JPH079715B2 - Magneto-optical recording medium - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium that records and reproduces information using heat and light such as laser light.

The prior art recording medium of the problems magneto-optical memory, MnBi, MnAlGe, MnSb, MnCuBi , GdFe, TbFe, GdCo, PtCo, TbCo, TbFeCo, GdFeCo, TbFeO 3, GdIG, GdTbFe, GdTbFeCoBi, CoFe 2 O 4 Materials such as are known. These are formed as a thin film on a transparent substrate such as plastic or glass by a method such as a vacuum vapor deposition method or a sputtering method. The characteristics common to these magneto-optical recording media are that the easy axis of magnetization is perpendicular to the film surface, and that the Kerr effect and the Faraday effect are large.

The requirements for such a medium are firstly that the Curie point is about 100 to 200 ° C. and the compensation point is near room temperature. Secondly, defects such as crystal grain boundaries that cause noise are relatively large. Third, it is possible to obtain a magnetically and mechanically uniform film over a relatively large area.

In response to such demands, in recent years, rare earth-transition metal amorphous perpendicular magnetic thin films have attracted much attention among the above materials.

However, in the magneto-optical recording medium composed of such a rare earth-transition metal amorphous thin film, when the magnetic thin film layer is stored in contact with the atmosphere, the rare earth is selectively corroded by oxygen or water in the atmosphere. It has been oxidised, recording information,
Reproduction becomes impossible.

Therefore, generally, much research has been conducted on a magneto-optical recording medium having a structure in which a protective layer is provided on the surface of the magnetic thin film layer.

Conventionally, as such a moisture-proof protective layer, an attempt has been made to provide an inorganic vacuum-deposited film or resin film of silicon monoxide, silicon dioxide, aluminum nitride, silicon nitride, zinc sulfide, or the like (JP-A-58-80142). No.) is disclosed.

In a magneto-optical recording medium, it is advantageous to record / reproduce from the substrate side, and a transparent substrate is used.

As the substrate for the optical disk, a resinous one is preferable in view of easiness of production, easiness of handling, and the like. Among these, acrylic resin, polycarbonate is particularly preferable in terms of transparency, productivity, economy and the like. Resin or the like is preferable.

An intermediate layer made of an inorganic material is usually formed on such a resinous substrate, and a magnetic thin film layer is formed via this intermediate layer.

This intermediate layer has a function as an interference layer, has a function of improving the C / N ratio, and a function of imparting corrosion resistance to prevent deterioration of the magnetic thin film layer.

As a material for such an intermediate layer, for example, silicon oxides such as SiO and SiO ₂ , AlN, Si ₃ N ₄ , ZnS, Si, and Ge have been proposed (JP-A-58-80142).

Of these, silicon nitride is preferable in terms of C / N ratio, durability, etc., but in the conventionally used film structure, C / N
Ratio, corrosion resistance, durability, etc. are still insufficient and further improvement is required.

II Object of the Invention The object of the present invention is to provide a magneto-optical device which has excellent recording / reproducing characteristics, prevents deterioration of the magnetic thin film layer, has excellent corrosion resistance and durability, and has excellent dimensional accuracy stability against warpage. To provide a recording medium.

III DISCLOSURE OF THE INVENTION Such an object is achieved by the present invention described below.

That is, the present invention is a magneto-optical recording medium having an intermediate layer formed of silicon nitride on a resin substrate and a magnetic thin film layer of a rare earth-transition metal on the intermediate layer, wherein the intermediate layer is oxygen. And an oxygen content on the substrate side of the intermediate layer is larger than that on the magnetic thin film layer side.

IV Specific Structure of the Invention Hereinafter, the specific structure of the present invention will be described in detail.

An embodiment of the magneto-optical recording medium of the present invention is shown in FIG.

Referring to FIG. 1, a magneto-optical recording medium 1 of the present invention comprises a substrate 2
It has an intermediate layer 3 on top.

The intermediate layer 3 of the present invention is formed of silicon nitride.

Si ₃ N ₄ generally has a stoichiometric composition, but it may be a bimodal one.

In this case, the average N / Si atomic ratio of the entire layer is about 0.7 to 1.2.

