U.S. patent application number 10/792727 was filed with the patent office on 2004-09-02 for glass material.
Invention is credited to Naito, Takashi, Namekawa, Takashi, Shintani, Toshimichi, Suzuki, Yasutaka, Takahashi, Ken, Terao, Motoyasu, Yamamoto, Hiroki.
Application Number | 20040170797 10/792727 |
Document ID | / |
Family ID | 15501407 |
Filed Date | 2004-09-02 |
United States Patent
Application |
20040170797 |
Kind Code |
A1 |
Yamamoto, Hiroki ; et
al. |
September 2, 2004 |
Glass material
Abstract
A glass including SiO.sub.2, Na.sub.2O, MgO, Al.sub.2O.sub.3,
and cobalt oxide, wherein the cobalt oxide is 4.5-85 wt % as an
oxide of CoO or 4.9-91 wt % as an oxide of Co.sub.3O.sub.4.
Inventors: |
Yamamoto, Hiroki;
(Hitachi-shi, JP) ; Naito, Takashi;
(Hitachioota-shi, JP) ; Namekawa, Takashi;
(Hitachi-shi, JP) ; Suzuki, Yasutaka; (Ishi,
JP) ; Takahashi, Ken; (Naka-gun, JP) ; Terao,
Motoyasu; (Tokyo, JP) ; Shintani, Toshimichi;
(Tokyo, JP) |
Correspondence
Address: |
ANTONELLI, TERRY, STOUT & KRAUS, LLP
1300 NORTH SEVENTEENTH STREET
SUITE 1800
ARLINGTON
VA
22209-9889
US
|
Family ID: |
15501407 |
Appl. No.: |
10/792727 |
Filed: |
March 5, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10792727 |
Mar 5, 2004 |
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10207050 |
Jul 30, 2002 |
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10207050 |
Jul 30, 2002 |
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09722503 |
Nov 28, 2000 |
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6440517 |
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09722503 |
Nov 28, 2000 |
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09432782 |
Nov 3, 1999 |
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6177169 |
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09432782 |
Nov 3, 1999 |
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09090382 |
Jun 4, 1998 |
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5985401 |
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Current U.S.
Class: |
428/64.1 ;
428/426; G9B/7.172; G9B/7.186 |
Current CPC
Class: |
G11B 7/2534 20130101;
G11B 7/2531 20130101; G11B 7/258 20130101; G11B 7/2535 20130101;
G11B 7/0045 20130101; G11B 7/24 20130101; C03C 3/091 20130101; Y10T
428/21 20150115; G11B 2007/24312 20130101; C03C 8/00 20130101; G11B
7/2585 20130101; Y10S 430/146 20130101; G11B 7/252 20130101; G11B
7/2548 20130101; C03C 3/087 20130101; G11B 7/005 20130101; Y10S
428/913 20130101; G11B 2007/24314 20130101; G11B 2007/24316
20130101; G11B 7/2433 20130101; C03C 3/062 20130101; C03C 3/078
20130101; G11B 7/2578 20130101; G11B 7/248 20130101; G11B 7/257
20130101; Y10T 428/31678 20150401 |
Class at
Publication: |
428/064.1 ;
428/426 |
International
Class: |
B32B 017/06 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 9, 1997 |
JP |
9-150646 |
Claims
What is claimed is:
1. A glass substrate for optical information recording medium,
comprising transition metal oxides or rare earth element oxides,
and silicon oxide, wherein said glass substrate contains said
transition metal oxides or rare earth element oxides in an amount
of 0.1% to 29% by weight, and said glass substrate is made of a
glass which varies in light density distribution.
2. A glass substrate for optical information recording medium
according to claim 1, wherein transition metals or rare earth
elements, for forming said transition metal oxides or said rare
earth element oxides, are selected from the group consisting of Ti,
V, Cr, Mn, Fe, Co, Ni, Cu, Nd, Ce, Pr, Sm, Eu, Tb, Ho, Er and
Tm.
3. A glass substrate for optical information recording medium
according to claim 2, wherein said transition metals or rare earth
elements is Co.
4. A glass substrate for optical information recording medium
comprising cobalt oxide and silicon oxide, wherein said glass
substrate contains said cobalt oxide in an amount of 0.1% to 29% by
weight as converted to CoO, and said glass substrate is made of a
glass which varies in light intensity distribution.
5. A glass substrate for optical information recording medium
according to claim 4, wherein said glass substrate is made of a
glass comprising SiO.sub.2: 6-80% by weight; alkali metal oxide:
0-20% by weight; and B.sub.2O.sub.3: 0-30% by weight, in addition
to said cobalt oxide.
6. A glass substrate for optical information recording medium
according to claim 1, wherein said glass substrate is made of a
glass comprising SiO.sub.2: 6-80% by weight; alkali metal oxide:
0-20% by weight; and B.sub.2O.sub.3: 0-30% by weight, in addition
to said transition metal oxides or rare earth element oxides.
