U.S. patent number RE45,642 [Application Number 13/912,572] was granted by the patent office on 2015-08-04 for polarizing element and liquid crystal projector.
This patent grant is currently assigned to Sony Corporation. The grantee listed for this patent is Sony Corporation. Invention is credited to Akio Takada.
United States Patent |
RE45,642 |
Takada |
August 4, 2015 |
Polarizing element and liquid crystal projector
Abstract
A polarizing plate having a desired extinction ratio in a
visible light region and light resistance against intense light,
and a liquid crystal projector using the above polarizing plate are
provided. A polarizing element includes a substrate transparent to
visible light, and inorganic particle layers in each of which
inorganic particles are linearly disposed, the inorganic particle
layers being disposed on the substrate at predetermined intervals
to form a wire grid structure, the inorganic particles each have an
elliptical shape having a major axis of the inorganic particles in
the disposed direction and minor axis in a direction perpendicular
thereto.
Inventors: |
Takada; Akio (Miyagi,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Sony Corporation |
Tokyo |
N/A |
JP |
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|
Assignee: |
Sony Corporation (Tokyo,
JP)
|
Family
ID: |
39837013 |
Appl.
No.: |
13/912,572 |
Filed: |
June 7, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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Reissue of: |
12026434 |
Feb 5, 2008 |
7957062 |
Jun 7, 2011 |
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Foreign Application Priority Data
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Feb 6, 2007 [JP] |
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2007-026348 |
Jun 28, 2007 [JP] |
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2007-170585 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G03B
21/008 (20130101); G03B 21/006 (20130101); G02B
5/3058 (20130101); G03B 21/005 (20130101); H04N
5/74 (20130101) |
Current International
Class: |
G02B
5/30 (20060101); G03B 21/00 (20060101); H04N
5/74 (20060101) |
Field of
Search: |
;359/485.05,487.03
;349/96,106 ;353/20 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2783491 |
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May 1998 |
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2000147253 |
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May 2000 |
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2001074935 |
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Mar 2001 |
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2001-330728 |
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3654553 |
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JP |
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2006-139283 |
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JP |
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2006323119 |
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JP |
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2006330108 |
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Dec 2006 |
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JP |
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2007058106 |
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Aug 2007 |
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JP |
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2008-083656 |
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Apr 2008 |
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JP |
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2008-216957 |
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Sep 2008 |
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JP |
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2010-044416 |
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Feb 2010 |
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JP |
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2012-103728 |
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May 2012 |
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JP |
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Other References
Japanese Office Action issued Apr. 16, 2013 for corresponding
Japanese Appln. No. JP2012-017006. cited by applicant .
Office Action issued in connection with Japanese Patent Application
No. 2013-126430, dated Jun. 3, 2014. (7 pages). cited by applicant
.
Office Action issued Feb. 17, 2015, for corresponding Japanese
Appln. No. 2013-126430 (2 pages). cited by applicant.
|
Primary Examiner: Font; Frank
Attorney, Agent or Firm: K&L Gates LLP
Claims
The invention is claimed as follows:
1. A polarizing element comprising: a first polarizing element
including a first substrate transparent to visible light, and first
inorganic particle layers in each of which first inorganic
particles are linearly disposed on the first substrate, the first
inorganic particle layers being disposed on the first substrate at
predetermined intervals to form a wire grid structure, wherein the
first inorganic particles each have an elliptical shape with a
major axis in a disposed direction and a minor axis in a direction
perpendicular thereto, wherein the first polarizing element further
includes convex portions, which are made of a material transparent
to visible light and which extend in one direction, provided on the
first substrate, wherein the first inorganic particle layers are
each provided on a top part or at least one of sidewall parts of
each of the convex portions; and a second polarizing element
including a second substrate transparent to visible light, and
second inorganic particle layers in each of which second inorganic
particles are linearly disposed on the second substrate, the second
inorganic particle layers being disposed on the second substrate at
predetermined intervals to form a wire grid structure, wherein the
second inorganic particles each have .Iadd.an elliptical
.Iaddend.shape .[.anisotropic properties in which a diameter.].
.Iadd.with a major axis .Iaddend.in a disposed direction .[.is
long.]. and a .[.diameter.]. .Iadd.minor axis .Iaddend.in a
direction perpendicular thereto .[.is short.]., wherein the second
polarizing element further includes reflection layers of
strip-shaped thin films, which are made of a metal and which extend
in one direction, provided on the second substrate at predetermined
intervals.[.;.]..Iadd., .Iaddend.and first dielectric layers
provided on the reflection layers, wherein the second inorganic
particle layers are provided on the first dielectric layers at
positions corresponding to those of the strip-shaped thin films,
and wherein the first and second substrates are adhered to each
other at rear surfaces thereof.
2. The polarizing element according to claim 1, wherein a
refractive index of the first inorganic particles in the disposed
direction is larger than that of the first inorganic particles in
the direction perpendicular to the disposed direction.
3. The polarizing element according to claim 2, wherein an
extinction coefficient of the first inorganic particles in the
disposed direction is larger than that of the first inorganic
particles in the direction perpendicular thereto.
4. The polarizing element according to claim 1, wherein the first
inorganic particle layers are formed by an oblique sputtering
method.
5. The polarizing element according to claim 1, wherein the first
inorganic particles include a single element selected from the
groups consisting of: Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni, Fe, Si,
Ge, Te, and Sn, an alloy thereof, or a silicide semiconductor
material.
6. The polarizing element according to claim 1, wherein the first
inorganic particles include a semiconductor material having a
bandgap energy of 3.1 eV or less.
7. The polarizing element according to claim 1, wherein the first
inorganic particle layers have a thickness of 200 nm or less.
8. The polarizing element according to claim 1, wherein the second
substrate is processed by a rubbing treatment so that the direction
of the rubbing treatment corresponds to the disposed direction of
the first inorganic particles, the polarizing element further
comprising antireflection layers of inorganic particles having
shape anisotropic properties, the antireflection layers being
provided on the surface of the second substrate so that the
direction of the inorganic particles corresponds to the disposed
direction of the first inorganic particles.
9. The polarizing element according to claim 1, further comprising
second dielectric layers, the second inorganic particle layers and
the second dielectric layers forming laminates, wherein at least
one of the laminates is provided on each of the first inorganic
particle layers.
10. The polarizing element according to claim 1, further comprising
a polarizing element protective layer transparent to light in a
service bandwidth as an outermost surface.
11. A liquid crystal projector comprising: a lamp; a liquid crystal
panel; and a polarizing element including a substrate transparent
to visible light; and first inorganic particle layers in each of
which first inorganic particles are linearly disposed on the
substrate, the first inorganic particle layers being disposed on
the substrate at predetermined intervals to form a wire grid
structure, wherein the first inorganic particles each have an
elliptical shape with a major axis in a disposed direction and a
minor axis in a direction perpendicular thereto, wherein the first
polarizing element further includes convex portions, which are made
of a material transparent to visible light and which extend in one
direction, provided on the first substrate, wherein the first
inorganic particle layers are each provided on a top part or at
least one of sidewall parts of each of the convex portions; and a
second polarizing element including a second substrate transparent
to visible light, and second inorganic particle layers in each of
which second inorganic particles are linearly disposed on the
second substrate, the second inorganic particle layers being
disposed on the second substrate at predetermined intervals to form
a wire grid structure, wherein the second inorganic particles each
have .Iadd.an elliptical .Iaddend.shape .[.anisotropic properties
in which a diameter.]. .Iadd.with a major axis .Iaddend.in a
disposed direction .[.is long.]. and a .[.diameter.]. .Iadd.minor
axis .Iaddend.in a direction perpendicular thereto .[.is short.].,
wherein the second polarizing element further includes reflection
layers of strip-shaped thin films, which are made of a metal and
which extend in one direction, provided on the second substrate at
predetermined intervals.[.;.]..Iadd., .Iaddend.and first dielectric
layers provided on the reflection layers, wherein the second
inorganic particle layers are provided on the first dielectric
layers at positions corresponding to those of the strip-shaped thin
films, and wherein the first and second substrates are adhered to
each other at rear surfaces thereof.
.Iadd.12. A polarizing element comprising: a substrate transparent
to visible light; reflection layers including strip-shaped thin
films, which include a metal and which extend in one direction,
provided on the substrate at predetermined intervals; dielectric
layers formed on the reflection layers; inorganic particle layers
in each of which inorganic particles are linearly disposed; and a
polarizing element protective layer transparent to light in a
service bandwidth formed as an outermost surface using SiO.sub.2,
wherein the inorganic particle layers are formed at positions
corresponding to positions of the strip-shaped thin films, on at
least one side surface part of the strip-shaped thin films on the
dielectric layers, and wherein the polarizing element has a wire
grid structure having a longitudinal direction which is a same
direction in which the inorganic particles are linearly
disposed..Iaddend.
.Iadd.13. A polarizing element comprising: a substrate transparent
to visible light; reflection layers including strip-shaped thin
films, which include a metal and which extend in one direction,
provided on the substrate at predetermined intervals; dielectric
layers formed on the reflection layers; and inorganic particle
layers in each of which inorganic particles are linearly disposed,
wherein the inorganic particle layers are formed at positions
corresponding to positions of the strip-shaped thin films, on at
least one side surface part of the strip-shaped thin films on the
dielectric layers, wherein the polarizing element has a wire grid
structure having a longitudinal direction which is a same direction
same in which the inorganic particles are linearly disposed,
wherein the substrate includes any one of glass, sapphire, and
quartz, and wherein the substrate has a concave-convex member
formed thereon, which has a pitch of 0.5 .mu.m or less, a line
width of 0.25 .mu.m or less, a depth of 1 nm or more..Iaddend.
.Iadd.14. A polarizing element comprising: a substrate transparent
to visible light; reflection layers including strip-shaped thin
films, which include a metal and which extend in one direction,
provided on the substrate at predetermined intervals; dielectric
layers formed on the reflection layers; inorganic particle layers
in each of which inorganic particles are linearly disposed; and a
polarizing element protective layer transparent to light in a
service bandwidth formed as an outermost surface using SiO.sub.2,
wherein the inorganic particle layers are formed at positions
corresponding to positions of the strip-shaped thin films, on both
side surface parts of top parts of the strip-shaped thin films on
the dielectric layers, and wherein the polarizing element has a
wire grid structure having a longitudinal direction which is a same
direction in which the inorganic particles are linearly
disposed..Iaddend.
.Iadd.15. A polarizing element comprising: a substrate transparent
to visible light; reflection layers including strip-shaped thin
films, which include a metal and which extend in one direction,
provided on the substrate at predetermined intervals; dielectric
layers formed on the reflection layers; and inorganic particle
layers in each of which inorganic particles are linearly disposed,
wherein the inorganic particle layers are formed at positions
corresponding to positions of the strip-shaped thin films, on both
side surface parts of top parts of the strip-shaped thin films on
the dielectric layers, wherein the polarizing element has a wire
grid structure having a longitudinal direction which is a same
direction in which the inorganic particles are linearly disposed,
wherein the substrate includes any one of glass, sapphire, and
quartz, and wherein the substrate has a concave-convex member
formed thereon, which has a pitch of 0.5 .mu.m or less, a line
width of 0.25 .mu.m or less, a depth of 1 nm or more..Iaddend.
.Iadd.16. A wire grid polarizing element comprising: a substrate
transparent to visible light; and reflection layers including
strip-shaped thin films, which include a metal and which extend in
one direction, provided on the substrate at predetermined
intervals, a dielectric layer provided on the reflection layers,
and an inorganic particle layer being disposed linearly, wherein
the inorganic particle layer is formed on both side surfaces of top
parts of the dielectric layer, and the inorganic particle layer is
disposed in a same direction in which the reflection layers
extend..Iaddend.
.Iadd.17. The wire grid polarizing element according to claim 16,
further comprising antireflection layers being provided between the
substrate and the reflection layers..Iaddend.
.Iadd.18. The wire grid polarizing element according to claim 16,
wherein the wire grid polarizing element further includes convex
portions, wherein the pitch of the convex portions is less than or
equal to 0.5 .mu.m, and the line width of the convex portions is
less than or equal to 0.25 .mu.m, and the height of the convex
portions is not less than 1 nanometer..Iaddend.
.Iadd.19. A liquid crystal projector comprising: a liquid crystal
panel; an incident polarizing plate; an emission polarizing plate;
wherein the emission polarizing plate comprising: a substrate
transparent to visible light; reflection layers including
strip-shaped thin films, which include a metal and which extend in
one direction, disposed provided on the substrate at predetermined
intervals; a dielectric layer provided on the reflection layers,
and an inorganic particle layer being disposed linearly, wherein
the inorganic particle layer is formed on the dielectric layer, and
the inorganic particle layer is disposed in a same direction in
which the reflection layers extend, and wherein the inorganic
particle layer of the emission polarizing plate is disposed to face
the liquid crystal panel..Iaddend.
.Iadd.20. The liquid crystal projector according to claim 19,
wherein the incident polarizing plate includes the inorganic
particle layer that is disposed to face the liquid crystal
panel..Iaddend.
.Iadd.21. The liquid crystal projector according to claim 19,
wherein the liquid crystal projector is a transmission
projector..Iaddend.
.Iadd.22. A liquid crystal display comprising: a liquid crystal
panel; a polarizing plate; wherein the polarizing plate comprising:
a substrate; a plurality of reflection layers disposed at a
predetermined interval, wherein the reflection layers extend in a
first direction and include a metal material; a dielectric layer
includes a dielectric layer material selected from the group
consisting of SiO2, Al2O3, and MgF2; and an inorganic particle
layer includes a plurality of inorganic particles having an
anisotropic shape including a first inorganic particle length in
the first direction that is greater than a second inorganic
particle length in a second direction along the first surface
perpendicular to the first direction, wherein the substrate has a
concave-convex member formed thereon, which has a pitch of 0.5
.mu.m or less, a line width of 0.25 .mu.m or less, a depth of 1 nm
or more..Iaddend.
