Abstract: A bistable nematic liquid crystal device cell is provided with a surface alignment grating on at least one cell wall and a surface treatment on the other wall. Such treatment may be a homeotropic alignment or a planar alignment with or without an alignment direction, and zero or a non zero pretilt. The surface profile on the monograting is asymmetric with its groove height to width selected to give approximately equal energy within the nematic material in its two allowed alignment arrangements. The monograting may be formed by a photolithographic process or by embossing of a plastics material. The cell is switched by dc pulses coupling to a flexoelectric coefficient in the material, or by use of a two frequency addressing scheme and a suitable two frequency material. Polarisers either side of the cell distinguish between the two switched states. The cell walls may be rigid or flexible, and are coated with electrode structures, e.g.

Abstract: A liquid crystal composition comprises a host material capable of exhibiting a smectic C phase, and a chiral dopant material which imparts or enhances chirality in the host material. The composition exhibits &tgr;-Vmin curves. The chiral dopant material comprises at least first and second chiral centers. The chiral centers individually produce, in the liquid crystal composition, different and complementary temperature coefficients of spontaneous polarization within a predetermined temperature range. The chiral centers are present in the liquid crystal composition in relative amounts such that regions of the &tgr;-Vmin curves across the predetermined temperature range are substantially coincident.

Abstract: When a ferroelectric liquid crystal display (FLCD) panel is addressed in such a manner as to cause adjacent or successive pixels to display different levels of greyscale, the viewer may perceive a pseudo edge effect caused by the perceived error in the transmission level at the transition between the two grey levels. In order to decrease this perceived error, the panel is addressed such that, at the transition between the two grey levels, for example between the grey levels “3” and “4”, the most significant bit of the addressing scheme incorporates an analogue grey level, for example a half level. This results in a perception level exhibiting a lower absolute error in the relative grey level than would be obtained if no special measures were taken to compensate for the perceived error at the transition. This compensation technique is applicable to addressing schemes utilizing temporal dither (TD) as well as spatial dither (SD).

Abstract: A fluorinated phenyl compound having the general formula [1]: wherein each of s, v and x=0 or 1, each of t and u=1, 2 or 3, and each of y and z=0, 1 or 2; A, B and C are independently selected from conjugated cyclic moieties including heterorings and fused rings; R1 and R3 may be independently cyano, or (C1-C12)alkyl, (C1-C12)alkoxy, (C1-C11) alkoxycarbonyl or (C1-C11)alkylcarbonyloxy which may be fluoro- and/or cyano-substituted; R2=H or F; R4=H or F; and R5=H or F. Such compounds have high transverse dipole moments and are potentially useful in liquid crystal compositions and in devices including same.

Abstract: The invention relates to multiplex addressing of a liquid crystal device comprising applying a strobe signal to one of a first plurality of electrodes of the device and a data signal to one of a second plurality of electrodes of the device. The strobe and data signals address a pixel of the device. The data signal comprises one of a SELECT data signal and a NON_SELECT which each have a duration and a discriminating duration which is no longer than the duration. During the discriminating duration the SELECT and NON_SELECT signals are different. The strobe signal comprises a first portion applied simultaneously with the discriminating duration of the data signal and a second portion applied after the discriminating duration of the data signal. By including a section at a larger voltage magnitude in the second portion of the strobe signal than is present in the first part of that signal, improved performance and addressing speed are obtainable.

Abstract: A ferroelectric liquid crystal display includes a cell comprising a layer of ferroelectric liquid crystal material contained between two transparent glass substrates having alignment layers for determining the surface alignment of the molecules in the liquid crystal material. The display further incorporates switching circuitry for switching the molecules in the liquid crystal material between a first state and a second state by means of a switching signal having a duration &tgr; and a voltage V. The liquid crystal material and the alignment layers are such that the cell exhibits a &tgr;-V response in the form of a curve having two minima separated by an intermediate maximum. Such a &tgr;-V response, which may be termed a double turnaround response, allows a high degree of discrimination between the switched and non-switched states beyond the turnaround point and offers potential addressing advantages.

