JP4496689B2 - Near-field optical recording / reproducing method and optical recording medium - Google Patents

Description

以上のようにして得られた光磁気記録媒体それぞれ５枚づつに対して、レーザー波長が６８０ｎｍで実効的なＮＡが１．２のＳＩＬヘッドの光学系の記録再生評価機により、記録再生特性を評価した。その結果の５枚の平均値を表２に示す。
【００５９】
【表２】

グルーブ深さがλ／１２である実施例１〜５、λ／１０である実施例８およびλ／３０である実施例９においては、良好なシグナル対ノイズ比（ＳＮＲ）が得られた。
【００６０】
実施例６はグルーブが底ぎりではなくＶ溝構造となったため、グルーブノイズが増加し結果としてＳＮＲが若干低下した。
【００６１】
実施例７はグルーブ底幅ｂが０．３５Ｐを超え、１８０ｎｍとなりランドが狭くなったため、シグナル強度が低下し、ＳＮＲが若干低下した。
【００６２】
一方、グルーブ深さがλ／６である１１４ｎｍであった比較例１はランドが極端に狭くなりＳＮＲが極端に低下し、信号の記録再生に適さなかった。
【００６３】
さらに比較例２のディスクはＳＩＬヘッドのトラッキングがはずれ、記録再生特性が測定できなかった。
【００６４】
【発明の効果】
本発明により、記録再生に関与するランドおよびグルーブ構造とフォーマット情報を記録するヘッダー部を有し、浮上式光学ヘッドにより近接場記録再生を行なう際に、最適なトラッキング・エラー信号強度およびシグナル対ノイズ比（ＳＮＲ）が得られるランドおよびグルーブ構造を有する表面記録再生型光記録媒体を得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rewritable optical recording disk substrate and an optical recording disk.
[0002]
[Prior art]
Optical recording media are portable recording media capable of high-capacity and high-density recording, and demand is rapidly increasing as rewritable media for recording moving images and the like as large-capacity storage files for computers with the recent development of multimedia. is there.
[0003]
In an optical recording medium, a guide groove for tracking servo is usually provided as a physical shape on a substrate where a laser beam is recorded / reproduced. Land).
[0004]
Therefore, the larger the land, the larger the mark width to be recorded, the greater the intensity of the reproduced signal, and the improved reproduced signal quality.
[0005]
However, in order to increase the recording density, it is necessary to reduce the track pitch, which is the interval between the grooves, and increase the information per recording area.
[0006]
For example, the track pitch of commercially available 3.5 inch diameter magneto-optical recording media is reduced to 1.6 μm with a recording capacity of 128 MB, 1.4 μm with a recording capacity of 230 MB, and 1.1 μm with a recording capacity of 640 MB. Has been.
[0007]
On the other hand, the recording density is limited by the laser beam spot size (˜λ / NA) determined by the light source laser wavelength (λ) of the recording / reproducing apparatus and the numerical aperture (NA) of the objective lens.
[0008]
For example, in the case of the above-described recording / reproducing apparatus for the 640 MB magneto-optical recording medium, the wavelength is 680 nm, the NA is 0.55, and the laser beam spot size is about 1240 nm.
[0009]
As a means for reducing the laser beam spot size and achieving high density, so-called near-field optical recording in which an optical head is brought close to a recording film and recording / reproducing has been attracting attention (for example, Applied Physics Letter (Appl. Phys. Lett.), Vol.68, p.141 (1996)). In this recording method, a solid immersion lens (hereinafter abbreviated as “SIL”) head is used, and by increasing the effective numerical aperture when using the SIL, the laser beam spot size is reduced, thereby achieving ultra-high recording. High density recording / reproduction can be realized.
[0010]
For example, in near-field optical recording using a SIL having a wavelength of 650 nm and an effective NA of 1.4, the laser beam spot size is about 460 nm, which is used in the above-described conventional recording / reproducing apparatus for a 640 MB magneto-optical recording medium. This is approximately 37% of the laser beam spot size.
