JPH06349121A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To suppress an increase in jitters by forming the magneto-optical recording medium which increases the margin of a recording laser power for CNR by the thickness on the grooves of a reflection layer larger than the film thickness on lands where recording is executed. CONSTITUTION:A substrate consisting of a polycarbonate resin is arranged in a sputtering device and is subjected to reactive sputtering by discharging the inside of the sputtering device to 3X10<-7> torr and using an Si target in an atmosphere of, for example, 5mol% content of gaseous oxygen under 10 mtorr pressure of a gaseous mixture composed of Ar and N2. A dielectric layer consisting of SiNx and having, for example, 100nm average film thickness is formed. A recording film having 25nm average film thickness is then formed by using a TbFeCo alloy under, for example, 3 torr pressure of the gaseous Ar. Further, a dielectric layer consisting of SiNx and having 30nm average film thickness is similarly formed. Finally, the reflection layer having 150nm average film thickness is formed by using an AlTi alloy target under 5 mtorr pressure of the gaseous Ar and is etched at about 15nm.

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 capable of recording, reproducing and erasing information by irradiating a recording film composed of a multi-layered thin film formed on a substrate with laser light. is there.

[0002]

2. Description of the Related Art In recent years, with the increase in the amount of information, there has been an urgent need to develop a recording medium capable of recording a large amount of information. Among them, optical discs that can record and reproduce high-density information using laser light have already been put into practical use.

Optical discs include a write-once type that can be recorded only once and a rewritable type that can erase recorded information and can be rewritten many times. When used as an external memory of a computer in the future, rewriting of information is possible. A rewritable type that can perform is promising.

In a rewritable optical disk, information is recorded and erased by heating the laser beam and applying an external magnetic field to change the magnetization direction of the magnetic layer, and the polarization direction of the laser beam is rotated by the Kerr Kerr effect. A method has been put into practical use in which high-density information recording / reproduction can be performed by reading information by using the. As the recording medium, first, a protective layer made of a dielectric material is provided on a substrate, then a recording layer mainly made of a ferromagnetic material is provided, and further, with or without a protective layer made of a dielectric material. A structure has been devised in which a magneto-optical effect is enhanced by providing a direct reflection layer and using the Faraday effect of light transmitted through the magnetic layer in addition to the Kerr effect. (For example, JP-A-59-217
No. 248 publication)

An optical modulation recording method is a recording method generally used for rewritable optical disks. In this method, the magnetization of the recording film is aligned in the direction opposite to the direction of the external magnetic field, and the recording location is locally heated by laser light corresponding to the signal to be recorded. When the temperature of the heated portion reaches near the Curie temperature, the coercive force becomes very small, the magnetization is reversed in the same direction as the external magnetic field, and a bit is formed. Since it is necessary to form a large bit in order to detect the bit by the reproduction signal, it is necessary to increase the laser power to increase the spread of heat.

[0006]

However, if the laser power is increased too much, the space between adjacent bits in the circumferential direction becomes small, especially at the inner peripheral portion of the disk, and when the bits are read, waveform interference may occur as a read signal. Wake up.
This waveform interference increases jitter.

This means that the reproduction signal amplitude is deteriorated,
It causes a decrease in CNR (Carrier / Noise Ratio).

The problem to be solved by the present invention is that the jitter does not increase even if the recording laser power increases, and
An object of the present invention is to provide a magneto-optical recording medium that can increase the margin of recording laser power with respect to R.

[0009]

In order to solve the above problems, the present invention comprises a transparent dielectric protective layer, a magnetic recording layer and a reflective layer on a substrate having a land and a groove. In a disc-shaped magneto-optical recording medium having a multi-layered recording film, the magneto-optical recording medium is characterized in that the film thickness on the groove portion of the reflective layer is larger than the film thickness on the land portion for recording. I will provide a.

When the reflection layer is formed such that the film thickness on the groove portion is larger than that on the land portion, the heat spread by increasing the laser power is dispersed in the circumferential direction (the interval between adjacent bits is narrowed). It is possible to conduct more in the radial direction (the direction in which heat escapes into the groove), not in the direction in which the heat is conducted. Therefore, even when recording is performed with a relatively large laser power, the bit interval does not become narrow, the read signal does not cause waveform interference, and the increase in jitter can be suppressed.

In order to form the reflection layer so that the film thickness on the groove portion is larger than that on the land portion, for example, after forming the reflection layer by a normal method, the surface of the reflection layer is formed by reverse sputtering. There is a method of etching so that the surface becomes smooth.

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

[0013] As the material of the protective layer made of a dielectric, typically optical constants and transmittance is large, large SiN _X effect of protecting the recording layer, SiO _X, AlSiON, AlSi
_{N, AlN, AlTiN, Ta 2} O 5, ZnS , and the like.

As a material for forming the recording layer made of a magnetic material, for example, an alloy of a transition metal such as TbFeCo or NdDyFeCo and a rare earth metal, or Ti or T
Examples include alloys to which corrosion resistance imparting metals such as a and Cr are added. Particularly, Ti, which has excellent corrosion resistance, is preferable.

A reflective layer is formed on the recording layer with or without a protective layer made of a dielectric material.

Examples of the material of the reflective layer include Al and alloys of Al with other metals. Among them, an alloy of Al and Ti, which is considered to have a large effect of protecting the recording film, is particularly preferable.

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.

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, the magneto-optical recording medium is rotated at a high speed, and the resin is spread by centrifugal force for application. The applied resin is then cured by UV irradiation. The spin coating method can also 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 provided on the surface opposite to the recording layer using a transparent material having high hardness. Is desirable. 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 optical disc formed as described above may be used alone or may be used by laminating two optical discs.

