U.S. patent application number 10/580294 was filed with the patent office on 2007-06-28 for silver alloy excellent in reflectance maintenance property.
Invention is credited to Tomokazu Obata, Hiroshi Yanagihara.
Application Number | 20070148033 10/580294 |
Document ID | / |
Family ID | 34675003 |
Filed Date | 2007-06-28 |
United States Patent
Application |
20070148033 |
Kind Code |
A1 |
Obata; Tomokazu ; et
al. |
June 28, 2007 |
Silver alloy excellent in reflectance maintenance property
Abstract
The present invention is a silver alloy including silver as the
main component and at least one precious metal element as a first
dopant element, and excellent in reflectance maintenance property.
In the present invention, the first dopant element is preferably
platinum, gold, palladium, rhodium, ruthenium and iridium. Also, in
the present invention, the silver alloy preferably includes, as a
second dopant element, at least one element selected from copper,
manganese, silicon, chromium, nickel, cobalt, iron, scandium,
zirconium, niobium, molybdenum, tantalum, tungsten, indium, tin,
lead, aluminum, calcium, germanium, gallium, bismuth, antimony,
strontium, hafnium, gadolinium, samarium, neodymium, lanthanum,
cerium, ytterbium and europium.
Inventors: |
Obata; Tomokazu; (Kanagawa,
JP) ; Yanagihara; Hiroshi; (Kanagawa, JP) |
Correspondence
Address: |
ROBERTS & ROBERTS, LLP;ATTORNEYS AT LAW
P.O. BOX 484
PRINCETON
NJ
08542-0484
US
|
Family ID: |
34675003 |
Appl. No.: |
10/580294 |
Filed: |
December 9, 2004 |
PCT Filed: |
December 9, 2004 |
PCT NO: |
PCT/JP04/18368 |
371 Date: |
May 23, 2006 |
Current U.S.
Class: |
420/505 ;
G9B/7.19 |
Current CPC
Class: |
C23C 14/185 20130101;
C22C 5/06 20130101; C23C 14/3414 20130101; G11B 7/2595 20130101;
G11B 7/266 20130101; G11B 7/2467 20130101; G11B 7/258 20130101;
G11B 7/2534 20130101; G11B 7/259 20130101 |
Class at
Publication: |
420/505 |
International
Class: |
C22C 5/06 20060101
C22C005/06 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 10, 2003 |
JP |
2003-411720 |
Claims
1. A silver alloy for use in a reflective film, comprising silver
as a main element and at least one precious metal element as a
first dopant element.
2. The silver alloy for use in a reflective film according to claim
1, wherein the first dopant element is at least any one of
platinum, palladium, gold, rhodium, ruthenium and iridium.
3. The silver alloy for use in a reflective film according to claim
1, comprising as a second dopant element at least one element
selected from gallium, dysprosium and thulium.
4. The silver alloy for use in a reflective film according to claim
1, comprising as a second dopant element at least one element
selected from magnesium, zinc, nickel, molybdenum, terbium,
gadolinium and erbium.
5. The silver alloy for use in a reflective film according to claim
1, comprising as a second dopant element at least one element
selected from aluminum, neodymium and holmium.
6. The silver alloy for use in a reflective film according to claim
1, comprising as a second dopant element at least one element
selected from copper, cobalt, tin, titanium, bismuth, scandium,
yttrium, praseodymium and manganese.
7. The silver alloy for use in a reflective film according to claim
1, comprising as a second dopant element at least one element
selected from germanium, indium, samarium, ytterbium, strontium,
boron, silicon, chromium, iron, zirconium, niobium, tantalum,
tungsten, rhodium, lead, calcium, antimony, hafnium, lanthanum and
cerium.
8. The silver alloy for use in a reflective film according to claim
1, wherein a total of the concentration of the first dopant element
and the concentration of the second dopant element are 0.01 to 5.0
atomic %.
9. The silver alloy for use in a reflective film according to claim
8, wherein the total of the concentration of the first dopant
element and the concentration of the second dopant element are 0.01
to 2.0 atomic %.
10. A sputtering target, comprising the silver alloy as defined in
claim 1.
11. The silver alloy for use in a reflective film according to
claim 2, comprising as a second dopant element at least one element
selected from gallium, dysprosium and thulium.
12. The silver alloy for use in a reflective film according to
claim 2, comprising as a second dopant element at least one element
selected from magnesium, zinc, nickel, molybdenum, terbium,
gadolinium and erbium.
