U.S. patent application number 10/982822 was filed with the patent office on 2005-03-24 for phase-change optical recording media.
This patent application is currently assigned to TOSOH CORPORATION. Invention is credited to Iigusa, Hitoshi, Inase, Toshio.
Application Number | 20050064132 10/982822 |
Document ID | / |
Family ID | 26607856 |
Filed Date | 2005-03-24 |
United States Patent
Application |
20050064132 |
Kind Code |
A1 |
Inase, Toshio ; et
al. |
March 24, 2005 |
Phase-change optical recording media
Abstract
A phase-change optical recording medium which attains a high
erasability in overwriting at a high linear velocity and has high
recording sensitivity, excellent OW cycling characteristics, and
excellent weatherability. The phase-change optical recording medium
comprises a substrate and formed thereon a multilayered film
comprising a protective layer and a recording layer and is that
information is recorded/erased based on reversible phase changes in
the recording layer between a crystalline phase and an amorphous
phase, wherein the protective layer is a film made of an oxide of
tantalum or aluminum and at least one carbide, and the content of
the carbide is from 1 to 40 mol %.
Inventors: |
Inase, Toshio; (Kanagawa,
JP) ; Iigusa, Hitoshi; (Kanagawa, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
TOSOH CORPORATION
Shinnanyo-shi
JP
|
Family ID: |
26607856 |
Appl. No.: |
10/982822 |
Filed: |
November 8, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10982822 |
Nov 8, 2004 |
|
|
|
10047089 |
Jan 17, 2002 |
|
|
|
Current U.S.
Class: |
428/64.4 |
Current CPC
Class: |
G11B 7/2533 20130101;
G11B 2007/25716 20130101; G11B 2007/2571 20130101; C23C 14/06
20130101; G11B 2007/25715 20130101; G11B 7/2534 20130101; G11B
7/2531 20130101; G11B 2007/24308 20130101; G11B 2007/25706
20130101; G11B 2007/25711 20130101; G11B 2007/2431 20130101; G11B
2007/24312 20130101; G11B 2007/24316 20130101; G11B 2007/24314
20130101; G11B 7/2585 20130101; G11B 2007/25708 20130101; G11B
7/2542 20130101; Y10S 430/146 20130101; G11B 7/2578 20130101 |
Class at
Publication: |
428/064.4 |
International
Class: |
B32B 003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 17, 2001 |
JP |
2001-009463 |
Jun 12, 2001 |
JP |
2001-177013 |
Claims
1-4. (Canceled)
5. A phase-change optical recording medium which comprises a
substrate and formed thereon a multilayered film comprising a
protective layer and a recording layer and in which information is
recorded/erased based on reversible phase changes in the recording
layer between a crystalline phase and an amorphous phase, wherein
the protective layer comprises an oxide of aluminum and at least
one carbide, the content of the carbide in the protective layer is
from 1 to 40 mol %, and the protective layer is in contact with the
recording layer.
6. The phase-change optical recording medium of claim 5, wherein
the protective layer contains one or more carbides selected from
the group consisting of carbides of silicon, titanium, tantalum,
and niobium.
7-12. (Canceled)
13. A phase-change optical recording medium which comprises a
substrate and formed thereon a multilayered film comprising a
protective layer and a recording layer and in which information is
recorded/erased based on reversible phase changes in the recording
layer between a crystalline phase and an amorphous phase, wherein
the protective layer comprises an oxide of aluminum, at least one
carbide, and one or more oxides of one or more elements selected
from the group consisting of indium, silicon, titanium, hafnium,
and zirconium, the content of the carbide in the protective layer
is from 1 to 40 mol %, and the protective layer is in contact with
the recording layer.
14. The phase-change optical recording medium of claim 13, wherein
the protective layer contains one or more carbides selected from
the group consisting of carbides of silicon, titanium, tantalum,
and niobium.
15-16. (Canceled)
Description
FIELD OF THE INVENTION
[0001] The present invention relates to rewritable optical
information recording media. More particularly, the invention
relates to phase-change optical recording media in which
information is recorded, reproduced, and erased based on phase
changes in the recording layer which are caused by a laser beam or
the like.
DESCRITPION OF THE RELATED ART
[0002] Phase-change optical recording disks are a kind of
rewritable optical recording disk, and information is recorded
therein based on reversible phase changes (mostly between
crystalline phase and amorphous phase) in the recording layer. In
the phase-change optical recording disks, in general, light
intensity modulation overwriting in the single recording layer is
possible with a single head and signals are read out based on a
change in reflectance accompanying a phase change. A feature of
these recording media hence resides in that they are highly
interchangeable with existing optical recording disks including
CD-ROMs. Because of this, such recording disks are recently being
investigated and developed enthusiastically as rewritable optical
recording disks, and are used as rewritable DVDs.
