U.S. patent application number 11/169922 was filed with the patent office on 2005-10-27 for optical recording medium.
This patent application is currently assigned to TOSOH CORPORATION. Invention is credited to Nishizawa, Keiichiro, Oono, Hideki, Oshima, Noriaki, Taniguchi, Takashi.
Application Number | 20050237914 11/169922 |
Document ID | / |
Family ID | 27481029 |
Filed Date | 2005-10-27 |
United States Patent
Application |
20050237914 |
Kind Code |
A1 |
Oshima, Noriaki ; et
al. |
October 27, 2005 |
Optical recording medium
Abstract
An optical recording medium comprising at least a land and a
groove where information-recording/reproducing is carried out by a
flying type optical head. The optical recording medium keep the
flying height of the flying optical head constant in the entire
region of the recording/reproducing area, and is provided with at
least one characteristic among the following characteristics: RP
which is dependent on land and groove parameters and the flying
height satisfied the relationship of H>Rp 01.H; centerline means
roughness Ra is in the range of 0.2 nm Ra 2.0 nm, and the layer
thickness of a liquid lubricant layer satisfies the relation of
.DELTA.Rp.ltoreq..lambda./16NA which is dependent on the effective
numerical aperature, laser wavelength and surface parameters is
satisfied where all parameters in the formula are defined in the
specification; and the height of a header area is different from
the height of a land portion.
Inventors: |
Oshima, Noriaki;
(Yokohama-shi, JP) ; Oono, Hideki; (Yonezawa-shi,
JP) ; Taniguchi, Takashi; (Sagamihara-shi, JP)
; Nishizawa, Keiichiro; (Yokohama-shi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Assignee: |
TOSOH CORPORATION
|
Family ID: |
27481029 |
Appl. No.: |
11/169922 |
Filed: |
June 30, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11169922 |
Jun 30, 2005 |
|
|
|
09777686 |
Feb 7, 2001 |
|
|
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Current U.S.
Class: |
369/283 ;
369/279; 369/94; G9B/11.045; G9B/11.048; G9B/7.029; G9B/7.039;
G9B/7.107; G9B/7.159 |
Current CPC
Class: |
G11B 7/122 20130101;
G11B 11/1058 20130101; G11B 11/10584 20130101; G11B 7/24 20130101;
G11B 11/10578 20130101; G11B 7/24085 20130101; G11B 7/007 20130101;
G11B 11/10586 20130101 |
Class at
Publication: |
369/283 ;
369/094; 369/279 |
International
Class: |
G11B 007/26 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 8, 2000 |
JP |
2000-035655 |
Mar 3, 2000 |
JP |
2000-063375 |
Mar 31, 2000 |
JP |
2000-101309 |
Jun 6, 2000 |
JP |
2000-174217 |
Claims
What is claimed is:
1. In an optical recording medium wherein at least a reflective
layer, a recording layer, a dielectric layer and a solid lubricant
layer are formed on a substrate in this order and
information-recording/reproducing is carried out by a flying
optical head, the optical recording medium being characterized in
that a centerline mean roughness Ra of a land and/or a groove
formed in the recording medium is in a range of 0.2
nm.ltoreq.Ra.ltoreq.2.0 nm.
2. The optical recording medium according to claim 1, wherein a
liquid lubricant layer having a layer thickness t is formed on the
solid lubricant layer in the relation of t.ltoreq.2Ra.
3. The optical recording medium according to claim 2, wherein in
analyzing by a distributive analysis method of a fragment ion peak
of a liquid lubricant with use of TOF-SIMS, an agglomerated state
of the lubricant forming the liquid lubricant layer on the
outermost surface is 10 .mu.m or less in diameter.
4. The optical recording medium according to claim 3, wherein an
optical recording layer and the solid lubricant layer are formed on
the substrate, and a layer composed of a perfluoropolyether
derivative is formed as the liquid lubricant layer on the surface
of the solid lubricant layer in a layer thickness of not less than
0.3 nm but less than 2.0 nm.
5. The optical recording medium according to claim 4, wherein in a
structure comprising a land and a groove, which takes part in
recording/reproducing, the depth of the groove as a guide groove is
20 nm or more but not more than 150 nm after the formation of the
solid lubricant layer.
6. The optical recording medium according to claim 5, wherein the
solid lubricant layer is a diamond-like carbon layer or a SiO.sub.2
layer.
7. The optical recording medium according to claim 5, wherein the
solid lubricant layer comprises a ultraviolet-ray-curable resinous
composition.
8. The optical recording medium according to claim 2, wherein at
least the reflective layer, an optical recording layer, the solid
lubricant layer and the liquid lubricant layer having a layer
thickness t1 which comprises a perfluoropolyether derivative are
formed on the substrate, and t2/t1>0.6 where t2 indicates the
layer thickness of the lubricant layer after having been immersed
in a solvent of the perfluoropolyether derivative.
9. The optical recording medium according to claim 8, wherein the
weight average molecular weight of the perfluoropolyether
derivative is 1000-10000.
10. The optical recording medium according to claim 2, wherein the
contact angle of water to the front surface of the liquid lubricant
layer is 70.degree. or more.
11. The optical recording medium according to claim 2, wherein the
liquid lubricant layer is a layer comprising a perfluoropolyether
derivative, a fluorine type polymer having at least one fluorine
atom in the monomer structure, or a compatibilized product thereof.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a rewritable optical
recording medium capable of information-recording, reproducing and
erasing according to a surface-recording/reproducing system by
using a flying optical head.
[0003] 2. Discussion of Background
[0004] An optical recording medium is a portable recording medium
permitting large volume/high density recording, and there have been
rapidly increasing demands of rewritable media for recording
dynamic images and so on as large volume preserving files for
computers in current fashion of multimedia.
[0005] In an optical recording medium, a guide groove (hereinbelow,
referred to as a groove) for trucking, by the aid of a servo, laser
beams to a position for recording/reproducing is generally formed
in a physical shape in the substrate, and information is recorded
in a convex portion (hereinbelow, referred to as a land) between
grooves in the substrate.
[0006] Accordingly, as the land is made larger, it is possible to
increase the width of marks for recording; the intensity of
reproducing signals can be increased, and the quality of
reproducing signals can be improved.
[0007] In order to perform high density recording, however, it is
necessary to increase an information quantity per recording surface
area by reducing the track pitch as the S distance between
grooves.
[0008] For example, in a commercialized magneto-optical recording
medium of 3.5 inch diameter, the track pitch has been reduced to
1.6 .mu.m in a recording medium having a recording capacity of 128
MB, 1.4 .mu.m in that of 230 MB and 1.1 .mu.m in that of 640
MB.
[0009] On the other hand, the recording density is limited by a
laser beam spot size (.about..lambda./NA) which is determined by a
laser wavelength (.lambda.) from a light source and a numerical
aperture (NA) of an objective lens.
[0010] For example, in the recording/reproducing device for the
above-mentioned 640 MB magneto-optical recording medium, the
wavelength is 680 nm and NA is 0.55, and therefore, the laser beam
spot size is about 1240 nm.
[0011] As means for reducing the laser beam spot size to achieve
high density recording, a so-called near-field optical recording
wherein recording/reproducing is conducted by bringing the optical
head close to the recording layer, has been noted (e.g., (Appl.
Phys. Lett.), vol. 68, p. 141 (1996)). In this recording method, a
solid immersion lens (hereinbelow, referred to as "SIL") head is
used, and recording/reproducing of super-high recording density can
be realized by increasing an effective numerical aperture with use
of SIL to thereby reduce the laser beam spot size.
[0012] For example, in the near-field optical recording using 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 about 37% of the laser
beam spot size used in the before-mentioned conventional
recording/reproducing device for 640 MB magneto-optical recording
medium.
[0013] In this surface recording/reproducing method, it is
necessary to bring the optical head close to the recording medium,
and accordingly, laser beams are not irradiated to the recording
layer through the substrate as in the conventional optical
recording medium, but a method for irradiating directly laser beams
to the recording layer without being passed through the substrate
is used.
[0014] Namely, the structure of the recording layer in the
conventional optical recording medium comprises generally
substrate/first protective layer/recording layer/second protective
layer/reflective layer. On the other hand, in the near-field
optical recording, it has an layer structure, contrary to the
above, of substrate/reflective layer/recording layer/protective
layer so that recording/reproducing is carried out by irradiating
laser beams from a layer surface side.
[0015] In this case, use of a flying slider head is proposed to
bring the optical head close to the recording layer.
[0016] Generally, when a track pitch P is in a size as much as an
optical spot, a groove as a guide groove functions as a diffraction
grating, and the intensity distribution of the beam spot is changed
by the effect of interference due to a track deviation in a region
where the 0-order diffraction light and the first-order diffraction
light overlap, whereby a tracking error signal can be detected.
[0017] The intensity of this signal is determined by the numerical
aperture NA of an objective lens, a track pitch and the wavelength
.lambda. of laser beams, and it is known that the maximum tracking
error signal is provided when the depth of a groove is .lambda./8n
(n: the refractive index of a substrate through which laser
passes).
[0018] However, there were the following problems in the near-field
optical recording system. Since the signal was obtained by a
coupling effect by the optical head at neighboring position and the
outermost surface of the disk in addition to the known diffraction
effect, the signal largely varied depending on a flying height of
the optical head. Further, with respect to designing of the depth
of grooves, the optimum depth for the near-field optical recording
could not be obtained by the conventional designing technique.
[0019] Further, the optical recording medium has a header area in
which a header comprising convex bumps or concave pits having a
format information is formed and a data area having a land and a
groove used for tracking the optical head and recording/reproducing
of data. The optical recording medium had such a problem that the
flying height of the head in recording/reproducing fluctuated
because the flying height of the head flying above the header area
was different from the flying height of the head flying above the
data area. In description of the present invention, the substrate
in which a land and a groove are formed is referred to as the
substrate having a land/groove structure, and the portion of a land
and the portion of a groove in the data area are referred
respectively to as the land portion and the groove portion.
[0020] Further, in the surface optical recording system, since it
is necessary to bring the optical head close to the medium, a
so-called head crush wherein the flying slider head hits the medium
is apt to occur. Accordingly, if the surface of the recording
medium has not sufficient lubricating properties, a slight change
in the flying height of the flying optical head from the recording
medium will cause the contact of the flying optical head to the
recording medium, with the result that the head and the recording
medium are broken. Further, since the laser spot diameter is small
in recording/reproducing of the recording medium, noises of
recording/reproducing signals become large if the surface roughness
of the recording medium is large, whereby sufficient SNR can not be
obtained and there is a trouble in recording/reproducing.
[0021] Thus, in the near-field recording medium according to the
recording/reproducing system for which the flying slider head is
used, it was difficult to keep the flying height of the flying
optical head constant in the entire recording/reproducing region
and to obtain an excellent recording/reproducing signal uniformly.
Further, there was the problem that the flying optical head
contacted the recording medium to thereby cause the breakage of the
head and the recording medium. Thus, it was difficult to obtain the
excellent recording/reproducing signal in view of reliability and
durability.
SUMMARY OF THE INVENTION
[0022] It is an object of the present invention to provide a
surface recording/reproducing type optical recording medium having
high reliability and durability, which is capable of obtaining an
excellent recording/reproducing signal uniformly by keeping the
flying height of an flying optical head constant in the entire
region of the recording/reproducing area, and preventing the head
and the recording medium from being broken by the contact of the
flying optical head to the recording medium.
[0023] Namely, in accordance with the optical recording medium in a
first aspect of the present invention, there is provided an optical
recording medium wherein at least a structure comprising a land and
a groove, which takes part in recording/reproducing, is formed on a
substrate, at least a reflective layer and a recording layer are
formed on the substrate in this order, and
information-recording/reproducing is carried out by a flying
optical head, the optical recording medium being characterized in
that when the depth from the maximum height of the land to the
centerline of the land and the groove is represented by Rp and the
flying height from the maximum height of the land to the optical
head is represented by H in an optional length on the radius of the
optical recording medium in a region for
information-recording/reproducing, Rp satisfies the relation of
H>Rp.gtoreq.0.1H. With the land/groove structure wherein Rp
satisfies such relation, it is possible to maintain a preferred
signal intensity and tracking characteristics.
[0024] According to the optical recording medium in a second aspect
of the present invention, there is provided an optical recording
medium wherein at least a reflective layer, a recording layer, a
dielectric layer and a solid lubricant layer are formed on a
substrate in this order and information-recording/reproducing is
carried out by a flying optical head, the optical recording medium
being characterized in that a centerline mean roughness Ra of a
land and/or a groove formed in the recording medium is in a range
of 0.2 nm.ltoreq.Ra.ltoreq.2.0 nm. By determining Ra in this range,
stable flying characteristics of the flying optical head can be
obtained, and a sufficient SNR can be obtained even when the laser
spot diameter is reduced.
[0025] A liquid lubricant layer may be or may not be formed on the
solid lubricant layer. However, when the liquid lubricant layer is
formed on the outermost surface of the recording medium so that the
layer thickness t of the lubricant layer satisfies the relation of
t.ltoreq.2Ra, influence to the optical characteristics by the
optical head, by the deposition of the liquid lubricant on a laser
beam transmitting portion of the flying optical head in
recording/reproducing, can be prevented.
[0026] Further, the agglomerated state of the liquid lubricant can
be measured by profiling fragment ions of the lubricant by a
secondary ion mass analyzer (TOF-SIMS). In this case, if the
agglomerated state of the liquid lubricant obtained by analyzing a
distribution of fragment ions with use of TOF-SIMS can be rendered
to be 10 .mu.m or less in diameter, influence to the optical
characteristics by the optical head by the deposition of the liquid
lubricant on the laser beam transmitting portion of the flying
optical head in recording/reproducing, can be prevented.