Abstract: A bistable nematic liquid crystal device cell is provided with a surface alignment grating on at least one cell wall and a surface treatment on the other wall. Such treatment may be a homeotropic alignment or a planar alignment with or without an alignment direction, and zero or a non zero pretilt. The surface profile on the monograting is asymmetric with its groove height to width selected to give approximately equal energy within the nematic material in its two allowed alignment arrangements. The monograting may be formed by a photolithographic process or by embossing of a plastics material. The cell is switched by dc pulses coupling to a flexoelectric coefficient in the material, or by use of a two frequency addressing scheme and a suitable two frequency material. Polarisers either side of the cell distinguish between the two switched states. The cell walls may be rigid or flexible, and are coated with electrode structures, e.g.

Abstract: A liquid crystal composition comprising (1) an achiral host mixture comprising (a) at least 20% by weight, based on the total weight of the host mixture, of a mixture of fluorinated phenylpyrimidine compounds capable of exhibiting an SmC phase, and (b) at least 10% by weight, based on the total weight of the host mixture, of at least one fluorinated terphenyl compound which enhances the phase sequence of said mixture, wherein the total amount of (a) and (b) is at least 50% by weight based on the total weight of the host mixture; and (2) at least one chiral dopant in an amount of not more than 10% by weight of the total weight of the composition.

Abstract: A bistable nematic liquid crystal device cell (1) is provided with a surface alignment grating on at least one cell wall (3) and a surface treatment on the other wall (4). Such treatment may be a homeotropic alignment or a planar alignment with or without an alignment direction, and zero or a non zero pretilt. The surface profile on the monograting is asymmetric with its grove height to width selected to give approximately equal energy within nematic material (2) in its two allowed alignment arrangements. The monograting may be formed by a photolithographic process or by embossing of a plastics material. The cell (1) is switched by dc pulses coupling to a flexoelectric coefficient in the material (2), or by use of a two frequency addressing scheme and a suitable two frequency material. Polarizers (13,13′) either side of the cell (1) distinguish between the two switched states. The cell walls (3,4) may be rigid or flexible, and are coated with electrode structures (6,7), e.g.

Abstract: In order to reduce the effects of impact on liquid crystal devices a polymer network is introduced into ferroelectric liquid crystal cells. A liquid crystal device comprises two spaced cell walls each bearing electrode structures and treated on at least one facing surface with an alignment layer, a layer of a smectic liquid crystal material enclosed between the cell walls, characterised in that the liquid crystal material contains a small amount of monomer. The liquid crystal material may also contain a photoinitiator. The monomer material may be cured to produce the polymer networks the curing many be carried out in the presence of an electric or magnetic field. Further, the monomer may be cured in an isotropic or liquid crystal phase.

Abstract: A mixture of a ferroelectric or anti-ferroelectric liquid crystal material and a monomer having a single photopolymeric functional group is injected in the space between two electrode substrates while heat is applied. After cooling of the mixture it is irradiated with ultraviolet light at a temperature at which the liquid crystal material remains in the smectic phase so as to polymerise the monomer. Areas of liquid crystal material requiring different threshold voltages for switching are thereby produced. Alternatively such areas can be produced by changing the conditions applied to a mixture of liquid crystal material with a suitable dopant so as to cause separation of the dopant out of the liquid crystal material in order to provide a polarity of nucleation points for controlling domain formation within the liquid crystal material. Such control of domain formation can be used to provide greyscale in a liquid crystal device.

Abstract: A light modulating device, such as a ferroelectric liquid crystal display (FLCD) comprises an addressable matrix and modulating elements or pixels and associated circuitry for selectively addressing each element in a series of addressing frames in order to vary the transmission level of each element relative to the transmissions levels of the other elements. Such addressing utilises a temporal dither addressing scheme for addressing at least part of each element within each frame with different combinations of temporal dither signals applied to separately addressable temporal bits within the frame to produce different transmission levels. In order to enable a large number of grey levels to be produced whilst limiting the perceived errors at transitions between different grey levels, the temporal bits are addressed in a first order in a first frame (or in a first spatial location) and in a second order, which is different to the first order, in a second frame (or in a second spatial location).

