JPH02297739A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain high C/N, high recording sensitivity and excellent long-term stability by properly selecting an element and its concentration to be added to a recording layer. CONSTITUTION:On a transparent substrate, there are successively formed an interference layer, rare earth-transition metal recording layer containing 1 - 15at.% Rh, reflecting layer and protective layer. The magneto-optical recording layer is 250 - 500Angstrom thick, and the interference layer is usually 400 - 1,500Angstrom thick, depending on the refractive index thereof and preferably, 500 - 1,000Angstrom . The reflecting layer is usually 100 - 1,000Angstrom thick, and preferably 200 - 600Angstrom . The protective layer is preferably 50 - 500Angstrom thick. The obtd. medium has high C/N, high recording sensitivity and excellent long-term stability.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a magneto-optical recording medium used for optical recording. Magneto-optical recording has been put into practical use as type memory. At present, thin films of rare earth metals and transition metals are most often used as the recording layer of magneto-optical recording media in terms of overall characteristics.

This magneto-optical recording medium can be used for recording and recording during laser beam irradiation.
In order to improve reproduction efficiency, a method has also been proposed in which a reflective layer is provided on the magneto-optical recording layer on the substrate. This method is excellent in that a high C/N ratio can be obtained by combining the Kerr effect and the Faraday effect. Conventionally, methods using At or A1 alloy as the reflective layer have been proposed.

However, when A1 or A1 alloy is used, there is a problem in terms of corrosion resistance against local corrosion. In other words, AI and A1 alloys have a natural oxide film on their surfaces, so they exhibit strong characteristics against general corrosion, but once a pinhole is formed, corrosion current concentrates, causing the pinhole to expand. This reaction is particularly noticeable in the presence of moisture.

The present inventors previously proposed a magneto-optical recording medium having a layer structure of substrate/interference layer/magneto-optical recording layer/reflection layer/protective layer (%Global Application No. 1.3-3292/A).

However, even with this layer structure, it is difficult to say that it has sufficient corrosion resistance, and the recording sensitivity is also not sufficient.

[Means to solve the problem]

As a result, by appropriately selecting the elements added to the recording layer and the elements added to the recording layer, a high C/N ratio, high recording sensitivity, and
It was discovered that a magneto-optical recording medium with excellent stability over time can be obtained.

[Structure of the invention]

The gist of the present invention is (1) a magneto-optical recording medium in which an interference layer, a RE-TM recording layer containing Rh at 1 to 1 atomic % (atX), a reflective layer, and a protective layer are sequentially provided on a transparent substrate. be.

The present invention will be explained in detail below.

First, substrates used in the present invention include glass, plastics such as acrylic resin and polycarbonate resin, and substrates with grooved resin formed on glass. be.

The magneto-optical recording layer is TbFe, TbFeCo, DyFeC
o.

It is a rare earth-transition metal-based perpendicularly magnetized film such as GdTbFe or NcLDyFeCo, and contains 1~/&at% of Rh.

The perpendicular magnetization film may be a single layer of rare earth-transition metal amorphous alloy thin film containing Rh at %/~/lr at%, but the composition is set to act! It may also be a multilayer recording layer in which mz and other rare earth-transition metal films are laminated.

By adding Rh to the recording layer, the corrosion resistance and recording sensitivity of the recording layer are improved.

If the Rh concentration is /at % at

On the other hand, when the Rh concentration exceeds / , t atX , C/N
The ratio becomes smaller and the anticorrosive effect is lost. Particularly preferably, it is -~gat%.

The thickness of the magneto-optical recording layer is 2! ;0-! ;00 is 0 In the present invention, an interference layer is provided between the substrate and the magneto-optical recording layer. This layer uses the light interference effect of a transparent film with a high refractive index to lower the reflectance and reduce noise.
This is to improve the N ratio. The interference layer may be a single layer film or a multilayer film. Metal oxides are used as the interference layer. Examples of metal oxides include tantalum oxide, aluminum oxide, and titanium oxide. These metal oxides are dense and prevent moisture and oxygen from entering from the outside, and are particularly suitable for use with mental oxide.

An interference layer made of tantalum oxide has lower internal stress than an interference layer made of nitride, and the probability of cracking is much smaller.

The composition of tantalum oxide is a stoichiometric composition ratio (Ta.

A composition close to 0, ) is preferred. Excess oxygen causes oxidation of the recording layer, lowers the refractive index, and weakens the interference effect.Also, if there is a lack of oxygen, corrosion will concentrate on the unoxidized areas, causing pinholes. As it becomes more likely to occur, light absorption of the film increases and the carrier level decreases.

In the preferred oxidation state, the refractive index is A 33 nm, where the complex refractive index is n*=n −i K, O≦n≦2.2, and l K l (o, lr
The thickness of this interference layer is within the range of 〇The thickness of this interference layer is the optimum thickness depending on the refractive index! ;00
A-10OOA is suitable.

The reflective layer provided on the recording layer is generally made of a material with high reflectivity, but Au, Ag, and Pt are expensive (Cu is prone to corrosion, so a thin film of an alloy of At or Al is usually used. .

Especially A1 contains Ta, Ti, Zr, Mo, Pt%V
Alloys containing at least seven types of Cr and Pd up to about 15 atomic % have high reflectance and low thermal conductivity (high CZN
Provides good characteristics in both ratio and sensitivity. Especially Ta, Ti
, Mo, and Cr are preferably used. The thickness of the reflective layer is usually about 100 to 100A, preferably 200-AO.
It is about OA. If it is too thick, the sensitivity will decrease, and if it is too thin, the reflectance will decrease.

A nitride 7' is used as a protective layer provided on the reflective layer.

