Liquid crystal mixtures for use over an active matrix substrate must have a high resistivity and, to maintain high value during the lifetime of the display, the materials must be very stable. Many such liquid crystal mixtures are known and used in twisted nematic displays but they are of low birefringence; very few high birefringence liquid crystals of this type are known. Several classes of liquid crystal which fulfill these criteria have been developed and formulated into low melting point mixtures suitable for use with UV curing prepolymers. The properties of PDLC films containing these new mixtures show that the high birefringence values now possible can lead to substantially increased contrast ratios.

Perfluorocyclobutane aromatic ether polymer (PFCB) is being researched as a planarization resin for color filters and active devices for flat panel displays. In addition, the material is being evaluated as the alignment layer as well as the color filter binder and the results will be reported here in. The results of the current study have shown PFCB to exhibit superior planarization to polyimide with efficiencies <90%. As an example, a typical 1.5 micrometers P-V (Peak-Valley) of a color filter can be reduced to about 120 nm with the application of about 5 micrometers of PFCB. In addition to efficiently smoothing color filter type patterns, the PFCB is being explored as a binder resin for the dye or pigment.

We have recently described initial results of a project directed towards the design and synthesis of low molecular weight ferroelectric liquid crystals (FLCs) for second order nonlinear optics (NLO) applications. FLCs with useful magnitude of the second order susceptibility (chi) ⁽²) and processibility not possible with poled polymers or crystals have been obtained. However, for some applications liquids are not appropriate. For these applications we have been exploring the use of FLC polymers (FLCPs), and more specifically FLCP glasses. IN our view FLCP glasses represent a novel type of solid, a truly noncrystalline solid with thermodynamically stable polar order. High molecular weight FLCPs, however, suffer from very high viscosity in the isotropic state, precluding some attractive processing approaches such as capillary filling. Building upon the pioneering work of the Wacker LC-silicones group, we herein report on the synthesis and some properties of members of a class of cyclic oligosiloxane FLCs combining some of the advantages of both low molecular weight FLCs and FLCPs.

Ferroelectric smectic C* liquid crystals have been shown to exhibit high speed, multistate electro-optic switching, particularly when incorporated into the surface stabilized ferroelectric liquid crystal (SSFLC) light valve. Certain applications utilizing IR modulation, waveguide, phase modulation, and fiber-optic devices can benefit from a birefringence higher than the value of (Delta) n equals 0.15 seen in typical FLC materials. By incorporating the highly conjugated diacetylene moiety into an FLC core, an increase in birefringence greater than (Delta) n equals 0.3 is achieved. Lateral fluorination of the core induces a strong preference for the tilted smectic C phase as compared to the unfluorinated materials which typically show the nematic phase. The effect of other substitutions is explored on the mesogenic properties of the basic core structure.

Physical properties of several fluorinated diphenyl-diacetylene and tolane liquid crystals are evaluated. These liquid crystals exhibit a high resistivity, high birefringence, low viscosity and modest dielectric anisotropy. Some difluoro compounds show a relatively low melting temperature and small heat fusion enthalpy, and are useful for formulating eutectic mixtures. The mixtures consisting of these fluorinated compounds are particularly useful for active matrix, photoactivated light valve, and polymer-dispersed liquid crystal displays.

Liquid crystal films that scatter light as a function of voltage are used as the active parts of optical switches and attenuators. The optical properties of the film are studied here and the distribution and efficiency of the scattering are counted. How light bends in a droplet is calculated using geometric optics, which can also be used to estimate the efficiency of scattering.

The optical properties of a thin film of a thermotropic liquid crystalline polymer, with one of the surfaces bounded by air and the other bounded by a glycerine surface reveals the presence of integer strength point defects in the material. Formation of point defects at the center of a nematic droplet of the polymer surrounded by its isotropic phase as the material is taken through a biphasic structure is observed and the small-angle light scattering from such a structure is discussed. These observations are used to argue that the material under study is a uniaxial nematic.

We measured the first and the higher order Bragg peaks corresponding to the layer thickness in the SmC and SmC_A phases by X-ray diffraction, and calculated the smectic order parameters of the two phases. We found that the smectic layer in the SmC_A phase is much more ordered than that in the SmC phase.

Backflow effects are familiar from twisted nematic devices, occurring when the electric field director reorientation initiates transient flow of the liquid crystal. We have been exploring similar effects in Surface Stabilized Ferroelectric Liquid Crystal (SSFLC) cells, carrying out computer simulations of coupled director reorientation--flow transients. Our simulations are based on an elastohydrodynamic model of the smectic C phase which accounts explicitly for its biaxial symmetry and layer structure. The elastic and dissipative constants used in the model are obtained from smectic C data or estimated on the basis of nematic values. The simulations show that under some circumstances, particularly in response to a reversal applied electric field, backflow can drastically alter the electro-optical response speed.

