JPH02198042A - Optical recording medium - Google Patents

Abstract

PURPOSE:To improve the recording sensitivity and C/N by providing an intermediate layer containing Si, N and an element selected from lanthanoids. CONSTITUTION:The intermediate layer 4 between a recording layer 5 and a substrate 2 contains Si, N and at least one element (X) selected from lanthanoids. By this method, the sensitivity and C/N of the medium is improved, and particularly when X includes La and Ce, this effect is more significant. The proportion of the amt. of X to the total amt. of X and Si in the intermediate layer 4 is preferably 5 - 50atomic%.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an optical recording medium such as a magneto-optical recording disk or a phase change type optical recording disk.

<Prior Art> Optical recording media are constructed by forming a recording layer on a rigid or flexible substrate.

Among such optical recording media, magneto-optical recording media usually use an amorphous magnetic thin film of rare earth elements and transition metals as a recording layer, and heat the recording layer to around the Curie temperature using light such as a laser beam. Information is recorded by applying a magnetic field from the outside as necessary to reverse the magnetization of the heated portion.

The recorded information is read out by irradiating the surface of the recording layer with readout light such as a laser beam and detecting the Kerr rotation angle of the readout light reflected on the surface of the recording layer.

In such magneto-optical recording media, improvements in recording sensitivity and C/
In order to obtain so-called enhancement effects such as improving the N ratio,
An intermediate layer made of a dielectric or the like is usually provided between the recording layer and the substrate.

Since the intermediate layer multiple-reflects the recording light at the layer interface, recording sensitivity can be improved. Furthermore, since the readout light is also subjected to multiple reflections, the C/N ratio is improved. Furthermore, since the Kerr rotation angle can be amplified by multiple reflections of the readout light, this effect also improves the C/N ratio.

Rare earth elements used in the recording layer include Gd, Tb%
Fe, Co, etc. are preferably used as transition metals such as Dy, and in particular, Tb-Fe-
Co, Dy-Tb-Fe-Co, Nd-Dy-Fe-C
A recording layer consisting of a material such as O is attracting attention.

However, since these rare earth element-transition metal amorphous magnetic thin films have low weather resistance such as corrosion resistance, it is necessary to provide a corrosion-resistant protective layer.

Various proposals have been made regarding the intermediate layer or corrosion-resistant protective layer having an enhancing effect, as described below.

For example, Japanese Patent Application Laid-Open No. 61-22458 discloses that an optical fiber having a dielectric material as an intermediate layer containing silicon nitride (Si, N4) as a main component and containing an additive component to have a refractive index of 2.1 or more is disclosed. A magnetic recording medium is disclosed, which provides corrosion resistance.

The aim is to improve the C/N ratio and the adhesion with the recording layer.

In addition, this publication includes La, as an example of the additive component.
Ce is listed.

Also, for example, in Japanese Patent Application Laid-Open No. 63-161551,
A magneto-optical recording medium is disclosed that has an intermediate layer containing an oxide of one or more rare earth elements, silicon oxide, and silicon nitride, and has improved corrosion resistance and C/N ratio.

Furthermore, in Japanese Patent Application Laid-Open No. 63-81643, Ti,
Zr, Hf, V, Nb% Ta, Cr
, MO%W, and a protective layer made of silicon and nitrogen are described.

This material has the effect of being excellent in corrosion resistance.

Furthermore, Japanese Patent Publication No. 62-31052 discloses an optical recording system in which a composite dielectric film of aluminum nitride and silicon nitride is provided between the substrate and the recording layer with n (refractive index) = 2.15 to 1, 70. The medium is disclosed. This product has an excellent protective effect.

In addition to the above-mentioned magneto-optical recording media, optical recording media include so-called phase-change optical recording media, in which information is recorded by changing the phase of the recording layer using heat such as laser light. There is also an optical recording medium in which information is read out by detecting changes in the reflectance of the recording layer that occur.

Even in such phase change type optical recording media, an enhancement layer that utilizes multiple reflections of light is provided to improve recording sensitivity and C.
Efforts are being made to improve the /N ratio.

<Problems to be Solved by the Invention> However, there are strict requirements for improving the weather resistance, C/N ratio, and recording sensitivity of magneto-optical recording media, and even magneto-optical recording media with the above-mentioned protective layer etc. Not enough. In addition, according to the research of the present inventors, weather resistance, C, /
It is difficult to simultaneously improve the N ratio and recording sensitivity with a protective layer or the like having the above composition.

