JPS6391841A - Optical recording medium - Google Patents

Abstract

PURPOSE:To improve recording sensitivity without impairing the magnetic characteristics of a magnetic recording layer and the high corrosion resistance thereof to moisture and oxygen by using a protective layer having such structure in which the packing rate is low near the recording layer and is higher the further from the recording layer. CONSTITUTION:The underlying protective layer 2, the recording layer 3, the protective layer 4 and a reflection layer 5 are provided on a writing side substrate 1a and further said substrate is stuck to a substrate 1b for protection via an adhesive layer 6. The protective layers 2 and 4 are formed by increasing a discharge gaseous pressure monotonously with time at the time of forming the layer 2 and conversely decreasing the discharge gaseous pressure with time at the time of forming the layer 4 so that the packing rate is low near the layer 3 and is higher the further from the layer 5. The part near the layer 3 is thereby coated with the protective films 2, 4 having the low packing rate hence low heat conductivity, by which the escape of heat from the layer 3 is prevented and the recording sensitivity is improved. The protective effect for the layer 3 is improved by forming the film having the denser structure of the higher packing rate the further therefrom.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an optical recording medium on which recording and reproduction can be performed using a light beam.

[Conventional technology]

Conventionally, optical recording media used in optical discs include rare earth-transition metal alloy thin films, non-r1M! Yu,
+ 4-+ HSt -claw, R7) 1 j $
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Reducible oxide thin films such as SO compounds, heat mode recording media, thermoplastic recording media, etc. are known. For example, as a magneto-optical recording medium formed of a rare earth-transition metal alloy thin film, MnB1. Polycrystalline thin films such as MnCuB1, GdCo, GdFe, TbFe, Dy
Fe.

GdTbFe, TbDyFe, GdFeCo, T
bAmorphous thin film such as FeCo, GdTbCo, Tb
Examples include single crystal thin films such as FeO3.

Among these thin films, there are various issues such as film formability when manufacturing large-area thin films at temperatures near room temperature, writing efficiency for writing signals with small photothermal energy, and readout of written signals with a good S/N ratio. Considering read efficiency and the like, the amorphous thin film is recently considered to be excellent for use in magneto-optical recording media. In particular, GdTbFe has a large Kerr rotation angle and a Curie temperature of about 150 to 200°C, and GdTbFeCo (Japanese Patent Laid-Open No. 58-1986) has a large Kerr rotation angle and excellent reproducibility.
39) etc. are optimal as magneto-optical recording media. However, the amorphous magnetic material used for the magnet body, which is generally made of a magnetic material such as GdTbFe, has a drawback of poor corrosion resistance. That is, when it comes into contact with the atmosphere or water vapor, its magnetic properties deteriorate and eventually it becomes completely oxidized and becomes transparent.

In order to eliminate such drawbacks, it has conventionally been possible to fill both sides of the optical memory material layer with a material that almost transmits the recording light and the reproducing light, for example, Si.
Disc-shaped recording media provided with protective layers of O, 5i02, Si3N4, and AIN have been proposed. In order to further enhance the protective effect, various materials for the protective layer are being studied.

[Problems to be Solved by the Invention] However, SiO, 5i02. Si3
When an inorganic material such as N4°AIN is used and its film thickness is increased in order to increase the protective effect, the thermal energy generated when the recording light is converted in the optical memory material is conducted to the protective film side and is lost. The proportion of things that end up being lost will increase. As a result, there is a problem that the temperature A of the recording layer due to the light beam is not sufficient, resulting in a decrease in recording sensitivity.

On the other hand, using an organic material with low thermal conductivity for the protective film is advantageous in terms of recording sensitivity, but it is insufficient in terms of protection and durability, which poses a practical problem.

The present invention has been made in view of these problems, and aims to provide an optical recording medium with improved recording sensitivity without impairing the magnetic properties of the magnetic recording layer or the excellent corrosion resistance against moisture and oxygen. purpose.

[Means for solving the problem] The above purpose is to provide a recording layer that can record or erase information by irradiating it with a light beam and heating it, and a recording layer that is provided adjacent to 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 structure in which the filling rate is low near the recording layer and increases as the distance from the recording layer increases. This can be achieved by using an optical recording medium.

That is, by covering the immediate vicinity of the recording layer with a protective film that has a low filling rate and therefore low thermal conductivity, it is possible to prevent heat from escaping from the recording layer and improve recording sensitivity, and at the same time to separate this film from the recording layer. Accordingly, by creating a film with a dense structure with a high filling rate, the protective effect on the recording layer was also enhanced.

In order to obtain these effects, the protective layer material is not limited to Si3N4 used in the examples described later, but also Sin, S
Any material that has been commonly used as a protective layer material for optical recording media can be used, such as i02, AIN, SiC, ZnS, etc.

