JPH09297943A - Magneto-optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease to widening of a recording magnetic domain during writing and deformation of recording domains in the adjacent tracks and to improve the track density by forming a nitride thin film as a first dielectric layer and specifying the material and coefft. of thermal conductivity of a second dielectric layer. SOLUTION: This magneto-optical recording medium is produced by successively forming a first dielectric layer 2, a recording layer 3, a second dielectric layer 4 and a reflecting layer 5 on a transparent substrate 1. Here, the substrate 1, the interval of tracks for recording is specified to <=1.0μm. The first dielectric layer 2 is composed of a nitride thin film. The coefft. of thermal conductivity of the second dielectric layer 4 is specified to <=1.0W/(m.K). Therefore, crosstalk due to thermal diffusion from the recording layer to the reflecting layer during recording and erasing can be decreased, and the margin for cross-erasing can be increased. Further, (ZnS)1-x (SiO2 ), wherein (x) ranges 0.1<=x<=0.4, for the second dielectric layer 4, widening of the recording domain during writing and deformation of recording domain in the adjacent tracks can be decreased, which improves the track density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magneto-optical recording medium for reproducing information by optical means and recording information using light and magnetism, and more particularly to a magneto-optical recording medium having a higher recording track density.

[0002]

2. Description of the Related Art For a magneto-optical recording medium, an increase in recording linear density and an increase in track density have been considered in order to increase the capacity.

As a technique for improving the track density, land-and-groove recording, which uses a groove, which has been used only as a guide groove of a conventional track, as a recording data area, is under study. Starting from this land & groove recording, in order to realize a magneto-optical recording medium with a narrow track pitch, the leakage of the recording signal from the adjacent track is prevented, and the signal by erasing the recording magnetic domain of the adjacent track by heat conduction at the time of recording. Level deterioration prevention technology is required. Although it is possible to prevent the deterioration of the signal level of the target track due to the writing of the adjacent track by making the beam spot diameter of the laser beam irradiated on the recording medium smaller, it is possible to mass-produce the short wavelength semiconductor laser. The current situation is that there are none.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to prevent a recording mark from leaking to an adjacent track in the process of recording information on a magneto-optical recording medium, and further to record a magnetic domain of the adjacent track in the process of recording and erasing. By preventing such deformation, the track density of the magneto-optical recording medium is improved.

[0005]

As a result of intensive studies to solve the above problems, the present inventors have used a substance having a thermal conductivity of not more than a predetermined amount for the second dielectric layer of the magneto-optical multilayer film. As a result, they have found that the above problems can be solved, and completed the present invention.

That is, the magneto-optical recording medium of the present invention is a magneto-optical recording medium in which a first dielectric layer, a recording layer, a second dielectric layer and a reflective layer are laminated in this order on an optically transparent substrate. , The distance between recordable tracks on the substrate is 1.0
μm or less, the first dielectric layer is made of a nitride thin film, and the thermal conductivity of the second dielectric layer is 1.0 W / (m
・ K) or less.

Hereinafter, the present invention will be described in detail.

In the magneto-optical recording medium, as shown in FIG. 1, a first dielectric layer 2 formed on an optically transparent substrate 1,
A laminated structure composed of the recording layer 3, the second dielectric layer 4 and the reflective layer 5 has been mainly used. This structure is so thin that the recording layer transmits light, and higher signal intensity can be obtained by using optical interference with the light reflected by the reflective layer, and is called a reflective structure. . The first dielectric layer and the second dielectric layer also have an effect of increasing the magneto-optical effect or controlling heat conduction. Further, in order to protect these thin films, an ultraviolet curable resin layer or the like may be further formed on the reflective layer 5 if necessary.

As a dielectric layer used in such a magneto-optical recording medium, SiN, AlN, SiAl have been conventionally used.
N, SiN: H, such as _{Tb-SiO 2, Ta 2 O} 5 have been proposed, in particular SiN in view of corrosion resistance, AlN, SiA
In and the like have been mainly used.