Description
[0001] This is a Continuation of application Ser. No. 09/722,503,
filed Nov. 28, 2000, which is a Continuation of U.S. application
Ser. No. 09/432,782, filed Nov. 3, 1999, now U.S. Pat. No.
6,177,169, issued Jan. 23, 2001, which is a continuation of U.S.
application Ser. No. 09/090,382, filed Jun. 4, 1998, now U.S. Pat.
No. 5,985,401, issued Nov. 16, 1999, the subject matter of which is
incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION
[0002] The present invention relates to an information recording
medium, and more particularly, to an optical information recording
medium, which is capable of reading out or recording with a high
recording density, and which has a high reliability in repeating
recording and regeneration operations.
[0003] Conventionally, compact disks (CD), laser disks (LD), and
the like are used widely as optical information recording media.
Currently, a DVD, which has seven times the recording density of a
CD, has come into practical use. The DVD is being developed as an
erasable recording-regenerating medium in addition to a read only
medium (DVD-ROM), wherein information is directly written onto the
substrate. Furthermore, the practical use of a DVD as a RAM for a
computer presently is under investigation.
[0004] With the DVD, high density recording can be achieved by
using a laser having a shorter wave length, such as 650 nm, than
the laser used for a CD (wave length approximately 780 nm).
However, in order to handle a large amount of information, such as
computer graphics and the like, it is necessary to achieve a higher
recording density, such as 1.5 to 2 times that of the conventional
high density recording. In order to achieve such a high recording
density, a semiconductor laser of green to blue color having a
shorter wave length (wave length 520-410 nm) than ever is under
development.
[0005] As another means to achieve a higher recording density, a
super resolution film can be employed. The super resolution film is
a thin film formed at a lower plane of the recording medium, with
which a high recording density can be achieved by the fact that it
is able to decrease the size of the beam spot of the incident light
passing through the film.
[0006] One of the mechanisms of the super resolution effect is an
absorption-saturation phenomenon, which is a phenomenon utilizing
non-linear optical characteristics of the super resolution film
such that the film allows light having a larger intensity than the
amount of its absorption-saturation to pass through the film and
absorbs any light having an intensity less than the amount of its
absorption-saturation. The spatial intensity of a laser beam
utilized in reading and writing has a Gaussian distribution.
Therefore, when the laser light beam passes through the super
resolution film, the laser light in the lower end portion of the
Gaussian distribution, where the intensity is low, is absorbed by
the film, and the laser light in the middle portion of the Gaussian
distribution, where the intensity is high, passes through the film.
Accordingly, the diameter of the laser beam is reduced as it passes
through the super resolution film.
[0007] An organic thin film made of a material in the
phthalocyanine group, as disclosed in JP-A-8-96412 (1996),
chalcogenide, fine particles of a compound semiconductor, and the
like are known at the present as materials which may be used for
the super resolution film described above. Additionally, trials to
use some organic materials, such as thermochromic materials of the
type disclosed in JP-A-6-162564 (1994), and photochromic materials
of the type disclosed in JP-A-6-267078 (1994), as the super
resolution film have been carried out.
[0008] However, the above-mentioned materials have problems in
reliability and productivity. That is, there has been a concern
about gradual deterioration of the organic thin film after repeated
recording and regenerating operations, because the energy density
of a laser beam is locally increased significantly during the
recording and regenerating operations. Therefore, a sufficient
guarantee period for the recording and regenerating operations is
scarcely obtained under a severe condition of use, wherein the
recording and regenerating operations are performed frequently,
such as when the disk is used as a RAM and the like for
computers.
[0009] On the other hand, chalcogenide is chemically unstable, and
so a long guarantee period can not be obtained for this material,
and the fine particles of a compound semiconductor provide
difficulties during the production process.
SUMMARY OF THE INVENTION
[0010] One of the objects of the present invention is to provide an
optical recording medium having a super resolution film, which can
guarantee repeated recording and regenerating operations for a
sufficiently long time, and which has a preferable productivity and
a high resolution effect.
[0011] A first aspect of the present invention to solve the above
issues is an optical information recording medium comprising a
substrate, whereon a recording layer for recording information is
formed; and a glass thin film, formed onto the substrate, having a
characteristics such that the intensity distributions of irradiated
light onto the glass and transmitted light through the glass vary
in a non-linear manner.
[0012] The substrate is desirably transparent to light, and for
instance, is made of inorganic materials, such as glass and the
like, and organic materials, such as polycarbonate, polyethylene
terephthalate, and the like are also desirable. Here, the term
glass refers to amorphous solid oxides and general amorphous
materials containing the above oxide as a main component.
[0013] Forming on a substrate includes both forming onto the
surface of a substrate directly and forming onto the surface of a
substrate indirectly via another layer, for instance, a protection
layer.
[0014] In accordance with the above composition, an information
recording disk, which has a large capacity, and which experiences
less deterioration after repeated reading out and writing, can be
provided.