For example, among the specific examples of dielectrics described in JP-A No. 61-22458, examples containing La and Ce include 5i-N, (90 mol%)-AI220° (6 mol% )
-La20s (4 mol%) StsN4 (90 mol%
)-Aβ, 0. (6 mol%) -CeO2 (4 mol%) SisN4 (90 mol%) -AgN (5 mol%)
-L, aiOs (5 mol%), all of which contain oxides and Aρ. As described above, when the intermediate layer contains oxygen, it is difficult to obtain sufficient recording sensitivity and it is difficult to obtain a sufficient C/N ratio.

In addition, although JP-A-61-22458 also discloses simple substances or nitrides of La and Ce as additive components, there are no specific examples of the oxygen-free intermediate layer obtained by adding these to 5isN. There is no description. Further, regarding the amount of the additive component added, there is only a description that it is 5 mol% or more.

The intermediate layer containing rare earth element oxide, silicon oxide, and silicon nitride described in JP-A No. 63-161551 contains oxygen, and therefore, as mentioned above, sufficient recording sensitivity cannot be obtained. (Also, it is difficult to obtain a sufficient C/N ratio.

Further, the various protective layers described in Japanese Patent Application Laid-Open No. 63-81643 do not have sufficient long-term protection performance against pit error rates at high temperatures.

The aluminum nitride silicon nitride composite film described in Japanese Patent Publication No. 62-31052 has insufficient electrical properties such as C/N ratio, recording sensitivity, etc.

Note that improvements in recording sensitivity, C/N ratio, etc. can be achieved even in optical recording media having so-called phase change type recording layers such as Te-based ones.
Similar to the magneto-optical recording medium mentioned above, this is one of the problems.

The present invention was made in view of the above-mentioned circumstances, and an object of the present invention is to provide a magneto-optical recording medium having high weather resistance, high C/N ratio, and high recording sensitivity.

<Means for Solving the Problems> Such objects are achieved by the following inventions (1) to (3).

(1) An optical recording medium having a recording layer on a substrate and an intermediate layer between the recording layer and the substrate, wherein the intermediate layer is composed of X (where X is at least one selected from lanthanide elements) An optical recording medium characterized in that it contains Si and N (representing a species element).

(2) The optical recording medium according to (1) above, wherein the X includes at least one of La and Ce.

(3) The content of X relative to the total of X and Si in the intermediate layer is 5 to 50% in atomic ratio, or
The optical recording medium according to 2).

<Function> In the optical recording medium of the present invention, the intermediate layer provided between the substrate and the recording layer contains at least one element selected from lanthanide elements, Si, and N.

In the present invention, since the intermediate layer contains at least one element selected from lanthanide elements, weather resistance is significantly improved.

Furthermore, since the intermediate layer of the optical recording medium of the present invention contains lanthanoids and does not contain oxygen, higher recording sensitivity and C/N ratio can be obtained than in the case where the intermediate layer does not contain lanthanoids.

Specific composition> Hereinafter, the specific configuration of the present invention will be explained in detail.

FIG. 1 shows an example of a magneto-optical recording medium as a preferred embodiment of the optical recording medium of the present invention.

The magneto-optical recording medium 1 shown in FIG. 1 has a protective layer 3, an intermediate layer 4, a recording layer 5, a protective layer 6, and a protective coat 7 on a substrate 2 in this order.

In the present invention, the intermediate layer 4 includes at least one element selected from lanthanide elements (hereinafter abbreviated as X).
, Si, and N.

In the present invention, there is no particular restriction on X, but if the intermediate layer 4 is
When at least one of Ce and Ce is included, the effects of the present invention will be even higher.

X is usually contained in the intermediate layer 4 as a non-stoichiometric nitride.

When two or more types of lanthanoid elements are contained, the ratio of their amounts is arbitrary.

A preferable combination and content of X contained in the intermediate layer 4 is one in which one or more of La and Ce are the main components, and other rare earth elements such as Y, Nd, Sm, and Gd are
The content may be about 0 at% or less.

In addition to these, Fe, Mg, Ca, Sr, Ba, etc. may be contained.

Among these elements, Fe is 10 at% or less, and
Other elements may be contained in a total of 10 at% or less.

