U.S. patent application number 10/025086 was filed with the patent office on 2002-12-05 for reverse reflectance mode direct-view liquid crystal display employing a liquid crystal having a characteristic wavelength in the non-visible spectrum.
Invention is credited to Chen, Gang, Gao, Jianmi, Hou, Jianan, Li, Shushan, Sun, Ruihai, Wang, Yong-Jing, Wu, Bao-Gang.
Application Number | 20020180913 10/025086 |
Document ID | / |
Family ID | 25363975 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020180913 |
Kind Code |
A1 |
Wu, Bao-Gang ; et
al. |
December 5, 2002 |
Reverse reflectance mode direct-view liquid crystal display
employing a liquid crystal having a characteristic wavelength in
the non-visible spectrum
Abstract
Disclosed are various reverse-mode direct-view liquid crystal
displays (LCD) employing a liquid crystal having a characteristic
wavelength in the non-visible spectrum, including reflective and
transflective mode displays, and methods of fabrication. In
accordance with the principles disclosed, a reflectance mode
direct-view LCD includes a polarizer, a reflector, and a
cholesteric liquid crystal (CLC) packed between the polarizer and
reflector and having a characteristic wavelength to reflect
non-visible spectrum. Portions of the CLC can selectively exhibit a
planar state or a focal-conic state, the portions of the CLC in the
planar state appearing black, and the portions of the CLC in the
focal-conic state appearing white to an observer of the LCD. A
transflective mode LCD is derived by further combination of
polarizers, transflective mirrors and internal light sources.
Inventors: |
Wu, Bao-Gang; (Murphy,
TX) ; Hou, Jianan; (Germantown, MD) ; Gao,
Jianmi; (Richardson, TX) ; Wang, Yong-Jing;
(Ossining, NY) ; Li, Shushan; (Plano, TX) ;
Sun, Ruihai; (Wylie, TX) ; Chen, Gang; (Plano,
TX) |
Correspondence
Address: |
HITT GAINES & BOISBRUN P.C.
P.O. BOX 832570
RICHARDSON
TX
75083
US
|
Family ID: |
25363975 |
Appl. No.: |
10/025086 |
Filed: |
December 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10025086 |
Dec 19, 2001 |
|
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09874519 |
Jun 4, 2001 |
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6462805 |
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Current U.S.
Class: |
349/115 |
Current CPC
Class: |
G02F 1/133555 20130101;
G02F 1/13718 20130101; G02F 1/133541 20210101 |
Class at
Publication: |
349/115 |
International
Class: |
G02F 001/1335 |
Claims
What is claimed is:
1. A direct-view liquid crystal display (LCD), comprising: a
polarizer; a reflector; and a cholesteric liquid crystal (CLC)
located in a gap between said polarizer and reflector such that
said CLC receives light reflected from said reflector, said CLC
having a characteristic wavelength in the non-visible spectrum and
capable of exhibiting a planar state or a focal-conic state.
2. The direct-view LCD recited in claim 1 wherein said CLC
comprises a mixture of a nematic liquid crystal and a chiral
dopant.
3. The direct-view LCD recited in claim 2 wherein said mixture
comprises about 60 percent to about 90 percent by weight of said
nematic liquid crystal and a balance of said mixture comprising
said chiral dopant.
4. The direct-view LCD recited in claim 1 wherein said gap ranges
from about 1 micron to about 6 microns.
5. The direct-view LCD recited in claim 1 wherein said gap ranges
from about 2 microns to about 3 microns.
6. The direct-view LCD recited in claim 1 wherein said LCD further
includes an alignment coating material.
7. The direct-view LCD recited in claim 6 wherein said alignment
coating material comprises a polyimide.
8. The direct-view LCD recited in claim 1 wherein said
characteristic wavelength of said CLC is in the infrared
spectrum.
9. The direct-view LCD recited in claim 8 wherein said
characteristic wavelength of said CLC is greater than about 780
nm.
10. The direct-view LCD recited in claim 8 wherein said
characteristic wavelength of said CLC is greater than about 700
nm.
11. The direct-view LCD recited in claim 8 wherein where said LCD
includes two alignment coating materials, and said coating
materials, said gap and said CLC, when in the focal conic state,
cooperate to act as a quarter wavelength retarder.
12. The direct-view LCD recited in claim 6 wherein said CLC further
includes said alignment coating material comprising a polyimide and
said gap is about 2 microns.
