JPH0476841A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To improve recording sensitivity and C/N by forming a reflecting layer of an alloy essentially consisting of at least one kind selected from inert metals and Ti. CONSTITUTION:The reflecting layer 5 of the magneto-optical recording medium 1 formed of an interference layer 3 consisting of the oxide, nitride or oxynitride of metals, a magneto-optical recording layer 4 consisting of a transition metal, rare earth metal and corrosion resistant metal, the reflecting layer 5, and a protective layer 6 on a substrate 2 is formed of the alloy essentially consisting of at least one kind selected from the inert metals, such as Au, Pt, Pd, Ag, and Cu, and Ti. The alloy of the Ti and the inert metals can be controlled in thermal conductivity by changing the compsn. ratios thereof and in addition, the reflectivity is improved by the reflecting layer consisting of Ti. The medium having the high C/N and the good recording sensitivity and the excellent corrosion resistance is obtd. in this way. The content of the inert metals is 3 to 97 atomic % and the film thickness of the reflecting layer 5 is preferably 10 to 20nm.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a magneto-optical recording medium in which recording and erasing are performed thermomagnetically and reproduction is performed magneto-optically.

[Conventional technology and issues]

2. Description of the Related Art In recent years, optical disk memories have been actively developed as recording media that can accommodate larger volumes and higher information densities. Among them, magneto-optical recording media that can be recorded, erased, and rewritten are attracting the most attention because of their practicality and wide range of uses.

Amorphous rare earth-transition metal alloys with excellent magneto-optical properties are most often used in the recording layer of magneto-optical recording media, but these alloys are easily corroded by moisture and require the addition of passivation-forming metals. This improves corrosion resistance.

In addition, since sufficient magneto-optical properties cannot be obtained for practical use only with the above-mentioned recording layer, it is necessary to add an interference layer, a recording layer, a reflective layer, etc. on the substrate.
The layer structure in which protective layers are sequentially formed allows both the Kerr effect and the Faraday effect to be used together, thereby improving recording and reproducing efficiency during laser beam irradiation.

In magneto-optical recording media in which a reflective layer is provided adjacent to a recording layer, a thin film of AI or A1 alloy is generally used as the reflective layer. However, AI is prone to local corrosion (and its high thermal conductivity significantly reduces recording sensitivity. AI forms a passive state on its surface, so it shows strong corrosion resistance against general corrosion; When a pinhole occurs, an anode reaction progresses in the pinhole area and a cathode reaction proceeds in other areas, forming a corrosion cell and causing localized deep erosion.Furthermore, in magneto-optical recording media, the recording layer Recording is performed by raising the temperature, but in such a structure where the recording layer and the reflective layer are adjacent to each other, if the reflective layer has high thermal conductivity, heat will escape from the recording layer through the reflective layer, causing the recording layer to deteriorate. The temperature does not rise sufficiently and the recording sensitivity decreases.

On the other hand, although the recording sensitivity can be improved using the A1 alloy, the composition exhibiting high corrosion resistance has a low reflectance, so it has the disadvantage that a sufficient C/N ratio cannot be obtained.

[Problem to be solved by the invention]

In view of the above problems, it is an object of the present invention to provide a magneto-optical recording medium that has high recording sensitivity and can obtain a sufficient C/N ratio.

[Means to solve the problem]

In a magneto-optical recording medium in which an interference layer, a recording layer, a reflective layer, and a protective layer are sequentially formed on a substrate, the reflective layer is made of Ti and Au.
S PtS PdS AgS By forming an alloy film made of an inert metal of Cu, corrosion resistance, recording sensitivity, and C/N are improved.
An improvement in the ratio can be achieved.

[Structure of the invention]

The present invention includes an interference layer made of a metal oxide, nitride, or oxynitride, a magneto-optical recording layer made of a transition metal, a rare earth metal, and a corrosion-resistant metal, a reflective layer, and a protective layer formed on a substrate. In the magneto-optical recording medium, the reflective layer has A us
P tSP cJSA gSCu is an alloy mainly composed of at least one selected from inert metals and Ti, and the inert metal content in the reflective layer is 3 to 97 atomic %, and the reflective layer film The present invention relates to a magneto-optical recording medium having a thickness of 10 to 200 nm.