[0022]

It has been found that the above method does not increase the jitter because the heat is diffused in the radial direction rather than the circumferential direction even if the recording laser power is increased.

[0023]

EXAMPLES The present invention will be described in more detail below with reference to examples and comparative examples.

(Embodiment) A substrate made of a polycarbonate resin having a thickness of 1.2 mm and an outer diameter of 90 mm and having spiral grooves with a pitch of 1.6 μm on one side has a substrate mounting portion capable of rotating and revolving. Place it inside the sputtering system and first set the inside of the sputtering system to 3 × 10 ^-7 torr.
Evacuate to below and the pressure of the mixed gas of Ar and N ₂ is 10 m
Reactive sputtering was performed using a Si target in a torr atmosphere containing 5 mol% of nitrogen gas to form a dielectric layer made of SiN _x having an average film thickness of 100 nm.

Next, when the Ar gas pressure is 3 mTorr, TbF
A recording layer having an average film thickness of 25 nm was provided using an eCo alloy target.

Further, a dielectric layer made of SiN _x having an average film thickness of about 30 nm was formed by the same method as described above. Finally, after forming a reflective layer with an average film thickness of about 150 nm using an AlTi alloy target with an Ar gas pressure of 5 mTorr, the Ar gas pressure was set to 1 mTorr and the average depth was only about 15 nm by the reverse sputtering method. Etched, thickness is about 135nm
A reflective layer having a smooth surface was formed. The etching rate at this time was 0.05 nm / sec.

The recording and reproducing characteristics of the recording film formed by the above method were measured with the use of a magneto-optical disk evaluation apparatus. A semiconductor laser with a wavelength of 830 nm was used for the measurement, the disc rotation speed was 2,400 rpm, the recording frequency was 3.9 MHz, the pulse width was 60 nsec, the recording bias magnetic field was 325 gauss, and the reproducing laser output was 1.5 mW. The CNR with respect to the recording laser power was examined at the position. The results are shown in Fig. 4.

(Comparative Example 1) On a substrate made of the polycarbonate resin used in the example, S was processed in the same manner as in the example.
A dielectric layer made of iN _{x is formed} to a thickness of 100 nm, a recording layer is formed to a thickness of 25 nm and a dielectric layer is formed to a thickness of 30 nm in the same manner as in the embodiment, and finally the reflective layer is etched in the same manner as the embodiment. Without doing so, a film having a thickness of 135 nm was formed.

The recording and reproducing characteristics of the recording film formed by the above method were measured by the same method as in the example, and the results are shown in FIG. From the results shown in FIG. 4, it can be understood that the disk of Comparative Example 1 is inferior in the margin of the recording laser power to the CNR as compared with the Example.

(Comparative Example 2) On a substrate made of the polycarbonate resin used in the example, S was processed in the same manner as in the example.
A dielectric layer made of iN _{x is formed} to a thickness of 100 nm, a recording layer is sequentially formed to a thickness of 25 nm and a dielectric layer is formed to a thickness of 30 nm in the same manner as in the embodiment, and finally an average film thickness is formed in the same manner as in the embodiment. 14
After providing a 0 nm reflective layer, etching was performed to an average depth of about 5 nm to form a reflective layer having an average film thickness of 135 nm.

The recording and reproducing characteristics of the recording film formed by the above method were measured with time in the same manner as in the example, and the results are shown in FIG. From the results shown in FIG.
It can be understood that the disc of Comparative Example 2 is inferior in the margin of the recording laser power to the CNR as compared with the Example.

(Comparative Example 3) On a substrate made of the polycarbonate resin used in the example, S was processed in the same manner as in the example.
A dielectric layer made of iN _{x is formed} to a thickness of 100 nm, a recording layer is formed to a thickness of 25 nm and a dielectric layer is formed to form a thickness of 30 nm in the same manner as in the example, and finally, the pressure of Ar gas is 5 mTorr and AlTi is formed.
After forming a reflective layer having an average film thickness of 150 nm using an alloy target, etching was performed at an Ar gas pressure of 10 mTorr and an average depth of approximately 15 nm to form a reflective layer having an average film thickness of 135 nm. The recording and reproducing characteristics of the recording film formed by the above method were measured with time in the same manner as in the example. As a result, the disc of Comparative Example 3 had a margin of the recording laser power with respect to the CNR as compared with the Example. You can see that it is inferior.

[Effect] Since the jitter does not increase even when the recording laser power increases, the margin of the recording laser power with respect to the CNR increases. The improvement of this margin reduces the probability of writing an erroneous signal with respect to fluctuations in the recording laser power due to disturbances such as laser noise, crosstalk, circuit noise, and vibration, and facilitates drive design.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a layer structure of a magneto-optical recording medium according to an example of the present invention.

FIG. 2 is a schematic cross-sectional view showing the layer structure of a magneto-optical recording medium of Comparative Example 1 of the present invention.

FIG. 3 is a schematic cross-sectional view showing the layer structure of a magneto-optical recording medium of Comparative Example 2 of the present invention.

FIG. 4 is a chart showing the relationship between recording laser power and CNR in Examples and Comparative Examples 1, 2, 3 and 4.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reflective layer 2 Protective layer made of a dielectric material 3 Recording layer made of a magnetic material 4 Protective layer made of a dielectric material ○ Example △ Comparative example 1 □ Comparative example 2 × Comparative example 3

Claims (1)

[Claims] 1. A disk-shaped magneto-optical recording medium having a multi-layered recording film including a protective layer made of a transparent dielectric material, a recording layer made of a magnetic material, and a reflective layer on a substrate having a land portion and a groove portion. 2. The magneto-optical recording medium as described above, wherein the film thickness on the groove portion of the reflective layer is larger than the film thickness on the land portion for recording.