[0015] In the first aspect of the invention, the recording layer
can be provided with a pit pattern representing the recording
information. The pit pattern is a device by which the information
is recorded in accordance with the arrangement of pits provided
onto the surface of the substrate. If this recording method is
employed, the recorded information can not be rewritten. However,
once a master die of the substrate having this recorded information
is made, a large number of substrates with the same information can
be manufactured readily. Therefore, this recording method is used
for recording movies, music, and computer programs.
[0016] The recording layer of the invention can also be a device
for recording information with optical energy. For recording
information with optical energy, an information recording substrate
using so-called phase changing organic materials or inorganic
materials, the crystalline structure of which varies when
irradiated by light, is used as the recording layer.
[0017] A second aspect of the present invention is an optical
information recording medium comprising at least a substrate, a
recording layer for recording information formed on the substrate,
and a reflecting film for reflecting light formed on the recording
layer, wherein the substrate is made of glass, the optical
transmittance of which increases in a non-linear manner
corresponding to an increase in intensity of the irradiated
light.
[0018] In accordance with the above composition, a reflection type
information recording disk, which has a large capacity and less
deterioration after repeated reading out and writing, can be
provided.
[0019] This second aspect of the invention provides an information
recording substrate of a type, which reflects incident light with a
reflecting film provided at a lower portion of the recording film,
and reads the information with reflected light.
[0020] The glass in the first or the second aspects of the
invention desirably contains at least an element selected from
transition metal elements and rare earth metal elements.
[0021] For the above transition metal elements and the rare earth
metal elements, particularly, at least an element selected from the
group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Nd, Ce, Pr, Sm, Eu,
Tb, Ho, Er, and Tm is desirable.
[0022] When the transition metal element or the rare earth metal
element forms a glass film, the metal element is desirably
contained in the range from 20% by weight to 90% by weight as an
oxide to the total weight of the glass. When the metal element
forms a glass substrate, the metal element is desirably contained
in the range from 0.1% by weight to 29% by weight as an oxide to
the total weight of the glass.
[0023] In the first aspect of the invention, the glass desirably
contains as oxide the following compounds: SiO.sub.2: 6-80% by
weight, R.sub.2O: 0-20% by weight (R=alkali metal element),
B.sub.2O.sub.3: 0-30% by weight, and CoO: 20-90% by weight.
[0024] In the second aspect of the invention, the glass desirably
contains cobalt oxide as CoO in the range of 0.1-29% by weight.
[0025] A third aspect of the present invention is an information
recording medium comprising at least a substrate, whereon a
recording layer for recording information is formed, and a super
resolution layer formed on the substrate, the optical transmittance
of which increases in a non-linear manner corresponding to an
increase in the intensity of the irradiated light, wherein an
output maintaining rate of the information recording medium after
repeating the recording by 10.sup.4 times is at least 90%.
[0026] The output maintaining rate is a value indicating how much
of the intensity of the electrical signal is maintained after
repeating the recording and regeneration by 10.sup.4 times, taking
the intensity of the electrical signal at the first regeneration of
information after performing the first recording with irradiation
of light as 100%. If the super resolution film is deteriorated by
repeating the irradiation of light, the spot size of the laser ray
which reaches the recording layer is expanded, and, as a result,
the electric output is decreased. That means that a super
resolution film which can maintain the initial output maintaining
rate as long as possible is desirable.
[0027] Furthermore, in accordance with a fourth aspect of the
present invention, an information recording medium is provided,
which comprises a transparent substrate, and a recording layer for
recording information which is formed onto the substrate, wherein
an output decrease in recorded signal at a frequency of 8 MHz is
less than -30 dB of the output at 1 kHz, and an output maintaining
rate after repeating the recording by 10.sup.4 times is at least
90%.
[0028] FIG. 8 is a graph indicating a relationship between the
recording frequency and the output for the information recording
media with and without the super resolution film of the present
invention. The medium with the super resolution film can record
signals of higher frequency components, because the spot size of
the laser beam reaching the recording layer is decreased. The above
composition indicates an index which represents how high a
frequency component can be recorded.
[0029] In accordance with a fifth aspect of the present invention,
glass comprising SiO.sub.2: 6-80% by weight, R.sub.2O: 0-20% by
weight (R=an alkali metal element), B.sub.2O.sub.3: 0-30% by
weight, CoO: 20-90% by weight, as equivalent oxide, respectively,
is provided.
[0030] The above glass can be mounted not only on a photo disk, but
also on various media, as a film having the super resolution
effect. For instance, a display apparatus, which generates light
when its fluorescent body is irradiated with a laser ray so as to
be excited, can produce a high resolution display by mounting the
grass film of the present invention onto a surface of the
fluorescent body, because the spot size of the laser ray can be
converged.
[0031] In accordance with a sixth aspect of the present invention,
a glass thin film containing cobalt oxide in the range of 20-90% by
weight as equivalent CoO is provided.