The silicon nitride intermediate layer 3 contains oxygen, but O / Si in the layer
The atomic ratio is 0.2 to 1.0, more preferably 0.2 to 0.6 as the average of the entire layer.

At this time, if the O / Si ratio is less than 0.2, the effect of improving the durability is lost.

On the other hand, if it exceeds 1.0, the apparent Kerr rotation angle decreases, which adversely affects the characteristics.

In such a thickness direction of the intermediate layer 3, there is a predetermined oxygen concentration distribution such that the oxygen content on the substrate side in the intermediate layer 3 becomes larger than that on the magnetic thin film layer 4 side described later.

The oxygen concentration distribution in the silicon nitride intermediate layer 3 is such that the O / Si atomic ratio at the positions of the silicon nitride intermediate layer 3 from the substrate 2 side to 1/4 is 1/4 from the magnetic thin film layer 4 side. The O / Si atomic ratio at the positions up to is 3 times or more, more preferably 5 times or more.

If this value is less than 3 times, the C / N ratio, corrosion resistance and durability deteriorate. On the other hand, when this value is 5 times or more, which is the preferable range described above, the C / N ratio and durability are significantly improved.

By having the above-mentioned oxygen concentration distribution in the silicon nitride intermediate layer 3, the following effects occur.

That is, firstly, by appropriately setting the oxygen concentration on the substrate side of the silicon nitride intermediate layer 3, reflection at the interface between the substrate (polycarbonate resin has a refractive index of about 1.57 at 830 nm) and the silicon nitride intermediate layer 3 Can be effectively prevented, and good recording / reproducing characteristics can be obtained.

Secondly, by suppressing the oxygen concentration in the silicon nitride intermediate layer 3 on the magnetic thin film layer 4 side to be low, it is possible to effectively prevent the deterioration of the magnetic thin film layer 4 containing Fe and Co as essential components described later. .

The oxygen concentration distribution may be continuous or discontinuous.

O / which exists in the thickness direction of the silicon nitride intermediate layer 3
The atomic ratio distribution of Si is measured, for example, by the method described below.

That is, first, the silicon nitride intermediate layer 3 is ion-etched from the magnetic thin-film layer 4 side at a constant etching rate, while SIMS (secondary ion mass spectrometry), AES (Auger spectroscopic analysis), ESCA, etc. are used for elemental analysis. I do. And
The time until the carbon C is detected after reaching the substrate 2 such as a polycarbonate resin is measured.

From the result of elemental analysis in the layer from the beginning of this required time to 1/4 and the time from 3/4 to reaching the substrate,
The O / Si average atomic ratio at a predetermined position in the layer is calculated.

Needless to say, the average O / Si atomic ratio of the entire layer can also be calculated.

In order to form the silicon nitride intermediate layer 3 having an oxygen concentration distribution in the film thickness direction as described above, Si ₃ N ₄ and SiO ₂ are used as targets, and the sputter rates of both are controlled to change them. While using the two-way sputtering method to form a film, or using reactive sputtering in which Si ₃ N ₄ is used as a target in an atmosphere containing oxygen to control the oxygen concentration and change the oxygen concentration to form a film. Si in an atmosphere containing nitrogen
Is used as a target to control the oxygen and nitrogen concentrations,
Reactive sputtering or the like that changes these to form a film is used.

The conditions for these sputterings may be conventional.

Further, according to this, it is also possible to appropriately use other vapor phase film forming methods, for example, vapor deposition and the like.

The thickness of the silicon nitride intermediate layer 3 thus formed is 50
It is 0 to 1500Å, more preferably 700 to 1000Å.

Incidentally, the silicon nitride intermediate layer is usually in an amorphous state.

Further, Ar or the like existing in the film forming atmosphere may be included.

In addition, a small amount of elements such as Al, Zn, Cr and Ba may be added depending on the case.

The substrate 2 on which the above-mentioned silicon nitride intermediate layer 3 is provided is made of resin.

Preferred resins include acrylic resins, polycarbonate resins, epoxy resins, polymethylpentene resins and the like.

Among these resins, a polycarbonate resin is preferable in terms of durability, particularly resistance to warping and the like.

