JPH11185313A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a recording film which hardly gives rise to a head crash and exhibits high durability without the impairment of optical characteristics by forming a transparent diamond-like carbon layer on a protective layer forming on a substrate and forming a lubricating layer thereon. SOLUTION: The optical recording medium is formed by laminating a first protective layer 12, the recording layer 13 consisting of a magneto-optical recording film, a second protective layer 14, the diamond-like carbon(DLC) layer 15 and the lubricating layer 16 on the substrate 11. Glass, polycarbonate, etc., are usable as the substrate 11. A transparent dielectric film of AlN, SiN, etc., are formed as the first protective layer 12 on the substrate 11. Further, the recording layer 13 consisting of the magneto-optical recording film of TbFeCo, DyFeCo, etc., is formed on the first protective layer 12. AlN, SiN, etc., are formed as the second protective layer 14 on the recording layer 13 and the DLC 15 is formed thereon. Finally, the lubricating layer 16 of a film thickness of >=0.3 to <=4.0 nm is formed, by which the recording medium is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable optical recording medium, and more particularly to a magneto-optical recording medium for recording, reproducing and erasing information by causing an optical change in a recording layer by a laser beam, or a phase change. It relates to a recording medium.

[0002]

2. Description of the Related Art An optical recording medium is a portable recording medium capable of large-capacity and high-density recording, and is a rewritable medium for recording moving images and the like as a large-capacity storage file of a computer accompanying the recent increase in multimedia. Demand is increasing rapidly.

[0003] Conventional rewritable optical recording media generally form a multilayer film including a recording layer on a disc-shaped substrate such as plastic, and irradiate a laser from the plastic substrate side to record.
Playing and erasing were performed.

On the other hand, so-called near-field optical recording, in which an optical head is brought close to a recording film for recording / reproducing, has attracted attention as a means for increasing the density (Appl. Phys. L.).
ett. 68, p. 141 (1996)).

In this recording method, Solid Imager is used.
By reducing the size of a laser beam spot using a Ssion Lens (hereinafter abbreviated as SIL) head, it is shorter than the recording limit (： λ / 2NA: NA is the numerical aperture of the objective lens) determined by the laser wavelength (λ) of the conventional light source. Reproduction with marks is possible, and recording and reproduction with an ultra-high recording density can be realized. In this near-field optical recording, it is necessary to bring the optical head close to the recording medium (〜100 n).
m) Instead of irradiating the recording film with the laser beam through the substrate as in the conventional optical recording medium, a method of directly irradiating the recording film with the laser beam without passing through the substrate is used.
That is, in a conventional optical recording medium, the recording film has a substrate /
In general, the first protective film / recording film / second protective film / reflective film is used, whereas in near-field optical recording, the substrate / reflective film / first protective film / recording film / second protective film is used. A laser beam is irradiated from the film surface side to perform recording / reproduction (surface recording / reproduction). At this time, the recording film and S
It has been proposed to use a floating slider head to approach the IL head.

[0006]

In the near-field optical recording, an extremely high recording density is possible as described above, but it is necessary to bring the optical head close to the recording film. In this case, a flying slider head collides with the recording film, that is, a so-called head crash easily occurs, and it is difficult to obtain a highly durable recording film.

It is an object of the present invention to provide a highly durable surface recording / reproducing optical recording film in which head crash is unlikely to occur.

[0008]

Means for Solving the Problems In view of the above situation, the present inventors have made intensive studies and as a result, have found that a surface recording / reproducing type optical recording medium using near-field optical recording has By forming a transparent diamond-like carbon film and a lubricating layer, it has been found that a recording film having high durability can be obtained without causing head crash without deteriorating optical characteristics, and the present invention has been completed.

That is, in the optical recording medium of the present invention, at least a recording layer and a protective layer are formed on a substrate in this order.
C), and a lubricating layer is formed on the diamond-like carbon layer.

