JP2001291243A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium having an optical groove depth in proximity field optical recording. SOLUTION: This optical recording medium is provided with a land and groove structure related to at least recording/reproducing on a substrate, at least a reflecting layer and a recording layer provided on the substrate in this order, and adapted to record/reproduce information by a floating type optical head. In the range of the optional length of about 10 μm on the radius of the area of the optical recording medium for recording/reproducing information, when a depth from a land maximum height to the center line of the land and the groove is Rp, and a floating height from a land maximum height to an optical head is H, Rp satisfies the relation of H>Rp>=0.1 H, preferably 0.8>=Rp>=0.1 H.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a rewritable optical recording medium.

[0002]

2. Description of the Related Art An optical recording medium is a portable recording medium capable of large-capacity, high-density recording, and 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 rapidly increasing.

In an optical recording medium, a groove (guide groove) for performing a tracking servo is usually provided in a physical shape on a substrate at a place where a laser beam is recorded / reproduced, and information (data) is formed between the grooves. The substrate between them is generally recorded on a convex portion (hereinafter referred to as a land).

[0004] Therefore, the larger the land, the larger the mark width to be recorded can be, the greater the intensity of the reproduction signal, and the higher the quality of the reproduction signal.

However, in order to increase the recording density, it is necessary to reduce the track pitch, which is the distance between grooves, to increase the information per recording area.
For example, the track pitch of a commercially available 3.5 inch diameter magneto-optical recording medium is 1.6 microns for a recording capacity of 128 MB, 1.4 microns for a recording capacity of 230 MB, and
It has been reduced to 1.1 microns with a size of 640 MB.

On the other hand, the recording density is limited by the laser beam spot size (.about..lamda. / NA) determined by the light source laser wavelength (.lambda.) Of the recording / reproducing apparatus and the numerical aperture (NA) of the objective lens.

For example, in the case of the above-mentioned recording / reproducing apparatus for a 640 MB magneto-optical recording medium, the wavelength: 680 nm, NA:
0.55 and the laser beam spot size is about 1
240 nm.

As a means for reducing the laser beam spot size and achieving higher density, so-called near-field optical recording, in which an optical head is brought close to a recording film to perform recording and reproduction, has attracted attention (for example, Applied Physics Letter). (Appl. Phys. Lett.), Vol.
p. 141 (1996)).

As one of the recording methods, Solid is used.
Using an Immersion Lens (hereinafter abbreviated as "SIL") head, increasing the effective numerical aperture when using SIL, reducing the laser beam spot size, and achieving ultra-high recording density recording / reproduction it can.

For example, wavelength: 650 nm, effective NA:
In near-field optical recording using an SIL of 1.4, the laser beam spot size is about 460 nm, which is about 37 nm of the laser beam spot size used in the above-mentioned recording / reproducing apparatus for the conventional 640 MB magneto-optical recording medium. %.

In this surface recording / reproducing method, it is necessary to bring the optical head close to the recording medium (up to 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, a substrate / first protective film / recording film / second protective film / reflection film is generally used, whereas near-field optical recording is performed. The optical recording medium used has a reverse structure of a substrate / reflective film / recording film / protective film, and irradiates a laser beam from the surface on the protective film side to record and reproduce information.

At this time, it has been proposed to use a floating slider head to bring the optical recording medium and the optical head closer to each other.

[0014]

Generally, when the track pitch becomes the size of a light spot, the groove functions as a diffraction grating, and an interference effect due to a track shift occurs in a region where the zero-order and first-order diffracted lights overlap. Since the intensity distribution of the beam spot changes, a tracking error signal can be detected.

The signal intensity is determined by the numerical aperture N of the objective lens.
A, determined by track pitch and laser wavelength λ,
It is known that the tracking error signal becomes maximum when the groove depth is λ / 8n (n is the refractive index of the substrate through which the laser passes).

However, in the case of the near-field optical recording system,
Since the signal is obtained by the coupling effect between the optical head located in the vicinity and the outermost surface of the disk in addition to the conventional diffraction effect, the signal greatly changes depending on the flying height of the optical head, and the design of the groove depth is the same as the conventional one. The design has a problem that the optimum depth for near-field optical recording cannot be obtained.