In the present invention, the first dielectric layer is made of a nitride thin film such as SiN, AlN, SiAlN in consideration of corrosion resistance, and only the second dielectric layer has a thermal conductivity of 1.0 W / (mK).
By using the following films, signal leakage (crosstalk) to adjacent tracks is reduced without sacrificing the weather resistance of the recording film, and the recording magnetic domains of adjacent tracks are deformed during recording and erasing. (Cross erase)
It became possible to prevent.

The reason why crosstalk and cross erase are reduced by the structure of the present invention is that the temperature in the plane of the magneto-optical recording layer is reduced by reducing heat diffusion from the magneto-optical recording layer to the metal reflection film at the time of recording / erasing. It is considered that this is because the distribution becomes steep and the temperature region in which magnetic domain inversion occurs is narrowed. By setting the thermal conductivity of the second dielectric layer to 1.0 W / (m · K) or less, crosstalk and cross erase are remarkably improved in high-density recording in which the track interval is 1.0 μm or less. .

Such an effect can be expected even in the conventional second dielectric layer using SiN and by setting the film thickness to 90 nm or more. However, in the present invention, the film thickness of the second dielectric layer is About 20 nm has a sufficient effect.

The first material for the second dielectric layer of the present invention is the first
Is (ZnS) _1-x (SiO ₂ ) _x , and the range of x is preferably 0.1 ≦ x ≦ 0.4. When x is less than 0.1, the thermal conductivity may exceed 1.0 W / (m · K), and further, ZnS has a crystalline property and grain boundaries are formed in the film, resulting in incompatibility. C / N may decrease due to noise due to grain boundaries. If x is larger than 0.4, the recording layer will be easily oxidized.

The second dielectric layer material of the present invention is the second
_Is (ZrO ₂ ) _1-x (SiO ₂ ) _x , and the range of x is preferably 0.1 ≦ x ≦ 0.4. Here, when x is less than 0.1, the property of ZrO _{2 as} a crystal appears, the film becomes less dense, and C / N may decrease due to noise due to grain boundaries, and when x is greater than 0.4, the recording layer Are easily oxidized.

The third material of the second dielectric layer of the present invention is the third
Si with a hydrogen content of 10 atomic% or more and 30 atomic% or less
N: H can be given. Here, the ratio of Si and N is about 3: 4. Further, when the hydrogen content is less than 10 atomic%, the thermal conductivity exceeds 1.0 W / (m · K), and when it is more than 30 atomic%, the film becomes unstable.

The material for the magneto-optical recording layer is Tb-Fe.
-Co, Dy-Fe-Co, Tb-Dy-Fe-Co,
Nd-Dy-Fe-Co, Nd-Gd-Fe-Co, etc. are illustrated.

The magneto-optical recording layer may be a single layer, but a Gd-Fe-Co film having a small coercive force and a Tb- having a large coercive force.
More preferably, it is a laminated film of Fe—Co films. By using such a laminated film, the formation of recording marks becomes more faithful to the temperature distribution and recording and erasing can be performed with high accuracy, so that crosstalk and cross erase can be further reduced. In particular, Gd-Fe-Co film and Tb-Fe-Co each _{Gd x (Fe 1-y Co} y) the composition of the film _1-x and Tb _u
(Fe _1-v Co _v ) _1-u , and the values of x, y, u, v are 0.22 ≦ x ≦ 0.27, 0.20 ≦ y ≦ 0.35, 0.20 ≦ u ≦ 0.24 and 0.06 ≦ v ≦ 0.15 are satisfied, and the Gd-Fe-Co film and the Tb-Fe-Co film are satisfied.
Film thickness ratio (Gd-Fe-Co layer thickness / Tb-Fe-C
A particularly good magneto-optical recording layer can be obtained when the o layer thickness) satisfies 0.1 or more and 0.7 or less.

The effect of reducing crosstalk and cross erase in the present invention can be obtained irrespective of the film thickness in the reflection type structure as shown in FIG. 1, but the optical properties of the first dielectric layer and the second dielectric layer are It is preferable to set the film thickness and the film thickness of the recording layer and the reflective layer within the ranges shown below in order to secure a good signal level. The optical film thickness is obtained by dividing the product of the refractive index and the film thickness by the wavelength of light, that is, n · d
Means / λ.

