JPH02302947A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To substantially prevent the elliptical polarization of light and to prevent the degradation in carrier output by adopting the 4-layered constitution consisting of a 1st dielectric protective layer, recording layer, 2nd dielectric protective layer, and metallic reflecting layer to form a magneto-optical recording layer and specifying the film thicknesses of the respective layers to specific ranges. CONSTITUTION:The magneto-optical recording layer provided on a substrate is made of the 4-layered constitution formed with the films of the 1st dielectric protective layer, the recording layer, the 2nd dielectric protective layer, and the metallic reflecting layer in this order. In addition, the film thicknesses of the respective layers are specified to the ranges of 950 to 1,300Angstrom 1st dielectric protective layer, 200 to 400Angstrom recording layer, 100 to 300Angstrom 2nd dielectric protective layer, and 200 to 800Angstrom metallic reflecting layer. The phase difference of reflected light is lessened in this way and the elliptical polarization of the plane of the polarization thereof is prevented. The fluctuation in C/N by driving is thus suppressed. Further, the sensitivity is improved and the dependency of the sensitivity on rotating speeds is lessened.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a magneto-optical recording medium, and in particular, the present invention relates to a magneto-optical recording medium, and in particular, the present invention relates to a magneto-optical recording medium, in which polarization is less elliptical, that is, a phase difference is small, and C/
It is used as a magneto-optical recording medium with little variation in N.

[Prior art and its problems] In recent years, magneto-optical recording media have been widely used for large-capacity data files and the like as media readable by laser light.

A magneto-optical recording medium is a form in which a thin film of a magneto-optical recording layer consisting of a dielectric protective layer and a recording layer is formed on a transparent substrate such as resin such as polycarbonate or glass by a vacuum film forming method such as sputtering. is common.

The recording layer includes Tb, Nd, Dy, and Gd.
Thin films of amorphous alloys containing rare earth metals such as Fe, Co, and other transition metals are used.

Furthermore, a thin film of dielectric protective layer is usually provided to protect the recording layer and enhance its properties.

In order to improve the sensitivity and C/N of the magneto-optical recording layer, when reading from the substrate side, the structure of the magneto-optical recording layer includes a first dielectric protective layer, a recording layer and a second dielectric layer. A magneto-optical recording layer with a so-called three-layer structure is used in which protective layers are formed in this order and the Kerr rotation angle is enhanced by utilizing repeated interference of light in the first dielectric protective layer.

In addition, in order to improve the bit shape and further increase the C/N, a magneto-optical film with an equi-reflective film structure is used, in which a thin film of a metal reflective layer is provided on the top layer of the magneto-optical recording layer with the 3N structure. Recording media are disclosed in JP-A-55-87332, JP-A-57-120253, and the like.

On the other hand, the Kerr effect causes rotation of the plane of polarization (Kerr rotation angle) and generally causes ellipseization.

This is the phase difference φ when light is reflected by a magneto-optical recording medium.
This is because

When a phase difference occurs, the carrier output decreases, causing a problem that the C/N ratio decreases.

Phase difference occurs not only when light is reflected by a magneto-optical recording medium, but also in the pickup optical system of a drive.

That is, the pickup has a reflective optical system such as a 45-degree mirror or beam splitter that guides the reflected light from the magneto-optical recording medium, and this reflective surface is usually made of a multilayer dielectric film and produces a phase difference. This is a contributing factor.

A further problem is that the phase difference δ of the pickup optical system is
There is a problem in that there is a large individual difference in C/N, and even if the same magneto-optical recording medium is used, the C/N obtained by each drive differs and varies.

The larger the phase difference Φ of the magneto-optical recording medium, the larger the variation in C/N due to the drive.

In other words, the optical system phase difference δ of the pickup generally oscillates around 0 degrees, but the phase difference φ of the magneto-optical recording medium is 0 degrees.
The closer the angle is, the less affected by individual differences in the pickup optical system.

Therefore, reducing the phase difference φ caused by the magneto-optical recording medium is an important issue in reducing the problem of C/N variation depending on the drive.

