JPH0760532B2 - Optical recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to an optical recording medium capable of recording / reproducing with a light beam.

[Conventional technology]

Conventionally, as an optical recording medium used for an optical disk, a rare earth-transition metal alloy thin film, a reducing oxide thin film such as a chalcogen compound utilizing a phase transition from amorphous to crystalline, a heat mode recording medium, Thermoplastic recording media and the like are known. For example, as a magneto-optical recording medium formed of a rare earth-transition metal alloy thin film, MnBi, M
Polycrystalline thin film such as nCuBi, GdCo, GdFe, TbFe, DyFe, GdTbFe,
Amorphous thin films such as TbDyFe, GdFeCo, TbFeCo, GdTbCo, TbFeO
There are single crystal thin films such as ₃ .

Among these thin films, the film forming property when manufacturing a large area thin film at a temperature near room temperature, the writing efficiency for writing a signal with small photothermal energy, and the written signal
Considering the reading efficiency and the like for reading with a good S / N ratio, the amorphous thin film has recently been considered to be excellent for a magneto-optical recording medium. In particular, GdTbFe has a large Kerr rotation angle, and in particular, GdTb with a Curie temperature of 150 to 200 ° C.
Fe and GdTbFeCo with large car rotation angle and excellent playback performance
(Japanese Patent Laid-Open No. 58-196639) is the most suitable as a magneto-optical recording medium. However, in general, an amorphous magnetic material used for a magnetic recording medium including a magnetic material such as GdTbFe is
It has the drawback of poor corrosion resistance. That is, when it comes into contact with the atmosphere or water vapor, the magnetic properties deteriorate, and eventually it is completely oxidized and becomes transparent.

In order to eliminate such a defect, conventionally, recording light and reproducing light are almost transmitted to both sides of the optical memory material layer, for example, SiO, Si.
A disc-shaped recording medium provided with a protective layer of O ₂ , Si ₃ N ₄ , and AIN has been proposed. In order to further enhance the protective effect, various protective layer materials are being studied.

[Problems to be Solved by the Invention] However, if an inorganic material such as SiO, SiO ₂ , Si ₃ N ₄ or AIN is used as the protective film and the film thickness is increased to enhance the protective effect, the recording light is A large proportion of thermal energy generated by conversion in the optical memory material is conducted to the protective film side and is lost. As a result, there is a problem that the temperature of the recording layer is not sufficiently increased by the light beam and the recording sensitivity is lowered.

On the other hand, it is advantageous to use an organic material having a low thermal conductivity for the protective film in terms of recording sensitivity, but it is not sufficient in terms of protection and durability, and there is a practical problem.

The present invention has been made in view of these problems, and provides an optical recording medium having an increased recording sensitivity without impairing the magnetic characteristics of the magnetic recording layer and the excellent corrosion resistance to moisture and oxygen. To aim.

[Means for Solving Problems] The above-mentioned object is to provide a recording layer capable of recording or erasing information by irradiating with a light beam and heating, and a recording layer provided in contact with at least one surface of this layer. An optical recording medium having a protective layer on a substrate, characterized in that the protective layer has a low filling factor in the vicinity of the recording layer and a higher filling factor as the distance from the recording layer increases. The optical recording medium can be achieved.

That is, by covering the immediate vicinity of the recording layer with a protective film having a low filling rate and thus a low thermal conductivity, heat is prevented from escaping from the recording layer and recording sensitivity is improved, and at the same time, the film is separated from the recording layer. Accordingly, the effect of protecting the recording layer was enhanced by forming a film having a dense structure with a high filling rate.

In order to obtain these effects, the protective layer material is not limited to Si ₃ N ₄ used in the examples described later, but SiO, SiO ₂ , AIN, SiC, Zn
Any material that has been commonly used as a protective layer material for optical recording media such as S can be used.

The protective layer in the optical recording medium of the present invention can be typically formed as follows. Ie. For example, a vacuum film forming method such as sputtering is used, and the discharge gas pressure used at that time is changed over time, or the substrate bias voltage applied at that time is changed over time. The former utilizes the fact that the filling rate decreases when the discharge gas pressure is increased, and the latter utilizes the fact that the filling rate increases when the substrate bias voltage is increased in the negative direction.

As the structure of the optical recording medium of the present invention, either a laminated structure or an air sandwich structure can be adopted.

An embodiment of the optical recording medium of the present invention having a laminated structure is shown in FIG. In this optical recording medium, a base protective layer 2 is formed on a writing side substrate 1a, a recording layer 3, a protective layer 4 and a reflective layer 5 such as Al are sequentially provided, and an adhesive layer 6 is further provided.
It is obtained by bonding it to the protective substrate 1b via.

Incidentally, as a recording layer satisfying the above requirements, a recording layer exhibiting a photothermomagnetic effect and a phase change type recording layer are typical.