[0003] In general, in phase-change optical recording media such as
phase-change optical recording disks, recording is conducted by
forming amorphous-phase recording marks in the crystalline phase
(erased state) of the recording layer with a laser beam, and
reproduced signals are obtained by detecting a difference in
reflectance between the crystalline phase and the amorphous phase.
Furthermore, light intensity modulation overwriting (direct
overwriting) is made possible with a combination of a single beam
and a single recording layer by modulating the intensity of the
laser beam between an intensity for conversion to amorphousness
(peak power) and an intensity for crystallization (bias power)
during signal recording (see FIG. 1). Thus, a large capacity
recording disk with high rate data transfer can be obtained.
[0004] Phase-change optical recording media are capable of direct
overwriting (DOW) as described above. However, these recording
media have a drawback that when a high linear velocity is used so
as to realize a higher transfer rate, the initial signals are not
completely erased through overwriting (OW) and unerased signals
remain. Namely, an increase in linear velocity results in a
worsened erasability.
SUMMARY OF THE INVENTION
[0005] An object of the invention is to provide phase-change
optical recording media which are effective in attaining diminution
in unerased signals and an improvement in the erasability in
overwriting at a high linear velocity and have high recording
sensitivity, satisfactory OW cycling durability, and satisfactory
weatherability.
[0006] The present inventors made intensive investigations under
the circumstances described above. As a result, they have found
that in a phase-change optical recording medium which comprises a
substrate and formed thereon a multilayered film comprising a
protective layer and a recording layer and in which information is
recorded/erased based on reversible phase changes in the recording
layer between a crystalline phase and an amorphous phase, the
erasability and durability in overwriting at a high linear velocity
can be improved by forming the protective layer so as to comprise
specific components. They have further found that this effect is
enhanced by regulating the proportion of a component in the
protective layer so as to be in a specific range. The invention has
been completed based on these findings.
[0007] The invention provides a phase-change optical recording
medium which comprises a substrate and formed thereon a
multilayered film comprising a protective layer and a recording
layer and in which information is recorded/erased based on
reversible phase changes in the recording layer between a
crystalline phase and an amorphous phase, wherein the protective
layer comprises an oxide of tantalum and at least one carbide, the
content of the carbide in the protective layer is from 1 to 40 mol
%, and the protective layer is in contact with the recording
layer.
[0008] The invention further provides a phase-change optical
recording medium which comprises a substrate and formed thereon a
multilayered film comprising a protective layer and a recording
layer and in which information is recorded/erased based on
reversible phase changes in the recording layer between a
crystalline phase and an amorphous phase, wherein the protective
layer comprises an oxide of aluminum and at least one carbide, the
content of the carbide in the protective layer is from 1 to 40 mol
%, and the protective layer is in contact with the recording
layer.
[0009] The invention furthermore provides a phase-change optical
recording medium which comprises a substrate and formed thereon a
multilayered film comprising a protective layer and a recording
layer and in which information is recorded/erased based on
reversible phase changes in the recording layer between a
crystalline phase and an amorphous phase, wherein the protective
layer comprises an oxide of tantalum, at least one carbide, and one
or more oxides of one or more elements selected from the group
consisting of indium, silicon, titanium, hafnium and zirconium, the
content of the carbide in the protective layer is from 1 to 40 mol
%, and the protective layer is in contact with the recording
layer.
[0010] The invention still further provides a phase-change optical
recording medium which comprises a substrate and formed thereon a
multilayered film comprising a protective layer and a recording
layer and in which information is recorded/erased based on
reversible phase changes in the recording layer between a
crystalline phase and an amorphous phase, wherein the protective
layer comprises an oxide of aluminum, at least one carbide, and one
or more oxides of one or more elements selected from the group
consisting of indium, silicon, titanium, hafnium and zirconium, the
content of the carbide in the protective layer is from 1 to 40 mol
%, and the protective layer is in contact with the recording
layer.
[0011] The protective layer preferably contains one or more
carbides selected from the group consisting of carbides of silicon,
titanium, tantalum, and niobium. The recording layer in each of
those phase-change optical recording media is preferably
constituted of an alloy of germanium, antimony, and tellurium or a
material containing the alloy as the main component.
[0012] Furthermore, the phase-change optical recording media of the
invention are preferably used in such a high-transfer-rate region
that the value of d/v, wherein d is the laser beam diameter
(d=.lambda./NA, wherein .lambda. is the wavelength of the laser
light and NA is the numerical aperture of the objective lens) and v
is the linear velocity, is less than 1.5.times.10.sup.-7 sec
(d/v<1.5.times.10.sup.-7 [s]).
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is an illustration showing a laser power pattern for
a recording/reproducing apparatus.
[0014] FIG. 2 is a sectional view showing the structure of part of
one embodiment of the phase-change optical recording media of the
invention.
[0015] FIG. 3 is a sectional view showing the structure of part of
each of the phase-change optical recording media obtained in
Examples of the invention and in the Comparative Examples.
[0016] FIG. 4 is an illustration showing a laser power pattern used
for recording 0.6 .mu.m marks.
