JPH087365A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To suppress the deterioration of groove characteristics and servo characteristics which is caused by the thickness reduction of a medium and repeated erasing and recording operations. CONSTITUTION:A first dielectric layer (Anm), a magneto-optical recording layer (Bnm) made of rare-earth metal and transition metal, a second dielectric layer (Cnm) and a reflective film layer (Dnm) are provided on a substrate. The layer thicknesses A, B, C and D are in ranges of 25-33nm, 13-17nm, 20-35 m and 60-100nm respectively. The first and second dielectric layers are made of Si and N. The reflective film layer is made of A1 containing 1.0-2.5wt.% of Cr.

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. More specifically, it relates to a magneto-optical recording medium having excellent productivity and excellent repetitive recording property.

[0002]

2. Description of the Related Art Among optical recording media, phase change type, photochromic type, magneto-optical type, etc. are known as rewritable types capable of writing and erasing. Among these rewritable types, the magneto-optical type has a feature that it is excellent in writing speed and repetition resistance. In recording on a magneto-optical recording medium, converged laser light is irradiated onto the medium to raise the temperature of the magneto-optical recording film to near the Curie point and apply a magnetic field to form an inverted magnetic domain.

Generally, such a magneto-optical recording medium has the following structure. Substrate / first dielectric layer (80
˜120 nm) / magneto-optical recording layer (20-30 nm) / second dielectric layer (30-50 nm) / reflection film (40-60 n)
m) is the film thickness configuration. The first dielectric and the second dielectric are S
In many cases, iN, SiC, the magneto-optical recording layer is made of TbFeCo, and the reflective film is made of Al.

The magneto-optical recording medium having such a conventional structure is
Usually, the first dielectric layer to the reflective film are formed by an in-line type sputtering apparatus composed of a plurality of chambers, but there is a problem that productivity is low because the first dielectric layer is thick.

However, when the thickness of the first dielectric layer is reduced in order to improve the productivity, there arises a problem that the groove characteristic and the servo characteristic of the medium are deteriorated by the continuous erasing / recording operation. It is considered that this is because the heat accumulated in the magneto-optical recording layer by the laser irradiation is transferred to the surface of the resin substrate and the groove shape of several tens nm is changed.

[0006]

In view of the above situation, the inventors of the present invention have made extensive studies and found that the first dielectric layer has a thinner structure than the conventional magneto-optical recording medium. Even with respect to the medium, a medium having little deterioration in groove characteristics and servo characteristics due to repeated erasure / reproduction was found, and the present invention was completed.

That is, the present invention provides at least a first substrate on a substrate.
A dielectric layer (film thickness: Anm), a magneto-optical recording layer (film thickness: Bnm) made of a rare earth metal and a transition metal, a second dielectric layer (film thickness: Cnm) and a reflective film layer (film thickness: Dnm). In the magneto-optical recording medium, the film thicknesses A to D are each 25 n
m ≦ A ≦ 33 nm, 13 nm ≦ B ≦ 17 nm, 20 nm
≦ C ≦ 35 nm, 60 nm ≦ D ≦ 100 nm, the first dielectric layer and the second dielectric layer are composed of silicon and nitrogen, and the reflective film layer is 1.0 to 2.5 wt% chromium. And a magneto-optical recording medium characterized by being composed of aluminum containing

The present invention will be described in detail below.

As the substrate used in the present invention, it is possible to use a transparent material such as glass, polycarbonate resin, acrylic resin or olefin resin.

The first dielectric layer and the second dielectric layer used in the present invention are composed of silicon and nitrogen, and if the film thicknesses are Anm and Cnm, respectively, 25 nm ≦
It has a film thickness of A ≦ 33 nm and 20 nm ≦ C ≦ 35 nm. The thickness of the first dielectric layer is preferably 25 nm ≦ A ≦ 30 nm from the viewpoint of substantially preventing heat transfer to the substrate side and thinning the medium. Such a dielectric layer can be obtained by sputtering a silicon target or a silicon nitride target under a nitrogen atmosphere.

The magneto-optical recording layer used in the present invention comprises a rare earth metal and a transition metal. Tb and D as rare earth metals
Transition metals such as y and Gd are Fe, Co, and Ni.
Etc. can be illustrated, and one or more kinds of each metal may be combined. Specifically, TbFe, TbC
o, TbFeCo, DyCo, DyFeCo, GdF
e, GdFeCo, TbFeNi, GdTbFeCo, etc. can be mentioned. Furthermore, in order to improve the corrosion resistance of the magneto-optical recording layer, Cr, Ti, Al, Ta, M
One or more metals such as o, Bi and Cu may be contained.