[0011]
In this surface recording / reproducing method, it is necessary to bring the optical head close to the recording medium. Therefore, unlike the conventional optical recording medium, the recording film is not irradiated with the laser beam through the substrate but directly on the recording film without passing through the substrate. A method of irradiating a laser beam is used.
[0012]
That is, the structure of the recording film is generally the substrate / first protective film / recording film / second protective film / reflective film in the conventional optical recording medium, whereas in the near-field optical recording, the substrate / Recording / reproduction is performed by irradiating a laser beam from the film surface side as a film structure having a reverse configuration of a reflective film / recording film / protective film.
[0013]
At this time, it has been proposed to use a floating slider head to bring the recording film and the optical head closer.
[0014]
[Problems to be solved by the invention]
In general, when the track pitch P becomes the size of the light spot, the groove serving as the guide groove serves as a diffraction grating, and the intensity of the beam spot due to the interference effect due to the track deviation in the region where the 0th-order and 1st-order diffracted light overlap. Since the distribution changes, a tracking error signal can be detected.
[0015]
This signal intensity is determined by the numerical aperture NA of the objective lens, the track pitch, and the laser wavelength λ, and 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). It has been known.
[0016]
However, in the case of the near-field optical recording system, 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, and thus greatly changes depending on the flying height of the optical head. As for the groove depth design, the conventional design has a problem that the optimum depth for near-field optical recording cannot be obtained.
[0017]
The present invention has a land portion and a groove portion involved in recording / reproduction and a header portion for recording format information. When performing near-field recording / reproduction with a floating optical head, the optimum tracking error signal intensity and signal-to-noise It is an object of the present invention to provide a surface recording / reproducing optical recording medium having lands and groove portions that can obtain a ratio (SNR).
[0018]
[Means for Solving the Problems]
As a result of intensive investigations in view of the above-mentioned present situation, the present inventors have at least a reflection film and a recording film on a substrate having a land portion and a groove portion involved in recording and reproduction and a header portion for recording format information. In the optical recording medium in which the dielectric film is formed and recording / reproduction is performed from the dielectric film side by the floating optical head, when the groove depth is D, the laser wavelength used for recording / reproduction is λ Then, D is λ / 36 or more and less than λ / 8, and the opening width (D-5 nm opening width) a at a position D-5 nm from the groove bottom portion, the groove bottom width b, and the groove bottom portion D × 1 / The opening width (1/2 opening width) c at position 2 satisfies the following relationship, and is formed by connecting one end of the D-5 nm opening width a, 1/2 opening width c, and groove bottom width b. Land shape is By having a convex shape in the direction on the plate surface, it found to be able to retain good signal strength and tracking characteristics, and have completed the present invention.
[0019]
0.10P ≤ a ≤ 0.95P
0 <b ≦ 0.35P
0.05P ≤ c ≤ 0.65P
The groove depth D in the present invention depends on the laser wavelength (λ) used for recording and reproduction, and is preferably λ / 36 or more and less than λ / 8.
[0020]
In the case of recording / reproducing with a conventional optical system, as described above, 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). Therefore, the groove depth is set to λ / 8n.
[0021]
However, in the case of the near-field optical recording method, in addition to the conventional diffraction effect, the signal is obtained by a coupling effect between the optical head located in the vicinity and the outermost surface of the disk. growing.
[0022]
Therefore, the groove depth is also less than λ / 8n, and the tracking error signal becomes maximum when the groove depth is less than λ / 8n.
[0023]
The shallower the groove depth, the wider the land used for signal recording / reproduction, and the greater the signal intensity. Therefore, the groove depth is more preferably λ / 36 or more and λ / 10 or less.
[0024]
On the other hand, when the groove depth becomes shallower than λ / 36, tracking of the guide groove becomes difficult, resulting in hindering recording and reproduction.