13. The silver alloy for use in a reflective film according to
claim 2, comprising as a second dopant element at least one element
selected from aluminum, neodymium and holmium.
14. The silver alloy for use in a reflective film according to
claim 2, comprising as a second dopant element at least one element
selected from copper, cobalt, tin, titanium, bismuth, scandium,
yttrium, praseodymium and manganese.
15. The silver alloy for use in a reflective film according to
claim 2, comprising as a second dopant element at least one element
selected from germanium, indium, samarium, ytterbium, strontium,
boron, silicon, chromium, iron, zirconium, niobium, tantalum,
tungsten, rhodium, lead, calcium, antimony, hafnium, lanthanum and
cerium.
16. The silver alloy for use in a reflective film according to
claim 2, wherein a total of the concentration of the first dopant
element and the concentration of the second dopant element are 0.01
to 5.0 atomic %.
17. The silver alloy for use in a reflective film according to
claim 3, wherein a total of the concentration of the first dopant
element and the concentration of the second dopant element are 0.01
to 5.0 atomic %.
18. The silver alloy for use in a reflective film according to
claim 4, wherein a total of the concentration of the first dopant
element and the concentration of the second dopant element are 0.01
to 5.0 atomic %.
19. An optical recording medium comprising a substrate and a silver
alloy on the substrate which silver alloy comprises silver and at
least one of platinum, palladium, gold, rhodium, ruthenium and
iridium as a first dopant element, and as a optional second dopant
element at least of gallium, dysprosium, thulium, magnesium, zinc,
nickel, molybdenum, terbium, gadolinium, erbium, aluminum,
neodymium, holmium, copper, cobalt, tin, titanium, bismuth,
scandium, yttrium, praseodymium, manganese, germanium, indium,
samarium, ytterbium, strontium, boron, silicon, chromium, iron,
zirconium, niobium, tantalum, tungsten, rhodium, lead, calcium,
antimony, hafnium, lanthanum and cerium.
20. A method for producing an optical recording medium which
comprises forming a film of a silver alloy on a substrate, which
silver alloy comprises a first dopant element selected from at
least one of platinum, palladium, gold, rhodium, ruthenium and
iridium; and which silver alloy optionally further comprises a
second dopant element selected from at least one of gallium,
dysprosium, thulium, magnesium, zinc, nickel, molybdenum, terbium,
gadolinium, erbium, aluminum, neodymium, holmium, copper, cobalt,
tin, titanium, bismuth, scandium, yttrium, praseodymium, manganese,
germanium, indium, samarium, ytterbium, strontium, boron, silicon,
chromium, iron, zirconium, niobium, tantalum, tungsten, rhodium,
lead, calcium, antimony, hafnium, lanthanum and cerium.
Description
TECHNICAL FIELD
[0001] The present invention relates to a silver alloy suitable as
a material for forming reflective films provided on optical
recording media, displays and the likes. Particularly, the present
invention relates to a silver alloy for reflective films capable of
maintaining the reflectance thereof even in long-term use.
BACKGROUND ART
[0002] Silver is recognized as a most preferable material as a
material for reflective films to be used in optical recording
media, displays and the like. This is because silver is high in
reflectance, and additionally, lower in price than gold that is
also high in reflectance. In the field of optical recording media
in these years, transition to recordable/rewritable media (CD-R/RW,
DVD-R/RW/RAM) takes place, and expanding importance of optical
recording media attaches importance to silver that is high in
reflectance and relatively low in cost as a central material for
use in reflective films.
[0003] On the other hand, silver involves a problem such that
silver is poor in corrosion resistance and is degraded in
reflectance by discoloration to black through corrosion. The root
causes for the corrosion of reflective films may vary with products
(recording media, displays and the like) to which the reflective
films are applied, in such a way that, for example, reflective
films of displays suffer from a fear that they are corroded due to
the atmospheric humidity or the like.
[0004] A reflective layer of an optical recording medium also
suffers from a fear of corrosion due to the atmosphere such as the
air, and furthermore, requires a consideration of corrosion caused
by the effects of the other constituent layers (the recording
layer, dielectric layer and the like) in contact with the
reflective layer in the recording medium. For example, a recordable
optical disk (CD-R, DVD-R, DVD+R or the like) has a structure in
which an organic azo or cyanine dye ink is coated on a
polycarbonate substrate and dried to form a recording layer, a
reflective layer is formed on the surface of the recording layer,
and the recording layer with the reflective layer is bonded to
another polycarbonate substrate with an ultraviolet cure adhesive.