According to the present invention, there is provided a surface recording having a land and a groove involved in recording / reproducing, and having a groove depth capable of obtaining an optimum tracking error signal intensity when performing near-field recording / reproducing with a floating optical head. It is intended to provide a reproduction type optical recording medium.

[0018]

Means for Solving the Problems The present inventors have made intensive studies in view of the above-mentioned situation, and as a result, completed the present invention.

That is, according to the present invention, at least a land and groove structure involved in recording / reproduction is provided on a substrate.
An optical recording medium in which at least a reflective layer and a recording layer are provided on a substrate in this order, and the recording and reproduction of information is performed by a floating optical head. , The depth from the maximum height of the land to the center line of the land and the groove is R
p, the flying height from the maximum height of the land to the optical head
The present invention relates to an optical recording medium characterized in that Rp satisfies the relationship of H> Rp ≧ 0.1H when H is set.

Hereinafter, the present invention will be described in detail.

In the present invention, the depth from the maximum height of the land to the center line of the land and groove is Rp, and the maximum height of the land is an arbitrary length on the radius in the area for recording and reproducing information on the optical recording medium. When the flying height from the optical head to the optical head is H, Rp satisfies the relationship of H> Rp ≧ 0.1H. These relationships will be described with reference to FIG. However, FIG. 1 does not accurately show the relative sizes of the optical head, the land, the groove, and the like.

In the present invention, the center line of the land and the groove is surrounded by the straight line and the roughness curve when one straight line is drawn with respect to the roughness curve of the land and the groove in an arbitrary length range. A straight line whose area is equal on both sides of the straight line. Specifically, in FIG.
It means that the area of (A) and the area of (B) are equal across the center line.

When the depth from the maximum height of the land to the center line is Rp, and the flying height from the maximum height of the land to the optical head is H, H> Rp ≧ 0.1H
It is important to satisfy the relationship.

FIGS. 2 and 3 show examples of an optical head having a slider portion which can be used in the present invention. FIG. 2 is a cross-sectional view of the optical head, in which information is recorded and reproduced by an optical lens 2 such as an SIL while the surface of the slider unit 1 floats relative to the surface of the optical recording medium. FIG.
FIG. 3 is a view of the optical head as viewed from a slider section.

In order to prevent the flying optical head from contacting the land, to obtain a stable tracking signal, and to avoid the influence of a defective land shape or the presence of foreign matter on the land, Rp and H Is preferably 0.8H ≧ Rp ≧ 0.1H, more preferably 0.1H ≧ Rp ≧ 0.1H.
5H ≧ Rp ≧ 0.1H.

Note that the center line of the land and the groove and the maximum height of the land are determined at an arbitrary length on a radius in a region of the optical recording medium where information is recorded and reproduced. This arbitrary length depends on the track pitch of the groove,
2 to 100 times the track pitch, preferably 10 to 5
By setting the length to 0 times, the land and groove states of the optical recording medium are reflected on Rp and the like. The arbitrary length may be set at an arbitrary position on the radius of the recording / reproducing area of the optical recording medium.

The center line of the land and the groove and the maximum height of the land are set at 20 parts of an arbitrary length of the cross-sectional shape of the optical recording medium.
It can be measured by a scanning electron microscope (SEM) at a magnification of 00 to 4000 or by an atomic force microscope (AFM). The flying height of the optical head may be measured by rotating the optical recording medium, actually flying the optical head, and measuring the flying height.

As the substrate material of the optical recording medium of the present invention,
There is no particular limitation as long as the land and groove structure can be formed. As such a substrate material,
Examples thereof include resin, glass, and a flat metal plate. Further, a header portion including format information indicating a recording position of the information may be formed on the substrate.
The header portion may be formed on the substrate at the same time when the land and groove structure is formed, or may be separately provided after the land and groove structure is formed on the substrate.

When a resin is used as the substrate material, the resin is not particularly limited as long as it is a thermoplastic resin that satisfies the characteristics of the optical disk substrate such as mechanical characteristics and transferability. Examples thereof include polycarbonate, polymethyl methacrylate, and amorphous resin. From transparent plastics such as polyolefin,
So-called super engineering plastics such as polyphenylene sulfide, polyarylate, polyetherketone, polyetheretherketone and the like can be used. By injection molding these resins using a mold (stamper), a substrate for an optical recording medium having a land and groove structure can be manufactured.