In addition, in the present invention, it is preferable that the intermediate layer 4 does not substantially contain oxygen and Al2. In the present invention, "containing substantially no oxygen" means that the oxygen content is 0.1 at
% or less, and "substantially not containing A2" means that the content of Al1 is lat% or less.

Since it does not contain oxygen, it has an excellent function of preventing oxidation of the recording layer, and also has a high refractive index, so C/N
It becomes an excellent intermediate layer in terms of ratio, sensitivity, etc.

Furthermore, since it contains a rare earth element, it is more effective in improving characteristics such as C/N ratio and sensitivity and ensuring weather resistance than in the case of containing Al1.

In addition to the lanthanoid elements, the intermediate layer 4 contains Si and N.
Contains.

Nitride of Si is usually St! Although it is expressed in the form of N, it may deviate from such a stoichiometric composition.

Note that the intermediate layer 4 is usually in an amorphous state.

The refractive index of such an intermediate layer 4 at 800 nm is preferably 2.0 to 3.0, more preferably 2.1 to 2.0.
It is 8.

If the refractive index is less than the above range, enhancement effects such as Kerr rotation angle amplification will be small and the output will be reduced.

Moreover, when the above range is exceeded, the output decreases and noise increases.

In such an intermediate layer 4, the content ratio of X to the total of X and Si, that is, 100X/(X+Si)
is preferably 5 to 50%, particularly 8 to 30% in atomic ratio.

If this value is less than the above range, the improvement in the C/N ratio and recording sensitivity will be insufficient, and if it exceeds the above range, problems will arise in weather resistance.

Further, the content of ON in the intermediate layer 4 is 10 to 50 in atomic ratio.
% is preferable.

If the N content is less than the above range, the intermediate layer will have absorption, which will impede optical properties.

Moreover, if it exceeds the above range, the C/N ratio and recording sensitivity will not be sufficiently improved.

Measurement of these atomic ratios is performed using Auger electron spectroscopy, ESCA%
This may be done using EPMA, SIMS, or the like.

Note that such an intermediate layer material may be provided as a protection H6 on the recording layer (on the opposite side of the substrate) to be described later, and used in combination with the intermediate layer 4.

When used together, the intermediate layer and the protective layer may have the same composition or may have different compositions within the prescribed scope of the present invention.

In order to form such an intermediate layer 4, a sputtering method is preferable, and it is particularly preferable to use a reactive sputtering method.

Specifically, lanthanide element targets and Si
Using a target and nitrogen as a reaction gas, Ar-
Preferably, the layer is formed by reactive binary sputtering in a Nz atmosphere.

In such a reactive binary sputtering method, the intermediate layer 4 having a desired composition can be obtained by adjusting the input power to each target and the reaction gas pressure.

In addition to the sputtering method, other vapor phase film forming methods such as C
It is also possible to use a VD method, a vapor deposition method, an ion blating method, etc. as appropriate.

The thickness of such intermediate layer 4 is preferably 30 to 300 nm, particularly 50 to 200 nm.

If this value is less than 30 nm, the output will be small and the weather resistance will be poor.

Moreover, if it exceeds 300 nm, sensitivity and production efficiency will decrease.

Note that as an impurity in the intermediate M, Ar or the like present in the film forming atmosphere may be included.

Others: Fe, Ni%Cr, Cu, Mn, Mg, Ca,
Elements such as Na% are present as impurities.

The protective layer 3 and the protective layer 6 are provided to improve the corrosion resistance of the recording layer 5, and at least one of them is
Preferably both are provided. These protective layers are preferably composed of inorganic thin films made of various oxides, carbides, nitrides, sulfides, or mixtures thereof. Further, as described above, the intermediate layer may be formed of the above-mentioned materials. The thickness of the protective layer is 30-300n
From the viewpoint of improving corrosion resistance, it is preferable that the thickness is about m.

Such a protective layer is preferably formed by various vapor phase deposition methods such as sputtering.

Information is magnetically recorded in the recording layer 5 by a modulated heat beam or a modulated magnetic field, and the recorded information is reproduced by magneto-optical conversion.

The material of the recording layer 5 is not particularly limited as long as it can perform magneto-optical recording, but it may be an amorphous film made of an alloy of rare earth metals and transition metals by sputtering, vapor deposition, etc. It is preferable that there be.

As the rare earth metal, it is preferable to use one or more of Tb, Dy, Nd, Gd, and Sm.

As the transition metal, Fe and CO are preferred.