Such a magneto-optical recording layer can be obtained by sputtering from a rare earth metal target and a transition metal target, for example. Thickness of magneto-optical recording layer (B
nm) is preferably 13 nm ≦ B ≦ 17 nm.

The reflective film layer used in the present invention has a thickness of 1.0-2.
It is made of aluminum containing 5% by weight of chromium, and the film thickness Dnm is 60 nm ≦ D ≦ 100 nm. The material and the thickness of the reflective film layer are related to the thickness of the first dielectric layer, so that it is possible to obtain the same recording / reproducing characteristics as before without deterioration of groove characteristics and servo characteristics during repeated erasing / recording. Will be decided. The thickness is preferably 80 to 100 nm from the viewpoint that the resistance to repeated erasure / recording increases. When the film thickness of the reflective film layer is less than 60 nm, the groove characteristics and the servo characteristics may be deteriorated, while the film thickness is 100 nm.
If it exceeds, the effect is saturated and only the increase of the recording power is caused, so that it may not be preferable as the characteristic of the magneto-optical recording medium. The chromium content is 1.0 to 2.
0% by weight is preferable, and for the purpose of enhancing corrosion resistance, A
A trace amount of a metal such as g, Ti, Mo or Ta may be contained.

In the magneto-optical recording medium of the present invention, a protective coat layer may be provided on the reflective film layer or a hard coat layer may be provided on the anti-dielectric layer side of the substrate, if necessary. You may use it as it is or by pasting it together.

[0015]

According to the present invention, even if the first dielectric is thinner than that of the conventional structure, the same optical characteristics and recording / reproducing characteristics as those of the conventional structure can be obtained. By specifying it, it is possible to suppress deterioration of groove characteristics and servo characteristics due to repeated erasure / recording, which is a drawback of a medium having a thin first dielectric film. Further, even if the reflective film layer is thick, the film forming rate of the reflective film layer is higher than the film forming rate of the dielectric layer, and therefore the productivity is not reduced. Further, the increase in recording power due to the thickening of the reflection film layer can be controlled by specifying the composition of the reflection film, and the corrosion resistance is excellent.

[0016]

【Example】

Examples 1 to 12 Magneto-optical recording was performed on a polycarbonate substrate having a diameter of 86 mm having a guide groove with a pitch of 1.6 μm by a sputtering device with a first dielectric layer SiN, and then by binary sputtering using Tb and FeCo targets. Layer, second dielectric layer Si
A reflection film layer of N, Al _98.5 Cr _1.5 (wt%) was formed in the configuration shown in Table 1. The composition of the magneto-optical recording layer is Tb data - target and FeCo data - to adjust the power supplied to the target, Tb ₁₉
(Fe ₉₂ Co ₈ ) ₈₁ at%.

The recording / reproducing characteristics of these samples as recording media were examined. The measuring device is a magneto-optical disc measuring device having a wavelength of 780 nm and an NA of 0.53. The measuring conditions are a measurement radius of 30 mm, a disc rotation speed of 1800 rpm, a recording / reproducing frequency of 3.7 MHz, and an applied magnetic field of 200 at the time of recording.
The CNR was obtained by changing the recording laser power as Oe. Erasure was performed with an applied magnetic field of -300 Oe and an erasing light power of 9.0 mW prior to recording.

Further, repeated erasure / recording characteristics of these samples as a recording medium were examined. The measuring device has a wavelength of 78
Using a magneto-optical disk measuring device with 0 nm and NA of 0.53, the measurement conditions are as follows: measurement radius 30 mm, disk rotation speed 18
Repeated erasure / recording was performed at 00 rpm, a recording / reproducing frequency of 5.0 MHz, an erasing power of 12 mW, and a recording power of 12 mW. When the groove signal and the servo signal of the track subjected to the repeated test were observed, no change was observed in the medium having the conventional structure as compared with that before the test.

Table 1 shows the amount of change in tracking servo, the optimum recording power, and the CNR at the optimum recording power. In addition,
The amount of change in the tracking servo is indicated by a value obtained by dividing the amplitude of the tracking error signal after the repeated test by the amplitude before the test, and the optimum recording power has the maximum difference between the carrier level and the second harmonic. Powerful.

[0020]

[Table 1]

Comparative Examples 1 to 7 Magneto-optical recording media having the structures shown in Table 2 were prepared in the same manner as in Example 1 except that the film thickness was changed. The amount of change in the tracking servo of these magneto-optical recording media was measured in the same manner as in Example 1, and the results are also shown in Table 2. In the medium having the thin structure (20 nm) of the first dielectric layer, the groove characteristics and the servo characteristics were changed.