13. The direct-view LCD recited in claim 1 wherein said
characteristic wavelength of said CLC is in the ultraviolet
spectrum.
14. The direct-view LCD recited in claim 13 wherein said
characteristic wavelength of said CLC is less than about 380
nm.
15. The direct-view LCD recited in claim 13 wherein said
characteristic wavelength of said CLC is less than about 450
nm.
16. The direct-view LCD recited in claim 13 wherein a surface of
said reflector at a boundary between said CLC and said reflector is
polished.
17. The direct-view LCD recited in claim 1 further comprising a
first electrode adjacent an inner surface of said polarizer and a
second electrode adjacent an inner surface of said reflector.
18. The direct-view LCD recited in claim 1 wherein said polarizer
comprises a first circular polarizer.
19. The direct-view LCD recited in claim 18 wherein said reflector
comprises a transflective mirror and said direct view LCD further
comprises a second circular polarizer located posterior to said
transflective mirror said second circular polarizer having a
polarity different from said first polarizer, and a light source
located posterior to said second circular polarizer.
20. The direct-view LCD recited in claim 18 further comprises a
mirror located posterior to said light source.
21. The direct-view LCD recited in claim 1 wherein said reflector
has a colored surface.
22. A method of fabricating a direct-view LCD comprising the steps
of: positioning a polarizer; positioning a reflector thereby
forming a gap between said polarizer and reflector; and packing
said gap with a cholesteric liquid crystal (CLC) such that said CLC
receives light reflected from said reflector, said CLC having a
characteristic wavelength in the non-visible spectrum and capable
of exhibiting a planar state or a focal-conic state.
23. The method as recited in claim 22 wherein fabricating said
direct-view LCD includes packing with said CLC comprising a mixture
of a nematic liquid crystal and a chiral dopant.
24. The method as recited in claim 22 wherein fabricating said
direct-view LCD includes packing with said mixture comprising about
60 percent to about 90 percent by weight of said nematic liquid
crystal and a balance of said mixture comprising said chiral
dopant.
25. The method as recited in claim 22 wherein fabricating said
direct-view LCD includes said forming said gap ranging from about 1
micron to about 6 microns.
26. The method as recited in claim 22 wherein fabricating said
direct-view LCD includes said forming said gap ranging from about 2
microns to about 3 microns.
27. The method as recited in claim 22 wherein fabricating said
direct-view LCD further includes coating said polarizer and said
reflector with an alignment coating material.
28. The method as recited in claim 27 wherein fabricating said
direct-view LCD further includes coating with said alignment
coating material comprising a polyimide.
29. The method as recited in claim 22 wherein fabricating said
direct-view LCD includes said packing said CLC having said
characteristic wavelength in the infrared spectrum.
30. The method as recited in claim 22 wherein said characteristic
wavelength of said CLC is greater than about 780 nm.
31. The method as recited in claim 22 wherein said characteristic
wavelength of said CLC is greater than about 700 nm.
32. The method as recited in claim 29 wherein fabricating said
direct-view LCD further includes coating said polarizer and said
reflector with an alignment coating material, and said coating
materials, said gap and said CLC, when in the focal conic state,
cooperate to act as a quarter wavelength retarder.
33. The method as recited in claim 27 wherein fabricating said
direct-view LCD further includes said alignment coating material
comprising a polyimide and said gap is about 2 microns.
34. The method as recited in claim 22 wherein fabricating said
direct-view LCD includes said packing said CLC having said
characteristic wavelength in the ultraviolet spectrum.
35. The method as recited in claim 34 wherein said characteristic
wavelength of said CLC is less than about 380 nm.
36. The method as recited in claim 34 wherein said characteristic
wavelength of said CLC is less than about 450 nm.
37. The method as recited in claim 34 wherein fabricating said
direct-view LCD further includes polishing a surface of said
reflector, said surface at a boundary between said CLC and said
reflector.
38. The method as recited in claim 22 wherein fabricating said
direct-view LCD further includes positioning a first electrode
adjacent an inner surface of said polarizer and positioning a
second electrode adjacent an inner surface of said reflector.
39. The method as recited in claim 22 wherein fabricating said
direct-view LCD includes positioning said polarizer comprising a
first circular polarizer.
40. The method as recited in claim 39 wherein fabricating said
direct-view LCD includes positioning said reflector comprising a
transflective mirror, and said fabricating further comprises
positioning a second circular polarizer posterior to said
transflective mirror said second circular polarizer having a
polarity different from said first polarizer, and positioning a
light source posterior to said second circular polarizer.
