JPS6124042A - Magnetooptic storage element - Google Patents

Abstract

PURPOSE:To assure thoroughly magnetooptic characteristics and to prevent the oxidation of a thin rare earth transition metallic alloy film by forming both the 1st transparent dielectric film and 2nd transparent dielectric film of silicone nitride films having different refractive indices. CONSTITUTION:An Si3N4 film 7 which is the 1st transparent dielectric film is fomed on a formed on a transparent substrate 1 and a thin GdTbFe alloy film 3 which is the thin rare earth transition metallic alloy film is formed thereon. An S3N4 film 8 which is the 2nd transparent dielectric film is formed thereon. An Al film 9 which is a reflecting film is formed on the film 8. The effect of increasing Kerr rotating angle is obtd. by the 1st transparent dielectric film having the large refractive index in the magnetooptic storage element made of the above-mentioned construction. On the other hand, the reflectivity can be increased by the 2nd transparent dielectric film having the small refractive index. The above-mentioned Si3N4 does not contain oxygen as the component thereof and therefore the danger that the thin rare earth transition metallic alloy film is oxidized is considerably decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a magneto-optical memory element that records, reproduces, erases, etc., information by irradiating it with laser light or the like.

<Technical background of the invention and its problems> In recent years, research has been actively conducted on magneto-optical storage elements as optical disks on which information can be rewritten.

Among these, storage media constructed using rare earth transition metal amorphous alloy thin films have the advantage that recording bits are not affected by grain boundaries and that it is relatively easy to create a recording medium film over a large area. It has attracted particular attention for one reason.

However, when a magneto-optical storage element is constructed using a rare earth transition metal amorphous alloy thin film as the above-mentioned recording medium, it is generally not possible to obtain sufficient magneto-optical effects (Kerr effect, Faraday effect). /N was insufficient.

As a countermeasure to this problem, the inventors of the present invention have already attempted to improve the device structure as described below.

FIG. 3 shows a partial side sectional view of a magneto-optical memory element whose structure has already been improved.

In FIG. 8, Natsu is a transparent substrate made of glass, polycarbonate, acrylic, etc. A transparent SiO film 2 (film thickness 120 nm), which is a first transparent dielectric film, is formed on the transparent substrate 1, and the SiO G, which is a rare earth transition metal film, is formed on film 2.
A dTbFe alloy thin film 8 (film thickness 15 nm) is formed,
A transparent 5i02 film 4 (50 nm thick), which is a second transparent dielectric film, is formed on the GdTbFe alloy thin film 8, and a Cu film 5 (50 nm thick), which is a reflective film, is formed on the Si'02 film 4.
nm) is supported. With the above structure, an apparent Kerr rotation angle as large as 1.75° was obtained.

The reason why it was possible to obtain a significantly thicker Kerr rotation angle by adopting the above element structure will be explained below.

Transparent substrate as shown in Figure 3! When the rare earth transition metal alloy thin film 8 is irradiated with a laser beam 6 from the side, the incident laser beam is repeatedly reflected inside the first transparent dielectric film 2, and as a result of interference, the apparent Kerr rotation angle increases. In this case, the larger the refractive index of the first transparent dielectric film 2, the greater the effect of increasing the Kerr rotation angle.

Furthermore, as shown in FIG. 8, by arranging the reflective film 5 on the back surface of the rare earth transition metal alloy thin film 8, the apparent Kerr rotation angle is increased, and the difference between the rare earth transition metal alloy thin film 8 and the reflective film 5 is increased. By interposing the second transparent dielectric film 4 in between, the apparent Kerr rotation angle is further increased.

Next, the principle of this action will be qualitatively explained.

A composite film of the second transparent dielectric film 4 and the reflective film 5 will be considered as one reflective layer A.

In FIG. 8, light that is incident from the transparent substrate 1 side, passes through the rare earth transition metal alloy thin film 3, is reflected by the reflective layer A, and then passes through the rare earth transition metal alloy thin film 8 again, and the transparent The light incident from the substrate 1 side and reflected on the surface of the rare earth-transition metal alloy thin film 80 is combined, but in this case, the incident light is caused by reflection on the surface of the rare-earth transition metal alloy thin film 3, resulting in an indispensable Kerr effect. When combined with the Faraday effect caused by the incident light passing through the inside of the rare earth transition metal alloy thin film 8, the apparent Kerr rotation angle increases.