[0017] FIG. 5 is a graphic presentation showing the linear-velocity
dependence of the erasability of samples of Example 1 and the
samples of Comparative Example 1.
[0018] FIG. 6 is a graphic presentation showing the peak power
dependence of CNR of a sample of Example 1.
DESCRIPTION OF THE REFERENCE NUMERALS
[0019] 21, 31: substrate
[0020] 22, 32: first protective layer
[0021] 23, 33: recording layer
[0022] 24, 34: second protective layer
[0023] 25, 35: reflective layer
[0024] 36: protective coating layer
DETAILED DESCRIPTION OF THE INVENTION
[0025] The invention will be described in detail below.
[0026] FIG. 2 is a sectional view showing the structure of part of
one embodiment of the phase-change optical recording media of the
invention. The phase-change optical recording medium shown in FIG.
2 comprises a substrate 21 and, superposed thereon, a first
protective layer 22, a recording layer 23, a second protective
layer 24 and a reflective layer 25.
[0027] The substrate 21 is not particularly limited in material as
long as it is sufficiently transparent in the wavelength region for
the laser to be used and satisfies property requirements for medium
substrates, such as mechanical properties. A glass, polycarbonate,
amorphous polyolefin, or the like can be used as the material.
[0028] The first protective layer 22 and the second protective
layer 24 each constituted of a film which comprises an oxide of
either tantalum or aluminum and at least one carbide and in which
the content of the carbide is from 1 to 40 mol %. Although even a
protective layer consisting only of an oxide of either tantalum or
aluminum can give a sufficiently high erasability, the high
recording sensitivity can be obtained by the incorporation of a
carbide while maintaining the high erasability to thereby attain
excellent recording/reproducing/erasure characteristics at a high
linear velocity. The protective layers preferably contain at least
one carbide selected from carbides of silicon, titanium, tantalum,
and niobium. The content of these carbides in the protective layers
is generally from 1 to 40 mol %, preferably from 5 to 35 mol %,
more preferably from 10 to 30 mol %, in terms of the total amount
thereof. In case where the content of the carbides exceeds 50 mol
%, the film may have an increased extinction coefficient (k) and
impaired transparency and thus become impractical for use in
phase-change optical recording media.
[0029] The first protective layer 22 and second protective layer 24
each may be a film which comprises an oxide of either tantalum or
aluminum, at least one carbide, and one or more oxides of one or
more elements selected from the group consisting of indium,
silicon, titanium, hafnium, and zirconium and in which the content
of the carbide is from 1 to 40 mol %.
[0030] The incorporation of one or more of oxides of indium,
silicon, titanium, hafnium, and zirconium in the protective layers
is effective in further enhancing the effect of improving recording
sensitivity.
[0031] In the case of using a protective layer comprising an oxide
of either tantalum or aluminum, at least one carbide, and one or
more oxides of one or more elements selected from the group
consisting of indium, silicon, titanium, hafnium, and zirconium,
this protective layer also preferably contains one or more carbides
selected from carbides of silicon, titanium, tantalum, and niobium.
The content of these carbides in this protective layer is generally
from 1 to 40 mol %, preferably from 5 to 35 mol %, more preferably
from 10 to 30 mol %, in terms of the total amount thereof. In case
where the content of the carbides exceeds 50 mol %, the film may
have an increased extinction coefficient (k) and impaired
transparency and thus become impractical for use in phase-change
optical recording media.
[0032] The recording layer 23 may be any of films which undergo
reversible phase changes, such as a Ge--Sb--Te thin film and an
In--Sb--Te thin film. It is, however, preferred to use an alloy of
germanium, antimony, and tellurium or a material containing the
alloy as the main component. The recording layer is formed so as to
be in contact with at least one of the protective layers. The
contact of the recording layer with the protective layer
accelerates the formation of crystal nuclei at the contact plane
(interface) to thereby enable crystallization to proceed more
rapidly. Although a Ge--Sb--Te thin film, an In--Sb--Te thin film,
or the like can be used as the recording layer, it is especially
preferred to use a Ge--Sb--Te thin film as the recording layer of
the phase-change optical recording media of the invention which
have the protective layers described above, because crystallization
in this recording layer is attributable mainly to nucleus
formation.
[0033] The reflective layer 25 is constituted of a film having a
high reflectance in the wavelength region for the laser to be used,
such as a film of an aluminum alloy or silver alloy.
[0034] Besides functioning to protect the recording layer, the
first and second protective layers function also to increase the
efficiency of light absorption by the recording layer and to bring
about an increased change in reflected-light amount through
recording. Because of this, the first and second protective layers
each are designed so as to have an optimal thickness while taking
account of the wavelength of the laser light to be used, the
thickness of the recording layer, etc.
[0035] In the invention, structures other than that described above
can be used. For example, the structure described above may be
modified so that a protective layer according to the invention is
used as one of the first and second protective layers and a
protective layer made of another material is used as the other
protective layer.
