JP2521664B2 - Magneto-optical disk - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention uses a rare earth-transition metal amorphous ferrimagnetic alloy thin film having an easy axis of magnetization in a direction perpendicular to the film surface as a recording layer. The present invention relates to a magneto-optical disk, and more particularly to a magneto-optical disk driven by a constant angular velocity rotation system during recording and reproduction.

(Prior Art) Rare earth-transition metal amorphous ferrimagnetic alloy thin film (hereinafter,
A magneto-optical disk that uses a perpendicularly magnetized film (abbreviated as RE-TM film) as a recording layer and uses the magneto-optical effect, especially the effect as much as possible, is promising as a rewritable optical recording medium. Is expected. Magneto-optical discs have the great advantage that erasing and repetitive recording are possible as compared with the optical discs of the write-once / non-erasable type that have already been put to practical use, such as a Te-C film as a recording layer, but at the time of recording / erasing Since a large magnet is required, the weight of the optical head increases and the access speed becomes slow.

By the way, as is well known, two types of optical disc drive systems have been put into practical use, a constant angular velocity rotation system (hereinafter referred to as CAV system) and a constant linear velocity rotation system (hereinafter referred to as CLV system). In the CLV method, the recording density can be made constant on the outer and inner circumference sides of the disc, so it is more advantageous in terms of recording capacity than the CAV method, in which the recording density decreases on the outer circumference side, but the relative distance between the optical head and the disc. Since it is necessary to change the rotation speed of the disk according to the positional relationship, the structure of the disk drive device becomes complicated and the access speed becomes slow.
In addition, it is difficult to perform special reproduction such as still, double speed, slow, etc., which is required in a moving picture memory such as a video disc. Therefore, the CLV method is suitable for the document file memory, and the CAV method is suitable for the code data file memory and the moving picture memory.

Even for magneto-optical disks, both CLV and CAV can be selected as the drive method depending on the field of application as a memory, but in order to compensate for the disadvantage of the magneto-optical disk that the access speed is slow due to the increase in the weight of the optical head. It is preferable to use the CAV method.

However, when the magneto-optical disk is driven by the CAV method, when recording is performed with the recording laser power, the recording magnetic field, and the recording frequency being constant, the supply of the laser beam to the RE-TM film necessary for forming one recording bit is performed. Energy density
It is large on the inner side of the disk and small on the outer side.
As a result, the recording sensitivity fluctuates and the reproduction C / N (carrier noise ratio of the reproduction signal) fluctuates due to variations in the recording bit shape. It is not preferable to keep the energy density supplied to the RE-TM film constant by controlling the recording laser power, the recording magnetic field, the recording frequency, etc., as it complicates the system.

(Problems to be solved by the invention) When the magneto-optical disk is driven by the CAV method in this way,
There is a problem that the recording sensitivity and the reproduction C / N are likely to change.

Therefore, it is an object of the present invention to provide a magneto-optical disk capable of uniform recording sensitivity and reproducing C / N over the entire surface of the disk when driven by the CAV method during recording and reproducing.

[Structure of the Invention] (Means for Solving Problems) The present invention is configured by sequentially stacking a recording layer made of a RE-TM film, a transparent interference layer, and a light reflection layer on a substrate having a guide groove. In a magneto-optical disk that has a structure and is driven by the CAV method during recording and reproduction, the thermal conductivity of the transparent interference layer is made smaller than the thermal conductivity of the recording layer and the light reflection layer, and the film thickness of the transparent interference layer. The above problem is solved by uniformly increasing the value from the inner circumference side to the outer circumference side along the disk radial direction.

(Function) In the structure in which the recording layer made of the RE-TM film, the transparent interference layer and the reflected light are sequentially laminated on the substrate, the transparent interference layer is the RE layer.
This is for increasing the reproduction signal output by increasing the rotation angle, which is insufficient in the single layer between TM and TM, by multiple reflection of the laser beam through the transparent interference layer. Here, since the thermal conductivity of the transparent interference layer is smaller than the thermal conductivity of the recording layer and the light reflecting layer, the heat flow in the magneto-optical disk is
It occurs in the direction from the RE-TM to the light reflection layer, that is, in the direction of the recording layer made of the RE-TM film → the transparent interference layer → the light reflection layer. In this case, the transparent interference layer has a function as a heat insulating layer that suppresses the flow of heat to the light reflecting layer. Since this heat insulation effect increases corresponding to the film thickness of the transparent interference layer, the film thickness of the transparent interference layer uniformly increases from the inner peripheral side to the outer peripheral side along the radial direction of the disk. According to the configuration, the recording threshold temperature relatively increases (recording sensitivity decreases) on the inner circumference side where the energy density supplied to the RE-MT film by the laser beam becomes relatively large when forming one recording bit, and On the outer peripheral side where the energy density becomes relatively small, the recording threshold temperature relatively decreases (recording sensitivity increases). This makes the recording sensitivity and the recording bit shape (reproduction C / N) uniform.

