U.S. patent application number 10/562050 was filed with the patent office on 2007-05-03 for liquid crystal device and a method for manufacturing thereof.
Invention is credited to Johan Felix, Bertil Helgee, Lachezar Komitov.
Application Number | 20070098918 10/562050 |
Document ID | / |
Family ID | 29738566 |
Filed Date | 2007-05-03 |
United States Patent
Application |
20070098918 |
Kind Code |
A1 |
Komitov; Lachezar ; et
al. |
May 3, 2007 |
Liquid crystal device and a method for manufacturing thereof
Abstract
The invention relates to a liquid crystal device comprising a
liquid crystal bulk layer and a surface-director alignment layer
comprising side-chains arranged to interact with the bulk layer,
wherein the orientation of the bulk layer molecules and the
orientation of said side-chains each is directly controllable by an
electric field via dielectric coupling, thus resulting in a
decreased total time period (rise and decay times) needed to switch
and relax the liquid crystal bulk molecules in response to an
applied external field. The invention also relates to a method for
manufacturing a liquid crystal device and a method of controlling a
liquid crystal bulk layer.
Inventors: |
Komitov; Lachezar;
(Goteborg, SE) ; Helgee; Bertil; (Vastra Frolunda,
SE) ; Felix; Johan; (Goteborg, SE) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Family ID: |
29738566 |
Appl. No.: |
10/562050 |
Filed: |
December 29, 2004 |
PCT Filed: |
December 29, 2004 |
PCT NO: |
PCT/SE04/00880 |
371 Date: |
December 23, 2005 |
Current U.S.
Class: |
428/1.1 ;
252/299.01; 428/1.2 |
Current CPC
Class: |
C09K 19/56 20130101;
G02F 1/1393 20130101; C09K 2323/03 20200801; G02F 1/133742
20210101; G02F 1/133738 20210101; C09K 2323/02 20200801; G02F
1/134363 20130101; C09K 19/02 20130101; G02F 1/133711 20130101;
C09K 2323/00 20200801; G02F 1/133769 20210101 |
Class at
Publication: |
428/001.1 ;
428/001.2; 252/299.01 |
International
Class: |
C09K 19/00 20060101
C09K019/00; C09K 19/52 20060101 C09K019/52 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 23, 2003 |
SE |
0301810.8 |
Nov 18, 2003 |
SE |
0303041.8 |
Mar 4, 2004 |
SE |
SE2004/00300 |
Claims
1. A liquid crystal device comprising a liquid crystal bulk layer
presenting a surface-director at a bulk surface thereof, and a
surface-director alignment layer comprising side-chains arranged to
interact with the bulk layer at said bulk surface for facilitating
the obtaining of a preferred orientation of the surface-director of
the bulk layer, wherein the orientation of the molecules of the
liquid crystal bulk layer and the orientation of said side-chains
of the surface-director alignment layer each is directly
controllable by an electric field via dielectric coupling.
2. A liquid crystal device according to claim 1, wherein the liquid
crystal bulk layer and the surface-director alignment layer exhibit
dielectric anisotropies (.DELTA..epsilon.) of opposite signs.
3. A liquid crystal device according to claim 1, wherein the liquid
crystal bulk layer and the surface-director alignment layer exhibit
dielectric anisotropies (.DELTA..epsilon.) of same sign.
4. A liquid crystal device according to claim 1 comprising a first
and a second surface-director alignment layer, wherein the liquid
crystal bulk layer and the first surface-director alignment layer
exhibit dielectric anisotropies (.DELTA..epsilon.) of opposite
signs, and the liquid crystal bulk layer and the second
surface-director alignment layer exhibit dielectric anisotropies
(.DELTA..epsilon.) of same sign.
5. A liquid crystal device according to claim 1, wherein the
surface-director alignment layer comprises structural parts
exhibiting dielectric anisotropies (.DELTA..epsilon.) of opposite
signs.
6. A liquid crystal device according to claim 2 further comprising
at least one confining substrate, and wherein an orthogonal
projection of said surface-director on said substrate, termed
projected surface-director, presents said preferred orientation in
a geometrical plane in parallel with said substrate, termed
preferred field-off planar orientation, and the orientation of the
molecules of said bulk layer is directly controllable by an applied
electric field to perform an out-of-plane switching of said
preferred planar orientation of the projected surface-director to a
field-induced vertical orientation.
7. A liquid crystal device according to claim 2 further comprising
at least one confining substrate, and wherein an orthogonal
projection of said surface-director on a geometrical plane
perpendicular to said substrate, termed projected surface-director,
presents said preferred orientation, termed preferred field-off
vertical orientation, and the orientation of the molecules of said
bulk layer is directly controllable by an applied electric field to
perform an out-of-plane switching of said preferred vertical
orientation of the projected surface-director to a field-induced
planar orientation.
8. A liquid crystal device according to claim 6, wherein the
electric field is applied normally to said at least one confining
substrate.
9. A liquid crystal device according to claim 3 further comprising
at least one confining substrate, and the orientation of the
molecules of said bulk layer is directly controllable by an applied
electric field to perform an in-plane switching of an initial first
planar orientation to a field-induced second planar orientation,
whereas an orthogonal projection of said surface-director, termed
projected surface-director, presents said preferred orientation in
a geometrical plane in parallel with said substrate, termed
preferred field-induced planar orientation.
10. A liquid crystal device according to claim 9, wherein the
electric field is applied in parallel with said at least one
confining substrate.
11. A liquid crystal device according to claim 1, wherein the
liquid crystal bulk layer comprises a nematic liquid crystal.
12. A liquid crystal device according to claim 1, wherein the
surface-director alignment layer comprises a polymer having a
polymeric backbone and side-chains attached thereto, said polymeric
backbone lacks directly coupled ring structures and each side-chain
of at least some of the side-chains, (i) comprises at least two
unsubstituted and/or substituted phenyls coupled via a coupling
selected from the group consisting of a carbon-carbon single bond
(--), a carbon-carbon double bond containing unit (--CH.dbd.CH--),
a carbon-carbon triple bond containing unit (--C.ident.C--), a
methylene ether unit (--CH.sub.2O--), an ethylene ether unit
(--CH.sub.2CH.sub.2O--), an ester unit (--COO--) and an azo unit
(--N.dbd.N--), (ii) exhibits a permanent and/or induced dipole
moment that in ordered phase provides dielectric anisotropy, and
(iii) is attached to the polymeric backbone via at least two
spacing atoms.
13. A liquid crystal device according to claim 12, wherein the
polymer is a polyvinyl acetal.
14. A method for manufacturing a liquid crystal device comprising
the steps of: providing a surface-director alignment layer on an
inner surface of at least one substrate, and sandwiching a liquid
crystal bulk layer between two substrates, said liquid crystal bulk
layer presenting a surface-director at a bulk surface thereof, and
said surface-director alignment layer comprising side-chains
arranged to interact with the bulk layer at said bulk surface for
facilitating the obtaining of a preferred orientation of the
surface-director of the bulk layer, wherein the orientation of the
molecules of the liquid crystal bulk layer and the orientation of
said side-chains of the surface-director alignment layer each is
directly controllable by an electric field via dielectric
coupling.
15. A method of controlling a liquid crystal bulk layer comprising
the step of aligning a liquid crystal bulk layer presenting a
surface-director at a bulk surface thereof by use of a
surface-director alignment layer comprising side-chains arranged to
interact with the bulk layer at said bulk surface for facilitating
the obtaining of a preferred orientation of the surface-director of
the bulk layer wherein the orientation of the molecules of the
liquid crystal bulk layer and the orientation of said side-chains
of the surface-director alignment layer each is directly
controllable by an electric field via dielectric coupling.
16. A liquid crystal device according to claim 7, wherein the
electric field is applied normally to said at least one confining
substrate.
17. A liquid crystal device according to claim 2, wherein the
liquid crystal bulk layer comprises a nematic liquid crystal.
18. A liquid crystal device according to claim 3, wherein the
liquid crystal bulk layer comprises a nematic liquid crystal.
19. A liquid crystal device according to claim 4, wherein the
liquid crystal bulk layer comprises a nematic liquid crystal.
20. A liquid crystal device according to claim 5, wherein the
liquid crystal bulk layer comprises a nematic liquid crystal.
Description
TECHNICAL FIELD
[0001] The present invention generally relates to the field of
liquid crystals. More specifically, the present invention relates
to a liquid crystal device comprising a liquid crystal bulk layer
presenting a surface-director at a bulk surface thereof, and a
surface-director alignment layer arranged to interact with the bulk
layer at said bulk surface for facilitating the obtaining of a
preferred orientation of the surface-director of the bulk
layer.
[0002] The invention also relates to a method for manufacturing a
liquid crystal device and a method of controlling a liquid crystal
bulk layer.
TECHNICAL BACKGROUND
[0003] Liquid crystals, widely used at present as electro-optical
media in display devices, are organic materials with anisotropic
physical properties. Liquid crystal molecules are generally long
rod-like molecules, so-called calamitic molecules, which have the
ability to align along their long axis in a certain preferred
direction (orientation). The average direction of the molecules is
specified by a vector quantity and is called director.
[0004] It may be noted, however, that there also exist liquid
crystal molecules that are disc-like, so-called discotic
molecules.
[0005] The operation of the liquid crystal displays is based on the
changes of the optical characteristics, such as light transparency,
light absorption at different wavelengths, light scattering,
birefringence, optical activity, circular dichroism, etc, of the
liquid crystal in the display caused by an applied electric field
(direct coupling).
[0006] One of the basic operational principle of liquid crystal
displays and devices is the switching of the orientation of the
liquid crystal molecules by an applied electric field that couples
to the dielectric anisotropy of the liquid crystal (dielectric
coupling). Such a coupling gives rise to an electro-optic response
quadratic with the applied electric field, i.e. independent of the
field polarity. There exist a number of different types of LCDs
(liquid crystal displays) whose operation is based on dielectric
coupling, especially dynamic scattering displays, displays using
deformation of homeotropically aligned nematic liquid crystal,
Schadt-Helfrich twisted nematic (TN) displays, super twisted
nematic (STN) displays, in-plane switching (IPS) nematic
displays.
[0007] For modern applications, a LCD should possess several
important characteristics, such as a high contrast and brightness,
a low power consumption, a low working voltage, short rise
(switching) and decay (relaxation) times, a low viewing angle
dependence of the contrast, a grey scale or bistability, etc. The
LCD should be cheap, easy to produce and to work with. None of the
prior-art LCDs is optimised concerning all the important
characteristics.
[0008] A nematic liquid crystal material exhibits the simplest
liquid crystalline structure, i.e. an anisotropic liquid. In a
nematic material, the liquid crystal molecules are aligned toward a
particular direction in space, but the centre of mass of molecules
is not ordered.
[0009] In most of the conventional nematic liquid crystal displays,
operating on the basis of the dielectric coupling, the electric
field is applied normally to the liquid crystal bulk layer (i.e.
normally to the confining substrates) and the liquid crystal bulk
molecules are switched by the electric field in a plane
perpendicular to the confining substrate surfaces (so-called
out-of-plane switching). These displays are usually slow, and
nearly all suffer from non-satisfactory angular dependence of the
contrast.
[0010] There is also another type of LCDs with in-plane switching,
in which the electric field is applied along the liquid crystal
bulk layer (i.e. in parallel with the confining substrates) and the
liquid crystal bulk molecules are switched in a plane in parallel
with the confining substrate surfaces. These displays exhibit a
very small angular dependence of the image contrast but the
resolution and the switching time are not satisfactory.
[0011] In the liquid crystal displays discussed above, the desired
initial alignment of the liquid crystal layer in the absence of an
external field, such as an electric field, is generally achieved by
appropriate surface treatment of the confining solid substrate
surfaces, such as by applying a so-called (surface-director)
alignment layer (also called orientation layer) on the confining
substrate surfaces facing said liquid crystal bulk. The initial
liquid crystal alignment is defined by solid surface/liquid crystal
interactions. The orientation of the liquid crystal molecules
adjacent the confining surface is transferred to the liquid crystal
molecules in the bulk via elastic forces, thus imposing essentially
the same alignment to all liquid crystal bulk molecules.
[0012] The director of the liquid crystal molecules near the
confining substrate surfaces (herein also called surface-director)
is constrained to point in a certain direction, such as
perpendicular to (also referred to as homeotropic or vertical) or
in parallel with (also referred to as planar) the confining
substrate surfaces. The type of alignment in liquid crystal
displays operating on the coupling between liquid crystal
dielectric anisotropy and applied electric field is chosen in
accordance with the sign of the dielectric anisotropy, the
direction of the applied electric field and the desired type of
switching mode (in-plane or out-of plane).
[0013] In out-of-plane switching liquid crystal cells employing a
liquid crystal bulk having a negative dielectric anisotropy, it is
important to uniformly orient the director of the liquid crystal
bulk molecules (in the field-off state) vertically to the substrate
surfaces (so-called homeotropic alignment).