[0036] The first and second protective layers, recording layer, and
reflective layer can be formed by a vacuum deposition technique
such as DC sputtering, RF sputtering or vacuum evaporation.
[0037] After these layers are formed, a protective coating layer
made of a synthetic resin or another material may be formed thereon
according to need.
[0038] The protective layer according to the invention is
applicable also to the so-called surface reproduction type optical
recording medium, which is produced by a process in which the
sequence of film deposition is reversed.
[0039] The invention will be explained below in more detail by
reference to the following Examples, but the invention should not
be construed as being limited to these Examples only.
EXAMPLE 1 AND COMPARATIVE EXAMPLE 1
[0040] Phase-change optical recording media having the structure
shown in FIG. 3 were produced in the following manner.
[0041] On a disk-form polycarbonate substrate 31 having a 0.7
.mu.m-wide groove formed with a pitch of 1.4 .mu.m was deposited a
first protective layer 32 comprising Ta.sub.2O.sub.5 and SiC (film
thickness: 100 nm) by simultaneous RF sputtering using a
Ta.sub.2O.sub.5 target and an SiC target. Thereafter, a recording
layer 33 comprising of Ge.sub.2Sb.sub.2Te.sub.5 (film thickness: 20
nm) was deposited thereon by DC sputtering using a
Ge.sub.2Sb.sub.2Te.sub.5 alloy target. Furthermore, a second
protective layer 34 comprising Ta.sub.2O.sub.5 and SiC (film
thickness: 20 nm) was deposited thereon by simultaneous RF
sputtering using a Ta.sub.2O.sub.5 target and an SiC target.
Thereafter, an Al--Cr alloy (chromium content: 3 wt %) film
(thickness: 150 nm) was formed as a reflective layer 35. An
ultraviolet-curable resin was applied thereto to form a protective
coating layer 36 having a thickness of 10 .mu.m. Thus, a
phase-change optical recording medium was completed.
[0042] In forming the protective layers in the structure described
above, the proportion of the power applied to the Ta.sub.2O.sub.5
target to the power applied to the SiC target was varied. Thus,
phase-change optical recording media were obtained in which the
compositions of the protective layers were of six kinds which
varied in SiC content from 1 to 40 mol % (Example 1, Samples 1 to
6). For the purpose of comparison, phase-change optical recording
media having SiC contents in the protective layers of 0, 50, and 70
mol %, respectively, were also produced (Comparative Example 1,
Samples 1 to 3).
EXAMPLE 2 AND COMPARATIVE EXAMPLE 2
[0043] The same procedure as in Example 1 was conducted, except
that Al.sub.2O.sub.3 was used in place of the Ta.sub.2O.sub.5 as a
component of the first protective layer and second protective
layer. Thus, phase-change optical recording media were obtained in
which the compositions of the protective layers were of six kinds
which varied in SiC content from 1 to 40 mol % (Example 2, Samples
1 to 6). For the purpose of comparison, phase-change optical
recording media having SiC contents in the protective layers of 0,
50, and 70 mol %, respectively, were also produced (Comparative
Example 2, Samples 1 to 3).
EXAMPLE 3
[0044] Phase-change optical recording media were produced in the
same manner as in Example 1, except that the first protective layer
and second protective layer were formed so as to contain 10 mol %
TiC (Example 3, Sample 1), 10 mol % TaC (Example 3, Sample 2), or
10 mol % Nb.sub.2C (Example 3, Sample 3) in place of the SiC.
EXAMPLE 4
[0045] Phase-change optical recording media were produced (Example
4, Samples 1 to 3) in the same manner as in Example 3, except that
Al.sub.2O.sub.3 was used in place of the Ta.sub.2O.sub.5 in the
first protective layer and second protective layer.
EXAMPLE 5
[0046] A phase-change optical recording medium was produced in the
same manner as in Example 1, except that a film consisting of
Ta.sub.2O.sub.5 and 10 mol % SiC was formed as the first protective
layer and a film comprising ZnS and 20 mol % SiO.sub.2 was formed
as the second protective layer.
EXAMPLE 6
[0047] A phase-change optical recording medium was produced in the
same manner as in Example 1, except that a film comprising ZnS and
20 mol % SiO.sub.2 was formed as the first protective layer and a
film comprising Ta.sub.2O.sub.5 and 10 mol % SiC was formed as the
second protective layer.
EXAMPLE 7
[0048] The same procedure as in Example 1 was conducted, except
that the sequence of film formation on the substrate was changed so
that the reflective layer (thickness: 150 nm), the first protective
layer (thickness: 20 nm), the recording layer (thickness: 20 nm),
and the second protective layer (thickness: 100 nm) were formed in
this order and the protective coating layer having a thickness of
0.1 mm was formed thereon. Thus, a surface reproduction type
phase-change optical recording medium having a reversed layer
constitution was produced.
COMPARATIVE EXAMPLE 3
[0049] A phase-change optical recording medium having the structure
shown in FIG. 3 was produced in the following manner.