.Iadd.23. A liquid crystal display comprising: a liquid crystal
panel; a polarizing plate; wherein the polarizing plate comprising:
a substrate; a plurality of reflection layers disposed at a
predetermined interval, wherein the reflection layers extend in a
first direction and include a metal material; a dielectric layer
includes a dielectric layer material selected from the group
consisting of SiO2, Al2O3, and MgF2; and an inorganic particle
layer includes a plurality of inorganic particles having an
anisotropic shape including first inorganic particle length that is
greater than a thickness of the inorganic particle layer, wherein
the substrate has a concave-convex member formed thereon, which has
a pitch of 0.5 .mu.m or less, a line width of 0.25 .mu.m or less, a
depth of 1 nm or more..Iaddend.
.Iadd.24. A polarizing plate comprising: a substrate; a plurality
of reflection layers disposed at a predetermined interval, wherein
the reflection layers extend in a first direction and include a
metal material; a dielectric layer includes a dielectric layer
material selected from the group consisting of SiO2, Al2O3, and
MgF2; and an inorganic particle layer includes a plurality of
inorganic particles having an anisotropic shape including a first
inorganic particle length in the first direction that is greater
than a second inorganic particle length in a second direction along
the first surface perpendicular to the first direction, wherein the
substrate has a concave-convex member formed thereon, which has a
pitch of 0.5 .mu.m or less, a line width of 0.25 .mu.m or less, a
depth of 1 nm or more..Iaddend.
.Iadd.25. A polarizing plate comprising: a substrate; a plurality
of reflection layers disposed at a predetermined interval, wherein
the reflection layers extend in a first direction and include a
metal material; a dielectric layer includes a dielectric layer
material selected from the group consisting of SiO2, Al2O3, and
MgF2; and an inorganic particle layer includes a plurality of
inorganic particles having an anisotropic shape including a first
inorganic particle length that is greater than a thickness of the
inorganic particle layer, wherein the substrate has a
concave-convex member formed thereon, which has a pitch of 0.5
.mu.m or less, a line width of 0.25 .mu.m or less, a depth of 1 nm
or more..Iaddend.
.Iadd.26. A polarizing plate comprising: a substrate; an
antireflection layer; a first dielectric layer includes a
dielectric layer material selected from the group consisting of
SiO2, Al2O3, and MgF2; a plurality of reflection layers disposed at
a predetermined interval, wherein the reflection layers extend in a
first direction and include a metal material; a second dielectric
layer includes a dielectric layer material selected from the group
consisting of SiO2, Al2O3, and MgF2; and an inorganic particle
layer includes a plurality of inorganic particles having an
anisotropic shape including a first inorganic particle length that
is greater than a thickness of the inorganic particle layer,
wherein the substrate has a concave-convex member formed thereon,
which has a pitch of 0.5 .mu.m or less, a line width of 0.25 .mu.m
or less, a depth of 1 nm or more, and wherein at least one of the
dielectric layers are provided between the reflection layer and the
antireflection layer..Iaddend.
Description
CROSS REFERENCES TO RELATED APPLICATIONS
The present application claims priority to Japanese Patent
Application JP 2007-026348 and JP 2007-170585 filed in the Japanese
Patent Office on Feb. 6, 2007 and Jun. 28, 2007, respectively, the
entire contents of which are incorporated herein by reference.
BACKGROUND
The present application relates to a polarizing element having
durability against intense light and a liquid crystal projector
using the polarizing element.
In a liquid crystal display device, it is necessary to dispose at
least one polarizing plate at a liquid crystal panel surface based
on an image forming principle. The function of the polarizing plate
is to absorb one of two polarized components (so-called P polarized
wave and S polarized wave) perpendicular to each other and to
transmit the other component. As the polarizing plate described
above, a dichroic polarizing plate in the form of a film containing
an iodine-based or a dye-based high molecular weight organic
material has been frequently used in the past.
As a general method for manufacturing a dichroic polarizing plate,
a method has been used having the steps of dyeing a polyvinyl
alcohol-based film with a dichroic material, such as iodine, and
then performing crosslinking using a crosslinking agent, followed
by performing uniaxial drawing. Since being formed by the drawing
as described above, this type of polarizing plate is liable to
shrink. In addition, since a polyvinyl alcohol-based film is formed
of a hydrophilic polymer, particularly under humidified conditions,
the film is very liable to deform. In addition, since the film is
used, the mechanical strength thereof is inevitably insufficient to
be used as an element. In order to avoid the above problem, a
method for using a transparent protective film may be used in some
cases.
In recent years, liquid crystal display devices have been
increasingly used in various applications, and the performances of
the devices have also been improved. Concomitant with the trend
described above, individual elements forming the liquid crystal
display devices are requested to have high reliability and
durability. For example, in a liquid crystal display device, such
as a transmission type liquid crystal projector, using a light
source having a large quantity of light, a polarizing plate
receives intense radiation. Hence, the polarizing plate used in the
above device as described above is requested to have superior heat
resistance. However, since the film-based polarizing plate
described above is formed of an organic material, improvement in
properties thereof has been naturally limited to a certain
level.
In order to solve the problem described above, an inorganic
polarizing plate having superior heat resistance has been sold
under the trade name "Polarcor" by Corning Inc., USA. This
polarizing plate is formed of silver particles dispersed in glass
and does not use an organic material such as a film, and the
principle of this polarizing plate is to use plasma resonance of
island-shaped particles. That is, light absorption caused by
surface plasma resonance which occurs when light is incident on
island-shaped particles of a noble metal or a transition metal is
used, and an absorption wavelength is influenced by the particle
shape and the dielectric constant of the surrounding material. When
the island-shaped particle has an ellipsoid shape, since resonance
wavelengths in the long-axis and the short-axis directions are
different from each other, polarization properties are obtained
thereby; in particular, a polarized component parallel with the
long axis at a long wavelength side is absorbed, and a polarized
component parallel with the short axis is transmitted. However, in
the case of Polarcor, a wavelength region in which the polarization
properties are obtained is a region in the vicinity of an infrared
region, and a visible light region requested for liquid crystal
display devices is not included. This is because of the physical
properties of silver used for the island-shaped particles.
In U.S. Pat. No. 6,772,608, a UV polarizing plate formed by
precipitating particles in glass by thermal reduction using the
above principle has been disclosed, and as a particular example,
silver used as metal particles has also been disclosed. In this
case, it is believed that absorption in the short axis direction is
used, which is different from the case of Polarcor described above.
Although the polarizing plate functions at around 400 nm as shown
in FIG. 1, since the extinction ratio is small and an absorption
band is very narrow, a polarizing plate capable of covering the
entire visible light region may not be obtained even if Polarcor
and the technique of U.S. Pat. No. 6,772,608 are used in
combination.
In addition, in J. Opt. Soc. Am. A Vol. 8, No. 4, pp. 619 to 624, a
theoretical analysis of an inorganic polarizing plate using plasma
resonance of metal island-shaped particles has been disclosed.
According to this document, it has been described that a resonance
wavelength of aluminum particles is shorter than that of silver
particles by approximately 200 nm, and hence when aluminum
particles are used, a polarizing plate, which can be used in a
visible light region, is probably manufactured.
In addition, in Japanese Unexamined Patent Application Publication
No. 2000-147253, various methods for forming a polarizing plate
using aluminum particles have been disclosed. Among the above
methods, it has been disclosed that glass primarily formed of
silicate is not preferable as a substrate since reaction occurs
between the glass and aluminum, and calcium aluminoborate glass is
suitably used (in paragraphs 0018 and 0019). However, glass formed
of silicate has been widely commercially used as an optical glass,
and highly reliable products thereof are available at a reasonable
price; hence, when the glass formed of silicate is not suitably
used, it is disadvantageous from an economical point of view. In
addition, a method for forming island-shaped particles by etching
using a resist pattern has also been disclosed (paragraphs 0037 and
0038). A polarizing plate used in a projector is generally
requested to have a size of approximately several centimeters and a
high extinction ratio. Accordingly, in order to form a
visible-light polarizing plate, a resist pattern size is requested
to be sufficiently smaller than a visible light wavelength, that
is, to be several tens of nanometers, and in addition, in order to
obtain a high extinction ratio, a pattern is preferably formed to
have a high density. In addition, in order to use a polarizing
plate for a projector purpose, a polarizing plate having a large
area is desirably formed. However, as a method for forming a high
density fine pattern by lithography, disclosed in this patent
document, electron beam lithography is to be desirably used in
order to obtain the pattern as described above. However, since the
electron beam lithography is a method for drawing each pattern
using electron beams, the productivity is inferior, and hence this
technique is not practical.
In addition, in Japanese Unexamined Patent Application Publication
No. 2001-147253, it has been disclosed that aluminum is removed by
chlorine plasma; however, in general, when etching is performed as
described above, chlorides adhere to sidewalls of an aluminum
pattern. The chlorides may be removed by a commercially available
wet etching liquid (such as SST-A2 by Tokyo Ohka Kogyo Co., Ltd.);
however, since this type of chemical liquid, which reacts with
aluminum chloride compounds, also reacts with aluminum although the
etching rate is slow, it is difficult to realize a desired pattern
shape by the method described above.
Furthermore, in Japanese Unexamined Patent Application Publication
No. 2000-147253, as another method, a method has been disclosed in
which aluminum is deposited on a patterned photoresist by oblique
deposition, followed by removing the photoresist (paragraphs 0045
and 0047). However, it is believed that in order to ensure adhesion
between a substrate and aluminum, aluminum is also preferably
deposited on the substrate to a certain extent. However, it means
that the shape of the aluminum film thus deposited is different
from a prolate spheroid, such as a prolate ellipsoid, which is a
suitable shape disclosed in paragraph 0015. In addition, in
paragraph 0047, it has been disclosed that by anisotropic etching
performed perpendicular to the surface, an excess deposit is
removed. In order to obtain the function as the polarizing plate,
shape anisotropic properties of aluminum are significantly
important. Hence, it is believed important to adjust the amount of
aluminum deposited on the resist portion and that on the substrate
surface by etching to obtain a desired shape; however, it may be
very difficult to control the amount of aluminum having a size of
submicron or less, such as 0.05 .mu.m, as disclosed in paragraph
0047, and hence it is questionable whether the method described
above is a highly productive manufacturing method. In addition, as
properties of the polarizing plate, a high transmittance is
desirable in the transmission axis direction; however, when glass
is used as the substrate, in general, several percentage of light
is inevitably reflected on the glass interface, and since
countermeasures have not been taken therefor, a high transmittance
is difficult to obtain.
In addition, according to Japanese Unexamined Patent Application
Publication No. 2002-372620, a polarizing plate formed by oblique
deposition has been disclosed. This method is to obtain
polarization properties by forming fine columnar structures by
oblique deposition using a transparent and an opaque substance with
respect to wavelengths in a service bandwidth, and since a fine
pattern can be easily obtained by this method unlike the method
disclosed in U.S. Pat. No. 6,772,608, it is believed that the
method has a high productivity; however, problems still exist. That
is, the aspect ratio of a fine columnar structure which is first
formed from the substance opaque to the wavelengths in the service
bandwidth, the distance between the fine columnar structures, and
the linearity thereof are important factors to obtain superior
polarization properties and are to be intentionally controlled in
view of reproducibility of the properties. However, in this method,
since the columnar structures are formed by a phenomenon in which
initial deposited layers made of deposition particles form shadow
areas, and following flying particles are not deposited on the
shadow areas, it has been difficult to intentionally control the
factors described above. As a method for improving the above
situation, a method for forming polishing marks in the substrate by
rubbing performed before deposition has been described; however,
the particle diameter of the deposition film is approximately at
most several tens of nanometers, and in order to control the
anisotropic properties of this type of particles, it might be
desired to intentionally form pitches on the order of submicron or
less. However, by general polishing sheets or the like, pitches on
the order of approximately submicron are the limit, and hence fine
polishing marks as described above are difficult to form by
rubbing. In addition, since the resonance wavelength of Al
particles largely depends on the refractive index of the
surrounding material, as described above, in this case, combination
between the transparent and the opaque substances is important;
however, in Japanese Unexamined Patent Application Publication No.
2002-372620, the combination to obtain superior polarization
properties in a visible light region has not been described. In
addition, as is the case disclosed in U.S. Pat. No. 6,772,608, when
glass is generally used as the substrate, several percentage of
light is inevitably reflected on the glass interface, and
countermeasures have not been taken therefor.
In addition, in Applied Optics Vol. 25, No. 2, 1986, pp. 311 to
314, a polarizing plate for infrared communication, which is called
Lamipol, has been described. This polarizing plate has a laminate
structure of Al and SiO2, and according to this document, a very
high extinction ratio is obtained. In addition, in J. Lightwave
Tec. Vol. 15, No. 6, 1997, pp. 1042 to 1050, it has been disclosed
that when Ge is used instead of Al which is responsible for the
light absorption of Lamipol, a high extinction ratio can be
realized at a wavelength of 1 .mu.m or less. In addition, from FIG.
3 of the above document, it may be expected to obtain a high
extinction ratio when Te (tellurium) is used. Although Lamipol is
an absorption type polarizing plate having a high extinction ratio,
as described above, since a laminate thickness of an absorption
substance and a transmission substance determines the size of a
light receiving surface, it is not preferably used for a projector
polarizing plate which is requested to have a large size of several
centimeters square.
In U.S. Pat. No. 6,122,103, a wire grid type polarizing plate has
been disclosed. This polarizing plate is formed from fine metal
wires disposed on a substrate at a pitch smaller than the
wavelength of light in a service bandwidth, and predetermined
polarization properties are obtained by reflecting a polarized
light component parallel with the fine metal wires and by
transmitting a polarized light component perpendicular thereto.
In addition, in U.S. Pat. No. 6,813,077, a method has been
disclosed in which a wire grid type polarizing element having a
three-layered structure is formed by forming dielectric layers and
metal layers on a metal lattice so as to cancels light reflected
from the metal lattice by an interference effect, and in which a
wire grid, which is generally a reflection type, is used as an
absorption type. It is believed that when an absorption type
polarizing plate is used by utilizing the optical properties
obtained from a multilayer structure, as described above, the
thickness and the optical properties of the metal layer formed on
the dielectric layer are important; however, in this patent
document, these important properties are not taken into
consideration. That is, in this patent document, the above
important properties have not been described, and hence the details
have not been known; however, in order to obtain the interference
effect as described above, light is necessary to pass through the
metal layer. When light passes, it means that in this step, part of
the light is absorbed in the metal film located at an upper side.
By the absorption, the transmittance in the transmission axis
direction is decreased, and this decrease is not preferable as the
properties of the polarization transmission axis; in particular, it
is not preferable for a liquid crystal display device which is
requested to have a high transmittance in a visible light region.
