JPH05217232A - Magneto-optical recording medium and its production - Google Patents

Abstract

PURPOSE:To enhance the sensitivity of a magneto-optical recording medium to a magnetic field by forming the layers of the multilayered structure of the magneto-optical recording layer of the recording medium by vapor deposition with the same target while stepwise varying the pressure of sputtering gas from low pressure to high pressure. CONSTITUTION:This magneto-optical recording medium has at least a dielectric layer, a magneto-optical recording layer and a dielectric layer on one side of the substrate and has a reflection layer on the upper dielectric layer if necessary. A protective coat layer and a hard coat layer may further be formed on the reflection layer and the other side of the substrate, respectively. The magneto-optical recording layer has a multilayered structure and the layers of the structure are formed by vapor deposition with the same target while stepwise varying the pressure of sputtering gas from low pressure to high pressure.

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 for recording and erasing thermomagnetically and reproducing magneto-optically, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, a high density optical disk memory has been actively developed as a recording medium capable of accommodating a large capacity of information. Among them, a magneto-optical recording medium capable of recording, erasing and rewriting has received the most attention due to its practicality and versatility.

Magneto-optical recording media include heavy rare earths such as Gd and Tb and Fe and C on a transparent substrate (glass or plastic).
It is a perpendicular magnetization film formed by an amorphous alloy film made of a transition metal such as o by a sputtering method or the like.

In the case of recording, this film is previously magnetized (initialized) in a fixed direction by an external magnetic field, and a semiconductor laser beam focused to about 1 μm is applied to the magneto-optical recording layer to perform recording. Film temperature of 150 to 3
When heated to 00 ° C (Curie temperature or higher, or magnetic compensation temperature of ferrimagnetic material) and at the same time a magnetic field is applied in the direction opposite to initialization, the temperature rises and the magnetization direction of the magnetic film with reduced coercive force is reversed. To do. And the change of the magnetization direction is maintained even at room temperature. That is, information can be recorded by modulating the intensity of the emitted laser light with a signal.

In the case of reproduction, when a linearly polarized laser beam is incident on a magnetic film and then reflected, a phenomenon in which the plane of polarization of the light rotates depending on the direction of magnetization, that is, a magneto-optical effect (Kerr effect) is utilized. In an actual device, the output of the semiconductor laser is lowered from that at the time of recording to irradiate the magneto-optical recording layer, and the reflected light is detected by the analyzer as a light intensity signal according to the direction of magnetization. This is converted into an electric signal by a photo detector and taken out as information.

In the case of erasing, the external magnetic field is directed in the opposite direction to that at the time of recording, and the semiconductor laser is continuously irradiated to align the direction of magnetization of the magneto-optical recording layer with the same direction as at the time of initialization, thereby erasing. be able to.

On the basis of the above-described principle of magneto-optical recording, the magneto-optical recording apparatus is provided with a magnetic head in addition to the optical head on the incident light side of the recording medium. It is effective to reduce the size of the head in order to reduce the size and thickness of the recording apparatus. If the size of the head can be reduced, the access speed can be increased. In particular, in order to miniaturize the magnetic head, it is better that the external magnetic field required for recording / erasing is smaller. That is, it is desired to develop a recording medium having a high magnetic field sensitivity. Furthermore, it is desirable that the magnetic field modulation type direct overwrite has a high magnetic field sensitivity and a wide magnetic field margin is taken into consideration in terms of medium compatibility, and these are important research items. However, when the magnetic field sensitivity is increased, the magnetic field margin is narrowed, which is a tendency of the conventional medium.

In many magneto-optical recording media, a dielectric layer, a magneto-optical recording layer, a dielectric layer, and a reflective layer are sequentially formed on a substrate by a sputtering method. In order to improve the magnetic field sensitivity and margin of the magneto-optical recording medium, the composition and composition of these films
The characteristics of the medium have been improved by changing the film thickness and sputtering conditions.

