JPS63255855A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To obtain a magneto-optical recording medium which has high recording sensitivity, less noises and excellent stability with lapse of time by constituting an intermediate protective layer and protective layer of specific materials. CONSTITUTION:The intermediate protective layer of the magneto-optical recording medium constituted by providing the intermediate protective layer, a magneto-optical recording layer and the protective layer successively on a substrate is a layer consisting of at least one compd. selected from a group consisting of aluminum oxide, tantalum oxide and nitride, and the protective layer is a layer consisting of SiO. The oxides of the aluminum and tantalum and the nitride are dense to prevent the infiltration of moisture and oxygen from the outside, is highly resistant to corrosion, is small in reactivity with the magneto-optical recording layer and has excellent adhesiveness to the resin in the case of using a resin substrate as the substrate. The content of 0 in the compsn. of SiO is particularly preferably about 0.5-1.6. The corrosion resistance of the recording is thereby sufficiently improved and the recording medium having the good durability and recording sensitivity and excellent productivity is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a magneto-optical recording medium used for optical recording.

(Prior art and its problems) Among optical memory devices, magneto-optical recording is at the closest stage to practical use for erasable memory, which allows additional recording and erasure. Rare earth and transition metal thin films are the best in terms of overall properties as magneto-optical recording media.
A fatal flaw is that it lacks corrosion resistance.

That is, many defects are exposed due to corrosion, such as a decrease in coercive force, which is a necessary condition for high-density recording, a decrease in Kerr rotation angle, which is a necessary condition for a high S/N ratio, and an increase in error rate.

Conventionally, two methods have been taken as countermeasures. That is, (i) adding additives to the recording layer to improve corrosion resistance;

(ii) Providing protective layers on both sides of the recording layer improves corrosion resistance.

The present invention has been made by focusing on a method using a protective layer.

That is, the magneto-optical recording medium of the present invention basically has a structure of a substrate, a protective layer, a recording layer, and a protective layer.

For convenience of explanation below, the protective layer between the substrate and the recording layer will be referred to as an intermediate protective layer, and the protective layer provided on the opposite side of the recording layer to the substrate will be referred to as a protective layer.

As the protective layer and intermediate protective layer, high melting point oxides such as He2□03 and high melting point nitrides such as StN and AfN have been proposed.

However, each of these substances has its own problems.
No material has been found that is satisfactory for forming both the intermediate protective layer and the protective layer.

This is because the physical properties required for an intermediate protective layer include not reacting with the recording layer, good adhesion to the substrate, excellent transparency, high refractive index, and excellent gas barrier properties. On the other hand, the physical properties necessary for a protective layer are common, such as not reacting with the recording layer and having excellent gas barrier properties, but transparency and refractive index are not required; rather, low thermal conductivity is more important. This is because the required physical properties are different for each.

The present inventors have conducted various studies regarding these protective layers and intermediate protective layers, and have found that by composing the intermediate protective layer and protective layer with specific materials, recording sensitivity is high, noise is low, and stability over time is improved. It has been found that a magneto-optical recording medium with excellent properties can be obtained.

[Structure of the invention]

The gist of the present invention is to provide a magneto-optical recording medium in which an intermediate protective layer, a magneto-optical recording layer and a protective layer are sequentially provided on a substrate, in which the intermediate protective layer is made of (a) aluminum oxide, (b) tantalum oxide and (c) A magneto-optical recording medium characterized in that the layer is made of at least one compound selected from the group consisting of nitrides, and the protective layer is a layer made of SiO.

The present invention will be explained in detail below.

First, examples of the substrate used in the present invention include glass, plastics such as acrylic resin and polycarbonate resin, metals such as aluminum, and substrates in which grooved resin is formed on glass.

The thickness of the substrate is generally about 1 to 2111111 mm.

As the magneto-optical recording layer, for example, TbFe, TbF
eCo.

Amorphous magnetic alloys of rare earths and transition metals such as TbCo, DyFeCo, and MnB1. A polycrystalline perpendicular magnetization film such as MnCuB1 is used. It is particularly effective for use in rare earth alloy magnetic films. The thickness of the magneto-optical recording layer is 30
0 to 1500 people, preferably 500 to 800 people.

In the present invention, a layer containing aluminum oxide, tantalum oxide, or nitride is formed as an intermediate protective layer between the substrate and the magneto-optical recording layer.