When glass or a flat metal plate is used as a substrate material, the land / groove structure is formed on these substrates by a so-called 2P method in which a land / groove structure is manufactured by photopolymer or the like. A substrate for an optical recording medium can be manufactured.

As the reflective layer of the optical recording medium of the present invention, a metal film having a high reflectivity can be used.
Precious metals such as u and Ag and alloys containing these precious metals are preferred.

The recording method for the optical recording medium of the present invention includes TbFeCo, DyFeCo, GdTbFeC
o, a magneto-optical recording method using a recording film such as NdDyFeCo, or a recording method such as a phase change recording method using a recording film such as GeSbTe, AgInSbTe, etc., in which recording can be performed by changing the polarization plane, reflectance, light phase, etc. It is not limited at all.

The information may be recorded only on the land portion or on both the land portion and the groove portion.

In the optical recording medium of the present invention, since a floating optical head is used for recording and reading information, it is preferable to form a lubricating layer on the outermost surface of the medium.

As the lubricating layer, any material having lubricity, such as silicone oil or fluoropolyether-based fluorine oil, can be used, but perfluoropolyether and perfluoropolyether derivatives are particularly desirable.

Examples of the perfluoropolyether derivative include alcohol-modified perfluoropolyether, ester-modified perfluoropolyether, isocyanate-modified perfluoropolyether, carboxyl group-modified perfluoropolyether, and piperonyl-modified perfluoropolyether. .

When the lubricating layer is provided, the film thickness is set to 0.1.
3-4.0 nm is preferred. If the thickness is less than 0.3 nm, the protection performance of the lubricating layer is insufficient, and the thin film may be easily damaged. If the thickness exceeds 4.0 nm, the slider head may stick to the disk and cause a crash.

When the optical recording medium of the present invention is applied to a near-field optical recording desk using a magneto-optical recording system, at least a reflective layer, a first protective layer, a magneto-optical recording layer, a second protective layer, It is preferable that a diamond-like carbon (DLC) layer and a lubricating layer are laminated.

Specifically, a laser beam reflecting layer made of Al, Cr, Cu, Ag, Au, an alloy thereof, or the like is formed as a reflective layer on a substrate obtained by injection molding by sputtering or was formed by a vacuum deposition method or the like, as the first protective layer _{AlN, SiN, Ta 2 O 5} , a transparent dielectric film such as ZnS-SiO ₂ by a sputtering method or a vacuum evaporation method, or the like. On this first protective layer, TbFeCo, DyFeCo,
A recording layer made of a magneto-optical recording film such as GdTbFeCo or NdDyFeCo is formed by a sputtering method or a vacuum evaporation method. Further, on this recording layer, AlN, S
iN, Ta ₂ O ₅ , ZnS—SiO ₂ or the like is formed by a sputtering method or a vacuum evaporation method, and a DLC film is formed thereon by a sputtering method or the like. Further, an optical recording medium is manufactured by forming a lubricating layer thereon by a method such as a dip pulling method.

The first protective layer only needs to have a thickness enough to protect the recording layer, and preferably has a thickness of 10 to 100 nm. The recording layer is required to have a thickness such that light does not transmit to the first protective layer, and preferably has a thickness of 30 to 200 nm. In addition to the role of protecting the recording layer, the second protective layer also controls the light absorption efficiency of the recording layer, and also increases 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 is designed in consideration of the laser wavelength to be used.
0-300 nm is preferred.

In the present invention, there is no limitation on one side or both sides of the disk. In a double-sided disk, a laminated film may be laminated on each side of a substrate having the land and groove structure provided on both sides of the substrate. There is no problem if both sides are laminated at the same time.

[0042]

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.

Examples 1-4 and Comparative Examples 1 and 2 A magneto-optical recording medium for near-field optical recording was manufactured as described below. That is, a master having a track pitch and a groove depth shown in Table 1 was manufactured using a UV mastering apparatus on a 110-nm-thick positive photoresist formed on a glass substrate, and a Ni stamper was manufactured from the master. . The groove depth was formed by controlling the exposure power during mastering.

A disc-shaped substrate made of polycarbonate and having a diameter of 130 mm was manufactured by injection molding using these stampers, and an Al alloy film (50 nm thick) and a SiN first protective layer (10 n
m), a magneto-optical recording layer (thickness: 20 nm) made of Tb ₂₀ (Fe ₉₀ Co ₁₀ ) ₈₀ , a second protective layer of SiN (30 nm), D
LC layers (film thickness: 20 nm) were sequentially formed by a sputtering method. Next, 0.5 nm of perfluoropolyether was formed by a dipping method as a lubricating layer of the flying head.