In this case, the polycarbonate resin may be any of an aliphatic polycarbonate, an aromatic-aliphatic polycarbonate and an aromatic polycarbonate, but an aromatic polycarbonate resin is particularly preferable. Of these, a polycarbonate resin made of bisphenol is preferable in terms of melting point, crystallinity, handling, and the like. Among them, the bisphenol A type polycarbonate resin is most preferably used.

The number average molecular weight of the polycarbonate resin is 10,000.
It is preferably about 15,000.

The refractive index at 830 nm of such a substrate 2 is usually about 1.55 to 1.59.

Since recording is performed through the substrate 2, the transmittance for writing light or reading light is 86% or more.

The substrate 2 is usually disk-shaped and has a thickness of about 1.2 to 1.5 mm.

A tracking groove may be formed on the surface of the disk-shaped substrate on which the magnetic thin film layer is formed.

The depth of the groove is about λ / 8n, especially λ / 6n to λ / 12n (here,
n is the refractive index of the substrate). The width of the groove is
It is about the track width.

Then, it is usually preferable to irradiate the writing light and the reading light from the back surface side of the substrate with the magnetic thin film layer located in the concave portion of the groove as a recording track portion.

With this configuration, the write sensitivity and the read C / N ratio are improved, and the tracking control signal is increased.

Further, the other substrate shape may be a tape, a drum, or the like.

The magnetic thin film layer 4 is formed on the silicon nitride intermediate layer 3 described above.

In the magnetic thin film layer 4 of the present invention, information is magnetically recorded by a modulated heat beam or a modulated magnetic field, and the recorded information is magnetic-optically converted and reproduced.

As the material of such a magnetic thin film layer 4, an alloy of a rare earth metal such as Gd and Tb and a transition metal such as Fe and Co is formed as an amorphous film by a sputtering or vapor deposition method. And Co are essential components.

In this case, the total content of Fe and Co is preferably 65 to 85 at%.

And the balance is substantially rare earth metals, especially Gd and / or Tb.

And, as a preferable example thereof, TbFeCo, GdFeCo, GdTbFe
There are Co etc.

In these magnetic thin film layers, Cr in the range of 10 at% or less,
Al, Ti, Pt, Si, Mo, Mn, V, Ni, Cu, Zn, Ge, Au, etc. may be contained.

In addition, as a rare earth element, Sc, Y, L in the range of 10 at% or less
a, Ce, Pr, Nd, Pm, Sm, Eu, Dy, Ho, Er, Tm, Yb, Lu
Etc. may be contained.

The thickness of such a magnetic thin film layer is preferably 0.01 to 1 μm.

Further, it is preferable to provide one or more kinds of various protective layers on the side of the magnetic thin film layer 4 opposite to the substrate 2.

In FIG. 1, a protective layer 5 and a protective film 6 are provided.

In this case, the material of the protective layer 5 is not particularly limited as long as it has a function as a protective layer, but is preferably an oxide or nitride thin film.

As the oxide, silicon oxide such as silicon monoxide and silicon dioxide, aluminum oxide, titanium oxide, zinc oxide and the like are preferable.

Further, as the nitride, silicon nitride, aluminum nitride, titanium nitride, boron nitride and the like are preferable.

Of these, silicon nitride is particularly preferable.

The thickness of such a thin film is about 0.1 to 10 μm.

The protective layer 5 may be formed by vacuum vapor deposition, sputtering or the like.

On the other hand, as the material of the protective film 6, generally known various organic substances may be used.

More preferably, a radiation-curable compound cured with radiation such as electron beam or ultraviolet ray is used.

The radiation-curable compound used is an acrylic double bond having an unsaturated double bond that is sensitive to ionization energy and exhibits radical polymerizability, an acrylic double bond such as methacrylic acid, or an ester compound thereof, or a diallyl phthalate. Examples include monomers, oligomers and polymers having or introduced in the molecule a group that is crosslinked by irradiation with radiation such as allyl double bond, unsaturated double bond such as maleic acid or maleic acid derivative, or polymerized and dried. it can.

A compound having a molecular weight of less than 2000 is used as the radiation-curable monomer, and a compound having a molecular weight of 2000 to 10,000 is used as the oligomer.

