JPH05242540A - Magneto-optical memory element - Google Patents

Abstract

PURPOSE:To provide the magneto-optical memory element having the structure which can increase a Kerr rotating angle and can prevent the deterioration of films constituting the element. CONSTITUTION:A dielectric film 2 consisting of TiO2, a magnetic material film 3 consisting of GdTbFe, a dielectric film 4 consisting of TiO2 and a reflection film 5 are formed on a glass substrate 1. Further, a dielectric film 6 consisting of TiO2 is formed for the purpose of protecting the reflection film 5, by that, the magneto-optical memory element is constituted.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical storage element for recording or erasing information with heat energy such as laser light and reproducing the information by utilizing the interaction between light and magnetism.

[0002]

2. Description of the Related Art In recent years, research and development of optical memory devices aiming at high-density, large-capacity and high-speed access have been vigorously carried out. Among them, a magneto-optical memory device capable of erasing information is considered to be particularly promising among optical memory devices because it can be applied to a file memory for characters and images and a rewritable video disk.

As a material for a magneto-optical memory, a polycrystalline thin film centering on MnBi was studied from the 1960s to the 1970s, but it was difficult to prepare the material, the recording energy was large, and the noise due to the crystal grain boundary was found. GdTbFe, TbDyFe, G
Alloy thin films of rare earths and transition metals, such as dCo, are the focus of material studies. Since these materials are amorphous, there are advantages that it is possible to form a film having a recording threshold according to the laser power used for recording, and that the quality of the reproduced signal is good because there is no grain boundary noise. .

[0004]

However, in this type of alloy thin film of a rare earth and a transition metal, the rare earth is easily oxidized, and even if a film having a predetermined composition ratio is first formed, the oxidation of the rare earth progresses with time and the transition metal. When the composition shifts to a rich composition, the vertical anisotropy required for high-density memory disappears in an extreme case, and even if it does not exist, there is a problem in that the recording characteristics change due to a change in coercive force, such as oxidation.

Further, there is a problem that the Kerr rotation angle is small and it is difficult to reproduce a signal.

Therefore, the present invention has been made in view of the above-mentioned problems, and it is possible to prevent the oxidation of a magnetic film formed of an alloy thin film of a rare earth and a transition metal, and to reduce the Kerr rotation angle. An object of the present invention is to provide a magneto-optical storage element having a structure that can be increased.

[0007]

In order to achieve the above object, the present invention provides a magnetic material as a transparent substrate and a recording medium having magnetic anisotropy in a direction perpendicular to a film surface made of an alloy of a rare earth and a transition metal. The magneto-optical storage element is characterized in that a body film, a reflective film, and a dielectric film are formed in this order.

The thickness of the dielectric film is preferably 50 nm or more.

[0009]

Since it has the reflection film and the dielectric film, it is possible to prevent the deterioration of the reflection film as the Kerr rotation angle increases.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a partial side sectional view of an embodiment of the magneto-optical storage element of the present invention. In the figure, 1 is a glass plate such as soda lime quartz, and the glass plate 1 has a width of 0.5-1.
5 μm, pitch 1.0 to 3.0 μm, depth 40 to 90 n
m guide grooves are formed. This guide groove is necessary for guiding the light beam to a predetermined position during recording / erasing.

Reference numeral 2 is a dielectric film of TiO ₂ . The dielectric film 2 has a refractive index of 2, 4 and is larger than that of the glass plate 1. The dielectric film 2 is provided to increase the Kerr rotation angle. Reference numeral 3 denotes a GdTbFe magnetic film, which is a magnetic film made of an alloy of a rare earth and a transition metal and having magnetic anisotropy in a direction perpendicular to the film surface.

Reference numeral 4 is a dielectric film of TiO ₂ . The dielectric film 4 increases the Kerr rotation angle, and the magnetic film 3 is used.
Is provided for the purpose of heat insulation between the reflection film 5 and the reflection film 5 to be described later, and to prevent the movement of atoms and electrons between the magnetic film 3 and the reflection film 5 to be described later.

