JPH06267128A - Magneto-optical disk - Google Patents

Abstract

PURPOSE:To enhance the recording sensitivity of a disk along the radial direction from the inner circumference side toward the outer circumference side while keeping uniform reflectance and uniform C/N ratio in reproduction. CONSTITUTION:A 1st dielectric protective layer 2, a recording layer 3 of an amorphous magnetic alloy consisting of a rare earth metal and an iron family transition metal, a 2nd dielectric protective layer 4 and a metallic reflecting layer 5 are successively formed on a doughnut-shaped substrate 1 to obtain the objective magneto-optical disk. The 1st and 2nd protective layers 2, 4 are formed so that the thickness of each of the layers 2, 4 is reduced along the radial direction of the disk from the inner circumference side toward the outer circumference side. The recording layer 3 and the reflecting layer 5 are formed in uniform thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical disk for recording / reproducing / erasing by using a laser beam, and more particularly to a magneto-optical disk suitable for high density recording.

[0002]

2. Description of the Related Art A magneto-optical disk has been attracting attention as one of large-capacity file memories. Among them, a magneto-optical disk that uses a perpendicularly magnetized film as a recording layer and uses the magneto-optical effect, especially the polar Kerr effect for reproduction, has the advantage that the recorded information can be rewritten. A wide range of applications such as memory and image file memory are being actively studied in various places.

As a recording medium, as shown in FIG. 5, a first dielectric protective layer 1 made of SiN is formed on a donut-shaped resin substrate 10 formed of polycarbonate or the like.
1. A recording layer 12 made of an amorphous magnetic alloy film such as TbFeCo formed by a combination of a rare earth metal and an iron group transition metal, a second dielectric protective layer 13 made of SiN, a metal such as an Al alloy. A four-layer structure in which the reflective layer 14 is formed in this order is known. (JP-A-62-277643)

The magneto-optical disk using these is already at a practical level, including in the field of code data file memory for personal computers, and its application is expected to be expanded. With the expansion of applications, further improvement in recording density and higher speed are required.

By the way, as a drive system of the magneto-optical disk, a constant angular velocity rotation system (CAV system) and a constant linear velocity rotation system (CLV system) are known. In the latter method, since it is necessary to change the rotation speed of the disk according to the position in the disk radial direction, the structure of the disk drive device becomes complicated and the access speed becomes slow. Therefore, in the magneto-optical disk, the former constant angular velocity rotation method is usually used. In this method, since the linear velocity becomes higher on the outer peripheral side, the energy density of the laser light to the recording film becomes smaller on the outer peripheral side than on the inner peripheral side. Therefore, the recording sensitivity and the recording bit shape change. The recording power and recording frequency of the laser light need to be set within a range in which these differences can be tolerated.

In recent years, in order to improve the recording density by the constant angular velocity rotation method, the recording frequency is increased from the inner peripheral side toward the outer peripheral side in the radial direction of the disk, so that the outer peripheral side has the same level as the inner peripheral side. A method has been proposed in which the recording density can be obtained. In this case, a phenomenon in which the energy density of the laser beam to the recording film becomes smaller on the outer peripheral side than on the inner peripheral side becomes apparent, and the recording power may become insufficient from the inner peripheral side to the outer peripheral side.

In order to solve such a problem, it is desired to increase the recording sensitivity from the inner circumference side to the outer circumference side along the disc radial direction. In order to realize this, various methods (A to D) for changing the disk configuration along the radial direction have been conventionally proposed.

A ... Changing the magnetic properties of the recording layer (JP-A-61-211851) B ... Changing the film thickness of the recording layer (JP-A-61-21185)
No. 4) C. Changing the film thickness of the reflection layer (Japanese Patent Laid-Open No. 61-21185)
No. 2) D ... Changing only the film thickness of one of the first and second protective layers. (Japanese Patent Laid-Open No. 61-211853, 62-277643, 62-277
(Gazette No. 645)

[0009]

However, each of the above-mentioned conventional examples has the following problems.

In the case of A, as the magnetic characteristics change,
The recording magnetic field sensitivity and magneto-optical effect (Kerr rotation angle) also change. In the case of B, the reflectance and magnetic characteristics change with the change in the film thickness of the recording layer. Furthermore, in the case of C above,
The reflectance changes. In the case of D, the film thickness of only one of the first and second protective layers is changed. In this case, however, the optical interference condition changes,
The reflectance and the effective Kerr rotation angle change.