[0014] An example of a method for establishing a homeotropic
alignment comprises coating the confining substrate surfaces with a
surfactant, such as lecithin or hexadecyltrimethyl ammonium
bromide. The coated substrate surfaces is then also preferably
rubbed in a predetermined direction, so that the field-induced
planar alignment of the liquid crystal molecules will be oriented
in the predetermined rubbing direction. This method may give good
results in laboratory studies, but has never found industrial
acceptance due to that long term stability is not obtained as the
alignment layer is slowly dissolved in the bulk liquid crystal (J.
Cognard, Mol. Cryst. Liq. Cryst., Suppl. Ser., 1982, 1, 1).
[0015] In out-of-plane switching liquid crystal cells employing a
liquid crystal bulk having a positive dielectric anisotropy, it is
important to uniformly orient the director of the liquid crystal
bulk molecules (in the field-off state) in parallel with the
substrate surfaces (so-called planar alignment). For twisted
nematic liquid crystal cells, it is also important to orient the
liquid crystal bulk molecules at a certain inclined orientation
angle (pre-tilt angle) to the substrate.
[0016] Known methods for establishing planar alignment is, for
instance, the inorganic film vapour deposition method and the
organic film rubbing method.
[0017] In the inorganic film vapour deposition method, an inorganic
film is formed on a substrate surface by vapour-deposition of an
inorganic substance, such as silicon oxide, obliquely to the
confining substrate so that the liquid crystal molecules are
oriented by the inorganic film in a certain direction depending on
the inorganic material and evaporation conditions. Since the
production cost is high, and the method thus is not suitable for
large-scale production, this method is practically not used.
According to the organic film rubbing method, an organic coating
of, for instance, polyvinyl alcohol, polyoxyethylene, polyamide or
polyimide, is formed on a substrate surface. The organic coating is
thereafter rubbed in a predetermined direction using a cloth of
e.g. cotton, nylon or polyester, so that the liquid crystal
molecules in contact with the layer will be oriented in the rubbing
direction.
[0018] Polyvinyl alcohols (PVA) are commercially rarely used as
alignment layers since these polymers are hydrophilic, hygroscopic
polymers that may adsorb moisture adversely affecting the molecular
orientation of the polymer and thus the liquid crystal device
performance. In addition, PVA may attract ions which also impairs
the liquid crystal device performance.
[0019] Also polyoxyethylenes may attract ions, thus resulting in
impaired liquid crystal device performance.
[0020] Polyamides have a low solubility in most commonly accepted
solvents. Therefore, polyamides are seldom used commercially in
liquid crystal device manufacturing.
[0021] Polyimides are in most cases used as organic surface coating
due to their comparatively advantageous characteristics, such as
chemical stability, thermal stability, etc.
[0022] In in-plane switching liquid crystal cells employing a
liquid crystal bulk having a positive or negative dielectric
anisotropy, it is important to uniformly orient the director of the
liquid crystal bulk molecules in parallel with the substrate
surfaces. The aligning methods used in this case are similar to
those used for out-of-plane switching of liquid crystal cells
employing a liquid crystal bulk having a positive dielectric
anisotropy.
[0023] In in-plane switching liquid crystal cells employing a
liquid crystal bulk having a positive dielectric anisotropy, the
initial field-off planar alignment of the liquid crystal bulk
molecules is perpendicular to the direction of the applied electric
field.
[0024] In in-plane switching liquid crystal cells employing a
liquid crystal bulk having a negative dielectric anisotropy, the
initial planar alignment of the liquid crystal bulk molecules is
along the direction of the applied electric field.
[0025] In all of the above disclosed methods of aligning the
director of the liquid crystal bulk molecules near the confining
substrates, a so-called (surface-director) alignment layer is
generally applied on the confining substrate surfaces facing said
liquid crystal bulk.
[0026] It may be noted, that in the prior art (e.g. in US
2002/0006480) alignment layers of materials having mesogenic groups
in their structure have been described. This type of layers is
primarily used to increase the interaction between the alignment
layer and the (mesogenic) liquid crystal bulk layer in the
field-off state, but the alignment layer is not described to be
substantially affected by an applied electric field (i.e. it is not
directly controllable by an electric field).
[0027] In the prior of art, there are in principal three different
techniques for changing the optical performance of liquid crystals
by accomplishing a new molecular orientation of the liquid crystals
that differs from the initial alignment.
[0028] The first, most widely used technique for re-orientating the
molecules is to apply an external electrical field over the entire
bulk liquid crystal layer. Due to direct coupling between the
electric field and some of the liquid crystal material parameters,
such as dielectric anisotropy, the field will directly reorient the
liquid crystal bulk molecules in a new direction if their initial
alignment does not correspond to a minimum energy of interaction of
the electric field with the liquid crystal bulk.
[0029] The second known technique for reorienting the molecules of
a liquid crystal layer is to design one or both of the confining
alignment surfaces as a photo-controlled "command surface". Such a
photo-controlled command surface is capable, when subjected to, for
instance, UV light, to change the direction of alignment imposed by
the surface on the liquid crystal molecules in contact with the
surface. The concept of "photo commanded surface" has been
described by K. Ichimura in a number of papers overviewed in
Chemical Reviews, 100, p. 1847 (2000). More specifically, an
azobenzene monolayer is deposited onto the inner substrate surface
of a sandwich cell containing a nematic liquid crystal layer. The
azobenzene molecules change their conformation from "trans" to
"cis" under illumination with UV light. The azobenzene molecules
are anchored laterally to the substrate surface by the aid of
triethoxysilyl groups. The trans-isomer of azobenzene moieties
imposes a homeotropic alignment of the nematic liquid crystal,
whereas the cis-isomer gives a planar orientation of the liquid
crystal molecules. Hence, the conformational changes of the
molecules in the alignment layer caused by the UV illumination will
result in a change of the alignment of the nematic liquid crystal
molecules. The relaxation to the initial alignment is obtained by
illuminating the sample with VIS-light or simply by heating it to
the isotropic state.
[0030] The third known principle for re-orientating liquid crystal
molecules involves the use of so-called Electrically Commanded
Surfaces (ECS). This principle is described in the published
International patent application No. WO 00/03288. The ECS principle
is used to primarily control a ferroelectric liquid crystalline
polymer layer. According to ECS principle, a separate thin
ferroelectric liquid crystalline polymer layer is deposited on the
inner surfaces of the substrates confining a liquid crystal bulk
material in a conventional sandwich cell. The ferroelectric
electric liquid crystalline polymer layer acts as a dynamic surface
alignment layer imposing a planar or substantially planar alignment
on the adjacent liquid crystal bulk material. More specifically,
when applying an external electric field across the cell--and
thereby across the surface alignment layer--the molecules in the
separate ferroelectric liquid crystalline polymer layer will
switch. This molecular switching in the separate polymeric layer
will, in its turn, be transmitted into the bulk volume via elastic
forces at the boundary between the separate alignment layer and the
bulk layer, thus resulting in a relatively fast in-plane switching
of the bulk volume molecules mediated by the dynamic surface
alignment layer. The ECS layer should be very thin (100-200 nm),
and should preferably be oriented in bookshelf geometry, i.e. with
smectic layers normal to the confining substrates. Furthermore, in
order to keep the ECS layer and its operation intact, the material
of ECS layer should be insoluble in the liquid crystal bulk
material.
[0031] To optimise the performance of liquid crystal devices, it is
desirable to decrease the total time period needed to switch and
relax the liquid crystal bulk molecules in response to an applied
external field. The total response time consists of a rise time
(switching of the liquid crystal molecules to a field-induced
orientation state) and a decay time (relaxation of the liquid
crystal molecules to a field-off orientation state). In prior art
liquid crystal devices, the rise time is generally shorter than the
decay time, for instance the rise time may be about 1/3 of the
total response time and the decay time may be about 2/3 of the
total response time.
[0032] The decay time of a prior art out-of-plane switching nematic
liquid crystal device is generally about 20-100 ms resulting in a
low image quality, in particular for moving images. The problem of
long decay times is more serious for liquid crystal devices having
large display areas, and in particular for out-of-plane switching
liquid crystal devices.
[0033] A liquid crystal device having a long rise time, and thus
long total response time, also provide a low image quality, in
particular for moving images. The problem of long rise times is
more serious for liquid crystal devices having large display areas,
and in particular for in-plane switching liquid crystal devices.
In-plane switching of the surface-director of the liquid crystal
molecules is somewhat restrained, and thus slowed down, by the
substrate surfaces. The rise time of prior art in-plane switching
nematic liquid crystal devices is generally about 10-20 ms.
[0034] FIG. 1 schematically shows the principle of a prior art
out-of-plane switching liquid crystal device 1 including a liquid
crystal bulk layer 2 having a negative dielectric anisotropy
(.DELTA..epsilon.<0) between confining substrates 3. In the
field-off state (E=0), the liquid crystal bulk molecules are
vertically aligned, via elastic forces, by a conventional
surface-director alignment layer (not shown) applied on the
confining substrate surfaces 3. When an external electric field is
applied (E.noteq.0) across the liquid crystal bulk layer 2 between
electrodes 4 on the confining substrates 3, the liquid crystal
molecules 2 are switched to a field-induced planar orientation.
However, the liquid crystal molecules 2 located near the confining
substrate surfaces 3 are not only affected by the applied electric
field, but also by the surface-director alignment layer, which
result in an elastic deformation D1 of the liquid crystal layer 2
near the substrate surfaces 3, as shown in FIG. 1. After removal of
the external field, the liquid crystal molecules 2 near the
surface-director alignment layer relax to their initial field-off
orientation, due to the solid surface/liquid crystal interactions.
The relaxation of the liquid crystal molecules 2 in this region
affects, via elastic forces, the orientation of the more remote
liquid crystal bulk molecules 2. Thus, the elastic deformation D1
that takes place in the liquid crystal layer 2 under an applied
electric field disappears and the initial uniform field-off
homeotropic alignment of the entire liquid crystal bulk layer 2 is
finally restored. However, as mentioned above, the relaxation to
field-off orientation is rather slow, thus resulting in a rather
long decay time.
[0035] The same type of problem is illustrated for the prior art
out-of-plane switching liquid crystal device 1' shown in FIG. 2,
said device 1' including a liquid crystal bulk layer 2' having a
positive dielectric anisotropy (.DELTA..epsilon.>0) between
confining substrates 3' coated with a conventional surface
alignment layer (not shown). In the field-off state (E=0), the
liquid crystal bulk molecules 2' exhibit a planar alignment. When
an external electric field is applied (E.noteq.0) across the bulk
liquid crystal layer 2' between electrodes 4' on the confining
substrates 3', the liquid crystal molecules 2' are switched to a
field-induced vertical orientation. An elastic deformation D2 of
the liquid crystal layer 2' near the substrate surfaces 3' is shown
in FIG. 2.
[0036] FIG. 3 schematically shows a top view of a prior art
in-plane switching liquid crystal device 1'' including a liquid
crystal bulk layer 2'' 1 having a positive dielectric anisotropy
(.DELTA..epsilon.>0) between confining substrates 3'' (only one
substrate is shown). In the field-off state (E=0), FIG. 3a, the
liquid crystal bulk molecules 2'' exhibit a planar alignment in a
first orientation direction obtained, via elastic forces, by a
surface-director alignment layer (not shown) applied on the
confining substrate surfaces 3' . When an external electric field
is applied (E.noteq.0), FIG. 3b, along the bulk liquid crystal
layer 2'' (i.e. in parallel with the confining substrates) between
electrodes 4'' placed as shown in FIG. 3, the liquid crystal
molecules 2'' are switched in-plane to a field-induced second
orientation direction along the orientation of the electric field.
However, the switching of the liquid crystal molecules 2'' will be
restrained, as shown in FIG. 3b, by the surface-director alignment
layer, thus resulting in a rather long rise time.
[0037] The same reasoning applies to an in-plane switching liquid
crystal device including a liquid crystal bulk layer having a
negative dielectric anisotropy (.DELTA..epsilon.<0).
SUMMARY OF THE INVENTION
[0038] In light of the above-mentioned drawback of the known liquid
crystal displays, a general object of the present invention is to
provide an improved liquid crystal device, an improved method for
manufacturing a liquid crystal device, and an improved method of
controlling a liquid crystal device. The invention is not directed
to displays only, but is useful in many other liquid crystal
devices.
[0039] According to a first aspect of the invention, there is
provided a liquid crystal device comprising a liquid crystal bulk
layer presenting a surface-director at a bulk surface thereof, and
a surface-director alignment layer comprising side-chains arranged
to interact with the bulk layer at said bulk surface for
facilitating the obtaining of a preferred orientation of the
surface-director of the bulk layer, wherein the orientation of the
molecules of the liquid crystal bulk layer and the orientation of
said side-chains of the surface-director alignment layer each is
directly controllable by an electric field via dielectric
coupling.