That is, a polarizing plate having an absorption effect does not
function when the optical anisotropic properties of an absorption
layer are not essentially controlled and is difficult to be used as
a practical polarizing plate.
In addition, in Japanese Unexamined Patent Application Publication
No. 2006-323119, an inorganic polarizing plate in which
semiconductor nanorods are dispersed in glass has been disclosed.
It has also been disclosed that superior polarization properties
are obtained in a visible light region; however, since this
polarizing plate is formed by a method similar to that for Polarcor
of Corning Inc., a drawing step is inevitably performed, and as a
result, a large size plate is difficult to obtain.
SUMMARY
It is desirable to provide a polarizing plate, which has a desired
extinction ratio in a visible light region and light resistance
against intense light, and a liquid crystal display device using
the above polarizing plate.
According to a first embodiment, there is provided a polarizing
element comprising: a substrate transparent to visible light; and
first inorganic particle layers in each of which first inorganic
particles are linearly disposed on the substrate, the first
inorganic particle layers being disposed on the substrate at
predetermined intervals to form a wire grid structure, wherein the
first inorganic particles each have an elliptical shape having a
major axis in a disposed direction and a minor axis in a direction
perpendicular thereto.
According to a second embodiment, as an optical constant of the
first inorganic particle layers, an optical constant of the first
inorganic particles in the disposed direction is preferably larger
than that of the first inorganic particles in the direction
perpendicular to the disposed direction.
In addition, according to a third embodiment, as the optical
properties of the first inorganic particle layers, the refractive
index of the first inorganic particles in the disposed direction is
preferably larger than that of the first inorganic particles in the
direction perpendicular thereto, and an extinction coefficient of
the first inorganic particles in the disposed direction is
preferably larger than that of the first inorganic particles in the
direction perpendicular thereto.
In addition, according to a fourth embodiment, the first inorganic
particle layers are preferably formed by an oblique sputtering
method.
According to a fifth embodiment, the first inorganic particles
preferably include a single element selected from Al, Ag, Cu, Au,
Mo, Cr, Ti, W, Ni, Fe, Si, Ge, Te, and Sn, an alloy thereof, or a
silicide semiconductor material.
Alternatively, according to a sixth embodiment, the first inorganic
particles preferably include a semiconductor material having a
bandgap energy of 3.1 eV or less.
According to a seventh embodiment, the first inorganic particle
layers preferably have a thickness of 200 nm or less.
In addition, according to an eighth embodiment, the polarizing
element of the first embodiment may further comprise convex
portions, which are made of a material transparent to visible light
and which extend in one direction, provided on the substrate, and
the first inorganic particle layers are each preferably provided on
a top part or at least one of sidewall parts of each of the convex
portions.
In addition, according to a ninth embodiment, the polarizing
element of the first embodiment may further comprise reflection
layers of strip-shaped thin films, which are made of a metal and
which extend in one direction, provided on the substrate at
predetermined intervals, and first dielectric layers provided on
the reflection layers, and the first inorganic particle layers are
preferably provided on the first dielectric layers at positions
corresponding to those of the strip-shaped thin films.
According to a tenth embodiment, in the above ninth embodiment, the
substrate is preferably processed by a rubbing treatment so that
the direction of the rubbing treatment corresponds to the disposed
direction of the first inorganic particles, and the polarizing
element may further comprise antireflection layers of inorganic
particles having shape anisotropic properties, the antireflection
layers being provided on the surface of the substrate so that the
direction of the inorganic particles corresponds to the disposed
direction of the first inorganic particles.
According to an eleventh embodiment, the polarizing element
according to the ninth embodiment may further comprise second
inorganic particle layers in each of which second inorganic
particles are linearly disposed; and second dielectric layers, the
second inorganic particle layers and the second dielectric layers
forming laminates, wherein at least one of the laminates is
provided on each of the first inorganic particle layers.
According to a twelfth embodiment, there is provided a polarizing
element comprising: the polarizing element according to the eighth
embodiment; and the polarizing element according to the ninth
embodiment, wherein the substrates thereof are adhered to each
other at the rear surfaces thereof.
According to a thirteenth embodiment, the polarizing element
described above may further comprise a polarizing element
protective layer transparent to light in a service bandwidth as an
outermost surface.
According to a fourteenth embodiment, there is provided a liquid
crystal projector comprising: a lamp; a liquid crystal panel; and
the polarizing element according to one of the first to the
thirteenth embodiments.
The polarizing elements of the embodiments each have a desired
extinction ratio in a visible light region and superior durability
to that of a related polarizing element.
In addition, since the liquid crystal projector of the embodiment
includes a polarizing element having superior light resistance
against intense light, a highly reliable liquid crystal projector
can be realized.
Additional features and advantages are described herein, and will
be apparent from, the following Detailed Description and the
figures.
BRIEF DESCRIPTION OF THE FIGURES
FIGS. 1A and 1B are schematic views each showing the structure of a
polarizing element of a first embodiment;
FIG. 2 is a cross-sectional view of a concave-convex member of a
substrate;
FIGS. 3A to 3C are cross-sectional views each showing a
concave-convex shape of a polarizing element surface of an
embodiment;
FIG. 4 is a schematic view showing the structure of oblique
sputtering deposition;
FIGS. 5A and 5B are schematic views each showing the structure of a
polarizing element of a second embodiment;
FIGS. 6A and 6B are schematic views each illustrating a function of
the polarizing element shown in FIGS. 5A and 5B;
FIG. 7 is a schematic longitudinal cross-sectional view of a
modified example of the structure of the polarizing element shown
in FIGS. 5A and 5B;
FIG. 8 is a view showing an example (1) of an emission-surface
stray-light countermeasure of the polarizing element shown in FIGS.
5A and 5B;
FIG. 9 is a view showing an example (2) of the emission-surface
stray-light countermeasure of the polarizing element shown in FIGS.
5A and 5B;
FIGS. 10A and 10B are schematic views each showing a modified
structure of the polarizing element of the second embodiment;
FIG. 11 is a view showing an example (1) of an emission-surface
stray-light countermeasure of the polarizing element having the
structure shown in FIGS. 10A and 10B;
FIG. 12 is a view showing an example (2) of the emission-surface
stray-light countermeasure of the polarizing element having the
structure shown in FIGS. 10A and 10B;
FIG. 13 is a cross-sectional view showing the structure of an
optical engine portion of a liquid crystal projector of an
embodiment;
FIG. 14A is a schematic view illustrating a method for performing
oblique sputtering deposition of Ge on a stationary substrate;
FIG. 14B is a graph showing measurement results of optical
constants of a Ge film formed by the method shown in FIG. 14A;
FIG. 15A is a schematic view illustrating a method for performing
sputtering deposition of Ge (incident in a vertical direction) on a
rotating substrate;
FIG. 15B is a graph showing measurement results of optical
constants of a Ge film formed by the method shown in FIG. 15A;
FIGS. 16A and 16B are graphs each showing measurement results of
optical constants of a Si film obtained by sputtering
deposition;
FIG. 17 is a graph showing polarization transmission properties of
a Ge film having an optical anisotropy;
FIGS. 18A and 18B are schematic views each showing a sample
structure of Example 2;
FIG. 19 is a graph showing results of optical properties of Example
2;
FIG. 20 is a graph showing results of optical properties of Example
3;
FIG. 21 is a graph showing optical constants of an inorganic
particle layer composed of Ag and having an optical anisotropy;
FIG. 22 is a graph showing polarization transmission properties of
a polarizing element having the inorganic particle layers shown in
FIG. 21;
FIGS. 23A and 23B are photographs each showing a surface texture of
an inorganic particle layer on a flat plate;
FIG. 24 is a graph showing polarization properties of a polarizing
element sample having the structure shown in FIG. 3C;
FIG. 25 is a view of element distribution mapping of a
cross-section of the polarizing element sample having the structure
shown in FIG. 3C;
FIGS. 26A and 26B are schematic views each showing an observation
result of an inorganic particle layer of the polarizing element
sample having the structure shown in FIG. 3C;
FIG. 27 is an electron beam diffraction image of the inorganic
particle layer of the polarizing element sample having the
structure shown in FIG. 3C;
FIG. 28 is a graph showing polarization properties of a polarizing
element sample having the structure shown in FIGS. 5A and 5B;
FIG. 29 is a graph showing transmission contrast of the polarizing
element sample having the structure shown in FIGS. 5A and 5B;
FIGS. 30A and 30B are schematic views each showing an observation
result of an inorganic particle layer of the polarizing element
sample having the structure shown in FIGS. 5A and 5B;
FIG. 31 is a SEM image of the polarizing element sample having the
structure shown in FIGS. 5A and 5B, when viewed in plan;
FIGS. 32A and 32B are schematic views each showing the relationship
between the major axis and the thickness of an inorganic particle
obtained by oblique sputtering deposition;
FIG. 33 is a view showing preconditions of a polarizing element in
an optical property simulation;
FIGS. 34A to 34C are graphs each showing optical properties of a
polarizing element when a material for an inorganic particle layer
is Ge particles or a Ge thin film;
FIGS. 35A and 35B are graphs each showing an aspect ratio
distribution of Ge particles, which is obtained when oblique
sputtering deposition is performed on a flat plate by changing a
substrate inclined angle .theta.;
FIG. 36 is a graph showing polarization properties of a polarizing
element sample having the structure shown in FIG. 3C;
FIGS. 37A to 37C are views each illustrating an oblique sputtering
method of Example 7;
FIG. 38 is a graph showing polarization properties of a Ge particle
layer sample of Example 7;
FIG. 39 is a graph showing the relationship between the contrast
and an aluminum height as a reflection layer of the polarizing
element having the structure shown in FIGS. 5A and 5B;
FIG. 40 is a graph showing polarization properties of a polarizing
element sample of Example 8;
FIG. 41 is a view showing irregularities of a texture structure
formed by a rubbing treatment;
FIG. 42 is a graph showing transmittance properties of a substrate
before and after a rubbing treatment;
FIG. 43 is a view showing a surface texture of a Ge particle film
(antireflection film) provided on a substrate processed by a
rubbing treatment;
FIG. 44 is a graph showing improvement in polarization properties
of an antireflection film by a rubbing treatment;
FIG. 45 is a graph showing polarization properties of a sample of
an inorganic particle layer made of Si of Example 10; and
FIG. 46 is a graph showing polarization properties of a sample of
an inorganic particle layer made of Sn of Example 10.
FIG. 47 is a view showing an alternate example (1) of an
emission-surface stray-light countermeasure of the polarizing
element shown in FIGS. 5A and 5B;
DETAILED DESCRIPTION
The present application will be described below in greater detail
with reference to the drawings according to an embodiment.
A polarizing element of an embodiment according comprises: a
substrate transparent to visible light; and linear inorganic
particle layers in which inorganic particles are continuously
disposed on the substrate, the inorganic particle layers being
disposed on the substrate at predetermined intervals to form a
one-dimensional lattice wire grid structure, wherein the inorganic
particles each have an elliptical shape having a major axis in the
disposed direction and a minor axis in a direction perpendicular
thereto. In addition, as an optical constant of the inorganic
particle layers, an optical constant of the inorganic particles in
the disposed direction is larger than that of the inorganic
particles in the direction perpendicular thereto. In particular,
the refractive index of the inorganic particles in the disposed
direction is larger than that of the inorganic particles in the
direction perpendicular thereto, and the extinction coefficient of
the inorganic particles in the disposed direction is larger than
that of the inorganic particles in the direction perpendicular
thereto.
In the polarizing element of this embodiment, convex portions,
which are formed of a material transparent to visible light and
which extend in one direction parallel with a primary surface of
the substrate, are provided on the substrate at predetermined
intervals, and the inorganic particle layers are each formed on a
top part or at least one of sidewall parts of each of the convex
portions.
FIGS. 1A and 1B each show a structural example of the polarizing
element of the first embodiment. FIG. 1A is a cross-sectional view
of a polarizing element 10, and FIG. 1B is a plan view of the
polarizing element 10.
As shown in FIGS. 1A and 1B, in the polarizing element 10,
inorganic particle layers 15 are selectively formed on one-side
surface parts of convex portions 14a provided on the surface of a
substrate 11 which is transparent to visible light, so that a wire
grid structure is formed of the inorganic particle layers 15 which
are disposed on the substrate 11 at predetermined intervals.
The substrate 11 is formed of a material, such as glass, sapphire,
or quartz, having a refractive index of 1.1 to 2.2 and being
transparent to light (visible light region in this embodiment) in a
service bandwidth. In this embodiment, glass, in particular, quartz
(refractive index: 1.46) or soda-lime glass (refractive index:
1.51), is preferably used. A component composition of the glass
material is not particularly limited, and for example, an
inexpensive glass material, such as silicate glass which is widely
used as an optical glass, may be used, so that manufacturing cost
can be reduced. In addition, as the substrate 11, a quartz
substrate or a sapphire substrate, having high thermal
conductivity, is advantageously used in a polarizing element for an
optical engine of a projector generating a large amount of
heat.
A concave-convex member 14 is formed of the convex portions 14a
having a rectangular cross-sectional shape, which are periodically
provided on the primary surface of the substrate 11 to extend in
one direction (absorption-axis Y direction) parallel with the
primary surface of the substrate 11 at a predetermined pitch, which
is smaller than a wavelength in a visible light region, in a
direction (transmission-axis X direction) perpendicular to the
absorption-axis Y direction of the substrate 11. In addition, the
concave-convex member 14 is provided so that the inorganic particle
layers 15 are to be formed thereon, and the wire grid structure of
the inorganic particle layers is determined by the machined size
and the pattern shape of the concave-convex member 14; hence, the
concave-convex member 14 is important to obtain predetermined
polarization properties of the polarizing element 10. That is, the
machined size and the pattern shape of the concave-convex member 14
are appropriately determined in accordance with targeted
polarization properties (extinction ratio) and/or an intended
visible light wavelength region. In particular, in FIG. 2, the
pitch (in the X direction) between grooves of the concave-convex
member 14 is 0.5 .mu.m or less, the line width (width of the convex
portion 14a) of the concave-convex member 14 is 0.25 .mu.m or less,
and the depth of the concave-convex member 14 is 1 nm or more.