As described above, in the above-mentioned conventional example, when the recording sensitivity is changed along the radial direction of the disk, the reflectivity, the magnetic characteristic, the effective Kerr rotation angle, etc. are changed accordingly. The reflectance is a characteristic item that directly affects the reproduction system, and the change in the magnetic characteristics and the effective Kerr rotation angle is the reproduction C / N.
This causes fluctuations in the carrier / noise ratio of the reproduced signal. Therefore, in each of the above-mentioned embodiments, there is a drawback that important reflectance and reproduction C / N fluctuation occur in the recording / reproduction characteristics, and the load on the reproduction system becomes large.

[0012]

SUMMARY OF THE INVENTION The present invention has been devised in view of the problems of the prior art, and makes the reflectance and the reproduction C / N uniform from the inner circumference side to the outer circumference side along the disk radial direction. It is an object of the present invention to provide a magneto-optical disk suitable for high density recording while keeping the recording sensitivity high.

[0013]

The present invention provides a first substrate on a substrate.
Of the first and second dielectric protection layers, wherein the dielectric protection layer, the amorphous magnetic alloy recording layer, the second dielectric protection layer, and the metal reflection layer are formed in this order. The film thickness is set to decrease from the inner peripheral side toward the outer peripheral side in the radial direction of the disc. This aims to achieve the above-mentioned object.

[0014]

In the present invention, since the first dielectric protective layer and the second dielectric protective layer are reduced from the inner circumference side to the outer circumference side of the disc, the reflectance and the reproduction C / N are made uniform. The recording sensitivity can be increased while maintaining it, and as a result, high density recording can be satisfactorily performed.

[0015]

1 is a sectional view of an embodiment of a magneto-optical disk according to the present invention. In this embodiment, the thickness is 1.2 mm and the diameter is 1
First of SiN on 30mm polycarbonate substrate 1
A dielectric protection layer 2, a TbFeCoTi amorphous magnetic alloy recording layer 3 having a thickness of 20 nm, a second dielectric protection layer 4 made of SiN, and a metal reflection layer 5 having a thickness of 30 nm made of an AlTi alloy. Has been done.

Here, the film thickness of the first and second dielectric protective layers 2 and 4 made of SiN uniformly decreases from the inner peripheral side to the outer peripheral side in the radial direction of the disk. . The film thicknesses of the first and second dielectric protective layers 2 and 4 are 110 [nm] at a radius of 30 [mm] near the innermost circumference of the recording area.
And 32 [nm], and 80 [nm] and 25 [nm] at a radius of 60 [mm] near the outermost circumference. On the other hand, the amorphous magnetic alloy recording layer 3 made of TbFeCo and the metal reflection layer 5 made of AlTi alloy
Has a substantially uniform film thickness over the entire surface of the disk. Each such layer is manufactured as follows.

The first and second dielectric protective layers 2 and 4 made of SiN films are formed by reactive sputtering using a Si target and a mixed gas of Ar and N ₂ (30% Nf ₂ ) as a sputtering gas. While rotating the substrate 1, power density 8 [w / c
m ² ], and the sputtering gas pressure is 2.5 × 10 ⁻¹ [Pa]. At this time, a self-made mask was set on the Si target so that the film thickness distribution of the SiN film in the disk radial direction was as described above.

The amorphous magnetic alloy recording layer 3 made of TbFeCoTi uses a Tb target and a FeCoTi target.
Using the original DC magnetron sputtering method, while rotating the substrate 1, Ar gas pressure 0.08 [Pa], Tb target and FeCo
The power density of each target is 1.5 [w / cm ² ]
And 3.0 [w / cm ² ]. Where TbFeCoTi
The film thickness distribution of the film should be almost uniform on the entire surface of the disk.
Self-made masks were placed on the Tb target and the FeCoTi target, respectively.

The metal reflection layer 5 made of AlTi alloy film is made of AlTi
It is manufactured by the RF or DC magnetron sputtering method using an alloy target. Here, the Ar gas pressure during film formation is 0.12 [P] by the RF magnetron sputtering method.
a] and the power density is 4 [w / cm ² ]. In this case, the AlTi film had a substantially uniform film thickness distribution over the entire surface of the disk without providing a special mask. However, when the AlTi film thickness changes along the disk radial direction, it is necessary to provide a desired mask on the AlTi alloy target so that a substantially uniform film thickness distribution can be obtained on the entire surface of the disk.

The presence or absence of a mask and the shape of the mask are appropriately selected in accordance with the type of sputtering apparatus and the sputtering conditions so that the film thickness distribution of each of the above-mentioned films is suitable for each material.

Next, with respect to this magneto-optical disk, Table 1 is shown.
The recording / reproducing characteristics were measured under the conditions shown in.

[0022]

[Table 1]

FIG. 2 shows the relationship between the recording threshold laser power (recording laser power at which the reproduction C / N rises) with respect to the disc radius. As a comparative example, the case where the first and second dielectric protective layers 2 and 3 made of SiN have a uniform film thickness as in the conventional example shown in FIG. The case corresponding to the innermost circumference (the film thickness of the first SiN is 110 [nm] and the film thickness of the second SiN is 32 [nm]) is indicated by the broken line.