[0027] According to the optical recording medium in a third aspect
of the present invention, there is provided an optical recording
medium wherein at least a reflective layer and a recording layer
are formed in this order on a substrate in which a land and a
groove for data-recording/reproducing and a header area are
provided, and information-recording/reproducing is carried out by a
flying optical head, the optical recording medium being
characterized in that when the effective numerical aperture of the
optical head used is represented by NA, the wavelength of laser
used is represented by .lambda., the depth from the maximum height
of the surface of the recording medium to the centerline of the
header is represented by Rph and the depth from the maximum height
of the surface of the recording medium to the centerline of the
land and the groove is represented by Rpd in an optional length on
the radius of the optical recording medium in a region for
information-recording/reproducing, the optical recording medium has
a shape in its surface satisfying the relation of
.DELTA.Rp.ltoreq..lambda.- /16NA where .DELTA.Rp represents the
absolute value obtained by subtracting the minimum value of Rpd
from the maximum value of Rph or the absolute value obtained by
subtracting the minimum value of Rph from the maximum value of Rpd,
whichever larger, the values of Rph and Rpd being obtained by
measuring at plural positions. With the satisfaction of such
relation by .DELTA.Rp, stable flying characteristics of the flying
optical head can be obtained in the entire
information-recording/reproduc- ing region of the optical recording
medium.
[0028] According to the optical recording medium in a fourth aspect
of the present invention, there is provided an optical recording
medium wherein at least a land portion and a groove portion, which
takes part in recording/reproducing, and a header area for
recording a format information are formed in a substrate;
information is recorded in at least the land portion, and
information-recording/reproducing is carried out, the optical
recording medium being characterized in that the height of the
header area is different from the height of the land portion. By
rendering the height of the header area to be different from the
height of the land portion, it is possible to detect the timing of
laser beams for recording/reproducing entering in the header
area.
[0029] When a plastic substrate obtained by molding a thermoplastic
resin is used for fabricating the optical recording medium of the
present invention, light showing the strongest relative intensity
between wavelengths 350-1500 nm is irradiated to the front surface
of the substrate, whereby noises caused by the surface roughness of
the substrate can be reduced.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 is a diagram showing in cross section an embodiment
of the optical recording medium of the present invention and
explaining the centerline of lands and grooves of the present
invention. The centerline of the lands and grooves means a straight
line such that when a single straight line is drawn to a roughness
curve of the data area having the lands and grooves, surface areas
surrounded by the straight line and the roughness curve are equal
at both sides of the straight line. Namely, it is meant that the
surface area of (A) and the surface area of (B) at opposite sides
with respect to the straight line (centerline) in FIG. 1 are
equal.
[0031] FIG. 2 is a partial cross-sectional view showing
diagrammatically an embodiment of the construction of the optical
recording medium of the present invention. The figure shows that a
reflective layer 22, a recording layer 23, a dielectric layer 24, a
solid lubricant layer 25 and a liquid lubricant layer 26 are formed
in this order on a substrate 21.
[0032] FIG. 3 is a partial cross-sectional view showing
diagrammatically an embodiment of the construction of a
magneto-optical recording disk of the present invention. The figure
shows that a reflective layer 32, a first dielectric layer 33, a
magneto-optical recording layer 34, a second dielectric layer 35, a
solid lubricant layer 36 and a liquid lubricant layer 37 are formed
in this order on a substrate 31.
[0033] FIG. 4 is a cross-sectional view showing diagrammatically an
embodiment of the construction of a double surface type
magneto-optical recording disk of the present invention. The figure
shows that a reflective layer 42, a first dielectric layer 43, a
magneto-optical recording layer 44, a second dielectric layer 45, a
solid lubricant layer 46 and a liquid lubricant layer 47 are formed
in this order on each of an upper face and a lower face of a
substrate 41.
[0034] FIG. 5(a) shows an optical recording medium 50 in accordance
with the present invention wherein concave or groove parts located
at 52 are shown in more detail in FIG. 5(b).
[0035] In FIG. 5(b), black parts 54 representing concave or groove
parts and white-gray parts 56 representing protruding parts are
shown.
[0036] FIG. 5(c) is a cross-section taken along line A-A' of FIG.
5(b), where Rpd and the Center Line are shown.
[0037] FIG. 5(d) is a cross-section taken along line B-B' of FIG.
5(b), where Rph and Center Line are shown.
[0038] FIG. 6(a) illustrates a header part and a land part where
black parts 54 representing concave or groove parts and white-gray
parts 56 representing protruding parts as shown.
[0039] FIG. 6(b) is a cross-section taken along line C-C' of FIG.
6(a) showing the Header Part and the Land Part in the case of
having a Header Part higher than a Land Part. FIG. 6(c) is a
cross-section taken along line C-C' of FIG. 6(a) showing a Header
Part and a Land Part in the case of having a Header Part lower than
a Land Part.
EXPLANATION OF REFERENCE NUMERALS
[0040] 11: Groove, 12: Land, 13: Flying optical head, 14: Flying
height, 15: Depth Rp from the maximum height of the front surface
of the recording medium to the centerline of a land and a groove,
21, 31, 41: Substrate, 22, 32, 42: Reflective layer, 23: Recording
layer, 33, 43: First dielectric layer, 34, 44: Magneto-optical
recording layer, 24: Dielectric layer, 35, 45: Second dielectric
layer, 25, 36, 46: Solid lubricant layer, 26, 37, 47: Liquid
lubricant layer
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0041] It is an object of the present invention to provide a
surface recording/reproducing type optical recording medium having
high reliability and durability, which is capable of obtaining an
excellent recording/reproducing signal uniformly by keeping the
flying height of a flying optical head constant in the entire
recording/reproducing region, and preventing the head and the
recording medium from being broken by the contact of the flying
optical head to the recording medium. The optical recording medium
has at least one characteristic feature among the characteristic
features described below.
[0042] The first characteristic feature of the optical recording
medium of the present invention resides in an optical recording
medium wherein at least a structure comprising a land and a groove,
which takes part in recording/reproducing, is formed on a
substrate, at least a reflective layer and a recording layer are
formed on the substrate in this order, and
information-recording/reproducing is carried out by a flying
optical head, the optical recording medium being characterized in
that when the depth from the maximum height of the land to the
centerline of the land and the groove is represented by Rp and the
flying height from the maximum height of the land to the optical
head is represented by H in an optional length on the radius of the
optical recording medium in a region for
information-recording/reproducing, Rp satisfies the relation of
H>Rp.gtoreq.0.1H.
[0043] Rp and H have preferably the relation of
0.8H.gtoreq.Rp.gtoreq.0.1H- , more preferably,
0.5H.gtoreq.Rp.gtoreq.0.1H. When Rp exceeds the flying height H,
the flying optical head will contact the land portion, and stable
flying is impossible. In consideration of a defect in the shape of
the land or the presence of foreign matters or the like, Rp is
preferably 0.8H or less. On the other hand, when Rp is less than
0.1H, it is difficult to take a tracking signal, and the effect of
the groove as a guide groove can not be expected.
[0044] The centerline of the lands and grooves in the present
invention means a straight line such that when a single straight
line is drawn to a roughness curve along lands and grooves in an
optional length on the radius of the optical recording medium in a
region for information-recording/reproducing, the surface areas
surrounded by the straight line and the roughness curve are equal
at both sides of the straight line. Specifically, it is meant that
the surface area of (A) and the surface area of (B) opposing with
respect to the centerline in FIG. 1 are equal. Further, the
centerline of lands and grooves or the maximum height of lands are
determined based on an optional length on the radius of the optical
recording medium in a region where the recording/reproducing of
information is conducted. The optional length should be 2-100
times, preferably 10-50 times as much as the track pitch, although
it varies depending on a size of the track pitch. With such,
conditions of the land and the groove in the optical recording
medium are reflected to Rp and so on. Further, the optional length
may be at any optional position as long as it is within the
recording/reproducing region of the optical recording medium.
[0045] The centerline of the lands and the grooves or the maximum
height of the lands can be obtained by measuring a portion having
an optional length in cross-sectional view of the optical recording
medium with use of a scanning electronic microscope (SEM) having a
magnification of 2000-4000 or an atomic force microscope (AFM).
Further, the flying height of the optical head can be measured by
rotating an optical recording medium to float the optical head.
[0046] The second characteristic feature of the optical recording
medium of the present invention resides in an optical recording
medium wherein at least a reflective layer, a recording layer, a
dielectric layer and a solid lubricant layer are formed on a
substrate in this order and information-recording/reproducing is
carried out by a flying optical head, the optical recording medium
being characterized in that a centerline mean roughness Ra of a
land and/or a groove formed in the recording medium is in a range
of 0.2 nm.ltoreq.Ra.ltoreq.2.0 nm.
[0047] In the recording region of the optical recording medium of
the present invention, a land(s) and a groove(s) are formed to
control the tracking of the optical head generating laser spot
beams when it flies above the recording medium.
Recording/reproducing with respect to the optical recording medium
may be conducted only to land portions, only to groove portions, or
to both the land portions and the groove portions. Accordingly, Ra
of the land portions and the groove portions is preferably in a
range of 0.2 nm.ltoreq.Ra.ltoreq.2.0 nm, more preferably, 0.5
nm.ltoreq.Ra.ltoreq.1.5 nm. When Ra is less than 0.2 nm, the
lubricating properties of the front surface of the recording medium
are poor, whereby the flying height of the optical head such as SIL
head or the like fluctuates. Accordingly, if SIL head contacts the
recording medium, crushing of SIL head or the recording medium is
apt to occur. Further, when Ra exceeds 2.0 nm, the noise level of
recording/reproducing signals becomes large whereby SNR decreases
and an error rate increases, with the result that there is a
problem of reduction in recording capacity, in the worst case,
recording/reproducing being impossible. Ra in the front surface of
the recording medium can be controlled by changing the layer
thickness of each of the reflective layer, the recording layer, the
dielectric layer and the solid lubricant layer when they are
formed, or by changing the partial pressure of gas when they are
formed by sputtering methods.
[0048] The liquid lubricant may be or may not be formed on the
solid lubricant layer. However, from the viewpoint of using the
flying optical head, it is desirable to form the liquid lubricant
layer on the outermost surface of the recording medium.
[0049] It is preferable that the layer thickness of the liquid
lubricant layer is not less than 0.3 nm but not more than 4.0 nm.
Further, it is preferable that the layer thickness t of the liquid
lubricant layer satisfies the relation of t.ltoreq.2Ra where Ra
indicates an average roughness of the centerline of the recording
medium having a layer structure up to the solid lubricant layer on
the substrate, more preferably, the layer thickness t satisfies the
relation of t.ltoreq.1.5Ra. If the layer thickness t of the liquid
lubricant layer exceeds 2Ra, and the SIL head contacts the
recording medium due to a change in the flying height of the flying
optical head from the recording medium, it is difficult that the
SIL head flies again above the recording medium. Further, the
liquid lubricant scatters from the recording medium rotated in
recording/reproducing, and the scattered lubricant is apt to
deposit on the SIL head. If the liquid lubricant adheres on the
front surface of the lens of SIL head through which laser beams
pass, the intensity of output laser beams or the intensity of input
laser beams is reduced whereby the durability of SIL head is
remarkably reduced.
[0050] The agglomerated state of the liquid lubricant can be
measured by profiling fragment ions of the lubricant by the
secondary ion mass analyzer (TOF-SIMS). In the liquid lubricant
layer of the optical recording medium of the present invention, it
is preferable that the agglomerated state of the liquid lubricant
obtained by analyzing a distribution of fragment ions of the
lubricant with use of TOF-SIMS shows 10 .mu.m or less in
diameter.
[0051] When the agglomerated state of the liquid lubricant exceeds
10 .mu.m in diameter, there takes place occurrence of the
deposition of the lubricant on the front surface of the optical
head in repeated recording/reproducing operations by the flying
optical head, whereby the front surface of the optical head is
stained and a defect in recording/reproducing is resulted.
[0052] In order to render the agglomerated state of the liquid
lubricant to be 10 .mu.m or less, it is preferable to form a layer
composed of a perfluoropolyether derivative on the front surface of
an optical recording medium having, for example, a spiral guide
groove (groove) or concentric guide grooves in a thickness of not
less than 0.3 nm but less than 2.0 nm, more preferably, 0.5 nm-1.8
nm.
[0053] With such groove structure, the liquid lubricant is
dispersed uniformly on the front surface of the recording medium,
and an excessive liquid lubricant accumulates in a lower portion of
the groove(s) while an upper portion of the groove(s) is covered
with the lubricant at the minimum necessary for lubrication.
Accordingly, even when recording/reproducing operations are
repeated by the flying head with an optical head, abnormality in
terms of optics due to the adhesion of the lubricant on the optical
head does not occur, and stable recording/reproducing/erasing
characteristics can be obtained.
[0054] When the layer thickness of the liquid lubricant is less
than 0.3 nm, sufficient lubrication characteristics can not be
obtained, and a flaw is easily caused on the front surface of the
recording medium by the flying optical head. When the layer
thickness of the liquid lubricant is 2.0 nm or more, there is no
problem in lubrication characteristics, however, the proportion of
free lubricant molecules which are not adsorbed in the surface of
the recording medium is increased so that the state of dispersion
exceeds 10 .mu.m in diameter.
[0055] It is preferable that the depth of the groove(s) is 20
nm-150 nm after the formation of the solid lubricant layer. When
the depth of the groove(s) is less than 20 nm, an amount of the
lubricant accumulated in a lower portion of the groove(s) is
insufficient. When an excessive lubricant exists in an upper
portion of the groove(s), the agglomerated state of the lubricant
exceeds 10 .mu.m in diameter. When the depth of the groove(s)
exceeds 150 nm, the covering of the upper portion of the groove(s)
by the lubricant layer is insufficient although the diameter of the
lubricant in an agglomerated state is 10 .mu.m or less, and
crushing of the flying optical head is apt to occur.