0.23 ≤ n ₁ · d ₁ / λ ≤ 0.30 0.04 ≤ n ₃ · d ₃ / λ ≤ 0.12 13 ≤ d ₂ ≤ 30 35 ≤ d ₄ where λ: recording Wavelength of light used for reproduction [n
m], n ₁ : refractive index of the first dielectric layer, d ₁ : film thickness [nm] of the first dielectric layer, n ₃ : refractive index of the second dielectric layer,
d ₃ : thickness of second dielectric layer [nm], d ₂ : thickness of recording layer [nm], d ₄ : thickness of reflective layer [nm].

The present invention is also effective in a narrow track pitch substrate. Particularly, in the case of the above-mentioned magneto-optical recording medium of the reflection type structure, it is preferable that the range of the groove depth 13 in the land & groove substrate shown in FIG.

Λ / (8 × Ns) ≦ groove depth [n
m] ≦ λ / (5 × Ns) Here, Ns is the refractive index of the substrate, and λ is the wavelength [nm] of light used for recording / reproducing. By setting the groove depth 13 in such a range, it is possible to further reduce crosstalk.

[0022]

【Example】

(Example 1, Comparative Example 1 and Comparative Example 2) Using a land & groove substrate having a groove depth 13 of 70 nm and a land-to-groove pitch 14 of 0.7 μm as shown in FIG.
As shown in FIG. 3, the first dielectric layer 22 is formed on the substrate 21.
As SiN by RF magnetron sputtering method,
The recording layer 23 is Tb _0.19 Fe _0.63 Co _0.08 , the second dielectric layer 24 is (ZnS) _0.8 (SiO ₂ ) _0.2 having a thermal conductivity of 0.6 W / (m · K), and the reflective layer 25 is Al _0.98. Cr _0.02 was formed by the DC magnetron sputtering method. Table 1 shows the film thickness of each layer and the optical film thickness with respect to light having a wavelength of 680 nm. Further, a protective coat 26 made of an ultraviolet curable resin was applied on the reflective layer 25 to manufacture a magneto-optical disk.

[0023]

[Table 1]

As Comparative Example 1, the second dielectric layer 24
With a thermal conductivity of 3.0 W / (mK) SiN (film thickness 20
nm, optical film thickness 0.076), and a magneto-optical disk having the same structure as in Example 1 was prepared. Furthermore, as Comparative Example 2, the second dielectric layer 24 has a thermal conductivity of 2.5 W / (m ·
A magneto-optical disk having the same structure as in Example 1 except that ZnS (K) of ZnS (film thickness 20 nm, optical film thickness 0.084) was used.

A wavelength of 680 nm was used for the above magneto-optical disk,
Recording / reproducing characteristics were measured in a magneto-optical recording / reproducing apparatus with NA = 0.55. Table 2 shows the measurement items and the measurement conditions.

[0026]

[Table 2]

The crosstalk was measured as follows. Signal strength C ₀ [dB] recorded on the land portion
The reproduction signal intensities C ₋₁ and C ₊₁ [dB] in the adjacent groove (−1, +1 track) with respect to were measured and taken as the crosstalk (CT) value by the following formula.

CT = ((C ₋₁ −C ₀ ) + (C ₊₁ −C ₀ )) / 2 The cross erase was measured as follows.

A signal is written on the land track (Tr ₀ ) with a writing laser power that maximizes the carrier level, and the erasing power is changed to measure the erasing power P ₀ at which C / N becomes zero. When erasing, writing is performed each time.

Writing is performed on Tr ₀ with a writing laser power that maximizes the carrier level, and the signal intensity C _org is measured.

After erasing 1500 times with the erasing power P _erase for the adjacent track (groove portion) Tr _{+ 1} , the signal strength C _after1 of Tr ₀ is measured.

After repeating the above operation, the erase power P _{erase is performed on the} adjacent track (groove portion) Tr _-1 .
After erasing 1500 times with, signal strength C of Tr _{0
Measure after2} .

The above steps ( ₁ ) to (3) are repeated using P _erase as a parameter to find the erasing power P ₁ which is 2 dB lower than C _org .

The cross erase margin (CEM) was determined by the following equation by the above measurement.

