JP2850129B2 - Optical recording medium - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an optical recording medium such as a magneto-optical recording disk and a phase-change optical recording disk.

<Prior Art> An optical recording medium is configured such that a recording layer is provided on a rigid or flexible substrate.

Among such optical recording media, a magneto-optical recording medium usually uses an amorphous magnetic thin film of a rare earth element-transition metal as a recording layer, and heats the recording layer to near the Curie temperature by light such as laser light, Information is recorded by applying a magnetic field from the outside as necessary to invert the magnetization of the heated portion.

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

In such a magneto-optical recording medium, improvement in recording sensitivity, C /
In order to obtain a so-called enhance effect such as improvement of N ratio,
Usually, an intermediate layer made of a dielectric or the like is provided between the recording layer and the substrate.

The intermediate layer multiple-reflects the recording light at the layer interface, so that the recording sensitivity can be improved. Further, since the readout light is also multiple-reflected, the C / N ratio is improved. Further, since the Kerr rotation angle can be amplified by multiple reflection of the reading light, the C / N ratio is also improved by this effect.

The rare earth elements used for the recording layer include Gd, Tb, and Dy.
As transition metals, Fe, Co, etc. are preferably used,
In particular, since the C / N ratio is high, Tb-Fe-Co, Dy-Tb-Fe
-Co and Nd-Dy-Fe-Co recording layers have attracted attention.

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

The following various proposals have been made for an intermediate layer or a corrosion-resistant protective layer having an enhancing effect.

For example, Japanese Unexamined Patent Publication (Kokai) No. 61-22458 discloses silicon nitride (Si ₃
A magneto-optical recording medium has been disclosed which has, as an intermediate layer, a dielectric containing N ₄ ) as a main component and an additive component having a refractive index of 2.1 or more, thereby providing corrosion resistance, C / N ratio and recording. The adhesion with the layer is improved.

Further, in addition to such a single-layer film, a mixed layer of an oxide and a nitride disclosed in JP-A-60-145525, a ZnS layer + Ge layer, and a silicon oxide layer disclosed in JP-A-62-245541 + Silicon nitride main component layer JP-A-62-298037 JP Oxide layer + oxide / nitride mixed layer + nitride layer JP-A-63-71958 JP JP 63-71958 A Dielectric layer having a refractive index of n <1.6 + n> 2.0 Dielectric layer JP-A-63-168857 Various types of multilayer films such as an oxide layer of an element selected from Al, Y, and Yb + a nitride, a silicide, a carbide, and an oxide layer have been proposed.

Further, as disclosed in Japanese Patent Application Laid-Open No. Sho 61-122,56, the oxidation state of the metal oxide is made to have a gradient, and in the case of Japanese Patent Application Laid-Open No. Sho 62-234253, n is varied in the film thickness direction. There is also proposed an intermediate layer having a compositional gradient of and having improved weather resistance and photoelectric conversion characteristics by changing the refractive index in the thickness direction.

In addition, in addition to the above-described magneto-optical recording medium, a so-called phase-change type optical recording medium, that is, information recording is performed by changing the phase of a recording layer by heat of a laser beam or the like. There is also an optical recording medium that reads information by detecting a change in the reflectance of a recording layer that occurs as a result.

Even in such a phase-change type optical recording medium, an intermediate layer utilizing multiple reflection of light is provided to improve recording sensitivity and C / N ratio.

<Problems to be Solved by the Invention> However, there is a severe demand for improving the C / N ratio and the recording sensitivity of an optical recording medium such as a magneto-optical recording medium. Absent.

The present invention has been made under the circumstances described above, and has as its object to provide an optical recording medium having an extremely high C / N ratio and recording sensitivity.

<Means for Solving the Problems> Such an object is achieved by the present invention of the following (1) and (2).

(1) A recording layer is provided on a substrate, and an intermediate layer is provided between the recording layer and the substrate. The intermediate layer has a periodic composition variation in a thickness direction. An optical recording medium of 2 to 50 °.