[0056] Although the distance between grooves, i.e., the track pitch
is not, in particular, limited, it is preferably 1.6 .mu.m or less
because it takes part in recording/reproducing of data.
[0057] The third characteristic feature of the optical recording
medium of the present invention resides in an optical recording
medium wherein at least a reflective layer and a recording layer
are formed in this order on a substrate in which a land and a
groove for data-recording/reproducin- g and a header area are
provided, and information-recording/reproducing is carried out by
an optical head, the optical recording medium being characterized
in that when the effective numerical aperture of the optical head
used is represented by NA, the wavelength of laser used is
represented by .lambda., the depth from the maximum height of the
surface of the recording medium to the centerline of the header is
represented by Rph and the depth from the maximum height of the
surface of the recording medium to the centerline of the land and
the groove is represented by Rpd in an optional length on the
radius of the optical recording medium in a region for
information-recording/reproducing, the optical recording medium has
a shape in its surface satisfying the relation of
.DELTA.Rp.ltoreq..lambda./16NA where .DELTA.Rp represents the
absolute value obtained by subtracting the minimum value of Rpd
from the maximum value of Rph or the absolute value obtained by
subtracting the minimum value of Rph from the maximum value of Rpd,
whichever larger, the values of Rph and Rpd being obtained by
measuring at plural positions.
[0058] FIG. 1 shows diagrammatically the shape in cross section of
an embodiment of the optical recording medium of the present
invention. In a recording/reproducing surface of the optical
recording medium, a groove 11 is formed in a spiral form for laser
tracking. Convex-type lands 12 are formed between grooves. Further,
a header having a format information (not shown) is formed in the
recording/reproducing surface. It should be noted that FIG. 1 does
not indicate correctly relative size/height of the optical head,
lands and grooves and so on.
[0059] As an optical recording/reproducing system, there are a
groove recording system in which data are written in a groove and a
land recording system in which data are written in a land. In
either recording system, it is important that the flying height 14
of a head 13 from a plane, as standard, in which data are written
should be constant in order to conduct recording/reproducing. When
the head flies above the recording medium, the shape of the front
surface of the recording medium influences largely the flying
height of the head. Namely, the flying height of the head varies
depending on the depth Rpd from the maximum height of the surface
of the recording medium to the centerline of the land and the
groove (Rp in figure) and the depth Rph from said maximum height to
the centerline of the header (not shown).
[0060] The centerline of the land and the groove is a straight
line, in the same manner as the case of the first characteristic
feature of the present invention, such that when a single straight
line is drawn to a roughness curve of lands and grooves in an
optional length on the radius of the optical recording medium in a
region of recording/reproducing of information, the surface areas
surrounded by the straight line and the roughness curve at both
sides of the straight line are equal. Further, the centerline of
the header is a straight line with respect to a roughness curve of
the header in the same manner as above.
[0061] The centerline of the land and the groove, the centerline of
the header, and the maximum height of the land or the header, i.e.,
the maximum height of the surface of the recording medium are
determined in an optional length on the radius of the optical
recording medium in a region for recording/reproducing
information.
[0062] The optional length, which varies depending on the track
pitch, is 2-100 times, preferably, 10-50 times as much as the track
pitch, whereby conditions of the land and the groove or the header
of the optical recording medium are reflected to Rpd, Rph and so
on. Further, the optional length may be determined at any optional
position as long as it is in a recording/reproducing region of the
optical recording medium.
[0063] The centerline of the land and the groove, the centerline of
the header and the maximum height of the surface of the recording
medium can be measured by a scanning electron microscope (SEM)
having a magnification of 2000-4000 or an atomic force microscope
(AFM) in an optional length portion in the shape in cross section
of the optical recording medium, in the same manner as in the case
of the first characteristic features of the present invention.
[0064] It is more preferable that the above-mentioned .DELTA.Rp
satisfies the relation of .DELTA.Rp.ltoreq..lambda./20NA in order
to obtain a uniform recording/reproducing signal intensity having
smaller fluctuation.
[0065] In particular, since the shape of the surface of the header
area of the recording medium is different from that of the data
area, it is important to minimize the difference between Rph of the
header area and Rpd of the data area so that the flying height of
the flying head does not fluctuate when the head enters into the
header area. The fluctuation of the flying head should be
suppressed to such an extent that crushing does not occur by the
contact of the head to the recording medium.
[0066] As a preferred method for reducing .DELTA.Rp, it is
preferable that convex bumps and/or concave pits are formed in the
header area of the substrate, and the depth Rph from the maximum
height of the surface of the medium to the centerline of the header
and the depth Rpd from the maximum height of the surface of the
medium to the centerline of the land and the groove have the
relation of .vertline.Rph-Rpd.vertline..ltoreq..l- ambda./16NA.
Further, they preferably have the relation of
.vertline.Rph-Rpd.vertline..ltoreq..lambda./20NA which makes
fluctuation smaller. Rph of the header area can be adjusted by
changing the surface area, the depth and the height of pits to be
formed.
[0067] Further, it is preferable to form a groove in the header
area wherein the relation of
.vertline.Rph-Rpd.vertline..ltoreq..lambda./16NA is satisfied.
Further, it is preferable to provide
.vertline.Rph-Rpd.vertline..ltoreq..lambda./20NA in order to make
fluctuation smaller and to obtain a uniform recording/reproducing
signal intensity. The shape of the groove to be formed may be
either in a circumferential direction or a radial direction, or
both directions with respect to the center of recording medium. Rph
can be adjusted by changing the depth and the width of the
groove.
[0068] By satisfying such conditions, a highly reliable optical
recording medium can be obtained wherein the flying height of the
head in the entire recording/reproducing region is made constant; a
uniform recording/reproducing signal can be obtained, and the
crushing to the head seldom occurs.
[0069] The fourth characteristic feature of the optical recording
medium of the present invention resides in an optical recording
medium wherein at least a land portion and a groove portion, which
takes part in recording/reproducing, and a header area for
recording a format information are formed in a substrate;
information is recorded in at least the land portion, and
information-recording/reproducing is carried out, the optical
recording medium being characterized in that the height of the
header area is different from the height of the land portion.
[0070] By providing a difference in elevation between the height of
the header area and the height of the land portion and using a
detector of division type detecting system, there is obtainable an
optical recording medium capable of detecting the timing of
starting of operation in the header area when the optical head has
entered from the data area to the header area.
[0071] Further, in recording information in the data area
comprising lands and grooves, it is generally necessary to increase
laser output. Therefore, a phenomenon that the wavelength of laser
shifts toward a side of long wavelength takes place. On the other
hand, at the time point that the optical head enters from the data
area to the header area in which a format information is recorded,
it is necessary to reduce the output of laser in order to read out
the format information. In this case, there arises a problem of
causing defocusing if the height of the data area is equal to the
height of the header area because the wavelength of the laser
returns to the original wavelength. To solve this problem, it is
necessary to reduce the weight of the optical head and increase the
response speed. Alternatively, the defocusing can be corrected by
providing a difference in elevation between the height of the
header area and the height of the land portion.
[0072] The difference in height between the header area and the
land portion in the present invention is preferably from 3 nm to
100 nm. When the difference in height is less than 3 nm, defocusing
by a shift of laser wavelength, which is caused by a difference of
laser output between the time of recording and the time of
reproducing, can not be corrected, and the intensity of a
height-difference signal indicating a difference in height between
the header area and the land portion, which is sufficiently
detected by a division type detector, can not be obtained, whereby
it is impossible to detect the timing of the optical head entering
into the header area.
[0073] On the other hand, when the difference in height exceeds 100
nm, the defocusing of laser has to be corrected in the data area
and the header area respectively, and the stability of flying of
the flying optical head used in the surface recording/reproducing
system is lost, whereby head crushing may occur.
[0074] In the present invention, it is sufficient that the height
of the header area is different from the height of the land
portion. Specifically, the height of the header area may be higher
than the height of the land portion, or the height of the header
area may be lower than the height of the land portion. "The height"
in the present invention means "the height" from the lowermost
portion of groove portions as standard. When the header area has no
groove portion, the lowermost portion of the groove portion
existing in a circumferential direction with respect to the header
area is taken as standard as the height of the header area. The
height of the header area should be different from the height of
the land portion.
[0075] The difference in height between the header area and the
data area in the present invention may be formed by a 2P method
with use of a stamper having a height-difference structure or an
injection molding method. Or, after a disk without having a
difference in height is produced by injection molding, the data
area is partially molten by heat or irradiation of light to thereby
make the height of the data area lower than the height of the
header area.
[0076] The optical recording medium of the present invention may
possess any of the above-mentioned first to fourth characteristic
features solely, or may possess two or more characteristic features
in combination optionally. Further, all the characteristic features
may be possessed in combination of these characteristic features.
In the later case, respective effect by these characteristic
features can be obtained complexly. Further, when certain
characteristic features have the same effect, such effect can
further be increased.
[0077] The optical recording medium of the present invention can be
preferably used for an optical recording medium according to a
surface recording/reproducing system wherein recording and/or
reproducing is conducted by irradiating laser light to the
recording layer without passing through the substrate, i.e.,
without passing through the substrate from a side at which the
recording layer and so on are formed, in particular, for a
near-field optical recording medium using near-field light. In
particular, it is preferably used as a near-field magneto-optical
recording medium using a magneto-optical recording system, as a
recording system. Further, with respect to the shape of the
recording medium, an optical recording disk having a circular
disk-like shape is preferred.
[0078] The recording system for the optical recording medium of the
present invention is not in particular limited as far as it is a
recording system capable of recording by a change of the
polarization plane, the reflectance, the phase of light, such as a
magneto-optical recording system comprising a recording layer such
as TbFeCo, DyFeCo, GdTbFeCo, NdDyFeCo or the like, or a
phase-change recording system comprising a recording layer such as
GeSbTe, AgInSbTe or the like.
[0079] Further, in fabricating the optical recording medium of the
present invention, when a plastic substrate obtained by molding a
thermoplastic resin is used, light indicating the strongest
relative intensity between wavelengths 350-1500 nm is irradiated to
the surface of the substrate, whereby noises caused by the surface
roughness of the substrate can be reduced.
[0080] In a high recording density recording system, study has been
made to increase the numerical aperture of the optical lens.
However, a reduction of C/N due to noise components which are
caused by the surface roughness of the substrate as the numerical
aperture is increased becomes troublesome. In particular, in a
near-field optical recording system, such phenomenon is remarkable,
and the reduction of noise components resulted from the surface
roughness of the substrate is required as a very important
technique. By reducing the noise components, excellent
recording/reproducing characteristics can be obtained.
[0081] In recent years, there is a report that noises can be
reduced by irradiating light to the substrate of an optical
recording medium by using a UV ozone cleaner with a low pressure
mercury lamp (Journal of the Magnetics Society of Japan, vol. 23,
Supplement, No, S1 (1999) MORIS '99). The mechanism described is as
follows. By irradiating light from a low pressure mercury lamp of a
U.V. ozone cleaner, active oxygen species are produced from oxygen
in air whereby the linkage of the polymer on the surface of the
substrate is cut and decomposed for ashing. As a result, the
surface roughness of the substrate is smoothened when a part of the
substrate material is decomposed to decrease, and noises resulted
from the surface roughness are reduced whereby C/N and the jitter
of the magneto-optical recording medium fabricated by using the
substrate can be improved.
[0082] However, in the above-mentioned treatment to the substrate,
adhesiveness between the substrate and the recording layer
decreases remarkably due to a reduction of molecular weight which
is caused by the decomposition of the surface of the substrate,
whereby the peeling-off of the recording layer takes place and the
mechanical strength of the substrate decreases due to a low
molecular weight which is caused by the irradiation of light from
the low pressure mercury lamp with the result of cutting the
linkage of polymer in the substrate. Accordingly, the substrate can
not be used practically.
[0083] Namely, when light of a ultraviolet region is used as
irradiation light, there is a large possibility of cutting the bond
of the molecules of the plastic substrate. In particular, when
light in a far ultraviolet ray region having a wavelength of less
than 300 nm is irradiated to the substrate, very active ozone is
generated by photoreaction with oxygen in air, whereby oxidative
destruction of the substrate surface is resulted, and the bond of
polymer constituting the substrate is cut, with the result of
reducing the molecular weight of the substrate.
[0084] When the recording layer and so on are formed on the
substrate having a low molecular weight, the peeling-off of the
recording layer is apt to occur. Further, the mechanical strength
of the substrate itself decreases whereby a defect such as cracking
is generated in the substrate in an acceleration durability
test.
[0085] As the light source for emitting light suitable for
irradiation in order to reduce noises due to the surface roughness
of the substrate, super-high pressure mercury lamp, high pressure
mercury lamp, flash UV lamp, metal halide lamp, xenon lap,
fluorescent lamp, arc lamp or halogen lamp can be exemplified.
[0086] On the other hand, since a large amount of far ultraviolet
rays is contained in light emitting from low pressure mercury lamp,
deep UV lamp, deuterium lamp or the like, they can not be used as
the light source in the present invention without contrivance.
[0087] In the present invention, the substrate is heated by
irradiating light. In this case, it is preferable that the
temperature on the surface of the substrate is 80.degree.
C.-150.degree. C. When the substrate surface temperature is less
than 80.degree. C., it is insuffcieint to make the surface
roughness of the substrate flat by heating, and it is not effective
to reduce the noises. When the substrate surface temperature
exceeds 150.degree. C., the mechanical properties of the substrate
itself become poor in addition to the groove being collapsed due to
the molten substrate surface, so that it is impossible to use.
[0088] The liquid lubricant layer used for the optical recording
medium of the present invention is not in particular limited as
long as a material having a lubricating performance such as
perfluoropolyether or the like is used. For example,
alcohol-modified perfluoropolyether, ester-modified
perfluoropolyether, isocyanate-modified perfluoropolyether,
carboxyl-group-modified perfluoropolyether, piperonyl-modified
perfluoropolyether or the like may be mentioned.