[0032] In the case of this glass film, the upper limit of the CoO
content is restricted, because, if CoO is added excessively, the
CoO is precipitated, and causes devitrification.
BRIEF DESCRIPTION OF THE DRAWINGS
[0033] The above and further objects and novel feature of the
present invention will more fully appear from the following
detailed description when the same is read in connection with the
accompanying drawings. It is to be expressly understood, however,
that the drawings are for purpose of illustration only and are not
intended as a definition of the limits of the invention.
[0034] FIG. 1 is a schematic cross section of a RAM disk according
to the present invention;
[0035] FIG. 2 is a schematic cross section of a simulated sample
according to the present invention;
[0036] FIG. 3 is a graph indicating a dependency of transmittance
on wave length of the glass thin film according to the present
invention;
[0037] FIG. 4 is a diagram showing an XPS of Co of a glass thin
film according to the present invention;
[0038] FIG. 5 is a graph indicating a relationship between
transmittance for light of 650 nm and CoO content;
[0039] FIG. 6 is a diagram showing a SIMS of a glass thin film
formed onto a glass substrate having a target composition;
[0040] FIG. 7 is a schematic cross section of a ROM disk according
to the present invention;
[0041] FIG. 8 is a graph indicating a reading out frequency
dependence of an output obtained from the ROM disk shown in FIG.
7;
[0042] FIG. 9 is a graph indicating a relationship between mark
length and variation in output obtained from the RAM disk shown in
FIG. 1;
[0043] FIG. 10 is a graph indicating a dependency of output on the
repeating of operations on the RAM disk shown in FIG. 1;
[0044] FIG. 11 is a graph indicating a relationship between CoO
content and variation in reading out of the output obtained from
the RAM disk shown in FIG. 1;
[0045] FIG. 12 is a schematic cross section of a RAM disk according
to the present invention;
[0046] FIG. 13 is a schematic cross section of a ROM disk according
to the present invention;
[0047] FIG. 14 is a graph indicating variations of laser beam
diameter when the glass film of the present invention is formed and
not formed; and
[0048] FIG. 15 is a block diagram of an apparatus using the photo
disk of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Embodiment 1
[0049] Details of the present invention will be explained
hereinafter with reference to various preferred embodiments.
[0050] The composition of a number of glass targets investigated in
the development of the present invention is indicated in Table
1.
1 TABLE 1 Composition (% by weight) Target Film No. SiO.sub.2
Na.sub.2O CaO MgO Al.sub.2O.sub.3 CO.sub.3O.sub.4 CoO (kind)
Q.sup.1) 1 70.4 13.6 7.8 4.0 1.3 2.9 -- glass .largecircle. 2 69.0
13.3 7.6 3.9 1.3 2.9 -- glass .largecircle. 3 51.8 10.0 5.7 2.9 1.0
28.6 -- glass .largecircle. 4 45.3 8.8 5.0 2.6 0.9 37.4 sint.sup.2)
.largecircle. 5 29.0 5.6 3.2 1.6 0.6 60.0 sint .largecircle. 6 14.5
2.8 1.6 0.8 0.3 80.0 sint .largecircle. 7 5.9 1.4 0.5 0.2 0.1 91.9
sint X 8 -- -- -- -- -- 100 sint X 9 51.8 10.0 5.7 2.9 1.0 -- 28.6
glass .largecircle. 10 29.0 5.6 3.2 1.6 0.6 -- 60.0 sint
.largecircle. 11 14.5 2.8 1.6 0.8 0.3 -- 80.0 sint .largecircle. 12
5.9 1.4 0.5 0.2 0.1 -- 91.9 sint X 13 -- -- -- -- -- -- 100 sint X
Remarks: .sup.1)Film quality .sup.2)sintered target
[0051] In Table 1, the column indicating the film quality was
provided with O when a uniform film was obtained in view of
transparency, uniformity, and the like, and with X when the
obtained film was not uniform.
[0052] In the present embodiment, a soda-lime group glass was used
as a mother glass, and a cobalt oxide, which had a large absorption
in the vicinity of 650 nm, was used as the transition metal. As raw
materials for the cobalt oxide, CO.sub.3O.sub.4 and CoO were
used.
[0053] The targets No. 1-No. 7 are composed of soda-lime glass and
CO.sub.3O.sub.4. Among them, targets No. 1-No. 3 were targets in
the form of a glass block, because they were vitrified. Targets No.
4 No. 7 were not vitrified, because the content of CO.sub.3O.sub.4
was too much to be vitrified. Therefore, a sintered body of a
mixture of glass powder and CO.sub.3O.sub.4 was prepared as a
sintered target.
[0054] Target No. 8 is a comparative example of a sintered target
made of only CO.sub.3O.sub.4.
