JPH039546B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Technical Field> The present invention relates to a magneto-optical storage element that records, reproduces, erases, etc. information by irradiating it with light such as a laser.

<Prior Art> In recent years, research has been actively conducted on magneto-optical storage elements as optical disks on which information can be written. Among these, storage media constructed using rare earth-transition metal amorphous alloy thin films have the advantage that the 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 is attracting particular attention for this 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 follows. FIG. 1 shows a partial side sectional view of a magneto-optical memory element whose structure has already been attempted to be improved. In the figure, 1 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. GdTbFe alloy thin film 3 which is a rare earth transition metal alloy thin film on top
(film thickness 15 nm) is formed, and the GdTbFe alloy thin film 3
A transparent SiO ₂ film 4, which is a second transparent dielectric film, is placed on top.
(thickness: 50 nm), and a Cu film 5 (thickness: 50 nm), which is a reflective film, is formed on the SiO ₂ film 4. In the above structure, the apparent Kerr rotation angle was as large as 1.75°.

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

As shown in FIG.
When the rare earth transition metal alloy thin film 3 is irradiated with The larger the refractive index of the first transparent dielectric film 2, the greater the effect of increasing the Kerr rotation angle.

In addition, as shown in FIG. 1, a rare earth transition metal alloy thin film 3
The apparent Kerr rotation angle is increased by arranging the reflective film 5 on the back surface of the film, and the apparent Kerr rotation angle is increased by interposing the second transparent dielectric film 4 between the rare earth transition metal alloy thin film 3 and the reflective film 5. The above Kerr rotation angle is further increased. Next, we will give a qualitative explanation of the principle of this action.

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. 1, light enters 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 3 again, and the transparent substrate 1 The light incident from the side and reflected on the surface of the rare earth transition metal alloy thin film 3 is combined, but in this case, the Kerr effect caused by the reflection of the incident light on the surface of the rare earth transition metal alloy thin film 3 and the incident light are combined. When combined with the Faraday effect caused by light passing through the inside of the rare earth transition metal alloy thin film 3, 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, if the layer thickness of the recording medium is increased, the rotation angle can be increased, but the intended purpose cannot be achieved because the incident laser beam is absorbed by the recording medium. 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 condition required for the reflective layer is that it has a high reflectance. In other words, the incident laser beam is not allowed to enter the reflective layer, and from an optical perspective, the reflective layer (second transparent dielectric film + reflective film)
It is necessary that the equivalent refractive index of is close to zero.
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 1 and the rare earth transition metal alloy thin film 3, and the reflective layer A on the back side of the rare earth transition metal alloy thin film 3, the car The effect of increasing the rotation angle can be obtained.

However, while the above-mentioned effects can be obtained, if a SiO film is selected as the first transparent dielectric film 2 and a SiO ₂ film is selected as the second transparent dielectric film 4, the rare earth transition metal alloy thin film 3 There was a problem with oxidation. The inventors have confirmed that the cause of this is the oxygen contained in the SiO film and SiO ₂ film. That is, during or after the formation of the SiO film and SiO ₂ film, internal oxygen components are separated and the rare earth transition metal alloy thin film 3 is oxidized.
However, when the rare earth transition metal alloy thin film 3 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.

<Purpose> The present invention has been made to solve the above problems, and provides a novel magneto-optical memory element that can sufficiently secure magneto-optical properties and prevent formation of a rare earth transition metal alloy thin film. The purpose is to

<Example> FIG. 2 is a partial side cross-sectional view of an example of a magneto-optical memory element according to the present invention. In the same figure, 1
is a transparent substrate made of glass, polycarbonate, acrylic, etc. A transparent SiN film 7 (film thickness 90 nm), which is a first transparent dielectric film, is formed on the transparent substrate 1, and a rare earth transition layer is formed on the SiN film 7. A metal alloy thin film, GdTbFe alloy thin film 3 (film thickness 35 nm), is formed.
A transparent AlN film 8 (film thickness: 40 nm), which is a second transparent dielectric film, is formed on the GdTbFe alloy thin film 3,
On the AlN film 8, an Al film 9 (thickness: 40 nm) is formed as a reflective film.
above) are formed.

What is particularly noteworthy about the magneto-optical memory element having the above structure is that an SiN film is used as the first transparent dielectric film, and an AlN film is used as the second transparent dielectric film.

The advantages of this structure will be explained below.

SiN and AlN are materials with high melting points and are extremely stable, and since both are nitrides, denser films can be formed compared to oxide films.

The first transparent dielectric film, SiN, has a refractive index of
On the other hand, AlN, which is the second transparent dielectric film, has a refractive index of about 1.9 to 1.8. Can be greater than the rate.

As described above, the larger the refractive index of the first transparent dielectric film is, the more the Kerr rotation angle can be increased, while the smaller the refractive index of the second transparent dielectric film, the higher the reflectance can be obtained. Therefore, the combination of SiN and AlN is extremely convenient. Furthermore, in the above structure
The SiN film 7 is good if it has a thickness of about ±10% with a peak thickness of 90 nm, and the AlN film 8 has a thickness of 40 nm.
A film thickness of about ±10% with respect to the peak value is good.

Since the SiN and AlN do not contain oxygen as a component, the risk of the rare earth transition metal alloy thin film being oxidized can be extremely reduced.

<Effects> According to the present invention, it is possible to ensure good corrosion resistance and information reproduction characteristics of a recording medium.

[Brief explanation of the drawing]

FIG. 1 is a partial side cross-sectional view of a conventional magneto-optical memory element, and FIG. 2 is a partial side cross-sectional view of an embodiment of the magneto-optic memory element according to the present invention. In the figure: 1: Transparent substrate, 2: First transparent dielectric film, 3: Rare earth transition metal alloy thin film, 4: Second transparent dielectric film, 5: Cu film, 6: Laser light, 7:
SiN film, 8: AlN film, 9: Al 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: The first transparent dielectric film and the second transparent dielectric film are both made of nitride, and the refractive index of the first transparent dielectric film is higher than the refractive index of the second transparent dielectric film. A magneto-optical memory element characterized by being made of a certain substance.