These include styrene, ethyl acrylate, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, diethylene glycol methacrylate, 1,6-hexane glycol diacrylate, 1,6-hexane glycol dimethacrylate, etc., but especially preferred as,
Pentaerythritol tetraacrylate (methacrylate), pentaerythritol acrylate (methacrylate), trimethylolpropane triacrylate (methacrylate), trimethylolpropane diacrylate (methacrylate), polyfunctional oligoester acrylate (Aronix M-7100, M-5400, M- 550
0, M-5700, M-6250, M-6500, M-8030, M-806
0, M-8100, etc., Toagosei), acrylic modified urethane elastomer (Nipporan 4040), or those into which a functional group such as COOH has been introduced, acrylate (methacrylate) of phenol ethylene oxide adduct, the following general A compound having an acrylic group (methacrylic group) or ε-caprolactone-acrylic group on the pentaerythritol condensed ring represented by the formula, 1) (CH ₂ = CHCOOCH ₂ ) _3- CCH ₂ OH (special acrylate A) 2) (CH ₂ = CHCOOCH ₂ ) _3- CCH ₂ CH ₃ (special acrylate B) 3) [CH ₂ = CHCO (OC ₃ H ₆ ) n-OCH ₂ ] _3- CCH ₂ CH ₃ (special acrylate C) In the formula, a compound of m = 1, a = 2, b = 4 (hereinafter referred to as a special pentaerythritol condensate A), a compound of m = 1, a = 3, b = 3 (hereinafter referred to as a special pentaerythritol condensate B) , M = 1, a = 6, b = 0 compound (hereinafter referred to as special pentaerythritol condensate C), m = 2, a = 6, b = 0 compound (hereinafter referred to as special pentaerythritol condensate D) , And special acrylates represented by the following general formula.

_{8) CH 2 = CHCOO- (CH} 2 CH 2 O) 4 -COCH = CH 2 ( special acrylate H) 12) AM-Nn-MA A: acrylic acid, M: dihydric alcohol N: dibasic acid (special acrylate L) As the radiation curable oligomer, a polyfunctional oligoester acrylate represented by the following general formula or Examples thereof include acrylic modified urethane elastomers, or products obtained by introducing a functional group such as COOH into these products.

(In the formula, R ₁ and R ₂ : alkyl, n: integer) Further, a radiation-curable chemical substance obtained by subjecting a thermoplastic resin to radiation-sensitive modification may be used.

Specific examples of such a radiation curable resin include acrylic double bonds such as acrylic acid, methacrylic acid, or their ester compounds showing an unsaturated double bond having radical polymerizability, such as diallyl phthalate. It is a resin in which a group such as an allyl double bond, an unsaturated bond such as maleic acid or a maleic acid derivative, which is crosslinked or polymerized by irradiation with radiation is contained or introduced in the molecule of the thermoplastic resin.

Examples of the thermoplastic resin that can be modified into a radiation curable resin include vinyl chloride copolymers, saturated polyester resins, polyvinyl alcohol resins, epoxy resins, phenoxy resins, and fibrin derivatives.

Other resins that can be used for radiation-sensitive modification include polyfunctional polyester resins, polyetherester resins, polyvinylpyrrolidone resins and derivatives (PVP olefin copolymers), polyamide resins, polyimide resins, phenolic resins, spiroacetal resins, An acrylic resin containing at least one of a hydroxyl group-containing acrylic ester and methacrylic ester as a polymerization component is also effective.

The thickness of the protective film 6 of such a radiation-curable compound is 0.1
-30 μm, more preferably 1-10 μm.

If the film thickness is less than 0.1 μm, a uniform film cannot be formed, the moisture-proof effect in an atmosphere with high humidity is not sufficient, and the durability of the magnetic thin film layer 4 is not improved. If it exceeds 30 μm, warpage of the recording medium or cracks in the protective film may occur due to shrinkage during curing of the resin film, which is not practical.

Such a coating film may be usually formed by combining various known methods such as spinner coating, gravure coating, spray coating and dipping. The layer forming conditions of the coating film at this time may be appropriately determined in consideration of the viscosity of the mixture of the coating film composition, the target coating film thickness, and the like.

In order to cure such a coating film to form a protective layer, the coating film may be irradiated with a radiation such as an electron beam or an ultraviolet ray.