[0089] Although the main chain structure of the perfluoropolyether
may be either a linear chain structure or a side chain structure,
the linear chain structure is in particular preferred in view of
lubricating properties. As the structure of its derivative, such
one having a functional group such as an ester group (--COOR), a
piperonyl group (3,4-methylenedioxybenzyl) or the like at both
terminals or an end of the main chain is preferred.
[0090] As the ester group, a C.sub.1-10 alkyl group which may be
substituted can be exemplified. Although such a functional group
may be introduced to either both terminals or one end of the
molecule, it is particularly desirable that the functional group
exists at both terminals because of its higher adsorption strength
to the underlayer.
[0091] The weight average molecular weight of the
perfluoropolyether derivative is from 1000 to 10000, more
preferably, from 2000 to 10000. If the weight average molecular
weight is less than 1000, the fluidity tends to be too high and the
distribution on the medium surface is apt to be non-uniform. If the
weight average molecular weight exceeds 10000, the fluidity tends
to be too low and it is difficult to obtain sufficient lubricating
properties. Further, in the derivative having a low molecular
weight in comparison with that having a high molecular weight, the
weight reduction due to thermal decomposition takes place from a
lower temperature. Accordingly, the derivative having a higher
molecular weight is superior in a long-term stability.
[0092] As such perfluoropolyether derivative, "Fomblin Z DEAL" and
"Fomblin AM-2001" (tradename) manufactured by Ausimont Company and
"DEMNUM SP" and "DEMNUM SY-3" (tradename) manufactured by Daikin
can be mentioned, for example. "Fomblin Z DEAL" has ester groups at
both terminals and "Fomblin AM-2001" has piperonyl groups at both
terminals, and they are compounds each having
--[(O--CF.sub.2-CF.sub.2).sub.p-(O)--C- F.sub.2).sub.q]- as the
main chain.
[0093] Further, "DEMNUM SP" and "DEMNUM SY-3" have an ester group
at one terminal and they are compounds having
F-(CF.sub.2-CF.sub.2-CF.sub.2-O).s- ub.n- as the main chain.
[0094] It is preferable that the remaining layer thickness of the
lubricant layer after the optical recording medium of the present
invention has been immersed in a solvent for dissolving the
perfluoropolyether derivative, is 60% or more of the layer
thickness before the immersion. As the solvent for dissolving the
perfluoropolyether derivative, a perfluoropolyether type solvent or
a perfluorocarbon type solvent may be mentioned.
[0095] It can be said that as the proportion of the remaining layer
thickness of the lubricant layer after it has been immersed in a
solvent for dissolving the perfluoropolyether derivative is large,
there is much liquid lubricant molecules adsorbed in the surface of
the solid lubricant layer. When the proportion of the remaining
layer thickness is less than 60%, there is no problem in
lubricating properties. However, since there are many free liquid
lubricant molecules which are not adsorbed in the surface of the
solid lubricant layer, lubricant molecules deposited on and
transferred to the flying optical head are recognized when the
flying optical head contacts the recording medium. Although the
liquid lubricant molecules deposited on the flying optical head are
decomposed by heat generated from laser or the like, a part of the
molecules may change in quality depending on the structure thereof
and a colored residue may be produced. When the residue deposits on
the lens, the transmittance decreases and the characteristics of
the optical system are deteriorated.
[0096] As a method for increasing the proportion of the remaining
layer thickness of the lubricant layer after it has been immersed
in the solvent for dissolving the perfluoropolyether derivative,
there is a method that the lubricant layer is once formed, and
then, the surface of the layer is washed by a solvent for
dissolving the perfluoropolyether derivative whereby the free
liquid lubricant molecules which are not adsorbed to a lubricating
underlayer are removed.
[0097] Further, it is preferable that the contact angle of water to
the surface of the lubricant layer of the optical recording medium
of the present invention is 70.degree. or more.
[0098] When the contact angle of water to the surface of the
lubricant layer is less than 70.degree., a much amount of water
molecules in air is absorbed in the surface of the medium.
Accordingly, the adsorbed moisture enters into a defective portion
in the recording layer to cause corrosion easily. When the contact
angle of water at the surface is 70.degree. or more, such problem
does not occur because water molecules are not adsorbed in the
surface of the medium.
[0099] The lubricant layer of the optical recording medium of the
present invention may comprise a perfluoropolyether derivative or a
fluorine type polymer having at least one fluorine atom in the
monomer structure or a compatibilized product thereof. Even when
these materials for the lubricant layer are used, the contact angle
of water to the lubricant layer changes depending on the material
used, the layer thickness of the lubricant layer and conditions for
coating. Accordingly, it is preferable to adjust the contact angle
to be 70.degree. or more.
[0100] FIG. 2 is a cross-sectional view showing diagrammatically an
embodiment of the structure of the optical recording medium of the
present invention. A reflective layer 22, a recording layer 23, a
dielectric layer 24, a solid lubricant layer 25 and a liquid
lubricant layer 26 are laminated on a substrate 21 in this
order.
[0101] There is no limitation to the substrate 21 as far as it has
the above-mentioned land/groove structure.
[0102] As resin for injection molding, there is no special
limitation as far as it is a thermoplastic resin satisfying the
properties of an optical disk substrate, such as mechanical
properties, transferring properties and,so on. For example,
transparent plastics such as polycarbonate, polymethyl
methacrylate, amorphous polyolefin or the like or so-called super
engineering plastics such as polyphenylene sulfide, polyallylate,
polyether ketone, polyether ether ketone or the like, may be
used.
[0103] Further, there is no problem in preparing the substrate by
so-called 2P method wherein the land/groove structure is formed in
photopolymer on a glass plate or a flat metal plate.
[0104] There is in particular no limitation to the reflective layer
22 as far as metal having a high reflectivity is used. For example,
metal such as Al, Ag, Au, Cu or the like may be used solely, or an
alloy containing any of them as the main component may be used.
[0105] The recording layer 23 is constituted by a layer capable of
recording by a change of the polarization plane, the reflectivity,
the phase of light and so on, e.g., a magneto-optical recording
layer such as TbFeCo, DyFeCo, GdTbFeCo, NdDyFeCo or the like, or a
phase-change recording layer such as GeSbTe, AgInSbTe or the like.
The recording layer 23 may be a single layer or a laminated layer
formed by laminating layers having different function or
composition.
[0106] As the dielectric layer 24, AlN, SiN, Ta.sub.2O.sub.5,
ZnS--SiO.sub.2 or the like may be used.
[0107] The reflective layer, the recording layer and the dielectric
layer can be formed by a thin film forming method such as a
sputtering method or a vacuum deposition method or the like.
[0108] As the solid lubricant layer 25, a layer comprising
diamond-like carbon (DLC) composed of carbon added with hydrogen or
nitrogen, SiO.sub.2 or a UV curing type resin composition, may be
exemplified. The diamond-like carbon layer and the SiO.sub.2 layer
can be formed by a sputtering method, an ion beam sputtering
method, a plasma CVD method or the like, and the UV curing type
resin is coated into a layer by a spin coating method followed by
curing by irradiating ultraviolet rays.
[0109] On this layer, further, the liquid lubricant layer 26 is
formed by a dipping/lifting method or the like to thereby prepare
the optical recording medium.
[0110] The dielectric layer may be formed between the reflective
layer and the recording layer without causing any trouble.
[0111] When the dielectric layer is formed between the reflective
layer and the recording layer, it is sufficient that the dielectric
layer has a layer thickness to an extent of protecting the
recording layer 23, specifically, a layer thickness of from 10 nm
to 100 nm is preferred. The recording layer 23 has preferably a
layer thickness of from 30 nm to 200 nm. The dielectric layer 24
has roles of controlling the light absorption efficiency to the
recording layer 23 and increasing the change of reflection light or
the Kerr rotation angle before and after the recording in addition
to the role of protecting the recording layer 23. Accordingly, the
layer thickness of the dielectric layer 24 should be designed in
consideration of the laser wavelength used, and is preferably from
20 nm to 300 nm.
[0112] In the present invention, there is no limitation with
respect to single surface recording or double surface recording
concerning the disk. In the double surface disk, the
above-mentioned laminated layers may be formed on a single surface
or both surfaces simultaneously.
EXAMPLES
[0113] Now, the present invention will be described in detail with
reference to Examples. However, the present invention is by no
means restricted by such specific Examples.
Examples 1-4 and Comparative Examples 1 and 2
[0114] Magneto-optical recording media for near-field optical
recording were prepared in a manner as described bellow. Namely,
original plates having track pitches and groove depths shown in
Table 1 were prepared by using glass substrates on which a positive
photo-resist having a thickness of 110 nm was formed and a UV
mastering device. Ni stampers were prepared from the original
plates. The groove depths were formed by controlling power of light
to be exposed in mastering.
[0115] With these stampers, disk-like substrates of polycarbonate
having a diameter of 130 mm were prepared by injection-molding to
fabricate optical recording media as shown in FIG. 3. Namely, on an
area of the substrates where the land and the groove were formed,
an Al alloy layer (layer thickness: 50 nm), a first SiN dielectric
layer (10 nm), a magneto-optical recording layer (layer thickness:
20 nm) comprising Tb.sub.20(Fe.sub.90Co.sub.10).sub.80, a second
SiN dielectric layer (layer thickness: 30 nm) and a DLC layer
(layer thickness: 20 nm) were successively formed by a sputtering
method. Then, as a lubricant layer for the flying head,
perfluoropolyether was formed in a thickness of 0.5 nm by a dipping
method.
[0116] Rp was observed by AFM at positions of 30 mm, 45 mm and 60
mm in radius, which were in a recording/reproducing region of the
thus obtained optical media, in a range of 9 .mu.m long in a radial
direction, which was 20 times as much as the track pitch. As a
result, values as shown in Table 1 were obtained at each point of
measurement.
1 TABLE 1 Track pitch Groove depth (nm) (nm) Rp (nm) Example 1 450
95 43 Example 2 450 70 32 Example 3 450 40 17 Example 4 450 20 8
Comparative 450 110 51 Example 1 Comparative 450 5 2.5 Example
2
[0117] The magneto-optical recording media thus obtained were set
on a glide tester, and the glide head with a piezo element
(manufactured by Glide Right Company: 70% slider, 0.012".times.6.0
gr., slider portion: 0.305.times.2.84 mm) was moved in a range of
27.0-62.0 mm in radius while it was rotated at a linear velocity of
7.5 m/s. The flying height of the glide head was 0.05 .mu.m at the
linear velocity of 7.5 m/s.
[0118] In the movement of the glide head, the voltage induced in
the piezo element was observed by an oscilloscope. In this case, a
voltage value exceeding 800 mV was counted in the judgment that
there was the contact (hit) to the recording medium.
[0119] The above-mentioned measurement was conducted for each 10
magneto-optical recording media of comparative Example 1 and
Examples 1-4 to measure the number of hits. Table 2 shows average
values of each 10 media as result.
[0120] In Comparative Example 1 having a groove depth of 110 nm in
which the depth Rp at the center showed 51 nm which exceeded the
flying height H, flaws recognizable by naked eyes generated in a
string form over the entire circumference of the media, and the
counted number of hits was very large.
[0121] In Example 1 having a depth Rp at the center of 43 nm which
was lower than the flying height H, string-like flaws were short
and light in degree, and the number of hits was small, whereby the
flying characteristics of the head could be maintained.
[0122] In Example 2 in which the depth Rp at the center was 0.64
times as much as the flying height H, Example 3 in which it was
0.34 times and Example 4 in which it was 0.16 times, no flaw was
recognized in the media, and excellent flying characteristics were
shown.
[0123] Further, in Comparative Example 2 in which the depth Rp at
the center was 0.05 times of the flying height H too, no flaw was
recognized in the media and excellent flying characteristics were
shown.
[0124] Next, to each 5 magneto-optical recording media of Examples
1-4 and comparative Example 2 for which the flying characteristics
were confirmed by the glide tester, the recording/reproducing
characteristics were evaluated by a recording/reproducing
evaluation device of an optical system of SIL head having a laser
wavelength of 680 nm and an effective NA of 1.2.
[0125] Table 2 shows average values of 5 media as result.
2 TABLE 2 Number of hits Flaw CNR (dB) Example 1 8 Slight 32.0
Example 2 3 Nil 45.1 Example 3 1 Nil 47.2 Example 4 0 Nil 48.5
Comparative 286 Large Example 1 Comparative 4 Nil Inmeasurable
Example 2
[0126] In Example 1, the carrier-noise ratio (CNR) was low.
However, excellent CNR was obtained in Examples 2, 3 and 4. On the
other hand, in the disks of Comparative Example 2, the tracking of
the SIL head was out, so that the measurement of the
recording/reproducing characteristics was impossible.
Example 5
[0127] A circular substrate of polycarbonate having a diameter of
130 mm with a guide groove having a track pitch of 0.43 .mu.m was
formed by injection-molding to prepare an optical recording medium
as shown in FIG. 2. Namely, on the substrate, an AlCr alloy having
a layer thickness of 50 nm was formed as a reflective layer by DC
sputtering method. Further, as a recording layer, TbFeCo having a
layer thickness of 20 nm was formed by DC sputtering method. On
this, as a dielectric layer, SiN having a layer thickness of 50 nm
was formed by a reactive DC sputtering method using a Si target in
an atmosphere of a mixture of Ar and N.sub.2. On this, further, as
a solid lubricant layer, diamond-like carbon (DLC) having a layer
thickness of 20 nm was formed by a reactive RF sputtering method
using a C target in an atmosphere of a mixture of Ar and CH.sub.4
to prepare a near-field magneto-optical recording medium.
Example 6
[0128] A near-field magneto-optical recording medium was prepared
by the same method as in Example 5 except that the layer thickness
of SiN was 200 nm and the partial pressure of N.sub.2 was 1.2 Pa in
laminating the SiN dielectric layer on the recording layer.