In this case, the organic dye ink in the recording layer and the
ultraviolet cure adhesive, both in contact with the reflective
layer, contain sulfur as a component thereof or as an impurity, and
accordingly, the reflective layer is exposed to a fear of corrosion
in the course of use thereof because silver is poor in resistance
to sulfidation. On the other hand, a rewritable optical disk
(CD-RW, DVD-RW, DVD+RW, DVD-RAM or the like) has a structure in
which a derivative layer, a recording layer, a dielectric layer and
a reflective layer are laminated in such a condition that the
reflective layer is in contact with the dielectric layer. Various
materials are available for the dielectric layer, but in these
years, materials to which zinc sulfide (ZnS) is applied are being
used (sometimes, for the purpose of controlling heat reserve, a
material made of zinc sulfide doped with silicon oxide, namely,
ZnS-20 mol % SiO.sub.2 or the like being applied). Consequently,
also in this case, there is a fear of corrosion due to a sulfide.
As described above, the reflective layer of an optical recording
medium is in such an environment that the reflective layer is in
contact with a layer containing sulfur or a sulfide, irrespective
as to whether the optical recording medium is recordable or
rewritable in type; thus, the resistance to sulfidation comes to be
more significant than the corrosion caused by the atmosphere
involving humidity or the like, and there is a fear that the
reflectance of the reflective layer is degraded by the long-term
use of the recording medium.
[0005] Additionally, there is a problem that a reflective film made
of silver is also thermally degraded in reflectance. The mechanism
involved in the reflectance degradation due to heating is not yet
elucidated, but it has been verified that heating of a thin silver
film causes a phenomenon in which local agglomeration occurs in the
thin film so as to expose the underlayer. Accordingly, the
reflective film of an optical recording medium, a plasma display or
the like is required to have a heat resistance because it possibly
undergoes heating.
[0006] For the purpose of coping with the reflectance degradation
of the reflective film as described above, there have
conventionally been developed silver alloys, for use in reflective
films, that are improved in corrosion resistance and heat
resistance while the reflectance being secured. These alloys mostly
include silver as the main component, and are doped with one or
more of various elements as dopant elements; examples of such
disclosed alloys include, for example, an alloy in which Ag is
doped with Ca, V or Nb. It has been disclosed that these silver
alloys are satisfactory in corrosion resistance, can maintain the
reflectance in service environment, and consequently, suitable for
reflective films (for the details of the conventional art, see
Patent Documents 1 and 2).
[0007] Patent Document 1: Japanese Patent Laid-Open No. Hei
6-243509
[0008] Patent Document 2: Japanese Patent Laid-Open No.
2003-6926
[0009] As for the above described silver alloys, improvements of
the corrosion resistance and heat resistance have been developed to
some extents. However, even these silver alloys are not absolutely
free from deterioration in service environment. Additionally, the
reflectance is not completely guaranteed against reflectance
degradation, and materials that can maintain the reflectance at a
higher level are desired.
[0010] In the field of optical recording devices, at present, red
semiconductor lasers (wavelength: 650 nm) are applied as recording
light sources, but blue lasers (wavelength: 405 nm) have almost
seen their way clear to practical use. Application of the blue
laser can ensure a memory capacity 5 to 6 times as large as the
memory capacity of an optical recording device available at
present, so that optical recording devices incorporating blue
lasers applied thereto will conceivably form the mainstream of the
next-generation optical recording devices. In this connection,
according to the present inventors, it has been verified that the
reflectance of a reflective film varies with the wavelength of the
incident laser light; in particular, it has been verified that
shorter-wavelength laser irradiation degrades the reflectance
irrespective as to whether corrosion occurs or not, and makes the
extent of the reflectance degradation due to corrosion frequently
larger than the longer-wavelength laser irradiation. Consequently,
for the purpose of producing recording media adaptable to the
development of the future recording light sources, it is desired to
develop a material that has a high reflectance even for the laser
irradiation in a shorter wavelength region, and furthermore, can
maintain the reflectance within a range of practical use.
[0011] The present invention has been achieved on the above
described background, and is aimed at providing a material that is
a silver alloy to form a reflective film of an optical recording
medium or the like, and is workable without degrading the
reflectance even in a long-term use. Additionally, the present
invention provides a material that has a high reflectance even for
a short wavelength laser light.
