JPH04310648A - Magneto-optical disk - Google Patents

Abstract

PURPOSE:To obtain a high-C/N magneto-optical disk by controlling the thickness of each layer of the multilayer film constituting a record holding film so that the phase difference generated in the record holding film is compensated by the phase difference generated in a substrate. CONSTITUTION:A ceramic layer 2, a recording layer 3, a ceramic layer 4 and a reflecting layer 5 are laminated in this order on a transparent polycarbonate substrate 1 to obtain a magneto-optical disk. The thickness of the layers 2, 3, 4 and 5 constituting the multilayer film is controlled so that the phase difference generated in the record holding film is compensated by the phase difference generated in the substrate 1. Accordingly, the thickness d2 of the ceramic layer 2 is adjusted to 600mum, the thickness d3 of the recording layer 3 to 200mum, the thickness d4 of the ceramic layer 4 to 110mum and the thickness d5 of the reflecting layer 5 to 600mum for example, to obtain a high C/N. Consequently, a high-C/N magneto-optical disk without any phase difference is obtained.

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 on which information is recorded, reproduced and erased using a laser beam.

0002

[Prior Art] Conventionally, the structure of a recording holding film in a magneto-optical disk has been disclosed in Japanese Patent Application Laid-open No. 60-117436 and Japanese Patent Application Laid-open No. 56-1.
37537, a multilayer film is used to prevent oxidation of the recording layer, which is a magnetic thin film, to utilize the Faraday effect in addition to the Kerr effect, and to increase the apparent Kerr rotation angle by utilizing multiple reflections. They often have a membrane structure. When a magneto-optical disk has a multilayer structure like this, the phase difference (δk) between the incident linear polarization direction and the direction orthogonal to it depends on the characteristics of the recording layer and the optical characteristics of other films. occurs, and the reflected light often becomes elliptically polarized. Further, when a birefringent material (the phase difference due to substrate birefringence is δs) is used for the magneto-optical disk substrate, the reflected light is similarly elliptically polarized. Therefore, there is a problem in that the Kerr rotation angle is substantially reduced and the reproduced signal strength is reduced. This reduction in the reproduction signal strength is proportional to cos δ, where δ is the phase difference of the magneto-optical disk. However, δ=δk +δs.

As a method for correcting the above phase difference, a method using a Babinet-Soleil compensator is known. In addition, this Babinet-Soleil compensator has a complicated structure, is very expensive, and requires a lot of effort to adjust. A method using a board has been devised.

0004

[Problem to be Solved by the Invention] However, in the above-mentioned technology, when a plurality of magneto-optical disks are to be played back by a plurality of magneto-optical playback devices, the phase difference of each disk is corrected for each playback device. This necessitates adjustment for this purpose, which detracts from the advantage of the magneto-optical disk as a replaceable medium.

The present invention has been made in view of these conventional problems, and its object is to provide a magneto-optical disk free of phase differences that cause a reduction in reproduction signal strength.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention aims to adjust the film thickness structure of a multilayer film constituting a recording holding film of a magneto-optical disk to cancel out the phase difference due to birefringence of a transparent substrate. It is characterized by having a film thickness configuration of .

[0007]

[Operation] Phase difference (δk + δ
s) is published in 1990, Journal of the Japanese Society of Applied Magnetics, Vol. 14, No. 2.
As described in pages 175 to 178 of the issue, it is possible to measure by making the phase difference of the optical head of the magneto-optical reproducing device variable using a Babinet-Soleil compensator. By measuring the phase difference of the disk in two polarization directions, parallel and perpendicular to the recording track of the disk, δk and δs
It is possible to separate and measure the Here, δs
has a nearly constant value depending on the material of the disk substrate and the molding conditions, but it is very difficult to control this to 0°. However, it is relatively easy to control δs within a range of ±10°. On the other hand, δk is a value determined by the wavelength of the laser beam and the refractive index and film thickness of each layer of the multilayer film constituting the record-holding film. Therefore, by making the film thickness of each layer of the multilayer film of the recording holding film such that the value of δk cancels out the value of δs, that is, δk + δs = 0, it is possible to create a magneto-optical disk with no phase difference. It is possible to obtain

[0008]

EXAMPLES The present invention will be explained in detail below based on examples.

