JPS63275060A - Magneto-optical recording medium - Google Patents

Abstract

PURPOSE:To improve corrosion resistance, durability, recording sensitivity and productivity by forming an intermediate protective layer of a metal oxide or metal nitride and forming a protective layer of a specific metal carbide. CONSTITUTION:The intermediate protective layer is formed of the metal oxide or metal nitride and the protective layer is formed of the metal carbide having >=40% reflectivity measured by light of 830nm wavelength. The carbides of Ti, Zr, Ta, Cr, and Mo are more preferable among the metal carbides and above all, the carbides of Ti, Ta and Mo are preferred. The metal oxide and metal nitride are dense to prevent infiltration of moisture and oxygen from the outside, have themselves the high corrosion resistance and small reactivity with a magneto-optical recording layer and have the high adhesiveness to a resin in the case of using a resin substrate as a substrate. The metal carbides are generally opaque and have high reflectivity. The recording sensitivity, corrosion resistance, stability with lapse of time and productivity are thereby improved.

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. As a recording layer of a magneto-optical recording medium, thin films of rare earth metals and transition metals are the most excellent in terms of overall characteristics, but a fatal flaw is that they lack corrosion resistance.

In other words, 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 A 1 g03 and high melting point nitrides such as SiN 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 means that the physical properties required for the intermediate protective layer are that it does not react with the recording layer, has good adhesion to the substrate, has excellent transparency, and has a large refractive index.
In contrast, the physical properties necessary for a protective layer include 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, and the required physical properties are different for each material.

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.
A magneto-optical recording medium characterized in that the intermediate protective layer is formed of a metal oxide or a metal nitride, and the protective layer is formed of a metal carbide having a reflectance of 40% or more when measured with light at a wavelength of 830 nm.

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 2M.

As the magneto-optical recording layer, for example, TbPe.

Amorphous magnetic alloys of rare earths and transition metals such as TbFeCo, TbCo, DyFeCo, and MnB1. Mn
A polycrystalline perpendicular magnetization film such as CuB1 is used. It is particularly effective for use in rare earth alloy magnetic films. The thickness of the magneto-optical recording layer is 300 to 1500, preferably 500 to 1,500.
There are 800 people.

In the present invention, a layer containing a metal oxide or metal nitride is formed as an intermediate protective layer between the substrate and the magneto-optical recording layer. As a metal oxide, Af203, Tag
's alone or a mixture of these metal oxides, or Aj! -Ta-0 complex oxide, etc. can be mentioned.

Furthermore, other elements such as St, Ti, Z
r, W, Mo, Yb, etc. alone in the form of oxides or Aj! , may be combined with Ta to form an oxide. These metal oxides are dense and prevent moisture and oxygen from entering from the outside, have high corrosion resistance, and have low reactivity with the magneto-optical recording layer.Also, when using a resin substrate as a substrate, it is difficult to interact with the resin. Excellent adhesion.

Specifically, metal nitrides include metal nitrides such as silicon, aluminum, and germanium, or two of these metals.
Examples include composite nitrides of more than one species or composite nitrides of these with niobium and tantalum (for example, 5iNbN+5iTaN, etc.). Among them, nitrides containing Si give good results.

Metal nitride is dense and prevents moisture and oxygen from entering from the outside, has high corrosion resistance, and has low reactivity with the magneto-optical recording layer. High adhesion.

The appropriate thickness of this intermediate protective layer is about 300 to 1,500 layers.

A protective layer made of metal carbide is provided on the magneto-optical recording layer. As the metal carbide, one is used that has a reflectance of 40% or more when visible light or laser light with a wavelength of 830 nm is irradiated onto a thin film with a thickness of 2000 Å or more formed on a clean and flat substrate.

Such metal carbides include Ti, Zr, lif
, V.

Examples include carbides of Nb5Ta, Cr, Mo, and W, and these may be used alone or in combination. Such metal carbides include TiC, ZrC, HfC, and VCs.
NbC.

TaC5CrC (CrsCz, CrtCz, etc.), M
Examples include oC (MozC, etc.), courtesy, etc.

These are generally opaque and highly reflective.

On the other hand, semimetal or semiconductor carbides include 5iC1B,
Although these are transparent, they do not have sufficient corrosion resistance.

Among the above metal carbides, Ti, Zr, Ta, Crs
Mo carbides are preferred, especially Ti, Ta,
Mo carbide is good. These carbides are more preferably amorphous.

The thickness of this protective layer is about 10 to 5000, preferably about 50 to 1000.