DISCLOSURE OF THE INVENTION
[0012] In order to solve the above described problems, the present
inventors selected appropriate dopant elements with silver as the
main component similarly to the conventional art. Consequently, the
present inventors have come up with the present invention by
discovering that the addition of a rare-earth metal element, as an
dopant element, higher than silver in melting point is effective in
maintaining the reflectance and is useful for improving the heat
resistance, the moisture resistance or the resistance to
sulfidation.
[0013] The present invention is a silver alloy for use in a
reflective film, including silver as a main element and at least
one precious metal element as a first dopant element.
[0014] Here, the precious metal as the first dopant element is
selected from platinum, palladium, gold, rhodium, ruthenium and
indium. Inclusion of at least one of these elements can lead to a
silver thin film useful for maintaining the high reflectance.
[0015] According to the investigations carried out by the present
inventors, it has been verified that a silver alloy, doped with
platinum, palladium or gold among the above described elements, can
maintain the various properties required for a reflective film at
specially high levels. Such a silver alloy is excellent both in
corrosion resistance and in heat resistance, and are suitable not
only for the reflective layer for use in an optical recording
medium but also for the reflective film for use in a display.
[0016] Further, in the present invention, the silver alloy is
preferably an alloy doped with at least one element, as a second
dopant element, selected from gallium, dysprosium, thulium,
magnesium, zinc, nickel, molybdenum, terbium, gadolinium, erbium,
aluminum, neodymium, holmium, copper, cobalt, tin, titanium,
bismuth, scandium, yttrium, praseodymium, manganese, germanium,
indium, samarium, ytterbium, strontium, boron, silicon, chromium,
iron, zirconium, niobium, tantalum, tungsten, rhodium, lead,
calcium, antimony, hafnium, lanthanum and cerium. These elements
have effects to improve, in cooperation with the first dopant
element, the resistance to sulfidation, moisture resistance and
heat resistance, and work in combination with the first dopant
elements.
[0017] In particular, a silver alloy doped with a second dopant
element of gallium, dysprosium or thulium is a preferable alloy
because such an alloy can effectively suppress the agglomeration
phenomenon which possibly occur in a thin film material in a
humidified environment.
[0018] Additionally, the dopant element concentration, namely,
total of the concentration(s) of the first dopant element(s) and
the concentration(s) of the second dopant element(s) is preferably
0.01 to 5.0 atomic %. When the addition amount is less than 0.01
atomic %, no effect of the reflectance maintenance is found. When
the dopant element concentration exceeds 5.0 atomic %, the
reflectance degradation becomes large depending on the service
environment and the incident laser light wavelength, and it becomes
impossible to ensure the reflectance. The concentration is
particularly preferably 0.01 to 2.0 atomic %, because this range of
concentration can maintain the reflectance at a higher level
irrespective of the service environment and the laser light
wavelength.
[0019] The above-described silver alloy, according to the present
invention, as the material for use in a reflective film, can be
produced by the melt casting method and the sintering method. The
production based on the melt casting method involves no particular
difficulties, and can produce the alloy by means of a general
method in which individual raw materials are weighed out, mixed by
melting, and the mixture is subjected to casting. The sintering
method also involves no particular difficulties, and can produce
the alloy by means of a general method in which individual raw
materials are weighed out, and subjected to sintering.
[0020] The silver alloy according to the present invention has
properties favorable for a reflective film, and suppresses the
reflectance degradation in the course of use. As described below,
the silver alloy according to the present invention exhibits a more
satisfactory reflectance and a more satisfactory maintenance of the
reflectance than conventional materials for use in reflective
films, even under irradiation with a short wavelength laser light.
As described above, the sputtering method is generally applied to
the production of reflective films of optical recording media and
the like. Accordingly, sputtering targets made of the silver alloy
according to the present invention can serve to produce optical
recording media, displays and the like each provided with a
reflective film having satisfactory properties.
[0021] As described above, according to the present invention, a
reflective film that is less degraded in reflectance even under
long-term use can be produced, and various devices to which
reflective films are applied, such as optical recording media,
displays and the like, can be made to have a long operation life.
The silver alloy according to the present invention also exhibits a
more satisfactory reflectance and a more satisfactory maintenance
of the reflectance than conventional materials for use in
reflective films, even under irradiation with a short wavelength
laser light. Accordingly, the silver alloy according to the present
invention is compatible with recording media for use in optical
recording devices each having a short wavelength laser as the light
source, such recording devices being anticipated to form the
mainstream of such devices.