FIG. 1 is a side sectional view of a magneto-optical disk showing a first embodiment of the present invention. In FIG. 1, 1 is a polycarbonate substrate. 2 and 4 are AlSiN ceramic layers. 3 is a NdDyTbFeCo recording layer. 5
is a reflective layer made of AlTi. The polycarbonate substrate No. 1 had spiral tracking grooves and formatting pit rows formed at a pitch of 1.6 μm by injection molding. The ceramic layers 2 and 4 are Si
The film was formed by RF reaction magnetron sputtering using a sintered Al target and introducing a mixed gas of nitrogen and argon. 3 NdDyTbFe
The Co recording layer was formed by DC magnetron sputtering using an NdDyTbFeCo alloy target and introducing argon gas. 5 A
The lTi reflective film was formed by DC magnetron sputtering using an AlTi metal target and introducing argon gas.

[0010] In the following measurements, a laser beam having a wavelength of 830 nm was used, and the linearly polarized direction of the incident light was parallel to the tracking groove formed on the substrate. Further, the δs of all the disks manufactured below was approximately -7°. Also,
2 ceramic layer, 3 recording layer, 4 ceramic layer, 5
The film thicknesses of the reflective layers are d2, d3, d4, and d5, respectively.
far.

In FIG. 2, d2 and d5 are set to 600 Å,
d3 is set to 100 Å, 200 Å, 300 Å, and 400 Å, and d4 is varied from 10 Å to 800 Å for each d3.
The results of measuring the phase difference (δk) generated in the recording-holding film after manufacturing a magneto-optical disk in which the optical density was changed to Å are shown. In FIG. 2, d3, in which the value of δk can be varied within a range of ±10°, is 100 Å and 200 Å. However, when d3 is 100 Å, the value of δk is ±10°
d4 is in a narrow range of approximately 700 Å to 800 Å, and δk changes sharply as d4 changes, making it difficult to control the value of δk in manufacturing.

In FIG. 3, d3 and d5 are each 100 Å.
, 600 Å, d2 is 300 Å, 400 Å, 50
0 Å, 600 Å, and d4 for each d2
The results of fabricating magneto-optical disks with varying values of δk and measuring δk are shown below. In FIG. 3, the value of δk can be varied within a range of ±10°, and the values of δk that do not change sharply are those with d2 of 300 Å, 400 Å, and 500 Å. Therefore, d2, d3, d4, d
5 to 300 Å, 100 Å, 480 Å, and 600 Å, respectively.
or 400 Å, 100 Å, 500 Å, 600 Å, respectively
Å or respectively 500 Å, 100 Å, 570 Å, 60
By setting it to 0 Å, δk can be set to 7°, creating a magneto-optical disk (hereinafter abbreviated as disk) with no phase difference.
I was able to obtain.

In FIG. 4, d3 and d5 are each 200 Å.
, 600 Å, d2 is 500 Å, 1000 Å, 1
The results are shown in which δk was measured by manufacturing disks in which the thickness of the ceramic layer 4 was changed for each d2 of 500 Å and 2000 Å. As can be seen from FIG. 4, for all d2 values, the value of δk was variable within a range of ±10° and the change in the value of δk was not steep. Therefore, similarly to the above, by appropriately selecting d2 and d4, δk could be set to 7°, and a disk with no phase difference could be obtained.

In FIG. 5, d3 and d5 are each 300 Å.
, 600 Å, d2 is 500 Å, 1000 Å, 1
The results are shown in which δk was measured by manufacturing disks in which the thickness of the ceramic layer 4 was changed for each d2 of 500 Å and 2000 Å. In Figure 5, δk
The value of δk can be varied within a range of ±10°, and δk
The case where the change in the value of is not steep is the case where d2 is 1500 Å. Therefore, as above, d2, d3, d4
, d5 are respectively 1500 Å, 300 Å, 40 Å,
By setting the thickness to 600 Å, δk could be set to 7°, and a disk with no phase difference could be obtained.

In FIG. 6, d3 and d5 are each 400 Å.
, 600 Å, d2 is 500 Å, 1000 Å, 1
The results of measuring δk of disks prepared with d4 of 500 Å and 2000 Å and varying d4 with respect to d2 are shown below. As can be seen from Figure 6, in this case δk
The value was always negative, and the desired result could not be obtained.

From the above, it can be seen that d3 is 100 Å or more3
When the thickness was less than 00 Å, the value of δk could be controlled within a range of ±10° by appropriately selecting the film thicknesses 2 and 4.