However, no effective means for this purpose has been proposed.

[Problems to be Solved by the Invention] The present invention has been made in view of the problems of the prior art, and aims to provide a magneto-optical recording medium in which the problem of C/N fluctuation depending on the drive is alleviated. The purpose is

Another object of the present invention is to provide a magneto-optical recording medium that has good sensitivity and has a small dependence of sensitivity on the number of disk rotations, with no difference in sensitivity caused by the drive.

Another object is to provide a magneto-optical recording medium with excellent durability.

[Means for Solving the Problems] The object of the present invention is to provide magneto-optical recording in which a first dielectric protective layer, a recording layer, a second dielectric protective layer and a metal reflective layer are formed in this order on a substrate. In a magneto-optical recording medium having a layer,
The thickness of the first dielectric protective layer is 950 to 1300A,
A magneto-optical recording medium characterized in that the recording layer has a thickness of 200 to 400 Å, the second dielectric storage layer has a thickness of 100 to 3 ooA, and the metal reflective layer has a thickness of 200 to 800 Å. achieved.

In the magneto-optical recording medium of the present invention, the magneto-optical recording layer has a four-layer structure of the first dielectric protective layer, the recording layer, the second dielectric protective layer and the metal reflective layer, and the film thickness of each layer is By setting it within a specific range, the absolute value of the phase difference due to the rotation of the polarization plane of the reflected light can be reduced to 15 degrees or less, making it difficult for polarization to become elliptical and preventing a drop in carrier output. .

Therefore, it is less susceptible to the effects of individual differences among drives, and the variation in C/H between drives is reduced.

Furthermore, the fluctuation in sensitivity due to the number of disk rotations is also small.

Furthermore, the durability is also relatively excellent.

Generally, the reflected light from the magneto-optical recording layer is caused by the Kerr effect.
Rotation and ellipticalization of the plane of polarization occur.

If the amplitude reflectance of the component with the polarization plane in the direction of the incident light is rXl, and the amplitude reflectance of the component perpendicular to it is ry, then rx=l rx l exp (iφ me) ry = l
It can be expressed as ry l exp (iφy).

Here, if the phase difference of the reflected light is Φ, then Φ = Φy - φ×, and if tanα = l rx I/I ry l, the Kerr rotation angle (θk) and Kerr ellipticity (ηk) are ja
n(2θk)=jan (2(X)CO8(φ)j a
n (2ηk)= tan (2a) sin
It can be expressed as (φ).

Therefore, an increase in the phase difference Φ of the magneto-optical recording medium results in a decrease in the Kerr rotation angle.

On the other hand, a pickup, which is essential for magneto-optical recording media, generally includes a 45-degree mirror in the optical path that guides the reflected light from the magneto-optical recording medium.
It has a reflective optical system like a beam splitter.

These reflective surfaces generate a phase difference δ between the P-polarized light and the S-polarized light (corresponding to the polarized light in the X and y directions of the light reflected from the magneto-optical recording medium). Then, the Kerr rotation angle 0 and Kerr ellipticity H of the finally received light are jan20=jan (2(X)cos (Φ-δ)t
It can be expressed as an2H=tan (2a)s in (Φ-δ).

In FIG. 1, which shows a graph of the change in C/N due to the phase difference δ of the pickup optical system, magneto-optical recording medium a has a phase difference φ of almost 0 for pickups A, B, and C, which have different phase differences δ. As for the difference in C/N between pickups, the decrease in C/N is slight and the difference in C/N between pickups is small. However, in magneto-optical recording media with a large phase difference φ, in pickup C, Φ and δ cancel each other out, so there is almost no drop in C/N, but in pickup B, Φ and δ are added together, resulting in
/N decrease is large.

After all, since the optical system phase difference δ of the pickup usually swings around 0 degrees, if the phase difference Φ of the magneto-optical recording medium is also placed close to 0 degrees, it will be less affected by individual differences in the pickup.

In the magneto-optical recording medium of the present invention, the C/N fluctuation caused by the drive is reduced by reducing the phase difference of the magneto-optical recording layer.