Alternatively, a metal oxide or the like is preferably used.The nitride is preferably silicon nitride, aluminum nitride, etc., and the metal oxide is preferably tantalum oxide or aluminum oxide, each alone or a composite oxide thereof. Particularly preferred are mental oxide and aluminum oxide.

Since these nitrides and oxides prevent moisture from entering from the outside, they can greatly suppress corrosion of the reflective layer. In addition, it is possible that the reflective layer is oxidized during the creation of the protective layer, but At
Alternatively, since the reflective layer of A1 alloy forms a strong oxide film on the surface, oxidation does not occur to a depth of several tens of amps or more.

The thicker the protective layer, the higher the protective ability, but the thicker the layer, the greater the drop in sensitivity. Therefore, the methods for forming the interference layer, recording layer, reflective layer, and protective layer on the substrate include sputtering, etc. physical vapor deposition (PVD), plasma CVD
A chemical vapor deposition method (CVD) such as the above is applied.

To form a magneto-optical recording layer, a reflective layer, and a protective layer using the PVD method, the usual method is to deposit each layer on a substrate by electron beam evaporation or sputtering using a target with a predetermined composition. It is.

Furthermore, a method using ion blating is also considered.

If the film deposition rate is too fast, it will increase the film stress, and if it is too slow, it will affect productivity, so it is usually set at 0. /A/sec~/θO
It is estimated to be about A/sec.

For the interference layer, RF with T a , O, target
A sputtering method, a DC or RF reactive sputtering method using Ar and O2 gas using a Ta target, an electron beam evaporation method, etc. are preferable. Among these, the DC reactive sputtering method using Ar, O, and gas using a Ta target is preferable because it allows the amount of oxygen to be controlled, the film formation rate is fast, and the rise in substrate temperature is small. . in this case,
Control of the refractive index can be easily achieved by changing the pressure.

〔Example〕

The present invention will be explained in more detail with reference to examples below, but the present invention is not limited to the following examples unless it exceeds the gist thereof.

EXAMPLE A polycarbonate substrate of 130 mB was introduced into a sputtering device, and the air was first evacuated to below EXlo'tor+r, and a Ta target was reactively sputtered using a mixed gas of Ar and O7 to form an interference layer on the goo made of Ta2O2. Formed.

After evacuating the chamber once, Ar was 100% Fe at this time,
. Rh was added to the magnetic layer by placing a Rh chip on a Co,6 target and performing sputtering. Rh
The concentration was &at% in the magnetic layer.

The T b Fe Co Rh layer was manufactured to have a thickness of 3θOA.

Furthermore, sputtering in AI metal Ar gas with a Ta chip arranged L A l 11? A JOOA reflective layer made of an alloy of T a 3 was formed. Furthermore, a protective layer made of tantalum oxide was provided by packing the Ta target with a mixed gas of Ar and 02. This disk was recorded and played back using a magneto-optical recording and reproducing device under the following conditions to determine the C/N ratio. , recording sensitivity was measured.

(Conditions) r=JOrun, CAV/10100
rp = / MHz, pulse width! ;00n
5eC Recording magnetic field 20θOe Reproduction power HegmW Also, this disc was heated to tO°Cj3 under RH condition/
An accelerated deterioration test of 000 hr was conducted, and the error rate before and after the test was measured.

C/N ratio is A/dB, recording sensitivity is tl, 2mW/
The increase in error rate in the 000 hr accelerated test was 20%. (See Table 1) Comparative Example 1 A disk having the same layer structure as in Example was produced except that Rh was not added to the recording layer.

The C/N ratio recording sensitivity and error rate of this disk were measured under the same conditions as in Example 1.

C/N ratio t, / dB 1 recording layer degree '1. The increase in tmW error rate was 300%.

Compared to Example γ, the recording sensitivity is 0.1 mW worse (and it can be seen that the corrosion resistance is significantly inferior (see table)) Comparative Example
A disk with the same layer structure was fabricated.

The Cr concentration in the recording layer was tat%.

The C/N ratio recording sensitivity and error rate of this disc were measured under the same conditions as in Example I.

C/N ratio! ; g dB, recording sensitivity da...! tdB,
The increase in error rate was 50%.

It can be seen that the C/N ratio, recording sensitivity, and corrosion resistance are all inferior compared to Example 1 (see Table 1) Comparative Example 3 A disk with the same layer structure as Example 1 except that the protective layer made of tantalum oxide was not provided. was created.

The C/N ratio, recording sensitivity, and error rate of this disc were measured under the same conditions as in Example 1.

C/NJt A/ds, recording sensitivity '1.3 mW,
-! - The increase in lar rate was 60%.

It can be seen that the recording sensitivity is slightly worse than in Example 1, and the corrosion resistance is also inferior. (Table/Reference) Table l [Effects of the Invention] According to the present invention, by adding Rh to the recording layer and making the layer structure of the film in the order of interference layer, recording layer, reflective layer, and protective layer,
A magneto-optical recording medium having a high C/N ratio, excellent stability over time, and extremely good recording sensitivity can be obtained.

Claims (4)

[Claims] (1) A magneto-optical recording medium comprising, on a transparent substrate, an interference layer, a rare earth transition metal recording layer containing 1 to 15 atomic % of Rh, a reflective layer, and a protective layer. (2) The magneto-optical recording medium according to claim 1, wherein the protective layer is made of tantalum oxide, aluminum oxide, or a composite oxide thereof. (3) The magneto-optical recording medium according to claim 1, wherein the interference layer is made of tantalum oxide, aluminum oxide, or a composite oxide thereof. (4) Reflective layer is Ta, Ti, Zr, V, Mo, Cr, P
Al containing at least one element selected from t, Pd
2. The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium is made of an alloy.