[0050] On a disk-form polycarbonate substrate 31 having a 0.7
.mu.m-wide groove formed with a pitch of 1.4 .mu.m was deposited a
first protective layer 32 comprising ZnS and SiO.sub.2 (film
thickness: 100 nm) by RF sputtering using a ZnS--SiO.sub.2 (20 mol
%) target. Thereafter, a recording layer 33 comprising
Ge.sub.2Sb.sub.2Te.sub.5 (film thickness: 20 nm) was deposited
thereon by DC sputtering using a Ge.sub.2Sb.sub.2Te.sub.5 alloy
target. Furthermore, a film comprising ZnS and SiO.sub.2 (film
thickness: 20 nm) was deposited thereon as a second protective
layer 34 by RF sputtering using a ZnS--SiO.sub.2 (20 mol %) target.
Thereafter, an Al--Cr alloy (chromium content: 3 wt %) film
(thickness: 150 nm) was formed as a reflective layer 35. An
ultraviolet-curable resin was applied thereto to form a protective
coating layer 36 having a thickness of 10 .mu.m. Thus, a
phase-change optical recording medium was completed.
[0051] The phase-change optical recording media obtained in
Examples 1 to 6 and Comparative Examples 1 to 3 were subjected to
initial crystallization of the recording layer with an
initialization apparatus.
[0052] Subsequently, amorphous marks having a length of 0.6 were
recorded at a linear velocity of 6 m/sec on tracks in the region
where the recording layer had been crystallized (recording pitch,
1.2 .mu.m; laser light wavelength, 680 nm; objective lens NA,
0.55). For this recording, a modulated laser power pattern shown in
FIG. 4 was used, which additionally had an off-pulse and in which
the off-pulse power (Poff) and reproducing power (Pr) each were 1
mW and the peak power duration and off-pulse duration were 50 ns
and 33 ns, respectively. Amorphous marks were recorded at a bottom
power (Pb) of 5 mW and at various peak powers (Pp). The Pp which
resulted in the maximum value of CNR is referred to as optimum Pp
(Pp.sub.0). Subsequently, amorphous marks were recorded at Pb=5 mW
and Pp=Pp.sub.0, and the amorphous marks were erased by irradiation
with laser beams having various powers. In this operation, the
change in carrier level through the erasure was measured and taken
as the erasability. The laser power which resulted in the maximum
value of the erasability is referred to as optimum Pb (Pb.sub.0).
Subsequently, amorphous marks (mark length, 0.6 .mu.m) were
recorded at a Pp of (Pp.sub.0-1) mW and a Pb of (Pb.sub.0-1) mW and
then erased with a laser of (Pb.sub.0-1) mW. This recording/erasure
operation was conducted 20 times per track (hereinafter, this step
is referred to as initialization).
[0053] Amorphous marks having a length of 0.6 .mu.m were recorded
on the initialized tracks at a linear velocity of 6 m/sec under the
laser power conditions of Pr=1 mW, Poff=1 mW, Pp=Pp.sub.0, and
Pb=Pb.sub.0 (recording pitch, 1.2 .mu.m). These recording marks
were erased at various linear velocities and various laser powers.
The change in carrier level through the erasure was measured and
taken as the erasability.
[0054] FIG. 5 shows the linear-velocity dependence of the
erasability of samples of Example 1 and Comparative Example 1 which
had various protective-layer compositions and of the sample of
Comparative Example 3. The proportion of Ta.sub.2O.sub.5 to SiC in
each protective layer was determined by forming a protective layer
under the same film deposition conditions and analyzing this layer
by fluorescent X-ray spectroscopy. FIG. 5 shows that the protective
layers according to the invention brought about higher degrees of
erasure than the protective layers of the Comparative Examples in a
high linear velocity region (the region where
d/v<1.5.times.10.sup.-7 [s], wherein d is the laser beam
diameter (d=.lambda./NA) and v is the linear velocity).
[0055] In FIG. 6 are shown the peak power dependence of CNR
(hereinafter referred to as "power curve") of the sample having
protective layers consisting only of Ta.sub.2O.sub.5 (Comparative
Example 1, Sample 1) and that of the sample having protective
layers comprising Ta.sub.2O.sub.5 containing 10 mol % SiC (Example
1, Sample 3). The intersection where each power curve in FIG. 6
crosses the straight line of CNR=30 dB is defined as recording
sensitivity (Pth).
[0056] The results of measurements of the erasability and Pth of
the samples of Examples 1 to 4 and Comparative Examples 1 and 2 are
shown in Tables 1 to 4. Furthermore, the results of measurements of
the erasability (8 m/s) of the samples of Examples 5 and 6 and
Comparative Example 3 are shown in Table 5. With respect to the
erasability, values of 25 dB or higher are satisfactory in
practical use and values of 28 dB or higher are more preferred.