The present invention will be explained in detail below.

1 to 3 schematically show the layer structure of a magneto-optical recording medium according to the present invention.

The substrate is polycarbonate or PMMA.

Examples include a substrate made of plastic such as amorphous polyolefin, or a substrate in which guide grooves are formed directly on glass, and a substrate in which guide grooves are formed on a flat plate of glass or plastic by a photopolymer method. The refractive index of the substrate is 1.4 to 1.
6. The thickness is preferably about 1.0 to 1.5 mm.

Generally, a dielectric film with high transparency and refractive index is used for the interference layer. Examples of the material include SiN, 5SiO
,% AI S iON, AI S 1NSAIN,
Examples include AlTiN and TazOa.

The refractive index n of these interference films is 1. 8<n<2. 8. The absorption coefficient preferably falls within the range of 0≦k<0.2. The thickness of the interference film is preferably 0 to 20% thicker than the thickness at which the reflectance on the substrate side is minimum, and in this case, the thickness of the interference film is 50 to 1100 nm. This interference film not only has an enhancement effect of improving the magneto-optical properties, that is, increasing the apparent Kerr rotation angle, but also has a protective effect of preventing penetration of moisture etc. from the substrate side to the recording layer.

The magneto-optical recording layer includes at least one rare earth metal such as Nd, Gd, Tb, and DV, and Fe and Co.

It consists of at least one transition metal such as Ni and a corrosion-resistant metal. Corrosion-resistant metals include Cr, Ti, V,
Passivation-forming metals such as Zr, Nb, and Ta, or inert metals such as Au, Pt, and Pd are suitable. By adding these metals up to about 10 atom%,
Corrosion resistance can be improved without deteriorating magneto-optical properties.

Specific examples of the magneto-optical recording layer include TbFeCo and TbFe.
Examples include CoCr, TbFeCoTi5 NdDyFeCo, and the like. The magneto-optical recording layer may be a single film or may have a structure in which a plurality of films having different magnetic properties are layered. The thickness of the magneto-optical recording layer is preferably 10 to 70 nm, preferably 20 to 40 nm through which laser light can sufficiently pass through.

As the reflective layer, an alloy whose main components are Ti and at least one of inert and highly reflective metals such as Au, PtS, Pc1S, Ag, and Cu is used. Au, PtSP
d, A Magneto-optical recording media in which a reflective layer is formed with an inert metal such as gSCu have a high reflectance, so a good C/N ratio can be obtained, but on the other hand, the recording sensitivity is greatly reduced due to high thermal conductivity. . In addition, since Ti is a metal with low thermal conductivity, when used alone as a reflective layer, it is difficult to cause heat diffusion and exhibits high recording sensitivity.
There was a drawback that a /N ratio could not be obtained. By changing the composition ratio of the alloy of Ti and inert metal, the thermal conductivity can be increased to 4. lXl0-'~1.0XIO-"cal/cm-
It can be adjusted arbitrarily within the range of deg-s, and the reflectance can be adjusted to
It can be improved more than a reflective film. In order to improve the reflectance, it is desirable that the amount of inert metals added such as Au, PtS, PdSAg, and Cu is 3 atomic % or more;
In order to achieve practical recording sensitivity, it is necessary that it be 97 atomic % or less. Ti is a metal with excellent strength and corrosion resistance, and the passive state formed by oxidation exhibits strong properties against corrosion. Furthermore, since the inert metal is chemically stable, the Ti-inert metal alloy thin film has high corrosion resistance.

An alloy made by adding 3 to 97 atomic percent of an inert metal to Ti has a high reflectance and low thermal conductivity, so when used as a reflective layer, it has a high C/N ratio and good recording sensitivity, and has good corrosion resistance. An excellent magneto-optical recording medium can be obtained.