Aluminum oxides include A ffi zo3, tantalum oxides include Ta, 05, and other oxides alone or in combination, or l/! -Ta-0 complex oxide, etc. can be mentioned. Furthermore, other elements such as Si+Ti+Zr, It4. Mo, Yb
etc. alone in the form of oxide or ^42. It may be combined with Ta to form an oxide. These aluminum,
Tantalum oxide is dense and prevents moisture and oxygen from entering from the outside, and has low reactivity with the magneto-optical recording layer, which provides corrosion resistance.Also, when using a resin substrate as a substrate, it has low reactivity with the resin. Excellent adhesion.

Specifically, nitrides include silicon, aluminum,
Metal nitrides such as germanium, composite nitrides of two or more of these, or composite nitrides of these with niobium, tantalum, etc. (SiNbN).

5iTaN, etc.). Among them, nitrides containing Si give good results.

Nitride is dense and prevents moisture and oxygen from entering from the outside.
It itself has high corrosion resistance and low reactivity with the magneto-optical recording layer, and also has high adhesion to the resin when a resin substrate is used as the substrate.

A protective layer made of SiO is provided on the magneto-optical recording layer, but
This Si0 layer is in a state deficient in oxygen compared to SiO□. For example, when this Si0 layer is produced by a sputtering method, a sintered target of SiO (St: 0 = approximately 1:1) is sputtered with an inert gas such as Ar, or a St target is normally used to obtain SiO□. This can be obtained by reducing the amount of 0□ in the Ar -0□ mixed gas. When produced using the same manufacturing method, SiO□ has a refractive index of 1.4 to 1.5, whereas SiO has a refractive index of 1.8 to 1.5.
This can be confirmed from the fact that it is about 2.3. in particular,
Gas flow rate ratio of Ar and 0□ Oz / Ar + Oz =
It is generally about 0.2 to 0.5, but it largely depends on the manufacturing equipment and film formation rate.

In general, the composition of SiO has the drawback that if there is too much O, it tends to react with the magneto-optical recording layer, and if it is too little, it tends to cause cranking.

Physical vapor deposition (PVD), chemical vapor deposition such as plasma CVD, etc. are used to form a protective layer of aluminum oxide, tantalum oxide, or nitride, a magneto-optical recording layer, and a SiO protective layer on a substrate. Applicable.

To form a magneto-optical recording layer and a protective layer made of SiO using the PVD method, each layer is deposited on a substrate by electron beam evaporation or sputtering using a SiO sintered target with a predetermined composition. is the usual method, but
In the case of electron beam evaporation, it is preferable to perform the evaporation while irradiating the film with high-energy particles, or to lower the Ar gas pressure during sputtering, since the density of the film increases and a stable film can be obtained.

Furthermore, a method of using a Si target in reactive ion blating and reactive sputtering 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 0.1 person/sec to 100 people/sec.
person/sec, preferably 1 person/sec to 20 people/sec
It is said that

The thickness of the protective layer made of SiO is selected from about 10 to 5,000 layers, preferably from about 50 to 1,000 layers.

In the present invention, in addition to the SiO protective layer, in order to reinforce the gas barrier properties of the SiO layer, a silicate glass layer such as SiO
Furthermore, it may be coated with a resin or the like, and when a nitride layer is used as an intermediate protective layer, about 100 to 300 A2□03+ StO layers are placed between the nitride layer and the substrate.
It is also good to provide a mixed film of □ and Teflon as an undercoat layer to improve adhesion.

[Example] Example 1 Using a polycarbonate substrate, a sintered target of 5 inches φA2□0° was coated with Ta, O, with a thickness of 1 inch and a diameter of 9 III.
A sintered pellet of lnφ was placed, and RF sputtering was performed in Ar gas to form an intermediate protective film of 800 layers. Aj of intermediate protective film! :Ta ratio (atomic ratio) was 2:8.

4 inch φ SiO target and Tb10m 1 mouth x 1
A target with a small piece of mm t placed on an Fe target was set up and evacuated to below 3 x 10-'torr.

Distance between substrate and target 95mm, Ar flow rate 30SCC
Let it be M. After press batter at a sputtering gas pressure of 3 n+torr, a TbFe film of L1000 was sputtered for 1 minute at a direct current power (DC) of 300 W, followed by an Ar flow of t30 SCCM% sputtering pressure of 3 mtorr in the same vacuum, followed by radio frequency (RF) ) SiO at 200W power
Sputter the target 1. 800 people deposited a SiO (Si:O=about 1:1) film. The SiO sputtering speed was as high as 7 people/sec, and there was no deterioration of the substrate.