41. The method as recited in claim 40 wherein fabricating said
direct-view LCD includes positioning a mirror posterior to said
light source.
42. The method as recited in claim 22 wherein fabricating said
direct-view LCD includes positioning a reflector with a colored
surface.
Description
CROSS-REFERENCE TO APPLICATION
[0001] This continuation-in-part application claims the benefit of
U.S. application Ser. No. 09/874,519, entitled, "Reverse-mode
Direct-view Liquid Crystal Display Employing a Liquid Crystal
Having a Characteristic Wavelength in the Non-visible Spectrum," to
Bao-Gang Wu, Jianan Hou, Jianmi Gao, Yong-Jing Wang, Shushan Li,
Rui Hai Sun and Gang Chen, filed on Jun. 4, 2001, commonly assigned
with the present invention and incorporated herein by reference as
if reproduced herein in its entirety.
TECHNICAL FIELD OF THE INVENTION
[0002] The present invention is directed, in general, to liquid
crystal displays and, more specifically, to reflective and
transflective black-and-white and color cholesteric liquid crystal
displays.
BACKGROUND OF THE INVENTION
[0003] The development of improved low-power-consumption flat-panel
liquid crystal displays (LCDs) is an area of very active research,
driven by the proliferation and demand for portable electronic
appliances, including computers and wireless telecommunications
devices. Moreover, as the quality of LCDs improve, and the cost of
manufacturing declines, LCDs may eventually replace conventional
display technologies, such as cathode-ray-tubes.
[0004] Cholesteric liquid crystal ("CLC") technology is a
particularly attractive candidate for many display applications.
CLC displays can be used to provide bi-stable and multi-stable
displays that, owing to their stability, do not require a
continuous driving circuit to maintain a display image, thereby
significantly reducing power consumption. Moreover, some CLC
displays can be easily viewed in ambient light without the need for
back-lighting; such displays are referred to as "reflective" mode
displays, while those requiring a back-light are referred to as
"transmissive" mode displays. The elimination of the need for
back-lighting is particularly significant in that lighting
requirements typically represent approximately 90 percent of the
total power consumption of conventional LC displays. While a
reflective mode display is suitable for some applications, and a
transmissive mode display is suitable for others, there are certain
applications in which it is desirable to have a display operable in
both reflective and transmissive modes, that is, a transflective
mode. Moreover, the visibility of a LC display is governed in part
by the contrast between the quality of bright and dark states of LC
cells in the display. For example, traditional normal mode CLC
displays, using CLCs having a characteristic wavelength for the
reflection of light in the visible spectrum, may have poor contrast
because of an unfavorably low brightness to darkness ratio.
[0005] Accordingly, to meet the growing demand for LCDs, there is a
need in the art for high contrast LCDs operable in reflective and
transflective modes.
SUMMARY OF THE INVENTION
[0006] To address the above-described deficiencies of the prior
art, the present invention provides a reverse mode direct-view
liquid crystal displays employing a liquid crystal having a
characteristic wavelength to reflect light in the non-visible
spectrum, including reflective and transflective mode displays, and
methods of fabricating such displays. In accordance with the
principles disclosed, the basic structure of the direct-view liquid
crystal display (LCD) includes a polarizer, a reflector and a
cholesteric liquid crystal (CLC) located in a gap between the
polarizer and reflector such that the CLC receives light reflected
from the reflector. The CLC has a characteristic wavelength in the
non-visible spectrum and is capable of exhibiting planar or
focal-conic states. Thus, portions of the LCD can be controlled to
selectively exhibit a planar state or a focal-conic state, thereby
achieving high contrast.
[0007] In one embodiment, the polarizer comprises a first circular
polarizer, the reflector comprises a transflective mirror and the
direct-view LCD further comprises a second circular polarizer
located posterior to the transflective mirror with a light source
located posterior to the second circular polarizer.
