JPH0711427A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To provide a magneto-optical recording medium generating lower noise at the time of reproduction than a conventional recording medium, having a high C/N ratio and excellent in reproducing characteristics as a magneto- optical recording medium with a reflecting film. CONSTITUTION:This magneto-optical recording medium has a reflecting film made of a thin amorphous Al alloy film. The reflecting film is, e.g. formed by sputtering an Al alloy contg. 5-20atomic% alloying component such as Ca.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium, and more particularly to a magneto-optical recording medium having a reflective film layer.

[0002]

2. Description of the Related Art Magneto-optical recording media are used for recording by reversing the magnetization of a magnetic thin film used as a recording medium by utilizing a temperature rise due to absorption of laser light, and utilizing the magneto-optical effect of the magnetic thin film. It is an external memory for playback. Since this magneto-optical recording medium is rewritable and has the high density of the optical recording medium (high information recording density), it is widely used in the field of mass filing systems for OA and the like. Is becoming.

The structure of such a magneto-optical recording medium comprises a transparent polycarbonate resin substrate or a glass substrate and a dielectric film, a magnetic thin film, a dielectric film, and a reflective film which are laminated in this order (dielectric film / A four-layer structure of magnetic thin film / dielectric film / reflection film) is generally used. Here, the role of the reflective film layer is to apparently increase the magneto-optical effect by causing multiple reflection of laser light during reproduction.
This is to increase the reproduction signal strength (carrier) and improve the reproduction characteristics, that is, the carrier-to-noise ratio (hereinafter referred to as C / N).

A pure Al (aluminum) thin film is the most general and widely used as a reflective film material for such a magneto-optical recording medium. However, although this pure Al thin film has the advantage of high reflectance (about 80%),
The Al thin film is often formed by a method such as sputtering or vapor deposition, and in that case, since the film is generally in a polycrystalline state, a large number of crystal grain boundaries exist in the film, and therefore, during reproduction, crystal There is a problem that the noise due to the reflection of laser light at the grain boundaries is large, and therefore the C / N is lowered and the reproduction characteristics are deteriorated (insufficient). From this point of view, at present, there is a demand for the development of a magneto-optical recording medium having a reflective film layer, which has a small noise during reproduction, a high C / N, and excellent reproducing characteristics.

[0005]

As described above, in the conventional magneto-optical recording medium using the pure Al thin film as the reflection film, the pure Al thin film is in the polycrystalline state,
There is a problem that the C / N at the time of reproduction is low and the reproduction characteristics are insufficient, and improvement is desired.

The present invention has been made in view of such circumstances, and an object thereof is to solve the problems of the conventional magneto-optical recording medium and to provide a magneto-optical recording medium having a reflective film layer. Therefore, it is intended to provide a magneto-optical recording medium which has a low noise during reproduction, a high C / N and excellent reproduction characteristics.

[0007]

In order to achieve the above object, the magneto-optical recording medium according to the present invention has the following structure. That is, the magneto-optical recording medium according to claim 1 is a magneto-optical recording medium having a layer of a reflective film, wherein the reflective film is an Al alloy thin film in an amorphous state.

The magneto-optical recording medium according to claim 2 is
The Al alloy thin film according to claim 1, wherein the Al alloy thin film is formed by sputtering.

[0009]

The magneto-optical recording medium according to the present invention, as described above,
A magneto-optical recording medium comprising a layer of a reflective film, since the reflective film is made of an Al alloy thin film in an amorphous state, due to this amorphous Al alloy thin film, compared to the conventional magneto-optical recording medium Noise during playback is small, C / N is high, and playback characteristics are improved.

That is, the Al alloy thin film in the amorphous state is
Since it is amorphous, it is not in a polycrystalline state and, at the same time, there is no grain boundary. Therefore, the reflective film made of such a thin film is
Unlike the conventional reflective film formed of a pure Al thin film, noise due to the reflection of laser light at the crystal grain boundaries during reproduction does not occur. On the other hand, the degree of noise generated due to causes other than that due to laser light reflection at the crystal grain boundaries does not particularly change. Therefore, according to the magneto-optical recording medium of the present invention, compared with the conventional magneto-optical recording medium, the noise generated as a whole is reduced, so that the C / N is increased and the reproducing characteristic is improved. Moreover, the amorphous Al alloy thin film is
Since the basic component is Al, it can have a reflectance similar to that of a pure Al thin film, and thus the above-mentioned reproduction characteristics can be improved with almost no decrease in reflectance.