The recording sensitivity and C/N ratio of this magneto-optical recording medium were measured using a dynamic characteristic detector equipped with an APD (avalanche photodiode) non-differential detector. The recording sensitivity was set to the recording power at which the second-order distortion was minimum.

Recording conditions: CLV (constant linear velocity) 4 m/s Radius 53 m position, recording between grooves Recording frequency 1.0 MHz duty 50% Reproducing conditions: CLV 4 m/s Reproducing power 0.8 mW Average value of 16 times Recording in this example Sensitivity 2.35mW, C/N ratio 34dB
In this example, the recording power was 20% compared to Comparative Example 1.
%, and the C/N ratio decreased by only 1 dB.

As for the static characteristics, in the Kerr rotation angle measurement, the Kerr rotation angle was 0.15°, the reflectance was 44%, and the Tb had a coercive force of 2.4 KG.
It had rich composition hysteresis.

Even when the medium with this configuration was placed in a high-temperature, high-humidity chamber at 70° C. and 85% RH for two days, no peeling occurred.

Comparative Example 1 The layers up to the TbFe layer were fabricated in the same manner as in Example 1, and then a protective layer having the same composition as the intermediate protective film was formed by 800 people.

The recording sensitivity and C/N ratio were measured under the same conditions as in Example 1, and the recording sensitivity was 2.85 mW and the C/N ratio was 35 dB. (It has been experimentally found that when reproducing using a differential optical system instead of an APD non-differential system, the C/N ratio in PCR generally improves by 10 dB.) Example 2 On a polycarbonate (PCR) substrate , a SiN film was deposited by reactive sputtering of a Si target with Ar:N at a flow rate ratio of 1:5, and then TbFeCo
A film of 1,000 layers and a SiO sintered target were sputtered at an Ar gas pressure of 3+*torr to form a 5 inch (Si: 0
= approximately 1:1) 800 people provided the membrane. Here, TbFeCo
The amount of Tb in the film is approximately 25 at%, and the amount of Co is 10 a in FeCo.
It was t%.

The C/N ratio and recording sensitivity of this magneto-optical recording medium were measured using a dynamic characteristic measuring machine equipped with a PIN differential detector.

The recording sensitivity was set to the recording power at which the second-order distortion was minimum.

Recording conditions: CAV (constant angular velocity) 1800 rpm radius 30
InI+1 position, recording between grooves Recording frequency 0.5 MHz duty 50% Reproduction conditions: CAV 1800 rpm Reproduction power 1.5 mW At this time, the C/N ratio was 53 dB and the recording sensitivity was 5.6 mW.
The C/N ratio was almost the same as that of SiN, and the recording sensitivity was improved by 10%.

Comparative Example 2 Under the same conditions as Example 2, S was applied on both sides of the TbFeCo recording layer.
The dynamic characteristics of the product provided with the iN layer were measured under the same conditions as in the example. C/N ratio is 53.5dB, recording sensitivity is 6
．． It was 4mW.

Comparative Example 3 Under the same conditions as Comparative Example 2, both sides of the recording layer were replaced with SiN layers.
The dynamic characteristics were measured using an i target of SiO, (x = approximately 0.7) obtained by reactive sputtering in Ar10□ gas. C/N ratio is 52dB
The recording sensitivity was 5.21.

[Effects of the Invention] The magneto-optical recording medium of the present invention has sufficiently improved corrosion resistance of the magneto-optical recording layer, has good durability, has good recording sensitivity, and is also excellent in productivity.

Applicant Mitsubishi Chemical Industries, Ltd. Agent Patent Attorney Yo Hase - (1 other person)

Claims (2)

[Claims] (1) In a magneto-optical recording medium in which an intermediate protective layer, a magneto-optical recording layer and a protective layer are sequentially provided on a substrate, the intermediate protective layer is made of (a) aluminum oxide, (b) tantalum oxide and (c) chip. 1. A magneto-optical recording medium characterized in that the layer is made of at least one compound selected from the group consisting of compounds, and the protective layer is a layer made of SiO. (2) The magneto-optical recording medium according to claim 1, wherein the nitride is a silicon-containing nitride.