(2) The intermediate layer contains at least one element X selected from Al, Sc, Y, a lanthanoid element and an actinoid element, Si and N, and has an atomic ratio of 100X / (X + Si) of 1 The optical recording medium according to (1), wherein the content of N is 10 to 50% in atomic ratio.

<Effect> The magneto-optical recording medium raises the temperature of the recording layer having a predetermined composition to near the Curie point by irradiation with a laser beam or the like, and generates a demagnetizing field in the recording layer or, in addition to this, from the outside if necessary. Information is recorded by the applied magnetic field.

The reading of the 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 reflects recording light and reading light at the interface thereof multiple times, thereby improving recording sensitivity and C / N ratio.

The optical recording medium of the present invention has an intermediate layer having a periodic composition change in the thickness direction as such an intermediate layer, so that the effect of improving the recording sensitivity and the C / N ratio is high.

<Specific Configuration> Hereinafter, a specific configuration of the present invention will be described in detail.

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

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.
Are sequentially provided.

In the present invention, the intermediate layer 4 has a periodic composition change in the thickness direction.

In the present invention, the cycle of the composition change is 2 to 50 °, particularly 3 to 40 °.

When this value is less than the above range, the composition does not substantially fluctuate, and the effect of the present invention is not realized.

In addition, when it exceeds the above range, the effect of the present invention is not sufficiently realized.

The intermediate layer 4 is composed of two or more elements, and it is only necessary that these elements have a composition variation in the thickness direction of the layer, and the composition is not particularly limited. If the layer has such a composition variation, a significant enhancement effect is realized.

In the present invention, the intermediate layer 4 preferably contains at least one element (hereinafter, abbreviated as X) selected from Al, Sc, Y, a lanthanoid element and an actinoid element, Si, and N. .

X is not particularly limited, but is preferably Al, Y, La, C
e, and more preferably, Al and La may be selected.

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

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

The intermediate layer 4 may contain Fe, Mg, Ca, Sr, Ba and the like.

Of these elements, Fe may be contained at 10 at% or less, and other elements may be contained at 10 at% or less in total.

 The intermediate layer 4 contains Si and N in addition to X.

Si and N are usually contained in the form of Si ₃ N ₄ , but may be deviated 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 near 800 nm is:
Preferably it is 2.0-3.0, more preferably 2.1-2.8.

If the refractive index is less than the above range, Kerr rotation angle amplification, etc.
The enhancement effect is small, and the output decreases.

In addition, when it exceeds the above range, the output decreases and the 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) may be 1 to 50%, particularly 5 to 30% in atomic ratio. preferable.

When the value is less than the above range, the improvement of the C / N ratio and the recording sensitivity is insufficient, and when the value exceeds the above range, a problem occurs in the weather resistance.

The content of N in the intermediate layer 4 is 10 to 50% in atomic ratio.
It is preferred that

If the content of N is less than the above range, the intermediate layer will have absorption, which causes a problem in optical characteristics.

If the ratio exceeds the above range, the improvement of the C / N ratio and the recording sensitivity becomes insufficient.

These atomic ratios are measured by Auger electron spectroscopy, ESCA, EP
What is necessary is just to perform by MA, SIMS, etc.

In addition, such an intermediate layer material is provided as a protective layer 6 on the recording layer described later (on the side opposite to the substrate) to form the intermediate layer 4.
Can also be used in combination. When used in combination, the compositions of the intermediate layer and the protective layer may be the same, or may be different from each other within a predetermined range of the present invention.

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

Specifically, using two targets of X target and Si target, also using nitrogen as a reaction gas, it is preferable that double-layered structure by reactive dual sputtering at Ar-N ₂ 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 order to provide a periodic composition variation in the thickness direction of the intermediate layer, for example, one or the other input power is periodically changed, or the distance between the substrate 2 and each target is periodically changed. What is necessary is just to fluctuate.

In addition to the sputtering method, other vapor phase film forming methods, for example,
A CVD method, a vapor deposition method, an ion plating method, or the like can be used as appropriate.

The thickness of such an intermediate layer 4 is 30 to 300 nm, especially 50 to 2 nm.
It is preferably set to 00 nm.