By the way, the amorphous state as described above
In order to form an Al alloy thin film as a reflective film, an element having a small solid solubility limit in equilibrium with Al, and a larger number of Al atoms and intermetallic compounds (Al _n X _m It is advisable to form an Al alloy thin film containing an appropriate amount of an element (X) having a composition and easily forming an intermetallic compound (n> m) as an alloying element by rapid solidification.

As the element (X), Ca, Sc, Ti,
V, Cr, Mn, Fe, Co, Ni, Sr, Y, Zr, Nb, Mo, Ru, R
h, Ba, La, Ce, Pr, Nd, Hf, Ta, W, Ir, Pt (hereinafter C
a)), and one or two of these
When the Al alloy thin film is rapidly cooled and solidified so as to contain one or more kinds of alloy components, a reflective film made of the Al alloy thin film in an amorphous state can be formed. At this time, it is desirable that the content of Ca or the like be 5 to 20 at%, and if it is less than 5 at%, it is difficult to form an Al alloy thin film in an amorphous state.
If it exceeds over%, the reflectance of the Al alloy thin film is lowered and the reproduction signal intensity itself is lowered, so that the noise reduction effect due to the use of the Al alloy thin film in the amorphous state tends to be lost. Therefore, regarding the Al alloy thin film as the reflection film of the magneto-optical recording medium, it is desirable that the composition contains 5 to 20 at% of one or more kinds such as Ca as an alloy component.

As a film forming method for forming an amorphous Al alloy thin film by rapid solidification as described above, a sputtering method can be mentioned. According to this method, an amorphous Al alloy thin film can be formed. Is. At this time, if the composition is set as described above and the present method is applied, an Al alloy thin film in an amorphous state can be reliably formed. The Al alloy thin film can be formed by various physical vapor deposition methods or chemical vapor deposition methods, but vapor deposition methods other than the sputtering method,
For example, in the case of the vacuum deposition method, it is difficult to form an Al alloy thin film in an amorphous state. As described above, the sputtering method is easier to form an Al alloy thin film in an amorphous state than other methods, but this is because the cooling rate until solidification is remarkably faster than other methods. Therefore, regarding the Al alloy thin film as the reflective film of the magneto-optical recording medium, it is desirable that the Al alloy thin film is formed by adopting sputtering because of the film forming method. Medium).

[0014]

【Example】

(Example 1) A transparent polycarbonate resin substrate was used as a substrate, and SiN was used as the first layer (dielectric film) on the substrate.
Film, TbFeCo film as second layer (magnetic thin film), SiN film as third layer (dielectric film), Al-Mn alloy thin film (Mn amount: 0 to 25 at%) of various compositions as fourth layer (reflection film) (4) was formed (film formation) in this order to prepare a magneto-optical recording medium (3.5 inch size) having a four-layer structure. At this time, the film thickness of each layer is 1000Å in the first layer, 250Å in the second layer, 350Å in the third layer, and 4th layer.
It was set to 500Å.

Film formation of each of the above layers was performed using a magnetron sputtering apparatus, and the substrate was water-cooled during film formation. Of these layers, pure Al is used as the sputtering target when forming the fourth layer (Al-Mn alloy thin film).
The composition (Mn amount) of the Al-Mn alloy thin film was adjusted by using a composite target in which Mn (purity 99.9%) chips were arranged on a (purity 99.99%) target and changing the number of chips or the chip positions at this time.