FIG. 1 shows a conventional magneto-optical recording medium. Then, FIG. 2 shows an example of measurement of recording characteristics of such a medium. The sputtering pressure of the magneto-optical recording layer is 1.5 mTo
If it is rr or less, the magnetic field sensitivity is good, but the margin becomes narrow. On the other hand, the sputtering pressure of the magneto-optical recording layer is set to 3 mTorr.
When it is more than r, the C / N is improved and the margin is widened, but the magnetic field sensitivity is deteriorated. Further, at an intermediate sputtering pressure, both characteristics will be averaged. As described above, it is difficult to satisfy both requirements in the magneto-optical recording layer under the single condition.

The measurement conditions of FIG. 2 are as follows. 3.5
The inch magneto-optical disk is rotated at 1800 rpm and the position of the inner peripheral portion 24.1 mm is measured. Erase power 7m
W, erase bias magnetic field 600 G, write power (peak) 7 mW, write power (bottom) 1 mW, read power 1 mW. Also, video band Wids 3.0K
Hz, writing frequency 2.9 MHz, pulse width 115 nanoseconds.

A measurement example will be described. The maximum value of C / N is lower (1.5 mTorr) when the sputtering gas pressure is higher.
r) shows a higher value than the case.

Focusing on the change in the C / N value due to the write bias magnetic field, after the C / N becomes maximum, it decreases with the bias magnetic field strength when the sputter gas pressure is low. In the case of high sputter gas pressure, the degree is very small, and C / N has a substantially constant value. If the range of the magnetic field from the maximum value of C / N to the value lower than the maximum value by 1 dB is called the magnetic field margin, it can be said that the magnetic field margin is 200 G to 500 G when the sputtering gas pressure is high.

Further, the magnetic field in which the bias magnetic field is increased from the smaller one and C / N has the maximum value is called a saturation bias magnetic field, and the bias magnetic field when C / N is 1 dB lower than that is called magnetic field sensitivity. To do. The magnetic field sensitivity is 125 G when the sputter gas pressure is low, and 200 G when the sputter gas pressure is high.

There is a magnetic field in which writing becomes impossible as the bias magnetic field is further reduced. If this magnetic field is called a C / N zero magnetic field, it is desirable that its absolute value is small in terms of characteristics. When the sputter gas pressure is low, the value is −150 G, and when the sputter gas pressure is high, the value is −300 G, which is a significant difference.

[0015]

As described above, the magnetic field sensitivity and the magnetic field margin are important characteristics in the magneto-optical recording medium, but the number of studies is surprisingly small. For example, in Japanese Unexamined Patent Publication No. 63-63154, a magneto-optical recording is possible in which a magneto-optical recording layer having a high coercive force and a magneto-optical recording layer having a low coercive force are stacked and highly sensitively recorded with a bias magnetic field of an appropriate size. A medium has been proposed. In this invention, as a high coercive force film,
TbCo, DyCo, DyFeCo and GdCo, GdCoFe are shown as the low coercive force film. in this case,
No matter which combination of the films is combined, another target must be prepared when the film is formed by sputtering, and two sputtering chambers are required, which causes a problem of large-scale equipment.

An object of the present invention is to provide a magneto-optical recording medium having good magnetic field sensitivity and magnetic field margin.

[0017]

In order to solve the above problems, the present invention provides a magneto-optical recording medium having a magneto-optical recording layer on a substrate, wherein the magneto-optical recording layer has a multi-layer structure and a multi-layer structure. A magneto-optical recording medium, wherein each layer is formed by vapor deposition while using the same target and gradually changing the sputtering gas pressure from a low pressure to a high pressure.

The layer structure of the magneto-optical recording medium of the present invention has at least a dielectric layer on a substrate, a magneto-optical recording layer having a multi-layered structure obtained by changing the sputtering conditions, a dielectric layer, and if necessary. It has a structure including a reflective layer. Further, a protective coat layer may be provided on the reflective layer, and a hard coat layer may be provided on the surface of the substrate opposite to the magneto-optical recording layer.