When using an electron beam, the radiation characteristics are as follows: acceleration voltage 10
It is expedient to use a radiation accelerator of 0 to 750 KV, preferably 150 to 300 KV, and to irradiate it with an absorbed dose of 0.5 to 20 megarads.

On the other hand, when ultraviolet rays are used, a photopolymerization sensitizer is usually added to the above-mentioned radiation-curable compounds.

The photopolymerization sensitizer may be any conventionally known one, for example, benzoin methyl ether, benzoin ethyl ether, α-methylbenzoin, benzoin series such as α-chlordeoxybenzoin, benzophenone, acetophenone, bisdialkylaminobenzophenone, etc. Examples thereof include ketones, quinones such as acetoraquinone and phenanthraquinone, and sulfides such as benzyl disulfide and tetramethylthiuram monosulfide.
The photopolymerization sensitizer is preferably in the range of 0.1 to 10% by weight based on the resin solid content.

Then, in order to cure the coating film containing such a photopolymerization sensitizer and the radiation-curable compound by ultraviolet rays, various known methods may be used.

For example, a UV bulb such as a xenon discharge tube or a hydrogen discharge tube may be used.

On such a protective film 6, a protective plate 8 is usually provided via an adhesive layer 7.

That is, the protective plate 8 is used only in the case of so-called single-sided recording in which recording / reproduction is performed only from the back surface (surface on the side where the magnetic thin film layer 4 is not provided) of the substrate 2.

The resin material of the protective plate 8 is not particularly required to have transparency, and various resins such as polyethylene, polyvinyl chloride, polystyrene, polypropylene,
Polyvinyl alcohol, methacrylic resin, polyamide,
Various types of thermoplastic resin such as polyvinylidene chloride, polycarbonate, polyacetal, fluororesin, phenol resin, urea resin, unsaturated polyester resin, polyurethane, alkyd resin, melamine resin, epoxy resin, silicon resin, etc. are used. It is possible.

In addition, various inorganic materials such as glass and ceramic are used as the protective plate 8.
You may use as.

The shape, dimensions, etc. of this product are substantially the same as those of the substrate 2 described above.

Such a protective plate 8 is bonded via the adhesive layer 7 as described above. The adhesive layer is usually an adhesive such as a hot melt resin and has a film thickness of about 1 to 100 μm.

On the other hand, instead of using the above-mentioned protective plate 8, one set of substrates having the above-mentioned magnetic thin film layer 4, the protective layer 5, the protective film 6 and the like is used, and both magnetic thin film layers are made to face each other and are bonded to each other. A so-called double-sided recording type may be used in which writing is performed from the back side of both substrates by bonding using the agent layer 7.

Further, it is preferable to provide a hard coat layer as various protective films on the back surface of the substrate 2 or the protective plate 8 (the surface on the side where the magnetic thin film layer 4 is not provided).

The material of the hard coat layer may be the same as the material of the protective film 6 described above.

V Effect of the Invention The magneto-optical recording medium of the present invention has a silicon nitride intermediate layer containing oxygen between the resinous substrate and the magnetic thin film layer and having a predetermined distribution in the oxygen concentration. Therefore, the recording and reproducing characteristics are excellent, and the deterioration of the magnetic thin film layer with time is small.

Especially when the substrate is made of polycarbonate resin,
The deterioration of the magnetic thin film layer over time is less. Moreover, the resistance to warping and the like is further improved.

VI Specific Examples of the Invention Hereinafter, the present invention will be described in more detail with reference to Examples of the present invention.

[Example 1] A silicon nitride intermediate layer was formed on a substrate made of a bisphenol A-based polycarbonate resin (molecular weight: 15000) having a diameter of 13 cm and a thickness of 1.2 mm to a thickness of 800 by reactive sputtering.
Layered in Å.

At the time of sputtering, in order to provide a predetermined oxygen concentration distribution in the silicon nitride intermediate layer, Si was used as a target at an operating pressure of 1 Pa in an Ar atmosphere containing oxygen and nitrogen, and the oxygen and nitriding concentrations were temporally controlled. did.

After forming the layer, the elemental analysis in the film was performed by Auger spectroscopic analysis while performing ion etching.
The O / Si atomic ratio (x ₁ ) up to the position 4 was 0.9, and the O / Si atomic ratio (x ₄ ) from the magnetic thin film layer side to the position 1/4 was 0.15.