[0010] The recording layer of the optical recording medium of the present invention is made of TbFeC.
o, DyFeCo, GdTbFeCo, NdDyFeC
o or other magneto-optical recording film, or GeSbTe, AgIn
It is composed of a film such as a phase change recording film such as SbTe, which can be recorded by changing the polarization plane, the reflectance, the phase of light, and the like.

The protective layer of the optical recording medium of the present invention is made of AlN, S
It is composed of a transparent dielectric film made of iN, Ta ₂ O ₅ , ZnS—SiO ₂ or the like.

The DLC layer of the optical recording medium of the present invention is preferably made of hydrogen-containing carbon, and has a refractive index at a wavelength of 633 nm in the range of 1.7 to 2.1. DL
C includes hydrogen-containing DLC and nitrogen-containing DLC, and hydrogen-containing DLC has higher transparency and is preferable for use in optical discs. The use of a nitrogen-containing DLC improves the levitation of the slider head.
It is preferable to reduce the absorption of light to 0 nm or less.

The DLC layer can be formed by a sputtering method, an ion beam sputtering method, a plasma CVD method or the like. To produce a hydrogen-containing DLC by sputtering, argon (Ar) and methane (CH ₄ ) or argon (A)
r) and a hydrogen (H ₂ ) atmosphere by sputtering a carbon (C) target. Increasing the flow rate of methane or hydrogen decreases the refractive index. Therefore, the refractive index of DLC can be controlled by the flow rate of methane or hydrogen during sputtering film formation. By setting the refractive index of the DLC to 1.7 or more, the impact when the slider head hits a defect is softened, and a head crash hardly occurs. Further, by setting the refractive index to be 2.1 or less, the film becomes transparent to a wavelength of 600 nm or more so that absorption can be almost ignored. Also, between 600 nm and 400 nm, the lower the refractive index at 633 nm, the lower the absorption. However, by setting the DLC layer thin according to the absorptance, the floating characteristics of the slider head can be reduced without substantially impairing the optical characteristics. improves.

The lubricating layer of the optical recording medium of the present invention can be used as long as it exhibits lubricating properties such as silicone oil or fluoropolyether-based fluorine oil, but perfluoropolyether and perfluoropolyether derivatives are particularly preferable. . Examples of the perfluoropolyether derivative include alcohol-modified perfluoropolyether, ester-modified perfluoropolyether, isocyanate-modified perfluoropolyether, carboxyl group-modified perfluoropolyether, and piperonyl-modified perfluoropolyether. The thickness of the lubricating layer of the present invention is 0.1.
It is preferably 3 nm or more and 4.0 nm or less. If the thickness is less than 0.3 nm, the protective performance of the lubricating layer will be insufficient, and the thin film will be easily damaged, and if it is more than 4.0 nm, the slider head will stick to the disk and crash easily.

When the present invention is applied to a magneto-optical recording medium, it is preferable that at least a first protective layer, a magneto-optical recording layer, a second protective layer, a diamond-like carbon layer, and a lubricating layer are laminated on a substrate. .

FIG. 1 is a partial cross-sectional view of an embodiment of the optical recording medium of the present invention having this structure. On a substrate 11, a first protective layer 12, a recording layer 13 composed of a magneto-optical recording film, and a second protective layer 1.
4, a diamond-like carbon layer 15 and a lubricating layer 16 are laminated.

The substrate 11 is not particularly limited as long as it satisfies the characteristics of a medium substrate such as mechanical characteristics, and glass, polycarbonate, amorphous polyolefin, super engineering plastic or the like can be used. A transparent dielectric film such as AlN, SiN, Ta ₂ O ₅ , ZnS—SiO ₂ or the like is formed as a first protective layer 12 on the substrate 11 by a sputtering method or a vacuum evaporation method. On the first protective layer 12, TbFeCo, DyFeC
o, a recording layer 13 made of a magneto-optical recording film of GdTbFeCo, NdDyFeCo, or the like is formed by a sputtering method, a vacuum evaporation method, or the like. AlN as the second protective layer 14 on the recording layer _{13, SiN, Ta 2 O 5} , a ZnS-SiO ₂ or the like formed by sputtering or a vacuum evaporation method or the like. A DLC film 15 is formed thereon by a sputtering method or the like. Further, a lubricating layer 16 is formed thereon by a method such as a dip pulling method.