[0055] In targets No. 9-No. 13, CoO was used as the raw material
for cobalt oxide. In these cases, target No. 9 was a glass target,
because target No. 9 had a Co content of 28.6% by weight and was
vitrified. Because targets No. 10-No. 12 were not vitrified, a
sintered target of the mother glass raw material and CoO was
used.
[0056] Target No. 13 is a comparative example of a sintered target
made of only CoO.
[0057] The glass block for the target was obtained by the steps of
weighing a designated amount of powdered raw materials, charging
the powdered raw materials into a crucible made of platinum,
heating the crucible to approximately 1500.degree. C. in an
electric furnace to melt the raw materials, and pouring the molten
glass into a graphite mold, which was pre-heated to approximately
400.degree. C. After the raw materials were molten completely, the
molten material was cooled rapidly, a stress relief was performed
by reheating the material to approximately 600.degree. C. and then
cooling it gradually, followed by polishing the back side of the
obtained glass block.
[0058] The sintered target was obtained by the steps of granulating
a designated amount of powdered raw materials, fabricating the
powder into a fabricated body in a die, and hot pressing the
fabricated body at a designated temperature after dewaxing. The
temperature for heat treatment was 900.degree. C. when the cobalt
raw material was CO.sub.3O.sub.4, and was 1200.degree. C. when the
cobalt raw material was CoO.
[0059] As a previous step the evaluation of the shape of the disk,
a glass sample for a preliminary test in the shape of a thin film
as shown in FIG. 2 was prepared, and fundamental material
characteristics of the glass thin film were determined. In FIG. 2,
the numeral 1 indicates a substrate, and the numeral 2 represents
the glass thin film. In the present investigation, a soda-lime
glass 0.55 mm thick and 30 mm square was used as the substrate
1.
[0060] The structure of the prepared film was evaluated by a thin
film X-ray diffraction method. Then, it was found that all the
prepared films were amorphous regardless of whether the target was
glass or a sintered body, and that glass films were formed.
[0061] FIG. 3 indicates the dependence of the transmittance of the
glass thin films formed using the targets shown in Table 1 on wave
length. The transmittance was measured using monochromatic light
obtained by treating white light from a light source with a
monochromator. In accordance with target No. 1, the peak indicating
an absorption was hardly observed around 300 nm, because of too
small a content of CO.sub.3O.sub.4. In accordance with targets No.
2-No. 4, the peak indicating the absorption by Co could be
observed, even though it is small, in the region of 500 nm-700 nm.
No. 3 glass had a transmittance of approximately 85% at a wave
length of 650 nm.
[0062] With the thin films of targets No. 5 and 6, the values of
the transmittance were sufficiently low. However, the transmittance
was decreased in accordance with decreasing wave length, and it was
indicated that the decrease in the transmittance was caused by
scattering. The glass of target No. 7 and the CO.sub.3O.sub.4 of
target No. 8 had a sufficiently low transmittance. However, they
were reduced in a spattering atmosphere, and a film having a
metallic luster was obtained. Therefore, the transmittance was
decreased by reflection.
[0063] On the other hand, in accordance with the glasses of targets
No. 9-No. 11, using a raw material of CoO, a peak indicating
absorption by Co was observed in the vicinity of the region of 500
nm-700 nm. The transmittance was decreased in accordance with the
increase in Co content. The thin film of target No. 11 containing
80% of Co had a transmittance of approximately 5% at wave length of
650 nm. The glass of target No. 12 containing CoO of 91.9%, and the
film of target No. 13, which was 100% CoO, indicated the same
results as target No. 8.
[0064] In order to investigate the difference in spectrum of the
transmittance curves in FIG. 3, the valence and oxide conditions of
the Co were analyzed by XPS. The XPS spectra of Co in the thin
films of targets No. 3 and 5 are indicated in FIG. 4. In the
spectrum of the thin film of target No. 3, a peak called a shake up
peak exists around 786 eV. It indicates the presence of a large
amount of Co.sup.2+. On the contrary, the shake up peak can not be
observed in the spectrum of the thin film of target No. 5. It
indicates an oxide condition of CO.sub.3O.sub.4 coexisting with
Co.sup.3+. Accordingly, scattering occurred, and the profile
indicated in FIG. 3 was obtained.
[0065] The same investigation was performed with other thin films,
and it was found that, if cobalt existed in the condition of
Co.sup.2+, the spectrum included the peak of absorption typical for
Co, such as in targets No. 2, 3, 10, and 11, and, if Co.sup.3+
existed, the spectrum became a curve accompanied with scatter, such
as in targets No. 5 and 6.
[0066] FIG. 5 indicates the relationship between the plotted
transmittance at a wave length of 650 nm versus the Co ion content
in a target based on the thin film transmittance curves of targets
No. 2, 3, 10, and 11. The transmittance was decreased in accordance
with increasing CoO content, and the transmittance became
approximately 30% when the CoO content was 60%.