The protective layer used on the reflective layer is formed of an inorganic protective film made of a dielectric material such as a metal or metalloid nitride, oxide, or oxynitride, or an organic protective film made of an ultraviolet curing resin, hot melt resin, etc. be done.

For the protective layer, these protective films may be applied alone, or an inorganic protective film and an organic protective film may be stacked in this order. As an inorganic protective film, for example, SiN, SiO, A
IS iON, AI S iON.

Dielectrics similar to those used for the interference layer, such as AlN5, AlTi0N, and Ta2es, may be used, but the composition of the inorganic protective film may or may not be the same as that of the interference layer. The thickness of the protective layer is preferably 20 to 200 nm in the case of an inorganic protective film, and preferably 1 to 50 μm in the case of an organic protective film.

The interference layer, magneto-optical recording layer, reflective layer, and inorganic protective film are formed using physical vapor deposition methods (PVD) such as sputtering and ion plating.
), or by chemical vapor deposition (CVD) such as plasma CVD, and the organic protective film is formed by applying it by spin coating, roll coating, etc. and then curing it.

[Effect]

A reflective layer mainly composed of an inert metal and Ti has a high reflectance at the interface with an adjacent magneto-optical recording layer, and can be used as a reflective layer. Furthermore, since this alloy has low thermal conductivity, it is difficult for heat to diffuse, and the recording and erasing sensitivity is improved compared to other reflective layers.

Furthermore, this reflective layer does not corrode because it is made of chemically inert metal. This alloy does not allow moisture, corrosive gases, etc. to pass through it, so corrosion does not occur in the magneto-optical recording layer. In addition, inert metals have excellent spreadability and can be added to the recording layer by adding them to the reflective layer.

It is possible to alleviate the stress caused by the protective layer and prevent the occurrence of cracks.

〔Example〕

Examples and comparative examples are shown below. It should be noted that the present invention is not limited to the following examples unless it departs from the scope of the invention.

Example 1 A polycarbonate substrate with a diameter of 130 mm was mounted on a sputtering device, and after the exhaust was evacuated to below 6.5 x 10-'torr, RF magnetron sputtering was performed on an Al5iON target using Ar gas.
A 5iON interference film was formed.

Next, using a TbFeCo alloy target on which a 5 mm square Cr chip was placed, T boFe s with a thickness of 25 OA was formed by DC magnetron sputtering in Ar gas.
ac Oscr *A recording layer was formed.

Subsequently, a Ti-pt reflective film having a thickness of 52°6 was formed by DC magnetron sputtering in Ar gas using a Ti target on which a 5 mm square Pt chip was mounted. As a result of ICP analysis, the composition of this reflective film was found to be 14 atomic % of Pt and 86 atomic % of Ti.

Finally, in Ar gas, the RF of the Al5iON target was
A film with a thickness of 750 mm was obtained by magnetron sputtering.
A 15iON protective film was formed.

The above film forming operations were performed continuously without breaking the vacuum.

The reflectance from the substrate side of a part of the inner mirror of the magneto-optical disk created in this way was measured and was 25.2%.
Met.

The recording and playback characteristics of this disc are determined by recording frequency - IMHz (
Duty ratio 50%), rotation speed = CAV 1800 rpm,
Measurement radius position = 30mm, reproduction laser power = 1mW
It was evaluated by As a result, the optimal recording laser power (defined as the recording laser power that minimizes second-order distortion during recording) is 4°0 mW, and the C/N ratio is 61.2 dB.
Met.

The optimum recording laser power was lower by 4.5 mW and 1.5 mW, respectively, than in Comparative Examples 1 and 2, and it is clear that the recording sensitivity was improved (see Table 1).

This disc was heated to 2000°C under the conditions of 80℃ and 85%RH.
An accelerated durability test of Hr was conducted to determine the byte error rate (BE).
R) was measured, and it was found that the BE after the test compared to the initial state
The rate of increase in R (BER after test/BER in initial state) was approximately 2.1, which was superior to the comparative example (see Figure 4).