In this paper we study the anchoring energy effects in the nematic liquid crystal confined to a submicron cylindrical cavity. Under the perpendicular anchoring conditions and (2K₂₄ + WR)/K₁₁ <2 it is shown that uniform axial director configuration becomes unstable. In this case the configuration transition occurs. We have obtained the transition threshold dependence on the uniform electric field applied along the cylindrical axis. The stability of the axial director alignment as a function of cavity radius is considered. Taking into account contributions from both the elastic energy and the surface anchoring energy we discuss some results of Landau- de Gennes theory for the uniformly distributed order parameter. Two cases are explored: W is proportional to S and to S² respectively. The order parameter and heat capacity dependencies on the temperature are calculated.

Correlation of structure of nematic-cholesteric mixtures and physical constants such as dielectric anisotropy (Delta) (epsilon) , microscopic force of twist (Beta) , coefficients of twist elasticity K₂₂ is investigated.

We have synthesized many ferroelectric side-chain liquid crystalline polymers exhibiting the Smectic C^* phase over a wide temperature range extending to sub-ambient temperatures. The tuning of the mesophase temperature has been achieved by incorporating two different mesogens as side groups attached to the siloxane backbone. These copolymers exhibit large values of spontaneous polarization which varies linearly through out the Smectic C^* phase. The pyroelectric coefficient and dielectric constants of these materials have been measured. The potential of these ferroelectric liquid crystals as pyroelectric detector materials will be examined.

Thermotropic liquid crystalline polymers (LCP) with mesogenic side-chain groups have been arousing much interest due to their possibilities for applications as electro-optical devices, because LCP exhibits both the mesomorphic inherent characteristics of liquid crystal (LC) and the mechanical characteristics of polymeric materials. Recently, various kinds of LCP have been synthesized, and their electro-optical properties have been studied extensively. The authors have reported on a large area-flexible light valve and a reversible and bistable electro- optical effect based on light scattering for (polymer/LC) composite films and, for smectic phase of (LCP/low molecular weight liquid crystal:LC) composite systems, respectively. The LCP/LC composite is highly transparent state upon application of a high frequency (1 kHz) a.c. electric field. The composite turns into a remarkable light scattering state upon the application of a low frequency (DC or several Hz) one.

The (polymer/liquid crystal) composite films were prepared from a solution of poly(dipropylfumarate) (Pdi-iPF) and nematic liquid crystal (LC) by a solvent casting method. The phase separated structure of the composite film was controlled by solvent evaporation rate. The light scattering (LS) profile of a (Pdi-iPF/LC:40/60 w/w) solution during solvent evaporation, exhibited a periodic structure, indicating that the phase separated structure was formed by spinodal decomposition. The aggregation structure of the composite film was investigated on the basis of a scanning electron microscope (SEM). SEM observation of the composite film suggested the presence of periodicity and dual connectivity of polymer and LC phases. The faster the solvent was evaporated, the smaller the LC channel (domain) size in the composite film was. The electro-optical behavior of the composite film was strongly depended on the LC channel (domain) size in the composite film. The transmittance increased, and also the rise and decay response times ((tau) _R and (tau) _D), decreased and increased, respectively, with an increase in size of LC channel (domain).

Dispersions of liquid crystals in polymeric matrices (PDLC) are used as light control devices because of the possibility of varying their light scattering through alignment changes arising from the application of electric fields. The scattering from such systems is very similar to that found with crystalline polymers which have been extensively studied in our laboratory for over 25 years. Studies of the scattering from spherulitic polymers have been modeled as that arising from anisotropic spheres. Theories and measurements have been made with parallel (V_v) and crossed (H_v) polarization as a function of the radii, anisotropy, and volume fraction of spheres, and the refractive index of the matrix.

The light scattering properties of polymer-dispersed liquid crystal (PDLC) films depend on several aspects of the film structure and nematic alignment. In this study we gauge the relative importance of some of these factors by varying the structure and properties of PDLC films in a systematic way, and measuring the variation in light scattering properties due to these changes. At high fields, the dependence of film scattering on the nematic refractive index follows the dependence predicted by the anomalous diffraction model for light scattering. In unpowered films, multiple scattering becomes important in films that consists of 3 - 4 layers of droplets or more. This effect is independent of the collection angle (f/#) of the detector, and is an important limitation when attempting to maximize the contrast ratio of PDLC projection devices that employ film scattering. I also show that the structure of the film several microns away from a droplet influences the scattering cross section of the droplet. This effect is illustrated by comparing the scattering of powered and unpowered films at different droplet densities.