[0067] Then, in order to evaluate the Co content in the prepared
glass thin films, a composition analysis of the film was performed
with a secondary ion mass spectrometer (SIMS). A plate cut out from
the glass having the same composition as the target was used as a
substrate, and a thin film having the same composition was
spattered onto the substrate. The analysis was performed from a
film forming direction to a depth direction, so that the
compositions of the film and the substrate could be evaluated
continuously. In the present embodiment, the investigation was
performed using target No. 3 as the target composition.
[0068] The results of the analysis are indicated in FIG. 6. It was
found that the Co content in the thin film was larger than that in
the substrate. The Si content in the thin film was smaller then
that in the substrate. However, the amounts of change were small,
and a large deflection in the composition could not be expected.
Therefore, the film composition can be regarded approximately as
being the same as that of the target composition.
[0069] In accordance with the above investigation, the Co oxide
content in the glass thin film is desirably in the range of from
4.5% by weight to 85% by weight as an oxide of CoO, and of from
4.9% by weight to 91% by weight as an oxide of CO.sub.3O.sub.4. If
CoO is less than 4.5% by weight, it is difficult to obtain a
sufficient absorption of light. If CoO exceeds 85% by weight, the
film bears a metallic luster, and the transmittance is
decreased.
Embodiment 2
[0070] Then, the super resolution effect was evaluated by
manufacturing ROM disks, whereon the glass film of the present
invention was formed.
[0071] FIG. 15 is a block diagram of an example of the optical
recording apparatus used with the optical disk of the present
invention. Using the optical recording apparatus having the above
composition, the performance of the ROM disk of the present
invention was evaluated. The same apparatus was used on other
embodiments.
[0072] FIG. 7 indicates a schematic cross section of the
manufactured ROM disk. In FIG. 7, the disk includes a polycarbonate
substrate 1, a glass thin film 2, a SiO.sub.2 protective film 5,
and a Al reflector 4, and pits 6 represent stored information.
[0073] The ROM disk was manufactured by the following steps First,
a pit pastern representing information was formed onto a
photoresist by a laser. The pit pattern was duplicated onto a Ni
die, and substrates were formed by injection molding polycarbonate
into the Ni die. A glass film 160 nm thick was formed onto the
substrate by spattering, and after a SiO.sub.2 protective film of
140 nm thick was formed thereon, an aluminum reflecting film 100 nm
thick was formed. In the present embodiment, the target No. 11 film
was formed as the glass thin film. As a comparative example, a ROM
disk without forming the glass film also was manufactured.
[0074] The frequency dependency of the regenerating output
intensity of the manufactured ROM disk was analyzed with a spectrum
analyzer. The results are indicated in FIG. 8. The regenerated
laser power is 4 mW. It was revealed that, in a case when the glass
thin film of target No. 11 was formed, the output level was high
until frequency components became higher than a case when the glass
thin film was not formed. Since the high frequency components of a
signal are written with a finer pit pattern on the ROM disk, the
above result indicated that the output was regenerated by reading
out a finer pit pattern when the glass film was formed. Therefore,
it was found that, when the glass film was formed, the super
resolution effect had been obtained.
[0075] The same investigations as the above were performed on other
glass films in Table 1, and the same super resolution effect was
confirmed on the glass films of targets No. 3-6, and No. 9-11.
[0076] Then, a RAM disk, wherein the glass thin films investigated
above were formed on the substrate, was manufactured, and its
characteristics were evaluated. A schematic cross section of the
RAM manufactured in accordance with the present invention is
indicated in FIG. 1. In FIG. 1, the disk includes a polycarbonate
substrate 1, a glass super resolution film 2, a recording film 3, a
reflecting film 4, and protective films 5, 5'. In accordance with
the present invention, a circular plate 0.6 mm thick and 120 mm in
diameter was used as the polycarbonate substrate 1. A glass film
300 nm thick was formed thereon by a spattering method to form the
super resolution film 2. After forming a ZnS--SiO.sub.2 protective
film 80 nm thick thereon, a Ge--Sb--Te group phase changing film
representing the recording film was formed approximately 20 nm
thick thereon by the same spattering method. Then, after forming a
protective film approximately 90 nm thick, an AlTi reflecting film
200 nm thick was formed thereon.
[0077] The glass thin film was formed by the following steps. That
is, a glass block or a sintered body 5 mm in thickness and 120 mm
in diameter was manufactured as a target, and a backing plate made
of copper was adhered onto the back side of the target with an
organic adhesive agent for vacuum. Spattering was performed using
Argon gas. The power was 200 mW. The film was formed uniformly by
rotating the substrate during the spattering. In the present
embodiment, the sample target No. 11 was used as the glass film. As
a comparative example, a RAM disk, whereon the grass film was not
formed, was manufactured.