In the magneto-optical recording medium of the present invention, by specifying the film thickness of the first dielectric protective layer in the range of 950 to 1300, the film thickness of the magneto-optical recording layer can be adjusted to the phase difference of the reflected light. Fluctuations due to changes can be reduced, and the characteristics are stabilized.

The magneto-optical recording medium of the present invention has a first dielectric protective layer, a recording layer, a second dielectric protective layer and a metal reflective layer formed on a transparent resin substrate such as glass or polycarbonate by a vacuum film forming method such as a sputtering method. A magneto-optical recording layer having a 4N configuration is formed by sequentially depositing thin films in this order.

The thickness of the recording layer is 200 to 40 OA.

If the film thickness is too small, the durability will decrease, if the film thickness is too large, the phase difference of the magneto-optical recording layer will become large, and if the film thickness is too small, the durability will deteriorate, which poses a problem.

The second dielectric protective layer has a thickness of 100 to 300A.

If the film thickness is too small, the sensitivity will decrease, and if the film thickness is too large, the durability will decrease or the sensitivity will vary greatly depending on the rotational speed of the magneto-optical recording medium, which poses problems.

The material for the thin film of the metal reflective layer of the magneto-optical recording medium of the present invention is preferably At, A, or U (gold) from the viewpoint of reflectance, and from the viewpoint of cost, A1 alone or an alloy thereof is preferred. . Furthermore, in order to improve the weather resistance of the magneto-optical recording layer, an alloy of A1 and Ta or TI is desirable.

The thickness of the metal reflective layer is preferably 200 to 800 Å. If the film thickness is too small, the absolute value of the phase difference will become large, and if it is too large, the heat capacity will become large.
This is not preferable because it causes a decrease in sensitivity, an increase in material cost, and an increase in manufacturing process time.

As described above, in the magneto-optical recording medium of the present invention, 4
By setting the film thickness of each layer constituting the magneto-optical recording layer in a specific range and combining them, the phase difference of the reflected light from the magneto-optical recording layer can be reduced, and the C/N by the drive can be reduced.
This results in improved sensitivity, reduced rotational speed dependence, and excellent durability.

As the recording layer of the magneto-optical recording layer of the magneto-optical recording medium of the present invention, thin films of various oxides and metals can be used. For example, MnB i , MnA 1Ge, MnC
Crystalline materials such as uB1, GdIC.

Single crystal materials such as BiSmErGaIG, B1SmYbCoGelG2, as well as GdCo, GdFe, TbFe
, DyFe, GdFeB1. GdTbFe, GdFeC
It is a thin film using an amorphous material such as TbFeCo, TbFeNi, or the like. Among these, a recording layer mainly composed of rare earth metals or transition metals is preferable in terms of sensitivity, C/N, etc., and an amorphous alloy of TbFeCoCr is most preferable since it has particularly good weather resistance.

Thin films of the first dielectric protective layer and the second dielectric protective layer are provided adjacent to and above and below the recording layer. A first dielectric protective layer having a car-enhancing effect on the recording layer is provided directly above the substrate, and a second dielectric protective layer is further provided as a protective layer for the recording layer on the recording layer provided thereon. form.

Examples of materials for the first dielectric protective layer and the second dielectric protective layer that can be used in the present invention include Siox
, SiNx, AlNx, and ZnS, dielectrics such as oxides, nitrides, and sulfides can be used. Among these, Si nitride, A1 nitride, or a mixture thereof is most preferred from the viewpoint of optical properties and protective function.

Further, it is preferable that the first dielectric protective layer and the second dielectric protective layer have a refractive index of 2.0 to 2.3.

The thin films of each layer constituting the magneto-optical recording layer described above are formed by a vacuum film forming method such as a sputtering method, an ion blating method, or a vacuum evaporation method. Among them, the sputtering method is the best, and the magnetron sputtering method and the like are used.