In this case, the total amount of Fe and CO is 65 to 85 at%
It is preferable that

The remainder is substantially rare earth metal.

The composition of the recording layer suitably used is TbFeCo.
, DyTbFeCo, NdDyFeCo, etc.

In addition, the recording layer contains Cr and A in a range of 10 at% or less.
Q, Ti, Pt, Si%Mo, Mn.

V, Ni%Cu, Zn, Ge, Au, etc. may be contained.

In addition, in the range of 10at% or less, Sc, Y, La, Ce
, Pr, Pm, Sm, Eu, Ho.

It may also contain other rare earth metal elements such as Er, Tm, Yb, and Lu.

The thickness of such a recording layer 5 is usually 10 to 11,000
It is about n.

Other materials for the recording layer include so-called phase change type materials, such as Te-5e, Te-3e-3n, Te-Ge, Te-
In, Te-5n, Te-Ge-5b-S, Te-G
e-As-3L, Te-3i, Te-Ge-3L-3
b, Te-Ge-B1. Te-Ge-In-Ga%Te
-5L -B 1-Ti2, Te-Ge-B i -I
n-3, Te-As-Ge-5b%Te-Ge-3e
-3. Te-Ge-5e, Te-As-Ge-Ga%
Te-Ge-3-In, 5e-Ge -TA%5e-
Te-As, 5e-Ge-Ti2-3b, 5e-Ge-
Bi, 5e-3 (all of the above, JP-B-54-41902, Patent No. 1004835, etc.) T e Ox (Te dispersed in Te oxide described in JP-A-58-54338, Patent No. 974257)
, TeaIl+PbO- (Patent No. 974258), Tea, +VO, (Patent No. 974257)
Te-TQ, Te-Tt2-Si, 5e-Zn-Sb,
Chalcogen system mainly composed of Te and Se such as Te-3e-Ga and TeNw Alloys that cause amorphous-crystalline transition such as Ge-5n and 5L-3nAg-Zn%Ag-Aj2-Cu% There are alloys such as Cu-AQ that cause a color change due to a change in crystal structure, and alloys that cause a change in crystal grain size such as In-3b.

Such a recording layer may be formed using a dry coating method such as a vapor deposition method, a sputtering method, an ion blating method, or the like. And the layer thickness is 20nm~11
It is assumed to be about 000n.

The substrate 2 is made of glass or resin, especially acrylic resin,
It is preferably made of polycarbonate resin, epoxy resin, polyolefin resin, etc., and is transparent to recording light and reproduction light. Further, the thickness thereof is usually about 0.5 to 3 mm, and the external shape is selected to be disc-shaped or other depending on the purpose.

The protective coat 7 is provided to improve corrosion resistance and scratch resistance, and is preferably composed of various organic substances, particularly acrylic substances that can be cured by radiation such as electron beams and ultraviolet rays. It is preferable that the protective coat 7 is composed of a radiation-curable compound having a double bond, and the thickness of the protective coat 7 is usually 1 to
The thickness is preferably about 100 μm.

The magneto-optical recording medium 1 composed of each of these layers can be made into a double-sided recording medium by bonding two sets of magneto-optical recording media l with the recording layer 5 on the inside. A protective plate can be attached to the media to create a single-sided recording medium.

In addition, when a protective plate is provided, the protective plate should normally be made of the same material as the substrate 2, but it does not need to be transparent (other materials can also be used. Any adhesive may be used, such as hot melt adhesive, thermosetting adhesive, anaerobic adhesive,
Radiation curable adhesives, etc.

<Example> Hereinafter, the present invention will be explained in further detail by giving specific examples of the present invention.

[Example 1] On a substrate 2 made of bisphenol A-based optical disk grade polycarbonate resin having a diameter of 130 mm and a thickness of 1.2 mm, a protective layer 3 made of glass was formed to a layer thickness of 40 nm by high-frequency magnetron sputtering.

On this protective layer 3, an intermediate layer 4 shown in Table 1 was formed by reactive binary sputtering. Note that a mixed gas of argon and nitrogen was used as the reaction gas, and Si and lanthanoid metals were used as the target. Furthermore, the composition of the intermediate layer was adjusted by changing the input power to each target.

Next, the recording layer 5 having the composition shown in Table 1 was formed on the intermediate layer 4 by sputtering to a layer thickness of 80 nm.