The substrate used in the present invention is, for example,
Examples thereof include substrates such as polycarbonate, polymethylmethacrylate, and amorphous polyolefin in which guide grooves are directly formed in resin or glass, substrates in which guide grooves are formed on a flat plate of glass or resin by a photopolymer method, and the like.

An inorganic dielectric having high transparency is used for the dielectric layer. Examples of the material include SiN _x and Si
O _x , AlSiON, AlSiN, AlN, AlTi
N, Ta ₂ O ₅ , ZnS and the like can be mentioned, but among them, S
iN _x is preferred. The refractive index of these dielectric layers is 1.8 to
A range of 2.5 is preferred.

The dielectric layer is formed by physical vapor deposition (PVD) such as sputtering or ion plating, or plasma CV.
It is formed by a chemical vapor deposition method (CVD) such as D.

The material constituting the magneto-optical recording layer of the present invention is, for example, TbFeCo, DyFeCo, TbF.
e, GdTbFeCo, NdDyFeCo, TbCo, and the like. Those amorphous alloys to which other metals are added for the purpose of improving oxidation resistance can also be used.

As the sputtering conditions for forming the magneto-optical recording layer, the sputtering gas pressure is changed. in this case,
Although the same target is used, the film formation rate varies depending on the sputtering gas pressure. Therefore, in order to control the film thickness, the film formation rate is obtained in advance and the sputtering time at each gas pressure is determined.

When the magneto-optical recording layer is formed into two layers, a film having a low sputtering gas pressure is formed on the first layer side, and then a film having a high sputtering gas pressure is formed. In the opposite case, the effect is small.
The layer thickness of the low gas pressure layer is 10 to 70% of the entire recording layer.
Is preferred. Here, the low sputtering gas pressure is preferably 1.5 mTorr or less, and the high sputtering gas pressure is preferably 3 mTorr or more.

In the case where the magneto-optical recording layer has three or more layers, a film having a low sputter gas pressure is formed on the first layer side, and a film having a high sputter gas pressure is sequentially formed. Also in this case, the layer thickness at low sputtering gas pressure (1.5 mTorr or less) is preferably in the range of 10 to 70% of the entire recording layer.

Examples of the material of the reflective layer include Al and alloys of Al and other metals. Al, Al-Ti alloys and Al-Cr alloys are preferable.

The reflective layer is formed by sputtering, physical vapor deposition (PVD) such as ion plating, or plasma CVD.
It is formed by a chemical vapor deposition method (CVD) or the like.

Both organic and inorganic materials are used for the material of the protective coat layer. When forming an organic protective coat layer, methods such as a dipping method, a spin coat method, a roll coater method, and a vapor deposition method are used. on the other hand,
When forming the inorganic protective coat layer, a method such as a sputtering method, a vapor deposition method, an impregnation method or the like is used.

Of these protective coating methods, the spin coating method using an ultraviolet curable resin is preferable because it is a simple and quick method. In this method, an ultraviolet curable resin is discharged onto a substrate using a dispenser, a disk is rotated at a high speed, and the resin is spread by centrifugal force to apply the resin. The applied resin is then cured by UV irradiation. Also,
The spin coating method can be suitably used for resins other than the ultraviolet curable resin. In any case, the resin used for the protective coat layer preferably has a pencil hardness of H or higher after curing.

The plastic substrate has insufficient scratch resistance, and in order to overcome such a drawback, a hard coat layer is formed on the surface opposite to the magneto-optical recording layer by using a transparent material having high hardness. It is desirable to provide it. As a means for hard coating, a method of applying and curing an organic polymer such as a UV-curable resin containing a polyfunctional urethane acrylate and a photopolymerization initiator by a spin coating method, a 2P method or the like, a silicon dioxide by a precipitation method or a sputtering method, etc. And the like, a ceramic hard coat layer is not suitable for mass production due to poor productivity, and thus a hard coat layer using an ultraviolet curable resin is preferable.