[0008] The foregoing has outlined, preferred and alternative
features of the present invention so that those skilled in the art
may better understand the detailed description of the invention
that follows. Additional features of the invention will be
described hereinafter that form the subject of the claims of the
invention. Those skilled in the art should appreciate that they can
readily use the disclosed conception and specific embodiment as a
basis for designing or modifying other structures for carrying out
the same purposes of the present invention. Those skilled in the
art should also realize that such equivalent constructions do not
depart from the spirit and scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] For a more complete understanding of the present invention,
and the advantages thereof, reference is now made to the following
descriptions taken in conjunction with the accompanying drawings,
in which:
[0010] FIGS. 1A and 1B illustrates a cross-sectional view of an
exemplary reverse mode reflective LCD structure, in accordance with
the principles of the present invention, and its operation when its
liquid crystal is in planar and focal-conic states,
respectively;
[0011] FIGS. 2A and 2B illustrates a cross-sectional view of an
exemplary reverse mode transflective LCD structure, in accordance
with the principles of the present invention, and its operation in
a transmissive manner when its liquid crystal is in planar and
focal-conic states, respectively; and
[0012] FIG. 3 illustrates exemplary embodiments of a method of
fabricating a direct-view LCD, in accordance with the principles of
the present invention.
DETAILED DESCRIPTION
[0013] As described with reference to the exemplary embodiments
illustrated in FIGS. 1-2 and method of fabrication in FIG. 3, the
present invention discloses the heretofore unrecognized capability
to construct a direct-view LCD by combining a CLC having a
characteristic intrinsic reflective wavelength, .lambda..sub.0,
reflecting light maximally in the non-visible spectrum, with one or
more linear, circular, or substantially circular, polarizers, and a
reflective or a transflective mirror. For purposes of the present
invention, visible light is defined as the range of the light
spectrum that the human visual system is relatively most sensitive
to, i.e., a relative sensitivity of about greater than 5%, compared
to the most sensitive wavelength, between about 450 nm to about 700
nm, with the non-visible spectrum laying above and below this
range.
[0014] In particular embodiments, the CLC comprises a mixture of a
nematic liquid crystal, and a chiral dopant. The mixture may
comprise about 60 percent to about 90 percent by weight of the
nematic liquid crystal, with a balance of the mixture comprising
the chiral dopant. In certain embodiments, the mixture contains
sufficient amounts of the appropriate dopant or combination of
dopants to produce a helical CLC structure having a characteristic
pitch that establishes a maximum reflective wavelength within
either an infrared or an ultraviolet region of the light spectrum.
In an exemplary embodiment, the infrared range may be greater than
700 nm and the ultraviolet range may be less than 450 nm.
[0015] In other embodiments, however, the infrared range may be
greater than 780 nm and the ultraviolet range may be 400 nm or
less. Portions of the CLC may be selectively controlled to exhibit
a planar state or a focal-conic state. Portions of the CLC in the
planar state within the direct-view LCD appear black to an
observer, and portions of the CLC in the focal-conic state within
the direct-view LCD appear white to an observer of the LCD.
[0016] Referring to FIGS. 1A and 1B, illustrated is a
cross-sectional view of a reverse reflectance mode LCD 100, and its
operation when CLC 140 is in planar and focal-conic states,
respectively. LCD 100 comprises a polarizer 110, a reflector 120,
thereby forming a gap 130 between the polarizer 110 and reflector
120, and a CLC 140 of the above described embodiments located in
the gap 130 such that said CLC 140 receives light reflected from
said reflector 120. The gap 130 generally ranges from about 1
micron to about 6 microns, and in certain preferred embodiments is
about 2 to about 3 microns. The polarizer 110 and reflector 120 may
be comprised of conventional materials well-known to those of
ordinary skill in the art. The reflector 120 for example may be
comprised of Aluminum.
[0017] With continuing reference to FIGS. 1A and 1B, LCD 100 may
also include first electrode 150 adjacent an inner surface of the
polarizer 110 and second electrode 160 adjacent an inner surface of
the reflector 120. Electrodes 150, 160 are preferably made from
conventional substantially transparent materials, such as indium
tin oxide (ITO), and optionally laminated onto a glass substrate.
The electrodes 150, 160 may further be optionally coated with an
alignment coating material, for example, comprising a polyimide.
Preferably, overlying polyimide layers on the two electrodes 150,
160 are buffed antiparallel to each other. The first and second
electrodes, 150, 160 are further coupled to a conventional driving
circuit (not shown) operative to cause the CLC 140 to selectively
transform to a planar or focal-conic state. When in the planar
state, the CLC 140 will reflect incident light having the same
polarity as polarizer 110 from external light source 170 maximally
at .lambda..sub.0, plus an associated bandwidth, but allow
nonreflected light 180 at substantially all wavelengths of light
outside of the reflected bandwidth to pass through without
effecting its polarity. When in the focal-conic state, however, the
CLC 140 is operative to optically retard and scatter at all
wavelengths, thereby changing the polarity of the nonreflected
light 180.