The recording / reproducing area of the optical recording medium obtained in this manner has a radius of 30 mm, 45 mm and 60 mm.
At a position corresponding to 20 times the track pitch,
When Rp was measured by AFM in the range of 9 μm in the radial direction, the values shown in Table 1 were shown at each measurement point.

[0046]

[Table 1]

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 ″ × 6.0gr, slider part: 0.305 × 2.8
4 mm) in a radius range of 27.0 to 62.0 mm. The flying height of this glide head is 7.5m / s.
Was 0.05 μm (50 nm).

The voltage induced in the piezo element when the glide head was moved was observed with an oscilloscope.
At this time, a voltage value exceeding 800 mV was judged as a contact (hit) with the recording medium and counted.

The above measurement was performed for each of the magneto-optical recording media of Comparative Example 1 and Examples 1 to 4, and the number of hits was measured. Table 2 shows the average value of the ten results.

In Comparative Example 1 in which the depth Rp of the center line is 51 nm exceeding the flying height H and the groove depth is 110 nm, scratches which can be confirmed with the naked eye occur in the form of stripes over the entire circumference of the medium, and the number of hits is also small. The count was extremely large.

When the depth Rp of the center line is 43 or less than the flying height H,
In Example 1, which is nm, the streak-like flaw was shorter and lighter than that in Comparative Example 1, the number of hits was reduced, and the flying characteristics of the head were secured.

The depth Rp of the center line is 0.64 of the flying height H.
Example 2 which is 2 times, Example 3 which is 0.34 times and 0.1
In Example 4 with a magnification of 6 times, no scratch was recognized on the medium, and good flying characteristics were exhibited.

Also, in Comparative Example 2 in which the depth Rp of the center line was 0.05 times the flying height H, no damage was found on the medium, and good flying properties were exhibited.

Next, the laser wavelength was 680 for each of the five magneto-optical recording media of Examples 1 to 4 and Comparative Example 2 whose flying characteristics were confirmed by a glide tester.
The recording / reproducing characteristics were evaluated using a recording / reproducing evaluator of the optical system of the SIL head having an effective NA of 1.2 nm.

Table 2 shows the average value of the five results.

[0056]

[Table 2]

In the first embodiment, the carrier-to-noise ratio (CN
R) is low, but in Examples 2, 3 and 4, good CN
R was obtained. On the other hand, in the disk of Comparative Example 2, the tracking of the SIL head was lost, and the recording / reproducing characteristics could not be measured.

[0058]

According to the optical recording medium of the present invention, it has lands and grooves involved in recording / reproducing, and when the near-field recording / reproducing is performed by the floating optical head, the optimum tracking error signal intensity can be obtained. Thus, a surface recording / reproducing optical recording medium having a given groove depth can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram schematically illustrating the relationship between the center line of lands and grooves, the maximum height of lands, Rp, and the flying height of an optical head according to the present invention.

FIG. 2 is a diagram illustrating an example of a cross-sectional view of an optical head that can be used in the present invention.

FIG. 3 shows a view of an optical head usable in the present invention as viewed from a slider portion.

[Explanation of symbols]

 1: slider part 2: optical lens

Claims (5)

[Claims] 1. An optical recording apparatus having at least a land and groove structure related to recording and reproduction on a substrate, at least a reflective layer and a recording layer provided on the substrate in this order, and recording and reproducing information by a floating optical head. In a medium, the depth from the maximum height of the land to the center line of the land and the groove is Rp, and the depth from the maximum height of the land to the optical length is an arbitrary length along the radius in the area for recording and reproducing information on the optical recording medium. When the flying height to the head is H, R
An optical recording medium, wherein p satisfies the relationship of H> Rp ≧ 0.1H. 2. The optical recording medium according to claim 1, wherein the arbitrary length is equivalent to 2 to 100 times the track pitch of the groove. 3. The optical recording medium according to claim 1, wherein information is recorded on a land. 4. The optical recording medium according to claim 1, wherein information is recorded on both the land and the groove. 5. The optical recording medium according to claim 1, wherein the recording method is a near-field recording / reproducing method.