The magneto-optical recording medium thus formed may be used alone or may be used by laminating two substrates so that the substrates are on the outside.

FIG. 3 shows an example of the film structure of the magneto-optical medium manufactured by the above method.

[0033]

【Example】

(Example 1) A case where a magneto-optical disk having two magneto-optical recording layers is manufactured by an in-line sputtering device will be described. The in-line sputtering device comprises a charging chamber, an extraction chamber, a degassing chamber and four sputtering chambers.

First, SiN _x was used as a dielectric layer on a polycarbonate substrate in the first sputtering chamber by RF magnetron sputtering to produce a sputtering gas pressure of 10 mTorr and 3 KW.
A film having a thickness of 1000 angstroms was formed under the above condition.

Next, the substrate was moved to the second sputtering chamber, and TbFeCo was formed as a magneto-optical recording layer by DC magnetron sputtering to a film thickness of 300 angstroms. And 1, 1.5, 3mTo
Select 2 conditions from sputter gas of rr and combine them to 1.5
The film was formed under the KW condition. Although the sputtering conditions were changed on the way, only the Ar gas flow rate was changed using the same target in the same sputtering chamber. In the third sputtering chamber, a dielectric layer of 250 Å was formed again under the same conditions as in the first sputtering chamber.

Further, Al is used as a reflective layer in the fourth sputtering chamber.
Was deposited by DC magnetron sputtering under the conditions of a sputtering gas pressure of 1.5 mTorr and 3 KW to 600 angstrom.

FIG. 4 shows the measurement results of the write bias magnetic field dependence of the magneto-optical disk manufactured by the above method.

As the first layer of the magneto-optical recording layer, 3 mTorr
No improvement in magnetic field sensitivity and magnetic field margin is observed when the film is formed at a high sputtering gas pressure of 1 and then a second magneto-optical recording layer is formed at a low sputtering gas pressure of 1.5 mTorr and 1 mTorr. . 1mTorr as the first layer,
When the sputtering gas pressure of 3 mTorr is combined as the second layer, the magnetic field sensitivity is 80 G, and the margin is from 80 G to 600.
G, C / N zero magnetic field -80G. Further, the first layer is 1.5 mTorr, and the second layer is 3 mTorr.
Magnetic field sensitivity of 100 when combined with the sputtering gas pressure of
G, the margin was 100 G to 600 G, and the C / N zero magnetic field was -130 G.

As described above, when the magneto-optical recording layer was formed at a low gas pressure and then at a high gas pressure, an improvement in characteristics not obtained by the single-layer film was obtained.

(Embodiment 2) A case will be described in which a magneto-optical recording layer is made into two layers by an in-line sputtering device and a magneto-optical disk having different thicknesses is manufactured. The sputtering conditions for the films other than the magneto-optical recording layer are the same as in Example 1. The first layer of the magneto-optical recording layer had a sputtering gas pressure of 1 mTorr, the second layer had a thickness of 3 mTorr, and the total film thickness was 300 Å and the power was 1.5 KW.

Table 1 shows the measurement results of the write bias magnetic field dependence of the magneto-optical disk manufactured by the above method.

[0042]

[Table 1]

From Table 1, the effect appears when the film thickness of the first layer is 10% or more of that of the magneto-optical recording layer, and the effect is maximized when the film thickness reaches 50%. If the ratio is 50% or more, the effect is reduced, but 70
It can be understood that up to%, the characteristics are improved as compared with the case where the magneto-optical recording layer is a single layer.

Example 3 A magneto-optical disk was manufactured by forming the magneto-optical recording layer into three layers with an in-line sputtering device. The sputtering conditions for the films other than the magneto-optical recording layer are the same as in Examples 1 and 2.

When the magneto-optical recording layer shown in FIG. 5 is composed of three layers, the total film thickness of the three layers is 300 angstroms, and the film thickness is divided into three equal parts with a power of 1.5 KW. The first layer is 1 mTorr, the second layer is 1.5 mTorr, and the third layer is 3 mT
The film was formed at a sputtering gas pressure of orr. In this case, the magnetic field sensitivity was 70 G, the margin was 70 G to 600 G, and the C / N zero magnetic field was −70 G.