The carrier and noise of the magneto-optical recording medium thus obtained were measured. At this time, the measurement conditions are as follows: recording frequency: 3.7 MHz, constant angular velocity: 1800 rpm, measurement track: radius 30 m position, duty: 33%, reproduction power: 1.5
The carrier and noise were measured at a recording power of mW and at which the secondary high frequency was minimal. The resulting Al-M
FIG. 1 shows the relationship between the amount of Mn in the n-alloy thin film (fourth layer: reflective film) and the carrier and noise.

In order to investigate the structure of the reflection film (Al-Mn alloy thin film), a composite target similar to the above is used on a glass substrate, and the film thickness is measured by a magnetron sputtering device similar to the above with the substrate cooled with water. : 2000 Å Al-Mn alloy thin film (Mn amount: 6, 10, 14 at%) was formed, and this was analyzed by X-ray diffraction. The result of the X-ray diffraction is shown in FIG.

As can be seen from FIG. 2, in the above Al-Mn alloy thin film, an Al peak was observed when the Mn content was 6 at%, but an Al peak was observed when the Mn content was 10 and 14 at%. However, only a broad peak indicating that the thin film is in the amorphous state was observed. From this, it can be said that in the case of the Al-Mn alloy thin film, the Mn content: 10 at% or more can surely bring the thin film into the amorphous state. In addition, the lower limit of the amount of alloying elements required to make the amorphous state is
In the case of Mn, it is between 6 and 10 at%, but this value is not the same for each alloying element and may be lower than that for Mn. For example, in the case of Ru, Cr, V, Mo, 8 in this order
At%, 6at%, 5at% and 5at%.

On the other hand, as can be seen from FIG. 1, the noise of the magneto-optical recording medium is caused by the Al-Mn alloy thin film (fourth layer: reflective film).
When the amount of Mn in the medium is 8 at% or less, it is relatively high, but when the amount of Mn is 10 at% or more, it is low. But the amount of Mn:
If it exceeds 20 at%, the carrier will decline. From the above, when an Al-Mn alloy thin film is used as the reflective film, the Mn amount: 8
It is desirable to set it to over at% and below 20 at%. Incidentally, the range of the desirable alloy element amount is not the same for each alloy element. For example, in the case of Mo, V, Cr, Co, Ta, 5-18 at%, 5-18 at%, 6-20 at%, respectively, in this order. 10 ~ 20at%, 10
~ 20at%, and the total range including these is 5
It will be ~ 20at%.

(Embodiment 2) In the case of Embodiment 1, the Al—Mn alloy thin film and the crystal in an amorphous state are included by changing the amount of Mn while keeping the sputtering conditions constant.
An Al-Mn alloy thin film was formed. On the other hand, in Example 2, the amount of Mn was kept constant (8 at%) and the sputtering conditions were changed to form an Al-Mn alloy thin film in an amorphous state and a polycrystalline Al-Mn alloy thin film. Except for the points described above, a magneto-optical recording medium having a four-layer structure having the same film thickness and the same size was prepared by the same method as in Example 1.

The carrier and noise of the above magneto-optical recording medium were measured by the same method as in Example 1. The results are shown in Table 1. When the Al-Mn alloy thin film of the reflective film is in an amorphous state, the noise value is lower than when it is a polycrystalline Al-Mn alloy thin film, so the C / N
It turns out that is high.

[0022]

[Table 1]

[0023]

The magneto-optical recording medium according to the present invention has the above-mentioned structure and functions, and is a magneto-optical recording medium having a layer of a reflective film, and has a small noise during reproduction. , C / N (carrier / noise ratio) is high and the reproduction characteristics are excellent. Therefore, it is possible to satisfy the demand for improvement of the reproduction characteristics of the magneto-optical recording medium and to achieve better reproduction. Play.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between an amount of added Mn and carriers and noise in an Al—Mn alloy thin film forming a reflective film of a magneto-optical recording medium according to Example 1.

FIG. 2 is a diagram showing a result of X-ray diffraction for an Al—Mn alloy thin film according to Example 1.

Claims (2)

[Claims] 1. A magneto-optical recording medium provided with a layer of a reflective film, wherein the reflective film is made of an Al alloy thin film in an amorphous state. 2. The Al alloy thin film according to claim 1, wherein the Al alloy thin film is formed by sputtering.