When the SiC content was in the range of from 1 to 40%, a
satisfactory balance between the erasability and recording
sensitivity was obtained. An excellent balance between these
properties was obtained when that content was in the range of from
10 to 30%. SiC contents of 50% and higher tended to result in
lowered recording sensitivity.
[0057] The same samples were further subjected to an overwriting
(OW) cycle test in which recording of amorphous marks having a
length of 0.6 .mu.m (recording pitch, 1.2 .mu.m) and recording of
amorphous marks having a length of 1.6 .mu.m (recording pitch, 3.2
.mu.m) were alternately conducted (i.e., overwriting was conducted)
under the laser power conditions of Pr=1 mW, Poff=1 mW,
Pp=Pp.sub.0, and Pb=Pb.sub.0. As a result, the samples of Examples
1 to 6 were ascertained to have higher cycling durability than the
samples of Comparative Examples 1 and 2.
[0058] Furthermore, the same samples were subjected to an
accelerated weathering test in which the samples were stored in an
atmosphere of 85.degree. C. and 95% RH for 250 hours. As a result,
the samples of Examples 1 to 6 were ascertained to have higher
weatherability than the samples of Comparative Examples 1 and
2.
[0059] The sample of Example 7 was subjected to a
recording/reproducing test. As a result, a satisfactory CNR and a
satisfactory erasability were obtained and the sample was
ascertained to be usable as a surface reproduction type optical
recording medium.
EXAMPLE 8 AND COMPARATIVE EXAMPLE 4
[0060] Phase-change optical recording media having the structure
shown in FIG. 3 were produced in the following manner.
[0061] On a disk-form polycarbonate substrate 31 having a 0.7
.mu.m-wide groove formed with a pitch of 1.4 .mu.m was deposited a
first protective layer 32 comprising Ta.sub.2O.sub.5, SiC, and
SiO.sub.2 (film thickness: 100 nm) by RF sputtering using a
Ta.sub.2O.sub.5 target and SiC material and SiO.sub.2 material
pieces placed thereon. Thereafter, a recording layer 33 comprising
Ge.sub.2Sb.sub.2Te.sub.5 (film thickness: 20 nm) was deposited
thereon by DC sputtering using a Ge.sub.2Sb.sub.2Te.sub.5 alloy
target. Furthermore, a second protective layer 34 consisting of
Ta.sub.2O5, SiC, and SiO.sub.2 (film thickness: 20 nm) was
deposited thereon by RF sputtering using a Ta.sub.2O.sub.5 target
and SiC material and SiO.sub.2 material pieces placed thereon.
Thereafter, an Al--Cr alloy (chromium content: 3 wt %) film
(thickness: 100 nm) was formed as a reflective layer 35. An
ultraviolet-curable resin was applied thereto to form a protective
coating layer 36 having a thickness of 10 .mu.m. Thus, a
phase-change optical recording medium was completed.
[0062] In forming the protective layers in the structure described
above, the numbers of SiC material pieces and SiO.sub.2 material
pieces placed on the Ta.sub.2O.sub.5 target were varied. Thus,
phase-change optical recording media were obtained in which the
protective layers had various compositions (Example 8, Samples 1 to
8). For the purpose of comparison, a phase-change optical recording
medium having protective layers having an SiC content of 50 mol %
and an SiO.sub.2 content of 10 mol % was also produced (Comparative
Example 4).
EXAMPLE 9
[0063] Phase-change optical recording media were produced in the
same manner as in Example 8, except that the first protective layer
and second protective layer were formed so as to contain 10 mol %
ZrO.sub.2 (Example 9, Sample 1), 10 mol % TiO.sub.2 (Example 9,
Sample 2), 10 mol % HfO.sub.2 (Example 9, Sample 3), or 10 mol %
In.sub.2O.sub.3 (Example 9, Sample 4) in place of the SiO.sub.2 and
to have an SiC content of 30 mol %.
EXAMPLE 10 AND COMPARATIVE EXAMPLE 5
[0064] Phase-change optical recording media were produced (Example
10, Samples 1 to 8) in the same manner as in Example 8, except that
Al.sub.2O.sub.3 was used in place of the Ta.sub.2O.sub.5 in the
first protective layer and second protective layer. For the purpose
of comparison, a phase-change optical recording medium having
protective layers having an SiC content of 50 mol % and an
SiO.sub.2 content of 10 mol % was also produced (Comparative
Example 5).
EXAMPLE 11
[0065] Phase-change optical recording media were produced (Example
11, Samples 1 to 4) in the same manner as in Example 9, except that
Al.sub.2O.sub.3 was used in place of the Ta.sub.2O.sub.5 in the
first protective layer and second protective layer.
EXAMPLE 12
[0066] Phase-change optical recording media were produced in the
same manner as in Example 1, except that the recording layer was
constituted of Ge.sub.1Sb.sub.2Te.sub.4 (Example 12, Sample 1) or
Ge.sub.1Sb.sub.4Te.sub.7 (Example 12, Sample 2) in place of
Ge.sub.2Sb.sub.2Te.sub.5, and that the protective layers were
formed so as to have an SiC content of 10 mol %.