(Embodiment) FIG. 1 is a block diagram of a magneto-optical disk according to an embodiment of the present invention, in which a disk-shaped transparent resin substrate 1, for example, a polycarbonate substrate provided with spiral guide grooves with a pitch of 2 μm is provided. RE-TM film, for example, a film thickness of 30
A recording layer 2 made of a TbCo film having a thickness of nm is formed, and a SiN film, for example, is provided as a transparent interference layer 3 on the recording layer 2. further,
On the transparent interference layer 3, a light reflection layer 4 made of, for example, an Al film having a film thickness of 50 nm is formed.

Here, as shown in the enlarged sectional view on the right side of FIG. 1 and FIG. 2, the transparent interference layer 3 has a film thickness at least in the recording area from the inner peripheral side to the outer peripheral side along the radial direction of the disc. Have increased uniformly.

The magneto-optical disk having this structure could be manufactured by the following procedure. First, after cleaning with Freon gas, the fully degassed polycarbonate substrate was placed on a substrate holder in a sputtering apparatus having a quaternary target of Tb, Co, Si ₃ N ₄ , and Al. After exhausting the inside of the sputtering equipment, introducing 5 mTorr of Ar gas, applying DC power to both Tb and Co targets simultaneously, and pre-sputtering for 5 minutes with the shutters on both targets closed. After that, both shutters were opened simultaneously and a TbCo film having a film thickness of 30 nm, that is, the recording layer 2 was formed in 45 seconds. At this time, the substrate holder was rotated at 60 rpm.

Next, apply RF power of 500 W to the Si ₃ N ₄ target,
While rotating the substrate holder, the SiN film as the transparent interference layer 3 was formed for 30 minutes. At this time, a self-made mask was placed on the Si ₃ N ₄ target so that the film thickness of the SiN film had a distribution as shown in FIG.

Next, RF power of 300 W is applied to the Al target to form an Al film having a film thickness of 50 nm, that is, the light reflection layer 4 in 6 minutes,
A magneto-optical disk having the structure shown in FIG. 1 was obtained.

A method of arranging a mask on a target and adjusting the position and shape of the mask to adjust the film thickness is commonly used as a film thickness control method in forming a sputtered film. The mask used when forming the SiN film as the transparent interference layer 3 had a shape such that the film thickness distribution between the SiNs was as shown in FIG. 2, and was manufactured based on the results of basic experiments. is there. The film thickness distribution can be controlled by the shape of the mask, and when the materials of the recording layer 2, the transparent interference layer 3 and the light reflection layer 4 are changed, the film thickness distribution of the transparent interference layer 3 is suitable for each material. The shape of the mask may be changed so that

The dynamic characteristics (recording / reproducing characteristics) of the magneto-optical disk shown in FIG. 1 were evaluated by a disk drive device having the specifications shown in Table 1.

The evaluation result is shown in FIG. As shown in FIG. 3, the magneto-optical disk according to the present invention obtained extremely stable recording sensitivity and reproducing C / N in the recording area by using the CAV type disk drive. The reason for this can be explained as follows. FIG. 4 shows 1 when the magneto-optical disk is driven by the disk drive device having the specifications shown in Table 1.
It is a figure which shows the relationship between the supply energy density E of a laser beam required for formation of a recording bit, and disk radius rd. E
Was derived from the following equations (1) and (2).

E = P · tp / {( πd 2/4) + dl} ...... (1) l = 2πrdν × tp ...... (2) where, P: recording laser power, tp: the laser beam irradiation time, d: Laser Spot diameter, l: disk movement distance at time tp, rd: disk radius, ν: disk rotation speed.

From Table 1 in equations (1) and (2), ν = 20rps (1200rpm), t
By substituting p = 400 nsec (average value), = 5 mW, and d = 1.3 μm, FIG. 4 is obtained.

As shown in FIG. 4, in the CAV system, the energy density supplied by the recording laser beam is a function of the disc radius rd. Therefore, in a magneto-optical disk having a uniform film thickness, the inner peripheral side has high sensitivity and the outer peripheral side has low sensitivity.