[0040] In a first embodiment of the device according to the
invention, the liquid crystal bulk layer and the surface-director
alignment layer exhibit dielectric anisotropies (.DELTA..epsilon.)
of opposite signs. This device makes it possible to shorten the
total response time by shortening the decay time, such as to below
20 ms, e.g. about 4-6 ms, and thus provide an improved image
quality, in particular for moving images and large display devices.
This effect is especially advantageous in out-of-plane switching
liquid crystal devices.
[0041] In a second embodiment of the device according to the
invention, the liquid crystal bulk layer and the surface-director
alignment layer exhibit dielectric anisotropies (.DELTA..epsilon.)
of same sign. This device makes it possible to shorten the total
response time by shortening the rise time, such as to below 10 ms,
e.g. about 1-5 ms, and thus provide an improved image quality, in
particular for moving images and large display devices. This effect
is especially advantageous in in-plane switching liquid crystal
devices.
[0042] In a third embodiment of the device according to the
invention, the surface-director alignment layer comprises
structural parts exhibiting dielectric anisotropies
(.DELTA..epsilon.) of opposite signs. This device is believed to
make it possible to shorten the total response time by shortening
the rise time as well as the decay time.
[0043] According to a second aspect of the invention, there is
provided a method for manufacturing a liquid crystal device
comprising the steps of providing a surface-director alignment
layer on an inner surface of at least one substrate, and
sandwiching a liquid crystal bulk layer between two substrates,
said liquid crystal bulk layer presenting a surface-director at a
bulk surface thereof, and said surface-director alignment layer
comprising side-chains arranged to interact with the bulk layer at
said bulk surface for facilitating the obtaining of a preferred
orientation of the surface-director of the bulk layer, wherein the
orientation of the molecules of the liquid crystal bulk layer and
the orientation of said side-chains of the surface-director
alignment layer each is directly controllable by an electric field
via dielectric coupling.
[0044] According to a third aspect of the invention, there is
provided a method of controlling a liquid crystal bulk layer
comprising the step of aligning a liquid crystal bulk layer
presenting a surface-director at a bulk surface thereof by use of a
surface-director alignment layer comprising side-chains arranged to
interact with the bulk layer at said bulk surface for facilitating
the obtaining of a preferred orientation of the surface-director of
the bulk layer, wherein the orientation of the molecules of the
liquid crystal bulk layer and the orientation of said side-chains
of the surface-director alignment layer each is directly
controllable by an electric field via dielectric coupling.
BRIEF DESCRIPTION OF THE DRAWINGS
[0045] FIG. 1 schematically shows a prior art out-of-plane
switching liquid crystal device exhibiting an initial vertical
alignment of the liquid crystal bulk layer.
[0046] FIG. 2 schematically shows a prior art out-of-plane
switching liquid crystal device exhibiting an initial planar
alignment of the liquid crystal bulk layer.
[0047] FIG. 3 schematically shows a prior art in-plane switching
liquid crystal device.
[0048] FIG. 4 schematically shows an embodiment of an out-of-plane
switching liquid crystal device according to the invention
exhibiting an initial vertical alignment of the liquid crystal bulk
layer, wherein the liquid crystal bulk layer and the
surface-director alignment layer exhibit dielectric anisotropies
(.DELTA..epsilon.) of opposite signs.
[0049] FIG. 5 and 6 schematically illustrate the difference between
the devices shown in FIG. 1 and FIG. 4, respectively, with regard
to elastic deformation.
[0050] FIG. 7 schematically shows an embodiment of an out-of-plane
switching liquid crystal device according to the invention
exhibiting an initial planar alignment of the liquid crystal bulk
layer, wherein the liquid crystal bulk layer and the
surface-director alignment layer exhibit dielectric anisotropies
(.DELTA..epsilon.) of opposite signs.
[0051] FIG. 8 and 9 schematically illustrate the difference between
the devices shown in FIG. 2 and FIG. 7, respectively, with regard
to elastic deformation.
[0052] FIG. 10 schematically shows an embodiment of an in-plane
switching liquid crystal device according to the invention, wherein
the liquid crystal bulk layer and the surface-director alignment
layer exhibit dielectric anisotropies (.DELTA..epsilon.) of
opposite signs.
[0053] FIG. 11 schematically shows arrays of interdigitated
electrodes.
[0054] FIGS. 12 and 13 schematically show embodiments of
out-of-plane switching liquid crystal devices according to the
invention, wherein the liquid crystal bulk layer and the
surface-director alignment layer exhibit dielectric anisotropies
(.DELTA..epsilon.) of same sign.
[0055] FIGS. 14 and 15 schematically show embodiments of
out-of-plane switching liquid crystal devices according to the
invention comprising two surface-director alignment layers
exhibiting dielectric anisotropies (.DELTA..epsilon.) of opposite
signs.
[0056] FIGS. 16 and 17 schematically show embodiments of
out-of-plane switching liquid crystal devices according to the
invention with a surface-director alignment layer having structural
parts exhibiting dielectric anisotropies (.DELTA..epsilon.) of
opposite signs.
[0057] FIGS. 18-20 show the rise and decay times measured for the
devices according to Examples 1-3, respectively, all devices
exhibiting an initial vertical alignment of the liquid crystal bulk
layer.
[0058] FIG. 21 shows the rise and decay times measured for the
device according to Example 5 exhibiting an initial planar
alignment of the liquid crystal bulk layer.
[0059] It shall be noted that the drawings are not to scale.
DETAILED DESCRIPTION OF THE INVENTION
[0060] The dielectric anisotropy (.DELTA..epsilon.) of a material
having an ordered molecular structure possessing a structural
anisotropy, such as a crystalline or a liquid crystalline
structure, is the difference between the dielectric constants
measured in perpendicular and parallel direction, respectively, to
the preferred molecular orientation in this material.
[0061] When an electric field is applied across a liquid crystal
material exhibiting a positive dielectric anisotropy
(.DELTA..epsilon.>0), the molecules will align their long axis
along (or substantially along) the direction of the electric
field.
[0062] When an electric field is applied across a liquid crystal
material exhibiting a negative dielectric anisotropy
(.DELTA..epsilon.<0), the molecules will align their long axis
perpendicular (or substantially perpendicular) to the direction of
the electric field.
[0063] The liquid crystal device according to the invention
includes a liquid crystal bulk layer presenting a surface-director
at a bulk surface thereof, and a surface-director alignment layer
comprising side-chains arranged to interact with the bulk layer at
said bulk surface for facilitating the obtaining of a preferred
orientation of the surface-director of the bulk layer, wherein the
orientation of the molecules of the liquid crystal bulk layer and
the orientation of said side-chains of the surface-director
alignment layer each is directly controllable by an electric field
via dielectric coupling.
[0064] The liquid crystal device preferably includes at least one
confining substrate, such as two confining substrates, at said bulk
surfaces.
[0065] The surface-director alignment layer(s) is (are) preferably
applied on the inner surface(s) of said substrate(s) confining the
liquid crystal bulk layer.
[0066] The liquid crystal bulk layer comprises a liquid crystal
material exhibiting a (non-zero) dielectric anisotropy, wherein the
molecular orientation of the molecules of the liquid crystal
material thus being directly controllable by an applied electric
field via dielectric coupling.
[0067] The surface-director alignment layer comprises a material
exhibiting a (non-zero) dielectric anisotropy and comprising
side-chains arranged to interact with said bulk layer, wherein the
molecular orientation of said side-chains thus being directly
controllable by an applied electric field via dielectric
coupling.
[0068] As used herein, the application of an electric field over a
material being "directly controllable by an applied electric field"
means that the initial orientation of the molecules in the material
will be affected, such as enhanced or changed (switched), as a
direct consequence of the applied field.
[0069] The liquid crystal bulk layer of the device according to the
invention is preferably a nematic liquid crystal.
[0070] The liquid crystal bulk layer may comprise a nematic liquid
crystal material having a uniform or deformed configuration. The
uniform configuration could, for instance, be planar, homeotropic
or tilted. The deformed configuration could, for instance, be
twisted (i.e. twisted nematic or cholesteric) or with splay and/or
bent elastic deformation.
[0071] The nematic liquid crystal molecules of the bulk layer may
be achiral or chiral.
[0072] Examples of suitable liquid crystal bulk layer materials
having positive and negative dielectric anisotropies, respectively,
are given in relation to the preferred embodiments described
below.
[0073] The material of the surface-director alignment layer may
either present liquid crystal properties or it may not present
liquid crystal properties.
[0074] Preferably, the material of the surface-director alignment
layer is a liquid crystal material, such as a nematic or smectic
liquid crystal material, or liquid crystal properties are induced
in an inter-phase between the surface-director alignment layer and
the bulk layer when the material of the surface-director alignment
layer is brought into contact with the liquid crystal bulk
layer.
[0075] Preferably, the surface-director alignment layer (per se or
induced in contact with the bulk layer) has a higher scalar order
parameter (S), and thus a higher elastic constant (K), than the
liquid crystal bulk layer. A higher scalar order parameter results
in a faster switching/relaxation, and thus a shorter response time.
The scalar order parameter of nematic liquid crystals is generally
around 0.5 and the scalar order parameter of smectic liquid
crystals is generally around 0.8-1.0. Thus, if a nematic bulk layer
is used, the surface-director alignment layer should preferably
provide a smectic order in contact with the bulk layer.
[0076] The material of the surface-director alignment layer may,
for instance, be a polymeric material, such as a chemically
modified polyvinylalcohol, polyvinyl acetal, polyimide,
polysiloxane, polyacrylate, polymethacrylate, polyamide, polyester,
polyurethane, etc.
[0077] The surface-director alignment layer may be produced by
first applying a coating of a polymer having reactive groups on a
substrate surface, and thereafter chemically attaching desired
side-chains to said polymer coating by reaction with the reactive
groups of the polymer, thus providing a desired surface-director
alignment layer.
[0078] The surface-director alignment layer may also be produced by
applying a coating of an already modified polymer on a substrate
surface.
[0079] Alternatively, the surface-director alignment layer may
comprise a chemically modified non-polymeric solid material, such
as gold surface, a silicon dioxide surface or a glass surface
(comprising silanol groups) having chemically attached
side-chains.
[0080] Examples of suitable surface-director alignment layer
materials having positive and negative dielectric anisotropies,
respectively, are given in relation to the preferred embodiments
described below. In the examples, one or more side-chains is/are
attached to a polymeric backbone (Z).
[0081] The following abbreviations are used in the formulas of this
application:
[0082] R1 and R2 are each independently an aliphatic hydrocarbon
chain, such as an alkyl, preferably comprising 1 to 20 carbon
atoms, such as 2 to 12 carbon atoms,
[0083] R3 (represents spacing atoms) is a an aliphatic hydrocarbon,
such as an alkyl, a siloxane, an ethylene glycol chain, or any
combination thereof, comprising at least 2, preferably 2 to 20,
such as 4 to 20, more preferably 5 to 20, carbon atoms or
heteroatoms (it shall be noted that the number of carbon atoms or
heteroatoms may be randomly varied along the polymer main
chain),
[0084] R4 is an aliphatic hydrocarbon chain, such as an alkyl,
preferably comprising 1 to 20 carbon atoms, such as 1 to 5 carbon
atoms,
[0085] R5 and R6 are each independently an aliphatic hydrocarbon, a
siloxane, an ethylene glycol chain, or any combination thereof,
preferably comprising 4 to 22, such as 6 to 20, more preferably 8
to 18, such as 9 to 15, carbon atoms or heteroatoms,
[0086] X and Y are each independently H, F, Cl, CN, or
CF.sub.3,
[0087] X.sub.1 and Y.sub.1 are each independently F or Cl,
preferably F, and
[0088] Z is part of a polymer main chain (polymeric back-bone).
[0089] In this context, it shall be noted that at least some of the
side-chains (S.sub.n) of the surface-director alignment layer
material should be free to move their molecular orientation as a
direct consequence of their dielectric coupling to an applied
electric field (i.e. directly controllable). Thus, the physical
intra-molecular interaction between said side-chains and the rest
of the surface-director alignment layer material should preferably
be weak. A low degree of interaction may, for instance, be obtained
by selecting a surface-director alignment layer material having a
weak physical intra-molecular interaction between said side-chains
and the rest of the material or by sterically preventing such
physical intra-molecular interaction, e.g. by the use of spacers
between said side-chains and the rest of the material.
