JP2553581B2 - Magneto-optical memory media - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical memory medium having improved information recording characteristics and reliability.

[Prior Art] A magneto-optical memory using a rare earth-iron group amorphous alloy thin film does not have sufficient read characteristics, and various proposals have been made for improving it. There is an exchange-coupling double-layer film composed of a recording layer having good recording characteristics and a reading layer having good reading characteristics (for example, JP-A-57-78652). In this exchange-coupling bilayer film, the read layer has a high Curie temperature and a low Curie temperature at room temperature with respect to the recording layer.

Further, in order to ensure the reliability of the medium, both sides of the magnetic layer are covered with protective films. However, the conventional single-layer magnetic film has a high degree of compactness in order to prevent the coercive force from changing over time, and therefore has a high internal stress (mainly 100 kg /
(mm ² or more) A protective film is required, and such a protective film has also been used to protect the bilayer film.

[Problems to be Solved by the Invention] However, a medium using a protective film having a high internal stress has poor environment resistance, and particularly when a plastic substrate such as polycarbonate is used as the substrate, film cracking occurs, There was a problem that the substrate was warped.

Further, in terms of characteristics, there is a problem that the medium having a high underlying internal stress has a high noise level.

[Means for Solving Problems] The present invention has been made for the purpose of eliminating the above-mentioned conventional drawbacks, and this object is to achieve a low Curie temperature and a low room temperature with respect to the recording layer. In a magneto-optical memory medium having an exchange-coupled two-layer structure magnetic body composed of a read layer having a coercive force, at least one side of the magnetic body is in contact with the internal stress and
This is achieved by providing a protective layer that is 80 kg / mm ² or less.

That is, the combination of the exchange-coupling two-layer film and the protective film layer with a low internal stress of 80 kg / mm ² or less suppresses the deterioration of coercivity with time to the same extent as before, and also the film cracks and the substrate. It is possible to provide a magneto-optical memory medium which is less likely to cause warping, that is, has improved environment resistance, and has improved information recording / reproducing characteristics.

As a protective layer material, various dielectrics such as SiN and Si
O, SiO ₂ , Al ₂ O ₃ , ZnS, AlN, etc. can be used.

The read layer and the recording layer of the exchange coupling two-layer film include, for example, GdFe, GdFeCo, GdFeCoCr (read layer), TbFe, and Dy.
Fe and TbDyFe (recording layer) can be used.

Example 1 A magneto-optical memory medium 1 of the present invention as shown in FIG. 1 was produced as follows. On the disc-shaped polycarbonate substrate 1, SiN is 700 Å as the base protection layer 2, and the readout layer 3
As the recording layer, 400 Å of TbFe as the recording layer, and 700 Å of SiN as the upper protective layer were sequentially formed by sputtering. Here, the upper and lower protective layers have a sputtering gas pressure of 0.2 P
and the internal stress was 80 kg / mm ² . The internal stress was measured by determining the warp of the disk when the film was formed on the glass disk by the interferometric method, and calculating the internal stress from this value.

As a sample for a high temperature durability test, a slide glass was placed in the same chamber as this, and the same film was sequentially formed.

For comparison, upper and lower protective layers, 0.07Pa, 0.10Pa, 0.
Films were formed at 15 Pa, and the internal stresses were set to 200, 150, and 100 kg / mm ² in order, respectively, and the comparative mediums 1, 2, and 3 similar to the above, and the magnetic layer was a single-layer TbFe with a thickness of 800 Å. Others are the same as above, 8
Comparative medium 4 having a protective film with an internal stress of 0 kg / mm ² was prepared.

The same film was formed on each slide glass as a sample for high temperature durability test.

Among these samples, those using slide glass were subjected to a high temperature endurance test at 250 ° C for 17 hours to measure the change in coercive force, and those using a disk-shaped substrate were
The appearance and the warpage of the substrate were measured by subjecting to a high temperature and high humidity test at ℃, 85%, 1000 hours. The results are shown in Tables 1 and 2.

The magneto-optical medium 1 of the present invention has a small change in coercive force even in a high temperature endurance test of 250 ° C. for 17 hours, which is practically no problem, and in a high temperature and high humidity test of 80 degrees, 85%, and 1000 hours. However, there were no abnormalities in appearance and warpage of the substrate.

On the other hand, in the comparative media 1, 2, and 3, in the high temperature and high humidity test, film cracks were generated in the outer peripheral portion, and warp of the substrate of 10 milliradian or more was generated.

Further, the comparative medium 4 showed a remarkable decrease in coercive force in a high temperature durability test at 250 ° C. for 17 hours.

Example 2 The upper and lower protective layers were formed into a film with a sputtering gas pressure of 0.4 Pa,
A magneto-optical memory medium 2 of the present invention similar to that of Example 1 was prepared except that the internal stress was set to 30 kg / mm ² or less, and the same environmental test as that of Example 1 was performed. The results are shown in Tables 1 and 2.

Also in the magneto-optical memory medium 2 of this example, there was no problem in practical use in terms of changes in coercive force, appearance of the disk, and warpage of the substrate.

Example 3 A magneto-optical memory medium was prepared in the same manner as in Example 1 except that the upper and lower protective layer materials and internal stresses thereof were as shown in Table 3, and the same environmental test as in Example 1 was conducted. The results are shown in Tables 4 and 5.

[Effects of the Invention] As described above, the magneto-optical memory medium of the present invention in which the protective layer having an internal stress of 80 kg / mm ² or less is formed on at least one side of the exchange-coupling bilayer film has a deterioration in coercive force with time. The environmental resistance and reliability were improved while being suppressed.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of the magneto-optical memory medium of the present invention. 1: Polycarbonate 2: Base SiN protective layer 3: Read-out layer, 4: Recording layer 5: Upper SiN protective layer

Claims (1)

(57) [Claims] 1. A magneto-optical memory medium having an exchange-coupled two-layer magnetic substance comprising a recording layer and a read layer having a high Curie temperature and a low coercive force at room temperature with respect to the recording layer. , The internal stress of 80kg / m is in contact with at least one side of the magnetic material.
A magneto-optical memory medium having a protective layer of m ² or less.