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

If it exceeds 300 nm, the sensitivity is lowered and the production efficiency is lowered.

Note that Ar or the like existing in the film formation atmosphere may be included as an impurity in the intermediate layer.

In addition, elements such as Fe, Ni, Cr, Cu, Mn, Mg, Ca, Na, and K can enter as impurities.

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

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

In the recording layer 5, information is magnetically recorded 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 is formed by forming an alloy of a rare earth metal and a transition metal as an amorphous film by sputtering, vapor deposition, or the like. Preferably, there is.

As the rare earth metal, one of Tb, Dy, Nd, Gd, and Sm is used.
It is preferred to use more than one species.

 Fe and Co are preferable as the transition metal.

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

 The balance is substantially a rare earth metal.

Preferred recording layer compositions include TbFeCo, Dy
There are TbFeCo, NdDyFeCo and the like.

In the recording layer, Cr, Al, T
i, Pt, Si, Mo, Mn, V, Ni, Cu, Zn, Ge, Au and the like may be contained.

In addition, Sc, Y, La, Ce, Pr, P
Other rare earth metal elements such as m, Sm, Eu, Ho, Er, Tm, Yb, and Lu may be contained.

The layer thickness of such a recording layer 5 is usually about 10 to 1000 nm.

In addition, as a material of the recording layer, a so-called phase transition type material such as Te-Se, Te-Se-Sn, Te-Ge, Te-In, Te-Sn, Te-
Ge-Sb-S, Te-Ge-As-Si, Te-Si, Te-Ge-Si-S
b, Te-Ge-Bi, Te-Ge-In-Ga, Te-Si-Bi-Tl, Te
-Ge-Bi-In-S, Te-As-Ge-Sb, Te-Ge-Se-S,
Te-Ge-Se, Te-As-Ge-Ga, Te-Ge-S-In, Se-Ge
-Tl, Se-Te-As, Se-Ge-Tl-Sb, Se-Ge-Bi, Se-
S (above, Japanese Patent Publication No. 54-41902, Japanese Patent No. 100004835, etc.) TeO _x (Japanese Patent Application Laid-Open No. 58-54338, Patent No. 974257)
Te dispersed in oxides), TeO _x + PbO _x (Patent No. 974258), TeO _x + VO _x (Patent No. 974257), other, Te-Tl, Te
-Tl-Si, Se-Zn- Sb, Te-Se-Ga, Te such TeN _x, chalcogen Ge-Sn mainly composed of Se, Si-Sn and the like of the amorphous - alloy Ag resulting crystalline transition Alloys such as -Zn, Ag-Al-Cu, and Cu-Al 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-Sb, and the like.

Such a recording layer may be provided by a dry coating method such as an evaporation method, a sputtering method, or an ion plating method. The thickness of the layer is set to about 20 nm to 1000 nm.

The substrate 2 is preferably made of glass or resin, particularly, acrylic resin, polycarbonate resin, epoxy resin, polyolefin resin or the like, and is transparent to recording light and reproduction light. The thickness is usually about 0.5 to 3 mm, and the outer shape is selected according to a disc shape or other purposes.

The protective coat 7 is provided for improving corrosion resistance and abrasion resistance, and is preferably made of various organic substances. In particular, acrylic coats which can be cured by radiation such as electron beams and ultraviolet rays. The radiation-curable compound having a double bond is preferably composed of a radiation-cured substance. The thickness of the protective coat 7 is usually 1 to
It is preferred to be about 100 μm.

The magneto-optical recording medium 1 composed of these layers can be used as a double-sided recording medium by bonding two sets of magneto-optical recording media 1 with the recording layer 5 inside. A single-sided recording medium can be obtained by bonding a protective plate to the recording medium.

When a protective plate is provided, the protective plate is usually
The same material as that of the substrate 2 may be used, but it is not necessary to be transparent, and other materials can be used. In addition, any known adhesive may be used for bonding, for example, a hot melt adhesive, a thermosetting adhesive, an anaerobic adhesive,
Radiation-curable adhesives and the like.