[0025]
Specifically, when a laser having a wavelength of 685 nm is used, it is preferably 19 nm or more and less than 86 nm, and more preferably 19 nm or more and 69 nm or less.
[0026]
The shape of the groove in the present invention is defined by an opening width a, a 1/2 opening width c and a groove bottom width b which are D-5 nm higher than the groove bottom.
[0027]
The preferred values of the opening width a and the groove bottom width b, which are D-5 nm higher than the groove bottom, vary depending on the track pitch P. a is 0.1 P or more and 0.95 P or less, b is greater than 0 and 0.35 P The following is preferred.
[0028]
The shape of the land and groove part of the present invention is a flat groove part in which the groove bottom width b is 0 or more.
[0029]
In the surface recording / reproducing system, when a so-called V-groove structure having b of 0 is generally used, the groove noise becomes large, and as a result, the signal-to-noise ratio (SNR) is deteriorated.
[0030]
On the other hand, if the value of b exceeds 0.35P, the land used for recording becomes narrow, resulting in a decrease in SNR.
[0031]
In the present invention, when the opening width a having a height of D-5 nm is less than 0.1 P, b cannot be made larger than 0, resulting in an increase in groove noise.
[0032]
On the other hand, when a is 0.95P or more, since the land portion can hardly be created, the signal decreases, and as a result, the SNR also decreases.
[0033]
Further, the ½ opening width c also varies depending on the track pitch of the land and groove, but is preferably 0.05 P or more and 0.65 P or less.
[0034]
If c is less than 0.05P, the opening width a having a height of D-5 nm cannot be made larger than 0 as in the case of less than 0.1P, resulting in an increase in groove noise.
[0035]
On the other hand, if c exceeds 0.65P, the land portion can hardly be created, and the signal is lowered. As a result, the SNR is also lowered.
[0036]
Specifically, when the track pitch is 0.45 μm, a is preferably 45 nm or more and 427.5 nm or less, b is greater than 0 and 157.5 nm or less, and c is preferably 22.5 nm or more and 292.5 nm or less.
[0037]
The land shape formed by connecting one end of the D-5 nm opening width a, 1/2 opening width c and groove bottom width b in the present invention is a shape having a convex curvature upward in the substrate surface. Features.
[0038]
If the shape connecting a, c, and b is concave in the upward direction of the substrate surface, the land becomes narrow, and if there is a clear corner in the shape connecting a, c, and b, it becomes a noise component. SNR decreases.
[0039]
The convex shape connecting a, c and b in the present invention can be created by subjecting a substrate on which a land and groove structure has been created in advance to heat treatment or irradiation with light such as ultraviolet rays. It becomes a mold shape.
[0040]
The substrate material in the present invention is not limited as long as it has the land and groove structure.
[0041]
The resin for injection molding is not particularly limited as long as it is a thermoplastic resin that satisfies the characteristics of an optical disk substrate such as mechanical properties and transferability. From transparent plastics such as polycarbonate, polymethyl methacrylate, and amorphous polyolefin, So-called super engineering plastics such as polyarylate, polyetherketone and polyetheretherketone can be used.
[0042]
Also, there is no problem in producing a substrate by a so-called 2P method in which lands and groove structures are produced on a glass or flat metal plate with a photopolymer.
[0043]
The recording method of the optical recording disk of the present invention includes a polarization plane, a reflectance, a light, such as a magneto-optical recording method comprising a recording film such as TbFeCo, DyFeCo, GdTbFeCo, NdDyFeCo, or a phase change recording method comprising a recording film such as GeSbTe, AgInSbTe. The recording method is not particularly limited as long as recording is possible by changing the phase or the like.
[0044]
In the present invention, since a floating optical head is used, it is preferable to form a lubricating layer on the outermost surface of the disk.
[0045]
The lubricating layer can be used as long as it exhibits lubricity, such as silicone oil or fluoropolyether fluorine oil, but perfluoropolyether and perfluoropolyether derivatives are particularly desirable.