[0090] The surface-director alignment layer in the device according
to the invention preferably comprises a polymer as defined in the
co-pending international patent application PCT/SE2004/000300. This
type of polymers comprises a polymeric backbone (Z), preferably a
polyvinyl acetal, and side-chains (S.sub.n) attached thereto,
wherein the polymeric backbone lacks directly coupled ring
structures, and each side-chain of at least some of the side-chains
comprises at least two unsubstituted and/or substituted phenyls
coupled via a coupling selected from the group consisting of a
carbon-carbon single bond (.dbd.), a carbon-carbon double bond
containing unit (--CH.dbd.CH--), a carbon-carbon triple bond
containing unit (--C.ident.C--), a methylene eter unit
(--CH.sub.2O--), an ethylene eter unit (--CH.sub.2CH.sub.2O--), an
ester unit (--COO--) and an azo unit (--N.dbd.N--), exhibits a
permanent and/or induced dipole moment that in ordered phase
provides dielectric anisotropy, and is attached to the polymeric
backbone via at least two spacing atoms, preferably at least five
spacing atoms. The preparation of this type of polymers is
described in PCT/SE2004/000300.
[0091] As used herein a "side-chain" means a grouping of atoms that
branches off from a straight-chain molecule, such as a polymeric
backbone.
[0092] As used herein "an unsubstituted phenyl" means a phenyl
group, such as --C.sub.6H.sub.4-- and --C.sub.6H.sub.5.
[0093] As used herein "a substituted phenyl" means a phenyl group
wherein one or more hydrogen atom(s) has (have) been replaced by
(a) different atom(s) or group(s).
[0094] As used herein "spacing atoms" means atoms linking a
side-chain to a polymeric backbone.
[0095] As used herein "directly coupled ring structures" means
fused ring structures and ring structures coupled with single or
multiple bonds only (i.e. ring structures coupled with one or more
bonds only).
[0096] Preferably, said polymeric backbone lacking directly coupled
ring structures comprises a first type of randomly distributed
units according to ##STR1## wherein S.sub.1 represents a first
side-chain comprising at least two unsubstituted and/or substituted
phenyls coupled via a coupling selected from the group consisting
of a carbon-carbon single bond (--), a carbon-carbon double bond
containing unit (--CH.dbd.CH--), a carbon-carbon triple bond
containing unit (--C.ident.C--), a methylene eter unit
(--CH.sub.2O--), an ethylene eter unit (--CH.sub.2CH.sub.2O--), an
ester group unit (--COO--) and an azo unit (--N.dbd.N--) and
exhibiting a permanent and/or induced dipole moment that in ordered
phase provides dielectric anisotropy, and at least two spacing
atoms through which the first side-chain is attached to the
polymeric backbone, and a second type of randomly distributed units
according to ##STR2## When the polymeric backbone comprises these
types of randomly distributed units, the polymer is a polyvinyl
acetal.
[0097] Furthermore, the polymeric backbone may preferably also
comprise a third type of randomly distributed units according to
##STR3## wherein S.sub.2 represents a second side-chain, being
different from S.sub.1, exhibiting a permanent and/or induced
dipole moment that in ordered phase provides dielectric anisotropy,
and at least two spacing atoms through which the second side-chain
is attached to the polymeric backbone. The dielectric anisotropy
provided by S.sub.2 may be different from the dielectric anisotropy
provided by S.sub.1.
[0098] Preferably, said second side-chain S.sub.2 comprises at
least two unsubstituted and/or substituted phenyls coupled via a
coupling selected from the group consisting of a carbon-carbon
single bond (--), a carbon-carbon double bond containing unit
(--CH.dbd.CH--), a carbon-carbon triple bond containing unit
(--C.ident.C--), a methylene eter unit (--CH.sub.2O--), an ethylene
eter unit (--CH.sub.2CH.sub.2O--), an ester unit (--COO--) and an
azo unit (--N.dbd.N--).
[0099] The polymeric backbone may also comprise a further (third or
fourth) type of randomly distributed units according to ##STR4##
wherein S.sub.3 represents a side-chain, being different from
S.sub.1 and S.sub.2, exhibiting no permanent and/or induced dipole
moment and thus providing no dielectric anisotropy. This type of
unit may be incorporated in the polymeric back-bone to obtain a
polymer exhibiting a certain desired dielectric anisotropy in
ordered phase using a desired specific side-chain S.sub.1,
optionally in combination with a desired specific side-chain
S.sub.2. Thus, the dielectric anisotropy of the polymer in ordered
phase may be reduced using a side-chain S.sub.3 exhibiting no
permanent and/or induced dipole moment and thus providing no
dielectric anisotropy.
[0100] The device according to the invention is preferably either
an out-of-plane switching or an in-plane switching liquid crystal
device.
1. Opposite Signs of Dielectric Anisotropy
[0101] In a first group of embodiments of the device according to
the invention, the liquid crystal bulk layer and the
surface-director alignment layer exhibit dielectric anisotropies
(.DELTA..epsilon.) of opposite signs. Said device is preferably an
out-of-plane switching liquid crystal device.
a) Out-of-Plane Switching Liquid Crystal Devices
[0102] In an out-of-plane switching device, according to this first
group of embodiments of the invention, having an initial planar
alignment, an orthogonal projection of said surface-director (of
the liquid crystal bulk layer) on the confining substrates, termed
projected surface-director, presents said preferred orientation in
a geometrical plane in parallel with said substrates, termed
preferred field-off planar orientation, and the orientation of the
molecules of said bulk layer is directly controllable by an applied
electric field to perform an out-of-plane switching of said
preferred planar orientation of the projected surface-director to a
field-induced vertical orientation.
[0103] In an out-of-plane switching device, according to this first
group of embodiments, having an initial vertical alignment, an
orthogonal projection of said surface-director (of the liquid
crystal bulk layer) on a geometrical plane perpendicular to said
substrates, termed projected surface-director, presents said
preferred orientation, termed preferred field-off vertical
orientation, and the orientation of the molecules of said bulk
layer is directly controllable by an applied electric field to
perform an out-of-plane switching of said preferred vertical
orientation of the projected surface-director to a field-induced
planar orientation.
[0104] In an out-of-plane switching device according to the
invention, the electric field is applied normally to the confining
substrates (i.e. normally to the liquid crystal bulk layer).
[0105] FIG. 4 shows part of an embodiment of an out-of-plane
switching liquid crystal device 5 according to the invention,
wherein surface-director alignment layers 6 are applied on the
inner surfaces of substrates 7 confining a liquid crystal bulk
layer 8. The liquid crystal bulk 8 exhibits a negative dielectric
anisotropy (.DELTA..epsilon.<0) and the surface-director
alignment layers 6 exhibit a positive dielectric anisotropy
(.DELTA..epsilon.>0).
[0106] The molecules (i.e. the side-chains) of the surface-director
alignment layers 6 have in this embodiment an initial vertical
orientation in relation to the confining substrate surfaces 7, thus
resulting in vertically or substantially vertically aligned liquid
crystal bulk molecules 8 in the field-off state (E=0). The
surface-director alignment layers 6 are also preferably
unidirectionally rubbed to obtain a preferred orientation of a
field-induced planar alignment of the liquid crystal bulk molecules
8.
[0107] It shall be noted that even though the device 5 shown in
FIG. 4 comprises two surface-director alignment layers 6 (two-sided
embodiment), the device according to the invention may
alternatively comprise, for instance, only one surface-director
alignment layer (one-sided embodiment).
[0108] When an external electric field is applied (E.noteq.0)
normally to the liquid crystal bulk layer 8 between electrodes 9 on
the confining substrates 7, the liquid crystal bulk molecules 8
aligned vertically or substantially vertically will, due to their
negative dielectric anisotropy, switch out-of-plane to a
field-induced planar orientation. The molecules (i.e. the
side-chains) of the surface-director alignment layers 6 will,
however, keep their initial vertical orientation which will be
enhanced and stabilized by the applied field due to their positive
dielectric anisotropy. In other words, the molecules (i.e. the
side-chains) of the surface-director alignment layers 6 will not
switch when an electric field is applied across the layers 6, thus
causing a strong elastic deformation D3 of the liquid crystal layer
8 near the substrate surface 7. When the external field is removed
(E=0), the vertically oriented molecules (i.e. the side-chains) of
the surface-director alignment layers 6 will promote a fast
relaxation from the field-induced planar orientation of the liquid
crystal bulk molecules 8 back to their field-off vertical
orientation. Thus, the elastic deformation D3 shown in FIG. 4 is
stronger than the elastic deformation D1 shown in FIG. 1, and
therefore the relaxation to the field-off orientation will in this
case be faster than in the case shown in FIG. 1. The comparison of
D1 and D3, respectively, is also schematically shown in FIG. 5 and
FIG. 6, respectively.
[0109] The liquid crystal bulk layer 8 may have a negative
dielectric anisotropy within the range of from -6 to -1, and the
surface-director alignment layers 6 may have a positive dielectric
anisotropy within the range of from 1 to 30.
[0110] Formulas I-X are examples of surface-director alignment
layer materials suitable for providing an initial field-off
vertical alignment in the above described embodiment (an
out-of-plane switching liquid crystal device). These polymers
comprise side-chains (S.sub.1) chemically bound to a polymer main
chain (Z), said side-chains exhibiting permanent and/or induced
dipole moments that in ordered phase provide positive dielectric
anisotropy. ##STR5## ##STR6## ##STR7##
[0111] Specific examples of this type of polymers suitable as
surface-director alignment layer materials in the above described
embodiment are represented by Formulas XI-XIII. ##STR8## ##STR9##
##STR10##
[0112] Formulas XIV-XVI are further examples of surface-director
alignment layer materials suitable for providing an initial
field-off vertical alignment in the above described embodiment (an
out-of-plane switching liquid crystal device). These polymers
comprise side-chains (S.sub.1) chemically bound to a polymer main
chain (Z), said side-chains exhibiting permanent and/or induced
dipole moments that in ordered phase provide positive dielectric
anisotropy and chemically bound side-chains (S.sub.3) exhibiting no
permanent and/or induced dipole moments and thus providing no
dielectric anisotropy. ##STR11## ##STR12## ##STR13##
[0113] Specific examples of this type of polymers suitable as
surface-director alignment layer materials in the above described
embodiment are represented by Formulas XVII to XXVIII: ##STR14##
##STR15## ##STR16## ##STR17## ##STR18## ##STR19## wherein R4 is
CH.sub.3 and (m+n)/o is within the range of from 25/50 to 43/14,
preferably above 40/20, such as 42/16, and m/n is within the range
of from 9/1 to 1/9, preferably 3/1 to 1/3, such as 2/1, and
##STR20## ##STR21## ##STR22## ##STR23## ##STR24## ##STR25##
[0114] Formula XXIX represents further examples of surface-director
alignment layer materials suitable for providing an initial
field-off vertical alignment in the above described embodiment (an
out-of-plane switching liquid crystal device). These polymers
comprise two different types of side-chains (S.sub.1 and S.sub.2)
exhibiting permanent and/or induced dipole moments that in ordered
phase provide positive dielectric anisotropy and side-chains
(S.sub.3) exhibiting no permanent and/or induced dipole moments and
thus providing no dielectric anisotropy. ##STR26##
[0115] Specific examples of this type of polymers suitable as
surface-director alignment layer materials in the above described
embodiment are represented by Formulas XXX to XXXII: ##STR27##
##STR28## wherein R4 is CH.sub.3, R5 is CH.sub.3, and (m+n)/o is
within the range of from 25/50 to 43/14, preferably above 40/20,
such as 42/16, and m/n is within the range of from 9/1 to 1/9,
preferably 3/1 to 1/3, such as 2/1, and ##STR29##
[0116] Instead of using a polymer, the side-chains of Formulas I to
XXXII can be chemically attached, as known to persons skilled in
the art, to a solid surface, such as a gold surface, a silicon
dioxide surface or a glass surface comprising silanol groups, to
form a suitable material for use as the surface-director alignment
layer in the device according to the invention.
[0117] It shall be noted that in an embodiment of an out-of-plane
switching device according to the invention comprising two
surface-director alignment layers applied on substrate surfaces
confining the liquid crystal bulk layer, and wherein the
surface-director alignment layer exhibit a positive dielectric
anisotropy and the liquid crystal bulk layer exhibit a negative
dielectric anisotropy, the dipole moments of the side-chains of
each surface-director alignment layer may either have the same
direction or opposite directions.
[0118] Such a device having two separate alignment layers
exhibiting the same directions of dipole moments is exemplified by
a device having two separate alignment layers of the material
according to Formula XIX (or Formula XVIII).
[0119] Such a device having two separate alignment layers
exhibiting the opposite directions of dipole moments is exemplified
by a device having one alignment layer of the material according to
Formula XIX (or Formula XVIII) and one alignment layer of the
material according to Formula XVII.
