JPH02199644A - Optical recording medium - Google Patents

Abstract

PURPOSE:To improve C/N and recording sensitivity by providing an intermediate layer between a recording layer and a substrate with periodic fluctuations in compsn. in the thickness direction thereof. CONSTITUTION:The intermediate layer 4 of the optical recording medium having the recording layer 5 on the substrate 2 and having the intermediate layer 4 between this recording layer 5 and the substrate 2 has the periodic fluctuations in the compsn. in the thickness direction. The periods of the fluctuations in the compsn. are 2 to 50Angstrom , more particularly preferably 3 to 40Angstrom . While the intermediate layer 4 has the effect of multiplex-reflecting recording light and reading out light at its boundary and improving the recording sensitivity and C/N, the intermediate layer has the periodic fluctuations in the compsn. in the thickness direction and, therefore, the recording sensitivity and the C/N are further improved.

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 Chierly temperature with 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.

Recording layers made of Dy-Tb-Fe-Go and Nd-Dy-Fe-Co are 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, JP-A No. 61-22458 discloses a magneto-optical recording medium having as an intermediate layer a dielectric material mainly composed of silicon nitride (SisN4) and containing an additive component such that the refractive index is 2.1 or more. A medium is disclosed, which is intended to improve corrosion resistance, C/N ratio, and adhesion to a recording layer.

In addition to such single layer films, JP 60-145525 A Mixed layer of oxide and nitride Japanese Unexamined Patent Publication No. 61-243977 ZnS layer + Ge layer Japanese Patent Application Publication No. 62-245541 Silicon oxide layer + silicon nitride main component layer Japanese Unexamined Patent Publication No. 62-298037 Oxide layer + oxide/nitride mixed layer +Nitride layer Japanese Unexamined Patent Publication No. 63-71958 Dielectric layer with refractive index n<1.6 +n>2.0 dielectric layer Japanese Unexamined Patent Application Publication No. 63-168857 Acid of element selected from Aβ, Y%Yb Compound layer + nitride, silicide, carbide, Or oxide layer Various multilayer films have also been proposed.

Furthermore, as disclosed in JP-A No. 62-234253, which gives a gradient to the oxidation state of a metal oxide in JP-A No. 61-122956, it is possible to change the oxidation state of a metal oxide at a constant value in the thickness direction. An intermediate layer has also been proposed that has a compositional gradient of , and has improved weather resistance and photoelectric conversion characteristics by, for example, changing the refractive index in the thickness direction.

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 intermediate layer that utilizes multiple reflection of light is provided to improve recording sensitivity and C/N ratio.

<Problems to be Solved by the Invention> However, there are strict demands for improving the C/N ratio and recording sensitivity of optical recording media such as magneto-optical recording media, and even if the intermediate layer described above is provided, it may not be sufficient. do not have.

The present invention has been made in view of the above-mentioned circumstances, and is effective for the purpose of providing an optical recording medium with extremely high C/NPc and recording sensitivity.

Means for Solving the Problems> Such objects are achieved by the present invention as described in (1) to (3) below.

(1) An optical recording medium having a recording layer on a substrate and an intermediate layer between the recording layer and the substrate, characterized in that the intermediate layer has periodic compositional fluctuations in the thickness direction. optical recording medium.

(2) The intermediate layer contains at least one member selected from Aβ, Sc, Y, a lanthanide element, and an actinide element.
The optical recording medium according to (1) above, containing a seed element, Si, and N.

(3) The optical recording medium according to (1) or (2) above, wherein the period of compositional fluctuation of the intermediate layer is 2 to 50 people.

In a magneto-optical recording medium, the temperature of a recording layer having a predetermined composition is raised to around the Curie point by irradiation with laser light, etc., and a demagnetizing field within the recording layer or in addition to this is applied externally as necessary. Information is recorded using a magnetic field.

Further, reading of recorded information is performed by irradiating the recording layer with laser light or the like and detecting the Kerr rotation angle of the light reflected from the recording layer.

In such recording/reading, the intermediate layer provided in contact with the recording layer multiple-reflects recording light and readout light at its interface, thereby improving recording sensitivity and C/N ratio.