In the magneto-optical memory element having the above structure, it is extremely important how to add the Faraday effect to the Kerr effect. Regarding the Faraday effect, the rotation angle can be increased by increasing the layer thickness of the recording medium, but since the incident laser beam is absorbed by the recording medium, the intended purpose cannot be achieved. Therefore, the appropriate layer thickness of the recording medium is approximately 10 to 50 nm, and the value is determined by the wavelength of the laser beam used, the refractive index of the reflective layer, etc. As can be seen from the above description, the requirement for the reflective layer is that it has a high reflectance. In other words, it is necessary to prevent the incident laser beam from entering the reflective layer, and from an optical point of view, it is necessary that the refractive index of the reflective layer (second transparent dielectric film semi-reflective film), which is a constraint, is close to 0. be. For this purpose, it is necessary that the value of the real part of the second transparent dielectric film is small and the value of the imaginary part is 0, and furthermore, the value of the real part of the reflective film is small.

As described above, by adding the configuration of the first transparent dielectric film 2 interposed between the transparent substrate l and the rare earth transition metal alloy thin film 3 and the reflective layer A on the back surface of the rare earth transition metal alloy thin film 3, the Kerr rotation angle can be adjusted. The effect of increasing can be obtained.

However, while the above-mentioned effects can be obtained, the SiO film is selected as the first transparent dielectric film 2, and the second transparent dielectric film 4
When the 5i02 film was selected as the 5i02 film, a problem occurred in that the rare earth transition metal alloy thin film 3 was oxidized. The inventor of the present invention has confirmed that the cause of this is the oxygen contained in the SiO film and the 5i02 film. That is, the above SiO film and 5
During or after the formation of the i02 film, the internal oxygen component is separated and the rare earth transition metal alloy thin film 8 is oxidized. However, since the rare earth transition metal alloy thin film 8 is oxidized, its ability as a magnetic recording medium is significantly inhibited, so the problem of oxidation is extremely serious. Furthermore, if the rare earth transition metal alloy thin film 3 is thin, even a slight oxidation will have a large effect, so extreme care must be taken.

<Object of the Invention> The present invention has been made to solve the above problems, and provides a novel magneto-optical memory element that can ensure sufficient magneto-optical properties and prevents oxidation of the rare earth transition metal alloy thin film. In order to achieve this object, the present invention provides a first transparent dielectric film, a rare earth transition metal alloy thin film, a second transparent dielectric film, and a reflective film on a transparent substrate. In a magneto-optical memory element coated in this order,
Both the first transparent dielectric film and the second transparent dielectric film are formed of silicon nitride films, and the refractive index of the first transparent dielectric film is higher than that of the second transparent dielectric film. The composition is set so that it is greater than the refractive index.

<Embodiment of the Invention> Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

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

In the figure, 1 is glass and polycarbonate.

A transparent substrate made of acrylic or the like, on which a first transparent dielectric film (transparent nitride silicone (SigN4)) is coated.
A film 7 (film thickness: 90 nm) is formed, a GdTbFe alloy thin film 3 (film thickness: 85 nm), which is a rare earth transition metal alloy thin film, is formed on this 5iBN4 film 7, and a second transparent dielectric material is formed on this GdTbFe alloy thin film 3. A transparent silicon nitride (SiaN4) film 8 (film thickness 40 nm) is formed as a film, and an At film 9 (film thickness 40 nm) as a reflective film is formed on this Si3N4 film 8.
0 nm or more). - In the magneto-optical memory element with the above structure, what is particularly noteworthy is that Si3, which has a high refractive index, is used as the first transparent dielectric film.
N4 film is used, and S with a low refractive index is used as the second transparent dielectric film.
This is because an i3 N4 film was used.

The advantages of this structure will be explained below.

(2) Since it is a Si3N4 film and a nitride, a denser film can be formed compared to an oxide film.

