JP2001351271A - Optical recording medium - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an optical recording medium, having high reliability, in which uniform signal recording and reproduction are obtained and crashing between the medium and an optical head hardly occurs. SOLUTION: The optical recording medium has a reflecting layer and a recording layer, laminated in this order on a substrate, having a header and lands/grooves and is used for recording and reproduction with a floating type optical head. When the effective numerical aperture of the optical head to be used is NA, the wavelength of the laser light to be used is λ, the depth from the surface of the medium at the maximum height to the center line of the header is Rph, and the depth from the surface at the maximum height to the center line of the lands/grooves is Rpd in any length along the radius in the recording and reproducing region, a relation of, for example, |Rpd (maximum)-Rph (minimum)|<=λ/16 NA is satisfied for each Rph and each Rpd measured at a plurality of points.

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.

[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 a conventional rewritable optical recording medium, generally, a multilayer film including a recording layer is formed on a plastic disk-shaped substrate obtained by injection molding, and recording, reproduction, and erasure are performed by irradiating a laser from the plastic substrate side. I was going.

In recent years, a surface recording / reproducing method for recording / reproducing by bringing an optical head close to a recording film has attracted attention as a means for achieving high recording. In this surface recording / reproducing method, it is necessary to bring the optical head close to the recording medium. Therefore, instead of irradiating the recording film with the laser beam through the substrate as in the conventional optical recording medium, the recording film is directly passed without passing through the substrate. A method of irradiating a laser beam is used.

That is, in the conventional optical recording medium, the recording film generally has a substrate / first protective film / recording film / second protective film / reflection film, whereas a surface recording medium has a general structure of a recording film. For example, recording / reproducing is performed by irradiating a laser beam from the surface side of the protective film as a reverse film structure of a substrate / reflective film / recording film / protective film (surface recording / reproducing).

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

In this surface recording / reproducing method, the distance between the floating optical head and the optical recording medium is very short, and even if the flying height of the head from the recording medium fluctuates slightly, the recording / reproducing signal is not changed. It is also conceivable that the strength varies and hinders recording / reproduction, and furthermore, the head and the recording medium are damaged due to the contact between the head and the optical recording medium.

An optical recording medium generally has a header portion having format information and a land / groove portion for recording / reproducing data. The flying height of the head when flying over the header portion and the land / groove portion are described. Is different from the flying height of the head at the time of flying, so that the flying height of the head at the time of recording and reproduction is fluctuated.

Conventionally, in an optical recording medium of the surface recording / reproducing method using a floating slider head, it is difficult to keep the flying height of the head constant over the entire recording / reproducing area, and it is difficult to obtain a uniform recording / reproducing signal. It was difficult.

[0010]

The problem to be solved by the present invention is to maintain a constant flying height of a head flying above an optical recording medium over the entire recording / reproducing area, thereby producing a uniform recording / reproducing signal. An object of the present invention is to provide a highly reliable optical recording medium which is obtained and is less likely to crash with the head.

[0011]

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

That is, at least a reflective layer and a recording layer are laminated in this order on a substrate provided with a header, lands and grooves for recording and reproducing data, and an optical recording medium for recording and reproducing information with a floating optical head. So,
The effective numerical aperture of the optical head to be used is NA, the wavelength of the laser to be used is λ, and the center line of the header from the maximum height of the recording medium surface at an arbitrary length on the radius in the area where information is recorded and reproduced on the optical recording medium. Rph, and the depth from the maximum height of the recording medium surface to the center line of the land and the groove is Rpd, the maximum value of Rph at each Rph and each Rpd value measured at a plurality of positions. The absolute value of the value obtained by subtracting the minimum value of Rpd from
When ΔRp is the larger of the absolute values of the values obtained by subtracting the minimum value of Rph from the maximum value of d, ΔRp ≦ λ / 16
The present invention relates to an optical recording medium having a surface shape satisfying a relationship of NA.

Hereinafter, the present invention will be described in detail.

FIG. 1 is a sectional view showing an example of the optical recording medium of the present invention. Reflective layer 12 and recording layer 1 on substrate 11
3. The dielectric layers 14 are laminated in this order.

The substrate 11 can be exemplified by resin, glass, or a flat metal plate. When a resin is used as the substrate material, the resin is not particularly limited as long as the resin is a thermoplastic resin that satisfies the characteristics of the optical disk substrate such as mechanical properties and transferability. From transparent plastics, so-called super engineering plastics such as polyphenylene sulfide, polyarylate, polyether ketone, polyether ether ketone, etc. 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, a light having a land and groove structure is produced by a so-called 2P method in which a land / groove structure is manufactured on such a base material by photopolymer or the like. A substrate for a recording medium can be manufactured.