Abstract: A liquid crystal device is provided with a pair of substrates (12, 16) containing a liquid crystal material (22). A wall structure comprising, for example, a plurality of walls (14) is provided between the two substrates. The wall structure provides mechanical strength to the device and resistance to flow of liquid crystal material which can cause deterioration in the device performance. The walls may extend in two mutually different directions (FIG. 8, 40) to provide mechanical strength and resistance to flow in two directions while the device can still be readily filled. The device is particularly applicable to a ferroelectric liquid crystal device.

Abstract: A ferroelectric liquid crystal display (FLCD), which comprises a cell including a layer of chiral smetic ferroelectric liquid crystal material contained between two substrates and at least one alignment layer for determining the surface alignment of the molecules in the liquid crystal material, is manufactured as follows. After selection of a suitable material for the alignment layer, the cell is filled by introducing liquid crystal material between the substrates to which the alignment layer is applied. After filling of the cell, a heat treatment is applied to the cell by raising the cell to an elevated temperature and maintaining the cell at that temperature for a predetermined period of time.

Abstract: A ferroelectric liquid crystal display comprises an addressable matrix of pixels, and addressing circuitry for selectively addressing each pixel in order to vary the transmission level of the pixel relative to the transmission levels of the other pixels. The addressing circuitry includes spatial and/or temporal dither circuits for addressing separately addressable subpixels with different spatial dither signals and/or for addressing each pixel or subpixel with different temporal dither signals in separate subframes.

Abstract: In order to the effects of impact on liquid crystal devices a polymer network is introduced into ferroelectric liquid crystal cells. A liquid crystal device comprises two spaced cell walls each bearing electrode structures and treated on at least one facing surface with an alignment layer, a layer of a smectic liquid crystal material enclosed between the cell walls, characterised in that the liquid crystal material contains a small amount of monomer. The liquid crystal material may also contain a photoinitiator. The monomer material may be cured to produce the polymer network; the curing may be carried out in the presence of an electric or magnetic field. Further, the monomer may be cured in an isotropic or liquid crystal phase.

Abstract: A passive liquid crystal device (FIG. 1) is driven in a multiplexed manner by a strobe signal (STB) applied in succession to a plurality of row electrodes and data signals (DATa, DATb) applied to a plurality of column electrodes. A resultant signal (RESa, RESb) comprising the combination of the strobe and data signals is applied to the pixels in the device. The liquid crystal device is sensitive to the polarity of the resultant signal. Typically a blanking pulse of a first polarity is applied followed by a resultant signal of the opposite polarity. A first data signal (DATa) is intended to change the state of the relevant pixel (SELECT) while a second data signal (DATa) is intended to leave the pixel in the same state (NON-SELECT). According to the invention the resultant signal (RESa, RESb) comprises at least a portion which is substantially continuously varying. This can be achieved by either or both of the strobe and data signals including such a portion or portions.

Abstract: A ferroelectric liquid crystal display comprises a matrix of pixels addressable by first and second sets of electrode tracks crossing one another at the locations of the pixels. The pixels ale addressed by applying data pulses to the first set of electrode tracks and strobe pulses to the second set of electrode tracks to switch certain pixels selected by the data pulses from a first state to a second state under the effect of the voltage difference between the data pulses and the strobe pulses, and blanking pulses are applied to the second set of electrode tracks to set the pixels to the first state in advance of the application of subsequent strobe pulses to switch selected pixels from the first state to the second state.

Abstract: A ferroelectric liquid crystal display (FLCD), which comprises a cell including a layer of chiral smetic ferroelectric liquid crystal material contained between two substrates and at least one alignment layer for determining the surface alignment of the molecules in the liquid crystal material, is manufactured as follows. After selection of a suitable material for the alignment layer, the cell is filled by introducing liquid crystal material between the substrates to which the alignment layer is applied. After filling of the cell, a heat treatment is applied to the cell by raising the cell to an elevated temperature and maintaining the cell at that temperature for a predetermined period of time.

Abstract: A liquid crystal device is provided with a pair of substrates (12, 16) containing a liquid crystal material (22). A wall structure comprising, for example, a plurality of walls (14) is provided between the two substrates. The wall structure provides mechanical strength to the device and resistance to flow of liquid crystal material which can cause deterioration in the device performance. The walls may extend in two mutually different directions (FIG. 8, 40) to provide mechanical strength and resistance to flow in two directions while the device can still be readily filled. The device is particularly applicable to a ferroelectric liquid crystal device.