BEST MODE FOR CARRYING OUT THE INVENTION
[0022] Hereinafter, a preferred embodiment of the present invention
is described together with comparative examples. Here, binary and
ternary silver alloys having various compositions with Ag as the
main component were produced; targets were produced from these
alloys, and thin films were formed therefrom by means of a
sputtering method. These thin films were subjected to corrosion
tests (accelerated tests) in various environments, and the
reflectance variations as observed after the corrosion tests were
examined.
[0023] In the production of each of the silver alloys, individual
metals were weighed out so as to give predetermined concentrations,
mixed by melting in a high frequency melting furnace to yield an
alloy. The molten alloy thus obtained was cast into a casting mold
to be solidified to yield an ingot, the ingot was forged, rolled
and heat treated, and thereafter shaped into a sputtering
target.
[0024] In the thin film production, a substrate (borosilicate
glass) and a target were placed in a sputtering apparatus, the
interior of the apparatus was evacuated to a vacuum of
5.0.times.10.sup.-3 Pa, and then argon gas was introduced into the
interior of the apparatus so as to give a pressure of
5.0.times.10.sup.-1 Pa. Sputtering conditions were such that film
formation was carried out with a direct current power of 4 kW for 8
seconds to attain a film thickness of 1200 .ANG.. It is to be noted
that the film thickness distribution fell within .+-.10%.
[0025] The thin film products were evaluated with respect to heat
resistance and moisture resistance. These properties were evaluated
as follows: a thin film was exposed to each corresponding
environment and the reflectance of the thin film after each test
was measured at a varying wavelength in a spectrophotometer; and
the observed reflectances at different wavelengths were compared
differentially with the corresponding reflectances of silver as the
reference levels, which were measured immediately after film
formation.
[0026] The heating test to examine the heat resistance of a thin
film was carried out as follows: the thin film was placed on a hot
plate, heated in an atmosphere at 250.degree. C. for 1 hour, and
the reflectance after heating was evaluated. The humidification
test to examine the moisture resistance of a thin film was carried
out as follows: the thin film was exposed to an atmosphere of a
temperature of 100.degree. C. and a humidity of 100%, and the
reflectance after humidification was evaluated; the exposure time
was varied to take two periods, namely, 24 hours (humidification
test I) and 100 hours (humidification test II). The results of
these corrosion tests are shown in Tables 1 to 3. The reflectances
shown in these tables are relative values based on the reflectances
of silver immediately after film formation which are set at 100.
The measured reflectance values are the values measured at the
wavelengths of 400 nm, 550 nm and 650 nm (respectively
corresponding to the wavelengths of blue, yellow and red lasers).
It is to be noted that each of these tables includes, for
comparison, the test results obtained for a thin film produced from
a target made of pure silver. TABLE-US-00001 TABLE 1 Incident light
wavelength: 400 nm Reflectance Humidi- Humidi- Immediately fica-
fica- Sulfur- Sample after Heating tion tion ation composition (at
%) deposition test test I test II test Ag-0.6 Pt 98.7 92.5 80.3
58.9 58.9 Ag-0.3 Au 100.6 85.4 28.1 25.9 25.9 Ag-0.6 Au 99.8 43.5
97.8 94.1 94.1 Ag-1.1 Au 86.0 91.7 77.1 88.1 88.1 Ag-1.0 Pd 97.0
91.8 92.5 87.3 87.3 Ag-1.0 Rh 95.2 76.1 93.0 78.8 78.8 Ag-1.1 Ru
93.1 90.3 90.4 64.4 64.4 Ag-2.7 Ir 98.1 90.5 95.8 84.4 84.4 Ag-0.3
Au-0.5 In 96.2 74.7 89.7 70.9 70.9 Ag-0.5 Au-0.5 In 97.9 74.5 88.6
39.4 39.4 Ag-0.5 Au-0.5 Cu 99.8 68.6 73.6 61.9 61.9 Ag-0.5 Pd-0.5
