JPS60209946A - Optomagnetic recording medium - Google Patents

Abstract

PURPOSE:To increase considerably the rotating angle of the plane of polarization of a recording layer and to improve the S/N ratio of a reproduction signal by using silicon as a high-refractive index interference layer. CONSTITUTION:A high-refractive index interference layer 3, an optomagnetic recording layer 2 and a reflecting layer 5 are provided on a transparent substrate 4. A glassy org. resin (polymethyl methacrylate, polycarbonate, polyvinyl chloride, etc.) is used as the substrate 4. Silicon (Si) (refractive index n=2.5) is used as the lyer 3. More specifically, the rotation of the plane of polarization is further increased by using Si in addition to the increase in the rotation of the plane of polarization with the structure of the reflected film.

Description

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

(Prior art and its problems) A magneto-optical recording medium is a rewritable optical disk memory medium. Does optical disk memory have high density, large capacity, and high speed access? −m −+ M
t'Ma d, -t hJ -r-II Ifl-P
#7&4ffl j It is considered to be J Mori. Among them, magneto-optical disks using magneto-optical recording media have attracted the most attention due to their rewritability, and have been actively researched and developed in recent years.1. There is.

The configuration of a conventionally known magneto-optical recording medium is as shown in FIG. 1, in which a support substrate 1 is made of glass.

A magneto-optical recording layer 2 made of a perpendicular magnetization film having magnetization in a direction perpendicular to the substrate is formed on a support substrate 1 using metal or organic resin. .

As the magneto-optical recording layer, MnB1, MnCuB1 +
PtCo.

Crystals such as MnAtGe + Gds Tb, Dy,
Amorphous magnetic thin films made by mixing rare earth elements such as Ho and transition metals such as Fe and Coo Ni in various compositions are known.

Magneto-optical recording media have the above-mentioned advantages in place of magnetic disk memories, but on the other hand, the playback signal level, that is, 8.
It has the disadvantage of a low 7N ratio. In particular, in the reproduction method based on the Kerr effect, in which reproduction is performed using reflected light from a magneto-optical recording medium, there were two types of media: Kerr's class of Kani/11 and Shika E (Oka S/N's Harada).

As a conventional method of improving the S/N ratio of the reproduced signal,
Improving the recording layer, that is, 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 improve the Kerr rotation angle. A Kerr rotation amplification method is used to increase the .

Regarding the latter Kerr rotation amplification method, a magneto-optical recording layer 2 is formed on a support substrate l as shown in FIG.
Further, a medium is known in which a high refractive index interference layer 3 of SIO or sio is formed on the recording layer 2. However, in this medium, when the recording layer 2 is easily oxidized, the 5iO9S used for the high refractive index interference layer 3 is
The disadvantage is that the oxygen in iO forms an oxide on the surface of the recording layer 2, and the Kerr rotation angle of the recording layer decreases over time. In addition, small dust, #1 dust, 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 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, can ignore the effects of small dust and dirt, and further improves Kerr rotation. It is an object of the present invention to provide a novel magneto-optical recording medium which has a function of amplifying the angle and can obtain an excellent reproduced signal S/N ratio.

(Structure of the Invention) According to the present invention, a high refractive index interference layer is provided on a transparent substrate,
A magneto-optical recording medium in which a magneto-optical recording layer is provided on the high refractive index interference layer and a reflective layer is provided on the magneto-optical recording layer, characterized in that silicon is used as the high refractive index interference layer. A magneto-optical recording medium is obtained.

(Detailed Description of Configuration) The present invention solves the problems of the prior art by employing the above-mentioned configuration. First, when a transparent substrate is used as the medium support substrate, a method can be adopted in which laser light for recording, reproducing, and erasing signals is made incident on the recording layer from the substrate side. According to this method, since the laser beam is not focused on the surface of the front substrate, small dust, chips, and dirt that adhere to the surface of the transparent substrate have almost no effect on recording, reproducing, and erasing performance.

A feature of the present invention is the use of silicon (St) as a high refractive index interference layer. St has a larger refractive index than Sin and 5i02, and therefore has a larger Kerr rotation angle amplification effect. In addition, St is a semiconductor laser wavelength of 780 to 830 n
There is no absorption at m. Furthermore, since the interference layer is not an oxide, no oxide of the recording layer material is formed at the interface between the interference layer and the magneto-optical recording layer. Record the formation of oxide layer! −
This leads to a decrease in the characteristics, especially the Kerr rotation angle, which deteriorates the performance of the recording medium.