The first protective layer 12 only needs to have a thickness that can protect the recording layer 13, and preferably has a thickness of 10 nm or more and 100 nm or less. The recording layer 13 needs to have a thickness such that light does not transmit to the first protective layer 12 and is 30 nm or more and 200 n
m or less is preferred. In addition to the role of protecting the recording layer, the second protective layer 14 also has the role of controlling the light absorption efficiency of the recording layer, and increasing the amount of change in reflected light before and after recording and the Kerr rotation angle. For this reason, the thickness of the second protective layer 14 is designed in consideration of the laser wavelength to be used, and is preferably 20 nm or more and 300 nm or less. Substrate 11 and first protective layer 1
It is also possible to insert a film having good thermal conductivity such as Al, Al alloy, Au, Ag or the like as a heat sink between the two to adjust the recording sensitivity.

In the case where the present invention is applied to a magneto-optical recording medium, another medium configuration is such that at least a reflective layer, a magneto-optical recording layer, a protective layer, a diamond-like carbon layer, and a lubricating layer are laminated on a substrate. It is characterized by the following.

FIG. 2 is a partial cross-sectional view of one embodiment of the optical recording medium of this configuration according to the present invention. Reflective layer 2 on substrate 21
2, first protective layer 23, magneto-optical recording layer 24, second protective layer 2
5, a diamond-like carbon layer 26 and a lubrication layer 27 are laminated.

The reflection layer 22 is made of Al, Al alloy, Au, Ag.
And the like, and the film thickness is preferably 10 nm or more and 200 nm or less in order to secure the reflectance. The first protective layer 23 and the second protective layer 25 are made of AlN, SiN, Ta.
It is a transparent dielectric film of ₂ O ₅ , ZnS—SiO ₂ or the like. The thickness of the magneto-optical recording layer 15 is preferably 8 nm or more in order to secure recording stability, and is preferably 40 nm or less in order to transmit light to the reflective layer to some extent to cause multiple reflection and increase the Kerr rotation angle. , 30 nm or less is more preferable.

With such a configuration, even if a substrate such as a plastic substrate whose substrate is easily deformed due to environmental changes is used, it is resistant to environmental changes, and even if the reflective layer is crystalline, noise due to crystal grains is reduced. a reflective layer 32 of thickness d ₁ on the substrate 31 as shown in FIG. 3, the magneto-optical recording layer 33 of thickness d _2, the protective layer 34 having a thickness d _3, diamond-like carbon layer having a thickness d ₄ 35, a lubricating layer 36 is laminated, and the thickness of each layer is 10 nm ≦ d ₁ ≦ 100 nm, 8 nm ≦ d ₂ ≦ 3
0 nm, 5 nm ≦ d ₃ , 30 nm ≦ d ₃ + d ₄ ≦ 100 n
m, preferably 5 nm ≦ d ₄ ≦ 60 nm. With such a configuration, it is possible to obtain a good magneto-optical output even with a thin recording film, and since the film thickness is small, the stress in the film is small, so that the film is less likely to be broken by impact of collision or environmental change. . In addition, TbFeCo, DyFeC
By directly laminating an amorphous magneto-optical recording layer such as o, GdTbFeCo, NdDyFeCo, etc., noise due to grains in the reflective layer is not emphasized.

[0023]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to only these Examples.