[0120] Examples of liquid crystal bulk layer materials having a
negative dielectric anisotropy, and being suitable in the above
described embodiment, are a mixture of MLC 6608
(.DELTA..epsilon.=-4.2) and MBBA (.DELTA..epsilon.=-0.8), a mixture
of MLC 6884 (.DELTA..epsilon.=-5.0) and MBBA
(.DELTA..epsilon.=-0.8), and a mixture of MDA 98-3099
(.DELTA..epsilon.=-6) and MBBA (.DELTA..epsilon.=-0.8), all of
which are nematic liquid crystal materials supplied by Merck.
[0121] FIG. 7 shows part of another embodiment of an out-of-plane
switching liquid crystal device 10 according to the invention,
wherein surface-director alignment layers 11 are applied on the
inner surfaces of substrates 12 confining a liquid crystal bulk
layer 13. The liquid crystal bulk 13 exhibits a positive dielectric
anisotropy (.DELTA..epsilon.>0) and the surface-director
alignment layers 11 exhibit a negative dielectric anisotropy
(.DELTA..epsilon.<0).
[0122] The molecules (i.e. the side-chains) of the surface-director
alignment layers 11 have in this embodiment an initial planar
orientation in relation to the confining substrate surfaces 12,
thus resulting in planar or substantially planar aligned liquid
crystal bulk molecules 13 in the field-off state (E=0). The
surface-director alignment layers 11 is also preferably
unidirectionally rubbed to obtain a preferred orientation of planar
alignment of the liquid crystal bulk molecules (in field-off
state).
[0123] It shall be noted that even though the device 10 shown in
FIG. 7 comprises two surface-director alignment layers 11
(two-sided embodiment), the device according to the invention may
alternatively comprise, for instance, only one surface-director
alignment layer (one-sided embodiment).
[0124] When an external electric field (E.noteq.0) is applied
normally to the liquid crystal bulk layer 13 between electrodes 14
on the confining substrates 12, the liquid crystal bulk molecules
13 aligned planar or substantially planar will, due to their
positive dielectric anisotropy, switch out-of-plane to a
field-induced vertical orientation. The molecules (i.e. the
side-chains) of the surface-director alignment layers 11 will,
however, keep their initial uniform planar orientation which will
be enhanced and stabilized by the applied electric field due to
their negative dielectric anisotropy. In other words, the molecules
(i.e. the side-chains) of the surface-director alignment layers 11
will not switch when an electric field is applied across the layers
11. When the external field is removed (E=0), the planar oriented
molecules (i.e. the side-chains) of the surface-director alignment
layers 11 will promote a fast relaxation from the field-induced
vertical orientation of the liquid crystal bulk molecules 13 back
to their initial field-off planar orientation. Thus, the elastic
deformation D4 shown in FIG. 7 is stronger than the elastic
deformation D2 shown in FIG. 2. The comparison of D2 and D4
respectively, is also schematically shown in FIG. 8 and FIG. 9,
respectively.
[0125] The liquid crystal bulk layer 13 may have a positive
dielectric anisotropy within the range of from 1 to 30, and the
surface alignment layers 11 may have a negative dielectric
anisotropy within the range of from -6 to -1.
[0126] Formulas XXXIII to XLIII are examples of surface-director
alignment materials suitable for providing an initial field-off
planar alignment in the above described embodiment (an out-of-plane
liquid crystal device). These polymers comprise side-chains
(S.sub.1) chemically bound to a polymer main chain (Z), said
side-chains exhibiting permanent and/or induced dipole moments that
in ordered phase provide negative dielectric anisotropy. ##STR30##
##STR31##
[0127] A specific example of a surface-director alignment material
suitable for providing an initial field-off planar alignment in the
above described embodiment (an out-of-plane switching liquid
crystal device) is the polymer according to Formula XLIV. This
polymer comprises side-chains (S.sub.1) exhibiting permanent and/or
induced dipole moments that in ordered phase provides negative
dielectric anisotropy and side-chains (S.sub.3) exhibiting no
permanent and/or induced dipole moments and thus providing no
dielectric anisotropy. ##STR32## wherein (m+n)/o is within the
range of from 25/50 to 43/14, preferably above 40/20, such as
43/18, and m/n is within the range of from 9/1 to 1/9, preferably
3/1 to 1/3, such as 1/1.
[0128] Another specific example of this type of polymers suitable
as surface-director alignment layer material in the above described
embodiment is represented by Formula XLV. ##STR33##
[0129] Instead of using a polymer, the side-chains of Formulas
XXXIII to XLV can be chemically attached, as known to persons
skilled in the art, to a solid surface, such as a gold surface, a
silicon dioxide surface or a glass surface comprising silanol
groups, to form a suitable material for use as the surface-director
alignment layer in the device according to the invention.
[0130] Examples of liquid crystal bulk layer materials having a
positive dielectric anisotropy, and being suitable in the above
described embodiment, are E44 (.DELTA..epsilon.=+16.8), E9
(.DELTA..epsilon.=+1 6. 5), and E70 A (.DELTA..epsilon.=+10.8), all
of which are nematic liquid crystal materials supplied by
BDH/Merck.
[0131] The embodiments shown in FIG. 4 and 7 include out-of-plane
switching liquid crystal devices, each device comprising a liquid
crystal bulk layer and a surface-director alignment layer
exhibiting dielectric anisotropies of opposite signs. It shall be
noted that the combination of a surface-director alignment layer
and a liquid crystal bulk layer exhibiting dielectric anisotropies
of opposite signs is also applicable and advantageous for in-plane
switching liquid crystal devices (described below), even though the
effect of a decreased decay time is more pronounced for
out-of-plane switching liquid crystal devices. Thus, the device
according to the invention wherein the liquid crystal bulk layer
and the surface-director alignment layer exhibit dielectric
anisotropies of opposite signs is preferably an out-of-plane
switching liquid crystal device.
b) In-Plane Switching Liquid Crystal Devices
[0132] In an in-plane switching device, according to said first
group of embodiments of the invention, having an initial first
planar alignment, an orthogonal projection of said surface-director
(of the liquid crystal bulk layer) on said substrates, termed
projected surface-director, presents said preferred orientation in
a geometrical plane in parallel with said substrate, termed
preferred field-off planar orientation, and the orientation of the
molecules of said bulk layer is directly controllable by an applied
electric field to perform an in-plane switching of said preferred
planar orientation of the projected surface-director to a
field-induced second planar orientation.
[0133] In in-plane switching devices according to the invention,
the electric field is applied in parallel with the confining
substrates (i.e. along the liquid crystal bulk layer).
[0134] FIG. 10 shows part of an embodiment of an in-plane switching
liquid crystal device 15 according to the invention, wherein
surface-director alignment layers 16 are applied on the inner
surfaces of substrates 17 (only one substrate is shown) confining a
liquid crystal bulk layer 18. The liquid crystal bulk 18 exhibits a
positive dielectric anisotropy (.DELTA..epsilon.>0) and the
surface-director alignment layers 16 exhibit a negative dielectric
anisotropy (.DELTA..epsilon.<0).
[0135] The molecules (i.e. the side-chains) of the surface-director
alignment layers 16 have in this embodiment an initial planar
orientation, in a first direction, in relation to the confining
substrate surfaces 17, thus resulting in planar or substantially
planar aligned liquid crystal bulk molecules 18 in the field-off
state (E=0), FIG. 10a. The surface-director alignment layers 16 is
preferably unidirectionally rubbed to obtain the preferred
field-off first planar orientation direction.
[0136] It shall be noted that the device 15 shown in FIG. 10 may
either comprise two surface-director alignment layers 16 (two-sided
embodiment) or alternatively only one surface-director alignment
layer 16 (one-sided embodiment).
[0137] When an external electric field is applied (E.noteq.0), FIG.
10b, along the liquid crystal bulk layer 18 (in parallel with the
confining substrates) between electrodes 19 placed as shown in FIG.
4, the liquid crystal bulk molecules 18 will, due to their positive
dielectric anisotropy, switch in-plane to a field-induced second
planar orientation direction along the direction of the applied
field. The molecules (i.e. the side-chains) of the surface-director
alignment layers 16 will, however, keep their initial first planar
orientation direction which will be enhanced and stabilized by the
applied field due to their negative dielectric anisotropy. In other
words, the molecules (i.e. the side-chains) of the surface-director
alignment layers 16 will not switch when an electric field is
applied along the layers 16. When the external field is removed
(E=0), the molecules (i.e. the side-chains) of the surface-director
alignment layers 16 having the first planar orientation direction
will promote a fast relaxation from the field-induced second planar
orientation direction of the liquid crystal bulk molecules 18 back
to their initial field-off planar first orientation direction.
[0138] Formulas XXXIII to XLV are examples of surface-director
alignment materials suitable for providing an initial field-off
planar alignment in the above described embodiment (an in-plane
switching liquid crystal device). As previously described, these
polymers comprise side-chains exhibiting permanent and/or induced
dipole moments that in ordered phase provide negative dielectric
anisotropy.
[0139] Instead of using a polymer, the side-chains of Formulas
XXXIII to XLV can be chemically attached, as known to persons
skilled in the art, to a solid surface, such as a gold surface, a
silicon dioxide surface or a glass surface comprising silanol
groups, to form a suitable material for use as the surface-director
alignment layer in the device according to the invention.
[0140] Examples of suitable liquid crystal bulk layer materials
having a positive dielectric anisotropy, and being suitable in the
above described embodiment, are E44 (.DELTA..epsilon.=+16.8), E9
(.DELTA..epsilon.=+16.5), and E70 A (A=+10.8), all of which are
nematic liquid crystal materials supplied by BDH/Merck.
[0141] Another similar embodiment of an in-plane switching liquid
crystal device according to the invention is a device comprising a
liquid crystal bulk exhibiting a negative dielectric anisotropy
(.DELTA..epsilon.<0) and at least one, preferably two,
surface-director alignment layer(s) exhibiting a positive
dielectric anisotropy (.DELTA..epsilon.>0).
[0142] Formulas XLVI to LXII are examples of surface-director
alignment materials suitable for providing an initial field-off
planar alignment in the above described embodiment (an in-plane
switching liquid crystal device). These polymers comprise
side-chains (S.sub.1) chemically bound to a polymer main chain (Z),
said side-chains exhibiting permanent and/or induced dipole moments
that in ordered phase provides positive dielectric anisotropy.
##STR34## ##STR35##
[0143] Formulas LXIII to LXVII are further examples of
surface-director alignment layer materials suitable for providing
an initial field-off planar alignment in the above described
embodiment (an in-plane switching liquid crystal device). These
polymers comprise side-chains (S.sub.1) exhibiting permanent and/or
induced dipole moments that in ordered phase provides positive
dielectric anisotropy and side-chains (S.sub.3) exhibiting no
permanent and/or induced dipole moments and thus providing no
dielectric anisotropy. ##STR36## ##STR37## ##STR38## ##STR39##
##STR40##
[0144] A specific example of this type of polymers suitable as
surface-director alignment layer material in the above described
embodiment is represented by Formula LXVIII. ##STR41##
[0145] Instead of using a polymer, the side-chains of Formulas XLVI
to LXVIII can be chemically attached, as known to persons skilled
in the art, to a solid surface, such as a gold surface, a silicon
dioxide surface or a glass surface comprising silanol groups, to
form a suitable material for use as the surface-director alignment
layer in the device according to the invention.
[0146] Examples of liquid crystal bulk layer materials having a
negative dielectric anisotropy, and being suitable in the above
described embodiment, are a mixture of MLC 6608
(.DELTA..epsilon.=-4.2) and MBBA (.DELTA..epsilon.=-0.8), a mixture
of MLC 6884 (.DELTA..epsilon.=-5.0) and MBBA
(.DELTA..epsilon.=-0.8), and a mixture of MDA 98-3099
(.DELTA..epsilon.=-6) and MBBA (.DELTA..epsilon.=-0.8), all of
which are nematic liquid crystal materials supplied by Merck.
2. Same Sign of Dielectric Anisotropy
[0147] In a second group of embodiments of the device according to
the invention, the liquid crystal bulk layer and the
surface-director alignment layer exhibit dielectric anisotropies
(.DELTA..epsilon.) of same sign. Said device is preferably an
in-plane switching liquid crystal device.
a) In-Plane Switching Liquid Crystal Devices
[0148] In an in-plane switching liquid crystal device, according to
said second group of embodiments of the invention, the orientation
of the molecules of said bulk layer is directly controllable by an
applied electric field to perform an in-plane switching of an
initial first planar orientation to a field-induced second planar
orientation, whereas an orthogonal projection of said
surface-director (of the liquid crystal bulk layer) on said
substrates, termed projected surface-director, presents said
preferred orientation in a geometrical plane in parallel with said
substrate, termed preferred field-induced planar orientation.
[0149] In an in-plane switching device according to the invention,
the electric field is applied in parallel with the confining
substrates (i.e. along the liquid crystal bulk layer).
[0150] An embodiment of an in-plane switching liquid crystal device
according to the invention is a device wherein both the liquid
crystal bulk and the surface-director alignment layers exhibit
positive dielectric anisotropies (.DELTA..epsilon.>0), said
surface-director alignment layers being applied on the inner
surfaces of substrates confining the liquid crystal bulk layer.