Reference numeral 5 denotes a GdTbFe magnetic substance film, which is a reflection film made of a magnetic substance made of an alloy of rare earth and a transition metal (that is, the same material as the magnetic substance film 3). This reflective film 5
Has the effect of increasing the car rotation angle (for example, Japanese Patent Application No. 55-8).
(See 5695) and the function of preventing the magnetic film 3 from being oxidized. That is, Gd, T which are the components of the reflective film 5
Since the rare earth metal of b is very easily oxidized, the reflection film 5 is first oxidized before the oxygen invading from the outside reaches the magnetic film 3, and thus the amount of oxygen reaching the magnetic film 3 can be reduced as much as possible. is there. Reference numeral 6 is a dielectric film of TiO ₂ for protecting the reflection film 5.

Next, a manufacturing method of one embodiment of the above-mentioned magneto-optical storage element will be described. The glass plate 1 has a disk shape and a thickness of about 0.5 to 2 mm. A resist film is applied to the glass plate 1 and an Ar laser, a HeCd laser or the like is applied while rotating the glass plate 1 in the applied state. Of the glass plate 1 by using the laser of FIG. 3 as a latent image with a guide groove having a predetermined width in the resist film and developing the recording resist film by dry etching with a gas such as CCl ₄ , CF ₄ + H ₂ or the like. To form.

According to the above guide groove forming method, since only the glass plate constitutes the substrate after forming the guide groove, it is resistant to moisture and the like. In addition to the above guide groove forming method, a method for forming a guide groove by injection molding or compression molding using a resin material such as PMMA or polycarbonate for the substrate, or a guide groove using an ultraviolet curable resin on a glass or PMMA resin substrate Although there is a method (2P method) of forming a recording medium, all of these forming methods use a resin material as an intermediary. Therefore, oxygen penetrates through the resin material due to the moisture permeability, the hygroscopicity, or the oxygen permeability of the resin material. There was a phenomenon that characteristics were deteriorated by oxidation of a rare earth / transition metal alloy thin film.

Next, on the glass plate 1 in which the guide groove is formed, the above-mentioned TiO ₂ 2, GdTbFe 3, FiO ₂ 4, Gd.
TbF5 and TiO ₂ 6 are sequentially coated. The coating of each of these films can be performed by means such as vapor deposition, sputtering, and ion plating, but GdTbFe3 must have magnetic anisotropy in the direction perpendicular to the film surface.
It is preferable to form each of the above films by high frequency sputtering because of the ease of providing the GdTbFe rare earth / transition metal alloy film with perpendicular magnetic anisotropy, and the reproducibility of film formation and the ease of obtaining uniformity.

At this time, in the case of the above-mentioned multilayer film structure, TiO 2
₂ 2, GdTbFe3, TiO ₂ 4, GdTbFe5, T
Since each film of iO ₂ 6 is formed, only two kinds of sputtering targets, TiO ₂ and GdTbFe, are required, so that the sputtering apparatus can be downsized and simplified. Since the GdTbFe3 layer is a recording medium, this film must have an easy axis of magnetization in the direction perpendicular to the film surface, while the GdTbFe5 layer is a reflective film, so that it is not a perpendicular magnetic film because of the stability of recording hits. Is good. The following method is adopted in order to make the films of GdTbFe3 and GdTbFe5 different. FIG. 2 shows changes in the coercive force of the formed film when the target is GdTbFe having a constant composition and the Ar pressure during sputtering is changed. As shown in the figure, even if the target is GdTbFe having a constant composition, the coercive force changes (that is, the composition of the film changes) only by changing the Ar pressure. Actually, when the Ar pressure is low, it is rich in Fe (A portion), and when the Ar pressure is high, it is rich in rare earth (Gd, Tb) (B portion).
Further, although not shown, a Fe-rich composition film having no perpendicular magnetic anisotropy is formed at a place where the Ar pressure is considerably low, and a rare earth (Gd, T
b) A rich composition film is formed. The rare earth-rich reflective film 5 is preferable from the viewpoint of preventing oxidation.