The reflective layer 12 is not particularly limited as long as it is a metal having a high reflectance. For example, Al, Ag, Au, C
A single metal such as u or an alloy containing these as main components can be used.

It is preferable that the headers are arranged substantially straight in the radial direction of the optical recording medium.

The recording layer 13 is not particularly limited as long as it can be used as an optical recording layer.
TbFeCo, DyFeCo, GdTbFeCo, Nd
Magneto-optical recording film such as DyFeCo, GeSbTe, AgI
A phase change recording film such as nSbTe can be used, and the recording layer may be a single layer or a laminated film in which films having different functions and compositions are laminated.

As the dielectric layer 14, SiN, AlN,
It is composed of a transparent dielectric material such as SiAlON or Ta ₂ O ₅ . Further, a solid lubricating layer such as diamond-like carbon (DLC) obtained by adding hydrogen or nitrogen to carbon may be laminated on the dielectric layer.

In the optical recording medium of the present invention, it is preferable to further 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.

FIG. 2 is a sectional view showing an example of a substrate used for the optical recording medium of the present invention. The recording / reproducing surface of the substrate has a spiral groove 2 for laser tracking.
1 is formed. A convex land 22 is formed between the grooves. Also, on the recording / reproducing surface of the substrate,
Although not shown, a header having format information is formed. However, FIG. 2 does not accurately show the relative size / height of the optical head, land, groove, and the like.

Optical recording / reproducing methods include a groove recording method of writing data on a groove and a land recording method of writing data on a land. In each recording method, it is important from the viewpoint of recording and reproduction that the flying height 25 of the head 24 with respect to the surface on which data is written is constant. When the head flies above the recording medium, the shape of the surface of the recording medium greatly affects the flying height of the head. That is,
The flying height of the head varies depending on the depth Rp26 from the maximum height of the recording medium to the center line of the land and the groove.

In the present invention, the center line of the land and the groove is defined as an arbitrary length on the radius of the information recording / reproducing area of the optical recording medium with respect to the roughness curve of the land and the groove in the arbitrary length range. When a single straight line is drawn, the straight line is such that the area surrounded by the roughness curve is equal on both sides of the straight line.

Further, 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 an area for recording and reproducing information on the optical recording medium. 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 in 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).

In the present invention, the effective numerical aperture of the optical head to be used is NA, the wavelength of the laser to be used is λ, and the recording medium is at an arbitrary length on the radius of the information recording / reproducing area of the optical recording medium. Assuming that the depth from the maximum height of the surface to the center line of the header is Rph, and the depth from the maximum height of the recording medium surface to the center line of the lands and grooves is Rpd, Rph and Rpd measured at a plurality of positions. , The absolute value of the value obtained by subtracting the minimum value of Rpd from the maximum value of Rph, or Rmax from the maximum value of Rpd.
Assuming that the larger of the absolute values of the values obtained by subtracting the minimum values of ph is ΔRp, ΔRp ≦ λ / 16NA, and in order to obtain a uniform recording / reproducing signal intensity with a smaller variation,
It is preferable to have a surface shape that satisfies the relationship of ΔRp ≦ λ / 20NA.

In particular, the header portion of the recording medium has a land /
Since the surface shape of the groove portion is different from that of the groove portion, it is important to reduce the difference in Rp between the header portion and the land / groove portion so that the flying height does not change when the flying head reaches the header portion. . Fluctuations in the flying height of the head need to be suppressed to such an extent that the head and the recording medium do not come into contact with each other to cause a crash.

As a method of reducing ΔRp, convex and / or concave pits are formed in the header portion of the substrate, the depth Rph from the maximum height of the medium surface to the center line of the header portion, and the depth of the medium surface. The depth Rpd from the maximum height to the center line of the land / groove portion is | Rph−Rpd | ≦ λ /
Preferably, the relationship is 16NA. In order to obtain a uniform recording / reproducing signal intensity with less variation |
It is preferable that Rph−Rpd | ≦ λ / 20NA.