Example 7
[0129] A near-field magneto-optical recording medium was prepared
by the same method as in Example 5 except that as a liquid
lubricating layer, a perfluoropolyether type lubricant ("Fomblin
ZDOL2000" (tradename) manufactured by Ausimont Company) was formed
in a thickness of 0.5 nm on the solid lubricant layer.
Example 8
[0130] A near-field magneto-optical recording medium was prepared
by the same method as in Example 5 except that in laminating the
SiN dielectric layer on the recording layer, the layer thickness of
SiN was 200 nm and the partial pressure of N.sub.2 was 1.2 Pa, and
as a liquid lubricant layer, a perfluoropolyether type lubricant
("Fomblin ZDOL2000" (tradename) manufactured by Ausimont Company)
was formed in a thickness of 3.0 nm on the solid lubricant
layer.
Comparative Example 3
[0131] A near-field magneto-optical recording medium was prepared
by the same method as in Example 5 except that in laminating the
SiN dielectric layer on the recording layer, the layer thickness of
SiN was 30 nm and the partial pressure of N.sub.2 was 0.4 Pa.
Comparative Example 4
[0132] A near-field magneto-optical recording medium was prepared
by the same method as in Example 5 except that in laminating the
SiN dielectric layer on the recording layer, the layer thickness of
SiN was 250 nm and the partial pressure of nitrogen gas was 1.4
Pa.
[0133] On the near-field magneto-optical recording media in
Examples 5-8 and Comparative Examples 3-4, the following evaluation
was conducted. Before the liquid lubricant was laminated on the
solid lubricant layer, the surface roughness Ra on the centerline
of the land portion and the groove portion at 3 points of 30, 40
and 50 mm of radial position of the recording media was measured by
an atomic force microscope (manufactured by Seiko Electronics), and
the Ra values of the recording media were determined based on
average values of 3 points of radial position of each of the land
portion and the groove portion. With respect to the recording media
on which the liquid lubricant was laminated, the layer thickness of
the liquid lubricant was calculated based on C1s spectrum at 3
points of 30, 40 and 50 mm of radial position by ESCA (manufactured
by Perkin-Elmer Company), and the layer thickness of the recording
media was determined by each average value of 3 points of radial
position. Further, each recording medium was rotated at 2400 per
minute to fly by dynamic loading a flying SIL head with a slider
having a laser wavelength of 680 nm and an effective numerical
aperture of 1.2 on its thin layer in a height of 100 nm above the
recording medium. Recording was conducted by irradiating pulsating
laser while the recording layer was heated to the Curie temperature
or more and a magnetic field by the coil in the SIL head was
modulated with 10 MHz. SNR recorded with 10 MHz was measured at 3
points of 30, 40 and 50 mm of radial position and SNR of the
recording medium was determined based on the average value.
[0134] The SNR value was obtained by measuring under the condition
that SNR became the maximum by adjusting the power for reproducing
on each medium. Successively, long-time seek tests were conducted
with the flying SIL having a slider. Each recording medium was set
on the spindle of a drive and it was rotated at 2400 per minute.
The SIL head was dynamic-loaded to fly it in a flying height of 100
nm above the recording medium and continuous seek was conducted for
2 hours at 7 Hz over a range of 30-50 mm in radius. After the seek
tests were finished, the SIL head was unloaded and the surface of
the slider of the head and the surface of the lens were observed.
In the observation, an optical microscope was used. A result of
evaluation is summarized in Table 3.
3 TABLE 3 Centerline mean Layer roughness Ra thickness (nm) of
liquid Result of Land Groove lubricant SNR observation of portion
portion (mm) (dB) SIL head Example 1 0.32 0.36 -- 25.1 No
deposition of foreign matter Example 2 1.85 1.90 -- 24.6 No
deposition of foreign matter Example 3 0.32 0.36 0.54 25.4 No
deposition of foreign matter Example 4 0.85 1.90 3.02 25.0 No
deposition of foreign matter Compara- 0.10 0.13 -- 25.3 Flake-like
tive foreign matter Example 1 on the surface of slider and lens
Compara- 2.37 2.44 -- 19.7 No deposition tive of foreign Example 2
matter
[0135] In Examples 5 and 6, the centerline mean roughness Ra of
each recording medium was in a range of 0.2 nm.ltoreq.Ra.ltoreq.2.0
nm, and in Examples 7 and 8, the centerline mean roughness Ra of
each recording medium was in a range of 0.2 nm.ltoreq.Ra.ltoreq.2.0
nm. Thus, the layer thickness t of the liquid lubricant satisfied
t.ltoreq.2Ra. SNR, in this case, respectively exceeded 24 dB to
show a sufficient SNR. In the observation of the SIL head after the
seek tests, there was no deposition of foreign matter or the liquid
lubricant on either the slider portion or the lens portion, and it
was found that the SIL head flied stably in the seek tests.
[0136] In Comparative Example 3, since Ra was small as 0.1 nm, SNR
showed a sufficiently high value as 25 dB. However, there was found
that a large number of flake-like foreign matters deposited on the
slider portion and the lens portion of the SIL head in the seek
tests, and the SIL head had frequently contacted the recording
medium during the flying.
[0137] In Comparative Example 4, SNR is only about 20 dB. The
reason is that Ra is too large because the noise level is high. In
the seek tests, there is no deposition of foreign matter or the
liquid lubricant on either the slider portion or the lens portion,
and it is found that the SIL head flies stably in the seeking
tests.
Example 9 and Comparative Example 5
[0138] On each disk-like substrate of polycarbonate having a
diameter of 130 mm in which a helical guide groove having a track
pitch of 0.45 .mu.m and a depth of 85 nm was formed, a reflective
layer of Al.sub.0.97Cr.sub.0.03 having a layer thickness of 50 nm
was formed by a DC sputtering method; a magneto-optical recording
layer of Tb.sub.20(Fe.sub.90Co.sub.10).sub.80 having a layer
thickness of 20 nm was formed by the DC sputtering method on this;
a dielectric layer of SiN having a layer thickness of 30 nm was
formed by a reactive RF sputtering method on this layer, and a
solid lubricant layer of diamond-like carbon having a layer
thickness of 20 nm was formed by the reactive RF sputtering method
on this layer.
[0139] After the formation of the solid lubricant layer, the depth
of the groove was measured by an atomic force microscope (AFM) to
find 94 nm.
[0140] Then, the media were immersed in a solution of
perfluoropolyether ("Fomblin ZDOL-2000" (tradename) manufactured by
Ausimont Company), which had a weight average molecular weight of
2400 and which had hydroxyl groups at both terminals of the
molecule, dissolved in a perfluoropolyether type solvent ("GALDEN
SV-70" (tradename) manufactured by Ausimont Company). By lifting up
the media, a liquid lubricant layer was formed on each of the
media. Thus, magneto-optical recording media were manufactured.
[0141] In the preparation of the magneto-optical recording media,
the layer thickness of the lubricant was changed to 0.5, 1.0 and
1.5 nm in Example, and the layer thickness of the lubricant layer
was changed to 0.2 and 2.5 nm in Comparative Example 5 by changing
the concentration of the solvent. The layer thickness of the
lubricant layers was measured by an X-ray photo-electron spectral
analyzing system (XPS).
[0142] Surface analysis was conducted on -CF.sub.2CH.sub.2OH
fragment ions (81 amu) in a state of dispersion of the lubricant on
the surface of each medium by using TOF-SIMS. In the measurement of
an agglomerated state of the lubricant, it was found that the
diameter was 0.3 .mu.m.
[0143] The magneto-optical recording media thus obtained were set
on a glide tester, and the glide head with a piezo element
(manufactured by Glide Right Company: 70% slider, 0.012".times.6.0
gr, slider portion: 0.305.times.2.84 mm) was moved in a range of
30-60,mm in radius while it was rotated at a linear velocity of 7.5
m/s to evaluate the glide characteristics. The flying height of the
glide head was 0.05 .mu.m at the linear velocity of 7.5 m/s. In the
seeking of the glide head, a voltage induced in the piezo element
was observed by an oscilloscope. The case that a voltage value
exceeds 800 mV was judged as the contact of the head to the medium,
and the number of times of contact was recorded.
[0144] Measurement was conducted for each 10 media. As a result, in
the magneto-optical recording media having a lubricant layer
thickness of 0.5, 1.0 and 1.5 nm in Example 9, the number of times
of contact was within 2 times, and the proportion of the media
having zero contact was excellent as 60% or more. In the
magneto-optical medium having a lubricant layer thickness of 0.2 nm
in Comparative Example 5, the number of times of contact was about
5 in average.
[0145] Then, the magneto-optical recording media having a lubricant
layer thickness of 1.0, 1.5 and 2.5 nm were set on a
recording/reproducing evaluation device of an optical system of a
near-field recording head having a laser wavelength of 680 nm and
an effective NA of 1.2, and evaluation was conducted on the
recording/reproducing characteristics. Recording was conducted to
the media by rotating the media at a linear velocity of 7.0 m/s,
irradiating laser adjusted so that the power was 6.0 mW in front of
the objective lens, and applying a magnetic field modulated to be
.+-.150 Oe at a frequency of 7.0 MHz from the coil of SIL head.
Then, reproducing was conducted by irradiating laser adjusted so
that the power was 1.0 mW in front of the objective lens.
[0146] In any of the media having the lubricant layer thickness of
1.0, 1.5 and 2.5 nm, CNR was 48 dB. However, when the
above-mentioned recording and reproducing were repeated 10 times on
the same track, no change of CNR was recognized in the media having
the lubricant layer thickness of 1.0 nm and 1.5 nm in Example 9,
but in the medium having the lubricant layer thickness of 2.5 nm in
Comparative Example 5, CNR decreased to 35 dB. The cause was
examined to find that the surface of the lens of SIL head was
stained in a dark color.
Example 10 and Comparative Example 6
[0147] Magneto-optical recording media were prepared by the same
method as in Example 9 except that substrates of polycarbonate in
which a helical guide groove having a track pitch of 0.35 .mu.m and
a depth of 120 nm was formed were used.
[0148] The depth of the groove after the formation of the solid
lubricant layer was measured to find 142 nm.
[0149] The magneto-optical recording media were prepared by
changing the layer thickness of the lubricant layer to 1.0 and 1.5
nm in Example 10 by changing the concentration of the solvent in
coating the lubricant layer, and in Comparative Example 6, the
layer thickness of the lubricant layer was 2.5 nm.
[0150] The diameter of the lubricant in an agglomerated state
measured by TOF-SIMS was 0.25 .mu.m.
[0151] Evaluation was made on the glide characteristics of the thus
obtained magneto-optical recording media by the same method as in
Example 9.
[0152] As a result of conducting the measurement for each 10 media,
the number of times of contact was within 3 times, and the
proportion of media having zero contact was excellent as 50%.
[0153] Then, evaluation was made on the recording/reproducing
characteristics of the media by the same method as in Example
9.
[0154] CNR was 44 dB in all media. When the above-mentioned
recording/reproducing were repeated 10 times on the same track, no
change of CNR was recognized in the media having the lubricant
layer thickness of 1.0 nm and 1.5 nm in Example 10, but in the
medium having the layer thickness of 2.5 nm in Comparative Example
6, CNR decreased to 30 dB. The cause was examined to find that the
surface of the lens of the optical lens was stained.
Example 11
[0155] Magneto-optical recording media were prepared by the same
method as in Example 9 except that substrates of polycarbonate in
which a helical guide groove having a track pitch of 0.45 .mu.m and
a depth of 150 nm was formed were used.
[0156] The depth of the groove after the formation of the solid
lubricant layer was measured to find 164 nm. In this case, the
layer thickness of the lubricant layer was changed to 0.5, 1.0 and
1.5 by changing the concentration of the solvent.
[0157] The diameter of the lubricant in an agglomerated state of
the thus prepared magneto-optical recording media measured by
TOF-SIMS was 0.2 .mu.m.
[0158] Evaluation was made on the glide characteristics of the thus
obtained magneto-optical recording media by the same method as in
Example 9.
[0159] Measurement was conducted for each 10 media. As a result,
the number of times of contact slightly increased in comparison
with Examples 9 and 10. However, the number was within 5 times in
all media, and the proportion of the media of zero contact was
15%.
Comparative Example 7
[0160] Magneto-optical recording media were prepared by the same
method as in Example 9 except that substrates of polycarbonate
having no guide groove were used.
[0161] In this case, the layer thickness of the lubricant layer was
changed to 0.5, 1.0, 1.5 and 2.5 nm by changing the concentration
of the solvent.
[0162] In the measurement of the agglomerated state of the
lubricant on the media having no guide groove by TOF-SIMS, the
state of dispersion changed depending on the layer thickness of the
lubricant: 15 .mu.m in the layer thickness of 0.5 nm; 18 .mu.m in
the layer thickness of 1.0 nm; 25 .mu.m in the layer thickness of
1.5 nm and 37 .mu.m in the layer thickness of 2.5 nm.
[0163] The optical head was floated above the thus obtained
magneto-optical recording media for a time corresponding to 10
times of the number of times of recording/reproducing. The state of
the surface of the optical head was observed. As a result, a stain
deposited on the surface of the lens of the optical head for all
the disks.
Example 12
[0164] On each disk-like substrate of polycarbonate having a
diameter of 130 mm in which a guide groove having a track pitch of
0.45 .mu.m was formed, a reflective layer of Al.sub.0.97Cr.sub.0.03
having a layer thickness of 50 nm was formed by a DC sputtering
method; a magneto-optical recording layer of
Tb.sub.20(Fe.sub.90Co.sub.10).sub.80 having a layer thickness of 20
nm was formed by the DC sputtering method on the reflective layer;
a dielectric layer of SiN having a layer thickness of 30 nm was
formed by a reactive RF sputtering method on the recording layer,
and further, a solid lubricant layer of diamond-like carbon having
a layer thickness of 20 nm was formed by the reactive RF sputtering
method on the dielectric layer.