Physical vapor deposition (PVD) such as sputtering is used to form each layer on the substrate, such as an intermediate protective layer of metal oxide or metal fluoride, a magneto-optical recording layer, and a protective layer made of metal carbide.
), chemical vapor deposition (CVD) such as plasma CVD, etc. are applied.

To form a magneto-optical recording 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. In the case of electron beam evaporation, the film is deposited while irradiating the film with high-energy particles, or during sputtering, the static gas pressure is lowered to increase the density of the film and produce a stable film. This is preferable because it allows

Further, methods using reactive ion blating and reactive sputtering are 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

In the present invention, in addition to the metal carbide protective layer, SiO and
It is preferable to laminate about 50 to 2000 layers, preferably about 100 to 1000 layers, of silicon oxide such as i02 on the metal silicide layer. As the SiO□-based protective layer, for example, deposition glass 7059 or 7740 manufactured by Corning Corporation may be used.

〔Example〕

Example 1 Using a polycarbonate substrate, a sintered pellet of Ta205 with a thickness of 1III11 and a diameter of 9 mm + φ was placed on a 5 inch φ Ant's sintering target, and RF was conducted in Ar gas.
Sputtering was performed to form an intermediate protective film for 800 people.

The A15Ta ratio (atomic ratio) of the intermediate protective film was 2:8.

4 inch φ MO□C target and Tb1O Sonoguchi x 1
A target in which a small piece of wt was placed on an Fe target was set up, and the atmosphere was evacuated to below 3×10-'torr.

Distance between substrate and target: 95 am, ArtJi amount: 3
03CCM. After press battering with a sputtering gas pressure of 3 mtorr, a TbFe film was prepared by sputtering with a direct current power (DC) of 300 W for 1 minute.
Subsequently, a MO□C target was sputtered in the same vacuum at an Ar flow rate of 30 SCCM, a sputtering pressure of 3 mtorr, and a direct current power (DC) of 300 W, and 800 people were deposited.

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 position, recording frequency 1. Q MHz duty 50% Playback conditions: CLV4m/S Playback power 0.81 Average value of 16 times In this example, recording sensitivity 2.3mW, C/N ratio 39dB
In this example, the recording power was improved by 20% and the C/N ratio was improved by 4 dB compared to Comparative Example 1 described later.

As for the static characteristics, in the Kerr rotation angle measurement, Tb has a Kerr rotation angle of 0.20°, a reflectance of 42%, and a coercive force of 2.5 KG.
It had rich composition hysteresis.

Further, when the recording layer was analyzed by X-ray diffraction, it was found to be amorphous.

It should be noted that the medium with this configuration was kept in a normal atmosphere for 40 days and then for a further 70 days.
It was kept in a high temperature and high humidity chamber at 85% RH for 200 hours, but no deterioration was observed in terms of optical observation and static properties.

In addition, Mo and C films with a thickness of 5000 were created on a glass substrate.
When light (laser light with a wavelength of 830 nm) was incident on the film from the outside air side, the reflectance was measured to be 60%.

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 d and the C/N ratio was 35 dB. (It has been experimentally found that when reproducing is performed using a differential optical system instead of the APD non-differential system, the C/N ratio generally improves by 10 dB in PCR.) Example 2 Same as Example 1 After that, 450 SiO□ films were formed using 100 W of radio frequency (RF) power under the same conditions. When the recording sensitivity and C/N ratio of this recording medium were measured under the same conditions as in the example, the recording sensitivity was 2. Qm
In this example, Comparative Example 1 had a W and C/N ratio of 39 dB.
The recording power was improved by 24% and the C/N ratio was improved by 4 dB compared to the previous version.

As for the static characteristics, in the Kerr rotation angle measurement, the Kerr rotation angle was 0.19°, the reflectance was 46%, and the Tb had a coercive force of 2.2 KG.
It had rich composition hysteresis.

The medium with this configuration was placed in a constant temperature and humidity chamber at 70°C and 85% RH.
No deterioration was observed in optical observation or static properties after holding for 1,000 hours. [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, and has good recording sensitivity. Good quality and excellent productivity.

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

Claims (4)

[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 formed of a metal oxide or a metal nitride, and the protective layer has a wavelength of 830 nm. 1. A magneto-optical recording medium formed of a metal carbide having a reflectance measured by light of 40% or more. (2) Metal carbide is Ti, Ta, Zr, Cr, or Mo
The magneto-optical recording medium according to claim 1, which is a carbide of. (3) The magneto-optical recording medium according to claim 2, wherein the metal carbide is a carbide of Ti, Ta or Mo. (4) The magneto-optical recording medium according to claim 1, further comprising a silicon oxide protective layer provided on the metal carbide.