In addition, the pitch, line width/pitch, concave portion depth
(convex portion height), convex portion length, and top line
width/bottom line width of the concave-convex member 14 are
preferably set in the following ranges. 0.05 .mu.m<pitch<0.8
.mu.m 0.1<line width/pitch<0.9 0.01 .mu.m<concave portion
depth<0.2 .mu.m 0.05 .mu.m<convex portion length
1.0.gtoreq.(top line width/bottom line width)
The concave-convex member 14 may be directly formed in the
substrate 11 or may be separately formed. As a method for forming
the concave-convex member 14, for example, there may be mentioned a
lapping method using a polishing sheet; a method in which after a
photoresist, which is used in semiconductor device manufacturing or
the like, is applied on a substrate and is then patterned by
exposure using a mask, the substrate is etched using the
photoresist thus patterned as a mask; and a method in which by
using a mold which is formed in accordance with dimensions of the
concave-convex member 14, a mold shape is transferred on a
substrate (nanoinprinting method), and an appropriate method may be
selected among the above methods.
The convex portion 14a of the concave-convex member 14 may have a
quadrangular, a trapezoidal, a sawtooth, or a triangular shape.
FIG. 3A shows one example in which the convex portion 14a of the
concave-convex member 14 has a rectangular cross-sectional shape,
and the inorganic particle later 15 is formed on one side surface
of the convex portion 14a. In addition, FIG. 3B shows one example
in which a convex portion 16a of a concave-convex member 16 has a
sawtooth cross-sectional shape, and the inorganic particle later 15
is formed on one side surface of the convex portion 16a, which is
provided perpendicular to the surface of the substrate 11. Since
the convex portion 16a is formed to have a sawtooth shaped
cross-section, adhesion of a film on the top part of the convex
portion 16a can be avoided. In addition, FIG. 3C shows one example
in which a convex portion 17a of a concave-convex member 17 has a
triangular cross-sectional shape, and the inorganic particle later
15 is formed on one side surface of the convex portion 17a.
Since the inorganic particle layers 15 are each formed on the top
part or at least one of the sidewall parts of each of the convex
portions 14a, the inorganic particle layers 15, which are made of
inorganic particles having shape anisotropic properties, each
having a desired fine shape, can be disposed to form a stripe
pattern on the surface of the substrate 11 and can be isolated from
each other. In addition, since the concave-convex member 14 is
mechanically formed, and the inorganic particle layers 15 are
formed thereon, the concave-convex member 14 can be stably formed,
and in addition, the shapes of the inorganic particle layers formed
thereon can be easily controlled.
Since the inorganic particle layer 15 is formed by adhering
inorganic particles to the top part or at least one sidewall part
of the convex portion 14a, the inorganic particles are linearly
disposed in one direction (absorption-axis Y direction) parallel
with the primary surface of the substrate 11. "The inorganic
particles are linearly disposed" indicates the state in which
inorganic particles are connected to each other to form a
strip-shaped continuous film or the state in which inorganic
particles aggregate to form independent islands each having an
appropriate size, and the islands are aligned in one direction to
form a discontinuous film. As long as grain boundaries are formed,
either one of the states described above may be used. In addition,
since the inorganic particle layers 15 are formed on the convex
portions 14a regularly provided at predetermined intervals, the
inorganic particle layers 15 form a stripe pattern (one-dimensional
lattice pattern), so that a wire grid structure is obtained.
In this embodiment, the inorganic particle has an elliptical shape
having a major axis in the disposed direction and a minor axis in a
direction perpendicular thereto. In addition, it is preferable that
the inorganic particles have a size smaller than the wavelength in
a service bandwidth and be completely isolated from each other.
In addition, as the optical constant of the inorganic particle
layer 15 of this embodiment according to the present invention, it
is important that the optical constant in the absorption-axis Y
direction (disposed direction of the inorganic particles) be larger
than that in the transmission-axis X direction (direction
perpendicular to the disposed direction of the inorganic
particles). In particular, the refractive index of the inorganic
particle layer 15 in the absorption-axis Y direction is larger than
that in the transmission-axis X direction, and the extinction
coefficient of the inorganic particle layer 15 in the
absorption-axis Y direction is larger than that in the
transmission-axis X direction. In order to obtain the above
properties, the inorganic particle layers 15 are formed by an
oblique sputtering method.
The oblique sputtering deposition in order to form the inorganic
particle layers 15 of this embodiment according to the present
invention is shown in FIG. 4. In this figure, although ion beam
sputtering is shown by way of example, the oblique sputtering
deposition is not limited thereto, and any sputtering method may
also be used.
In FIG. 4, reference numeral 1 indicates a stage supporting the
substrate 11, reference numeral 2 indicates a target, reference
numeral 3 indicates a beam source (ion source), and reference
numeral 4 indicates a control plate. The stage 1 is inclined by a
predetermined angle .theta. with respect to a normal line direction
of the target 2, and the substrate 11 is disposed so that the
longitudinal direction of the convex portions 14a of the
concave-convex member 14 is perpendicular to an incident direction
of inorganic particles emitted from the target 2. The angle .theta.
is set, for example, in the range of 0.degree. to 15.degree.. Ions
emitted from the beam source 3 irradiate the target 2. Inorganic
particles kicked out of the target 2 by the irradiation of ion
beams are incident on the surface of the substrate 11 in an oblique
direction and adhere thereto. In this step, when the flat control
plate 4 is disposed over the substrate 11 with a predetermined
distance therebetween (such as 50 mm), the direction of particles
incident on the substrate 11 can be controlled, so that particles
can be deposited only on the sidewall parts of the convex portions
14a. In this case, the thickness of the inorganic particle layer 15
is preferably 200 nm or less.
As described above, when the incident direction of inorganic
particles is controlled by inclining the substrate 11 with respect
to the target 2 in deposition by a sputtering method, the inorganic
particle layers 15 each selectively formed on the top part or at
least one of sidewall parts of each of the convex portions 14a are
obtained. In each of the inorganic particle layers 15, the
inorganic particles are linearly disposed which have an elliptical
shape having a major axis in the disposed direction and a minor
axis in the direction perpendicular thereto, and in which the
optical constant of the inorganic particle layer 15 in the
absorption-axis Y direction is larger than that in the
transmission-axis X direction.
In this embodiment, as a material (material forming inorganic
particles) for the inorganic particle layer 15, a material
appropriate as the polarizing element 10 is preferably to be
selected in accordance with a service bandwidth. That is, a metal
material and a semiconductor material are suitably used as the
above material, and in particular, as the metal material, for
example, there may be mentioned Al, Ag, Cu, Au, Mo, Cr, Ti, W, Ni,
Fe, Si, Ge, Te, Sn, or an alloy thereof. In addition, as the
semiconductor material, for example, Si, Ge, Te, or ZnO may be
mentioned. Furthermore, a silicide material, such as FeSi (in
particular, .beta.-FeSi2), MgSi2, NiSi2, BaSi2, CrSi2, or CoSi2,
may also be preferably used.
In addition, when a semiconductor material is used for the
inorganic particle layer 15, the absorption function relates to
bandgap energy of the semiconductor. The reason for this is that
light having energy equal to or less than the bandgap energy is
absorbed. Hence, when a semiconductor material is used for a
visible light polarizing element, the bandgap energy is necessary
to be equal to or less than that of a service bandwidth. For
example, in the case in which visible light is used, for absorption
at a wavelength of 400 nm or more, a material having a bandgap
energy of 3.1 eV or less is necessarily used. The bandgap energy
also depends on the size of particles as described in OYO BUTURI,
Vol. 73, No. 7, 2004, pp. 917 to 923, and in particular, when the
size is decreased to several nanometers, the bandgap energy tends
to rapidly increase; hence, in consideration of the size effect as
described above, the material and the thickness thereof are to be
appropriately determined. From the point as described above, a
semiconductor material having a small bandgap energy in the bulk
state is preferable, and for example, Ge is a preferable material
for a visible light polarizing element since having a small bandgap
energy of 0.67 eV (wavelength of approximately 1.85 .mu.m) in the
bulk state.
By the structure as described above, the polarizing element 10 has
a desired extinction ratio in a visible light region and also has
superior durability to that of a related polarizing element.
In addition, if desired, when the front and the rear surfaces of
the substrate are coated with antireflection films, reflection at
the interface between air and the substrate is prevented, and as a
result, the transmission-axis transmittance can be improved. As the
antireflection film, for example, there may be used a low
refractive-index film of MgF2 or the like, which is generally used,
or a multilayer film composed of a low refractive-index film and a
high refractive-index film. In addition, after the structure shown
in FIGS. 1A and 1B is formed, when a material, such as SiO2,
transparent in a service bandwidth region is applied on surfaces of
the above structure as a protective film so that the thickness
thereof has no influences on the polarization properties, it is
preferable since the reliability, such as humidity resistance, is
effectively improved. However, since the optical properties of
inorganic particles are influenced by the refractive index of the
surrounding material, the polarization properties may be changed in
some cases when the protective film is formed. In addition, since
the reflectance to incident light is also changed by the optical
thickness (refractive index.times.thickness of protective film) of
the protective film, a protective film material and the thickness
thereof are to be determined in consideration of the above
influences. As the protective film material, a material having a
refractive index of 2 or less and an extinction coefficient of
approximately zero is preferable. As the material described above,
SiO2 and Al2O3 may be mentioned by way of example. The materials
mentioned above may be formed into films, for example, by a general
vacuum film formation method (such as a chemical vapor deposition
method, a sputtering method, or an evaporation method), or a spin
coating method or a dipping method, which uses a sol in which the
above material is dispersed in a liquid. Furthermore, a
self-organizing film as disclosed in J. Microelectromechanical
Systems Vol. 10, No. 1, 2001, pp. 33 to 40 may also be used. In
order to improve humidity resistance, a hydrophobic self-organizing
film is preferable. Perfluorodecyltrichlorosilane (FDTS) and
Octadecanetrichlorosilane (OTS) may be mentioned by way of example.
Since having hydrophobic properties, the above materials are also
effective in terms of anti-fouling. The materials mentioned above
are commercially available from chemical drug producers, such as
Gelest Inc., USA, and film formation can be performed by dipping.
In addition, the film formation may also be performed by vapor
phase growth, and an exclusive machine therefor is sold by Applied
Microstructure Inc., USA. In the case of a silane-based
self-organizing film as described above, in order to improve the
adhesion, after SiO2 is applied on the polarizing element by the
method described above to form an adhesive layer, the
self-organizing film may be deposited.
Next, the structure of a polarizing element of a second
embodiment.
In this embodiment, reflection layers in the form of strip-shaped
thin films, which are made of a metal, which extend in one
direction parallel with a primary surface of a substrate, and which
are provided thereon with predetermined intervals, and dielectric
layers formed on the reflection layers are provided, and the
inorganic particle layers are formed on the dielectric layers at
positions corresponding to those of the strip-shaped thin
films.
FIGS. 5A and 5B are schematic views each showing a structural
example of the polarizing element of the second embodiment
according to the present invention. FIG. 5A is a cross-sectional
view of a polarizing element 20, and FIG. 5B is a plan view of the
polarizing element 20.
As shown in FIGS. 5A and 5B, inorganic particle layers 25 are
selectively formed on laminate structures composed of dielectric
layers 23 and thin films 22a forming reflection layers 22 provided
on a surface of a substrate 21 which is transparent to visible
light, and hence a wire grid structure is formed in which the
inorganic particle layers 25 are disposed on the substrate 21 with
predetermined intervals.
In this embodiment, the substrate 21 is formed from the same
material as that for the substrate 11 of the first embodiment.
As the reflection layers 22, the strip-shaped thin films 22a, which
are made of a metal and which extend in one direction
(absorption-axis Y direction) parallel with the primary surface of
the substrate 21, are provided thereon. As a material for the
reflection layer 22, various materials may be used. For example, a
metal, such as Al, Ag, Cu, Mo, Cr, Ti, Ni, W, Fe, Si, Ge, or Te, or
a semiconductor material may be used. In addition, besides the
metal materials, for example, an inorganic film or a resin film,
which has a high surface reflectance by coloring or the like, may
also be used.
The thin films 22a are disposed on the surface of the substrate 21
with a pitch smaller than the wavelength of a visible light region
and are formed (metal lattice), for example, by patterning of the
above metal film using a photolithographic technique. The
reflection layers 22 have a function as a wire grid type polarizer,
and among various types of light incident on the surface of the
substrate 21, a polarized wave (TE wave (S wave)) having an
electric field component in a direction (Y-axis direction) parallel
with the longitudinal direction of the wire grid is attenuated, and
a polarized wave (TM wave (P wave)) having an electric field
component in a direction (X-axis direction) perpendicular to the
longitudinal direction of the wire grid is allowed to pass.
In addition, the pitch, line width/pitch, thin film height
(thickness, lattice depth), and thin film length (lattice length)
of the reflection layer 22 (thin film 22a) are preferably set in
the following ranges. 0.05 .mu.m<pitch<0.8 .mu.m 0.1<line
width/pitch<0.9 0.01 .mu.m<thin film height<1 .mu.m 0.05
.mu.m<thin film length
The dielectric layers 23 are formed on the surface of the substrate
21 from an optical material, such as SiO2, transparent to visible
light by a general vacuum film formation method, such as a
sputtering method, a vapor phase growth method, or an evaporation
method, or a sol-gel method (method for applying a sol by a spin
coating method or the like, followed by thermal-curing to form a
gel). The dielectric layer 23 is formed as an underlayer for the
inorganic particle layer 25 and is also formed to have a thickness
so as to shift the phase of a polarized light passing through the
inorganic particle layer 25 and reflected by the reflection layer
22 by a half wavelength with respect to a polarized light reflected
by the inorganic particle layer 25, which will be described later.
In particular, the thickness may be appropriately set in the range
of 1 to 500 nm. The dielectric layer 23 is preferably formed to
enhance an interference effect by adjusting the phase of the
polarized light and to have a thickness shifting the phase by a
half wavelength. However, since the reflected light can be absorbed
by the inorganic particle layer, which has an absorption effect,
and improvement in contrast can be realized even if the film
thickness is not optimized, the film thickness may be practically
determined in consideration of desired polarization properties in
combination with an actual manufacturing process. A practical film
thickness is in the range of 1 to 500 nm.