[0165] Then, these media were immersed for 1 minute in a solution
(0.1 vol. %) of perfluoropolyether ("Fomblin Z DEAL" (tradename)
manufactured by Ausimont Company), which had a weight average
molecular weight of 2000 and which had ester groups at both
terminals of the molecule, dissolved in a perfluoropolyether type
solvent ("GALDEN SV-70" (tradename) manufactured by Ausimont
Company). Then, the media were lifted up and they were again
immersed in the perfluoropolyether type solvent ("GALDEN SV-70"
(tradename) manufactured by Ausimont Company) for 1 minute. By
lifting up the magneto-optical recording media again, a lubricant
layer having a layer thickness of 2 nm was formed. Thus, the
magneto-optical recording media were prepared. The thus prepared
magneto-optical recording media were immersed in the
perfluoropolyether type solvent ("GALDEN SV-70" (tradename)
manufactured by Ausimont Company) for 1 minute and the media were
lifted up. In the measurement of the layer thickness of the
lubricant layer, the layer thickness was 1.4 nm and the ratio of
the remaining layer was 70%.
[0166] Then, the prepared magneto-optical recording media were set
on a glide tester, and the glide head with a piezo element
(manufactured by Glide Right Company: 70% slider, 0.012".times.6.0
gr) was moved for seeking in a range of 30-60 mm in radius while
the media were rotated at a linear velocity of 7.5 m/s to evaluate
the glide characteristics. The flying height of the glide head was
0.05 .mu.m at the linear velocity of 7.5 m/s.
[0167] A voltage induced in the piezo element in the seeking by the
glide head was observed by an oscilloscope. The time at which a
voltage value exceeded 800 mV was judged as the head contacted the
media, and the number of times of contact was recorded.
[0168] Measurement was conducted on 10 magneto-optical recording
media in total prepared by the above-mentioned method. As a result,
the number of times of contact was within 5 in respective media,
and the proportion of the media of zero contact was excellent as
70% or more.
[0169] Then, these media were set on a recording/reproducing
evaluation device of an optical system of SIL having a laser
wavelength of 680 nm and an effective NA of 1.2 to evaluate the
recording/reproducing characteristics. Recording was conducted to
the media by rotating each medium at a linear velocity of 7.0 m/s
and irradiating laser adjusted so that the power was 6.0 mW in
front of the objective lens while a magnetic field modulated to be
a magnitude of .+-.150 Oe at a frequency of 7.0 MHz was applied
from the coil of SIL head. Next, reproducing was conducted by
irradiating laser adjusted so that the power was 1.0 mW in front of
the objective lens.
[0170] CNR was 43 dB, and no change of CNR was recognized in a case
that similar recording and reproducing were repeated 10 times on
the same track.
Example 13
[0171] Layers were laminated up to the solid lubricant layer by the
same method as in Example 12. Then, magneto-optical recording media
were immersed for 1 minute in a solution (0.1 vol. %) of
perfluoropolyether ("DEMNUM SP" (tradename) manufactured by Daikin
Company), which had a weight average molecular weight of 3200 and
which had an ester group at one terminal of the molecule, dissolved
in a perfluoropolyether type solvent ("GALDEN SV-70" (tradename)
manufactured by Ausimont Company). The media were lifted up and
they were again immersed for 1 minute in the perfluoropolyether
type solvent ("GALDEN SV-70" (tradename) manufactured by Ausimont
Company). By lifting up the media, a lubricant layer having a layer
thickness of 2 nm was formed. Thus, magneto-optical recording media
were prepared.
[0172] The thus obtained media were immersed in the
perfluoropolyether type solvent ("GALDEN SV-70" (tradename)
manufactured by Ausimont Company) for 1 minute. After the media
were lifted up, the layer thickness of the lubricant layer was
measured. The layer thickness was 1.6 nm and the proportion of the
remaining layer thickness was 80%.
[0173] Then, evaluation was made as to the glide characteristics of
the thus obtained magneto-optical recording media by the same
method as in Example 12.
[0174] Measurement was conducted to 10 magneto-optical recording
media prepared by the same method as described above. As a result,
the number of times of contact was within 3 in all the media, and
the proportion of the media of zero contact was excellent as
80%.
[0175] Subsequently, on the recording/reproducing characteristics
of the magneto-optical recording media, evaluation was made by the
same method as in Example 12.
[0176] CNR was 43 dB, and no change of CNR was recognized even in a
case that the same recording and reproducing were repeated 10 times
on the same track.
Comparative Example 8
[0177] Layers were laminated up to the solid lubricant layer by the
same method as in Example 12 to prepare magneto-optical recording
media without forming any lubricant layer thereafter.
[0178] Evaluation was made by the same method as in Example 12 on
the glide characteristics of the thus obtained magneto-optical
recording media. Noises generated in the seeking, and thin flaws
were partly produced in the surface of the disks after the
seeking.
Comparative Example 9
[0179] Layers were laminated up to the solid lubricant layer by the
same method as in Example 12. Then, the media were immersed for 1
minute in a solution (0.06 vol. %) of perfluoropolyether ("Fomblin
Z DEAL" (tradename) manufactured by Ausimont Company), which had a
weight average molecular weight of 2000 and which had ester groups
at both terminals of the molecule, dissolved in a
perfluoropolyether type solvent ("GALDEN SV-70" (tradename)
manufactured by Ausimont Company). By lifting up the media, a
lubricant layer of a layer thickness of 2 nm was formed. Thus,
magneto-optical recording media were prepared.
[0180] The thus obtained media were immersed in the
perfluoropolyether type solvent ("GALDEN SV-70" (tradename)
manufactured by Ausimont Company) for 1 minute. After the media
were lifted up, the layer thickness of the lubricant layer was
measured. The layer thickness was 0.8 nm, and the proportion of the
remaining layer thickness was 40%.
[0181] Evaluation was made by the same method as in Example 12 on
the glide characteristics of the magneto-optical recording
media.
[0182] Measurement was conducted on 10 magneto-optical recording
media. As a result, the number of times of contact. was within 4 in
all media, and the proportion of the media of zero contact was
excellent as 70%.
[0183] Subsequently, on the recording/reproducing characteristics
of the magneto-optical recording media, evaluation was made by the
same method as in Example 12.
[0184] CNR was 43 dB. However, when similar recording/reproducing
were repeated 10 times on the same track, CNR decreased to 38 dB.
The cause was examined to find that the lubricant deposited on the
lens surface of SIL head turned to a dark color.
Comparative Example 10
[0185] Layers are laminated up to the solid lubricant layer by the
same method as in Example 12. Then, the media were immersed for 1
minute in a solvent (0.06 vol. %) of perfluoropolyether ("Fomblin
AM2001" (tradename) manufactured by Ausimont Company), which had a
weight average molecular weight of 2400 and which had piperonyl
groups at both terminals of the molecule, dissolved in a
perfluoropolyether type solvent ("GALDEN SV-70" (tradename)
manufactured by Ausimont Company). By lifting up the media, a
lubricant layer of a layer thickness of 2 nm was formed. Thus,
magneto-optical recording media were prepared.
[0186] The thus obtained media were immersed in a
perfluoropolyether type solvent ("GALDEN SV-70" (tradename)
manufactured by Ausimont Company) for 1 minute. The media were
lifted up and the layer thickness of the lubricant layer was
measured. The layer thickness was 1.0 nm, and the proportion of the
remaining layer thickness was 50%.
[0187] Then, evaluation was made by the same method as in Example
12 on the magneto-optical recording media.
[0188] Measurement was conducted on 10 magneto-optical recording
media. As a result, the number of times of contact was within 10
times in all media, and the proportion of the media of zero contact
was excellent as 60%.
[0189] Subsequently, evaluation was made on the
recording/reproducing characteristics of the magneto-optical
recording media by the same method as in Example 12.
[0190] CNR was 43 dB. However, when the similar recording and
reproducing were repeated 10 times on the same track, CNR decreased
to 35 dB. The cause was examined to find that the lubricant adhered
on the lens surface of SIL head turned to a dark color.
Example 14
[0191] On each disk-like substrate of polycarbonate having a
diameter of 130 mm in which a guide groove having a track pitch of
0.45 .mu.m was formed, a reflective layer of Al.sub.0.97Cr.sub.0.03
having a layer thickness of 50 nm was formed by a DC sputtering
method. On this, a magneto-optical recording layer of
Tb.sub.20(Fe.sub.90Co.sub.10).sub.80 having a layer thickness of 20
nm was formed by the DC sputtering method. On this, a dielectric
layer of SiN having a layer thickness of 30 nm was formed by a
reactive RF sputtering method. On this, further, a solid lubricant
layer of diamond-like carbon having a layer thickness of 20 nm was
formed by the reactive RF sputtering method.
[0192] Then, the media were immersed for 1 minute in a solution
(0.01 vol. %) of perfluoropolyether ("Fomblin ZDOL4000" (tradename)
manufactured by Ausimont Company), which had a weight average
molecular weight of 4000 and which had --CH.sub.2OH at both
terminals of the molecule, dissolved in a perfluoropolyether type
solvent ("GALDEN SV-70" (tradename) manufactured by Ausimont
Company). By lifting up the media, 10 magneto-optical recording
media on which a lubricant layer having a layer thickness of 1 nm
was formed, were prepared.
[0193] In the measurement of the contact angle of water to the
surface of the thus obtained magneto-optical recording media, the
contact angle was 80.degree..
[0194] Then, these media were put in an environmental tester and
left for 1000 hours under environmental conditions of 80.degree. C.
and 85% RH. In the observation of 10 media taken, no abnormality
was recognized on the layer plane in all media.
Example 15
[0195] 10 Magneto-optical recording media were prepared by
laminating layers up to the solid lubricant layer by the same
method as in Example 14, and then, forming a lubricant layer having
a layer thickness of 5 .mu.m by spin-coating a fluorine type
polymer solution ("Cytop CTX809A" (tradename) manufactured by Asahi
Glass Company, Limited) on the media.
[0196] In the measurement of the contact angle of water to the
surface of the thus obtained media, the contact angle was
120.degree..
[0197] Then, these media were put in an environmental tester and
left for 1000 hours under environmental conditions of 80.degree. C.
and 85% RH. In the observation of 10 media taken, no abnormality
was recognized on the layer plane in all media.
Comparative Example 11
[0198] 10 Magneto-optical recording media were prepared by
laminating layers up to the solid lubricant layer by the same
method as in Example 14. The contact angle of water to the surface
of the recording media was measured. The contact angle was
50.degree..
[0199] Then, these media were put in an environmental tester and
left for 1000 hours under environmental conditions of 80.degree. C.
and 85% RH. In the observation of 10 media taken, a corroded
portion was recognized in the layer plane of all media.
Comparative Example 12
[0200] 10 Magneto-optical recording media were prepared by
laminating layers up to the solid lubricant layer by the same
method as in Example 14; immersing for 1 minute the media in a
solution (0.004 vol. %) of perfluoropolyether ("Fomblin ZDOL4000"
(tradename) manufactured by Ausimont Company), which had a weight
average molecular weight of 4000 and which had -CH.sub.2OH at both
terminals of the molecule, dissolved in a perfluoropolyether type
solvent ("GALDEN SV-70" (tradename) manufactured by Ausimont
Company), and lifting up the media to form a lubricant layer having
a layer thickness of 0.3 nm.
[0201] The contact angle of water to the surface of the thus
obtained magneto-optical recording media was measured. The contact
angle was 65.degree..
[0202] Then, the media were put in an environmental tester and left
for 1000 hours under environmental conditions of 80.degree. C. and
85% RH. In the observation of 10 media taken, a corroded portion
was recognized on the layer plane in 8 media.
Example 16
[0203] On disk-like substrates of polycarbonate having a diameter
of 130 mm in which a guide groove having a track pitch of 0.45
.mu.m was formed, a reflective layer of Al.sub.0.97Cr.sub.0.03
having a layer thickness of 50 nm was formed by a DC sputtering
method. On this, a recording layer of
Tb.sub.20(Fe.sub.90Co.sub.10).sub.80 having a layer thickness of 20
nm was formed by the DC sputtering method. On this, a dielectric
layer of SiN having a layer thickness of 30 nm was formed by a
reactive RF sputtering method.
[0204] Then, by spin-coating a fluorine-type polymer solution
("Cytop CTX809A" (tradename) manufactured by Asahi Glass Company,
Limited) on the media, 10 magneto-optical recording media with a
lubricant layer having a layer thickness of 5 .mu.m were
prepared.
[0205] The thus obtained magneto-optical recording media were set
on a glide tester, and the glide head with a piezo element
(manufactured by Glide Right Co.: 70% slider, 0.012".times.6.0 gr)
was moved for seeking in a range of 30-60 mm in radius while the
media were rotated at a linear velocity of 7.5 m/s to evaluate the
glide characteristics. The flying height of the glide head was 0.05
.mu.m at the linear velocity of 7.5 m/s. The voltage induced in the
piezo element in the seeking by the glide head was observed by an
oscilloscope. The time at which a voltage value exceeded 800 mV was
judged as the head contacted the media, and the number of times was
recorded.
[0206] Measurement was conducted on 10 magneto-optical recording
media. As a result, the number of times of contact was excellent as
within 30 times in respective media.
[0207] Then, these media were set on a recording/reproducing
evaluation device of an optical system of SIL having a laser
wavelength of 680 nm and an effective NA of 1.2 to evaluate the
recording/reproducing characteristics. Recording was conducted to
the media by rotating each medium at a linear velocity of 7.0 m/s
and irradiating laser adjusted so that the power was 6.0 mW in
front of the objective lens while a magnetic field modulated to be
a magnitude of .+-.150 Oe at a frequency of 7.0 MHz was applied
from the coil of SIL head. Then, reproducing was conducted by
irradiating laser adjusted so that the power was 1.0 mW in front of
the objective lens.