Materials for the substrate of the magneto-optical recording medium of the present invention include polycarbonate, polymethyl methacrylate, epoxy, glass, etc., but polycarbonate and polymethyl methacrylate exhibit the characteristics of the optical recording medium of the present invention most effectively. , a resin substrate such as epoxy.

Among the resin substrates, polycarbonate substrates have advantages such as low water absorption and high glass transition temperature, and are preferably used in the optical recording medium of the present invention.

The top and side surfaces of the magneto-optical recording layer of the magneto-optical recording medium of the present invention can also be covered with an organic resin protective layer made of an ultraviolet curable resin or the like.

Alternatively, a double-sided recording type magneto-optical recording medium can be obtained by bonding the substrates with the surface without the magneto-optical recording layer facing outward via an adhesive layer such as a hot-melt resin.

[Effects of the Invention] In the magneto-optical recording medium of the present invention, the magneto-optical recording layer provided on the substrate is formed by forming the first dielectric protective layer, the recording layer, the second dielectric protective layer and the metal reflective layer in this order. The first dielectric protective layer has a four-layer structure, and the thickness of each layer is 950 mm.
The recording layer is 200 to 400A, the second dielectric protective layer is 100 to 300A, and the metal reflective layer is 20A to 1300A.
By specifying the range from 0 to 800 A, the phase difference of the reflected light can be reduced, the polarization plane can be prevented from becoming elliptical, and the variation in C/N due to the drive can be suppressed, and the sensitivity can be improved and the sensitivity can be improved. The rotation speed dependence can also be reduced.

The novel effects of the magneto-optical recording medium of the present invention will be further clarified by the following Examples and Comparative Examples.

[Example-1: Diameter 130 mm with guide groove provided on one side by injection molding
A magneto-optical recording layer was formed on the surface of a polycarbonate substrate having a thickness of 1.2 mrn, on which the guide groove was provided, by the following procedure.

The substrate was set on a rotating substrate holder of a sputtering device, and the film forming chamber of the sputtering device was heated to an argon gas pressure of 1 m.
Create an atmosphere of mTorr and place 1. By applying OKW RF power and using magnetron sputtering method,
A thin film of 950A SiNx as the first dielectric protective layer,
On top of that is a 300A T b Fe as a magneto-optical recording layer.
A thin film of Co Cs- was formed, and then a thin film of SiNx of 2 00A was applied as a second dielectric protective layer on top of that, and finally a thin film of SiN
A thin film of AlTa alloy having a of 2 atomic % was formed as a metal reflective layer to a thickness of 350 Å to form a magneto-optical recording layer.

Next, a coating liquid of an ultraviolet curable resin is applied to the top and side surfaces of the magneto-optical recording layer at 3000 rpm using a spin code method.
m, applied for 20 seconds, irradiation intensity 100mW/c
Cured by irradiating ultraviolet rays of m for 1 minute, and
An organic resin protective layer with a thickness of . As the ultraviolet curing resin, #5D-17 manufactured by Dainippon Ink Co., Ltd. was used.

Two samples of the magneto-optical recording medium prepared under the above conditions were prepared, the surface of the substrate without the magneto-optical recording layer facing outward,
On the organic resin protective layer, hot melt adhesive #XW-13 manufactured by Toagosei Kagaku Co., Ltd. was melted at 130°C and applied to a thickness of 10 μm using a roll coater, followed by pressure bonding. A sample of a double-sided recording type magneto-optical recording medium was obtained.

[Example 2] A sample of a double-sided recording type magneto-optical recording medium was obtained under the same conditions as in Example 1, except that the thickness of the first dielectric protective layer was 1100A.

[Example 31 A sample of a double-sided recording type magneto-optical recording medium was obtained under the same conditions as Example 1 except that the thickness of the first dielectric protective layer was 1300A.

Comparative Example 1 A sample of a double-sided recording type magneto-optical recording medium was obtained under the same conditions as in Example 1, except that the thickness of the first dielectric protective layer was 90 OA.

[Comparative Example 2] A sample of a double-sided recording type magneto-optical recording medium was obtained under the same conditions as in Example 1 except that the thickness of the first dielectric protective layer was 1350 mm.