The Rph of the header can be adjusted by changing the area, depth, and height of the pit. Also, a groove is formed in the header portion, and | Rph-Rpd | ≦ λ / 16N
It is preferable that the relationship be A. In order to obtain a uniform recording / reproducing signal intensity with a smaller variation, | Rph
-Rpd | ≦ λ / 20NA is preferable. The shape of the groove may be any one of a circumferential direction and a radial direction with respect to the center of the recording medium, or may be both directions. Rph can be adjusted by changing the depth and width of the groove. Also, near-field optical recording, in which an optical head is brought close to a recording film for recording and reproduction, is an effective method because a floating head is used.

By satisfying these conditions, the flying height of the head becomes constant over the entire recording / reproducing area, a uniform recording / reproducing signal can be obtained, and a highly reliable optical recording medium which is unlikely to crash with the head. Is obtained.

[0035]

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 circular substrate made of polycarbonate and having a diameter of 130 mm and having a spiral land / groove portion having a track pitch of 0.43 μm and a header portion on both front and rear surfaces was manufactured by an injection molding method. Depending on the stamper used at this time, a radius of 20 to 6
In a region excluding the 0 mm header, the groove depth of the substrate is 90 nm, and the header portion has a depth of 90 n.
m concave pits were arranged.

A reflective layer, a recording layer, a dielectric layer and a solid lubricating layer were laminated in this order on both front and back surfaces of the substrate. An AlCr alloy having a thickness of 50 nm was laminated as a reflective layer by DC sputtering. Further, as a recording layer, Tb having a thickness of 20 nm is used.
FeCo was laminated by DC sputtering. A 50 nm-thick Si layer is formed thereon as a dielectric layer by a reactive DC sputtering method using a Si target in a mixed atmosphere of Ar and N _2.
N was laminated. On top of this, Ar is used as a solid lubricating layer.
A 20 nm-thick diamond-like carbon (DLC) was laminated by a reactive RF sputtering method using a C target in a mixed atmosphere of CH ₂ and CH ₄ to produce a magneto-optical recording medium capable of double-sided recording and reproduction.

Example 2 A 130 mm diameter circular substrate made of polycarbonate having a spiral land / groove portion with a track pitch of 0.43 μm and a header portion on both front and back surfaces was manufactured by an injection molding method. Depending on the stamper used at this time, a radius of 20 to 6
In a region excluding the 0 mm header, the groove depth of the substrate is 90 nm, and the header portion has a depth of 90 n.
m grooves were arranged in an arc shape.

A reflective layer, a recording layer, a dielectric layer, and a solid lubricating layer were laminated in this order on both front and back surfaces of the substrate. An AlCr alloy having a thickness of 50 nm was laminated as a reflective layer by DC sputtering. Further, a 20 nm-thick TbFe is used as a recording layer.
Co was laminated by DC sputtering. As a dielectric layer, 50 nm-thick SiN was stacked as a dielectric layer by a reactive DC sputtering method using a Si target in a mixed atmosphere of Ar and N ₂ . On top of this, Ar and C are used as a solid lubricating layer.
Reactive R with the C target in a mixed atmosphere of H ₄
A 20 nm-thick diamond-like carbon (DLC) was laminated by the F sputtering method to produce a magneto-optical recording medium capable of double-sided recording and reproduction.

COMPARATIVE EXAMPLE 1 Double-sided recording was performed in the same manner as in Example 1 except that the height of the header was equal to the land on both the front and back surfaces of the substrate, and the surface was formed without pits or grooves in the header. A reproducible magneto-optical recording medium was manufactured.

The following evaluations were made on the unidirectional surface of the near-field magneto-optical recording media manufactured by the methods of Examples 1 and 2 and Comparative Example 1. First, radial positions 20, 30, 4 of the recording medium
At five locations of 0, 50, and 60 mm, the surface shapes of the header portion and the land / groove portion in a range of 21.5 μm in the radial direction corresponding to 50 times the track pitch were measured with a scanning electron microscope, and the shapes were measured. From the results, the depth Rp from the maximum height to the center line was calculated.