<Example> Hereinafter, the present invention will be described in more detail with reference to specific examples of the present invention.

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

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

The composition of the intermediate layer 4 was measured by Auger spectroscopy, and was measured while etching to determine the period of the composition change in the thickness direction.

Table 1 shows the composition change cycle and composition of the intermediate layer 4. The composition shown in Table 1 is the average composition of the intermediate layer.

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

Further, a protective layer 6 having the same composition as the protective layer 3 is formed on the recording layer 5.
Was formed to a thickness of 100 nm by high-frequency magnetron sputtering, and a protective coat 7 was formed on the 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 by a spinner coat, and then irradiating ultraviolet rays for 15 seconds to cure by crosslinking. Layered. Protective coat 7
Was 5 μm in thickness.

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

 The following measurement was performed on the sample.

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

Linear velocity 4.0m / sec Recording signal 2MHz pulse (duty 50%) Applied magnetic field 250Oe Laser wavelength 830nm Reproduction power 1.0mW RBW 30kHz VBW 100Hz (2) C / N ratio Linear velocity 4.0m / sec Recording signal 2MHz pulse Recording power The value used as the recording sensitivity in (1) above Applied magnetic field 250 Oe Laser wavelength 830 nm Reproduction power 1.0 mW RBW 30 kHz VBW Measured at 100 Hz.

 Table 1 shows the results.

[Comparative Example 1] An intermediate layer was provided in the same manner as in Example 1 except that a Si-Al alloy, a Si-Y alloy and Si were used as sputter targets, thereby producing a magneto-optical recording medium sample (Sample No. 1
01, 102, 103).

The same measurement as in Example 1 was performed on these samples.

 Table 1 shows the results.

The samples shown in Table 1 were subjected to a storage test for 2000 hours in an atmosphere of 80 ° C. and 85% RH. Did not deteriorate until 2000 hours.

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

That is, the sample of the present invention having a periodic composition change 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 characteristics.

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

Recording layer In ₄₉ Sb ₄₉ Sn ₂ Sputtered film Intermediate layer A composition fluctuation of 10 ° was provided by binary sputtering. The average composition was Al / (Si + Al) = 10% N = 20 at%.

The recording power and C / N ratio of this optical recording medium were measured under the following conditions.

(Measurement conditions) Rotation speed 1800rpm Laser wavelength 830nm Lens NA 0.5 Recording signal 3.7Mhz (Duty 50%) As a result of measurement, recording power was 8mW and C / N ratio was 50dB.

Comparative Example 2 A phase-change optical recording medium was manufactured in the same manner as in Example 2, except that the sputter target was an Si-Al alloy and the intermediate layer had no composition fluctuation.

 For this, the same measurement as in Example 2 was performed.

As a result, the recording power was 10 mW, and the C / N ratio was 47 dB.

 From these results, the effect of the present invention is clear.

<Effect of the Invention> The optical recording medium of the present invention has a high recording sensitivity and a high C / N ratio because the intermediate layer has a periodic composition change.

[Brief description of the drawings]

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. DESCRIPTION OF SYMBOLS 1 ... Magneto-optical recording medium 2 ... Substrate 3 ... Protective layer 4 ... Intermediate layer 5 ... Recording layer 6 ... Protective layer 7 ... Protective coat

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Masaru Takayama 1-1-13 Nihonbashi, Chuo-ku, Tokyo Inside TDK Corporation (56) References JP-A-61-237242 (JP, A) (58) Survey Field (Int.Cl. ⁶ , DB name) G11B 11/10 521 G11B 7/24 533

Claims (2)

(57) [Claims] A recording layer on the substrate, an intermediate layer between the recording layer and the substrate, a periodic composition variation in a thickness direction, and a period of the composition variation of the intermediate layer. Is 2 to 50 °. 2. The intermediate layer contains at least one element X selected from Al, Sc, Y, a lanthanoid element and an actinoid element, Si and N, and has an atomic ratio of 100X / (X + Si). The optical recording medium according to claim 1, wherein the content of N is 1 to 50%, and the content of N is 10 to 50% in atomic ratio.