Regarding the sample of the magneto-optical recording medium obtained as described above, the phase difference φ indicating the ellipticalization of the polarization of the reflected light, the sensitivity, the C/N, and the rotation speed dependence of the sensitivity were evaluated under the following measurement conditions. .

Phase difference φ・: In the measurement system whose main parts are shown in Figure 2 ζ, the emitted light from the semiconductor laser 1 is
The light was focused onto the magneto-optical recording medium 3 by using the following method.

(At this time, the reflected light 4 from the magneto-optical recording medium 3 undergoes rotation and ellipticalization of the plane of polarization due to the Kerr effect.

This ovalization occurs due to the phase difference between the amplitude components x, ry that are resolved into the incident light polarization plane and the plane orthogonal thereto. ) A Babinet Soleil compensator is placed in the optical path of the reflected light 4 in alignment with the quinary phase axis direction of the X or Y axis, r x, r
The phase amount between y was compensated.

Then, the light passing through the Babinet-Soleil compensator 5 is linearly polarized so that the amount of light passing through the analyzer 6 set at the extinction light position is minimized, and the phase amount generated in the magneto-optical recording medium 3 is calculated. Compensated. The amount of compensation was measured and used as a measured value of the phase difference Φ of the magneto-optical recording medium.

Sensitivity: The rotation speed of the magneto-optical recording drive is 180 Orp.
m, and the measured value of the write power (Pw
) was taken as the sensitivity.

C/N': Measured using a laser beam with a wavelength of 780 nm and a carrier frequency of 3.71 MHz at a drive rotation speed of 1800 rprn. Note that the phase difference of the optical pickup of the drive was adjusted to be zero.

Rotational speed dependence of sensitivity: Rotational speed 1800 rpm
The difference (ΔPw) between the sensitivity when the rotation speed was 2400 rprn and the sensitivity when the rotation speed was 2400 rprn was determined.

The measurement results are shown in Table 1.

Table 1 [Example-4 Example 2 except that the thickness of the recording layer was 20OA]
A sample of a double-sided recording type magneto-optical recording medium was prepared under the same conditions as described above.

[Example-5] Example-2 except that the thickness of the recording layer was 40OA.
A sample of a double-sided recording type magneto-optical recording medium was prepared under the same conditions as described above.

[Comparative Example 3] Example 2 except that the thickness of the recording layer was 15OA.
A sample of a double-sided recording type magneto-optical recording medium was prepared under the same conditions as described above.

[Comparative Example-4 Example-2 except that the thickness of the recording layer was 45oX
A sample of a double-sided recording type magneto-optical recording medium was prepared under the same conditions as described above.

Table 2 shows the results of measuring each characteristic of the magneto-optical recording medium samples obtained as described above.

Table 2 [Example-6] Example-2 except that the thickness of the recording layer was 10OA
A sample of a double-sided recording type magneto-optical recording medium was prepared under the same conditions as described above.

[Example 7] Except that the thickness of the second dielectric protective layer was 300A,
A sample of a double-sided recording type magneto-optical recording medium was prepared under the same conditions as in Example-2.

[Comparative Example-5] A sample of a double-sided recording type magneto-optical recording medium was prepared under the same conditions as in Example-2 except that the thickness of the second dielectric protective layer was 75A.

Comparative Example-4] Except that the film thickness of the second dielectric protective layer was 35OA,
A sample of a double-sided recording type magneto-optical recording medium was prepared under the same conditions as in Example-2.

Table 3 shows the results of measuring each characteristic of the magneto-optical recording medium samples obtained as described above.

Table 3 [Example-8] A sample of a double-sided recording type magneto-optical recording medium was prepared under the same conditions as in Example-2 except that the thickness of the metal reflective layer was 20OA.

Example 9] A sample of a double-sided recording type magneto-optical recording medium was prepared under the same conditions as Example 2, except that the thickness of the metal reflective layer was 25 OA.