[0208] CNR was 42 dB, and no change of CNR was recognized even in a
case that similar recording and reproducing were repeated 10 times
on the same track.
Example 17
[0209] Layers were laminated up to the dielectric layer by the same
method as in Example 16. Then, media were immersed for 1 minute in
a solution (0.1 vol. %) of a fluorine type polymer ("Teflon AF1600"
(tradename) manufactured by Du Pont), dissolved in a fluorine type
solvent ("Fluorinert FC-75" (tradename) manufactured by Sumitomo
3M). By lifting up the media, magneto-optical recording media with
a lubricant layer having a layer thickness of 10 nm were
prepared.
[0210] The glide characteristics of the thus obtained
magneto-optical recording media were evaluated by the same method
as in Example 16. The number of times of contact was excellent as
within 20.
[0211] Then, the recording/reproducing characteristics of these
media were evaluated by the same method as in Example 16.
[0212] CNR was 43 dB, and no change of CNR was recognized even in a
case that the same recording and reproducing were repeated 10 times
on the same track.
Comparative Example 13
[0213] Layers were laminated up to the dielectric layer by the same
method as in Example 16. Then, magneto-optical recording media were
produced without forming a lubricant layer.
[0214] The glide characteristics of the thus obtained
magneto-optical recording media were evaluated by the same method
as in Example 16. At the time of initiating seeking, the head
contacted severely the media to generate noises. Accordingly, it
was impossible to evaluate on the entire surface.
Comparative Example 14
[0215] Layers were laminated up to the dielectric layer by the same
method as in Example 16. Then, an acrylic type overcoating agent
("Daicure Clear SD-318" (tradename) manufactured by DAINIPPON INK
AND CHEMICALS, INC.) was spin-coated on the media followed by
irradiating UV to form a lubricant layer having a layer thickness
of 5 .mu.m. Thus, magneto-optical recording media were
prepared.
[0216] The glide characteristics of the thus obtained
magneto-optical recording media were evaluated by the same method
as in Example 16. The number of times of contact was within 50 in
all media.
[0217] Then, evaluation was made on the recording/reproducing
characteristics of these media by the same method as in Example 16.
Although CNR was 42 dB, CNR decreased to 20 dB when the same
recording/reproducing were repeated 10 times on the same track. The
cause was examined to find that the color in the medium surfaces in
the portion to which recording/reproducing were conducted,
changed.
Example 18
[0218] On disk-like substrates of polycarbonate having a diameter
of 130 mm in which a guide groove having a track pitch of 0.45
.mu.m was formed, a reflective layer of Al.sub.0.97Cr.sub.0.03
having a layer thickness of 50 nm was formed by a DC sputtering
method. On this, a recording layer of
Tb.sub.20(Fe.sub.90Co.sub.10).sub.80 having a layer thickness of 20
nm was formed by the DC sputtering method. On this, a dielectric
layer of SiN having a layer thickness of 30 nm was formed by a
reactive RF sputtering method.
[0219] Then, 10 magneto-optical recording media with a lubricant
layer having a layer thickness of 1 .mu.m were prepared by
spin-coating on these media a fluorine-type polymer solution
("Cytop CTX809A" (tradename) manufactured by Asahi Glass Company,
Limited) added with 0.1 vol. % of perfluoropolyether ("Fomblin Z
DEAL" (tradename) manufactured by Ausimont Company) which had a
weight average molecular weight of 2000 and which had ester groups
at both terminals of the molecule.
[0220] The transmittance of light of the lubricant layer in a case
that the lubricant layer having a layer thickness of 1 .mu.m was
formed on a substrate of quartz was 95% or more in a range of a
wavelength from 300 to 1000 nm.
[0221] The glide characteristics of the thus obtained
magneto-optical recording media were evaluated by the same method
as in Example 16. The flying height of the glide head was 0.05
.mu.m at a linear velocity of 7.5 m/s.
[0222] As a result of measuring the 10 magneto-optical recording
media, the number of times of contact was within 5 in all media,
and the proportion of the media in terms of the number of times of
contact was excellent as 80% or more.
[0223] Then, the recording/reproducing characteristics of these
media were evaluated in the same manner as in Example 16. CNR was
43 dB, and no change of CNR was recognized even in a case that the
same recording/reproducing were repeated 10 times on the same
track.
Example 19
[0224] Layers were laminated up to the dielectric layer by the same
method as in Example 18. Then, media was immersed for 1 minute in a
solution obtained by dissolving 0.1 vol. % of a fluorine type
polymer solution ("Teflon AF1600" (tradename) manufactured by Du
Pont) added with 0.01 vol. % of perfluoropolyether (Fomblin Z DOL"
(tradename) manufactured by Ausimont Company) which had an weight
average molecular weight of 2000 and which had alcohol groups at
both terminals of the molecule, by a fluorine type solvent
("Fluorinert FC-75" (tradename) manufactured by Sumitomo 3M). By
lifting up the media, magneto-optical media with a lubricant layer
having a layer thickness of 10 nm were prepared.
[0225] The glide characteristics of the thus obtained
magneto-optical recording media were evaluated by the same method
as in Example 16. As a result of conducting the measurement to 10
magneto-optical media, the number of times of contact was within 6
in all media, and the proportion of media having 0-contact was
excellent as 70%.
[0226] Then, the recording/reproducing characteristics of these
media were evaluated by the same method as in Example 16. CNR was
43 dB, and no change of CNR was recognized even in a case that the
same recording/reproducing were repeated 10 times on the same
track.
Example 20
[0227] circular substrates of polycarbonate having a diameter of
130 mm which had spiral land/groove portions having a track pitch
of 0.43 .mu.m and a header portion in both front and rear surfaces
were prepared by injection-molding. By a stamper used in this case,
the depth of the groove in each substrate in a region of 20-60 mm
in radius excluding the header portion was 90 nm and concave pits
having a depth of 90 nm were arranged in the header portion.
[0228] On both front and rear surfaces of the substrates, a
reflective layer, a recording layer, a dielectric layer and a solid
lubricant layer were laminated in this order. As the reflective
layer, AlCr alloy having a layer thickness of 50 nm was laminated
by a DC sputtering method. Further, as the recording layer, TbFeCo
having a layer thickness of 20 nm was laminated by the DC
sputtering method. On this, as the dielectric layer, SiN having a
layer thickness of 50 nm was laminated by a reactive DC sputtering
method using a Si target in an atmosphere of a mixture of Ar and
N.sub.2. On this, further, diamond-like carbon (DLC) having a layer
thickness of 20 nm was laminated as the solid lubricant layer by
the reactive RF sputtering method using a C target in an atmosphere
of a mixture of Ar and CH.sub.4. Thus, double-side recordable
magneto-optical recording media were prepared.
Example 21
[0229] Circular substrates of polycarbonate having a diameter of
130 mm which had spiral land/groove portions having a track pitch
of 0.43 .mu.m and a header area in both front and rear surfaces
were prepared by injection-molding. By a stamper used in this case,
the depth of the groove in each substrate in a region of 20-60 mm
in radius excluding the header was 90 nm, and an arc-like groove
having a depth of 90 nm was formed in the header area.
[0230] In both front and rear surfaces of the substrates, a
reflective layer, a recording layer, a dielectric layer and a solid
lubricant layer were laminated in this order. As the reflective
layer, AlCr alloy having a layer thickness of 50 nm was laminated
by a DC sputtering method. As the recording layer, TbFeCo having a
layer thickness of 20 nm was laminated by the DC sputtering method.
On this, as the dielectric layer, SiN having a layer thickness of
50 nm was laminated by a reactive DC sputtering method using a Si
target in an atmosphere of a mixture of Ar and N.sub.2. Further on
this, diamond-like carbon (DLC) having a layer thickness of 20 nm
was laminated as the solid lubricant layer by the reactive RF
sputtering method using a C target in an atmosphere of a mixture of
Ar and CH.sub.4. Thus, magneto-optical recording media capable of
recording/reproducing at both surfaces were prepared.
Comparative Example 15
[0231] Magneto-optical recording media capable of
recording/reproducing in both surfaces were prepared by the same
method as in Example 20 except that the height of the header area
was equal to the land in both front and rear surfaces of the
substrates, and the header area had no pit and groove.
[0232] The following evaluation was conducted on one surface of
near-field magneto-optical recording media prepared by the method
described in Examples 20 and 21 and Comparative Example 15. First,
the shape of the surface in the header area and the land/groove
portions in a range of 21.5 .mu.m in radial direction, which
corresponded to 50 times of the track pitch, at 5 positions of 20,
30, 40, 50 and 60 mm in radius of the recording media was measured
by a scanning electronic microscope. Based on a result of the
measured shape, the depth Rp from the maximum height to the
centerline was calculated.
[0233] Subsequently, the flying height characteristics of the
recording media were evaluated. First, the recording media were set
on the spindle of a glide tester (manufactured by Hitachi
Electronics Engineering, Ltd.). Then, the recording media was each
rotated at a linear velocity of 7 m/sec so that the flying height
of the glide head (manufactured by Glide Right Co.) with a piezo
element (70% slider, 6.0 gr) from the recording media was 50 nm
constantly. The effective voltage values of signal outputted from
the piezo element at 5 radial positions of 20, 30, 40, 50 and 60 mm
of each recording medium were measured. Then, SNR was measured. The
recording medium was rotated 2400 per minute, and a flying type
optical head (.lambda./16 NA: 35.4 nm, .lambda./20NA: 28.3 nm) with
a slider having a laser wavelength of 680 nm and an effective
numerical aperture of 1.2 was floated at a height of 50 nm above
the thin layer surface of the recording medium by a dynamic load.
Recording was conducted while the recording layer was heated to the
Curie temperature or more by irradiating pulsed laser and the
magnetic field of the coil on the SIL head was modulated with 10
MHz. During the recording with 10 MHz, SNR was measured at 5 radial
positions of 20, 30, 40, 50 and 60 mm of the recording medium. The
values of SNR are obtained by measuring under such conditions that
SNR becomes the maximum by adjusting power in reproducing. A result
of evaluation to each medium is summarized in Table 4.
4 TABLE 4 Rp(nm) Effective Land/groove voltage value SNR Radius
(mm) Header area(Rph) portion(Rpd) Difference (mV) (dB) Example 20
20 18.2 37.6 19.4 153 25.1 30 16.5 38.3 21.8 148 25.8 40 17.3 37.7
20.4 138 25.8 50 19.1 39.8 20.7 145 25.4 60 19.3 39.9 20.6 150 25.3
.DELTA. Rp 23.4 Example 21 20 26.8 38.2 11.4 132 26.3 30 25.9 37.4
11.5 121 26.6 40 27.1 38.0 10.9 114 26.5 50 26.5 37.6 11.1 116 26.2
60 27.8 39.7 11.9 125 25.8 .DELTA. Rp 13.8 Comparative 20 1.8 38.7
36.9 379 18.7 Example 15 30 2.1 38.2 36.1 351 19.0 40 1.6 39.5 37.9
362 18.9 50 1.1 37.1 36.0 344 18.4 60 1.9 40.3 38.4 386 17.9
.DELTA. Rp 39.2
[0234] In Examples 20 and 21, the difference of Rp of the header
area and the land/groove portions at the same radial positions is
small, and accordingly, .DELTA.Rp is small as 23.4 nm (39.9-16.5
nm) and 13.8 nm (39.7-25.9 nm) in a range of 20-60 mm in radius.
Further, any value at each point in the range of 20-60 mm in a
radial direction satisfied the relation of
.vertline.Rph-Rpd.vertline..ltoreq..lambda./16NA in a flying height
of 50 nm. In Comparative Example 15, Rp became smaller in
comparison with the land/groove portions because the header area
had no pit and groove. Therefore, .DELTA.Rp did not satisfy the
relation of .DELTA.Rp.ltoreq..lambda./16NA because of 39.2 nm
(40.3-1.1 nm) in the range of 20-60 mm in radius. Further, output
signals from the piezo element indicate excellent values such as
160 mV or less in the range of 20-60 mm in radius in Examples 20
and 21, and show that the fluctuation of the flying height of the
head is small and stable flying characteristics are provided. On
the other hand, in Comparative Example 15, the voltage values
indicate that the intensity is twice or more as 340-380 mV and that
the fluctuation of the flying height of the head is large because
there is a large difference of Rp between the header area and the
land/groove portions. In evaluation of SNR, Examples 20 and 21
showed excellent results as 25-27 dB in the range of 20-60 mm in
radius. However, Comparative Examples 15 showed that noises became
large due to a fluctuation of the flying height of the head, and
SNR was low as 20 dB or less.
Example 22
[0235] A substrate of polycarbonate having a diameter of 130 mm and
a thickness of 1.2 mm was prepared by attaching stampers each
having a track pitch of 0.45 .mu.m and a depth of groove of 65 nm
in a land portion and a groove portion in the data area wherein a
header area was 42 nm lower than the land portion, at both mirror
plates of metallic dies and conducting injection-molding.
[0236] By using the substrate, a magneto-optical medium having a
double surface structure as shown in FIG. 4 was prepared by the
following method using sputtering methods.
[0237] Namely, on the substrate, an Al-3 wt % Cr alloy film (film
thickness: 50 nm) as a reflective layer was formed by DC sputtering
method. On this layer, a first dielectric layer of SiN was formed
(in a thickness of 5 nm) by a reactive RF sputtering method using a
Si target in an atmosphere of a mixture of Ar and N.sub.2. On this,
a magneto-optical recording layer of
Tb.sub.20(Fe.sub.90Co.sub.10).sub.80 was formed (in a layer
thickness of 20 nm) by DC sputtering method using simultaneously a
Tb target and a Fe.sub.90Co.sub.10 target. On this, further, a
second dielectric layer of SiN was formed (in a thickness of 30 nm)
by a reactive RF sputtering method using a Si target in an
atmosphere of a mixture of Ar and N.sub.2. On this, a DLC layer
having a refractive index of 1.85 at 633 nm was formed (in a layer
thickness of 20 nm) by a reactive RF sputtering method using a C
target in an atmosphere of a mixture of Ar and CH.sub.4.