The average O / Si atomic ratio (x) and N / Si atomic ratio (y) of the entire film were 0.3 and 0.8, respectively.

21at% Tb, 68at% Fe, 7a on top of this silicon nitride intermediate layer
A t% Co, 4at% Cr alloy thin film was sputtered to a thickness of 800Å to form a magnetic thin film layer.

The target used was an Fe target mounted on a Tb, Co, or Cr chip.

A protective layer of Si ₃ N _{4 is formed} on this magnetic thin film layer by sputtering to a film thickness of 1000Å, and a coating composition containing the following radiation-curable compound is formed on this protective layer as a protective film by spinner coating. did.

(Coating composition) Polyfunctional oligoester acrylate 100 parts by weight Photosensitizer 5 parts by weight After applying such a coating composition, it was irradiated with ultraviolet rays for 15 seconds to be crosslinked and cured to obtain a cured film.

The film thickness at this time was 5 μm.

The same process as above was performed on the back surface of the substrate. Further, a polycarbonate resin protective plate having a diameter of 13 cm was adhered onto the protective film with an adhesive to obtain a sample of the present invention (Sample No. 1). According to this, various samples were prepared in the same manner as in No. 1 except that the silicon nitride intermediate layer of Sample No. 1 was a silicon nitride intermediate layer having the oxygen concentration distribution shown in Table 1 below.

For the above samples, the following characteristic values were measured.

(1) C / N ratio (storage deterioration) C / N ratio at the initial stage and C / N after storage at 60 ° C, 90% RH for 1000 hours
The amount of change in the ratio was measured under the following conditions.

Rotation speed 4m / sec Carrier frequency 500KHz Resolution 30KHz Recording power (830nm) 3 to 4mW Reproduction power (830nm) 1mW (2) Bit error rate Bit of EFM signal after initial storage at 1000C and 90% RH for 1000 hours The error rate was measured.

The results are shown in Table 1.

From the results shown in Table 1, the effect of the present invention is clear.

That is, in the present invention shown in No. 1 to No. 5, x ₁ is
Since it is larger than x ₄ , the C / N ratio, the bit error rate, and these values after storage show good results.

In this case, in No. 1 to No. _{4 in} which x ₁ / x ₄ is 3 or more, the increase in bit error rate after storage is extremely small.
In particular, No. 1 and No. 2 show extremely excellent results because the values of x ₁ / x ₄ , x and y are within the optimum range, and x ₁ / x
₄ is 5 or more, and x is 0.2 to 1.0, especially 0.2 to 0.6, and y is
It can be seen that the effect of preventing storage deterioration is extremely large when it is 0.7 to 1.2.

[Brief description of drawings]

FIG. 1 is a sectional view of a magneto-optical recording medium showing an example of the present invention. DESCRIPTION OF SYMBOLS 1 ... Magneto-optical recording medium, 2 ... Substrate 3 ... Silicon nitride intermediate layer, 4 ... Magnetic thin film layer, 5 ... Protective layer, 6 ... Protective film, 7 ... Adhesive layer, 8 ...... Protective plate

Claims (5)

[Claims] 1. A magneto-optical recording medium having an intermediate layer formed of silicon nitride on a resin substrate and having a magnetic thin film layer of a rare earth-transition metal on the intermediate layer, wherein the intermediate layer contains oxygen. A magneto-optical recording medium containing the above-mentioned intermediate layer, wherein the oxygen content on the substrate side is larger than that on the magnetic thin film layer side. 2. An O / Si atomic ratio in the silicon nitride intermediate layer at a position 1/4 from the substrate side of the silicon nitride intermediate layer in the silicon nitride intermediate layer at a position 1/4 from the magnetic thin film layer side. The magneto-optical recording medium according to claim 1, wherein the O / Si atomic ratio is 3 times or more. 3. The average O / Si atomic ratio of the entire silicon nitride intermediate layer is 0.2 to 1.0.
A magneto-optical recording medium according to item. 4. An average N / Si atomic ratio of the entire silicon nitride intermediate layer is 0.7 to 1.2.
A magneto-optical recording medium according to any one of the items. 5. The magneto-optical recording medium according to any one of claims 1 to 4, wherein the resin substrate is a polycarbonate resin.