[0078] FIG. 9 indicates a relationship of recording mark length
versus regenerating output intensity of the RAM disk, whereon
recording marks of the same shape were formed with an equal
interval. The laser power for reading out was 2 mW. In accordance
with FIG. 9, it was revealed that the present embodiment, whereon
the glass film of target No. 11 was formed, had higher regenerating
outputs than the comparative example, which did not have the glass
film, in the shorter mark length region. Therefore, it was revealed
that regeneration was possible to the shorter mark length when the
glass film is formed. Accordingly, the super resolution effect
could tee confirmed with the RAM disk.
[0079] The same results as the case of the RAM disk were obtained
when all the glass films shown in Table 1 were investigated.
[0080] Then, a spatial intensity distribution of the reflecting
light in the cases when the above super resolution effect was
obtained were investigated. FIG. 14 indicates schematically the
intensity distribution of laser light in the laser beam forwarding
direction both in the case when the glass film was formed and the
super resolution effect was obtained, and in the case when the
glass film was not formed. In accordance with FIG. 14, it was
revealed that the spatial intensity distribution was approximately
a Gaussian distribution in the case when the grass film was not
formed, but the distribution of the beam was deflected toward the
laser beam forwarding direction when the glass film was formed.
[0081] Simultaneously, it was revealed that the beam diameter Q' at
the beam intensity necessary for reading out became smaller in
comparison with the case when the glass film was not formed.
[0082] In accordance with the above results, it was revealed that
the intensity and the intensity distribution of the reading out
light could be varied by using the grass film such as provided in
the present embodiment. Furthermore, it was revealed that the super
resolution effect could be obtained in the above case.
Embodiment 3
[0083] Next, deterioration of the film by repeated regeneration was
evaluated. The evaluation was performed by repeatedly irradiating
the manufactured RAM disk with a regeneration signal light and
detecting the regenerated output. The pit pitch was 0.3 .mu.m. The
glass thin film of target No. 11 was used. As a comparative
example, a phthalocyanine group organic thin film was selected, and
the same evaluation was performed.
[0084] FIG. 10 indicates a relationship between the output versus
the repeated number of operations. In accordance with FIG. 10, it
was revealed that the output of the disk formed with the organic
group thin film was decreased gradually over the repeated
regenerations approximately 10,000 times. On the contrary, the
output of the disk formed with the glass thin film of the present
invention was hardly decreased by repeating the regeneration over
10,000 times. As explained above, it was revealed that the optical
disk of the present invention maintained the super resolution
effect even after repeated regeneration.
[0085] The high stability against repeated regeneration could be
obtained when the glass thin film, with which the super resolution
effect was obtained in the above embodiment 2, among other glass
films in Table 1, was used as the glass thin film.
Embodiment 4
[0086] Then, the composition of the glass thin film was
investigated. First, paying attention to the content of cobalt
oxides in the glass film, a relationship between the cobalt content
and the output power was investigated by manufacturing the same RAM
disk as the disk in the embodiment 2. The mark length was 0.3
.mu.m. The laser power was 2 mw. FIG. 11 indicates a relationship
between the cobalt consent and the output. The output power was
increased in accordance with an increasing cobalt content, and it
was found that a high output could be obtained even with a small
mark length. In other words, it was found that the super resolution
effect could be increased in accordance with an increasing cobalt
content. Furthermore, it was found that the output exceeded 5 dB
when the cobalt content was equal to or more than 20%, in which
case it was possible to beat the output as a signal. However, when
the cobalt content was less than 20%, the output was less than 5
dB, and it was impossible to beat the output as a signal.
[0087] The ROM disk shown in FIG. 7 was manufactured, and the
output to the high frequency component was evaluated by a spectrum
analyzer. Then, it was revealed that the high frequency component
could be read out when the cobalt content was equal to or more than
20%, but when the cobalt content was less than 20%, any significant
effect of adding cobalt could not be observed.
[0088] In accordance with the above investigation, the cobalt
content desirably should be equal to or more than 20% by weight in
any ease of both a ROM and a RAM. In accordance with the
investigation in the embodiment 1, the cobalt content desirably
should be equal to or less than 91% by weight.
[0089] Furthermore, chemical elements to be contained in the glass
film were investigated. The mother glass was soda lime glass. The
glass containing an oxide of at least one element selected from the
group consisting of Ti, V, Cr, Mn, Fe, Co, Ni, and Cu among
transition metallic elements, and Nd, Ce, Pr, Sm, Eu, Tb, Ho, Er,
and Tm among rare earth elements had an absorbing spectrum typical
of the respective element, and the same super resolution effect as
the embodiment 2 could be obtained by using a laser beam having a
wavelength band capable of absorption.
[0090] In accordance with the above results, an optical disk having
the super resolution effect could be obtained by using the glass
thin film containing at least one element selected from the group
consisting of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Nd, Ce, Pr, Sm, Eu,
Tb, Ho, Er, and Tm among transition metallic elements and rare
earth elements.
[0091] Next, the composition of the mother glass was investigated.