[0046]
Examples of the perfluoropolyether derivative include alcohol-modified perfluoropolyether, ester-modified perfluoropolyether, isocyanate-modified perfluoropolyether, carboxyl group-modified perfluoropolyether, piperonyl-modified perfluoropolyether, and the like.
[0047]
The thickness of the lubricating layer of the present invention is preferably from 0.3 nm to 4.0 nm.
If the thickness is less than 0.3 nm, the protective performance of the lubricating layer is insufficient, and the thin film tends to be damaged. If the thickness is 4.0 nm or more, the slider head sticks to the disk and tends to crash.
[0048]
When the present invention is applied to a near-field optical recording disk using a magneto-optical recording medium, at least a first protective layer, a magneto-optical recording layer, a second protective layer, a diamond-like carbon (DLC) layer, and a lubricating layer are formed on the substrate. Is preferably laminated.
[0049]
Specifically, a reflective film such as Al is formed on the substrate by sputtering or vacuum deposition, and then a transparent dielectric such as AlN, SiN, Ta ₂ O ₅ , ZnS—SiO _{2 is used} as the first protective layer. A film is formed by sputtering or vacuum deposition. A recording layer made of a magneto-optical recording film such as TbFeCo, DyFeCo, GdTbFeCo, or NdDyFeCo is formed on the first protective layer by a sputtering method or a vacuum deposition method. Further, AlN, SiN, Ta ₂ O ₅ , ZnS—SiO ₂ or the like is formed as a second protective layer on the recording layer by sputtering or vacuum vapor deposition, and a DLC film is formed thereon by sputtering or the like. Further thereon, a recording medium is formed by forming a lubricating layer by a method such as a dip pulling method.
[0050]
The first protective layer only needs to have a thickness that can protect the recording layer, and a thickness of 10 nm to 100 nm is preferable. The recording layer needs to have a thickness that does not allow light to pass through to the first protective layer, and preferably has a thickness of 30 nm to 200 nm. In addition to protecting the recording layer, the second protective layer also has a role of controlling the light absorption efficiency to the recording layer, and increasing the amount of change in reflected light and Kerr rotation angle before and after recording. For this reason, the thickness of the second protective layer is designed in consideration of the laser wavelength to be used, and is preferably 20 nm or more and 300 nm or less. It is also possible to adjust the recording sensitivity by inserting a film having good heat conduction such as Al, Al alloy, Au, Ag, etc. as a heat sink between the substrate and the first protective layer.
[0051]
In the present invention, the single-sided and double-sided discs are not limited at all. In a double-sided disc, the laminated film may be laminated one side at a time, or there is no problem even if both sides are laminated simultaneously.
[0052]
【Example】
EXAMPLES Hereinafter, although this invention is demonstrated further in detail based on an Example, this invention is not limited only to these Examples.
[0053]
(Examples 1-9 and Comparative Examples 1-2)
The magneto-optical recording medium for near-field optical recording shown in Table 1 was manufactured as described below.
[0054]
A stamper in which the cross-sectional shapes of lands and grooves having a track pitch of 0.45 microns were changed using a UV mastering apparatus on a positive type photoresist having a different thickness was prepared. The cross-sectional shape of the groove was formed by controlling the exposure power during mastering.
[0055]
A disk-shaped substrate made of polycarbonate having a diameter of 130 mm is manufactured by injection molding, and an Al alloy film (film thickness 50 nm), a SiN first protective layer (film thickness 10 nm), Tb ₂₀ (Fe ₉₀ ) are formed on the groove and header forming surface of the substrate. A magneto-optical recording layer (thickness 20 nm) made of Co ₁₀ ) ₈₀ , a SiN second protective layer (thickness 30 nm), and a DLC layer (thickness 20 nm) were sequentially formed by sputtering.
[0056]
Next, 0.5 nm of perfluoropolyether was formed by a dipping method as a lubricating layer of the flying head.