Since the optical recording medium of the present invention has an intermediate layer having periodic compositional fluctuations in the thickness direction as such an intermediate layer,
Highly effective in improving recording sensitivity and C/N ratio.

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 [4] has periodic compositional fluctuations in the thickness direction.

In the present invention, the period of compositional variation is preferably 2 to 50 people, particularly 3 to 40 people.

If this value is less than the above range, the composition will not substantially change, and the effects of the present invention will not be achieved.

Furthermore, if the amount exceeds the above range, the effects of the present invention will not be fully realized.

The intermediate layer 4 may be composed of two or more types of elements, and the composition of these elements may vary in the thickness direction of the layer, and there is no particular restriction on the composition, but in particular, an intermediate layer between the following compositions may be used. When the layers have such compositional variations, significant enhancement effects are realized.

In the present invention, the intermediate layer 4 includes AP, Sc.

It is preferable to contain at least one element selected from Y, a lanthanide element, and an actinide element (hereinafter abbreviated as X), Si, and N.

There is no particular restriction on X, but preferably AI2, Y, La
, Ce, and more preferably An and La.

X is usually contained as a nitride in the intermediate layer 4, but it may be contained in a nitride with a stoichiometric composition deviated from the equilibrium stoichiometric composition.

When X is composed of two or more types of elements, the quantitative ratio thereof is arbitrary.

The intermediate layer 4 may contain Fe%Mg, Ca, Sr%Ba, etc.

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 to X, the intermediate layer 4 contains Si and N.

Si and N are usually contained in the form of 5isN4, but may be deviated from such stoichiometric composition.

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

The refractive index of such an intermediate layer 4 at around 800 nm is preferably 2.0 to 3.0, more preferably 2.1 to 3.0.
It is 2.8.

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 1 to 50%, particularly 5 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 N in the intermediate N4 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, causing problems in optical properties.

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

These atomic ratios can be measured using Auger electron spectroscopy, ESCA,
This may be performed using EPMA, SrMS, or the like.

Note that such an intermediate M material can be provided as a protective layer 6 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 compositions of the intermediate layer and the protective layer may be the same or different within the prescribed range 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, it is preferable to form the layer by reactive binary sputtering in an Ar--N* atmosphere using an X target and a Si target and using nitrogen as a reactive gas.

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 order to provide periodic compositional fluctuations in the thickness direction of the intermediate layer, for example, the input power may be periodically changed, or the distance between the substrate 2 and each target may be periodically changed. good.

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 Ar or the like present in the film forming atmosphere may be included as an impurity in the intermediate layer.

Others: Fe, Ni, Cr%Cu%Mn, Mg, Ca,
Elements such as Na and Ni enter 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 material may be used as the intermediate material. The thickness of the protective layer is 3o~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.
β, Tf, Pt%Sf, Mo%Mn.

(2) NL, Cu, Zn, Ge, Au, etc. may be contained.

In addition, in the range of 10at% or less, Sc%Y, Las C
es Pr, Pm, Sm, Eu, Ho, Er, Tm, Y
Other rare earth metal elements such as b% Lu may be contained.

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-3b-5. Te-Ge
-As-5t,Te-5i1Te-Ge-8L-Sb
%Te-Ge-Bi, Te-Ge-In-Ga, Te
-3i -Bi-Tf2, Te-Ge-B i -1n
-5sTe-As-Ge-5b%Te-Ge-5e-3
．． Te-Ge-3e%Te-As-Ge-Ga,Te
-Ge-5-In% 5e-Ge -Tff, 5e-T
e-As, 5e-Ge-742-5b, 5e-Ge-B
i, 5e-S (Japanese Patent Publication No. 54-41902, Patent No. 1004835, etc.) Tea, (Japanese Patent Publication No. 58-54338, Patent No. 9742
Te dispersed in Te oxide described in No. 57), T e Ox + P b O, l (Patent No. 974
258), Teom + vox (Patent No. 9742)
No. 57) Others: Te-Tf2, Te-Tf-Si,
5e-Zn-Sb, Te-5e-Ga.

Chalcogen system mainly composed of Te and Se, such as T e N There are alloys that cause color changes due to structural changes, and alloys that cause changes in crystal grain size such as In-5b.