[0238] Then, a reflective layer, a first dielectric layer, a
magneto-optical recording layer, a second dielectric layer and a
DLC layer were formed on the opposite surface in the same manner as
for the other surface.
[0239] After the formation of the DLC layer, a near-field
magneto-optical recording medium was completed by lifting up the
recording medium from a 0.01 wt % solution of piperonyl-modified
perfluoropolyether ("Fomblin:AM2001" (tradename) manufactured by
Ausimont Company) using a perfluoropolyether type solvent ("GALDEN
SV-70" (tradename) manufactured by Ausimont Company) to form a
lubricant layer having a thickness of 1.5 nm.
[0240] The layer thickness of the lubricant layer was calculated by
using an X-ray photo-electron spectral method (XPS) and observing
the ClS peak intensity.
Example 23
[0241] A substrate of polycarbonate having a diameter of 130 mm and
a substrate thickness of 1.2 mm was prepared by attaching stampers
each having a track pitch of 0.45 .mu.m and a depth of groove of 65
nm in a land and a groove in the data area wherein the header area
was 90 nm lower than the land portion at both mirror plates of
metallic dies and conducting injection-molding. Then, a near-field
magneto-optical recording medium was prepared by forming layers and
coating a lubricant agent in the same manner as Example 22.
Comparative Example 16
[0242] A substrate of polycarbonate having a diameter of 130 mm and
a thickness of 1.2 mm was prepared by attaching stampers each
having a track pitch of 0.45 .mu.m in a land portion and a groove
portion in the data area wherein there was no difference of height
between the data area and the header area at both mirror plates of
metallic dies and conducting injection-molding. Then, a near-field
magneto-optical recording medium was prepared by forming layers and
coating a lubricant agent in the same manner as Example 22.
[0243] With respect to the thus obtained near-field magneto-optical
recording disk, signals generated from the header area at the time
when the optical head entered from the data area to the header area
were observed by using a near-field magneto-optical recording
medium evaluation device having a detector divided vertically in a
beam propagating direction. As a result, signals at the time when
the optical head entered into the header area could be detected as
difference signals in the division type detector in Examples 22 and
23. However, in the disk of Comparative Example 16, any difference
signal could not be detected, and the timing of the header area
could not be obtained.
Example 24
[0244] A substrate of polycarbonate having a diameter of 130 mm and
a substrate thickness of 1.2 mm was prepared by attaching stampers
each having a track pitch of 0.45 .mu.m and a depth of groove of 65
nm in a land and a groove in the data area wherein the header area
was 30 nm higher than the land portion at both mirror plates of
metallic dies, and conducting injection-molding.
[0245] By using the substrate, layers were formed on both surfaces
of the substrate by the following method using sputtering
methods.
[0246] First, an Al-3 wt % Cr alloy layer (layer thickness: 50 nm)
as a reflective layer was formed by a DC sputtering method. On
this, a first dielectric layer of SiN was formed (in a thickness of
5 nm) by a reactive RF sputtering method using a Si target in an
atmosphere of a mixture of Ar and N.sub.2. On this, a
magneto-optical recording layer comprising
(Fe.sub.90Co.sub.10).sub.80 was formed (in a layer thickness of 20
nm) by the DC sputtering method using simultaneously a Tb target
and a Fe.sub.90Co.sub.10 target. On this, further, a second
dielectric layer of SiN was formed (in a layer thickness of 30 nm)
by a reactive RF sputtering method using a Si target in an
atmosphere of a mixture of Ar and N.sub.2. On this, a DLC layer
having a refractive index of 1.85 at 633 nm was formed (in a layer
thickness of 20 nm) by a reactive RF sputtering method using a C
target in an atmosphere of a mixture of Ar and CH.sub.4.
[0247] Subsequently, a reflective layer, a first dielectric layer,
a magneto-optical recording layer, a second dielectric layer and a
DLC layer were formed on the opposite surface in the same manner as
the above-mentioned surface.
[0248] After the formation of the DLC layer, a near-field
magneto-optical recording medium was completed by lifting up the
recording medium from 0.01 wt % solution of piperonyl-modified
perfluoropolyether ("Fomblin:AM2001" (tradename) manufactured by
Ausimont Company) using a perfluoropolyether type solvent ("GALDEN
SV-70" (tradename) manufactured by Ausimont Company) to form a
lubricant layer having a thickness of 1.5 nm.
[0249] The layer thickness of the lubricant layer was calculated by
using an X-ray photoelectron spectral method (XPS) and observing
the CiS peak intensity.
Example 25
[0250] A substrate of polycarbonate having a diameter of 130 mm and
a substrate thickness of 1.2 mm was prepared by attaching stampers
each having a track pitch of 0.45 .mu.m and a depth of groove of 65
nm in a land and a groove in the data area wherein the header area
was 85 nm higher than the land portion at both mirror plates of
metallic dies and conducting injection-molding. Then, a near-field
magneto-optical recording medium was prepared by forming layers and
coating a lubricant agent in the same manner as Example 24.
Example 26
[0251] A substrate of polycarbonate having a diameter of 130 mm and
a thickness of 1.2 mm was prepared by attaching stampers each
having a track pitch of 0.45 .mu.m in a land portion and a groove
portion in the data area wherein there was no difference of height
between the data area and the header area at both mirror surfaces
of metallic dies and conducting injection-molding. Then, UV light
from a high pressure mercury lamp was irradiated in an amount of an
integrated light quantity of 1500 mJ/cm.sup.2 in conversion into
365 nm.
[0252] In the measurement of the height of the land portion and the
header area after the irradiation of UV, it was found that the
header area was high by 18 nm.
[0253] By using the substrate, a near-field magneto-optical
recording medium was prepared by forming layers and coating a
lubricant agent in a same manner as Example 24.
Comparative Example 17
[0254] A substrate was formed by injection-molding according to
Example 26 provided that no UV was irradiated. A near-field
magneto-optical recording medium was prepared by forming layers and
coating a lubricant agent on the substrate in the same manner as
Example 24.
[0255] With respect to the thus obtained near-field magneto-optical
recording disk, signals from the header area at the time when the
optical head entered from the data area to the header area were
observed by using a near-field magneto-optical recording medium
evaluation device having a detector divided vertically in a beam
propagating direction. As a result, signals at the time when the
optical head entered into a header area could be detected as
difference signals in the division type detector in Examples 24, 25
and 26. However, in the disk of Comparative Example 17, any
difference signal could not be detected, and the timing of the
header area could not be obtained.
Example 27
[0256] A substrate of polycarbonate having a diameter of 130 mm and
a track pitch of 0.85 .mu.m was prepared by injection-molding.
Light from an ultra-high pressure mercury lamp (wavelength
providing the strongest relative intensity: 436 nm) was irradiated
for 30 sec to a groove surface (recording surface) side of the
substrate.
[0257] A thermo-label was attached to the substrate under the same
condition, and the surface temperature of the substrate was
measured to find 105.degree. C.
[0258] By using the substrate, layers were formed on the substrate
by the following method using sputtering methods.
[0259] First, on the substrate, an Al-3 wt % Cr alloy layer (layer
thickness: 50 nm) as a reflective layer was formed by a DC
sputtering method. On this, a first dielectric layer of SIN was
formed (in a thickness of 5 nm) by a reactive RF sputtering method
using a C target in an atmosphere of a mixture of Ar and N.sub.2.
On this, a magneto-optical recording layer of
Tb.sub.20(Fe.sub.90Co.sub.10).sub.80 was formed (in a layer
thickness of 20 nm) by a DC sputtering method using simultaneously
a Tb target and a Fe.sub.90Co.sub.10 target. On this, further, a
second dielectric layer of SiN was formed (in a layer thickness of
30 nm) by a reactive RF sputtering method using a Si target in an
atmosphere of a mixture of Ar and N.sub.2. On this, a DLC layer
having a refractive index of 1.85 at 633 nm was formed (in a layer
thickness of 20 nm) by a reactive RF sputtering method using a C
target in an atmosphere of a mixture of Ar and CH.sub.4.
[0260] After the formation of the DLC layer, a near-field
magneto-optical recording medium was completed by lifting up the
recording medium from a 0.01 wt % solution of piperonyl-modified
perfluoropolyether ("Fomblin:AM2001" (tradename) manufactured by
Ausimont Company) using a perfluoropolyether type solvent ("GALDEN
SV-70" (tradename) manufactured by Ausimont Company) to form a
lubricant layer having a thickness of 1.5 nm.
[0261] The layer thickness of the lubricant layer was calculated by
using an X-ray photo-electron spectral method (XPS) and observing
the ClS peak intensity.
[0262] Then, the medium was set on a recording/reproducing
evaluation device of an optical system of SIL head having a laser
wavelength of 680 nm and an effective NA of 1.2 to evaluate the
recording/reproducing characteristics. Recording was conducted to
the medium by rotating the medium at a linear velocity of 7.0 m/s
and irradiating laser adjusted so that the power was 6.0 mW in
front of the objective lens while a magnetic field modulated to be
a magnitude of .+-.150 Oe at a frequency of 7.0 MHz was applied
from the coil of SIL head. Next, reproducing was conducted by
irradiating laser so that the power was 1.0 mW in front of the
objective lens, and the noise level and CNR of the recording medium
were measured.
[0263] Further, a cross-cut peeling test was conducted to examine
the adhesion strength of the recording layer.
[0264] The cross-cut peeling test was conducted by cutting 100
square areas with a knife, peeling off a tape, and counting the
number of square areas remaining on the disk. A result is shown in
Table 5.
5 TABLE 5 C/N Noise level Cross-cut peeling (dB) (dBm) test Example
27 43.4 -59.2 100/100 Example 28 44.2 -60.1 100/100 Example 29 45.5
-61.2 100/100 Example 30 43.4 -59.2 100/100 Example 31 44.8 -60.7
100/100 Example 32 44.7 -60.6 100/100 Example 33 44.4 -60.4 100/100
Comparative 38.5 -55.3 100/100 Example 18 Comparative 45.24 -61.1
0/100 Example 19
Example 28
[0265] A substrate of polycarbonate was prepared in the same manner
as Example 27. Irradiation of light was conducted for 30 sec by
using a flash UV lamp (wavelength providing the strongest relative
intensity: 546 nm) to measure the surface temperature in the same
manner as Example 27. The temperature was 102.degree. C.
[0266] Further, a magneto-optical recording medium was prepared in
the same manner as Example 27, and a cross-cut peeling test was
conducted. Results are shown in Table 5.
Example 29
[0267] The irradiation of light, the measurement of the surface
temperature and the preparation of a magneto-optical recording
medium were conducted in the same manner as Example 27 except that
a high pressure mercury lamp (wavelength providing the strongest
relative intensity: 365 nm) was used as a light source. The
measurements of noise level and CNR and a cross-cut peeling test
were conducted in the same manner as Example 27. Results are shown
in Table 5.
[0268] The surface temperature under these conditions was
110.degree. C.
Example 30
[0269] The irradiation of light, the measurement of the surface
temperature and the preparation of a magneto-optical recording
medium were conducted in the same manner as Example 27 except that
a metal halide lamp (wavelength providing the strongest relative
intensity: 546 nm) was used as a light source. The measurements of
noise level and CNR and a cross-cut peeling test were conducted in
the same manner as Example 27. Results are shown in Table 5.
[0270] The surface temperature under these conditions was
110.degree. C.
Example 31
[0271] The irradiation of light, the measurement of the surface
temperature and the preparation of a magneto-optical recording
medium were conducted in the same manner as Example 27 except that
an arc lamp (wavelength providing the strongest relative intensity:
850 nm) was used as a light source. The measurements of noise level
and CNR and a cross-cut peeling test were conducted in the same
manner as Example 27. Results are shown in Table 5.
[0272] The surface temperature under these conditions was
120.degree. C.
Example 32
[0273] The irradiation of light, the measurement of the surface
temperature and the preparation of a magneto-optical recording
medium were conducted in the same manner as Example 27 except that
a fluorescent lamp (wavelength providing the strongest relative
intensity: 630 nm) was used as a light source. The measurements of
noise level and CNR and a cross-cut peeling test were conducted in
the same manner as Example 27. Results are shown in Table 5.
[0274] The surface temperature under these conditions was
105.degree. C.
Example 33
[0275] The irradiation of light, the measurement of the surface
temperature and the preparation of a magneto-optical recording
medium were conducted in the same manner as Example 27 except that
a halogen lamp (wavelength providing the strongest relative
intensity: 630 nm) was used as a light source. The measurements of
noise level and CNR and a cross-cut peeling test were conducted in
the same manner as Example 27. Results are shown in Table 5.
[0276] The surface temperature under these conditions was
102.degree. C.
Comparative Example 18
[0277] A substrate of polycarbonate prepared without irradiation of
light was used, and a magneto-optical recording medium was prepared
in the same manner as Example 27. The measurements of noise level
and CNR and a cross-cut peeling test were conducted under the same
conditions. Results are shown in Table 5.
Comparative Example 19
[0278] The irradiation of light, the measurement of the surface
temperature and the preparation of a magneto-optical recording
medium were conducted in the same manner as Example 27 except that
a low pressure mercury lamp (wavelength providing the strongest
relative intensity: 254 nm) was used as a light source. The
measurements of noise level and CNR and a cross-cut peeling test
were conducted in the same manner as Example 27. Results are shown
in Table 5.
[0279] The surface temperature under these conditions was
1180.degree. C.
* * * * *