EXAMPLE 13
[0067] A phase-change optical recording medium was produced in the
same manner as in Example 1, except that the recording layer was
constituted of an Ag--In--Sb--Te alloy (Ag, 4 atomic %; In, 6
atomic %; Sb, 61 atomic %; Te, 29 atomic %) in place of
Ge.sub.2Sb.sub.2Te.sub.5, and that the protective layers were
formed so as to have an SiC content of 10 mol %.
[0068] The phase-change optical recording media obtained in
Examples 8 to 13 and Comparative Examples 4 and 5 were subjected to
initial crystallization of the recording layer with an
initialization apparatus.
[0069] Subsequently, amorphous marks having a length of 0.6 .mu.m
were recorded at a linear velocity of 6 m/sec on tracks in the
region where the recording layer had been crystallized (recording
pitch, 1.2 .mu.m; laser light wavelength, 680 nm; objective lens
NA, 0.55). For this recording, a modulated laser power pattern
shown in FIG. 4 was used, which additionally had an off-pulse and
in which the off-pulse power (Poff) and reproducing power (Pr) each
were 1 mW and the peak power duration and off-pulse duration were
50 ns and 33 ns, respectively. Amorphous marks were recorded at a
bias power (Pb) of 5 mW and at various peak powers (Pp). The Pp
which resulted in the maximum value of CNR is referred to as
optimum Pp (Pp.sub.0). Subsequently, amorphous marks were recorded
at Pb=5 mW and Pp=Pp.sub.0, and the amorphous marks were erased by
irradiation with laser beams having various powers. In this
operation, the change in carrier level through the erasure was
measured and taken as the erasability. The laser power which
resulted in the maximum value of the erasability is referred to as
optimum Pb (Pb.sub.0). Subsequently, amorphous marks (mark length,
0.6 .mu.m) were recorded at a Pp of (Pp.sub.0-1) mW and a Pb of
(Pb.sub.0-1) mW and then erased with a laser of (Pb.sub.0-1) mW.
This recording/erasion operation was conducted 20 times per
track.
[0070] Amorphous marks (mark length, 0.6 .mu.m) were recorded on
the initialized tracks at Pb=Pb.sub.0 mW and a linear velocity of 6
m/sec to examine the recording power (Pp) dependence of CNR.
Furthermore, amorphous marks having a length of 0.6 .mu.m were
recorded on the initialized tracks at a linear velocity of 6 m/sec
under the laser power conditions of Pr=1 mW, Poff=1 mW,
Pp=Pp.sub.0, and Pb=Pb.sub.0 (recording pitch, 1.2 .mu.m). These
recording marks were erased at various linear velocities and
various laser powers. The change in carrier level through the
erasion was measured and taken as the erasability.
[0071] The results of examination of the erasability and Pth of the
samples of Examples 8 to 11 are shown in Tables 6 to 9,
respectively. For the purpose of comparison, the results of
examination of some of the samples of Example 1 and Comparative
Examples 1 and 4 and the results of the examination of some of the
samples of Example 2 and Comparative Examples 2 and 5 are also
shown in Tables 6 and 8, respectively. Furthermore, the results of
examination of the erasability of the samples of Examples 12 and 13
as obtained at a linear velocity of 12 m/s are shown in Table 10.
For the purpose of comparison, the results of examination of Sample
3 of Example 1 and the sample of Comparative Example 3 are also
shown in Table 10. These Tables show that the effect of improving
recording sensitivity was enhanced by adding an oxide of silicon,
zirconium, titanium, hafnium, or indium. The Tables further show
that the Ge--Sb--Te recording layers attained higher erasabilty
than the Ag--In--Sb--Te recording layer.
[0072] The samples of Examples 8 to 11 were further subjected to a
direct overwriting (DOW) cycle test in which amorphous marks having
a length of 0.6 were recorded (recording pitch, 1.2 .mu.m) under
the laser power conditions of Pr=1 mW, Poff=1 mW, Pp=Pp.sub.0, and
Pb=Pb.sub.0. As a result, these samples were ascertained to have
higher cycling durability than the samples of Comparative Examples
1 and 2.
[0073] Furthermore, the samples of Examples 8 to 11 were subjected
to an accelerated weathering test in which the samples were stored
in an atmosphere of 85.degree. C. and 95% RH for 250 hours. As a
result, these samples were ascertained to have higher
weatherability than the samples of Comparative Examples 1 and
2.
[0074] According to the invention, phase-change optical recording
media can be obtained which are effective in attaining diminution
in unerased signals and an improvement in the erasability in
overwriting at a high linear velocity and which have high recording
sensitivity, satisfactory OW cycling characteristics, and
satisfactory weatherability. Consequently, phase-change optical
disks capable of high-rate data transfer and having high durability
can be produced according to the invention.