[Example 10] A sample of a double-sided recording type magneto-optical recording medium was prepared under the same conditions as in Example 2, except that the thickness of the metal reflective layer was 45 OA.

[Example 11] A sample of a double-sided recording type magneto-optical recording medium was prepared under the same conditions as in Example 2, except that the thickness of the metal reflective layer was 80 OA.

[Comparative Example 7] A sample of a double-sided recording type magneto-optical recording medium was prepared under the same conditions as in Example 2, except that the thickness of the metal reflective layer was increased to 15oU.

Comparative Example 8 A sample of a double-sided recording type magneto-optical recording medium was prepared under the same conditions as in Example 2, except that the thickness of the metal reflective layer was 850.

Table 4 shows the results of measuring each characteristic of the magneto-optical recording medium samples obtained as described above.

Table 4 [Example-12] The film thickness of the second dielectric protective layer was 10OA, and the composition of the metal reflective layer was an Al-T1 alloy containing 3 at% Ti, and the film thickness was 50OA. Except for this, a sample of a magneto-optical recording medium was prepared under the same conditions as in Example-2.

[Example 13] A sample of a magneto-optical recording medium was prepared under the same conditions as in Example 2, except that the thickness of the second dielectric protective layer was 20 OA and the thickness of the metal reflective layer was 50 OA. Created.

[Example 14] A sample of a magneto-optical recording medium was prepared under the same conditions as in Example 2, except that the second dielectric protective layer had a thickness of 30 OA and the metal reflective layer had a thickness of 50 OA. Created.

[Comparative Example-9] A sample of a magneto-optical recording medium was prepared under the same conditions as in Example-2, except that the thickness of the second dielectric protective layer was 75A, and the thickness of the metal reflective layer was 500A. It was created.

[Comparative Example-10] A sample of a magneto-optical recording medium was prepared under the same conditions as in Example-2, except that the thickness of the second dielectric protective layer was 35OA, and the thickness of the metal reflective layer was 50OA. Created.

Table 5 shows the results of measuring each characteristic of the magneto-optical recording medium samples obtained as described above.

Table 5

[Brief explanation of the drawing]

FIG. 1 is a graph showing the amount of decrease in C/N of the magneto-optical recording medium due to the phase difference δ of the pickup optical system. FIG. 2 is a schematic diagram showing the main parts of a measurement system for phase difference Φ caused by a magneto-optical recording medium. 1... Semiconductor laser 2... Collimating lens 3... Magneto-optical recording medium 4... Reflected light from the magneto-optical recording medium 5...
Babinet Soleil Compensation Board 6 ・・・ Analyzer ＼ l ＼ l Procedural Amendment Form

Claims (7)

[Claims] (1) In a magneto-optical recording medium having a magneto-optical recording layer in which a first dielectric protective layer, a recording layer, a second dielectric protective layer and a metal reflective layer are formed in this order on a substrate, the first The dielectric protective layer has a thickness of 950 to 1300 Å, the recording layer has a thickness of 200 to 400 Å, the second dielectric protective layer has a thickness of 100 to 300 Å, and the metal reflective layer has a thickness of 20 Å.
A magneto-optical recording medium characterized by having a thickness of 0 to 800 Å. (2) The magneto-optical recording medium according to claim 1, wherein the metal reflective layer is a thin film of an Al (aluminum) alloy. (3) The magneto-optical recording medium according to claim 1, wherein the metal reflective layer is a thin film of an Al alloy containing Ta (tantalum) and/or Ti (titanium). (4) The magneto-optical recording medium according to claim 1, wherein the recording layer is a thin film of an amorphous alloy made of a rare earth metal and a transition metal. (5) The magneto-optical recording medium according to claim 1, wherein the recording layer is a thin film of an amorphous alloy of TbFeCoCr. (6) The magneto-optical recording medium according to claim 1, wherein the first dielectric protective layer and the second dielectric protective layer are Si nitride, Al nitride, or a mixture thereof. (7) The magneto-optical recording medium according to any one of claims 1, 2, and 3, wherein the metal reflective layer has a thickness of 250 to 450 Å.