As a material forming the dielectric layer 23, a general material,
such as SiO2, Al2O3, or MgF2, may be used. These materials
mentioned above may be formed into a thin film by a general vacuum
film formation method, such as a sputtering method, a vapor phase
growth method, or an evaporation method, or a method in which a sol
material is applied on a substrate, followed by thermal-curing. In
addition, the refractive index of the dielectric layer 23 is
preferably set in the range of more than 1 to 2.5. Since the
optical properties of the inorganic particle layer 25 are
influenced by the refractive index of the surrounding material,
polarizing element properties can also be controlled by the
dielectric layer material.
The inorganic particle layer 25 is formed by adhering inorganic
particles to the dielectric layer 23 at a position corresponding to
that of the thin film 22a so that the inorganic particles are
linearly disposed in one direction (absorption-axis Y direction)
parallel with the primary surface of the substrate 21. In addition,
since the inorganic particle layers 25 are formed above the
respective thin films 22a regularly provided with predetermined
intervals, the inorganic particle layers 25 form a stripe pattern,
and hence the wire grid structure is formed.
In FIGS. 5A and 5B, the inorganic particle layer 25 has the
structure in which island-shaped inorganic particles 25a having a
prolate ellipsoid shape are disposed so that the long axis
direction thereof is parallel with the longitudinal direction
(Y-axis direction) of the thin film 22a and so that the short axis
direction is in a direction (X-axis direction) perpendicular
thereto. In addition, it is preferable that the inorganic particles
25a have a size smaller than the wavelength in a service bandwidth
and be completely isolated from each other.
As the optical constant of the inorganic particle layer 25 of this
embodiment according to the present invention, the optical constant
in the absorption-axis Y direction (disposed direction of the
inorganic particles) is larger than that in the transmission-axis X
direction (direction perpendicularly to the disposed direction of
the inorganic particles). In particular, the refractive index of
the inorganic particle layer 25 in the absorption-axis Y direction
is larger than that in the transmission-axis X direction, and the
extinction coefficient in the absorption-axis Y direction is larger
than that in the transmission-axis X direction. In order to obtain
the properties described above, the inorganic particle layers 25
are formed by an oblique sputtering method. The details of the
oblique sputtering method are the same as those of the method shown
in the first embodiment. In addition, a material for the inorganic
particle layer 25 is the same as that for the inorganic particle
layer 15 of the first embodiment.
In the polarizing element 20 thus formed of this embodiment, the
front surface of the substrate 21, that is, the surface on which
the strip-shaped thin films 22a, the dielectric layers 23, and the
inorganic particle layers 25 are formed is used as a light incident
surface. In addition, by using the following four functions, that
is, the light transmission, reflection, interference, and selective
light absorption of a polarized wave by optical anisotropic
properties, the polarizing element 20 attenuates a polarized wave
(TE wave (S wave)) having an electric field component (Y-axis
direction) parallel with a wire grid longitudinal direction of the
reflection layer 22 and transmits a polarized wave (TM wave (P
wave)) having an electric field component (X-axis direction)
perpendicular to the wire grid longitudinal direction.
That is, as shown in FIG. 6A, the TE wave is attenuated by the
selective light absorption function, which is for a polarized wave,
of the optical anisotropic properties of the inorganic particle
layer 25 formed of the inorganic particles 25a having shape
anisotropic properties. The thin films 22a function as a wire grid
and each reflect a TE wave passing through the inorganic particle
layer 25 and the dielectric layer 23, as shown in FIG. 6B. In this
step, when the dielectric layer 23 is formed so that the phase of
the TE wave passing through the inorganic particle layer 25 and
reflected by the thin film 22a is shifted by a half wavelength, the
TE wave reflected by the thin film 22a and a TE wave reflected by
the inorganic particle layer 25 cancel each other by the
interference and are attenuated. As described above, the selective
attenuation of the TE wave can be performed. A thickness to shift
the phase by a half wavelength is preferable; however, since the
inorganic particle layer itself has an absorption effect,
improvement in contrast can be realized even if the thickness of
the dielectric layer is not optimized, and hence the thickness may
be practically determined in consideration of desired polarization
properties together with economical efficiency in the actual
manufacturing process. reflection layer side. Also in this case, by
the selective absorption effect of the inorganic particle layer, a
transmission contrast equivalent to that described above can be
obtained. As described later, the reason for this is that the
intensity of the transmission contrast depends on the thickness of
the reflection layer. In the case in which the above method is
actually used, for example, in an optical engine portion (FIG. 13)
of a liquid crystal projector of an embodiment according to the
present invention, when a polarizing plate of the embodiment
according to the present invention is used as an incident
polarizing plate 10A in order to avoid undesirable reflected light
to a liquid crystal panel, a surface (the inorganic particle layer
25 side in FIGS. 6A and 6B) of the polarizing plate is disposed to
face the liquid crystal panel side. By the configuration as
described above, undesired reflected light returns to a light
source side. When the polarizing plate of this embodiment according
to the present invention is also used as an emission polarizing
plate 10B or 10C, the surface (the inorganic particle layer 25 side
in FIGS. 6A and 6B) of this polarizing plate may be disposed to
face the liquid crystal panel side. The direction of light incident
on the polarizing plate is reversed between the use as an incident
polarizing plate and the use as an emission polarizing plate;
however, regardless of the direction of light incident on the
polarizing plate, equivalent transmission contrast is obtained as
described above, and hence practical problems may not occur.
The polarizing element 20 may be formed, for example, as described
below. That is, after a metal film and a dielectric film are formed
on the substrate 21, and a lattice pattern is formed by patterning
the metal film and the dielectric film using a photolithographic
technique or the like, the inorganic particle layers 25 are formed
by an oblique sputtering deposition method. By adjusting an
incident angle in the oblique sputtering deposition, particles can
be intensively deposited in the vicinities of top parts of convex
portions formed of the strip-shaped thin films 22a and the
dielectric layers 23.
Besides the above method, a method may also be used in which a
one-dimensional lattice pattern is formed on a transparent
substrate using a transparent material, and metal layers,
dielectric layers, and inorganic particle layers are sequentially
formed on top parts of convex portions of this lattice pattern by
oblique deposition. Furthermore, another method may also be used in
which after a metal film, a dielectric film, and an inorganic
particle film are sequentially formed on a substrate, these layers
are simultaneously etched to form a one-dimensional lattice
pattern.
Furthermore, as shown in FIG. 7, after the reflection layers 22 are
formed on the substrate 21 to have a one-dimensional lattice
pattern, the dielectric layer 23 is formed all over the substrate
21. Hence, the dielectric layer 23 has a concave-convex shape
having convex portions over the strip-shaped thin films 22a and
concave portions therebetween. Subsequently, by an oblique
sputtering deposition method, the inorganic particle layers 25 are
formed on side surfaces of top parts of the convex portions of the
dielectric layer 23, so that a polarizing element having the same
effect as that of the example shown in FIGS. 5A and 5B can be
formed. The area on which the inorganic particle layer 25 is formed
is not limited to one side surface of the top part of the
dielectric layer 23 as shown in the figure and may be formed on
both side surfaces of the top part.
In addition, as the polarizing element of this embodiment according
to the present invention, a polarizing element having the structure
in which the dielectric layers 23 shown in FIGS. 5A and 5B are
omitted may also be used. That is, when the inorganic particle
layers 25 are selectively formed on the thin films 22a forming the
reflection layers 22 provided on the surface of the substrate which
is transparent to visible light, a wire grid structure is obtained
in which the inorganic particle layers 25 are disposed on the
substrate 21 with predetermined intervals. Even by the structure
described above, a desired extinction ratio (contrast:
transmission-axis transmittance/absorption-axis transmittance) can
be obtained in a visible light region.
Next, as an emission-surface stray-light countermeasure (ghost
countermeasure) for a liquid crystal projector, an example in which
selective light absorption layers are provided on a rear surface
side of the polarizing element 20 will be described.
FIG. 8 is a side cross-sectional view showing a schematic structure
of a polarizing element 20A. In this figure, the same constituent
elements as those of the above polarizing element 20 are designated
by the same reference numerals, and a detailed description thereof
is omitted.
In the polarizing element 20A of this embodiment, the reflection
layers 22 having a one-dimensional lattice pattern are formed on a
surface (one surface) of the substrate 21, and on the reflection
layers 22, the dielectric layers 23 and the inorganic particle
layers 25 are sequentially formed. In addition, on the rear surface
(opposite side surface) of the substrate 21, selective light
absorption layers 28 having optical anisotropic properties for a
polarized wave are provided, each of which is composed of a convex
portion 26 of a dielectric material and a second inorganic particle
layer 27 formed on a top part or at least one of side surface parts
of this convex portion 26.
In the polarizing element 20 which is not provided with the
selective light absorption layers 28 having optical anisotropic
properties for a polarized wave, since the rear surface of the
substrate 21 has a mirror surface, return light, which passes
through the polarizing element and is reflected by another optical
element, such as a lens, disposed following the polarizing element,
is again reflected by the above mirror surface. The stray light as
described above causes degradation in image quality, such as ghost,
in a liquid crystal projector.
In this embodiment, when the selective light absorption layers 28
having optical anisotropic properties for a polarized wave, having
the above structure, are provided at the rear surface side of the
substrate 21, the above stray light is absorbed, and reflection by
the reflection layers 22 is prevented. The convex portions 26
forming the selective light absorption layers 28 having optical
anisotropic properties for a polarized wave are formed from the
same material as that for the dielectric layer 23 and are also
formed into a one-dimensional lattice pattern extending in the same
direction as that of the strip-shaped thin films 22a of the
reflection layers 22. The second inorganic particle layer 27 is
formed of inorganic particles linearly disposed on the top part or
the side surface part of the convex portion 26 and is formed from a
material similar to that for the inorganic particle layer 25
provided at the front surface side of the substrate 21, and hence
the selective light absorption effect for incident light from the
rear surface of the substrate 21 can be obtained.
As a method for forming the convex portions 26, as is the method
for forming the dielectric layers 23, a sputtering method, a
sol-gel method, or the like may be used. The formation of the
convex shape is preferably formed by pattern processing using a
photolithographic technique or press formation by a nanoinprinting
method. As a method for forming the second inorganic particle
layers 27, oblique deposition similar to that for the inorganic
particle layers 25 provided at the front surface side of the
substrate 21 is preferable. The second inorganic particle layer 27
is formed on the top part, one side surface part, or two side
surfaces of the convex portion 26.
Alternatively, as another method for manufacturing the polarizing
element 20A, by using the polarizing element 10 shown in FIGS. 1A
and 1B and the polarizing element 20 shown in FIGS. 5A and 5B, the
rear surfaces of the substrates 11 and 21 may be adhered to each
other with a transparent adhesive to form the polarizing element
20A as shown in FIG. 47. In this case, the inorganic particles of
the inorganic particle layers 15 and those of the inorganic
particle layers 25 are preferably disposed in the same
direction.
Next, as another ghost countermeasure for a liquid crystal
projector, an example in which an antireflection layer is provided
between the substrate 21 and the reflection layer 22 will be
described.
FIG. 9 is a side cross-sectional view showing a schematic structure
of a polarizing element 20B. In this figure, the same constituent
elements as those of the above polarizing element 20 are designated
by the same reference numerals, and a detailed description thereof
is omitted.
The polarizing element 20B of this embodiment is formed for a
purpose similar to that for the above polarizing element 20A. That
is, in the polarizing element 20B of this embodiment,
antireflection layers 29 are provided between the substrate 21 and
the reflection layers 22. By the antireflection layers 29 provided
under the reflection layers 22 having a one-dimensional lattice
pattern, reflection of incident light from the rear surface of the
substrate 21 is prevented.
As the antireflection layer 29, for example, a black layer, such as
a carbon black layer, is preferably used. By the layer as described
above, the incident light from the rear surface of the substrate 21
can be efficiently absorbed. In addition, besides carbons, an
oxygen-deficient silicon oxide layer or a low reflection-material
layer having a reflectance lower than that of the reflection layer
22 may also be used. Alternatively, a layer similar to the
inorganic particle layer 25 may be used as the antireflection layer
29. In addition, in the example shown in the figure, in order to
decrease the reflectance by obtaining an interference effect
between the reflection layer 22 and the antireflection layer 29, a
dielectric layer 2a is provided. The dielectric layers 2a and the
antireflection layers 29, having a lattice pattern, can be
simultaneously obtained when the reflection layers 22 are formed by
patterning.
In addition, as another ghost countermeasure for a liquid crystal
projector, the following method may also be used. That is, a
rubbing treatment is performed on the surface of the substrate 21
so as to form a texture structure of irregularities in which fine
streaks are aligned in one direction in accordance with the
disposed direction of the inorganic particles 25a of the inorganic
particle layers 25 which are subsequently formed on the above
surface, and thin films (antireflection layers) of inorganic
particles having shape anisotropic properties may then be formed by
the above-described oblique sputtering method on the surface
processed by the rubbing treatment in accordance with the disposed
direction of the inorganic particles 25a. By the texture structure
described above, the alignment properties of the inorganic
particles are improved so that the long axis directions thereof are
along the longitudinal directions of the fine streaks, and the
polarization properties of the thin film are improved, so that the
ghost countermeasure effect can be enhanced. In addition, an
increase in transmission contrast properties as the polarizing
element can also be expected.
As one variation of the second embodiment, at least one laminate
structure of the dielectric layer 23 and the inorganic particle
layer 25 may be further provided on the inorganic particle layer 25
to form a multilayer structure. An example of this multilayer
structure is shown in FIGS. 10A and 10B.
In a polarizing element 30 shown in FIGS. 10A and 10B, the
strip-shaped thin film 22a forming the reflection layer 22, the
dielectric layer 23, and the inorganic particle layer 25 are formed
on the substrate 21 in that order from the bottom, and on the above
inorganic particle layer 25, a laminate structure 26a of the
dielectric layer 23 and the inorganic particle layer 25 is further
formed, so that a wire grid structure is formed. In addition, on a
laminate structure la thus formed, another laminate structure la
may be further provided. Accordingly, the transmission-axis
direction contrast is increased at a desired wavelength by
increasing the interference effect between the layers, and at the
same, an undesirable reflection component from a polarizing element
can be decreased in a wide range in transmission type liquid
crystal display devices; hence, as a result, by a polarizing
element having a film thickness smaller than that of the polarizing
element 20 having the structure shown in FIGS. 5A and 5B, a high
contrast and a low reflection can be realized.