1 TABLE 1 SiC content Erasability Pth Sample [mol %] [dB] [mW]
Comparative 0 31.4 10.3 Example 1-1 Example 1-1 1 29.5 9.8 Example
1-2 5 29.0 9.7 Example 1-3 10 28.5 9.3 Example 1-4 30 28.9 8.5
Example 1-5 35 28.5 8.7 Example 1-6 40 28.0 8.9 Comparative 50 26.5
9.9 Example 1-2 Comparative 70 25.0 10.3 Example 1-3
[0075]
2 TABLE 2 SiC content Erasability Pth Sample [mol %] [dB] [mW]
Comparative 0 31.4 11.5 Example 2-1 Example 2-1 1 29.7 9.9 Example
2-2 5 29.5 9.6 Example 2-3 10 28.7 9.4 Example 2-4 30 28.3 8.9
Example 2-5 35 28.0 9.0 Example 2-6 40 27.8 9.1 Comparative 50 26.0
9.9 Example 2-2 Comparative 70 24.5 11.0 Example 2-3
[0076]
3 TABLE 3 Erasability Pth Sample Carbide [dB] [mW] Example 3-1 TiC
28.3 9.2 Example 3-2 TaC 27.8 9.5 Example 3-3 Nb.sub.2C 28.0
9.3
[0077]
4 TABLE 4 Erasability Pth Sample Carbide [dB] [mW] Example 4-1 TiC
28.5 9.5 Example 4-2 TaC 28.3 9.7 Example 4-3 Nb.sub.2C 28.2
9.6
[0078]
5 TABLE 5 First Second Maximum protective protective erasabiulity
Sample layer layer [dB] Example 5 Ta.sub.2O.sub.5 + SiC ZnS -
SiO.sub.2 33 Example 6 ZnS - SiO.sub.2 Ta.sub.2O.sub.5 + SiC 36
Comparative ZnS - SiO.sub.2 ZnS - SiO.sub.2 25 Example 3 (linear
velocity: 8 m/s)
[0079]
6 TABLE 6 SiC SiO.sub.2 Erasability Pth Sample [mol %] [mol %] [dB]
[mW] Comparative 0 0 31.4 10.3 Example 1 Example 1-1 1 0 29.5 9.8
Example 1-2 5 0 29.0 9.7 Example 1-3 10 0 28.5 9.3 Example 8-1 10 5
28.5 9.1 Example 8-2 10 10 28.3 8.7 Example 8-3 10 20 28.2 8.3
Example 8-4 10 30 28.2 8.0 Example 8-5 10 40 28.0 7.5 Example 8-6
20 10 28.5 8.4 Example 8-7 30 10 28.6 8.5 Example 8-8 40 10 27.8
8.8 Comparative 50 10 26.2 9.7 Example 4
[0080]
7 TABLE 7 Erasability Pth Sample Oxide [dB] [mW] Example 9-1
ZrO.sub.2 28.4 8.1 Example 9-2 TiO.sub.2 27.8 8.0 Example 9-3
HfO.sub.2 28.0 7.8 Example 9-4 In.sub.2O.sub.3 28.2 7.8
[0081]
8 TABLE 8 SiC SiO.sub.2 Erasability Pth Sample [mol %] [mol %] [dB]
[mW] Comparative 0 0 31.4 11.5 Example 2 Example 2-1 1 0 29.7 9.9
Example 2-2 5 0 29.5 9.6 Example 2-3 10 0 28.7 9.4 Example 10-1 10
5 28.4 9.1 Example 10-2 10 10 28.2 8.8 Example 10-3 10 20 28.0 8.4
Example 10-4 10 30 28.0 8.0 Example 10-5 10 40 27.5 7.5 Example
10-6 20 10 28.0 8.5 Example 10-7 30 10 28.0 8.7 Example 10-8 40 10
27.5 9.0 Comparative 50 10 26.0 9.9 Example 5
[0082]
9 TABLE 9 Erasability Pth Sample Oxide [dB] [mW] Example 11-1
ZrO.sub.2 28.2 8.3 Example 11-2 TiO.sub.2 27.6 8.2 Example 11-3
HfO.sub.2 27.8 8.0 Example 11-4 In.sub.2O.sub.3 28.0 7.9
[0083]
10 TABLE 10 Recording Erasability Sample Protective layer layer
[dB] Example 1-3 Ta.sub.2O.sub.5 + SiC Ge.sub.2Sb.sub.2Te.sub.5
28.5 Example 12-1 Ta.sub.2O.sub.5 + SiC Ge.sub.1Sb.sub.2Te.sub.4
29.1 Example 12-2 Ta.sub.2O.sub.5 + SiC Ge.sub.1Sb.sub.4Te.sub.7
28.8 Example 13 Ta.sub.2O.sub.5 + SiC AgInTeSb 21.2 Comparative ZnS
- SiO.sub.2 Ge.sub.2Sb.sub.2Te.sub.5 15.1 Example 3 (12 m/s)
* * * * *