Example 1, Comparative Example 1 and Comparative Example 2 An optical recording medium for near-field optical recording having a structure as shown in FIG. 2 was manufactured as described below. Track pitch 0.45
Al-3 wt% Cr as a reflective layer 22 on a disk-shaped substrate 21 made of polycarbonate having a diameter of 130 mm
An alloy film (thickness: 50 nm) was formed by DC sputtering. On this, a first protective layer 23 made of SiN is formed by Ar and N
Reactivity R using Si target in mixed atmosphere of ₂
It was formed by the F sputtering method (film thickness: 5 nm). Tb on this
_The magneto-optical recording layer 24 made of ₂₀ (Fe ₉₀ Co ₁₀ ) ₈₀ is
A target and an Fe ₉₀ Co ₁₀ target were formed by a DC simultaneous sputtering method (film thickness: 20 nm). Further, a second protective layer 25 made of SiN was formed thereon by a reactive RF sputtering method using a Si target in a mixed atmosphere of Ar and N ₂ (thickness: 30 nm). A DLC layer 26 having a refractive index of 1.85 at 633 nm was formed thereon by a reactive RF sputtering method using a C target in a mixed atmosphere of Ar and CH ₄ (film thickness: 20 nm).

After the DLC layer 26 has been formed, piperonyl-modified perfluoropolyether (manufactured by Audimont, trade name “Fomblin”) using a perfluoropolyether solvent (manufactured by Ausimont, trade name “Galden SV-70”) : AM2001 ”), and the lubricating layer 27 was applied by lifting the recording medium from the solution to complete the magneto-optical recording medium.

At this time, the thickness of the lubricating layer is changed to 0.2, 0.5, 1.
Magneto-optical recording media were prepared in which the thickness was changed to 0, 2.0, 3.0, and 4.5 nm. The thickness of the lubricating layer was calculated by observing the C _1S peak intensity using X-ray photoelectron spectroscopy (XPS).

Further, as Comparative Example 1, DLC was
The layer up to the layer 26 is laminated in the same manner as in the first embodiment, and the magneto-optical recording medium not coated with the lubricating layer 27 and the substrate 21 as the comparative example 2
To the magneto-optical recording layer 24 are laminated in the same manner as in the first embodiment.
A second protective layer 25 made of SiN is laminated to a thickness of 50 nm,
The magneto-optical recording medium having the lubricating layer 27 coated thereon with a thickness of 2.0 nm was manufactured without the C layer 26.

The magneto-optical recording medium obtained as described above was set on a glide tester, and the linear velocity was 7.5 m / s.
Glide head with a piezo element (made by Glidelight: 70% slider, 0.01
2 "x 6.0 gr) was sought within a radius of 30 to 60 mm. The flying height of this glide head was 7.5 m in linear velocity.
/ S is 0.05 μm. The voltage induced in the piezo element when the glide head was sought was observed with an oscilloscope. At this time, a voltage value exceeding 800 mV was judged as contact with the recording medium and counted.

The above measurements were performed on each of the ten magneto-optical recording media of Example 1, Comparative Examples 1 and 2, and the lubricating layer thickness of Example 1 was 0.5, 1.0. ,
The 2.0 and 3.0 nm magneto-optical recording medium had no visible scratches, the number of hits was less than 3, and the ratio of the medium having zero hits was as good as 40% or more. In the magneto-optical recording medium of Example 1 having a lubricating layer thickness of 0.2 nm, the number of hits was about 5 on average, and there was no crash. In the magneto-optical recording medium having a lubricating layer thickness of 4.5 nm in Example 1,
Several scratches occurred on 3 out of 10 sheets. The remaining media had less than 5 hits. In each of the magneto-optical recording media of Comparative Example 1 in which the lubricating layer was not formed and Comparative Example 2 in which the DLC layer was omitted, both media crashed as soon as the head was loaded.

From the above results, the lubricating layer preferably has a thickness of 0.3 nm or more and 4.0 nm or less. Also, the DLC layer 26
It was found that the absence of the medium resulted in poor flying characteristics of the medium.