We have fabricated 1.8-inch and 86,400-pixel poly-Si TFT-LCDs with a novel TFT structure and a storage capacitance (Cst) arrangement. The TFTs have a self-aligned offset structure which is made by a simple process without using an additional mask. With this structure, we have reduced the OFF current, and hence, attained a high ON/OFF current ratio of 10⁷. A novel Cst line arrangement called 'modified Cst on gate' was adopted. Gate lines and Cst lines are arranged alternatively, and the (n-1)-th Cst line is connected to the n-th gate line at the line's end. The Cst line works as redundancy of the gate line. Consequently, we have obtained TFT arrays with no line-defects (240 gate lines). By using these techniques, we have succeeded in fabricating a high-performance 1.8-inch poly-Si TFT-LCD panel for a projection TV.

The TSTN^TM (triple super twisted nematic) LCD is a successful method for obtaining color by stacking three panels, each of which subtracts out a primary color. Because the individual pixels of the three panels must line up to form one fully colored pixel, collimated light is needed. Incandescent lamps are easy to collimate, but are not as popular as fluorescent lamps in the display industry because of poorer efficacy, lifetimes, and color saturation. Fluorescent lamps are inherently diffuse sources that are difficult to collimate. By covering the inside of a hot cathode fluorescent lamp with a reflective MgO layer, small apertures can be made as bright as 50,000 foot lamberts. Individual lenses, centered on each aperture, can collimate these apertured sources.

We report here on analog modulation effects in ferroelectric liquid crystal (FLC) materials and electrical drive schemes that are appropriate to FLC/VLSI spatial light modulations (SLMs). The deformable-helix ferroelectric (DHF) effect paired with fixed-charge drive can give sub- millisecond grey-scale response with VLSI-compatible drive voltages. New DHF materials with long-pitch nematic phases give superior alignment quality and contrast ratio. We present analog FLC driver circuits suitable for VLSI implementation, and show that providing adequate read/write isolation in optically addressed FLC/VLSI SLMs requires special care.

A full-color video projector uses an active matrix LCD to modulate low-intensity addressing light in a photoactivated liquid crystal light valve projection system. This hybrid modulator delivers high aperture ratio for a bright, high-contrast projected image.

In supertwisted nematic (STN) display technology, a chiral compound is added to a nematic liquid crystal in order to induce a twisting helix. This helix is then bound into some angular configuration by surface anchoring energies on the plate of the LCD. Due to this confinement of the helix, deformations occur in its structure when a voltage is applied. One of the most interesting deformations which can occur is the striped domain instability. By constructing a cell such that the cholesteric-nematic threshold voltage (V_th) is higher than the domain formation voltage (V_c) we can induce 3 dimensional periodic deformations in the molecular orientation of the liquid crystalline material before the helical geometry of the cell is destroyed. We have constructed several types of Liquid Crystal Diffraction Devices (LCDD) based on this principle. Here we describe the theory of operation, device construction, and performance of such switchable LCDDs.

We use simulation methods based on those proposed by Baur, Windscheid, Berreman, etc. to get the complex transmission of the liquid crystal (LC) cell as a function of the properties of the LC material, cell dimensions, and the applied voltage. As a result, we obtain a complex locus representing the set of possible combinations of amplitude and phase as a function of the voltage applied to the cell. We propose criteria to estimate the suitability of the LC-cell for requirements for the modulation of phase and amplitude. Synthesis of the cell for given requirements is made by an appropriate selection of the thickness of the LC layer, angle of polarizers to rubbing direction, total twist angle, properties of the LC material, and wavelength of the light. The proposed criteria describe the ability of the LC spatial light modulator phase and amplitude of the lightwave and also give information about the difference between the desired and the realized transfer function.

The nonlinearity of the wire-grid liquid crystal light valve (WG-LCLV) is used to implement the nonlinear joint transform correlator for optical pattern recognition. Experimental results and computer simulations show the nonlinear characteristic of the WG-LCLV can produce well defined correlation peak and high peak to noise energy ratio.

Diffractive optical elements can be easily made and tested using programmable spatial light modulators (SLM's). We discuss limitations imposed by using SLM's for such purposes and present experimental results showing a variety of applications.

OASLMs incorporating an a-Si:H photosensor and ferroelectric liquid crystal have proved their high performance in optoelectronic processing systems. The final step in their development is to establish a long mean time between failures, consistent responsibility, gain, resolution, and gray level response. Some subtle properties of the alignment layers, the liquid crystals, and the operating conditions create bottlenecks to producing consistently performing devices. We examine these bottleneck issues and explore ways to extend the reliability of device performance.