The magneto-optical recording layer is set to have a thickness that allows a portion of laser light used for recording, reproduction, and erasure to pass through. As a result, the reproduction laser beam is reflected with a large polarization plane rotation due to the Kerr rotation received on the surface of the recording layer and the Faraday rotation received as the recording layer moves back and forth. The reflective layer provided above the recording layer has the role of reflecting light that has passed through the recording layer, and also has the role of a protective layer that prevents the recording layer from deteriorating from the upper side of the recording 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. On top of a transparent substrate 4, a refractive index interference layer 3, a magneto-optical recording layer 2, and a reflective layer 5 are provided. has. As the transparent substrate 4, a glass organic resin (polymethyl methacrylate, polycarbonate, polyvinyl chloride, etc.) is used. Silicon (St) (refractive index n
=2.5) is used. Si has a refractive index of 1,000,000 compared to SiO and 5iO1. As the magneto-optical recording layer 2, MnB1,
Crystals such as MnCuB1 + P tCo + MnAtGe or Gd, Tb, Dy.

An amorphous magnetic thin film composed of various compositions of rare earth elements such as Ho and transition metals such as Fe and CorNi is used. As the reflective layer 5, AI−+Cu+Cr
A metal such as +Ag+Au is used. Laser light 6 used for recording and reproduction enters from the side of transparent substrate 4, records information on recording layer 2, and records information on recording layer 2 and reflective layer 5.
Information is reproduced from the rotation of the plane of polarization based on the Kerr rotation angle and the Faraday rotation angle using the reflected light. By setting the film thickness of the recording layer 2 to a thickness that allows partial transmission of the wavelength of the laser light used for reproduction, the rotation of the polarization plane during reproduction can be increased, for example, transparent In a configuration in which a magneto-optical recording layer is formed on a substrate to a thickness of t-200 mm and a reflective layer is further formed on top of the layer, the rotation of the plane of polarization is twice that of a configuration without a reflective 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 increasing the polarization plane rotation by the above-mentioned reflective film structure, the polarization plane rotation is further amplified by using Sl. That's true.

The polarization plane rotation amplification effect changes depending on the film thickness of the refractive index interference layer 3 shown in FIG. 3, and also changes depending on the wavelength of the laser beam used during reproduction. However, the higher the refractive index of the high refractive index interference layer, the higher the amplification factor of polarization plane rotation. For example, as the high refractive index interference layer 3, 5i (n=2.
5) In the case of using i and the case of using 5iO (n=1.9)t-, the amplification factor of the polarization plane rotation is larger in the case of Sk, reaching a maximum of 5 times.

Glass is used as a transparent substrate, and Si is 600^ thick.

Thickness 200A (7) GdTbFs J[, Thickness 1000A
In the magneto-optical recording medium according to the present invention produced by the AOAui['i continuous process, the wavelength is 830 nm.
The polarization plane rotation based on the Kerr rotation angle and Faraday rotation angle at
The nine-plane rotation is greatly increased by the effects of both the high refractive index interference layer and the reflective film structure.

In general, in magneto-optical recording, the S/N ratio of the reproduced signal is 8/Noc, where the polarization plane rotation angle is 09 and the reflectance is R.
It is known that θ・[−. In the embodiment of the present invention, the reflectance R is - compared to the case of using only the GdTbFe film.
However, the S/N ratio is only 93.
It can be seen that this is improved by 3 times.

Next, regarding the corrosion resistance and oxidation resistance of the recording layer, since the recording layer is arranged between the high refractive index interference layer and the reflective layer,
It is completely shielded from the atmosphere, and both the high refractive index interference layer 9 and the reflective layer are not made of oxide.Furthermore, each layer is manufactured in succession in a high vacuum, so the interface between each layer is not exposed to the atmosphere. Therefore, although the recording layer is relatively thin, no change in the recording layer over time or deterioration of the characteristics is observed.

(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, corrosion resistance and oxidation resistance can be improved by forming a structure in which the recording layer is sandwiched between a high refractive index interference layer and a reflective layer, and by using a non-oxide Sii electric layer and a metal reflective film. The St dielectric layer serves as a protective layer between the substrate and the recording layer and is particularly effective when a water-permeable organic resin is used as the substrate.

[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. In the figure 1... Support substrate, 2... Magneto-optical recording layer, 3...
...High refractive index interference layer, 4...Transparent substrate, 5...Reflection layer, 6...Laser light

Claims (1)

[Claims] In the magneto-optical recording medium, a high refractive index interference layer is provided on a transparent substrate, a magneto-optical recording layer is provided on the high refractive index interference layer, and a reflective layer is provided on the magneto-optical recording layer. 1. A magneto-optical recording medium characterized in that silicon is used as an index interference layer.