JPS6252743A - Optical recording medium - Google Patents

Abstract

PURPOSE:To improve the corrosion resistance to oxygen, moisture, etc. by providing a laminated body consisting of protective layers consisting of rare earth metals which do not exhibit vertical magnetic anistropy and metallic layers having excellent protectiveness. CONSTITUTION:An undercoating layer 22 consisting of, for example, SiO or Si3N4, the highly protective metallic layer 23a, rare earth protective layer 23b, recording layer 24, rare earth protective layer 23c and highly protective metallic layer 23d are successively provided on a writing side substrate 21a consisting of plastic or glass, etc. A spacer layer 25 and a reflection layer 26 are provided thereon. The recording layer 24 is exemplified by the recording layer consisting of >=1 kinds among Gd, Tb and Dy exhibiting the vertical magnetic anistropy and >=1 kinds among Fe, Co and Ni or the recording layer consisting of a chalcogen compd. having the photomagnetic effect. Such rear earth metal is extremely oxidizable; therefore, said metal itself is oxidized by positively taking oxygen and moisture contained in the other auxiliary layers, etc. into said metal, thus said metal acts as the protective layer by preventing the intrusion of the oxygen and moisture into the recording layer.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to improving the corrosion resistance of magneto-optical recording media.

[Conventional technology]

Conventionally, as a magneto-optical recording medium formed of a rare earth-transition metal alloy thin film, MnB1. Polycrystalline pJ films such as Mn(:uBi, GdCo, GdFe, TbFe,
DtFe, GdTbFe.

TbD7Fe, GdFe(:o, TbFeCo,
Amorphous heavy 1113 films such as GdTbCo and single crystal thin films such as Gd1G are known.

Among these ulgI, we have the following characteristics: excellent film-forming performance in which a large-area B film is manufactured at a temperature close to room temperature, writing efficiency in which signals are written with small photothermal energy, and readout of written signals with a good S/)l ratio. Recently, the amorphous thin film is considered to be excellent for use in magneto-optical recording media, taking into account readout efficiency and other factors. In particular, GdTbFe
Since it has a large Kerr rotation angle and a single Curie point of around 150°C, it is suitable for magneto-optical recording media. Furthermore, as a result of research aimed at improving the Kerr rotation angle, the inventors found that GdTbFeCo has a sufficiently high Kerr rotation angle, and S
It has been found that readout with a good /N ratio is a popular magneto-optical recording medium.

However, amorphous magnetic materials used in magnetic recording media, including magneto-optical recording media such as GdTbFe, generally have a drawback of poor corrosion resistance. . That is, when it comes into contact with air or water vapor, its magnetic properties deteriorate, and eventually it becomes completely oxidized and becomes transparent. Further, such deterioration of recording characteristics due to oxidation is a common drawback not only in magneto-optical recording media but also in optical recording media.

In order to eliminate such defects, conventionally, L of the recording layer is
Disk-shaped optical recording media have been proposed in which a protective cover made of a transparent material, such as a protective layer of 5i07 or SiO is provided, or a magnetic recording layer is sealed with an inert gas.

That is, in the conventional optical recording medium, for example, as shown in FIG.
Protective layer +4. It is obtained by bonding the reflective layer 15 and the image substrate 11b via the adhesive layer 1B.

[Problem that the invention seeks to solve]

However, even with this configuration, there is a problem in that the recording layer is oxidized due to seepage of oxygen and moisture from the auxiliary layer such as the protective layer or the undercoat layer, resulting in deterioration of recording characteristics and failure to obtain sufficient corrosion resistance.

An object of the present invention is to provide an optical recording medium that has better corrosion resistance than conventional recording media.

[Means for solving problems]

This objective is achieved by the following optical recording medium.

That is, in an optical recording medium having an optically recordable and reproducible recording layer on a substrate, a protective layer made of a rare earth metal that does not exhibit perpendicular magnetic anisotropy and a metal layer with excellent protective properties are used. This is an optical recording medium characterized by being provided with a laminate of the following.

@Protective layer made of rare earth metal that does not exhibit direct magnetic anisotropy (
Hereinafter, it will be abbreviated as rare earth protective layer. ) is 5ffl, G
It consists of one or more alloys selected from the group consisting of d, Tb, Dy, )to.

Since these rare earth metals are very easily oxidized, they actively take in oxygen and moisture contained in other auxiliary layers and become oxidized themselves, preventing oxygen and moisture from entering the recording layer and forming a protective layer. It works as a.