[0018] With continuing reference to FIGS. 1A and 1B, in one
exemplary embodiment, the polarizer 110 is a conventionally made
first circular polarizer, comprising for example, a linear
polarizer and a quarter wavelength retarder. The polarizer 110 may
preferably be positioned on the outer surface of the first
electrode 150; those skilled in the art, however, will recognize
that the polarizer 110 alternatively could be positioned on the
inner surface of the first electrode 150, or the polarizer 110
could have a first electrode integrally formed therewith.
[0019] With continuing reference to FIGS. 1A and 1B, in another
exemplary embodiment, the reflector 120 is positioned on the outer
surface of the second electrode 160; those skilled in the art,
however, will recognize that the reflector 120 alternatively could
be positioned on the inner surface of the second electrode 160, or
the reflector 120 could have a second electrode integrally formed
therewith, and thereby minimize parallax effects. Furthermore, the
reflector 120 can have a colored surface, such that the reflected
light appears to an observer to have substantially the same color
as the reflector 120. Thus, different portions (i.e., pixels) of
the display may have different colored reflectors, providing a
multi-color display. Alternatively, a color filter (not shown) may
be used to provide a single or multi-color display.
[0020] With continuing reference to FIG. 1A, shown is the operation
of a preferred embodiment of LCD 100 when CLC 140 is in the planar
state. Nonreflected light 180, including visible light, is
circularly polarized as it passes through the polarizer 110. The
polarity of the light 180 is either right or left circularly
polarized, depending on the handedness of polarizer 110 when
configured to be a circular polarizer. According to the principles
of the present invention, the polarity of the light 180 is
substantially unaffected as it passes through the CLC 140.
Moreover, because .lambda..sub.0 is in the nonvisible region of the
spectrum, substantially all light 180 in the visible region of the
spectrum reaching the CLC 140 will not be reflected by the CLC 140.
The light 180 passing through the CLC 140 retains its polarity,
until it is reflected by reflector 120, which will cause the
handedness of the circular polarity to be reversed. For example, if
the polarizer 110 has right-hand circular polarity, the light 180
reflected by reflector 120 and received by CLC 140 will have
left-hand circular polarity. Because the polarity of the light 180
passing through CLC 140 is reversed upon reflection from reflector
120, polarizer 110 will block the exit of light 180. In one
preferred embodiment, where .lambda..sub.0 is in the ultraviolet
spectrum, polishing a surface 125 of reflector 120 at a boundary
between CLC 140 and reflector 120 is thought to minimize changes to
the polarity of light 180, thereby maximizing the blockage of light
180 reaching polarizer 110. Thus, an observer of LCD 100 when CLC
140 is in the planar state will observe the LCD to be black.
[0021] Turning now to FIG. 1B, shown is the operation of a
preferred embodiment of LCD 100 when CLC 140 is in the focal-conic
state. Due to the light retarding and scattering properties of CLC
140 when in the focal-conic state, the polarity of nonreflected
light 180 passing through polarizer 110 is altered both prior and
subsequent to reflection by reflector 120 and received by the CLC
140. As noted above, because .lambda..sub.0 is in the nonvisible
region of the spectrum, substantially all light 180 in the visible
region of the spectrum reaching the CLC 140 will not be reflected
by the CLC 140. Consequently, at least a portion of the light 180
will have a circular polarity of the same handedness as circular
polarizer 120, and therefore exit LCD 100. And because
.lambda..sub.0 is in the nonvisible region of the spectrum,
substantially all light in the visible region of the spectrum will
pass through the CLC and appear to an observer of the LCD 100 as a
white display. In a preferred embodiment, where .lambda..sub.0 is
in the infrared spectrum, the LCD 100 further includes an alignment
coating material and the gap 130 thickness is about 2 microns.
Preferably the alignment coating material, for example a polyimide,
is coated over electrodes 150, 160 and the two coatings are rubbed
anti-parallel to each other. The alignment coating material, gap
130 and CLC 140 when in the focal conic state cooperate to act as a
quarter wavelength retarder. The polarity of the light 180 is
thereby favorably altered to match that of polarizer 110, allowing
increased amounts of light 180 to exit LCD 100. Thus, an observer
of the reflective LCD 100 when CLC 140 is in the focal-conic state
will observe the LCD to be white. In summary, the LCD 100 is
capable of a substantially black and white display, corresponding
to the CLC 140 in the planar and focal-conic state,
respectively.