Further, a protective layer 6 having the same composition as the protective layer 3 was formed on the recording layer 5 to a thickness of 1100 nm by high-frequency magnetron sputtering, and a protective coat 7 was formed on this protective layer 6.
The protective coat 7 is formed by applying a coating composition containing a polyfunctional oligoester acrylate and a photosensitizer onto the protective layer 6 using a spinner coat, and then cross-linking and curing it by irradiating it with ultraviolet rays for 15 seconds. Layered. The thickness of the protective coat 7 was 5 μm.

In this way, magneto-optical recording medium samples having intermediate layers and recording layers of various compositions were obtained.

The following measurements were performed on the above sample.

(1) Weather resistance A storage test was carried out for 2000 hours at 80° C. and 85% RH, and the error rate was measured under the same conditions as in (2) below.

Table 1 shows the value obtained by dividing the error rate after storage by the initial error rate.

(2) C/N ratio linear velocity 4. Om/sec frequency
2 MHz Recording power (830 nm) The power indicates the recording sensitivity measured in (3) below. The applied magnetic field was 2500e.

Reproduction power (830nm) 1.0mW RB W 30 kHzV B
Measured at W 100 Hz.

(3) Recording Sensitivity Recording and reproduction are performed under the following conditions, and the power at which the second harmonic becomes the minimum is shown as the recording sensitivity in Table 1.

Linear speed 4. Om/sea recording signal
2MHz pulse (DAT 50%) Applied magnetic field 2500e Laser wavelength 830nm Reproduction power 1.0mW RB W 30 kHzV B W
100 Hz [Comparative Example 1] A sample having the dielectric material described in JP-A-61-22458 as the intermediate layer 4 (sample No. 1o)
t) A sample having an intermediate layer 4 containing an oxide of a rare earth element, silicon oxide and silicon nitride described in JP-A-63-161551 (sample No.
102), a sample having an intermediate layer 4 made of Nb5iN (sample No. 103) described in JP-A No. 63-81643, and Al2N, S is N4 described in JP-A-62-31052. Sample with intermediate layer 4 containing (sample No. 104
) was prepared according to Example 1, and the same measurements as in Example 1 were performed.

The results are shown in Table 1.

From the results shown in Table 1, the effects of the present invention are clear.

That is, the sample of the present invention has high weather resistance, high C/N ratio, and high recording sensitivity. In contrast, the comparative sample cannot improve all of these properties.

Example 21 A phase change optical recording medium having the following recording layer and intermediate layer was produced.

Recording layer I n 4ts b 411S n *Sputter film-formed intermediate layer La/ (S i +La)=0.
IN''30at% The recording power and C/N ratio of this optical recording medium were measured under the following conditions.

(Measurement conditions) Rotation speed 180Orpm Laser wavelength 830nm Lens NA
O,5 recording layer number 3.7M
Hz (duty 50%) As a result of measurement, the recording power was 9 mW, and the C/N ratio was 4.
It was 8dB.

[Comparative example 2] Sample No. of Comparative Example 1 was used as the intermediate layer.

The same measurements as in Example 2 were carried out by replacing the sample with No. 101.

As a result, the recording power was 11 mW, and the C/N ratio was 4.
It was 5 dB.

The effects of the present invention are clear from these Examples.

<Effects of the Invention> The optical recording medium of the present invention has excellent weather resistance, C/N ratio, and recording sensitivity because the intermediate layer contains at least one element selected from lanthanide elements, Si, and N. All of these features have been improved, resulting in an extremely practical optical recording medium.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an example of a magneto-optical recording medium which is a preferred embodiment of the optical recording medium of the present invention. Explanation of symbols 1... Magneto-optical recording medium, 2... Substrate, 3... Protective layer, 4... Intermediate layer, 5... Recording layer, 6... Protective layer, 7... Protective coat FIG, 1

Claims (2)

[Claims] (1) An optical recording medium having a recording layer on a substrate and an intermediate layer between the recording layer and the substrate, wherein the intermediate layer is composed of X (where X is at least one selected from lanthanide elements) An optical recording medium characterized in that it contains Si and N (representing a species element). (2) The optical recording medium according to claim 1, wherein the X contains at least one of La and Ce. (3) The content of X to the total of X and Si in the intermediate layer is 5 to 5 in atomic ratio.
The optical recording medium according to claim 1 or 2, wherein the optical recording medium is 50%.