Here, in FIG. 7, in order to compare a disk with a phase difference and a disk without a phase difference, d2 and d in FIG.
3, d4, and d5 as shown in Table 1, six types of disks, a, b, c, e, and f, were prepared with a radius of 30 mm and a rotation speed of 18 mm.
This figure shows the results of measuring the C/N when a recording signal of a single frequency of 3.7 MHz is reproduced at 00 rpm. As can be seen from FIG. 7, the highest C/N was obtained for disk c. Therefore, by setting the thickness of each layer of the record-holding film so that the phase differences generated between the record-holding film and the substrate cancel each other out, it is possible to obtain a disk with no phase difference and a high C/N. Ta.

[Table 1] Note that the present invention should not be considered limited to this example, and various changes are possible without departing from the gist of the present invention. For example, the material of each layer constituting the recording holding film may be SiN in addition to SiAlN as a ceramic layer.
In addition to NdDyTbFeCo, NdDyFeCo, Tb
FeCo, GdTbFe, etc., as a reflective layer, Al, A
There is no problem even if lTa or the like is used individually, and by combining the respective materials and appropriately selecting the film thickness of each layer, it was possible to obtain a disk with no phase difference.

Furthermore, even if the film thickness of the reflective layer changes, it hardly affects the value of δk, and by appropriately selecting the other film thicknesses of the other recording holding films, it is possible to obtain a disc with no phase difference. was completed.

It goes without saying that similar results can be obtained if the wavelength of the laser beam is, for example, 780 nm or 670 nm in addition to 830 nm.

[0020]

As explained above, according to the present invention, the thickness of each layer of the multilayer film constituting the record-holding film in a magneto-optical disk can be adjusted by changing the phase difference generated in the record-holding film to the phase difference generated in the substrate. A magneto-optical disk with no phase difference and a high C/N can be obtained by creating a film thickness configuration that cancels out the .

[Brief explanation of drawings]

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

[Fig. 2] Magneto-optical disks were fabricated with d2 and d5 set to 600 Å, d3 set to 100 Å, 200 Å, 300 Å, and 400 Å, and d4 varied from 10 Å to 800 Å for each d3, and the results of measuring δk are shown. FIG.

[Figure 3] d3 and d5 are 100 Å and 600 Å, respectively.
and d2 is 300 Å, 400 Å, 500 Å, 600
3 is a diagram showing the results of measuring δk of magneto-optical disks prepared with d4 varied with respect to each d2.

[Figure 4] d3 and d5 are 200 Å and 600 Å, respectively.
and d2 is 500 Å, 1000 Å, 1500 Å, 2
000 Å, magneto-optical disks were fabricated in which d4 was varied for each d2, and δk was measured.

[Figure 5] d3 and d5 are 300 Å and 600 Å, respectively.
and d2 is 500 Å, 1000 Å, 1500 Å, 2
000 Å, magneto-optical disks were fabricated in which d4 was varied for each d2, and δk was measured.

[Figure 6] d3 and d5 are 400 Å and 600 Å, respectively.
and d2 is 500 Å, 1000 Å, 1500 Å, 2
000 Å, magneto-optical disks were fabricated in which d4 was varied for each d2, and δk was measured.

[Figure 7] C due to the phase difference of the recording holding film of a magneto-optical disk
FIG. 3 is a diagram showing changes in the value of /N.

[Explanation of symbols]

1 Substrate made of polycarbonate 2 Ceramic layer 3 made of SiAlN NdDy
Recording layer 4 made of TbFeCo Ceramic layer 5 made of SiAlN Reflection layer made of AlTi

Claims (2)

[Claims] 1. In a magneto-optical disk having a record-holding film on a transparent substrate, the thickness of each layer of a multilayer film constituting the record-holding film is determined by determining the thickness of each layer when a laser beam used for reproduction is reflected on the record-holding film. A magneto-optical disk characterized in that the film thickness is such that a phase difference generated between a component in an incident linearly polarized direction and a direction orthogonal to the incident linearly polarized direction cancels out a phase difference generated in the transparent substrate. . 2. An optical device in which a ceramic layer, a magnetic thin film layer having an axis of easy magnetization perpendicular to the film surface, a ceramic layer, and a recording holding film consisting of a reflective layer are laminated in this order on a transparent substrate. In the magnetic disk, the thickness of the magnetic thin film layer is 100 Å or more and 300 Å or less, and the thickness of each layer constituting the record-holding film is such that the phase difference generated during reflection in the record-holding film is 2. The magneto-optical disk according to claim 1, wherein the magneto-optical disk has a film thickness of -10[deg.] or more and 10[deg.] or less.