[0151] The molecules (i.e. the side-chains) of the surface-director
alignment layers have in this embodiment an initial planar
orientation, in a first direction, in relation to the confining
substrate surfaces, thus resulting in planar or substantially
planar aligned liquid crystal bulk molecules in the field-off state
(E=0). The surface-director alignment layers are preferably
unidirectionally rubbed to obtain the preferred field-off first
planar orientation direction.
[0152] The device may either comprise two surface-director
alignment layers (two-sided embodiment) or alternatively only one
surface-director alignment layer (one-sided embodiment).
[0153] When an external electric field is applied (E.noteq.0) along
the liquid crystal bulk layer (in parallel with the confining
substrates) between electrodes, the liquid crystal bulk molecules
will, due to their positive dielectric anisotropy, switch in-plane
to a field-induced second planar orientation direction along the
direction of the applied field. The molecules (i.e. the
side-chains) of the surface-director alignment layers will, also
switch in-plane to a field-induced second orientation direction due
to their positive dielectric anisotropy when an electric field is
applied along the layer and in parallel with the confining
substrates. The in-plane switching molecules (i.e. the side-chains)
of the surface-director alignment layers will thus promote a fast
switching from the field-off first planar orientation direction of
the liquid crystal bulk molecules to their field-induced second
planar orientation direction. Thus, the switching of the liquid
crystal bulk molecules to the field-induced orientation direction
will in this case be faster, at lower applied voltage, than the
in-plane switching of a prior art liquid crystal device having a
non-switching surface-director alignment layer (shown in FIG. 3).
In this context, it shall however be noted that the
surface-director alignment layer(s) of this device according to the
invention does not mediate the in-plane switching of the liquid
crystal bulk molecules, which orientation is directly controllable
via dielectric coupling. The surface-director alignment layer(s)
does not drive but merely facilitates said in-plane bulk
switching.
[0154] The liquid crystal bulk layer of the device according to
said embodiment may have a positive dielectric anisotropy within
the range of from 1 to 30, and the surface-director alignment
layers may have a positive dielectric anisotropy within the range
of from 1 to 30.
[0155] It is believed to be advantageous if the positive dielectric
anisotropy of the surface-director alignment layers has a larger
positive value (more positive), preferably much larger, than the
positive dielectric anisotropy of the liquid crystal bulk
layer.
[0156] Formulas XLVI to LXVIII are examples of surface-director
alignment materials suitable for providing an initial field-off
planar alignment in the above described embodiment (an in-plane
switching liquid crystal device). As previously described, these
polymers comprise side-chains exhibiting permanent and/or induced
dipole moments that in ordered phase provides positive dielectric
anisotropy.
[0157] Instead of using a polymer, the side-chains of Formulas XLVI
to LXVIII can be chemically attached, as known to persons skilled
in the art, to a solid surface, such as a gold surface, a silicon
dioxide surface or a glass surface comprising silanol groups, to
form a suitable material for use as the surface-director alignment
layer in the device according to the invention.
[0158] In an in-plane switching liquid crystal device, according to
the invention, having a surface-director alignment layer and a
liquid crystal bulk layer exhibiting dielectric anisotropies of
same sign, it may be advantageous to use two electrode arrays 20,
21, each array consisting of two interdigitated electrodes 22,
arranged so that the electric field obtainable within the first
electrode array 20 is substantially perpendicular to the electric
field obtainable within the second electrode array 21 (FIG. 11).
Each array 20,21 is applied on a confining substrate 23. In this
embodiment both the switching and the relaxation of the liquid
crystal bulk molecules occur in the presence of an applied electric
field, and a short response time is easily attainable.
[0159] Another similar embodiment of an in-plane switching liquid
crystal device according to the invention, is a device wherein both
the liquid crystal bulk layer and the surface-director alignment
layer(s) exhibit negative dielectric anisotropies
(.DELTA..epsilon.<0).
[0160] When an external electric field (E.noteq.0) is applied along
the liquid crystal bulk layer (i.e. in parallel with the confining
substrates), the liquid crystal bulk molecules will, due to their
negative dielectric anisotropy, switch in-plane from a field-off
first planar orientation direction to a field-induced second planar
orientation direction perpendicular the direction of the applied
electric field. The molecules (i.e. the side-chains) of the
surface-director alignment layers will, also switch in-plane from a
field-off first planar orientation direction to a field-induced
second orientation direction due to their negative dielectric
anisotropy when an electric field is applied along the layer(s) and
in parallel with the confining substrates. The in-plane switching
molecules (i.e. the side-chains) of the surface-director alignment
layer(s) will thus promote a fast switching from the field-off
first planar orientation direction of the liquid crystal bulk
molecules to their field-induced second planar orientation
direction. Thus, the switching of the liquid crystal bulk molecules
to the field-induced orientation direction will in this case be
faster than the in-plane switching of a corresponding prior art
liquid crystal device having a non-switching surface-director
alignment layer. Also in this case, it shall be noted that the
surface-director alignment layer of the device according to the
invention does not mediate the in-plane switching of the liquid
crystal bulk molecules, it merely facilitates said switching.
[0161] The liquid crystal bulk layer of the device according to
this embodiment may have a negative dielectric anisotropy within
the range of from -6 to 1, and the surface alignment layers may
have a negative dielectric anisotropy within the range of from -6
to -1.
[0162] It is believed to be advantageous if the negative dielectric
anisotropy of the surface-director alignment layers has a larger
negative value (more negative), preferably much larger, than the
negative dielectric anisotropy of the liquid crystal bulk
layer.
[0163] Formulas XXXIII to XLV are examples of surface-director
alignment materials suitable for providing an initial field-off
planar alignment in the above described embodiment (an in-plane
switching liquid crystal device). As previously. described, these
polymers comprise side-chains exhibiting permanent and/or induced
dipole moments that in ordered phase provide negative dielectric
anisotropy.
[0164] Instead of using a polymer, the side-chains of Formulas
XXXIII to XLV can be chemically attached, as known to persons
skilled in the art, to a solid surface, such as a gold surface, a
silicon dioxide surface or a glass surface comprising silanol
groups, to form a suitable material for use as the surface-director
alignment layer in the device according to the invention.
[0165] Examples of liquid crystal bulk layer materials having a
negative dielectric anisotropy, and being suitable in the above
described embodiment, are a mixture of MLC 6608
(.DELTA..epsilon.=-4.2) and MBBA (.DELTA..epsilon.=-0.8), a mixture
of MLC 6884 (.DELTA..epsilon.=-5.0) and MBBA
(.DELTA..epsilon.=-0.8), and a mixture of MDA 98-3099
(.DELTA..epsilon.=-6) and MBBA (.DELTA..epsilon.=-0.8), all of
which are nematic liquid crystal materials supplied by Merck.
[0166] It shall be noted that the combination of a surface-director
alignment layer and a liquid crystal bulk layer exhibiting
dielectric anisotropies of same sign is also applicable and
advantageous for out-of-plane switching liquid crystal devices
(described below), even though the effect of a decreased rise time
is more pronounced for in-plane switching liquid crystal devices.
Thus, the device according to the invention wherein the liquid
crystal bulk layer and the surface-director alignment layer exhibit
dielectric anisotropies of same sign is preferably an in-plane
switching liquid crystal.
b) Out-of-Plane Switching Liquid Crystal Devices
[0167] In an out-of-plane switching liquid crystal device according
to said second group of embodiments of the invention, the
orientation of the molecules of said bulk layer is directly
controllable by an applied electric field to perform an
out-of-plane switching of an initial vertical orientation to a
field-induced planar orientation, whereas an orthogonal projection
of said surface-director (of the liquid crystal bulk layer) on the
confining substrates, termed projected surface-director, presents
said preferred orientation in a geometrical plane in parallel with
said substrates, termed preferred field-induced planar
orientation.
[0168] In an out-of-plane switching liquid crystal device according
to the invention, the electric field is applied normally to the
confining substrates (i.e. normally to the liquid crystal bulk
layer).
[0169] FIG. 12 schematically shows part of an embodiment of an
out-of-plane switching liquid crystal device 24 according to the
invention, in the field-off state (E=0), wherein both the
surface-director alignment layers 25 (only one layer is shown) and
the liquid crystal bulk 26 exhibit negative anisotropy
(.DELTA..epsilon.<0), said surface-director alignment layers 25
being applied on the inner surfaces of substrates confining the
liquid crystal bulk layer 26.
[0170] The molecules (i.e. the side-chains) of the surface-director
alignment layers 25 have in this embodiment an initial vertical
orientation in relation to the confining substrate surfaces, thus
resulting in vertically or substantial vertically aligned liquid
crystal bulk molecules 26 in the field-off state (E=0), as shown in
FIG. 12. The surface-director alignment layers 25 are also
preferably unidirectionally rubbed to obtain a preferred direction
of a field-induced planar alignment of the liquid crystal bulk
molecules 26.
[0171] The device may either comprise two surface-director
alignment layers (two-sided embodiment) or alternatively only one
surface-director alignment layer (one-sided embodiment).
[0172] When an external field is applied (E.noteq.0) normally to
the liquid crystal bulk layer 26 between electrodes 27 on the inner
surfaces of the confining substrates, the liquid crystal bulk
molecules 25 will, due to their negative anisotropy, switch
out-of-plane to a field-induced planar orientation defined by the
rubbing direction.
[0173] The molecules (i.e. the side-chains) of the surface-director
alignment layers 25 will, due to their negative dielectric
anisotropy, also switch out-of-plane to a field-induced planar
orientation defined by the rubbing direction. The out-of-plane
switching molecules (i.e. the side-chains) of the surface-director
alignment layers 25 will thus promote a fast switching from the
field-off vertical orientation of the liquid crystal bulk molecules
26 to the field-induced planar orientation. Thus, the switching of
the liquid crystal bulk molecules 26 from the field-off vertical
orientation to a field-induced planar one will be faster, at lower
applied voltage, than in the out-of-plane switching of a prior art
liquid crystal device having non-switching surface-director
alignment layers. It should, however, be noted that the
surface-director alignment layers 25 of said device does not,
according to the invention, mediate the out-of-plane switching of
the liquid crystal bulk molecules 26, which orientation is directly
controllable by the applied field via dielectric coupling. The
surface-director alignment layers 25 merely facilitates said
out-of-plane switching.
[0174] The liquid crystal bulk layer 26 of the device according to
said embodiment may have a negative dielectric anisotropy within
the range of -6 to -1, and the surface-director alignment layers
25, may have a negative dielectric anisotropy within the range of
-6 to -1.
[0175] It is believed to be advantageous if the surface-director
alignment layers 25 has a larger negative value (more negative),
preferably much larger, than the negative dielectric anisotropy of
the liquid crystal bulk 26.
[0176] Formulas LXIX to LXXII are examples of surface-director
alignment materials suitable for providing an initial field-off
vertical alignment in the above described embodiment (an
out-of-plane switching liquid crystal device). These polymers
comprise side-chains (S.sub.1) chemically bound to a polymer main
chain (Z), said side-chains exhibiting permanent and/or induced
dipole moments that in ordered phase provide negative dielectric
anisotropy. ##STR42##
[0177] Formula LXXIII represents additional examples of
surface-director alignment layer materials suitable for providing
an initial field-off vertical alignment in the above described
embodiment (an out-of-plane switching liquid crystal device). These
polymers comprises side-chains (S.sub.1) exhibiting permanent
and/or induced dipole moments that in ordered phase provide
negative dielectric anisotropy and side-chains (S.sub.3) exhibiting
no permanent and/or induced dipole moments and thus providing no
dielectric anisotropy. ##STR43## ##STR44##
[0178] A specific example of this type of polymers suitable as
surface-director alignment layer material in the above described
embodiment is represented by Formula LXXIV.
[0179] Instead of using a polymer, the side-chains of Formulas LXIX
to LXXIV can be chemically attached, as known to persons skilled in
the art, to a solid surface, such as a gold surface, a silicon
dioxide surface or a glass surface comprising silanol groups, to
form a suitable material for use as the surface-director alignment
layer in the device according to the invention.
[0180] In another similar embodiment of an out-of-plane switching
liquid crystal device according to said second group of embodiments
of the invention, the orientation of the molecules of said bulk
layer is directly controllable by an applied electric field to
perform out-of-plane switching of initial planar orientation to a
field-induced vertical orientation, whereas an orthogonal
projection of said surface-director (of the liquid crystal bulk
layer) on a geometrical plane perpendicular to said substrates,
termed projected surface-director, presents said preferred
orientation termed preferred field-induced vertical
orientation.