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, etc., and the layer thickness thereof is 20 nmA-1.
It is assumed to be about 000 nm.

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 material is made of a radiation-cured compound having a double bond. Further, the thickness of the protective coat 7 is usually 1 to 1.
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 1 with the recording layer 5 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 2 mm, a protective layer N3 made of glass was deposited to a layer thickness of 40 nm by high-frequency magnetron sputtering.

An intermediate layer 4 was formed on this protective layer 3 by reactive binary sputtering. Note that a mixed gas of argon and nitrogen was used as a reaction gas, and metals Sf and X were used as targets. Furthermore, the composition of the intermediate layer was adjusted by periodically changing the input power to each target. Then, in order to ensure in-plane uniformity of the intermediate layer, the substrate 2 was rotated around the central axis at a constant speed. Also, the board 2
The desired intermediate layer could also be obtained by revolving around an axis different from its central axis and periodically varying the distance to each target.

The composition of the intermediate N4 was measured by Auger spectroscopy, and the period of composition variation in the thickness direction was determined by measuring while etching.

Table 1 shows the period of compositional fluctuation and the composition of the intermediate layer 4.

Note that the composition shown in Table 1 is the average composition of the intermediate layer.

Next, Record N5 having the composition shown in Table 1 was deposited 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 is 51. cm.

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) 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 (duty 50%) Applied magnetic field 2500e Laser wavelength 830nm Reproduction power 1.0mW RB W 30 kHzV B W
100 Hz (2) C/N ratio linear velocity 4. Om/sec Recording signal 2MHz pulse recording power
The recording sensitivity was measured in (1) above: Applied magnetic field: 2500e Laser wavelength: 830 nm Reproduction power: 1.0 mW RBW: 30 kHz V B W: 100 Hz.

The results are shown in Table 1.

[Comparative Example 1] 5i-Aj2 alloy, 5i-Y as sputter target
An intermediate layer was formed in the same manner as in Example 1 except that the alloy and Si were used, and magneto-optical recording medium samples were produced (sample No. 101°102.103).

The same measurements as in Example 1 were performed on these samples.

The results are shown in Table 1.

For each sample shown in Table 1, 8°C85%
When a storage test was carried out for 2000 hours in an RH atmosphere, sample No. 12 was stored for 500 hours, and sample N
o, 103 showed deterioration after 1000 hours, others 20
No deterioration was observed until 00 hours.

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

That is, the sample of the present invention, which has periodic compositional fluctuations in the thickness direction of the intermediate layer, has high recording sensitivity and high C/N ratio. In contrast, a comparative sample in which the intermediate layer has a uniform composition cannot improve all of these properties.

[Example 2] A phase change optical recording medium having the following recording layer and intermediate layer was produced.

Recording Layer I n 49S b 4ss n x Sputter Film Formation Intermediate Layer Composition variation was provided at a period of 10 by binary sputtering. The average composition is Aj2/ (S i +AA)=l O%N=20a
It was t%.

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
0.5 recording signal 3.7M
Hz (duty 50%) As a result of measurement, the recording power was 8 mW, and the C/N ratio was 5.
It was 0dB.

[Comparative Example 2] Same as Example 2 except that the sputtering target was S1-AI2 alloy and the intermediate layer had no compositional variation.
A phase change type optical recording medium was fabricated.

The same measurements as in Example 2 were performed on this product.

As a result, the recording power was 10 mW, and the C/N ratio was 4.
It was 7dB.

From these results, the effects of the present invention are clear.

<Effects of the Invention> The optical recording medium of the present invention has high recording sensitivity and high C/N ratio because the intermediate layer has periodic compositional fluctuations.

[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 3C

Claims (3)

[Claims] (1) An optical recording medium having a recording layer on a substrate and an intermediate layer between the recording layer and the substrate, characterized in that the intermediate layer has periodic compositional fluctuations in the thickness direction. optical recording medium. (2) The intermediate layer is at least one selected from Al, Sc, Y, a lanthanide element, and an actinide element.
The optical recording medium according to claim 1, containing a seed element, Si, and N. (3) The optical recording medium according to claim 1 or 2, wherein the period of compositional fluctuation of the intermediate layer is 2 to 50 Å.