In 94.1 89.7 89.8 82.2 82.2 Ag (for 102.3 1.6 45.9 37.5 37.5
comparison)
[0027] TABLE-US-00002 TABLE 2 Incident light wavelength: 550 nm
Reflectance Immediately Humidi- Humidi- Sulfur- Sample after
Heating fication fication ation composition (at %) deposition test
test I test II test Ag-0.6 Pt 99.6 98.4 90.4 90.6 71.9 Ag-0.3 Au
100.5 73.0 58.3 69.7 54.5 Ag-0.6 Au 100.5 66.4 100.0 82.6 62.3
Ag-1.1 Au 96.9 96.0 88.9 84.6 73.9 Ag-1.0 Pd 99.0 97.5 97.5 72.4
79.1 Ag-1.0 Rh 97.2 87.1 97.3 97.9 61.7 Ag-1.1 Ru 97.4 96.6 95.7
91.4 3.7 Ag-2.7 Ir 99.4 95.5 98.4 95.8 50.1 Ag-0.3 Au-0.5 In 98.9
94.6 94.8 91.2 67.3 Ag-0.5 Au-0.5 In 99.6 85.9 95.9 93.1 69.3
Ag-0.5 Au-0.5 Cu 100.3 87.8 85.7 83.6 57.5 Ag-0.5 Pd-0.5 In 98.1
96.1 95.5 91.8 76.5 Ag (for 100.8 1.5 78.4 67.8 39.6
comparison)
[0028] TABLE-US-00003 TABLE 3 Incident light wavelength: 650 nm
Reflectance Immediately Humidi- Humidi- Sulfur- Sample after
Heating fication fication ation composition (at %) deposition test
test I test II test Ag-0.6 Pt 99.7 99.2 92.9 92.6 81.7 Ag-0.3 Au
100.6 79.6 67.8 79.1 70.0 Ag-0.6 Au 100.6 76.0 100.2 86.7 74.3
Ag-1.1 Au 100.3 98.4 91.9 88.6 83.7 Ag-1.0 Pd 99.8 99.0 98.6 77.1
87.3 Ag-1.0 Rh 97.6 89.7 97.8 98.1 71.3 Ag-1.1 Ru 98.1 97.7 97.2
92.1 12.5 Ag-2.7 Ir 99.6 96.4 98.7 96.2 62.7 Ag-0.3 Au-0.5 In 99.2
85.8 95.0 92.4 75.4 Ag-0.5 Au-0.5 In 99.8 87.3 96.6 94.0 78.1
Ag-0.5 Au-0.5 Cu 100.3 92.8 85.9 84.8 71.5 Ag-0.5 Pd-0.5 In 98.8
97.3 96.2 93.2 84.3 Ag (for 100.6 11.6 86.0 78.6 53.5
comparison)
[0029] As can be seen from these results, as a general tendency,
with decreasing incident light wavelength, the reflectance was
lowered. When binary and ternary alloys were judged in a
comprehensive manner in terms of heat resistance, moisture
resistance and sulfide resistance, it was verified that the alloys
are more excellent than silver in all the wavelength bands.
[0030] Next, the applicability as a practical reflective film was
evaluated for each silver alloy film according to the present
invention. Actually, this evaluation was carried out on the basis
of two evaluation methods: one was a convenient simulated
evaluation method that was devised by the present inventors and the
other was an evaluation method in which an optical recording medium
was actually produced and the performance (presence or absence of
error) thereof was examined. The reason why the former simulated
evaluation was carried out in the present invention is as follows:
in an optical recording medium taken as an example, the optical
recording medium is composed of a large number of layers including,
in addition to the reflective layer, a substrate and a recording
layer, and including, depending on the type of the medium, a
dielectric layer, a heat release layer and the like; and for the
purpose of evaluating the adaptability of the reflective layer of
the optical recording medium, it is necessary that these
constituent layers are formed on the substrate to produce the
recording medium, and then the recording medium is evaluated, and
this is troublesome.
[0031] For optical recording media in practical use, it is
relatively easy to produce such media for an evaluation purpose.
However, high-density large-capacity recording media under
development for practical use in future, such as HD-DVD disks and
Blu-lay disks, become more complex in structure and have reflective
layers to work as semitransparent reflective layers that are
anticipated to be used as further thinner films (the film thickness
of the reflective layer of an optical recording medium currently
used being around 1000 to 1200 .ANG.; but the reflective layer of
such a next generation optical recording medium being developed for
a film thickness of 200 .ANG. or less). As for such media to be
complex as described above, it is difficult to actually produce and
evaluate them.