On the other hand, if the film thickness of the transparent interference layer 3 is uniformly increased from the inner circumference side to the outer circumference side as in the magneto-optical disk of the present invention, the recording layer 2 to the light reflection layer 4 are formed on the inner circumference side. The heat loss to the outer peripheral side is relatively large and the sensitivity is low, and the heat loss on the outer peripheral side is relatively small and the sensitivity is high. Therefore, the recording sensitivity is uniform in the radial direction of the disc, and the shape (size) of the recording bit is also uniform.
Is also uniform.

In order to further clarify the effect of the above-described magneto-optical disk according to the present invention, a magneto-optical disk based on the conventional technique was prototyped and evaluated using the same disk drive device. In the trial manufacture of the magneto-optical disk based on the prior art, during the manufacturing process of the magneto-optical disk based on the present invention described above,
The mask for controlling the film thickness provided on the front surface of the Si ₃ N ₄ target was removed in the sputtering system, and a 30 nm thick recording layer was formed on the substrate.
After forming the TbCo film, a SiN film having a uniform thickness of 100 nm as a transparent interference layer and an Al film having a thickness of 50 nm as a light reflecting layer were sequentially laminated.

FIG. 5 shows the result of evaluation of the magneto-optical disk based on this prior art with the disk drive device shown in Table 1. The tendency estimated from the calculation result shown in FIG. 4 is clearly shown. That is, the recording threshold laser power increases as it moves to the outer peripheral side, and the reproduction C / N decreases on the outer peripheral side because the recording bit size becomes insufficient on the outer peripheral side.

The present invention is not limited to the above-described embodiments, and the present invention is effective when, for example, a RE-TM film used for the recording layer is made of a material other than TbCo.

In addition to SiN, SiO, S
It is possible to use iO ₂ , Si ₃ N ₄ , ZnS, AlN, CaF ₂ , ITO or the like.
As a material for the transparent resin substrate, not only polycarbonate but also polymethylmethacrylate, epoxy, etc. can be widely selected.

However, in the present invention, when the thermal conductivity of the transparent interference layer is smaller than that of the recording layer and the light reflection layer, that is, when the transparent interference layer functions as a heat insulating layer, the recording layer, It is desirable that the materials of the transparent interference layer and the light reflecting layer are a combination satisfying such a condition.

Furthermore, the present invention is not limited to the magneto-optical disk having the structure shown in FIG. 1, and the present invention is also applicable to a magneto-optical disk having a structure in which a transparent interference layer is interposed between the substrate and the recording layer. Can be applied. In addition, the present invention can be variously modified and implemented without departing from the gist.

[Effects of the Invention] The magneto-optical disk according to the present invention is used for recording and reproduction.
Even if the recording is performed by the CAV method and the recording laser power, the recording magnetic field, and the recording frequency are constant, uniform recording sensitivity and reproducing C / N are obtained over the entire surface of the disc.

[Brief description of drawings]

FIG. 1 is a sectional view of a magneto-optical disk according to an embodiment of the present invention, FIG. 2 is a view showing a film thickness distribution of a transparent interference layer in a disk radial direction in the magneto-optical disk of the embodiment, and FIG. FIG. 4 is a diagram showing the relationship between the disc radius, the recording threshold laser power, and the reproduction C / N when the magneto-optical disc of the embodiment is driven by a CAV disc drive, and FIG. 4 shows recording in the disc radius direction in the CAV system. FIG. 5 shows the energy density distribution, and FIG. 5 shows a conventional magneto-optical disk as a CAV.
FIG. 6 is a diagram showing a relationship between a disc radius, a recording threshold laser power, and a reproduction C / N when the disc is driven by a disc drive apparatus of a system. 1 ... Transparent resin substrate, 2 ... Recording layer made of RE-TM film,
3 ... Transparent interference layer, 4 ... Light reflecting layer.

Claims (1)

(57) [Claims] 1. A rare earth element on a substrate having a guide groove.
A magneto-optical disk which is formed by sequentially stacking a recording layer made of a transition metal amorphous ferrimagnetic alloy thin film, a transparent interference layer and a light reflection layer, and is driven by a constant angular velocity rotation method during recording and reproduction. Has a thermal conductivity smaller than that of the recording layer and the light reflection layer, and the thin film of the transparent interference layer increases uniformly from the inner circumference side to the outer circumference side along the disc radial direction. A magneto-optical disk characterized by being present.