JP2001256674A - Surface reading type optical recording medium - Google Patents

Abstract

(57) [Problem] To provide a surface readout type optical recording medium having a high SNR, excellent head flying characteristics and durability. SOLUTION: This is a surface-reading type optical recording medium in which at least a reflective layer, a recording layer and a protective layer are laminated in this order on a substrate, and a thickness of 0.5 to 50 is provided between the substrate and the reflective layer.
A base layer made of a metal film containing at least one element selected from the group consisting of IVA group, VA group, and VIA group in the periodic table is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rewritable surface-reading type optical recording medium, and more particularly, to a surface-reading type optical magnetic recording medium in which information is recorded, reproduced and erased by a laser beam and a magnetic field, or only a laser beam. The present invention relates to a surface read type phase change recording medium on which information is recorded, reproduced, and erased.

[0002]

2. Description of the Related Art Optical recording media are portable recording media capable of large-capacity, high-density recording, and have been in demand as rewritable media for recording large-capacity files and moving images of computers accompanying the recent increase in multimedia. Is rapidly increasing.

A magneto-optical recording medium is generally formed by forming a multilayer film including a recording layer on a transparent disk-shaped substrate such as plastic.
Recording and erasing are performed by irradiating a laser while applying a magnetic field, and reproduction is performed by reflected light of the laser. Conventionally, the recording method is
So-called optical modulation recording, in which recording is performed by applying a fixed magnetic field in the opposite direction after erasing by applying a fixed magnetic field, has been the main focus.In recent years, a magnetic field modulation method that modulates a magnetic field according to a recording pattern while irradiating a laser, Attention has been paid to a method capable of performing recording (direct overwrite) in one rotation and accurately recording even at a high recording density.

Further, a phase change recording method utilizing a reversible phase change between a crystalline phase and an amorphous phase can be directly overwritten and has recently been used.

Conventionally, a laser for recording / reproducing has been irradiated onto a recording film through a substrate, and so-called near-field optical recording, which is a method of recording / reproducing by bringing an optical head close to the recording film, has attracted attention as a means for increasing the density. (Appl. Ph.
ys. Lett. 68, p. 141 (1996)).

As one of the recording methods, Solid is used.
The conventional recording limit determined by the laser wavelength (λ) of the light source by using an Immersion Lens (hereinafter abbreviated as SIL) head and reducing the laser beam spot size (（λ / 2NA: NA is the numerical aperture of the objective lens) There is a method that enables reproduction with a shorter mark, 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 (up to 100 nm). A method is used in which a recording film is directly irradiated with a laser beam without passing through the recording film.

That is, in the conventional optical recording medium, the recording film is generally composed of a substrate / first protective layer / recording layer / second protective layer / reflective layer, whereas near-field optical recording. In this example, the recording / reproducing is performed by irradiating a laser beam from the surface side of the film (surface reading type recording) with a reverse structure of the substrate / reflection layer / first protective layer / recording layer / second protective layer.

Recently, a surface recording method in which recording and reproduction are performed by irradiating a laser through a protective coating layer on a thin film with a lens NA of 1 or less has been proposed (JM).
agn. Soc. Jpn. 68, S1, p. 269 (1
999)).

In near-field optical recording, a floating slider head is often used to bring the recording film and the SIL head close to each other. Since the distance between the head and the recording medium is very short (〜100 nm), there is a problem with the interface between the head and the recording medium (such as a head crash) as in the case of the hard disk drive. In addition, there is a problem that the SNR is reduced due to the surface property of the thin film and that the durability of the recording medium against direct exposure to the air is secured.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide an SN
An object of the present invention is to provide a surface-reading type optical recording medium having a high R and excellent head flying properties and durability.

[0012]

Means for Solving the Problems The present inventors have made intensive studies in view of the above-mentioned situation, and as a result, have found that a surface read-out having at least a reflective layer, a recording layer and a protective layer laminated on a substrate in this order. In the optical recording medium of the type, by providing an underlayer made of a single metal or alloy having a thickness of 0.5 to 50 nm between the substrate and the reflective layer, the SNR and the head flying property were improved, and the durability was improved. The inventors have found that the optical recording medium is a surface readout type optical recording medium, and have completed the present invention.

Hereinafter, the present invention will be described in more detail.

FIG. 1 is a partial cross-sectional view of an embodiment of a surface read type optical recording medium according to the present invention.

The substrate 11 is not particularly limited as long as it satisfies the characteristics of a medium substrate such as mechanical characteristics, and glass, thermoplastic resin such as polycarbonate, amorphous polyolefin, thermoplastic engineering plastic, etc. can be used. Pits, lands, and guide grooves may be provided on the substrate for recording information.

As the underlayer 12 provided on the substrate 11,
It is composed of a metal film of simple metal or alloy, and the film thickness is
In order to prevent an increase in noise and a decrease in SNR, 0.5 to 5
0 nm, preferably 1 to 30 nm.