[0181] FIG. 13 shows part of an embodiment of an out-of-plane
switching liquid crystal device 28 according to the invention, in
the field-off state (E=0), wherein both the surface-director
alignment layers 29 (only one layer is shown) and the liquid
crystal bulk 30 exhibit positive anisotropy
(.DELTA..epsilon.>0), said surface-director alignment layers 29
being applied on the inner surfaces of substrates confining the
liquid crystal bulk layer 30.
[0182] The molecules (i.e. the side-chains) of the surface-director
alignment layers 29 have in this embodiment an initial planar
orientation in relation to the confining substrate surfaces, thus
resulting in planar or substantially planar aligned liquid crystal
bulk molecules 30 in the field-off state (E=0). The
surface-director alignment layers 29 are also preferably
unidirectionally rubbed to obtain a preferred direction of the
field-off planar alignment of the liquid crystal bulk molecules
30.
[0183] The device may either comprise two surface-director
alignment layers 29 (two-sided embodiment) or alternatively only
one surface-director alignment layer 29 (one-sided embodiment).
[0184] When an external field is applied (E.noteq.0) normally to
the liquid crystal bulk layer 30 between electrodes 31 on the inner
surfaces of the confining substrates, the liquid crystal bulk
molecules 30 will, due to their positive anisotropy, switch
out-of-plane to a field-induced vertical orientation.
[0185] The molecules (i.e. the side-chains) of the surface-director
alignment layers 29 will, due to their positive dielectric
anisotropy, also switch out-of-plane to a field-induced vertical
orientation when an electric field is applied normally to the
confining substrates. The out-of-plane switching molecules (i.e.
the side-chains) of the surface-director alignment layers 29 will
thus promote a fast switching from the field-off planar orientation
of the liquid crystal bulk molecules 30 to the field-induced
vertical orientation. Thus, the switching of the liquid crystal
bulk molecules 30 from the field-off planar orientation to a
field-induced vertical one will be faster, at lower applied
voltage, than in the out-of plane switching of a prior art liquid
crystal device having a non-switching surface-director alignment
layer. It should, however, be noted that the surface-director
alignment layers 29 of the device according to the invention does
not mediate the out-of-plane switching of the liquid crystal bulk
molecules 30, which orientation is directly controllable by the
applied field via dielectric coupling. The surface-director
alignment layers 29 merely facilitates said out-of-plane
switching.
[0186] The liquid crystal bulk layer 30 of the device according to
said embodiment may have a positive dielectric anisotropy within
the range of 1 to 30, and the surface-director alignment layers 29
may have a positive dielectric anisotropy within the range of 1 to
30.
[0187] It is believed to be advantageous if the positive dielectric
anisotropy of the surface-director alignment layers 29 has a larger
positive value (more positive), preferably much larger, than the
positive dielectric anisotropy of the liquid crystal bulk 30.
[0188] Formulas XLVI to LXVIII are examples of surface-director
alignment materials suitable for providing an initial field-off
planar alignment in the above described embodiment (an out-of-plane
switching liquid crystal device). As previously described, these
polymers comprise side-chains exhibiting permanent and/or induced
dipole moments that in ordered phase provides positive dielectric
anisotropy.
[0189] Instead of using a polymer, the side-chains of Formulas XLVI
to LXVIII can be chemically attached, as known to persons skilled
in the art, to a solid surface, such as a gold surface, a silicon
dioxide surface or a glass surface comprising silanol groups, to
form a suitable material for use as the surface-director alignment
layer in the device according to the invention.
[0190] Variants of the hitherto described first and second group of
embodiments of the device according to the invention, are devices
comprising two surface-director alignment layers exhibiting
dielectric anisotropies (.DELTA..epsilon.) of opposite signs. This
type of devices is believed to provide a short total response time,
in particular a short decay time for an out-of-plane switching
liquid crystal device.
[0191] FIG. 14 illustrates part of an embodiment of an out-of-plane
switching liquid crystal device 32 according to the invention,
wherein asymmetric (in view of dielectric anisotropy)
surface-director alignment layers 33,34 are applied on the inner
surfaces of substrates confining a liquid crystal bulk layer 35.
The liquid crystal bulk 35 exhibits a negative dielectric
anisotropy (.DELTA..epsilon.<0) and the first surface-director
alignment layer 33 exhibits a negative dielectric anisotropy
(.DELTA..epsilon.<0) and the second surface-director alignment
layer 34 exhibits a positive dielectric anisotropy
(.DELTA..epsilon.>0).
[0192] The molecules (i.e. the side-chains) of the surface-director
alignment layers 33,34 have in this embodiment an initial vertical
orientation in relation to the confining substrate surfaces, thus
resulting in vertically or substantially vertically aligned liquid
crystal bulk molecules 35 in the field-off state (E=0), as shown in
FIG. 14a. The surface-director alignment layers 33,34 are also
preferably unidirectionally rubbed to obtain a preferred
orientation of a field-induced planar alignment of the liquid
crystal bulk molecules 35.
[0193] When an external electric field is applied (E.noteq.0)
normally to the liquid crystal bulk layer 35 between electrodes 36
on the confining substrates, a bent deformation in the liquid
crystal bulk layer 35 is induced, as shown in FIG. 14b, thus giving
rise to a flexoelectric polarization P.sub.f1. The applied electric
field couples to the flexoelectric polarization and, depending on
the polarity of the applied electric field, the bent deformation
will increase or decrease, thus giving rise to a linear
electro-optic response.
[0194] FIG. 15 illustrates part of an embodiment of an out-of-plane
switching liquid crystal device 37 according to the invention,
wherein asymmetric (in view of dielectric anisotropy)
surface-director alignment layers 38,39 are applied on the inner
surfaces of substrates confining a liquid crystal bulk layer 40.
The liquid crystal bulk 40 exhibits a positive dielectric
anisotropy (.DELTA..epsilon.>0) and the first surface-director
alignment layer 38 exhibits a positive dielectric anisotropy
(.DELTA..epsilon.>0) and the second surface-director alignment
layer 39 exhibits a negative dielectric anisotropy
(.DELTA..epsilon.<0).
[0195] The molecules (i.e. the side-chains) of the surface-director
alignment layers 38,39 have in this embodiment an initial planar
orientation in relation to the confining substrate surfaces, thus
resulting in planar or substantially planar aligned liquid crystal
bulk molecules 40 in the field-off state (E=0), as shown in FIG.
15a. The surface-director alignment layers 38,39 are also
preferably unidirectionally rubbed to obtain a preferred
orientation of the field-off planar alignment of the liquid crystal
bulk molecules 40.
[0196] When an external electric field is applied (E.noteq.0)
normally to the liquid crystal bulk layer 40 between electrodes 41
on the confining substrates, a splay deformation in the liquid
crystal bulk layer 40 is induced, as shown in FIG. 15b, thus giving
rise to a flexoelectric polarization P.sub.f1. The applied electric
field couples to the flexoelectric polarization and, depending on
the polarity of the applied electric field, the splay deformation
will increase or decrease, thus giving rise to a linear
electro-optic response.
3. Structural Parts of the Surface-Director Alignment Layers
Exhibiting Opposite Signs of Dielectric Anisotropy
[0197] In a third group of embodiments of the device according to
the invention, the surface-director alignment layer(s) comprise(s)
structural parts exhibiting dielectric anisotropies
(.DELTA..epsilon.) of opposite signs. This type of device is
believed to provide a short decay time as well as a short rise
time, both for an in-plane switching liquid crystal device and an
out-of-plane switching liquid crystal device.
[0198] It is believed that said structural parts exhibiting
dielectric anisotropies (.DELTA..epsilon.) of opposite signs
preferably should be homogeneously distributed in the
surface-director alignment layer.
[0199] The device according to this third group of embodiments may
either comprise two surface-director alignment layers (two-sided
embodiment) or alternatively only one surface-director alignment
layer (one-sided embodiment).
[0200] A surface-director alignment layer comprising structural
parts exhibiting dielectric anisotropies (.DELTA..epsilon.) of
opposite signs is obtainable using, for instance, materials
comprising dimeric chemical structures having a first structural
part of positive dielectric anisotropy (.DELTA..epsilon.>0) and
a second structural part of negative dielectric anisotropy
(.DELTA..epsilon.<0).
[0201] Formula LXXV represents examples of surface-director
alignment layer materials suitable for providing an initial
field-off planar alignment in the above described embodiment (an
out-of-plane or in-plane switching liquid crystal device). These
polymers comprise side-chains (S.sub.1) chemically bound to a
polymer main chain (Z), said side-chains having dimeric structures,
each one comprising a first structural part exhibiting a permanent
and/or induced dipole moment that in ordered phase provides
positive dielectric anisotropy and a second structural part
exhibiting a permanent and/or induced dipole moment that in ordered
phase provides negative dielectric anisotropy ##STR45##
[0202] Instead of using a polymer, the side-chains of Formula LXXV
can be chemically attached, as known to persons skilled in the art,
to a solid surface, such as a gold surface, a silicon dioxide
surface or a glass surface comprising silanol groups, to form a
suitable material for use as the surface-director alignment
layer.
[0203] Formulas LXXVI to LXXX are examples of surface-director
alignment layer materials suitable for providing an initial
field-off vertical alignment in an out-of-plane switching liquid
crystal device according to the above described embodiment. These
polymers comprises side-chains (S.sub.1) chemically bound to a
polymer main chain (Z), said side-chains having dimeric structures,
each one comprising a first structural part exhibiting a permanent
and/or induced dipole moment that in ordered phase provides
positive dielectric anisotropy of and a second structural part
exhibiting a permanent and/or induced dipole moment that in ordered
phase provides negative dielectric anisotropy ##STR46##
[0204] Instead of using a polymer, the side-chains of Formulas
LXXVI to LXXX can be chemically attached, as known to persons
skilled in the art, to a solid surface, such as a gold surface, a
silicon dioxide surface or a glass surface comprising silanol
groups, to form a suitable material for use as the surface-director
alignment layer.
[0205] FIG. 16 illustrates part of an embodiment of an out-of-plane
switching liquid crystal device 42 according to the invention
having an initial field-off vertical orientation and comprising
surface-director alignment layers (only one layer is shown),
applied on substrate surfaces 43, having a dimeric structure
comprising a first structural part 44 of positive dielectric
anisotropy (.DELTA..epsilon.>0) and a second structural part 45
of negative dielectric anisotropy (.DELTA..epsilon.<0). The
liquid crystal bulk layer 46 has a negative dielectric anisotropy
(.DELTA..epsilon.<0).
[0206] FIG. 16a illustrates the field-off state (E=0) and FIG. 16b
illustrates the field-induced state (E.noteq.0).
[0207] Materials comprising trimeric chemical structures having a
first structural part of positive dielectric anisotropy
(.DELTA..epsilon.>0), a second structural part of negative
dielectric anisotropy (.DELTA..epsilon.<0), and a third
structural part of negative (.DELTA..epsilon.<0) or positive
(.DELTA..epsilon.>0) dielectric anisotropy may also be useful in
this third group of embodiments of the invention. The third
structural part may be similar or different as compared to the
first and second structural parts. Thus, chemical structures
comprising two or more structural parts, wherein each structural
part exhibits a positive or negative dielectric anisotropy and two
of said three structural parts exhibit dielectric anisotropies of
opposite signs, may be useful in a device according to this third
group of embodiments according to the invention.
[0208] Formulas LXXXI to LXXXIII are examples of surface-director
alignment layer materials suitable for providing an initial
field-off planar alignment in the above described embodiment (an
out-of-plane or an in-plane switching liquid crystal device). These
polymers comprises side-chains (S.sub.1) chemically attached to a
polymer main chain (Z), said side-chains having trimeric
structures, each one comprising a first structural part exhibiting
a permanent and/or induced dipole moment that in ordered phase
provides positive dielectric anisotropy (.DELTA..epsilon.>0), a
second structural part exhibiting a permanent and/or induced dipole
moment that in ordered phase provides negative dielectric
anisotropy negative dielectric anisotropy (.DELTA..epsilon.<0),
and a third structural part exhibiting a permanent and/or induced
dipole moment that in ordered phase provides either negative
(.DELTA..epsilon.<0) or positive (.DELTA..epsilon.>0)
dielectric anisotropy. ##STR47##
[0209] Instead of using a polymer, the side-chains of Formulas
LXXXI to LXXXIII can be chemically attached, as known to persons
skilled in the art, to a solid surface, such as a gold surface, a
silicon dioxide surface or a glass surface comprising silanol
groups, to form a suitable material for use as the surface-director
alignment layer.
[0210] FIG. 17 illustrates part of an embodiment of an out-of-plane
switching liquid crystal device 47 according to the invention
having an initial field-off planar orientation and comprising
surface-director alignment layers (only one layer is shown),
applied on substrate surfaces 48, having a trimeric structure
comprising a first structural part 49 of positive dielectric
anisotropy (.DELTA..epsilon.>0), a second structural part 50 of
negative dielectric anisotropy (.DELTA..epsilon.<0), and a third
structural part 51 of positive dielectric anisotropy
(.DELTA..epsilon.>0). The liquid crystal bulk layer 52 has a
positive dielectric anisotropy (.DELTA..epsilon.>0).