CEM = (P ₁ −P ₀ ) / ((P ₁ + P ₀ ) / 2) These measurement results are shown in Table 3. As shown in Table 3, when comparing Example 1 with Comparative Example 1, the C / N is almost the same, but the crosstalk is about 4 dB, the cross erase margin is about 40%, and good results are obtained in Example 1. Was given. Further, in Comparative Example 2, the crosstalk and the cross erase margin were as bad as those of Comparative Example 1, and the C / N was lowered by about 2 dB as compared with Example 1 due to noise due to the grain boundary of ZnS.

[0036]

[Table 3]

(Example 2) As Example 2, the second dielectric layer 24 is made of (Zr) having a thermal conductivity of 0.8 W / (mK).
A magneto-optical disk having the same structure as in Example 1 was prepared except that O ₂ ) _0.8 (SiO ₂ ) _0.2 (film thickness 20 nm, optical film thickness 0.074) was used. Using this magneto-optical disk in the same magneto-optical recording / reproducing apparatus as in Example 1, the same recording / reproducing characteristics as in Example 1 were measured. The measurement results are shown in Table 3.

As shown in Table 3, the C / N ratios of Example 2 and Comparative Example 1 are almost the same, but the crosstalk is about 3 dB, the cross erase margin is about 40%, and the good results are obtained in Example 2. Was obtained. In the case where the second dielectric layer 24 _and ZrO ₂ containing no SiO ₂ is a cross-talk, but the cross-erase margin is almost the same level as in Example 2, the noise due to ZrO ₂ grain boundary C /
N decreased by about 2.5 dB.

Example 3 As Example 3, the second dielectric layer 24 is made of SiN: H having a thermal conductivity of 0.7 W / (m · K).
A magneto-optical disk having the same structure as in Example 1 was prepared except that the film thickness was 25 nm and the optical film thickness was 0.076. Here, SiN: H was deposited by sputtering using a Si target in an atmosphere of argon and ammonia. SiN:
The hydrogen content in H was about 20 atom% as measured by the hydrogen forward scattering method (HFS method), and the ratio of Si and N was about 3: 4 as measured by Auger electron spectroscopy. The same recording / reproducing characteristics as in Example 1 were measured for this disk in the same magneto-optical recording / reproducing apparatus as in Example 1. The measurement results are shown in Table 3.

As shown in Table 3, the C / N ratios of Example 3 and Comparative Example 1 are almost the same, but the crosstalk is about 5 dB, the cross erase margin is 40% or more, and the good results are obtained in Example 3. Was obtained.

(Example 4, Example 5 and Comparative Example 3) As Example 4, the recording layer 23 was made of Gd _0.25 (Fe) with a thickness of 5 nm.
_0.75 Co _0.25 ) _0.75 and Tb _0.22 (Fe with a film thickness of 15 nm
_A magneto-optical disk having the same structure as that of Example 1 was prepared _{except that} the laminated structure was _0.90 Co _0.10 ) _0.78 . In addition, as Example 5, the recording layer 23 is formed of Gd _0.25 (Fe _0.75 C with a thickness of 10 nm).
o _0.25 ) _0.75 and Tb _0.22 (Fe _0.90 Co with a film thickness of 10 nm)
_A magneto-optical disk having the same structure as that of Example 4 was prepared _{except that} the laminated structure was _0.10 ) _0.78 . Further, as Comparative Example 3, the second dielectric layer 24 is made of S having a thermal conductivity of 3.0 W / (m · K).
A magneto-optical disk having the same structure as in Example 5 was prepared except that iN (film thickness 20 nm, optical film thickness 0.076) was used. The recording / reproducing characteristics of these discs were measured in the same magneto-optical recording / reproducing apparatus as in Example 1 as in Example 1. The measurement results are shown in Table 3.

As shown in Table 3, in Example 4, the C / N is slightly higher than in Example 1, and the crosstalk is about 2 dB, and the cross erase margin is about 10%. It was Further, in the fifth embodiment, the noise is high, so that the C / N is lower than that in the fourth embodiment.
The cross erase margin is also worse than in Example 4, but the second dielectric layer 24 has a thermal conductivity of 3.0 W / (m ·
In comparison with Comparative Example 3 in which K) of SiN was used, the crosstalk and cross erase margin of Example 5 were better.