■ The Si3N4 film, which is the first transparent dielectric film, is formed to have a refractive index of approximately 2.0, while the Si3N4 film, which is the second transparent dielectric film, is formed to have a refractive index of 1.9 to 1. By forming the film so that the relative refractive index of the first transparent dielectric film is about .8.

The refractive index is made larger than that of the second transparent dielectric film, and as a result,
As described above, the effect of increasing the Kerr rotation angle can be obtained by the first transparent dielectric film having a high refractive index, while the reflectance can be increased by using the second transparent dielectric film having a low refractive index. That is, the above combination of 5iBN4 films having different refractive indexes is extremely convenient. In the above structure, the Si3N4 film 7 is good if it has a thickness of about ±10% with a peak thickness of 90 nm, and the 5iBN4 film 8 has a thickness of about 40 nm.
A film thickness of approximately ±110 nm with a peak of nm is suitable.

(2) Since the above-mentioned Si3N4 does not contain oxygen as a component, the risk of the rare earth transition metal alloy thin film being oxidized can be extremely reduced.

Next, a method of forming 5iBN4 films, which are films of the same nitride, with different refractive indexes will be described, taking as an example a method of manufacturing by sputtering.

In the method for manufacturing 5iBN4 film by sputtering method, high-purity Si is used as the target, and Ar is used as the gas.
A 5iBN4 film is fabricated by reactive sputtering using a mixed gas of N2 and N2 gas or only N2 gas.

It depends on the 5iBN4 films produced under various sputtering conditions; when the film is formed under low gas pressure conditions, the refractive index is high, and when the film is formed under high gas pressure conditions, the refractive index is low. Therefore, depending on the sputtering conditions, a transparent dielectric film having a desired refractive index can be obtained.

Note that in the above embodiment, 5i was used as the silicon nitride film.
Although the BN4 film has been described as an example, the present invention is not limited thereto.

In other words, the silicon nitride film does not necessarily have to be a polycrystalline film of 5iBN4; for example, Si is replaced with N2 or N2+.
Any Si nitride formed by sputtering in Ar gas may be used.

Furthermore, although the above embodiments have been explained using reactive sputtering using a Si substrate, the present invention is not limited thereto; for example, vapor deposition may be used, and Si3N
Sputtering may be performed from target No. 4. In short, any film forming method that can change the refractive index of the film formed depending on the film forming conditions can be applied to the present invention.

It is presumed that the difference in refractive index between the first and second silicon nitride films as described above is mainly due to the difference in the density of the produced films and/or the difference in the composition ratio of nitrogen and silicon.

<Effects of the Invention> As described above, according to the present invention, by using a combination of silicon nitride films having different refractive indexes, it is possible to ensure good corrosion resistance and information reproduction characteristics of a recording medium.

[Brief explanation of drawings]

Figure t' is a partial side sectional view showing the configuration of an embodiment of the magnetic optical memory element according to the present invention, and Figure 2 is a characteristic diagram showing the relationship between the refractive index and gas pressure of a film produced by sputtering. , FIG. 3 is a partial side sectional view showing the structure of a conventional magneto-optical memory element. l...Transparent substrate, 3...Rare earth transition metal alloy thin film, 6...Laser light, 7...First transparent dielectric film (Si3N4 film), 8...Second transparent dielectric Membrane (S
i3N4 film), 9... Reflective film (A4 film).

Claims (1)

[Scope of Claims] 1. A magneto-optical memory element comprising a transparent substrate coated with a first transparent dielectric film, a rare earth transition metal alloy thin film, a second transparent dielectric film, and a reflective film in this order, comprising: Both the first transparent dielectric film and the second transparent dielectric film are formed of silicon nitride films, and the refractive index of the first transparent dielectric film is lower than the refractive index of the second transparent dielectric film. A magneto-optical memory element characterized in that it is configured to have a large size. 2. The first and second transparent dielectric films are produced by sputtering, and due to the difference in production conditions, the first transparent dielectric film has a large refractive index and the second transparent dielectric film has a small refractive index. The magneto-optical memory element according to claim 1, characterized in that it has a body membrane structure.