[0032] Consequently, for the purpose of evaluating the adaptability
of a formed thin film as a reflective film without producing an
optical recording medium, the present inventors has adopted a
method, as a convenient method, in which such a film is exposed in
a predetermined environment, and thereafter the surface appearance
of the film is observed to evaluate the adaptability of the thin
film to practical use.
[0033] In this method, the humidification test is carried out as
follows: first, a formed thin film is allowed to stand (for 20 to
30 minutes) in a cooling atmosphere set at a temperature
(preferably 10.degree. C.) lower than room temperature to be
sufficiently cooled together with the substrate; the thus cooled
thin film is exposed in a humidification environment; and the thin
film is taken out and dried, and thereafter a surface appearance of
the thin film is observed. The humidification environment is
preferably an atmosphere at a temperature of 100.degree. C. and
with a humidity of 100%, and the exposure time in this case is
preferably set at 20 minutes. In the heating test, a formed thin
film is directly placed together with the substrate in a heating
environment; the heating environment is preferably an air
atmosphere at 250.degree. C., and the exposure time in this case is
preferably set at 60 minutes.
[0034] The observation of the surface appearance is conducted to
evaluate the evaluation of the degree of generation of silver
agglomerates (hereinafter referred to as black spots) occurring as
black spots on the thin film surface after having been exposed in
each environment. This is based on the consideration that: as a
form of deterioration of a heated silver alloy film, silver
agglomerates are locally generated on the surface of the film;
silver agglomerates conceivably affect the properties of a
reflective film; and accordingly, the evaluation of the generation
degree of the black spots allows the adaptability as a reflective
film to be determined. In this evaluation, the black spots to be
counted are preferably those each having a size of 1 to 10 .mu.m.
Such clear definition of the spots to be evaluated allows the
evaluation to be facilitated. Such a size as described above
matches the size of marks to be used for record reproduction in an
optical recording medium.
[0035] The evaluation of the generation degree of the black spots
may be carried out, for example, by taking a photo of the surface
of the thin film, and by subjecting the photo to image processing
to derive the rate of the area of the black spots. As a more
convenient method, there is one in which evaluation is carried out
by taking as a reference the surface condition (in this case,
almost no black spots being generated) of a silver thin film
immediately after formation thereof and by assessing the surface
condition of a thin film after heating, relatively to the
reference, through classification into a few levels.
[0036] In the present embodiment, the humidification environment
was set to be an atmosphere at a temperature of 100.degree. C. and
with a humidity of 100%, with the exposure time set at 20 minutes.
In the simulated evaluation of a thin film in the present
embodiment, different types of 120 .ANG. and 1200 .ANG. silver
alloy thin films were produced, and each thin film was cooled and
thereafter exposed in the above described humidification
environment to be subsequently subjected to optical microscopic
observation of the surface appearance thereof. The surface
condition of a silver thin film immediately after the production
thereof was taken as a reference to be graded as "level 1," and the
surface condition evaluation was carried out in terms of 5 grades
in the degrading order of the surface condition from level 1 (in
the order of increasing number of the black spots) in such a way
that the properties of the films were assessed through
classification into level 1 to level 5. The results thus obtained
are shown in Table 4. TABLE-US-00004 TABLE 4 Samples (at %) Level
Binary alloy Ternary alloy Film thickness: 1200 .ANG. 1 Ag-1.0 Pt
Ag-2.0 Pd Ag-1.0 Pd-1.0 Dy 2 Ag-0.5 Pt-2.0 Ga 3 Ag-1.0 Au 4 5
Ag-1.0 Ir Ag-1.0 Rh Ag-1.0 Ru Ag-1.0 Os Film thickness: 120 .ANG. 1
Ag-1.0 Pd-1.0 Dy Ag-0.5 Pt-2.0 Ga 2 Ag-1.0 Au 3 Ag-2.0 Pd 4 5
Ag-1.0 Ir Ag-1.0 Rh Ag-1.0 Ru Ag-1.0 Os Level 1 refers to the
surface condition of silver immediately after deposition.
[0037] As a result of the simulated test, it is inferred that
excellent, in properties, among the binary alloys are those
containing platinum, palladium or gold, and excellent, in
properties, among the ternary alloys is that containing dysprosium
or gallium as the second dopant element.