When the media of Examples 4 and 5 are compared, the coercive force at room temperature is 20 kOe or more, which is a sufficiently large value, but near the Curie temperature of Tb-Fe-Co. In the medium, it was less than half that of Example 4. For this reason, it is considered that in Example 5, the magnetic domains became unstable at high temperatures and the crosstalk and cross erase margin deteriorated.

[0044]

The magneto-optical recording medium of the present invention causes less expansion of the recording magnetic domain at the time of writing and deformation of the recording magnetic domain of the adjacent track, as compared with the conventional magneto-optical recording medium of the thin film structure.
As a result, it is possible to reduce crosstalk, increase the cross erase margin, and improve the track density. Further, a sufficient effect can be obtained when the thickness of the second dielectric layer is as thin as about 20 nm, which is also excellent in productivity.

[Brief description of drawings]

FIG. 1 is a partial sectional view showing an example of the structure of a magneto-optical recording medium.

FIG. 2 is a conceptual diagram showing a structure of a land & groove substrate.

FIG. 3 is a partial sectional view showing the structure of a magneto-optical disk according to an embodiment of the present invention.

[Explanation of symbols]

 1, 21 ... Transparent substrate 2, 22 ... First dielectric layer 3, 23 ... Recording layer 4, 24 ... Second dielectric layer 5, 25 ... Reflective layer 26 ... UV curable resin layer 11 ... Groove 12 ... Land 13 ... Groove depth 14 ... Pitch of land and groove

Claims (7)

[Claims] 1. A first dielectric layer on an optically transparent substrate,
In a magneto-optical recording medium having a recording layer, a second dielectric layer and a reflective layer laminated in this order, the recordable track spacing of the substrate is 1.0 μm or less, and the first dielectric layer is a nitride. A magneto-optical recording medium comprising a thin film, wherein the second dielectric layer has a thermal conductivity of 1.0 W / (m · K) or less. 2. The second dielectric layer is (ZnS) _1-x (SiO 2
₂₎ is composed of _x, the magneto-optical recording medium according to claim 1, wherein the range of x is equal to or is 0.1 ≦ x ≦ 0.4. 3. The second dielectric layer is (ZrO ₂ ) _1-x (Si
_{2. The} magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium is composed of O ₂ ) _x , and the range of x is 0.1 ≦ x ≦ 0.4. 4. The magneto-optical recording medium according to claim 1, wherein the second dielectric layer is made of SiN: H having a hydrogen content of 10 atomic% or more and 30 atomic% or less. 5. The recording layer is a Gd-Fe-Co layer and Tb-F.
The magneto-optical recording medium according to claim 1, wherein the magneto-optical recording medium is composed of two layers of an e-Co layer. 6. The composition of the Gd—Fe—Co layer is Gd _x (F
e _1-y Co _y ) _{1-x (} 0.22 ≦ x ≦ 0.27, 0.20
≦ y ≦ 0.35), and the composition of the Tb-Fe-Co layer is Tb _u (Fe _1-v Co _v ) _1-u (0.20 ≦ u ≦ 0.2).
4, 0.06 ≦ v ≦ 0.15), and the above Gd−
The film thickness ratio of the Fe-Co layer and the Tb-Fe-Co layer (Gd-F
The magneto-optical recording medium according to claim 5, wherein the ratio of (e-Co layer thickness / Tb-Fe-Co layer thickness) is 0.1 or more and 0.7 or less. 7. The magneto-optical recording medium according to claim 1, wherein the optical thicknesses of the first dielectric layer and the second dielectric layer, and the thicknesses of the recording layer and the reflective layer are in the following ranges. . 0.23 ≤ n ₁ · d ₁ / λ ≤ 0.30 0.04 ≤ n ₃ · d ₃ / λ ≤ 0.12 13 ≤ d ₂ ≤ 30 35 ≤ d ₄ λ: of the light used for recording / reproducing Wavelength [nm], n ₁ :
Refractive index of first dielectric layer, d ₁ : thickness of first dielectric layer [nm], n ₃ : refractive index of second dielectric layer, d ₃ : thickness of second dielectric layer [nm] , D ₂ : the thickness of the recording layer [n
m], d ₄ : film thickness of the reflective layer [nm]