Subsequently, the flying characteristics of the recording medium were evaluated. First, the recording medium was set on a spindle of a glide tester (manufactured by Hitachi Electronics Engineering Co., Ltd.). Subsequently, the recording medium was rotated at a linear velocity of 7 m / sec so that the flying height of the glide head (manufactured by Glidelight) with a 70% slider with a piezo element and a load of 6.0 g from the recording medium was constant at 50 nm. did. Radial position 20, 3 of recording medium
The effective voltage value of the signal output from the piezo element was measured at five locations of 0, 40, 50, and 60 mm. Subsequently, the SNR was measured. The recording medium is rotated at 2,400 revolutions per minute, and a floating optical head (λ / 16NA: 35.4 nm, λ / 20NA: 28.35 nm) having a slider with a laser wavelength of 680 nm and an effective numerical aperture of 1.2 on the thin film surface.
3 nm) on the recording medium by dynamic loading
m, and irradiating a pulse of laser to warm the recording layer to the Curie temperature or higher while recording while modulating the coil magnetic field on the SIL head at 10 MHz.
The SNR when recording at 0 MHz was measured at five radial positions 20, 30, 40, 50, and 60 mm on the recording medium. The value of the SNR was obtained by adjusting the reproduction power of each medium and measuring the SNR under the condition that the SNR was maximized. Table 1 summarizes the results of each evaluation.

[0043]

[Table 1]

In the first and second embodiments, the difference in Rp between the header portion and the land / groove portion at the same radius position is small, so that ΔRp is 23.4 nm (39.9-16.5 nm) in the range of radius 20 to 60 mm. ), 13.8n
m (39.7-25.9 nm). In addition, any value at each point in the radial direction of 20 to 60 mm has a flying height of 5 mm.
For 0 nm, the relationship of | Rph-Rpd | ≦ λ / 16NA was satisfied.

In Comparative Example 1, since there were no pits or grooves in the header portion, Rp was smaller than that in the land / groove portion. Therefore, ΔRp is 3 for a radius of 20 to 60 mm.
9.2 nm (40.3-1.1 nm) and ΔRp ≦ λ / 1
6NA was not satisfied.

In the first and second embodiments, the output signal from the piezo element is 160 mV in a radius of 20 to 60 mm.
The values are as good as follows, indicating that the flying height fluctuation of the head is small and the flying characteristics are stable. On the other hand, in Comparative Example 1, the voltage value is 340 to 380 mV, which is twice or more the intensity, and the R value of the header portion and the land / groove portion is larger.
Since p is largely different, it indicates that the flying height fluctuation of the head is large. In the evaluation of SNR, Examples 1 and 2 showed good results of 25 to 27 dB at a radius of 20 to 60 mm. However, in Comparative Example 1, noise increased due to fluctuations in the head flying height, and the SNR was 20 dB or less. And a low value.

[0047]

According to the present invention, by keeping the flying height of the head flying above the recording medium constant over the entire recording / reproducing area, a uniform recording / reproducing signal can be obtained and a crash with the head occurs. An optical recording medium which is difficult and has high reliability can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a sectional view showing an example of a substrate used for the optical recording medium of the present invention.

[Explanation of symbols]

 11: Substrate 12: Reflective layer 13: Recording layer 14: Dielectric layer 21: Groove 22: Land 24: Head 25: Head flying height 26: Center line depth Rp

Claims (5)

[Claims] An optical recording medium in which at least a reflective layer and a recording layer are laminated in this order on a substrate provided with a header, lands and grooves for recording and reproducing data, and a floating optical head records and reproduces information. The effective numerical aperture of the optical head to be used is NA, the wavelength of the laser to be used is λ, and the header is determined from the maximum height of the recording medium surface at an arbitrary length along the radius in the area where information is recorded and reproduced on the optical recording medium. Is the depth from the maximum height of the recording medium surface to the center line of the land and groove, and Rph is the depth from the maximum height of the recording medium surface to Rpd.
And Rpd from the maximum value of Rph to Rpd
When the larger of the absolute value of the value obtained by subtracting the minimum value of Rph or the absolute value of the value obtained by subtracting the minimum value of Rph from the maximum value of Rpd is defined as ΔRp, the surface satisfying the relationship ΔRp ≦ λ / 16NA An optical recording medium having a shape. 2. The optical recording medium according to claim 1, wherein format information is recorded on the header by convex or concave pits. 3. In each Rph and each Rpd value measured at a plurality of positions, | Rph−Rpd | ≦ λ / 16
3. The optical recording medium according to claim 2, wherein a convex or concave pit is formed in the header so as to satisfy the relationship of NA. 4. In each Rph and each Rpd value measured at a plurality of positions, | Rph−Rpd | ≦ λ / 16
The optical recording medium according to any one of claims 1 to 3, wherein a groove is formed in the header so as to satisfy a relationship of NA. 5. The optical recording medium according to claim 1, wherein the recording method is a near-field optical recording method.