The underlayer 12 is made of group IVA of the periodic table,
It is preferable to use a metal film containing at least one element selected from the group VA and group VIA elements. Elements constituting a metal film containing such an element include Ti,
Simple metals such as Zr, Hf, V, Nb, Ta, Cr, Mo and W, CrTa, CrTi, TiTa, TiZr
And alloys such as CrZr.
By being composed of a metal film containing at least one or more elements selected from the group consisting of V, Nb, Ta, Cr, Mo and W, not only SNR and head flying property,
It is particularly preferable because the optical recording medium has improved durability.

It is not preferable that the underlayer 12 is made of a magnetic metal, particularly in the case of magneto-optical recording, because it adversely affects the recording / reproducing characteristics. In addition, when an alloy is used as compared with a single metal, the particle diameter tends to be smaller and noise tends to be lower.

As the reflective layer 13, a metal film having a high reflectivity can be used. For example, Ru, Rh, Pd, O
noble metals such as s, Ir, Pt, Au, Ag, Cu, Al,
Alternatively, a metal film made of an alloy containing 90 to 100% of an alloy of these metals is more preferable.

Preferred metal films constituting the reflection layer include Au, Ag, AlCr, AlTi, AlTa, and Au.
Ti, AuCr, AuTa, AuCu, AgPd, Cu
Examples thereof include Ti, CuTa, and CuCr.

By forming the reflective layer 13 after the formation of the underlayer 12, it is considered that the crystal grain size of the reflective layer is reduced and noise is reduced, and that the head flying characteristics are improved by averaging the grain size. However, such a prediction has no influence on the present invention.

The recording layer 14 may be made of any material that has a perpendicular magnetization and a large coercive force, such as TbFeCo or TbFeCo.
A material mainly composed of bFeCo can be exemplified.
The coercive force of the recording layer is preferably as large as possible in order to stably retain recorded information, but is preferably 5 kOe or more for a magneto-optical recording medium for near-field magneto-optical recording.

Also, a phase change recording medium utilizing a reversible phase change between a crystalline phase and an amorphous phase can be used as the recording layer. In this case, since heat generated in the recording layer is large, it is preferable to form a protective layer between the reflective layer 13 and the recording layer 14.

As the protective layer 15, for example, SiN, A
It can be made of a transparent dielectric such as 1N, SiAlON, Ta ₂ O ₅ , or a mixed material of ZnS and SiO ₂ .
In order to improve the flying characteristics of the slider head,
The protective layer 15 includes a transparent dielectric layer and diamond-like carbon (DLC) obtained by adding hydrogen or nitrogen to carbon.
It may be a laminate with a solid lubricating layer.

Further, by forming a liquid lubricating layer of an extremely thin perfluoropolyether or the like on the protective layer 15 by a method such as a dip pulling method, the floating characteristics of the slider head are further improved.

For forming the underlayer, the reflective layer, the recording layer, the protective layer and the solid lubricating layer, a vacuum thin film forming technique such as a vacuum evaporation method and a sputtering method can be used.

Further, the surface-reading type optical recording medium of the present invention has a NA by forming a protective coat layer made of an acrylic ultraviolet curable resin or the like after the protective layer 15 is formed.
Can also be used as a surface-reading type optical recording medium for an optical system having 1 or less. For forming the protective coating layer, a vacuum thin film forming technique, a dip pulling method, a spin coating method, or the like can be used.

[0028]

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 A medium for surface reading type magneto-optical recording having a structure as shown in FIG. 2 was manufactured. That is, the track pitch is 0.45 μm.
A Cr underlayer 22 is formed to a thickness of 10 nm by DC sputtering on a polycarbonate substrate 21 having a guide groove of m, and a reflective layer 23 made of Au is formed to a thickness of 50 nm by DC sputtering. did. On top of this, Tb _0.20 (F
e _0.77 Co _0.20 Ta _0.03 ) _0.80 of the recording layer 24
It was formed to a thickness of 0 nm by DC sputtering.

Further, a protective layer 2 made of SiN is further formed thereon.
5 was formed by a reactive DC sputtering method using a Si target in a mixed atmosphere of Ar and N ₂ to form a solid lubricating layer 26 made of diamond-like carbon (DLC) of 65 nm.
And it was 15nm formed by a reactive RF sputtering method using a C target in a mixed atmosphere of CH _4. After forming the DLC layer, a perfluoropolyether-based lubricating layer 27 was applied to a thickness of 1 nm by a pull-up method to complete a surface read type magneto-optical recording medium.

Embodiment 2 In the same manner as in Embodiment 1, the underlayer 22 is made of Ti, Zr, H
f, V, Nb, Ta, Mo, W, Cr _0.8 Ta _0.2 , a surface read type magneto-optical recording medium was manufactured.

Example 3 In the same manner as in Example 1, the reflective layer 23 was made of Ag _0.99 Pd.
A surface read type magneto-optical recording medium having a value of _0.01 was manufactured.

Embodiment 4 In the same manner as in Embodiment 1, the underlayer 22 is made of Cr _0.8 Ta _0.2
A surface read type magneto-optical recording medium having a different underlayer thickness was manufactured.

Embodiment 5 In the same manner as in Embodiment 1, the track pitch is 0.55 μm.
After the formation of the DLC layer, a protective coat layer made of an acrylic ultraviolet curable resin was formed by spin coating to a thickness of 10 μm.
Then, a perfluoropolyether-based lubricating layer 27 was applied by a pull-up method to a thickness of 1 nm to produce a surface read type magneto-optical recording medium.