In the above embodiments, soda lime glass was used as the mother
glass. However, the same effect could be obtained by using
borosilicate glass containing boron. However, when the content of
SiO.sub.2 was less than 6% by weight, the stability as glass was
low, and crystallization and the like could occur when containing
an oxide of the transition element or the rare earth element. When
the content of SiO.sub.2 exceeded 80% by weight, the above oxide
could be hardly included into the glass structure, and it was
difficult to obtain a stable glass. In accordance with the above
results, the content of SiO.sub.2 desirably should be in the range
from 6% by weight to 80% by weight.
[0092] When the content of alkaline oxide in the glass exceeded 20%
by weight, the durability of the glass decreased, and obtaining a
stable glass was difficult. Accordingly, the content of the
alkaline oxide desirably should be equal to or less than 20% by
weight.
[0093] Furthermore, when the consent of boron oxide in the glass
exceeded 30% by weight, the oxide of the transition metal or the
rare earth element was hardly included in the glass structure, and
obtaining a stable glass was difficult. Therefore, the content of
boron oxide desirably should be equal to or less than 30% by
weight.
[0094] In addition to the above indispensable components, an oxide
of alkaline earth elements, alumina, zirconia, and the like are
desirably contained in the glass as a glass stabilizing agent.
Embodiment 5
[0095] Next, the super resolution effect was investigated by
manufacturing glass substrates containing a transition metallic
element. FIG. 12 indicates schematically a cross section of a
manufactured RAM disk. In FIG. 12, the disk includes a glass
substrate 12, a recording film 3, a reflecting film 4, and
protective films 5, 5'. The thickness of the substrate was 0.6 mm,
and a track was formed onto the surface of the substrate by
reactive ion etching using a photoresist as a mask. FIG. 13
indicates schematically the cross section of the ROM disk
manufactured using the same substrate. In FIG. 13, the disk
includes a glass substrate 12, a reflecting film 4, and a recording
mark 6 representing written information. In the present embodiment,
soda lime glass was used as the mother glass, and CoO was contained
therein as the transition metallic oxide. The super resolution
effect was investigated using the same evaluating method as the
embodiment 2 by varying the consent of CoO in the range of 0.01-30%
by weight.
[0096] The composition of the manufactured glass substrate, the
evaluated results in vitrification and the super resolution are
indicated in Table 2. In the evaluated results of the
vitrification, the case when glass was formed without causing
crystallization was indicated with O, and the case when
crystallization or devitrification was caused was indicated with X.
The evaluated results of the super resolution effect were indicated
by the mark length of 0.3 .mu.m and the output at the space length.
The reading out laser wavelength was 650 nm.
2 TABLE 2 S.R.E. Composition (% by weight) Vitrifi- (output/ No.
SiO.sub.2 Na.sub.2O CaO MgO Al.sub.2O.sub.3 CoO cation dB)*.sup.1
14 72.5 14.0 8.0 4.1 1.4 0.01 .largecircle. 5 15 72.5 14.0 8.0 4.1
1.4 0.05 .largecircle. 5 16 72.5 14.0 8.0 4.1 1.4 0.10
.largecircle. 10 17 71.8 13.9 7.9 4.0 1.4 1.00 .largecircle. 16 18
65.9 12.7 7.3 3.7 1.3 9.1 .largecircle. 33 19 51.8 10.0 5.7 2.9 1.0
28.6 .largecircle. 41 20 50.7 9.8 5.6 2.9 1.0 30.0 X -- 21 66 9
B.sub.2O.sub.39 1 5 10.0 .largecircle. 33 22 49 9 26 1 5 10
.largecircle. 35 23 43 9 32 1 5 10 X -- Remarks: *.sup.1Super
Resolution Effect
[0097] In accordance with the specimens No. 14-19, and 21-23, no
crystallization nor devitrification were observed, and stable
glasses could be manufactured. The glass of specimen No. 20 caused
a phase separation after pouring, and so a stable glass could not
be obtained.
[0098] In view of the above result, the content of Coo in the glass
desirably should be equal to or less than 29%.
[0099] The glasses of specimen No. 21-23 were the same as the
glasses of specimen No. 14-19, except for replacing their CaO with
B.sub.2O.sub.3.
[0100] Regarding the regenerating output, outputs not less than 10
dB could be obtained when the cobalt content was equal to or more
than 0.10% by weight, and it was possible to read them out as
signals. On the contrary, when the cobalt content was equal to or
less than 0.05% by weight, the outputs were as small as less than 5
dB, and it was impossible to read them out.
[0101] In accordance with the above results, the content of cobalt
desirably should be in the range of 0.10-29% by weight. The above
effects were similar with the glasses which contained
B.sub.2O.sub.3 instead of CaO.
[0102] In accordance with the present invention, an information
recording disk having a large capacity, and a small deterioration
against repeated reading out and writing in operations, can be
provided. The present invention can provide an optical disk having
a large capacity when manufacturing it with a conventional optical
disk manufacturing process.
* * * * *