the polarization plane is up to three times that of a configuration with only a magneto-optical recording layer.

The feature of the magneto-optical recording medium shown in FIG. 3, which is an embodiment of the present invention, is that in addition to the increased rotation of the plane of polarization due to the above-mentioned reflective film structure, an 8i interference layer 3 is provided between the transparent substrate and the magneto-optical recording layer. The polarization plane rotation amplification effect changes depending on the film thickness of the high refractive index interference layer 3 shown in FIG. 3, and also varies depending on the reproduction laser beam wavelength. However, the higher the refractive index of the high refractive index interference layer, the higher the amplification factor of polarization plane rotation.

For example, when using 8i (n = 2.5) as the high refractive index interference layer 3 and when using 8i0 (n = 1.9), the amplification factor of polarization plane rotation is larger in the case of Si, and the maximum Glass is used as the transparent substrate, and the thickness is 600X.
! ! -Sa 200 x (7) GdTbFe film, thickness 1
In the magneto-optical recording medium according to the present invention in which a 3oX (D8i film and a 500X thick Au film are successively fabricated by sputtering), the polarization plane rotation based on the Kerr rotation angle and the Faraday rotation angle at a wavelength of 830 nm. is 15 times that of a GdTbFe film alone, and the rotation of the polarization plane is greatly increased by the structure with two Si interference layers and a reflective layer. In general, in magneto-optical recording, the reproduction signal signal ratio is is 8/Noc θ, where θ is the polarization plane rotation angle and R is the reflectance.
In the embodiment of the present invention, the reflectance R is only about 179, which is known to be 87.
The N ratio according to the present invention is 5 compared to the single-layer structure of the magneto-optical recording layer.
It can be seen that the improvement is doubled.

Next, regarding the corrosion resistance and oxidation resistance of the recording layer, the recording layer is
It is completely shielded from the atmosphere because it is sandwiched between two 8i interference layers, and the 8i is chemically stable because the drying layer is not an oxide.
Furthermore, since each layer is manufactured successively in a high vacuum, the interface between each layer is not exposed to the atmosphere, so even though the recording layer is relatively thin, there is no change in the recording layer over time or deterioration of its characteristics.

(Effects of the Invention) Although the present invention has a simple configuration, it is possible to significantly increase the rotation angle of the polarization plane of the recording layer and improve the reproduced signal S/N ratio. Furthermore, the recording layer is sandwiched between two interference layers, and by using an 8i interference layer that is not an oxide, corrosion resistance and oxidation resistance can be improved. The Si interference layer is chemically stable) and works as a protective layer, particularly when a water-permeable organic resin is used as the substrate, and exhibits its effectiveness.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the structure of a conventional magneto-optical recording medium, FIG. 2 is a sectional view showing the structure of a conventional magneto-optical recording medium having a high refractive index interference layer, and FIG. 3 is an embodiment of the present invention. FIG. 3 is a cross-sectional view showing an example configuration.

Claims (1)

[Claims] A first high refractive index interference layer is provided on a transparent substrate, a magneto-optical recording layer is provided on the first high refractive index interference layer, and a second high refractive index interference layer is provided on the magneto-optical recording layer. , and a reflective layer is provided on the second high refractive index interference layer. A magneto-optical recording medium characterized by using silicon as a second high refractive index interference layer.