[0211] FIG. 17a illustrates the field-off state (E=0) and FIG. 17b
illustrates the field-induced state (E.noteq.0).
EXAMPLES
[0212] A liquid crystal display glass substrate having a thickness
of 1.10 mm was used. One side of the substrate was provided with an
indium tin oxide (ITO) layer (electrode material) having a surface
resistance of 80 .OMEGA./cm.sup.2. Addressing electrode structures
were provided using a conventional photolithography process known
to persons skilled in the art. The glass substrate was cut into
pieces with a size of 9.5.times.12.5 mm, and the edges were ground.
Also glass substrates of the size 25.4.times.25.4 mm have been
used.
[0213] The substrates were then washed several times in distilled
water in an ultra-sonic bath, dried and then washed two times in
isopropanol. The substrates were thereafter moved into a
clean-room.
[0214] The ITO side of the substrates was spin coated with a
surface-director alignment layer material, dissolved in
tetrahydrofuran (THF) to a concentration of about 0.1% w/w
(concentrations up to 0.5% w/w have been tested). The speed was
3000-4000 rpm and coating was performed during 30 seconds.
[0215] After coating, the substrates were heated for approximately
5-10 minutes at a temperature of 125.degree. C. to remove the
solvent (THF) and form an alignment layer. Drying can be performed
in an oven or on a hot plate and/or under vacuum. Then the
substrates were thereafter set to cool down.
[0216] It shall be noted that also two-step processes comprising
heating for about 5-10 minutes at 60.degree. C. followed by heating
for about 10-30 minutes at 130.degree. have been tested with
acceptable results. However, it may be noted that temperatures over
room temperature are in principle not necessary for the drying
step.
[0217] The applied surface-director alignment layer, on top of the
ITO layer, was buffed with a nylon cloth using a drum diameter of
120 mm, a drum speed of 300 rpm, a linear speed of 15 mm/sec, and a
pile contact length of about 0.5 mm. All substrates were buffed in
the same direction.
[0218] Two substrates, one substrate being rotated 180.degree. to
make the buffing direction antiparallel in the cell, were
thereafter put together to a cell using UV-glue (Norland NOA68),
and spacers in a string at two of the edges. An alternative is to
spray spacers from an ethanol dispersion onto the cell surface. The
cell was put under pressure in a UV-exposure box for 15 minutes.
Small electric cords were ultra-sonically soldered to each
ITO-surface of the cell.
[0219] A nematic liquid crystal, in isotropic phase, was then
introduced into the cell by means of capillary forces (this can be
done with or without vacuum applied).
[0220] It shall be noted that the device described above is of a
relatively simple type. Devices can be of much larger size and can
be addressed in different ways, such as by using a passive
matrix-addressed type or an active matrix-addressed type. In these
cases, steps involving complex microelectronics productions steps
are involved. In all examples below, the solvents were dried before
use thereof by passing the reaction solvents through a short
chromatography column containing ICN Alumina N super 1 from ICN
Biomedicals GmbH Germany.
[0221] In all the examples below, standard reactions well-known to
a person skilled in the art were used for the preparation of the
polymers.
[0222] The maximum degree of functionalisation in the examples
below is, due to statistical reasons 86%. Hence, a minimum of 14%
of the initial hydroxyl groups remain after completion of the
reaction.
EXAMPLE 1
Out-of-Plane Switching Liquid Crystal Device Having an Electrically
Stabilised Vertically Aligned Surface-Director Alignment Layer
Preparation of Surface-Director Alignment Layer Material
[0223] In a 100 ml flask, 0.70 g of
4'-(11,11-diethoxy-undecyloxy)-biphenyl-4-carbonitrile (side-chain
precursor I) (see D Lacey et al, Macromolecular Chemistry and
Physics 200, 1222-1231 (1999)), 0.081 g of octanal, 0.198 g of
polyvinyl alcohol (PVA) (number average molecular weight of about
15 000 g/mol), and 0.10 g of p-toluenesulfonic acid (TsOH) were
dissolved in 20 ml of dry N,N-dimethylformamide (DMF) and stirred
at about 55.degree. C. for 24 hours.
[0224] The reaction mixture was then poured into 150 ml of methanol
and a polymer was precipitated. The precipitate was collected and
dissolved in 5 ml of chloroform and re-precipitated in 100 ml of
methanol. The re-precipitation was repeated twice.
[0225] The yield was 0.29 g of polymer (i.e. 40% calculated on the
amount of added polyvinyl alcohol). Losses were due to the presence
of low molar mass polymer that was removed in the workup procedure
(i.e. the precipitation procedure).
[0226] .sup.1H--NMR spectrum of the obtained polymer was in
accordance with structure A of Scheme I. The side-chain molar ratio
I/octanal in the polymer as determined using NMR was found to be
2/1 (=o/n in structure A). Furthermore, (o+n)/p was found to be
about 42/16.
[0227] The side-chain formed from side-chain precursor I is
attached to the polymeric backbone via spacing atoms in the form of
--(CH.sub.2).sub.10--. ##STR48## Manufacturing of a Liquid Crystal
Device According to the Invention
[0228] The ITO side of the substrates was coated, as described
above, with polymer A (=Formula XIX) prepared as described above.
It shall be noted, however, that any one of the structures
according to Formulas I to XXXII may be used in this
embodiment.
[0229] The polymer layer (about 100 nm) was rubbed unidirectionally
very lightly to induce a small pre-tilt of the mesogenic
side-chains of the polymer, and the cell was thereafter
assembled.
[0230] The sandwich cell (cell gap about 3 .mu.m) was then filled
with the nematic mixture MBBA/MLC6608 (Merck, Germany), 40/60 wt %,
MBBA exhibiting .DELTA..epsilon.=-0.8 and MLC 6608 exhibiting
.DELTA..epsilon.=-4.2.
[0231] In this cell, the polymer layer acts as a surface-director
alignment layer.
[0232] The alignment of the cell after cooling to room temperature
was inspected by means of a polarising microscope and it was found
to be uniform vertical.
[0233] The response rise and decay times were measured in a set-up
comprising a polarising microscope, a photodetector, an
oscilloscope and a puls-generator.
[0234] The electro-optic response of the cell with vertical
alignment, under application of unipolar impulses with low
frequency (about 1 Hz), is depicted in FIG. 18. At a voltage (U) of
9.2 V, the measured rise and decay time were about 1.9 and 3.8 ms,
respectively. Thus, the measured decay time is about 5 times
shorter than the decay time usually measured in out-of-plane
switching liquid crystal cells with an initial vertical
alignment.
EXAMPLE 2
Out-of-Plane Switching Liquid Crystal Device Having an Electrically
Stabilised Vertically Aligned Surface-Director Alignment Layer
[0235] Example 1 was repeated except that the sandwich cell was
filled with the nematic mixture MBBA/MLC6884 (Merck, Germany),
40/60 wt %, MLC 6884 exhibiting .DELTA..epsilon.=-5.0 and MBBA
exhibiting .DELTA..epsilon.=-0.8.
[0236] At a voltage (U) of 6.1 V, the measured rise and decay time
were about 2.5 and 1.8 ms, respectively, as shown in FIG. 19.
EXAMPLE 3
Out-of-Plane Switching Liquid Crystal Device Having an Electrically
Stabilised Vertically Aligned Surface-Director Alignment Layer
Preparation of Surface-Director Alignment Layer Material
[0237] In a 100 ml flask, 0.11 g of
4'-(11,11-diethoxy-undecyloxy)-biphenyl-4-carboxylic acid
4-ethoxycarbonyl-phenyl ester (side-chain precursor III), 0.07 g of
4'-(11, 11-diethoxy-undecyloxy)-4'-undec-10-enyloxy-biphenyl
(side-chain precursor VII), 0.018 g of octanal, 0.037 g of PVA
(number average molecular weight of about 15 000 g/mol), and 0.03 g
of TsOH, were dissolved in 10 ml of dry DMF and stirred at about
55.degree. C. for 48 hours.
[0238] The reaction mixture was then poured into 150 ml of methanol
and a polymer was precipitated. The precipitate was collected and
dissolved in 5 ml of chloroform and re-precipitated in 100 ml of
methanol. The re-precipitation was repeated twice.
[0239] The yield was 0.09 g of polymer. Losses were due to the
presence of low molar mass polymer that was removed in the workup
procedure.
[0240] .sup.1H--NMR spectrum of the obtained polymer was in
accordance with structure H of Scheme II.
[0241] The side-chain formed from side-chain precursor III is
attached to the polymeric backbone via spacing atoms in the form of
--(CH.sub.2).sub.10-- and the side-chain formed from side-chain
precursor VII is attached to the polymeric backbone via spacing
atoms in the form of --(CH.sub.2).sub.10--. ##STR49## ##STR50##
Manufacturing of a Liquid Crystal Device According to the
Invention
[0242] Example 1 was repeated except that the ITO side of the
substrates was coated, as described above, with polymer H (=Formula
XXXII) prepared as described above. The polymer layer was, however,
not rubbed. Furthermore, the sandwich cell was filled with the
nematic material MLC6884 (Merck, Germany) exhibiting
.DELTA..epsilon.=-5.0.
[0243] At a voltage (U) of 5.2 V, the measured rise and decay time
were about 2.7 and 2.7 ms, respectively, as shown in FIG. 20.
EXAMPLE 4
Out-of-Plane Switching Liquid Crystal Device Having an Electrically
Stabilised Planar Aligned Surface-Director Alignment Layer
Preparation of Surface-Director Alignment Layer Material
[0244] In a 100 ml flask, 1.0 g of
2-[4-(11,11-diethoxy-undecyloxy)-3-(4-ethoxy-phenylazo)-phenoxy]-propioni-
c acid butyl ester (side-chain precursor IX), 0.205 g of octanal,
0.25 g of PVA (number average molecular weight of about 15 000
g/mol), and 0.1 g of TsOH were dissolved in 25 ml of dry THF and
stirred at about 60.degree. C. for 24 hours.
[0245] The reaction mixture was then poured into 250 ml of methanol
and a polymer was precipitated. The precipitate was collected and
dissolved in 5 ml of chloroform and re-precipitated in 100 ml of
methanol. The re-precipitation was repeated twice.
[0246] The yield was 0.56 g of polymer. Losses were due to the
presence of low molar mass polymer that was removed in the workup
procedure.
[0247] .sup.1H--NMR spectrum of the obtained polymer was in
accordance with structure J of Scheme III. The side-chain molar
ratio IX/octanal in the polymer as determined using NMR was found
to be 1/1 (=o/n in structure J). Furthermore, (o+n)/p was found to
be about 43/18.
[0248] The side-chain formed from side-chain precursor IX is
attached to the polymeric backbone via spacing atoms in the form of
--(CH.sub.2).sub.10--. ##STR51## Manufacturing of a Liquid Crystal
Device According to the Invention
[0249] The ITO side of the substrates was coated, as described
above, with polymer J (=Formula XLIV) prepared as described above.
It shall be noted, however, that any one of the structures
according to Formulas XXXIII to XLV may be used in this
embodiment.
[0250] The polymer layer (about 100 nm) was rubbed unidirectionally
to ensure uniform planar alignment of the mesogenic side-chains of
the polymer, and the cell was thereafter assembled.
[0251] The sandwich cell (cell gap about 3 .mu.m) was then filled
with the nematic mixture E7 (BDH/Merck) exhibiting
.DELTA..epsilon.>0.
[0252] In this cell, the polymer layer acts as a surface-director
alignment layer.
[0253] The alignment of the cell after cooling to room temperature
was inspected by means of a polarising microscope and it was found
to be uniform planar.
[0254] The rise and decay times were measured in a set-up
comprising a polarising microscope, a photo-detector, an
oscilloscope and a puls-generator.
[0255] The electro-optic response of the cell with planar
alignment, under application of unipolar impulses with low
frequency (about 1 Hz), was found to be about 0.5 ms and 4 ms for
rise and decay times, respectively.
EXAMPLE 5
Out-of-Plane Switching Liquid Crystal Device Having an Electrically
Stabilised Planar Aligned Surface-Director Alignment Layer
[0256] Example 4 was repeated except that the sandwich cell was
filled with the nematic material E70 A (BDH/Merck) exhibiting
.DELTA..epsilon.=+10.8.
[0257] At a voltage (U) of 5.6 V, the measured rise and decay time
were about 1.1 and 1.6 ms, respectively, as shown in FIG. 21.
[0258] While the invention has been described in detail and with
reference to specific embodiments thereof, it will be apparent for
one skilled in the art that various changes and modifications can
be made therein without departing from the spirit and scope
thereof.
* * * * *