Example 2 and Comparative Example 3 As described below, an optical recording medium for near-field optical recording having a structure as shown in FIG. 1 was manufactured. Disc-shaped substrate 1 made of polycarbonate with a track pitch of 0.45 μm and a diameter of 130 mm
A first protective layer 12 made of AlSiN is formed on Ar and N _2.
Formed by a reactive RF sputtering method using an AlSi target in a mixed atmosphere (film thickness: 50 nm). On this, a magneto-optical recording layer 13 made of Tb ₂₂ (Fe ₈₅ Co ₁₅ ) ₇₈ was formed by a DC simultaneous sputtering method using a Tb target and an Fe ₈₅ Co ₁₅ target (film thickness: 70 nm). Further, a second protective layer 14 of SiN was formed thereon by a reactive RF sputtering method using a Si target in a mixed atmosphere of Ar and N ₂ (film thickness: 80 nm). 633 nm on this
The DLC layer 15 having a refractive index of 1.9 was formed of Ar and CH ₄
Formed by a reactive RF sputtering method using a C target in a mixed atmosphere (film thickness: 30 nm).

After the DLC layer 15 is formed, piperonyl-modified perfluoropolyether (manufactured by Ausimont, trade name “Fomblin”) using a perfluoropolyether solvent (manufactured by Ausimont, trade name “Galden SV-70”) : AM2001 "), and the lubricating layer 16 was applied to 1.5 nm by pulling up the recording medium from the solution to complete the magneto-optical recording medium.

As Comparative Example 3, the substrate 11 to the magneto-optical recording layer 13 were laminated in the same manner as in Example 2, the second protective layer 14 of SiN was laminated to a thickness of 105 nm, and the DLC layer 15 was formed.
Was omitted to produce a magneto-optical recording medium coated with a 1.5 nm lubricating layer 16.

The optical recording medium obtained as described above was set in a glide tester, and a glide test was performed in the same manner as in Example 1. When the measurement was performed on ten magneto-optical recording media of Example 2 and Comparative Example 3, respectively,
In Example 2, there were no visible scratches, the number of hits was 5 or less, and the ratio of the medium having zero hits was 30%. In Comparative Example 3, each medium crashed as soon as the head was loaded. From the above results, it was found that the flying characteristics of the medium were not good without the DLC layer 15.

(Example 3) A medium having the same structure as that of Example 1, the lubricating layer 27 having a thickness of 2.0 nm, and the refractive index by changing the ratio of CH _{4 to} Ar as a condition for forming the DLC layer 26. To change the refractive indices of 1.6, 1.65,
1.75, 1.9 and 2.0 media were produced.

The optical recording medium obtained as described above was set in a glide tester, and a glide test was performed in the same manner as in Example 1. When the measurement was performed on each of the ten magneto-optical recording media of Example 3, the magneto-optical recording media of Example 3 having a refractive index of 1.75, 1.9, and 2.0 had no visible scratches. The number of hits is 5 or less for the medium with a refractive index of 1.75, and the ratio of the medium with zero hits is 3
In the medium having 0% and the refractive index of 1.9, the ratio of the medium having three or less hits is 50%, and the medium having the refractive index of 2.0 is less than 3 in the medium having zero hits. The proportion was 50%. Example 3 has a refractive index of 1.6, 1.65
In the case of the magneto-optical recording medium described above, several thin scratches are visible when loaded, and the number of hits is 2 for the medium having a refractive index of 1.6.
There is no medium with zero hits within 0 and a refractive index of 1.6.
In all of the media of No. 5, there was no media in which the number of hits was zero with no more than 12 hits.

(Embodiment 4) As described below, FIG.
A magneto-optical recording medium for near-field optical recording having a structure as shown in FIG. An Al-3 wt% Cr alloy film (50 n thick) is formed as a reflective layer 32 on a disc-shaped substrate 31 made of polycarbonate having a track pitch of 0.45 μm and having a diameter of 130 mm.
m) was formed by a DC sputtering method. On top of this, Tb ₂₀
A magneto-optical recording layer 33 made of (Fe ₉₀ Co ₁₀ ) ₈₀ was formed by a DC simultaneous sputtering method using a Tb target and an Fe ₉₀ Co ₁₀ target (film thickness: 20 nm). In addition, S
The protective layer 34 made of iN was formed by a reactive RF sputtering method using a Si target in a mixed atmosphere of Ar and N ₂ (film thickness: 30 nm). A DLC layer 35 having a refractive index of 1.85 at 633 nm was formed thereon by a reactive RF sputtering method using a C target in a mixed atmosphere of Ar and CH ₄ (film thickness: 20 nm).