Comparative Example 1 A medium for surface reading type magneto-optical recording having a structure as shown in FIG. 3 was manufactured. On a polycarbonate substrate 31 provided with a guide groove having a track pitch of 0.45 μm, a reflective layer 32 made of Au was formed to a thickness of 50 nm by DC sputtering.

On top of this, Tb _0.20 (Fe _0.77 Co _0.20 Ta
_0.03 ) The recording layer 33 composed of _0.80 is DC-coated to a thickness of 20 nm.
It was formed by a sputtering method. Further, a protective layer 34 of SiN was further formed thereon by a reactive DC sputtering method using a Si target in a mixed atmosphere of Ar and N ₂ to a thickness of 65 nm.
A solid lubricating layer 35 made of diamond-like carbon (DLC) was formed to a thickness of 15 nm by a reactive RF sputtering method using a C target in a mixed atmosphere of Ar and CH ₄ .

After the formation of the DLC layer, a lubricating layer 36 of perfluoropolyether was applied to a thickness of 1 nm by a pull-up method to complete a surface read type magneto-optical recording medium.

The SNR measurements shown below were performed on the surface readout type magneto-optical recording media of Examples 1 to 4 and Comparative Example 1.

A surface read type magneto-optical recording medium is set on a spindle, and the medium is rotated at a linear velocity of 10 m / s. A slider SIL head having a laser wavelength of 680 nm and an effective numerical aperture of 1.2 was levitated to a height of 100 nm on the thin film surface, and the recording layer was heated to a temperature higher than the Curie temperature by irradiating a laser in a pulsed manner. 1
Recording while modulating at 6 MHz (mark length: 0.3
μm). Here, the coil magnetic field at the time of recording is set to 120 Oe.
And The SNR is measured by changing the recording power, and the SNR is measured.
The value at which was saturated was taken as the SNR value of the sample. The reproduction power is 0.8 mW.

Further, the following glide test was performed.

A magneto-optical recording medium is set on a spindle and rotated. Introduction Waffle burnishing head (Glide Height, Flying Height: 25 nm)
Is used to seek once between a radius of 20 to 60 mm. Next, the disk is sought by a glide head with a piezo element (Flying Height: 50 nm, manufactured by Glide Height Co., Ltd.), and the voltage value induced in the piezo element is monitored. Hits with a voltage value of 500 mV or more are counted as hits. Very good hit count 0-2, 3-5
Is good, 6 to 9 is slightly good, and 10 or more is bad.

Table 1 shows the SNR measurement results, the glide test results, and the results of the accelerated durability test for 250 hours in an environment of 80 ° C. and 85% RH. In the results of the glide test and the durability test, x indicates poor, Δ indicates somewhat good, ○ indicates good, and ◎ indicates very good.

Table 2 shows the SNR of the sample of Example 4.
Is dependent on the thickness of the underlayer.

The samples of the examples were compared with the comparative examples in SN.
R, it can be seen that not only the head flying property but also the durability have been improved.

The recording characteristics of the surface read type magneto-optical recording medium of Example 5 were measured using a slider head having an optical system with a laser wavelength of 680 nm and an effective numerical aperture of 0.8. A good SNR value of 23 dB was obtained at 0.4 μm, and it was confirmed that the medium could be used as an overcoated surface readout type magneto-optical recording medium.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

According to the present invention, it is possible to obtain a surface-reading type optical recording medium which not only has an improved SNR and a flying height of the head but also has an excellent durability.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a structure of an example of a surface read type optical recording medium of the present invention.

FIG. 2 is a partial cross-sectional view showing the structure of the first embodiment of the present invention.

FIG. 3 is a partial sectional view showing the structure of Comparative Example 1 of the present invention.

[Explanation of symbols]

 11, 21, 31: Substrate 12, 22: Underlayer 13, 23, 32: Reflective layer 14, 24, 33: Recording layer 15, 25, 34: Protective layer 26, 35: Solid lubricating layer 27, 36: Lubricating layer

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) G11B 11/105 546 G11B 11/105 546F

Claims (4)

[Claims] 1. A surface-reading optical recording medium comprising a substrate, on which at least a reflective layer, a recording layer, and a protective layer are laminated in this order, a thickness of 0.5 to 0.5 mm between the substrate and the reflective layer.
A surface-reading type optical recording medium, comprising a base layer made of a single metal or an alloy of 50 nm. 2. The method according to claim 1, wherein the underlayer is made of a group IVA or VA of the periodic table.
2. The surface-readable optical recording medium according to claim 1, comprising a metal containing at least one element selected from the group VIA elements. 3. An underlayer comprising V, Nb, Ta, Cr, Mo.
3. The surface-reading type optical recording medium according to claim 1, wherein the optical recording medium is made of a metal containing at least one element selected from the group consisting of W and W. 4. The surface-reading type optical recording medium according to claim 1, wherein the reflection layer is made of a metal containing noble metal, Cu, Al, or an alloy of these metals. .