[0022] Turning now to FIGS. 2A and 2B, illustrated is a
cross-sectional view of an exemplary embodiment of a reverse
transflectance mode LCD 200, showing its operation in a
transmissive manner when its liquid crystal 240 in gap 230 is in
planar and focal-conic states, respectively. The polarizer is
preferably a first circular polarizer 210 and the reflector is a
transflective mirror 220. Transflective mirror 220 is operative to
reflect external incident light from the front of LCD 200 or
transmit incident light from the rear. The transflective mirror 220
may be made of conventional materials well known to those of
ordinary skill in the art, for example Aluminum. LCD 200 may
include conventional first 250 and second 260 electrodes and driver
(not shown), analogous to that described for LCD 100, including the
alternative embodiments detailed above.
[0023] With continuing reference to FIGS. 2A and 2B, LCD 200
further includes a second circular polarizer 215 positioned
posterior to the transflective mirror 220, and internal light
source 290 positioned posterior to the second circular polarizer
215. For example, the light source 290 may be a conventional LCD
backlight, such as an electro-luminescent panel. The second
circular polarizer 215 has a polarity different than the first
circular polarizer 210, and preferably of the opposite handedness.
In one preferred embodiment, a surface of the transflective mirror
220 may be polished at a boundary between the CLC 240, analogous to
that described for LDC 100. Optionally, LCD 200 fabrication may
further include positioning a mirror 295 posterior to the light
source 290. Mirror 295 reverses the polarity of the light blocked
by the second circular polarizer 215, thus increasing the amount of
light passing through polarizer 215.
[0024] With continuing reference to FIGS. 2A and 2B, in the
exemplary embodiment, the first circular polarizer 210 is
positioned on the outer surface of first electrode 250. Those
skilled in the art, however, will recognize that the first circular
polarizer 210 could alternatively be positioned on the inner
surface of the first electrode 250, or the first circular polarizer
210 could have the first electrode 250 integrally formed therewith.
Similarly, although the transflective mirror 220 is positioned on
the outer surface of the second electrode 260, the transflective
mirror 220 could be positioned on the inner surface of the second
electrode 260, or the transflective mirror 220 could have the
second electrode 260 integrally formed therewith. Furthermore, the
transflective mirror 220 can have a colored surface, such that
reflected light appears to an observer to have substantially the
same color as the transflective mirror 220. Moreover, different
portions (i.e., pixels) of the display could have different colored
transflective mirrors, whereby a multi-color display can be
provided. Alternatively, a color filter can be used to provide a
single or multi-color display.
[0025] With continuing reference to FIG. 2A, the operation of LCD
200 in the transmissive mode is depicted when CLC 240 is in a
planar state. Light emitted from light source 290 is circularly
polarized on passing through the second circular polarizer 215 and
transflective mirror 220. Non-visible light having the same
polarity as polarizer 215 at .lambda..sub.0 and its associated
bandwidth will be reflected by the CLC 240, while other wavelengths
of non-reflected light 280, including visible light, will pass
through the CLC 240. According to the principles of the present
invention, the polarity of the non-reflected light 280 is
substantially unaffected on passing through CLC 240 when the CLC
240 is in a planar state. Consequently, the non-reflected light 280
on reaching the first circular polarizer 210, will be blocked
because the polarity of the first and second circular polarizers
210 and 220 are of different, preferably opposite handedness.
Similar to that described for LCD 100, in a preferred embodiment,
polishing a surface of the transflective mirror 220 at a boundary
between the CLC 240 and the transflective mirror 220 reduces
disturbance of the polarity of the non-reflected light 280.
Therefore, an observer of the LCD 200 operating in the transmissive
mode will observe a black state corresponding to portions of the
CLC 240 in the planar state.
[0026] Turn now the FIG. 2B, the operation of LCD 200 in the
transmissive mode is depicted when CLC 240 is in a focal-conic
state. Because of the light scattering and retarding effects of the
focal-conic structure, the polarity of non-reflected light 280 is
altered as it passes through portions of the CLC 240 in the
focal-conic state. Consequently, a portion of the light 280 will
have a circular polarity handedness corresponding to the handedness
of first circular polarizer 210, and will thus exit LCD 200.