As a method for manufacturing the polarizing element 30 of this
embodiment, the following three methods may be mentioned by way of
example. That is, as a first method, after a reflection layer
material (metal lattice material), and a dielectric film are
laminated on the substrate 21, and a one-dimensional lattice
pattern is formed, for example, by a nanoinprinting or a
photolithographic technique using etching or the like, particles
are deposited by an oblique sputtering deposition method. According
to the above method, by adjusting an incident angle in the oblique
sputtering deposition, inorganic particles can be intensively
deposited in the vicinities of top parts of convex portions of the
dielectric layers 23. In addition, as a second method, after a
concave-convex member having a one-dimensional lattice pattern is
formed on a transparent substrate using a transparent material, a
reflection layer material, a dielectric layer material, and an
inorganic particle material are sequentially and repeatedly
deposited by oblique deposition in accordance with the number of
laminates. In addition, as a third method, a laminate structure
composed of a dielectric film and an inorganic particle thin film
is repeatedly formed on a thin film (metal lattice film) for a
reflection layer in accordance with the number of laminates,
followed by etching. The inorganic particle material may have an
imperfect island shape as long as it has a grain boundary. In
addition, the dielectric layers 23 and the inorganic particle
layers 25 may be formed by a method including sputtering deposition
and etching in combination with a method using oblique sputtering
deposition. When the above manufacturing processes are carried out,
the type of substrate material is not particularly limited;
however, when the substrate is used for a projector generating a
large amount of heat, quartz or sapphire, having a high thermal
conductivity, is preferably used.
Incidentally, in the polarizing element 30 having the structure as
described above, since the light emission surface (reflection layer
22) is formed of a metal, when light returns, the reflectance is
unfavorably increased. Accordingly, also in this embodiment, the
emission-surface stray-light countermeasure described above is
preferably used.
FIGS. 11 and 12 each show an example of an emission-surface
stray-light countermeasure of this embodiment.
FIG. 11 shows an example in which the structure shown in FIG. 8 is
used in this embodiment.
A polarizing element 30A is formed such that in the polarizing
element 30, on the surface (rear surface) of the substrate 21
opposite to that on which the reflection layers 22 are formed,
there are provided the selective light absorption layers 28 having
optical anisotropic properties for a polarized wave, each of which
is composed of the convex portion 26 of a dielectric material and
the second inorganic particle layer 27 formed on the top part or at
least one side surface part of the convex portion 26.
FIG. 12 shows an example in which the structure shown in FIG. 9 is
used in this embodiment.
A polarizing element 30B is formed such that in the polarizing
element 30, the antireflection layers 29 are provided under the
reflection layers 22 having a one-dimensional lattice pattern, and
the dielectric layers 2a are provided between the reflection layers
22 and the antireflection layers 29 in order to obtain the
interference effect. In this embodiment, in FIG. 12, the dielectric
layer 2a under the reflection layer 22 may not be provided, and the
antireflection layer 29 may be directly provided under the
reflection layer 22. In addition, when the antireflection layer 29
is formed from the same material as that for the inorganic particle
layer 25, improvement in contrast can be obtained; however, in
order to simply prevent reflection of return light, as the
antireflection layer 29, a layer (low reflection layer) having a
reflectance lower than that of the reflection layer 22 may be
provided thereunder. As a low reflection material, any material
having a reflectance lower than that of the reflection layer 22 has
the effect, and for example, carbon, an oxide film, such as
oxygen-deficient SiO2, metal particles, or semiconductor particles
may also be used.
In the case in which the antireflection layer 29 and the dielectric
layer 2a are provided under the reflection layer 22, or the
antireflection layer 29 is directly formed under the reflection
layer 22, when these films are formed before a film for the
reflection layers is formed and are simultaneously etched when the
reflection layers 22 are formed by etching, these layers can be
formed only under the strip-shaped thin films 22a of the reflection
layers 22, and hence it is possible not to give any influences on
the transmission properties.
In addition, in the second embodiment, if desired, when the front
and the rear surfaces of the substrate are coated with
antireflection films, reflection at the interface between air and
the substrate is prevented, and as a result, the transmission-axis
transmittance can be improved. As the antireflection film, for
example, there may be used a low refractive-index film of MgF2 or
the like, which is generally used, or a multilayer film composed of
a low refractive-index film and a high refractive-index film In
addition, after the structure shown in FIGS. 5A and 5B or FIG. 7 is
formed, when a material, such as SiO2, transparent in a service
bandwidth region is applied on surfaces of the above structure as a
protective film so that the thickness thereof has no influences on
the polarization properties, it is preferable since the
reliability, such as humidity resistance, is effectively improved.
However, since the optical properties of inorganic particles are
influenced by the refractive index of the surrounding material, the
polarization properties may be changed in some cases when the
protective film is formed. In addition, since the reflectance to
incident light is also changed by the optical thickness (refractive
index.times.thickness of protective film) of the protective film, a
protective film material and the thickness thereof are to be
determined in consideration of the above influences. As the
protective film material, a material having a refractive index of 2
or less and an extinction coefficient of approximately zero is
preferable. As the material described above, SiO2 and Al2O3 may be
mentioned by way of example. The materials mentioned above may be
formed into films, for example, by a general vacuum film formation
method (such as a chemical vapor deposition method, a sputtering
method, or an evaporation method), or a spin coating method or a
dipping method, which uses a sol in which the above material is
dispersed in a liquid. Furthermore, a self-organizing film, as
disclosed in J. Microelectromechanical Systems Vol. 10, No. 1,
2001, pp. 33 to 40, may also be used. In order to improve humidity
resistance, a hydrophobic self-organizing film is preferable.
Perfluorodecyltrichlorosilane (FDTS) and Octadecanetrichlorosilane
(OTS) may be mentioned by way of example. Since having hydrophobic
properties, the above materials are also effective in terms of
antifouling. The materials mentioned above are commercially
available from chemical drug producers, such as Gelest Inc., USA,
and film formation can be performed by dipping. In addition, the
film formation may also be performed by vapor phase growth, and an
exclusive machine therefor is sold by Applied Microstructure Inc.,
USA. In the case of a silane-based self-organizing film as
described above, in order to improve the adhesion, after SiO2 is
applied on the polarizing element by the method described above to
form an adhesive layer, the self-organizing film may be
deposited.
Next, a liquid crystal projector of an embodiment will be
described.
The liquid crystal projector of this embodiment according to the
present invention has a lamp as a light source, a liquid crystal
panel, and one of the polarizing elements 10, 20, 20A, 20B, 30,
30A, and 30B.
FIG. 13 is a cross-sectional view showing a structural example of
an optical engine portion of a liquid crystal projector of this
embodiment.
The engine portion of a liquid crystal projector 100 has an
incident side polarizing element 10A, a liquid crystal panel 50, an
emission pre-polarizing element 10B, and an emission main
polarizing element 10C for red color LR; an incident side
polarizing element 10A, a liquid crystal panel 50, an emission
pre-polarizing element 10B, and an emission main polarizing element
10C for green color LG; an incident side polarizing element 10A, a
liquid crystal panel 50, an emission pre-polarizing element 10B,
and an emission main polarizing element 10C for blue color LB; and
a cross dichroic prism which synthesizes the three types of light
emitted from the individual emission main polarizing elements 10C
and which emits the synthesized light to a projector lens. The
polarizing elements 10, 20, and 30 of the embodiments are used as
the incident side polarizing element 10A, the emission
pre-polarizing element 10B, and the emission main polarizing
element 10C, respectively.
In the liquid crystal projector 100 of this embodiment, after light
emitted from a light source lamp (not shown) is separated into the
red light LR, the green light LG, and the blue light LB by a
dichroic mirror (not shown), these three types of light are
injected into the respective incident side polarizing elements 10A,
are then polarized thereby, and are further spatial-modulated by
the respective liquid crystal panels 50, and these three types of
light thus processed are then emitted therefrom. Subsequently, the
red light LR, the green light LG, and the blue light LB thus
emitted pass through the respective emission pre-polarizing
elements 10B and emission main polarizing elements 10C, are then
synthesized in the cross dichroic prism 60, and are subsequently
emitted from the projector lens (not shown). Even when the light
source lamp is a high power type, since the polarizing elements 10,
20, and 30 of the embodiments have superior light resistance
against intense light, a highly reliable liquid crystal projector
can be realized.
In addition, the polarizing elements of the embodiments are not
limited to application for the liquid crystal projector and are
preferably used as a polarizing element to be used in high
temperature environments. For example, the polarizing elements of
the embodiments according to the present invention may be used as a
polarizing element for car navigation systems and/or liquid crystal
displays.
EXAMPLES
Hereinafter, the verification results of polarization properties of
the polarizing element of the embodiment will be described.
Example 1
First, the optical properties of inorganic particle layers formed
by the oblique sputtering deposition shown in FIG. 4 were
verified.
In FIGS. 14A and 14B, experimental results of an optical anisotropy
enhancement effect by the oblique ion beam sputtering are shown. As
shown in FIG. 14A, by an ion beam sputtering method, Ge particles
were sputtered in a 10.degree. direction with respect to the
surface of a stationary glass substrate 41 and deposited thereon,
so that a Ge particle film 44 was formed. In FIG. 14B, measurement
results of optical constants (refractive index and extinction
coefficient) of the Ge particle film 44 thus formed are shown. The
measurement was performed using a spectral ellipsometer. The
thickness for this measurement was 10 nm. In this experiment, since
optical anisotropic properties were generated, the in-plane optical
constants were different; that is, refractive indexes n in
different directions were different from each other, and extinction
coefficients k in different directions were also different from
each other. In addition, for comparison purposes, when Ge particles
were deposited on the substrate 41 in a direction perpendicular
thereto while the substrate 41 is rotated, as shown in FIG. 15A, as
the optical constants of the Ge particle film 44 thus obtained, the
refractive index n and the extinction coefficient k both showed no
optical anisotropic properties, as shown in FIG. 15B, and the
individual optical constants were close to literature values.
In addition, after the composition of the target 2 was changed from
Ge to Si, a Si particle film was formed on the glass substrate 41
under the same conditions as those in the case of the Ge sputtering
deposition, and the optical constants were measured. The results
are shown in FIGS. 16A and 16B.
Also in the case of Si, when sputtering deposition was performed in
a 10.degree. direction with respect to the surface of the glass
substrate 41 (FIG. 16A), since optical anisotropic properties were
generated, it was found that in-plane optical constants in
different directions were different from each other; that is, the
refractive indexes n in different directions were different from
each other, and the extinction coefficients k in different
directions were also different from each other. In addition, when
sputtering deposition was performed perpendicular to the substrate
41 while the substrate 41 was rotated (FIG. 16B), optical
anisotropic properties of the optical constants, that is, of the
refractive index n and the extinction coefficient k, were not
generated.
Next, the polarization transmittance was obtained by simulation
calculation in the case in which the Ge particle film 44 was formed
to have a thickness of 20 nm on the glass substrate 41 under the
conditions shown in FIG. 14A. The results are shown in FIG. 17. In
this case, the polarization transmittances were calculated using an
optical constant in the X-axis direction for light in which its
electric field vibrated parallel with the X-axis direction and an
optical constant in the Y-axis direction for light in which its
electric field vibrated in the Y-axis direction. According to the
results, because of the optical anisotropic properties, the
transmittances in different polarization directions were different
from each other. That is, when a film having optical anisotropic
properties as described above is used for a material for a
polarizing element, improvement in properties thereof can be
expected.
Example 2
Next, influences of the optical anisotropic properties of the
inorganic particle layer on a polarizing element were investigated.
In particular, by using the polarizing elements having the
structures shown in FIGS. 1A and 1B and FIGS. 5A and 5B, the
polarization properties thereof were obtained by a rigorous
coupling wave analysis (RCWA). In this measurement, as shown in
FIGS. 18A and 18B, the structure was formed in which inorganic
particle layers 45 made of Ge were provided on the glass substrate
41 to form a wire grid structure, and the dimensions of the
inorganic particle layers 45 were set such that the pitch was 150
nm and the line width (Ge lattice direction width) was 37.5 nm. In
addition, when the inorganic particle layers 45 had the optical
anisotropic properties (by the method shown in FIG. 14A), the
thickness was assumed to 100 nm, when the inorganic particle layers
45 had no optical anisotropic properties (by the method shown in
FIG. 15A), the thickness was assumed to 10 nm, and the calculation
was performed based on the above conditions. The results are shown
in FIG. 19.
According to the results shown in FIG. 19, when the optical
anisotropic properties were not present (data shown by dotted lines
indicated as "bulk"), in a visible region having a wavelength of
550 nm or less (that is, in the green and the blue region) which
was important for an optical engine application such as a
projector, although the thickness was small, the absorption-axis
transmittance was high and the reflectance was also high as
compared to the case in which the optical anisotropic properties
were present (data shown by solid lines indicated as "oblique"). On
the other hand, when the optical anisotropic properties were
present, the absorption-axis transmittance was low and the
reflectance was also low. Accordingly, as the absorption type,
preferable properties were obtained. In this calculation, when the
optical anisotropic properties were not present, the thickness was
assumed to 10 nm. When the thickness is increased, the
absorption-axis transmittance is decreased; however, at the same
time, the reflectance is unfavorably increased. Hence, preferable
properties as a polarizing element having the optical anisotropic
properties cannot be obtained by the thickness adjustment.
Example 3
FIG. 19 shows the example in which the inorganic particle layer was
a single layer, and results similar to those described above can
also be obtained for a polarizing element having the multilayer
structure of inorganic particle layers, shown in FIG. 10.
In the polarizing element having a multilayer structure,
polarization properties obtained when inorganic particle layers of
Ge were formed by the method shown in FIG. 14A to have the optical
anisotropic properties, and polarization properties obtained when
inorganic particle layers of Ge were formed by the method shown in
FIG. 15A were calculated by a rigorous coupling wave analysis
(RCWA). In addition, the multilayer structure used in this example
was composed of Ge (15 nm), an Al reflection layer (240 nm), a SiO2
dielectric layer (205 nm), and a Ge inorganic particle layer (90
nm) provided at the front surface side of the substrate in that
order therefrom (value in the parentheses indicates the thickness),
and the dimensions of the inorganic particle layers were set such
that the pitch was 150 nm, and the line width (Ge lattice direction
width) was 37.5 nm. In addition, in order to suppress the influence
of stray light caused by re-reflection of return light returning to
a polarizing element emission surface, a Ge layer was provided at
the substrate side closer than the reflection layer. The
calculation results are shown in FIG. 20.