[0022]

[Table 2]

Comparative Examples 8 to 9 Magneto-optical recording media having the structures shown in Table 3 were prepared in the same manner as in Example 1 except that the film thickness was changed. The tracking servo change amount, the optimum recording power, and the CNR at the optimum recording power of these magneto-optical recording media were measured in the same manner as in Example 1, and the results are also shown in Table 3.

[0024]

[Table 3]

From the above, in the thin structure of the first dielectric layer, the heat accumulated in the magneto-optical recording layer at the time of erasing / recording is transmitted to the substrate, and the shape of the groove, which is a minute structure of the substrate, changes due to repeated erasing / recording. However, it is considered that by increasing the film thickness of the reflective film, heat conduction in the substrate direction is reduced and deterioration due to repeated erasure / recording can be suppressed.

Further, the change of the tracking servo is 1.2
The change of the error rate of the samples exceeding 50% exceeded 50%.
The change from about 1.2 to 1.15 is about 20%,
For samples from 1.15 to 1.1 the change is about 10%,
Below 1.1, the change was about 5%, and below 1.05 no change was observed.

When the thickness of the second dielectric layer is 35 nm, there is an effect of thickening the reflection film to reduce the change of the tracking servo, but when it is 40 nm, such an effect can be obtained even if the reflection film thickness is increased. Absent. It is considered that this is because the heat conduction from the magneto-optical recording layer to the reflective film becomes insufficient.

When the reflection film thickness is 120 nm, the suppression of change is saturated as compared with 100 nm, and even if the reflection film thickness is set to exceed 100 nm, the effect of improving the repeated erasure / recording is not obtained. If it exceeds 100 nm, the recording power only increases.

Example 13 A sample in which the thickness of the reflection film of Al not containing Cr was changed was manufactured according to Example 1. The sample was composed of a polycarbonate substrate / first dielectric layer (25 nm) / TbFeCo layer (1
5 nm) / second dielectric layer (35 nm) / Al reflective film. The thickness of the Al reflection film is 50, 60, 80, 100 nm
And The recording power and CNR of the recording and reproducing characteristics of these samples were measured in the same manner as in Example 1. The CNR of 45 dB or more was obtained for each sample. The recording power is shown in FIG.
The recording power has a large value of 6.0 mW even when the Al film thickness is 50 nm, and the increase of the recording power due to the film thickness increase is about 1.0 mW at the film thickness of 20 nm. As described above, when Al containing no Cr is used as the reflective film, the recording power is large and the increase in recording power due to the increase in the film thickness is large as compared with the case of using Al containing Cr.
It is disadvantageous to increase the film thickness and improve the resistance to repeated erasure / recording tests.

Example 14 Samples having different Cr contents and film thicknesses were manufactured according to Example 1. The composition of the sample is a polycarbonate substrate / first dielectric layer (25 nm) / TbFeCo layer (15 nm) / second
Dielectric layer (35 nm) / reflection film.

The reflective film is made of Al ₉₉ Cr ₁ , Al ₉₈ Cr ₂ , Al
There are four kinds of _97.5 Cr _2.5 and Al ₉₇ Cr ₃ (wt%), and the film thicknesses are 50, 60, 80, 100 and 120 nm, respectively.

Repeated erasing / recording tests were performed on these samples under the same conditions as in Example 1. FIG. 2 shows the tracking error change after the repeated erasure / recording test.

80 for a sample with a Cr content of 2.5 (wt%)
In the samples of 1 wt% and 2 wt%, the change in tracking error is 1.15 or less at a thickness of 60 nm or more, and 1.1 or less at 80 nm or more. On the other hand, in the sample having a Cr content of 3 wt%, the tracking error change cannot be sufficiently reduced even if the film thickness is increased.

[Brief description of drawings]

FIG. 1 is a diagram showing a reflection film thickness dependence of an optimum recording power of a sample using an Al reflection film.

FIG. 2 is a diagram showing a tracking error change when a material and a film thickness of an AlCr reflective film are changed.

Claims (1)

[Claims] 1. A substrate having at least a first dielectric layer (film thickness: Anm), a magneto-optical recording layer (film thickness: Bnm) made of a rare earth metal and a transition metal, and a second dielectric layer (film thickness: Cnm).
And a reflective film layer (film thickness: Dnm), the film thicknesses A to D are 25 nm ≦ A ≦ 33 nm and 13 n, respectively.
m ≦ B ≦ 17 nm, 20 nm ≦ C ≦ 35 nm, 60 nm
≦ D ≦ 100 nm, the first dielectric layer and the second dielectric layer are composed of silicon and nitrogen, and the reflective film layer is composed of aluminum containing 1.0 to 2.5% by weight of chromium. A magneto-optical recording medium characterized by the following.