Similar to that described for LCD 100, in a preferred embodiment,
LCD 200 further includes an alignment coating material on
electrodes 250, 260 and having an adjusted gap 230 thickness of
about two microns to create a quarter wavelength retarder effect
when the CLC 240 is in the focal conic state, thereby increasing
the amount of light 280 exiting LCD 200. Therefore, an observer of
LCD 200 operating in the transmissive mode will observe a white
state corresponding to portions of the CLC 240 in the focal-conic
state. Thus the LCD 200 is capable of a substantially black and
white display, corresponding to the CLC 240 in the planar and
focal-conic state, respectively.
[0027] The operation of LCD 200 in a reflective mode using external
incident light source 270, when its liquid crystal is in planar and
focal-conic states, is substantially the same as described above
for LCD 100 and illustrated in FIGS. 1A and 1B.
[0028] Turning now to FIG. 3, illustrated is an exemplary
embodiment of a method of fabricating a reverse mode direct-view
LCD 300, in accordance with the principles of the present
invention. The LCD is fabricated by positioning a polarizer 310,
positioning a reflector 320, thereby forming a gap 330 between the
polarizer and reflector, and packing the gap 340 with a CLC having
a .lambda..sub.0 in the non-visible spectrum and capable of
exhibiting a planar state or a focal-conic state. Conventional
packing techniques, such as capillary or vacuum filling, well known
to those skilled in the art, may be used. Packing with the CLC
includes packing a mixture of a nematic liquid crystal and a chiral
dopant. In certain embodiments, the mixture comprises about 60
percent to about 90 percent by weight of the nematic liquid crystal
and a balance of the mixture comprises the chiral dopant. One of
ordinary skill in the art will understand that the chiral dopant
may, in some embodiments, contain a combination of chiral dopants
to produce the desired .lambda..sub.0 in an ultraviolet or infrared
region of the spectrum. In certain embodiments, forming the gap 330
results in gaps ranging from about 1 micron to about 6 microns and
in certain preferred embodiments, about 2 micron to about 3
microns. When .lambda..sub.0 is in the infrared spectrum, the gap
is preferably about 2 microns. In yet other preferred embodiments,
when .lambda..sub.0 falls within the ultraviolet spectrum, the
reflector is polished 325. Fabricating the LCD 300 further includes
positioning conventional first and second electrodes 350, 360; as
discussed above the electrodes could alternately be formed and
positioned integrally with the polarizer 310 or reflector 320. In
certain preferred embodiments, alignment coating materials rubbed
antiparallel to each other may be coated 345 onto the
electrodes.
[0029] With continuing reference to FIG. 3, alternative embodiments
of fabricating the LCD 300, including fabricating an LCD for
operation in the transflective mode, are also illustrated.
Fabrication may further include positioning the reflector
comprising a transflective mirror 327, and positioning the
polarizer comprising a first circular polarizer 312. Fabrication
further includes positioning a second circular polarizer 315
posterior to the transflective mirror, the second circular
polarizer having a polarity different from the first polarizer,
preferably of opposite handedness, and positioning an internal
light source 390 posterior to the second circular polarizer. In
certain preferred embodiments, fabricating further includes
positioning a mirror 395 posterior to the light source.
EXAMPLES
[0030] Five different types of direct-view LCDs were prepared
according to the present invention: reflective reverse-mode and
transflective reverse-mode, each having a .lambda..sub.0 in either
an infrared or ultraviolet region of the light spectrum. For all
five preparations, unless otherwise indicated, two pieces of four
inch square glass substrates, were laminated with electrode
material comprising ITO having a resistance of 60 .OMEGA. per
square inch. The ITO layers were then coated with an alignment
coating material of polyimide (PI-150; Nissan Chemical Industries,
Ltd., Houston, Tex.). The polyimide coatings were buffed
anti-parallel to each other. The electrodes were then laminated to
a polarizer and a reflector, described below, to form test
cells.
[0031] The desired electronic waveforms were applied on the cell as
described in U.S. Pat. No. 5,625,477, entitled, "Zero Field
Multistable Cholesteric Liquid Crystal Display;" U.S. Pat. No.
5,889,566, entitled, "Multistable Cholesteric Liquid Crystal
Devices Driven By Width-Dependent Voltage Pulses;" and U.S. Pat.
No. 5,933,203, entitled, "Apparatus for and Method Of Driving A
Cholestric Liquid Crystal Flat Panel Display," all to Bao-Gang Wu,
et. al., which are commonly assigned with the present invention,
and incorporated herein by reference as if reproduced herein in its
entirety. Using the apparatus described in the above cited
references, every pixel of the cell can be switched between planar
state and focal conic states. All nematic liquid crystals and
chiral dopants were obtained from EM industries (Hawthorne,
N.Y.).