The protective layer in the optical recording medium of the present invention can typically be formed as follows. Namely. There are methods such as using a vacuum film forming method such as sputtering and changing the discharge gas pressure used at that time over time, and changing the substrate bias voltage applied at that time 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 bonded 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 write-side substrate 1a, a recording layer 3, a protective layer 4, and a reflective layer 5 such as At are sequentially provided, and a protective layer 5 is further provided via an adhesive layer 6. This was obtained by bonding it to the substrate lb.

Note that typical recording layers that meet the above requirements include a recording layer exhibiting a photothermal magnetic effect and a phase change recording layer.

[Example] Hereinafter, the case where the present invention is applied to a magneto-optical recording medium will be described in more detail 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 with an OA of about 100 OA as a base protective layer 2, a GdTbFeCo film with an OA of about 15 OA as a recording layer 3, a 5iN11!2 film with an OA of about 1,000 OA as a protective layer 4, and finally a reflective layer 5. An A1 film was continuously formed at approximately 70 OA by high frequency sputtering without breaking the vacuum. This was bonded to a protective polycarbonate substrate ib via an adhesive layer 6 made of a hot melt adhesive to form a magneto-optical recording medium.

During this production, when forming the protective layer 2, the discharge gas pressure was set to 2, so that the filling rate of the protective layer 2 and the protective layer 4 is low near the recording layer 3 and increases as the distance from the recording layer 3 increases.
It increases monotonically with time from mTorr to 100 ttrTarr, and conversely increases to 100 ttrTarr when forming the protective layer 4.
The film was formed by decreasing the discharge gas pressure over time from 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 example and the recording power on the disk surface.

For comparison, protective layer 2 and protective layer 4 were used at a discharge gas pressure of 5 m.
A magneto-optical recording medium having the same layer structure was produced in the same manner as described above, except that the film was formed at a fixed Torr and a conventional protective layer was used. Regarding this, the same measurements as above were performed. The measurement results of this comparative sample are shown at 8 in Figure 2.

Furthermore, in order to examine the durability of both of the obtained magneto-optical recording media, a 200-hour humidity test was conducted in a constant temperature and humidity layer at 45°C and a relative humidity of 95%, and the rotation angle θ after the humidity test was maintained. The rate of deterioration of the magnetic force He from the initial value was measured. The results are shown in Table 1.

As is clear from FIG. 2, the recording medium according to the present invention is
Recording sensitivity is improved compared to conventional recording media. Further, as shown in Table 1, the recording medium according to the present invention had the same durability as the conventional recording medium, and no particular deterioration of the magnetic properties was observed.

Example 2 When forming the protective layer 2, the substrate bias pressure was increased from Ov to 12
The voltage was increased in the negative bias direction with time until it reached 00V.

When forming the protective layer 4, on the contrary, the substrate bias voltage was decreased from -200 V to Ov with time. In other respects, an optical recording medium according to the present invention having the same film structure was produced in the same manner as in Example 1.

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

Further, in order to examine the durability, a moisture resistance test similar to that in Example 1 was conducted, and the results are shown in Table 1.

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

Example 3 When forming the protective layer 2, the discharge gas pressure was increased in steps of 5 mTorr from 5 mTorr to too mTarr so that the filling rate of the protective layer 2 and the protective layer 4 was changed stepwise. 50 people each deposited a film for a total of 10
00 as the protective layer 2, and when forming the protective layer 4, the discharge gas pressure was changed from 100 mTorr to 5 mTorr at 5A.
The number of participants was reduced in increments of 50 people, for a total of 1,000 people. Other than this, a magneto-optical recording medium having the same film structure was produced in the same manner as in Example 1. A solid line 10 in the diagram f52 shows the relationship between the linear velocity of the magneto-optical recording medium of this example and the recording power on the disk surface.

Further, in order to examine the durability, a moisture resistance test similar to that in Example 1 was conducted, and the results are shown in Table 1.

As seen in FIG. 2 and Table 1, the Q sensitivity values were almost the same as in Example 1, and no particular deterioration was observed in terms of durability.

Table 1 [Effects of the Invention] As explained in detail above, in the optical recording medium of the present invention, the recording sensitivity was increased while the magnetic properties and excellent durability were substantially maintained. Therefore, it has become a medium with extremely high performance and reliability.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing one embodiment 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 Patent applicant: Canon Co., Ltd. Agent: Wakabayashi Chusenho (Mon1Se-0 Xu 2 times)

Claims (1)

[Claims] 1) In an optical recording medium having on a substrate a recording layer capable of recording or erasing information by irradiating with a light beam and heating it, and a protective layer provided adjacent to at least one surface of this layer. . An optical recording medium, characterized in that the protective layer has a structure in which the filling factor is low in the vicinity of the recording layer and increases as the distance from the recording layer increases.