[0038] Next, DVD-R media having as a reflective layer thin films
made of the silver alloys according to the present invention were
actually produced and were evaluated for the properties as the
reflective film of an optical recording medium. In this test, there
were used as substrates polycarbonate substrates (120 mm in
diameter, 0.6 mm in plate thickness, 0.17 .mu.m in groove depth,
0.3 .mu.m in groove width, and 0.74 .mu.m in groove pitch) with
preformatted pattern formed thereon, produced with an injection
molding machine equipped with a stamper. On the upper side of each
substrate, a metal-containing azo recording ink was coated by way
of spin coating and dried, and thereafter, a reflective film was
formed so as to have a film thickness of 1200 .ANG. with a
sputtering target produced in the present embodiment. To each
substrate, a polycarbonate substrate the same in size as the
substrate concerned was bonded with an ultraviolet curable resin to
produce a DVD-R medium.
[0039] Then, with an optical disk evaluation apparatus (optical
disk evaluation apparatus, ODU1000, manufactured by Pulstec
Industrial Co., Ltd.), the jitter values, PI8 errors and PO errors
of the thus produced DVD-R media in the initial condition
subsequent to the production thereof were measured, and were
verified to fall within the ranges of the DVD specifications. After
the verification, the DVD-R media were subjected to an accelerated
environment test in which the DVD-R media were exposed in an
environment at a temperature of 80.degree. C. and with a relative
humidity of 85%, and the DVD-R media after the accelerated
environment test were subjected to the measurement of the
individual values by means of the evaluation apparatus.
[0040] FIGS. 1 to 3 show relations between humidification time and
jitter value, PI8 error value and PO error, respectively, which
were all measured in this test. These figures also show the results
obtained by applying the same tests to a DVD-R medium having a
reflective film made of pure silver and commercially available
DVD-R media.
[0041] As can be seen from these figures, it has been verified that
the recording media each provided with a reflective film made of a
silver alloy according to the present invention each clear the
specifications for the individual values, and have a long-term
stability, even after a long time humidification. On the contrary,
the recording medium provided with a reflective film made of pure
silver failed to be recognized by the recording device and became
unusable after humidification for 150 hours. It was also verified
that the jitter values of the commercially available products
exceeded the specification, and although the error values of these
commercial products were able to clear the specifications, the
properties of these commercial products were inferior to those of
the recording media according to the present embodiment.
[0042] Additionally, Table 5 shows results obtained as follows:
DVD-R media each provided with a reflective film made of a silver
alloy different in composition from those examined above were
produced; the DVD-R media thus produced were exposed in a
humidification environment in the same manner as described above;
and thereafter, the results shown in Table 6, namely, the jitter
values, PI8 errors and PO errors thereof were measured.
TABLE-US-00005 TABLE 5 Jitter value PI8 error PO error After After
After expo- expo- expo- sure to sure to sure to Initi- humid-
Initi- humid- Initi- humid- ally ity ally ity ally ity Examples
Ag-0.5 Pt-0.1 Zn 7.7 7.8 47 211 2 14 Ag-1.0 Au-0.2 Mo 7.7 7.9 51
251 3 17 Ag-1.0 Pd-1.0 Pr 7.8 7.9 59 252 3 12 Ag 8.2 11.7 207 299
25 83 Comparative Examples Commercial product 8.6 10.7 224 305 31
73 from Company A Commercial product 8.3 .gtoreq.11.9 185
.gtoreq.318 45 .gtoreq.104 from Company B Specification 8.00 or
less 280 or less 182 or less
[0043] Also from this table, it was verified that the individual
values of the recording media each provided with a silver alloy
according to the present invention as a reflective layer cleared
the specifications even after the humidification, and each had a
long-term stability. The evaluations carried out by producing these
media coincided with the already performed, simulated test, and the
long-term stability was owned by each of the recording media,
anticipated to have satisfactory properties in the simulated test,
each provided with a reflective film containing at least any one of
platinum, palladium, gold, dysprosium and gallium. Consequently, it
has been verified that the simulated test carried out in the
present embodiment is a convenient method for assessing the
properties of a silver alloy without actually producing a recording
medium.
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] FIG. 1 is a graph showing the results (jitter values) of an
accelerated environment test carried out on DVD-R media each
provided with one of the reflective films according to present
Embodiment;
[0045] FIG. 2 is a graph showing the results (PI8 error values) of
the accelerated environment test carried out on the DVD-R media
each provided with one of the reflective films according to present
Embodiment; and
[0046] FIG. 3 is a graph showing the results (PO error values) of
the accelerated environment test carried out on the DVD-R media
each provided with one of the reflective films according to present
Embodiment.
* * * * *