A suitable thickness of the rare earth protective layer is usually 20 to A. If it is thinner than 20A, oxidation will extend through this rare earth protective layer to the recording layer, making it impossible to obtain the desired effect.In the present invention, in order to prevent the oxidation of the rare earth protective layer from reaching the interface with the recording layer, The thickness needs to be 20A or more. On the other hand, if the rare earth protective layer is thicker than 100A,
If a thin layer made of a rare earth metal alloy is formed, which is undesirable because the recording or reproducing beam does not reach the recording layer with a sufficient amount of light, this thin layer itself becomes ferromagnetic. but,
If the thickness is less than 100%, the thin layer will not have the property of perpendicular magnetization and will lose its magnetic properties due to oxidation, so the thickness is usually less than 100%. The layer does not affect the magnetic properties of the recording layer or the recording/reproduction using this layer. In addition, in optical recording media that utilize the magneto-optical effect, the thickness of the recording layer was reduced to several hundreds, and a reflective layer was provided with a rare species protection layer in between, aiming to increase the rotation angle due to the Faraday effect. Also in the structure, the thickness of the rare earth protective layer is preferably 20 to A as described above. Formation of such a rare earth protective layer is performed, for example, by sputtering.

Specifically, the highly protective metal layer laminated in contact with the rare earth protective layer (hereinafter abbreviated as highly protective metal layer) is An
, Ti, Cr, and Si.

The highly protective metal layer works together with the rare earth protective layer to
This further improves the corrosion resistance of the recording layer.

That is, in the case of an optical recording medium in which a rare earth protective layer and a highly protective metal layer are sequentially laminated from the side close to the recording layer, the auxiliary layer laminated above the highly protective metal layer or the substrate contains The highly protective metal layer first prevents oxygen, moisture, etc. from entering the optical recording medium from entering into the interior of the optical recording medium, due to its denseness and high oxidizing properties. With respect to oxygen, moisture, etc. that penetrate into the rare earth protection layer, the rare-F protection layer exerts the above-mentioned action, thereby preventing the recording layer from being eroded.

In addition, in the case of an optical recording medium in which a highly protective metal layer and a rare species protective layer are sequentially formed from the side close to the recording layer, moisture, oxygen, etc. may enter the optical recording medium inward. The rare earth protective layer first suppresses this, and even if moisture, oxygen, etc. reach the highly protective metal layer, this highly protective metal layer prevents it from further invading the recording layer located inside. be done.

The thickness of the highly protective metal layer is suitably about 20 to 100 Å. If the film thickness is thinner than 2OA, it will not be able to play the role of the above-mentioned cooperative protective effect, and if it is thicker than 1GOA, the amount of transmitted light for recording/reproducing light will decrease, and heat will also escape through this layer, resulting in aging and readout. It becomes less efficient.

In order for the recording layer to have a corrosion resistance of 1, it is preferable that the rare earth protective layer and the highly protective metal layer are sequentially formed as yi layers from the side closer to the recording layer.

In addition, in order to improve corrosion resistance, it is preferable that the two-layer structure consisting of a road protection layer and a highly protective metal layer be laminated in contact with the recording layer. When providing various auxiliary layers on an optical recording medium,
Depending on the degree of corrosion resistance required for the recording layer, 81 auxiliary layers may be sandwiched between the recording layer and the above-mentioned two-layer structure. However, if sufficient corrosion resistance can be obtained even on one side, for example, when marking is directly formed on a glass substrate and oxidation is sufficiently prevented on this substrate side, it is preferable to provide a It is not necessary to provide the two-layer structure only on both sides of the recording layer.

A schematic cross-sectional view of an embodiment of the optical recording medium of the present invention having a laminated structure is shown in FIG.

s8' side board 2 made of plastic or glass, etc.
1a, an undercoat layer 22.1a made of, for example, SIO, 513N4. Highly protective metal layer 23a, rare earth protective layer 23b, Q layer 24. Rare earth protective layer 23C1 Highly protective metal layer 23d
are sequentially provided, and a spacer layer 25 and a reflective layer 26 are provided thereon. 27 is an adhesive layer, and 21b is a protective substrate.

The material of the recording layer 24 does not matter as long as it is a thin layer that can be optically recorded and reproduced, but for example, Gd exhibiting perpendicular magnetic anisotropy,
Examples include a recording layer having a magneto-optical effect made of one or more of Tb and Dr and one or more of Fe, Go, and Ni, or a recording layer made of a chalcogen compound.