As is clear from FIG. 2, the magneto-optical disk according to the present embodiment suppresses the increase in the recording threshold laser power with the increase in the disk radius, as compared with the comparative sample example.

Next, in order to improve the recording density by the CAV method, the recording / reproducing characteristics were measured when a method of increasing the recording frequency from the inner circumference side to the outer circumference side along the disk radial direction was used. With a recording frequency of 6.2 [MHz] and a recording pulse width of 50 [ns] at a radius of 30 [mm] near the innermost circumference, the recording frequency increases as the disc radius increases from the inner circumference side to the outer circumference side. Was increased in proportion to the disc radius, and the recording pulse width was decreased in inverse proportion to the disc radius. Other conditions were the same as in Table 1.

FIG. 3 shows the relationship between the recording threshold laser power and the disk radius when this method is used. Here, similar to FIG. 2, the present example sample and the comparative example sample are shown. In this method, normal CA
Compared to the V system, the energy density of the laser light to the recording film is more remarkable on the outer peripheral side than on the inner peripheral side, so that the recording threshold power increases remarkably as the disk radius increases. However, in the magneto-optical disk according to the present invention, the increase in the recording threshold laser power due to the increase in the disk radius is significantly suppressed as compared with the comparative sample, so that the load on the reproducing system is significantly reduced. Become.

FIG. 4 shows the reproduction C of the magneto-optical disk of the present invention when recorded with the reflectance and the recording laser power of 9 [mw].
The results of measuring / N with respect to the disc radius are shown. The magneto-optical disk according to the present invention has a substantially uniform reflectance and reproducing C / C in the recording area from the innermost circumference to the outermost circumference.
N was obtained. These characteristics were obtained when recording and reproducing by either the normal CAV method or the CAV method compatible with high recording density.

The above-mentioned characteristics are such that the film thicknesses of the first and second dielectric protective layers 2 and 4 made of SiN are uniform along the radial direction of the disk from the inner circumference side to the outer circumference side. On the other hand, the film thickness of the recording layer 3 of the amorphous magnetic alloy made of TbFeCoTi and the metal reflective layer 5 made of the AlTi alloy are made substantially uniform over the entire surface of the disc.
It can be realized for the first time.

The present invention is not limited to the above-mentioned embodiments, and the film thickness of each layer can be appropriately selected according to the desired characteristics without departing from the scope of the invention.

The present invention is also applicable when a material other than TbFeCo, such as GdTbFeCo or DyTbFeCo, is used as the amorphous magnetic alloy recording layer formed by combining a rare earth metal and an iron group transition metal. It is feasible. Also, the first
And as the second dielectric protection layer, in addition to SiN, ZnS, AlN,
SiO ₂ or the like can be used. Further, as the metal reflection layer, Al, AlCr, AlNi, AuCu or the like may be used in addition to the AlTi alloy.

[0031]

The present invention is constructed as described above, and
According to this, the magneto-optical disk can increase the recording sensitivity at the same time while keeping the reflectance and the reproducing C / N uniform from the inner circumference side to the outer circumference side along the disk radial direction. As a result, it is possible to provide an excellent magneto-optical disk, which has never been used, that high-density recording can be realized.

[Brief description of drawings]

FIG. 1 is a sectional view of a magneto-optical disk showing an embodiment of the present invention.

FIG. 2 is a diagram showing a relationship (result of a comparative experiment) between a disk radius and a recording threshold laser power during recording and reproduction.

FIG. 3 is a diagram showing a relationship between a disc radius and a recording threshold laser power at the time of recording / reproducing (results of another comparative experiment).

FIG. 4 is a diagram showing a reflectance and a reproduction C / N with respect to a disc radius of the embodiment in FIG.

FIG. 5 is a sectional view showing a conventional magneto-optical disk.

[Explanation of symbols]

 1 substrate 2 first dielectric protective layer 3 amorphous magnetic alloy recording layer 4 second dielectric protective layer 5 metal reflective layer

Claims (2)

[Claims] 1. A magneto-optical disk comprising a substrate on which a first dielectric protective layer, an amorphous magnetic alloy recording layer, a second dielectric protective layer and a metal reflective layer are sequentially formed. A magneto-optical disk, wherein the film thicknesses of the first and second dielectric protective layers are set so as to decrease from the inner peripheral side toward the outer peripheral side along the disk radial direction. 2. The magneto-optical disk according to claim 1, wherein the amorphous magnetic alloy recording layer and the metal reflective layer are provided with a substantially uniform thickness along the disk radial direction.