When the optical anisotropic properties were not present (data
shown by dotted lines indicated as "isotropy"), as was the case of
the single layer (FIG. 19), in a visible region having a wavelength
of 550 nm or less, the absorption-axis reflectance was high and the
transmission-axis transmittance was low as compared to those
obtained when the optical anisotropic properties were present (data
shown by solid lines indicated as "anisotropy"). Accordingly, as an
absorption type polarizing element, the above properties were not
preferable. As described above, the effect of the optical
anisotropic properties on the polarization properties of the
polarizing element was significant.
Example 4
When inorganic particle layers having the optical anisotropic
properties as described above are used for a polarizing element,
the polarization properties can be improved. In addition, the
optical constants of the inorganic particle layer preferably
satisfy such that the transmission-axis direction optical constant
is smaller than the absorption-axis direction optical constant,
that is, it is important to satisfy the relationships in which the
transmission-axis direction refractive index is smaller than the
absorption-axis direction refractive index and in which the
transmission-axis direction extinction coefficient is smaller than
the absorption-axis direction extinction coefficient. Examples
illustrating the above relationships are shown in FIGS. 21 and
22.
FIG. 21 shows the optical constants of an Ag film (inorganic
particle layer 25) of a polarizing element having the structure
shown in FIGS. 5A and 5B, the Ag film being formed by an oblique
sputtering deposition method using Ag to form the inorganic
particle layer 25. Also in this case, the optical anisotropic
properties were obtained as was the case of Ge. However, as shown
in FIG. 21, in the vicinity of a wavelength of 550 nm, the
relationship between the refractive indexes in the X and Y
directions was reversed, and in the vicinity of a wavelength of 440
nm, the relationship between the extinction coefficients in the X
and Y directions was reversed.
As was the case shown in FIG. 17, FIG. 22 shows the results of the
polarization transmittance obtained when the Ag film thickness was
20 nm, which were obtained by calculation using the optical
constants of the Ag film (inorganic particle layer 25) shown in
FIG. 21. The polarization transmittance was decreased as the
wavelength was decreased, and in the vicinity of a wavelength of
450 nm, the relationship between the polarization transmittances in
the X and Y directions was reversed. This was caused by the
reversion of the optical constant shown in FIG. 21, and when the
above inorganic particle layer is used for a polarizing element,
the reversion property as described above is not preferable since
it indicates a decrease in polarization transmittance. In addition,
when the extinction coefficient along the absorption axis is large,
the absorption index is high, and along the transmission axis,
light incident from an air layer is preferably transmitted without
being attenuated and/or reflected. That is, a lower refractive
index is more preferable (since the refractive index of air is 1).
Accordingly, as the preferable optical constants of the inorganic
particle layer, the optical properties in a service bandwidth are
not reversed, and the transmission-axis direction optical constant
is smaller than the absorption-axis direction optical constant;
that is, in other words, the relationships are satisfied so that
the transmission-axis direction refractive index is smaller than
the absorption-axis direction refractive index and so that the
transmission-axis direction extinction coefficient is smaller than
the absorption-axis direction extinction coefficient.
Example 5
Next, the relationship between the optical anisotropic properties
and the inorganic particles of the polarizing element of the
embodiment according to the present invention was investigated.
(1) Inorganic Particle Layer on a Flat Plate
First, by using a substrate having a smooth and flat surface, which
was a single crystal Si substrate provided with a SiO2 film having
a thickness of 10 nm, a Ge particle film was formed under the same
conditions as those in Example 1 (oblique sputtering deposition,
and sputtering deposition in a direction perpendicular to the
substrate surface), and the shape of Ge particles of the Ge
particle film was observed by an atomic force microscope
(hereinafter referred to as "AFM"). The results are shown in FIGS.
23A and 23B.
In a sample obtained by oblique sputtering deposition, shown in
FIG. 23A, individual particles were clearly observed, and in the
particles, shape anisotropic properties were generated such that
the diameter in the direction perpendicular to the Ge incident
direction was the major axis and the diameter in the Ge incident
direction was the minor axis. On the other hand, in a sample formed
by sputtering deposition in a direction perpendicular to the
substrate surface, shown in FIG. 23B, since the particle size was
very small, and a very smooth film surface was formed, which were
observed at the same magnification as that described above, the
shape of the particle could not be observed.
(2) Polarizing Element 10
Next, a sample of a polarizing element having the structure shown
in FIG. 3C was formed. In this example, first, a polymer layer
(mr-I 8010E manufactured by Micro Resist Technology GmbH) applied
on a quartz substrate was press-molded by a thermal nanoinprinting
method using a mold having a one-dimensional lattice pattern
(pitch: 150 nm, line/space ratio: 0.7, and depth: 150 nm) so that
the mold pattern was transferred to the polymer layer, and the
quartz substrate was etched by CF4 gas and Ar gas using the polymer
layer thus processed as a resist mask, so that the substrate 11
provided with the convex portions 17a extending in one direction at
predetermined intervals was obtained. Subsequently, by using the
ion beam sputtering apparatus shown in FIG. 4, the inorganic
particle layers 15 made of Ge having a thickness of 30 nm were
formed by the oblique sputtering deposition of Example 1 at a
substrate inclined angle .theta. of 5.degree., and a polarizing
element protective layer was formed by a vapor phase growth method
using SiO2 to have a thickness of 15 nm, so that the sample was
obtained. In addition, a multilayer film of SiO2/Ta2O5 was formed
as an antireflection film at a rear surface side of the substrate
11 by sputtering. The polarization properties of the obtained
polarizing element sample were investigated. As a result, as shown
in FIG. 24, optical anisotropic properties were obtained in which
the transmittance of the absorption axis was lower than that of the
transmission axis.
Analysis of the element distribution was performed for a
cross-section of this polarizing element sample using a TEM, and it
was found that as shown by element distribution mapping in FIG. 25,
the inorganic particle layers 15 made of Ge were each formed from
the top part to the sidewall of the convex portion 17a of the
substrate primarily formed of Si. Based on this result, the
inorganic particle layer 15 of this polarizing element sample was
observed in detail. The results are shown in FIGS. 26A and 26B.
FIG. 26A is a schematic cross-sectional view in combination with
the element analysis result. In addition, FIG. 26B is a schematic
plan view, observed from above.
As shown in FIG. 26B, the inorganic particle layers 15 were each
formed from the top part to the sidewall part of the
one-dimensional lattice convex portion 17a along the longitudinal
direction thereof, and in addition, the inorganic particle layers
15 were each observed as a strip or a belt shape formed of
inorganic particles 15a which had shape anisotropic properties and
were continuously disposed. In addition, each inorganic particle
15a was clearly observed, and it was also observed that the long
axis direction of the inorganic particle was the disposed direction
and that the short axis direction was perpendicular thereto.
In addition, an electron beam diffraction image of the Ge part in
FIG. 25 was investigated, and as shown in FIG. 27, since no clear
bright lines were observed, it was found that the crystal structure
of the Ge particles 15a forming the inorganic particle layer 15 was
amorphous. The amorphous indicates that the Ge particle has no
crystallographic orientation. In addition, it has been known that
in general, the structure of a Ge film formed by low-temperature
growth tends to be placed in an amorphous state (Dubey M, Mclane G
F, Jones K A, Lareau R T, Eckart D W, Han W Y, Roberts C, Dunkel J,
West L C, Mat. Res. Soc. Symp. Proc. Vol. 340, pp. 411 to 416
(1994).
(3) Polarizing Element 20
Next, a sample of a polarizing element having the structure shown
in FIGS. 5A and 5B was formed. In this example, after an aluminum
lattice having a pitch of 150 nm and a lattice depth of 200 nm was
formed as the reflection layers 22 on the substrate 21 made of
glass (Corning 1737), and the dielectric layers 23 were then formed
using SiO2 on the reflection layers 22 to have a thickness of 30
nm, oblique sputtering deposition was performed under the same
conditions as those of the polarizing element 10 of this example,
so that Ge particle layers having a thickness of 30 nm were formed
as the inorganic particle layers 25. Subsequently, as a topmost
layer, a film of SiO2 having a thickness of 30 nm was formed as a
protective film, so that the polarizing element sample shown in
FIGS. 5A and 5B was formed. In FIG. 28, the polarization properties
of this polarizing element sample are shown. The transmittance of
the absorption axis was approximately zero, and the reflectance was
also low. In addition, the ratio of transmittance in this case is
shown as contrast in FIG. 29. The contrast was 3,000 or more in a
green region centered at a wavelength of 550 nm and was 1,500 or
more in an entire visible light region including a blue region at a
wavelength of approximately 450 nm, and hence superior properties
as the polarizing element were obtained.
The cross-section of this polarizing element sample was observed,
and it was found that as shown in a schematic view shown in FIG.
30A, the inorganic particle layers 25 made of Ge were each formed
from the top part to the sidewall of the one-dimensional lattice
reflection layer 22 and dielectric layer 23, which were provided on
the substrate 21.
In addition, in FIGS. 30B and 31, the observation results of this
polarizing element sample viewed from above are shown. FIG. 30B is
a schematic view, and FIG. 31 is a SEM image used for forming the
above schematic view.
The inorganic particle layers 25 were each formed from the top part
to the sidewall part of the one-dimensional lattice dielectric
layer 23 along the longitudinal direction thereof, and in addition,
the inorganic particle layers 25 were each observed as a strip or a
belt shape formed of the inorganic particles 25a which had shape
anisotropic properties and were continuously disposed. In addition,
each inorganic particle 25a was observed such that the long axis
direction of the inorganic particle was the disposed direction and
the short axis direction was perpendicular thereto.
From the above results, it is found that the inorganic particles of
the polarizing element of the example according to the present
invention have shape anisotropic properties by oblique sputtering
deposition and are formed so that when the inorganic particles are
disposed in a one-dimensional lattice pattern, the long axis
directions of the inorganic particles are aligned in the lattice
direction of the one-dimensional lattice. In addition, the
inorganic particles are placed in an amorphous state. It is
believed that in the present invention, the above-described
properties of the inorganic particles relates to the expression of
the optical anisotropic properties. The particles having shape
anisotropic properties are formed by oblique sputtering deposition,
and the expression of the shape anisotropic properties is called
Steering Effect (Jikeun Seo, S.-M. Kwon, H.-Y. Kim, and J.-S. Kim,
Phys. Rev. B67, 121402 (2003).
In addition, by oblique sputtering deposition, as shown in FIGS.
32A and 32B, the shape of a deposited particle is changed with the
change in thickness (thickness of an inorganic particle in the
growth direction), and the optical anisotropic properties are
influenced thereby. That is, when a major axis diameter a of the
inorganic particle is larger than a thickness b thereof (FIG. 32A),
the optical anisotropic properties are shown in two directions (X
and Y directions) on the substrate, and the particle major axis
diameter a direction is the absorption axis. On the other hand,
when the major axis diameter a of the inorganic particle is smaller
than the thickness b thereof (FIG. 32B), the optical anisotropic
properties are shown in the thickness direction of the inorganic
particle and in the in-plane axis direction, and the particle
thickness b direction is the absorption axis; hence, the directions
of the optical anisotropic properties shown in FIGS. 32A and 32b
are substantially reversed. In the polarizing elements 10 and 20 of
the example according to the present invention, since the lattice
direction is used as the absorption axis, as the thickness is
increased, the polarization properties are degraded. Hence, as
shown in FIG. 32A, the lattice direction is preferably used as the
absorption direction in the state in which the particle major axis
diameter a is larger than the particle thickness b.
In addition, although a thin film (such as a germanium thin film)
having no optical anisotropic properties is formed on the
dielectric layer 23 instead of the inorganic particle layer 25,
when the thickness of the thin film is optimized, the reflectance
in the absorption-axis direction can be suppressed. However, in
this case, the reflection is suppressed dominantly by the
interference effect, the wavelength band is narrow, and since
absorption occurs in the transmission-axis direction, the
transmission-axis transmittance is disadvantageously decreased.
Furthermore, since the interference effect is sensitive to the
thickness, in order to obtain desired properties, strict control of
the thicknesses of the dielectric layer 23 and the germanium thin
film are to be appropriately performed. On the other hand, in the
present invention, since germanium particles having optical
anisotropic properties are used, the degree of designing freedom is
high, and also manufacturing can be easily performed.
Accordingly, by a rigorous coupling wave analysis (RCWA), the
optical anisotropic properties of the inorganic particle layer 25
of the polarizing element 20 were simulated for two cases in which
a thin film and fine particles were used for forming the inorganic
particle layer 25 in order to obtain the difference therebetween.
In this case, the reflection layer 22 was formed from Al to have a
thickness of 200 nm, a lattice pitch of 150 nm, and an Al width of
45 nm, the dielectric layer 23 was formed from SiO2 to have a
thickness of 30 nm. In addition, the dependences of the
absorption-axis reflectance, the transmission-axis transmittance,
and the transmission contrast on the thickness of the Ge thin film
and the thickness of the Ge particle were calculated at a
wavelength of 450 nm. In addition, as the optical constants of the
Ge thin film, the values in FIG. 15B were used, and in order to
obtain the optical constants of the Ge particles, in consideration
of an increase in anisotropic properties when the Ge particles are
formed into a lattice pattern, calculation was performed assuming
that, in accordance with the model shown in FIG. 33, the particles
sufficiently smaller than a wavelength of incident light were
distributed in the dielectric layer and aligned in the axis
direction. Furthermore, calculation was performed assuming that the
volume fraction of Ge in the dielectric layer 23 was 0.4, and the
aspect ratio of Ge was 20.
The results are shown in FIGS. 34A to 34C. FIG. 34A shows the
results of the absorption-axis reflectance, FIG. 34B shows the
results of the transmission-axis transmittance, and FIG. 34C shows
the results of the transmission contrast. It was found that
compared to the case of the Ge thin film, in the case of the Ge
particles, the contrast was not rapidly changed, the transmittance
was high, and the thickness range in which the reflectance could be
decreased was wide.