[0032] A reflective reverse-mode type LCD (designated LCD-1) having
a , in the infrared range was prepared in the following way. A
circular polarizing plate, comprising a quarter wave length
retarder(1/4 .lambda.) having a maximum transmittance at 550 nm and
linear polarizer, was laminated onto the first substrate. A
reflector, comprising a thin reflective aluminum layer, was coated
onto the second substrate. Unless otherwise indicated, spacers were
used to form a gap of about 3 microns between the polarizer and
reflector. A liquid crystal mixture containing by weight about
90.1% ZLI-5400-100.TM. (nematic liquid crystal), and chiral dopant,
comprising about 3.8% ZLI-4571.TM., and 6.1% ZLI-811.TM., was
packed into the gap. A second reflective reverse-mode type LCD
(designated LCD-2) having a .lambda..sub.0 in the ultraviolet range
was prepared by filling a similarly fabricated cell with a liquid
crystal mixture containing about 63.1% by weight ZLI-5400-100.TM.,
and chiral dopant comprising by weight: about 22.4% CB-15.TM., 6.5%
ZLI-4572.TM., and 8.0% ZLI-3786.TM., and using the same front
surface and backside configuration as described above.
[0033] The resulting reflective reverse-mode type LCDs have a
.lambda..sub.0 centered at about 780 nm and about 400 nm, for LCD-1
and LCD-2, respectively. For both LCDs, planar state and focal
conic states are stable for at least one month in the absence of an
electrical field. And for both LCDs, the planar state appears as
black and the focal conics state appears as white.
[0034] A third reflective reverse-mode type LCD (designated LCD-3)
having a .lambda..sub.0 in the infrared range was prepared as
described above, but with the following modifications. The
polyimide alignment coating comprised a mixture of by weight 25%
SE1211.TM. and 75% SE5291.TM., both from Nissan Chemical
Industries. A liquid crystal mixture containing by weight about
91.2% MLI-6625.TM. (nematic liquid crystal), and chiral dopant,
comprising about 6% CB-15.TM. and 3% ZLI-4578.TM., was packed into
the gap. In this configuration, when in the focal conic state,
LCD-3 produces a 1/4 .lambda. effect centered at 550 nm. This in
turn increases the amount of light exiting LCD-3, thereby making
the cell appear a brighter white to an observer.
[0035] A transflective reverse-mode type LCD (designated LCD-4)
having a characteristic wavelength in the infrared range was
prepared by filling the cell with a liquid crystal mixture
containing the same relative amounts of ZLI-5400-100.TM.,
ZLI-4572.TM. and ZLI-3786.TM. as described above for LCD-1. A first
circular polarizing plate, similar to that described above, was
laminated onto the front surface of the display. A conventional
transflective mirror was positioned on the backside of the cell,
and a second circular polarizing plate was laminated onto the
backside of the transflective mirror. Finally, back-lighting was
placed behind the backside of the second circular polarizing plate.
A second transflective reverse-mode type LCD (designated LCD-5)
having a characteristic wavelength in the ultraviolet range was
prepared by filling the cell with a liquid crystal mixture
containing the same relative amounts by weight of ZLI-5400-100.TM.,
CB-15.TM., ZLI-4572.TM., and ZLI-3786.TM. as described above for
LCD-2, and using the same front surface and backside configuration
as described above for LCD-4.
[0036] The resulting transflective reverse-mode type LCDs have a
.lambda..sub.0 centered at about 780 nm and about 400 nm, for LCD-4
and LCD-5, respectively. For both LCDs, planar state and focal
conic states are stable at least one month in the absence of an
electrical field. In the transmissive mode, when the back-light was
on, the planar state appears as black and the focal conics state
appears as white. Similarly, in the reflective mode, when the
back-light was off, the planar state appears as black and the focal
conics state appears as white.
[0037] From the foregoing detailed description, it is apparent that
the present application discloses novel reverse-mode direct-view
liquid crystal displays employing liquid crystal having a
characteristic wavelength to reflect light in the non-visible
spectrum, including reflective and transflective displays.
[0038] Although the present invention and its advantages have been
described in detail, those skilled in the art should understand
that they can make various changes, substitutions and alterations
herein without departing from the spirit and scope of the
invention.
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