After the formation of the DLC layer 35, piperonyl-modified perfluoropolyether (manufactured by Ausimont, trade name "Fomblin") using a perfluoropolyether-based solvent (manufactured by Ausimont, trade name "Galden SV-70") : AM2001 ”), the lubricating layer 36 was applied to 2.0 nm by pulling up the recording medium from the solution to complete the magneto-optical recording medium.

Effective NA at laser wavelength of 680 nm
The media of Examples 1 and 4 were set in a recording / reproducing evaluator of the optical system of the SIL head of 1.2, and the recording / reproducing characteristics were evaluated. While rotating at a linear velocity of 7 m / s, while irradiating a laser so that the laser output before the objective lens becomes 6 mW, ± 150 Oe at a frequency of 7 MHz.
A magnetic field modulated by the magnitude of was applied from a coil provided in the SIL head to record on the medium. When reproduction was performed while irradiating a laser so that the laser output before the objective lens was 1 mW, the carrier (C) level was the same in Examples 1 and 4, but noise (N) was obtained.
As for the level, the fourth embodiment is 2d in comparison with the first embodiment.
B was low, and the carrier-to-noise ratio (CNR) was 43 dB in Example 1 and 45 dB in Example 4.

[0040]

According to the present invention, a surface recording / reproducing type optical recording medium which has a small number of hits suitable for near-field optical recording, hardly causes head crash, and has high durability can be obtained. Further, even if a substrate such as a plastic substrate which is easily deformed due to environmental changes is used, the film is hardly broken. Also, even if the reflective layer is crystalline, it is possible to reduce noise due to crystal grains.

[Brief description of the drawings]

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

FIG. 2 is a partial sectional view showing the structure of another example of the optical recording medium of the present invention.

FIG. 3 is a partial sectional view showing the structure of another example of the optical recording medium of the present invention.

[Explanation of symbols]

 11, 21, 31: Substrate 22, 32: Reflective layer 12, 23: First protective layer 13, 24, 33: Recording layer 14, 25: Second protective layer 34: Protective layer 15, 26, 35: DLC layer 16 , 27, 36: Lubrication layer

Claims (6)

[Claims] 1. An optical recording medium in which at least a recording layer and a protective layer are formed in this order on a substrate, a diamond-like carbon layer is formed on the protective layer, and a lubricating layer is further formed on the diamond-like carbon layer. An optical recording medium characterized by the above-mentioned. 2. The optical recording medium according to claim 1, wherein the diamond-like carbon layer is made of carbon containing hydrogen, and has a refractive index of 1.7 to 2.1 at a wavelength of 633 nm. 3. The lubricating layer has a thickness of 0.3 nm or more and 4.0 n or more.
3. The optical recording medium according to claim 1, wherein m is equal to or less than m. 4. The method according to claim 1, wherein at least a first protective layer, a magneto-optical recording layer, a second protective layer, a diamond-like carbon layer, and a lubricating layer are laminated on the substrate in this order.
4. The optical recording medium according to 2 or 3. 5. A substrate according to claim 1, wherein at least a reflective layer, a magneto-optical recording layer, a protective layer, a diamond-like carbon layer, and a lubricating layer are laminated on the substrate in this order.
The optical recording medium according to the above. 6. A reflective layer having a thickness d ₁ on the substrate, the magneto-optical recording layer having a thickness d _2, protective layer having a thickness d _3, layered diamond-like carbon layer having a thickness d _4, a lubricating layer in this order The thickness of each layer is 10 nm ≦ d ₁ ≦ 100 nm, 8 nm ≦ d ₂ ≦ 3
0 nm, 5 nm ≦ d ₃ , 30 nm ≦ d ₃ + d ₄ ≦ 100 n
6. The optical recording medium according to claim 5, wherein m, 5 nm ≦ d ₄ ≦ 60 nm.