Example 6
Next, the relationship between the aspect ratio of the inorganic
particle and the contrast of the polarizing element was
investigated.
(1) Oblique Sputtering Deposition on a Flat Plate
First, Ge particle layers having a thickness of 30 nm were formed
on a flat Si substrate at substrate inclined angles .theta. of
20.degree. and 10.degree. using the ion beam sputtering apparatus
shown in FIG. 4. The samples obtained thereby were observed by a
SEM, and any 40 Ge particles in a SEM image were extracted and were
measured to obtain the size (long diameter or major axis diameter
(major axis length) and short diameter or minor axis diameter
(minor axis length)), so that the aspect ratio was obtained.
FIGS. 35A and 35B are each showing the result of the aspect ratio
using a histogram analysis. According to the results shown by the
histogram, the distribution tends to shift toward a high aspect
ratio side in the case shown in FIG. 35B (substrate inclined angle
.theta.: 10.degree.) as compared to the case shown in FIG. 35A
(substrate inclined angle .theta.: 20.degree.). In addition, the
average long axis lengths of the Ge particles were 30 nm and 63 nm
at substrate inclined angles .theta. of 20.degree. and 10.degree.,
respectively, and the average aspect ratios were 3.2 and 4.0 at
substrate inclined angles .theta. of 20.degree. and 10.degree.,
respectively.
In addition, by using samples which included Ge particle layers
having a thickness of 10 nm formed on a flat glass substrate
(Corning 1737) at substrate inclined angles .theta. of 20.degree.
and 10.degree. by the ion beam sputtering apparatus shown in FIG.
4, the transmittance was measured, and the transmittance ratio at a
wavelength of 550 nm was obtained as the contrast. In addition, an
x direction and a y direction correspond to those shown in FIG.
14A. The results are shown in Table 1. As the substrate inclined
angle .theta. was decreased, the aspect ratio of the Ge particle
tended to increase, and in addition, the contrast also tended to
increase.
TABLE-US-00001 TABLE 1 Substrate Ge particle inclined angle
Transmittance (%) Long axis Aspect .theta. (degree) x direction y
direction Contrast length (nm)* ratio* 20 63.2 72.4 1.1 30 3.2 10
58.4 74.9 1.3 63 4.0 *average value
(2) Polarizing Element 10
Polarizing element samples were formed under the same conditions as
those for the polarizing element 10 of Example 5 except that the
oblique sputtering deposition for forming the inorganic particle
layers 15 were performed at substrate inclined angles .theta. of
10.degree. and 20.degree.. The transmittances of this sample in the
transmission axis and the absorption axis were measured, and the
transmittance ratio at a wavelength of 550 nm was obtained as the
contrast. The results are shown in FIG. 36 and Table 2. Also in the
polarizing element of this example according to the present
invention, as the substrate inclined angle .theta. was decreased,
the contrast tended to increase.
TABLE-US-00002 TABLE 2 Substrate inclined angle Transmittance (%)
.theta. (degree) x direction y direction Contrast 20 88.3 37.2 2.4
10 90.7 33.9 2.7
As described above, although inorganic particles having shape
anisotropic properties can be formed into films on the substrate by
oblique sputtering deposition, the aspect ratio, which is a ratio
between the major axis diameter and the minor axis diameter of the
inorganic particle, depends on the incident angle (substrate
inclined angle .theta. in FIG. 4) of the inorganic particles, and
as the angle is decreased, the aspect ratio increases. In addition,
as the aspect ratio increases, the transmission contrast
simultaneously increases. As described above, using Steering Effect
by the oblique sputtering deposition, a polarizing element having
superior properties can be realized.
Example 7
By changing the type of film formation method (dry process), Al
particle layers were formed on the substrate. In this example, the
following three dry processes were used.
(a) Electron Beam Deposition (FIG. 37A)
A substrate inclined by 10.degree. with respect to the normal line
direction of an evaporation source containing Al was set at a
distance of 80 cm apart from the evaporation source, and electron
beam deposition was performed at a film formation rate of 0.3
nm/sec.
(b) Magnetron Sputtering (FIG. 37B)
A substrate inclined by 10.degree. with respect to the normal line
direction of an Al target was set at a distance of 40 cm apart from
the target, and magnetron sputtering deposition was performed at a
film formation rate of 0.1 nm/sec.
(c) Ion Beam Sputtering (FIG. 37C)
The sputtering deposition method shown in FIG. 4 by way of example
in the present invention was performed. In this method, a substrate
was set at an angle of 45.degree. at a distance of approximately 15
cm apart from the Al target, and ion beam sputtering deposition was
performed at a film formation rate of 0.2 nm/sec.
In this example, the same substrate as the substrate 11 of the
polarizing element 10 of Example 5 was used and was set so that the
Al incident direction was set along a direction (y direction)
perpendicular to the lattice longitudinal direction (x direction)
as shown in FIG. 14A. In addition, the thicknesses of the Al
particle layers were all set to 10 nm.
The transmittances of the samples thus obtained were measured. The
results are shown in FIG. 38.
Among the three types of samples, since the sample obtained by the
ion beam sputtering had a high transmittance, and the difference in
transmittance in the x and y directions was large, it was found
that ion beam sputtering was the most favorable film formation
method.
Example 8
Among the polarizing elements of the embodiments, in the polarizing
element 20 having the structure shown in FIGS. 5A and 5B, when the
height (thickness) of the reflection layer 22 is changed, the
transmission contrast of the polarizing element can be easily
controlled. As one example, in FIG. 39, the calculation result of
the relationship between the transmission contrast and the
reflection layer thickness (Al height) of the one-dimensional
lattice reflection layer 22 made of Al and having a pitch of 150 nm
and an aluminum width of 37.5 nm are shown, the result being
obtained by a rigorous coupling wave analysis (RCWA).
In addition, in the polarizing element 20 having the structure
shown in FIGS. 5A and 5B, when the height (thickness) of the
dielectric layer 23 is changed, the optical properties of the
polarizing element can be easily controlled. In this example, the
one-dimensional lattice reflection layers 22 made of Al and having
a thickness (Al height) of 200 nm, a pitch of 150 nm, and a lattice
width of 50 nm, the dielectric layers 23 made of SiO2 and having
different thicknesses of 0, 19, 37, 56, and 74 nm obtained by RF
sputtering deposition, and the inorganic particle layers 25 made of
Ge particles and having a thickness of 30 nm were provided on the
substrate 21 made of glass (Corning 1737) to form five types of
samples of the polarizing element 20 of the example according to
the present invention, and by using the samples thus obtained, the
relationships of the dielectric layer thickness with the
transmission-axis transmittance, the contrast, and the
absorption-axis reflectance were obtained at wavelengths of 450,
550, and 650 nm. The results are shown in Table 3.
TABLE-US-00003 TABLE 3 Dielectric Absorption-axis reflectance
Transmission-axis layer thickness (%) transmittance (%) Contrast
(nm) .lamda. = 450 nm .lamda. = 550 nm .lamda. = 650 nm .lamda. =
450 nm .lamda. = 550 nm .lamda. = 650 nm .lamda. = 450 nm .lamda. =
550 nm .lamda. = 650 nm 0 19 18 26 72 82 86 1,800 2,929 3,440 19 8
3 3 72 83 86 3,130 3,952 4,315 37 3 2 2 78 84 86 2,167 3,652 3,913
56 11 10 8 75 83 85 1,875 3,773 4,739 74 30 22 21 73 85 86 1,460
4,250 5,369
From the results thus obtained, for example, when it is desired to
decrease the absorption-axis reflectance, the thickness of the
dielectric layer 23 may be set in the range of 19 to 37 nm. In
addition, when the polarizing element is used for application in
which reflection may not cause any serious problems, the thickness
of the dielectric layer 23 may be decreased to zero. This means a
decrease in number of manufacturing steps, and hence the
productivity can be improved. In addition, since a high contrast is
realized at a wavelength in the range of 450 to 650 nm, the
polarizing element can be preferably applied to a projector used in
a wide service bandwidth.
On the other hand, as for the transmittance, a high transmittance
is realized such as 70% or more at a wavelength of 450 nm and 80%
or more at wavelengths of 550 and 650 nm. When the pitch of the
lattice is further decreased, the transmittance can be further
improved.
In addition, the contrast can be adjusted by the height of the
metal lattice. When a higher contrast is preferable, the height of
an Al lattice may be increased, and when a lower contrast is
preferable, the height may be decreased.
Next, in FIG. 40, the polarization properties are shown which were
obtained when the height of an Al reflection layer of a polarizing
element having the same structure as that of the polarizing element
20 of Example 5 was set to 30 nm. In this case, since the thickness
of the reflection layer was small (the Al height was low), the
contrast in a blue region was approximately 3; however, the
reflectance was suppressed to 2% or less by the effect of Ge fine
particles as the case shown in FIG. 28. In the case of a polarizing
element having the properties as described above, as shown by the
SEM image of FIG. 31, Ge particles are deposited on sidewalls of
the convex portions formed of the reflection layers and the
dielectric layers, and hence a superior shape is formed as an
anisotropic optical absorbing element. The above may also be said
for the polarizing element 10 shown in FIGS. 1A and 1B and FIGS. 3A
to 3C.
In the polarizing elements of the example according to an
embodiment, when the lattice shape (the shapes and heights of the
convex portions 14a in FIG. 2 and the reflection layer
22/dielectric layer 23 in FIGS. 5A and 5B, the pitch of the
one-dimensional lattice pattern, and the like) and Steering Effect
(the size, the aspect ratio, the alignment properties, and the like
of the inorganic particles) are used in combination, a fine
particle shape preferably used for an absorption type polarizing
element can be realized.
Example 9
In the polarizing element 20 shown in FIGS. 5A and 5B, as an
emission-surface stray-light countermeasure (ghost countermeasure),
after a rubbing treatment is performed on the surface of the
substrate 21 so as to form a texture structure in which fine
streaks are formed in one direction so as to correspond to the
disposed direction of the inorganic particles 25a which are
subsequently formed, a thin film (thin film to be formed into the
antireflection layers 29 (hereinafter referred to as
"antireflection film")) made of inorganic particles having shape
anisotropic properties may be formed on the surface processed by
the rubbing treatment so as to correspond to the disposed direction
of the inorganic particles 25a. In particular, when a texture
structure is mechanically formed in the surface of the substrate 21
by a polishing material, such as a polishing tape, and an
antireflection film made of inorganic particles is then formed by
an oblique sputtering deposition method, inorganic particles having
shape anisotropic properties by Steering Effect can be obtained as
is the case of the inorganic particle layers 25 to be formed on the
lattice; hence, the polarization effect of the inorganic particles
is enhanced, and as a result, a ghost suppression effect can be
enhanced. Hereinafter, a particular example which was actually
carried out will be described.
In this example, by using D20000 manufactured by Nihon Micro
Coating Co., Ltd. as a polishing material, the effect described
above was verified. Corning 1737 glass was used as the substrate,
and the texture was formed by rubbing the surface of the substrate
in one direction with D20000. The substrate surface after the
texture was formed was measured by an AFM, and the measurement
result is shown in FIG. 41. The horizontal axis indicates the
position on the substrate, and the vertical axis indicates the
height of irregularities. The average pitch of the irregularities
of the substrate surface was 160 nm. In addition, the
transmittances of the substrate were measured before and after the
formation of the texture, and it was found that the transmittances
before and after the formation of the texture were not changed from
each other, as shown in FIG. 42. That is, by the method described
above, precise machining on the order of nanometers can be easily
performed without degrading the transmission properties of the
substrate.
Subsequently, by using the ion beam sputtering apparatus shown in
FIG. 4, oblique sputtering deposition was performed on the textured
substrate at a substrate incident angle .theta. of 5.degree. to
form an antireflection film of Ge particles having a thickness of
10 nm. In this step, the sputtering deposition was performed on the
substrate so that the relationship between the Ge incident
direction and the substrate was set such that the y direction in
FIG. 14A was the texture longitudinal direction. By using the
sample thus obtained, the shapes of the Ge particles of the
antireflection film were observed by an AFM, and it was found that
the Ge particles were aligned along the texture as shown in FIG.
43.
In FIG. 44, the transmission properties of this sample are shown.
In addition, for comparison purposes, by using a glass substrate
made of Corning 1737, which was not processed by the rubbing
treatment, and an antireflection film which was formed under the
same conditions as described above, a comparative sample was
formed, and the transmission properties thereof were also
investigated. In FIG. 44, "textured substrate" indicates the
example sample, and "non-textured substrate" indicates the
comparative sample. From the results shown in FIG. 44, although
both samples showed polarization properties by Steering Effect;
however, in the case of the "textured substrate", the transmittance
in the x direction was much higher than that in the y direction,
and hence the difference in transmittance between in the x and the
y directions is large, so that superior polarization properties are
obtained.
According to an embodiment, the example sample (the textured
substrate provided with the antireflection film formed thereon) is
used, and the layered structure of the polarizing element 20 shown
in FIGS. 5A and 5B is formed thereon. Subsequently, when the
reflection layers 22 and the dielectric layers 23 are formed by
pattern processing, the antireflection film is simultaneously
processed to have a lattice pattern, so that the antireflection
layers 29 are formed. As a result, the effect of the ghost
countermeasure can be enhanced, and at the same time, as the
polarizing element, improvement in transmission contrast properties
can also be expected.
Example 10
According to the above examples, in the most cases, the polarizing
elements were described using Ge by way of example; however,
inorganic particles having shape anisotropic properties can be
formed using another material. Hence, by appropriately selecting a
material, a polarizing element to be used at a targeted wavelength
can be formed.
FIGS. 45 and 46 are graphs showing polarization properties of the
polarizing element 10 shown in FIG. 3C including Si and Sn,
respectively, as inorganic particles having a thickness of 30 nm.
In this case, the antireflection films on the rear surface are not
formed. In the cases in which the above materials are used,
although the reflectance is slightly higher than that of Ge, the
transmission-axis polarization properties in a blue region are
high, and depending on applications, the above materials may also
be used for a polarizing element.
It should be understood that various changes and modifications to
the presently preferred embodiments described herein will be
apparent to those skilled in the art. Such changes and
modifications can be made without departing from the spirit and
scope of the present subject matter and without diminishing its
intended advantages. It is therefore intended that such changes and
modifications be covered by the appended claims.
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