The present invention is particularly effective when applied to an optical recording medium having a recording layer having a magneto-optical effect exhibiting perpendicular magnetic anisotropy.

〔Effect of the invention〕

The optical recording medium of the present invention has a rare earth protective layer and a highly protective gold layer.
Due to the cooperative corrosion-inhibiting action with the layers, the corrosion resistance against oxygen, moisture, etc. is further improved compared to an optical recording medium having only each of them.

〔Example〕

EXAMPLES In order to explain the present invention more specifically, Examples are shown below.

Example 1 An optical recording medium having the structure shown in FIG. 1 was manufactured as follows.

A SiO film of about 100 OA is formed as an undercoat layer 22 on the acrylic plastic substrate 21a, and then
A highly protective metal #23a made of Si is provided with a thickness of about 10 OA, and a rare earth protective layer 23b made of a GdTb (11) film with a thickness of 2 OA is formed thereon by sputtering using a high frequency sputtering device 5e. 1BOA GdTb
A recording layer 24 made of a magnetic film of FeCo exhibiting perpendicular magnetic anisotropy was formed. On that hill, Lf repeats the above method,
A rare earth protective layer 23c with a thickness of 20A and GdTb (1:1) and a highly protective metal layer 23d made of Si with a thickness of ~100 nm were provided.

Next, a spacer layer 25 of about 1,200 mm is applied to the top.
An optical recording medium of the present invention was obtained by vapor-depositing a Si film of approximately 1 in 1000 as the reflective layer 26, and bonding it to the protective plastic substrate 21b using a silicone adhesive as the adhesive layer 27. .

Rotation angle θk from the obtained optical recording medium, coercive force He
Along with the measurement, a 200-hour humidity test was conducted in a constant temperature and humidity chamber at 45° C. and 85% relative humidity. The results are shown in Table 1. The numerical values in Table 1 represent the ratios when initial A1 is set to 1.0.

Example 2 In Example 1, ~50 Cr films were used as the highly protective metal layers 23a and 23d instead of the Si film, and Tb films were used as the rare-1-protective layers 23b and 23e instead of the GdTb film. An optical recording medium having the same layer structure as in Example 1 was prepared except for the above.

A moisture resistance test similar to that in Example 1 was conducted. The results are shown in Table 1.

Comparative Example 1 Rare earth protective layers 23b, 23c and highly protective metal layer 23a
, 23d tl-An optical recording medium was prepared in the same manner as in Example 1, except that no lamination was performed, and a moisture resistance test was performed on the optical recording medium. The results are shown in Table 1.

Comparative Example 2 An optical recording medium was prepared in the same manner as in Example 1, except that the highly protective metal layers 23a and 23d were not laminated, and a moisture resistance test was conducted on the optical recording medium. The results are shown in Table 1.

It is clear from the comparison of Example 1.2 and Comparative Example 1.2 that the optical recording medium of the present invention shows no deterioration in magnetic properties.
Corrosion resistance is improved.

Table 1

[Brief explanation of drawings]

FIG. 1 is a schematic diagram for explaining the structure of an optical recording medium of the present invention, and FIG. 2 is a schematic diagram for explaining the structure of a conventional optical recording medium. 11a, 2+a...Writing side board 12.22
... Undercoat layer 13.24 ... Recording layer 14 ... Protective layer 18, 27 ... Adhesive layer 23a, 23d ... Highly protective metal layer 23b, 23c ... Rare earth protective layer 11b, 21b...Protective substrate 25...Spacer layer 15.28...Reflective layer Patent applicant Canon Co., Ltd. Agent Tadashi Wakabayashi 2
figure

Claims (1)

[Claims] 1) An optical recording medium having an optically recordable/readable recording layer on a substrate, which includes a protective layer made of a rare earth metal that does not exhibit perpendicular magnetic anisotropy and has excellent protective properties. An optical recording medium characterized by being provided with a laminate including a metal layer. 2) The rare earth metal that does not exhibit perpendicular magnetic anisotropy is Sm,
The optical recording medium according to claim 1, which is one or more elements selected from the group consisting of Gd, Tb, Dy, and Ho. 3) The metal with excellent protective properties is Al, Ti, Cr, Si
The optical recording medium according to claim 1, which is one or more elements selected from the group consisting of: 4) The optical recording medium according to claim 1, wherein the recording layer is a thin layer exhibiting perpendicular magnetic anisotropy and having a magneto-optical effect. 5) The optical recording medium according to claim 1, wherein the laminate is laminated in contact with the recording layer.