[0046]

The magneto-optical recording medium of the present invention has a magnetic field sensitivity,
Both characteristics of the magnetic field margin are improved at the same time. Therefore, by using the magneto-optical recording medium of the present invention, the magneto-optical recording device can be downsized and thinned. Further, the magneto-optical recording medium of the present invention is excellent in magnetic field sensitivity even in the direct overwrite of the magnetic field modulation method, and is therefore excellent in medium compatibility.

[Brief description of drawings]

FIG. 1 is an example of a film structure of a conventional magneto-optical recording medium.

[Explanation of symbols]

 1 Hard Coat 2 Substrate 3 Dielectric Layer 4 Magneto-optical Recording Layer 5 Dielectric Layer 6 Reflective Layer 7 Protective Coat

FIG. 2 is a write magnetic field and C / N of a conventional magneto-optical recording medium.
It is a chart which shows the relationship with a value.

[Explanation of symbols]

Solid line When the sputter gas pressure of the recording layer is 1.5 mTorr Dashed line When the sputter gas pressure of the recording layer is 3.0 mTorr

FIG. 3 is an example of a film structure of a magneto-optical recording medium of the present invention.

[Explanation of symbols]

 1 Hard coat 2 Substrate 3 Dielectric layer 4a Magneto-optical recording layer 1st layer 4b Magneto-optical recording layer 2nd layer 4c Magneto-optical recording layer 3rd layer 5 Dielectric layer 6 Reflective layer 7 Protective coat

FIG. 4 is a chart showing the relationship between the write magnetic field and the C / N value of a magneto-optical recording medium having a magneto-optical recording layer of two layers according to the present invention.

[Explanation of symbols]

(Solid line) Sputtering gas pressure of the recording layer is 3.0 mTorr
And 1.5 mTorr (broken line) Sputtering gas pressure of the recording layer is 3.0 mTorr
And 1.0 mTorr (dashed line) The sputtering gas pressure of the recording layer is 1.0 mTorr.
In the case of a combination of rr and 3.0 mTorr (two-dot chain line), the sputtering gas pressure of the recording layer is 1.5 mTo
In case of combination of rr and 3.0 mTorr

FIG. 5 is a chart showing the relationship between the write magnetic field and C / N of a magneto-optical recording medium having a multi-layered magneto-optical recording layer according to the present invention. (Solid line) Sputtering gas pressure of the recording layer is 1.0 mTorr
(Layer thickness ratio 50%) and 3.0 mTorr (Layer thickness ratio 50%)
(Dashed line) Sputtering gas pressure of the recording layer is 1.0 mTorr
(Layer thickness ratio 33%) and 1.5 mTorr (Layer thickness ratio 33%)
And 3.0 mTorr (layer thickness ratio 33%) combination

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masayuki Yamato Inventor Masayuki Yamato 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihon Kokan Co., Ltd. (72) Hideki Obayashi 24-1-1 Rokuzaki, Sakura City, Chiba Prefecture 210

Claims (2)

[Claims] 1. A magneto-optical recording medium having a magneto-optical recording layer on a substrate, wherein the magneto-optical recording layer has a multilayer structure, and each layer of the multilayer structure uses the same target, and the sputtering gas pressure is from low pressure to high pressure. A magneto-optical recording medium, characterized in that the magneto-optical recording medium is formed by vapor deposition while being changed stepwise. 2. A method of manufacturing a magneto-optical recording medium in which a magneto-optical recording layer is formed on a substrate by a vapor deposition method, the same target is used when forming the magneto-optical recording layer, and the sputtering gas is supplied from a low pressure to a high pressure. A method for manufacturing a magneto-optical recording medium having a magneto-optical recording layer having a multi-layer structure, characterized in that the film is formed by vapor deposition while being changed stepwise.