Example 2 The interference layer, recording layer, and protective layer other than the reflective layer were formed under the same conditions as in Example 1.

For the reflective layer, a TlPt alloy film of film Jli9F49OA was formed by DC magnetron sputtering in Ar gas using a Ti target on which a 5 mm square PT chip was mounted. As a result of analysis by ICP, Pt4 atomic%, Ti
It was 96 atomic %.

The recording and reproducing characteristics of this disc were evaluated in the same manner as in Example 1. The results are shown in Table 1 and Figure 4.

Example 3 The interference layer, recording layer, and protective layer other than the reflective layer were formed under the same conditions as in Example 1.

For the reflective layer, a 590 A (DT) iPt alloy film was formed by DC magnetron sputtering in Ar gas using a PT ditat on which a 5 mm square Ti chip was mounted. As a result of ICP analysis, Pt was 97 atomic %,
The Ti content was 3 atomic %.

The recording and reproducing characteristics of this disc were evaluated in the same manner as in Example 1. The results are shown in Table 1 and Figure 4.

Example 4 The interference layer, recording layer, and protective layer other than the reflective layer were formed under the same conditions as in Example 1.

For the reflective layer, a Ti--Cu alloy film with a thickness of 460 Å was formed by DC magnetron sputtering in Ar gas using a Ti target on which a 5 mm square Cu chip was mounted. As a result of analysis by ICP, Cul 1 atomic%, T
The i content was 89 atom%.

This disk was evaluated in the same manner as in Example 1.

The results are shown in Table 1 and Figure 4.

Comparative Example 1 The interference layer, recording layer, and protective layer other than the reflective layer were formed under the same conditions as in Example 1.

The reflective layer was made of Al with a thickness of 450 Å by DC magnetron sputtering in Ar gas using an AI tube.
A film was formed.

This disk was evaluated in the same manner as in Example 1.

The results are shown in Table 1 and Figure 4.

Comparative Example 2 The interference layer, recording layer, and protective layer other than the reflective layer were formed under the same conditions as in Example 1.

For the reflective layer, an Al--Ti alloy film having a thickness of 450 AO was formed by DC magnetron sputtering in Ar gas using an AI stud on which a 5 mm square Ti chip was mounted. As a result of ICP analysis, A188 atomic%, Ti
It was 12 atom%.

This disk was evaluated in the same manner as in Example 1.

The results are shown in Table 1 and Figure 4.

Engraving of the drawings in Table 1 (no changes to the contents) Figure ■ Figure Figure 3, Magneto-optical recording medium 3...Interference layer 5...Reflection layer 7 Inorganic protective film 2/Substrate 4...Magneto-optical recording Layer 6/Protective layer 8: Organic protective film [Effects of the invention] The magneto-optical recording medium of the present invention has excellent recording and reproducing characteristics and corrosion resistance.

[Brief explanation of drawings]

1, 2, and 3 schematically show the layer structure of the magneto-optical recording medium according to the present invention, and FIG. 4 shows the byte error rate (BER) in the accelerated durability test of the example.
) shows the change in the rate of increase (BER after test/BER in initial state). 1. Magneto-optical recording medium 2. Substrate

Claims (1)

[Claims] 1. An interference layer made of a metal, metalloid oxide, nitride, or oxynitride on a substrate, and a magneto-optical recording layer made of a transition metal, a rare earth metal, and a corrosion-resistant metal; A magneto-optical recording medium formed by sequentially forming a reflective layer and a protective layer, characterized in that the reflective layer is made of an alloy whose main components are at least one selected from inert metals and Ti. recoding media. 2. The magneto-optical recording medium according to claim 1, wherein the inert metal is Au, Pt, Pd, Ag, or Cu. 3. The magneto-optical recording medium according to claim 1, characterized in that the content of inert metal in the reflective layer is 3 to 97 atomic %, and the thickness of the reflective film layer is 10 to 200 nm. .