[0057]
The groove depth and groove shape shown in Table 1 were measured using an atomic force microscope (AFM) for the shape of the recording medium after film formation.
[0058]
[Table 1]

For each of the five magneto-optical recording media obtained as described above, the recording / reproduction characteristics were measured by the optical recording / reproduction evaluation machine of the SIL head having a laser wavelength of 680 nm and an effective NA of 1.2. evaluated. Table 2 shows the average value of the five results.
[0059]
[Table 2]

In Examples 1 to 5 where the groove depth is λ / 12, Example 8 where λ / 10 is λ / 10, and Example 9 where λ / 30 is λ, a good signal-to-noise ratio (SNR) was obtained.
[0060]
In Example 6, the groove was not a bottom but a V-groove structure, so that the groove noise increased and, as a result, the SNR slightly decreased.
[0061]
In Example 7, since the groove bottom width b exceeded 0.35P and the land became narrower at 180 nm, the signal intensity was lowered and the SNR was slightly lowered.
[0062]
On the other hand, in Comparative Example 1 where the groove depth was 114 nm, which was λ / 6, the land became extremely narrow and the SNR was extremely lowered, which was not suitable for signal recording and reproduction.
[0063]
Further, in the disc of Comparative Example 2, the tracking of the SIL head was lost, and the recording / reproducing characteristics could not be measured.
[0064]
【The invention's effect】
According to the present invention, there is a land and groove structure involved in recording / reproduction and a header portion for recording format information, and optimum tracking error signal strength and signal-to-noise when performing near-field recording / reproduction with a floating optical head. A surface recording / reproducing optical recording medium having a land and groove structure with which the ratio (SNR) can be obtained can be obtained.

Claims (4)

On a substrate having a header part for recording groove part and the format information is a land and a guide groove involved in at least recording, at least a reflective film, a recording film and the dielectric film using the optical recording medium which is formed, on floating the type optical head, the dielectric film intends line recording and reproducing by irradiating a laser beam from the side near field optical recording and reproducing method of the optical recording medium, the depth of the groove formed on the optical recording medium is D, the wavelength of the to use for recording and reproduction laser beam is taken as lambda, the near-field optical recording and reproducing method characterized by the the lambda / 36 or more lambda / 10 or less D. Using an optical recording medium in which at least a reflective film, a recording film, and a dielectric film are formed on a substrate having at least a land part that is involved in recording / reproduction and a groove part that is a guide groove and a header part that records format information. In a near-field optical recording / reproducing method for performing recording / reproduction by irradiating a laser beam from the dielectric film side of the optical recording medium with an optical head, the depth of the groove formed on the optical recording medium is D, and recording / reproduction is performed. A near-field optical recording / reproducing method characterized in that a signal-to-noise ratio of 45 dB or more is obtained by setting D to λ / 36 or more and λ / 10 or less, where λ is the wavelength of the laser light used in the above. 3. An optical recording medium for use in the near-field optical recording / reproducing method according to claim 1 or 2, comprising at least a land that is involved in recording / reproduction and a groove that is a guide groove and a header that records format information. When the depth of the groove is D, the wavelength of the laser beam used for recording / reproduction is λ, and the track pitch of the guide groove is P, D is λ / 36 or more and λ / 10 or less, and D from the bottom of the groove An opening width (D-5 nm opening width) a at a position of −5 nm, a groove bottom width b, and an opening width (1/2 opening width) c at a position D × 1/2 from the groove bottom satisfy the following relationship. An optical recording medium characterized by the above.
0.10P ≦ a ≦ 0.95P 0 <b ≦ 0.35P 0.05P ≦ c ≦ 0.65P Claim land shape formed by connecting one end of the D-5 nm aperture width a, 1/2 aperture width c and a groove bottom width b is characterized by having a shape of a convex in the upward direction of the substrate surface 3 The optical recording medium described.