[Examples] Hereinafter, the case where the present invention is applied to a magneto-optical recording medium will be described more specifically with reference to Examples.

Example 1 A magneto-optical recording medium having the structure shown in FIG. 1 was prepared as follows.

On the disk-shaped polycarbonate resin substrate 1a, a SiN film as a base protection layer 2 of about 1000Å and as a recording layer 3 GdTbFeC
o About 150Å film, again about 1000Å SiN film as protective layer 4,
Finally, an Al film of about 700 liters was continuously formed as the reflection layer 5 by optical frequency sputtering without breaking the vacuum. This was bonded to a protective polycarbonate substrate 1b via an adhesive layer 6 made of a hot melt adhesive to form a magneto-optical recording medium.

In this production, the filling rate of the protective layer 2 and the protective layer 4 was low in the vicinity of the recording layer 3, and the filling rate was high as the protective layer 2 and the protective layer 4 were separated from the recording layer 3.
The pressure was monotonically increased with time from Torr to 100 mTorr, and conversely, when forming the protective layer 4, the discharge gas pressure was decreased with time from 100 mTorr to 2 mTorr. A solid line 7 in FIG. 2 shows the relationship between the linear velocity of the magneto-optical recording medium of this embodiment and the recording power on the disk surface.

For comparison, the protective layer 2 and the protective layer 4 are set at a discharge gas pressure of 5 mTo
A magneto-optical recording medium having the same layer structure was prepared by the same method as described above except that the protective layer was fixed to rr to form a film, which was used as a conventional protective layer. For this, the same measurement as above was performed. The measurement result of this comparative sample is shown by the broken line 8 in FIG.
Indicated by. Furthermore, in order to investigate the durability of the obtained both magneto-optical recording media, it was measured in a constant temperature and humidity layer at 45 ° C and a relative humidity of 95%.
A humidity resistance test is performed for 0 hours, and the rotation angle θ after the humidity resistance test
The rates of deterioration of k and coercive force Hc from the initial values were measured.
The results are shown in Table 1.

As is clear from FIG. 2, the recording medium according to the present invention is
The recording sensitivity is improved as compared with the conventional recording medium. Further, as seen in Table 1, the durability of the recording medium according to the present invention was the same as that of the conventional recording medium, and no deterioration in magnetic characteristics was observed.

Example 2 When forming the protective layer 2, the substrate bias voltage was changed from 0V to -200V.
It increased in the negative bias direction with time. On the contrary, when the protective layer 4 was formed, the substrate bias voltage was decreased from −200 V to 0 V with time. Other than this, the magneto-optical recording medium according to the present invention having the same film structure was manufactured by the same method as in Example 1.

A solid line 9 in FIG. 2 shows the relationship between the linear velocity of the magneto-optical recording medium in this example and the recording power on the disk surface.

In addition, Table 1 shows the results of the same moisture resistance test as in Example 1 for examining the durability.

As shown in FIG. 2 and Table 1, the recording sensitivity showed almost the same value as that of Example 1, and no particular deterioration was observed in terms of durability.

Example 3 When the protective layer 2 was formed, the discharge gas pressure was changed from 5 mTorr to 100 m so that the filling rates of the protective layer 2 and the protective layer 4 were changed stepwise.
Increase to 5mTorr in increments of Torr, 50 at each gas pressure
A total of 1000 Å is formed by depositing Å to form a total of 1000 Å. When forming the protective layer 4, conversely, the discharge gas pressure is reduced from 100 mTorr to 5 mTorr in 5 Å increments of 50 Å total 1000 Å
A film was formed. Other than this, a magneto-optical recording medium having the same film structure was manufactured by the same method as in Example 1. The solid line 10 in FIG. 2 shows the relationship between the linear velocity of the magneto-optical recording medium of this embodiment and the recording power on the disk surface. In addition, Table 1 shows the results of the same moisture resistance test as in Example 1 for examining the durability.

As shown in FIG. 2 and Table 1, the recording sensitivity showed almost the same value as in Example 1, and no particular deterioration was observed in terms of durability.

[Effects of the Invention] As described in detail above, in the optical recording medium of the present invention, the recording sensitivity was increased while substantially maintaining the magnetic characteristics and the excellent durability. Therefore, it became a medium with extremely high performance and reliability.

[Brief description of drawings]

FIG. 1 is a diagram showing one mode of the optical recording medium of the present invention, and FIG. 2 is a diagram showing test results in Examples. 2, 4: Protective layer 3: Recording layer

Claims (1)

[Claims] 1. An optical system having, on a substrate, a recording layer capable of recording or erasing information by irradiating with a light beam and heating, and a protective layer provided in contact with at least one surface of the layer. In the recording medium, the protective layer has a structure in which the filling rate is low in the vicinity of the recording layer and increases as the distance from the recording layer increases.