Thus, the above TiO ₂ 2, GdTbFe
When a multilayer film of 3, TiO ₂ 4, GdTbFe 5, and TiO ₂ 6 is formed, Ti is used as a sputtering target.
GdTbF having an easy axis of magnetization in a direction perpendicular to the film surface by appropriately adjusting the Ar pressure using only two kinds of O ₂ and GdTbFe
e3, and GdT having an easy axis of magnetization in a direction parallel to the film surface
Create bFe5. The thickness of TiO ₂ 2 is 50 to 10
0 nm, GdTbFe3 film thickness is 10-30 nm, Ti
An appropriate element structure is obtained if the film thickness of O ₂ 4 is 30 to 100 nm, the film thickness of GdTbFe 5 is 100 nm or more, and the film thickness of TiO ₂ 6 is 50 nm or more.

In addition to the above embodiments, the following embodiments are possible. That is, the material of the dielectric film 2 is Si ₃ N ₄ , S
iO, ZnS, CeO ₂ , ZrO ₂ , Sb ₂ O ₃ , Nd
Either ₂ O ₃ or CeF ₃ is used. Since these have a refractive index of 1.7 to 2.5, which is about the same as TiO ₂ (refractive index 2.4), the film thickness is equivalent to the above value. Further, GdTbDyFe and TbDyF are used as materials for the magnetic film 3 and the reflection film 5.
Other rare earth-transition metal alloys such as e and GdCo, or these rare earth-transition metal alloys to which an impurity element is added may be used.

Further, as shown in FIG. 3, a PMMA resin substrate 7 may be attached to the upper surface of the glass plate 1 in which guide grooves are formed. As a result, the glass plate 1 can be prevented from cracking, so that the device can be easily handled. The resin substrate 7 may be formed by a photopolymer method. In this case, it is more effective to form the resin substrate 8 on the back surface by the same manufacturing method as that of the resin substrate 7 as shown in FIG. Further, the gist of the present invention is to provide a transparent substrate, a magnetic film having magnetic anisotropy in a direction perpendicular to a film surface made of an alloy of rare earth and a transition metal, and a reflective film made of the same material as the magnetic film. This is a magneto-optical storage element formed by stacking layers in order, and this configuration makes it possible to prevent oxygen and moisture from permeating from the back surface.

Therefore, various configurations can be adopted without departing from the gist. For example, the structure of the magneto-optical storage element having the structure without the dielectric film 2 shown in FIGS. 1 and 3 may be used.

[0023]

As described above, according to the present invention, the Kerr rotation angle can be increased and the reflection film can be effectively protected.

[Brief description of drawings]

FIG. 1 is a partial side sectional view of an embodiment of a magneto-optical storage element of the present invention.

FIG. 2 is a diagram showing a relationship between an argon pressure during film formation and a coercive force of a magnetic film.

FIG. 3 is a partial side sectional view of another embodiment of the magneto-optical storage element of the present invention.

[Explanation of symbols]

 1 glass plate 2,4,6 dielectric film 3 magnetic film 5 reflective film 7,8 resin substrate

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Akira Takahashi 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Prefecture Sharp Corporation (72) Hideka Yamaoka 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside the company

Claims (2)

[Claims] 1. A transparent substrate, a magnetic film as a recording medium having magnetic anisotropy in a direction perpendicular to a film surface made of an alloy of a rare earth and a transition metal, a reflective film, and a dielectric film, A magneto-optical storage element, which is formed in this order. 2. The magneto-optical storage element according to claim 1, wherein the dielectric film has a film thickness of 50 nm or more.