Proceedings Volume 1257

Liquid Crystal Displays and Applications

J. William Doane, Zvi Yaniv
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Proceedings Volume 1257

Liquid Crystal Displays and Applications

J. William Doane, Zvi Yaniv
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 1 April 1990
Contents: 3 Sessions, 16 Papers, 0 Presentations
Conference: Electronic Imaging: Advanced Devices and Systems 1990
Volume Number: 1257

Table of Contents

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Table of Contents

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  • Developments in Polymer-Dispersed Liquid Crystals
  • Optical Elements Using Liquid Crystal Materials
  • Liquid Crystal Materials and Display Applications
  • Optical Elements Using Liquid Crystal Materials
Developments in Polymer-Dispersed Liquid Crystals
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Phase diagram and phase separation in LC/prepolymer mixture
Yoshinori Hirai, Satoshi Niiyama, Hiroshi Kumai, et al.
A new method to obtain liquid crystal and polymer composite(LCPC) material is reported. This material is a new electro-optic material which can control scattering and transparent states in an electric field. e obtained this material by the photo-polymerization-induced phase separation from liquid crystal and prepolymer mixture where both monomer and oligonier are used as prepolymer. We have found new type of phase diagram in this mixture which has a nematicisotropic line in addition to binodal and spinodal lines. Electro-optic properties of this material are strongly affected by the point on the phase diagram at which the polymerization-induced phase separation starts. This method enables us to control these properties such as voltage-transmittance characteristics. Typical devices using these materials are also shown. They have high contrast ratio and high transmittance in ON state and are suitable for display devices. Drive voltage can be reduced by optimizing this material and the device with high contrast ratio about 200:1 in low drive voltage below 6Vrms was obtained.
Polymer-dispersed liquid crystal films formed by e-beam cure
Nuno A. Vaz, George W. Smith, G. Paul Montgomery Jr.
Polymer-dispersed liquid crystal (PDLC) films are useful in electro-optic applications because they can be switched electrically between opaque and transparent states. We have prepared PDLC films using electron-beam radiation (e-beam cure). The resulting films exhibit promising mechanical, electro-optic, and thermal response. Compared with the ultraviolet cure process, e-beam cure has the advantage of not requiring photoinitiators. In addition, e-beam cure is characterized by a fast cure rate. The e-beam cure method may, therefore, be a good candidate for production of PDLC ifims.
Dielectric losses in a polymer-dispersed liquid crystal film
Jack R. Kelly, Desmond L. Seekola
We have measured the dielectric response of PDLC films containing liquid crystal droplets of E7 in a polymethylmethacrylate (PMMA) matrix as a function of frequency (0-10KHz) and temperature (25°C-11O°C). The liquid crystal composition of the films was varied from 0% to 60%. A principal objective of this study was to understand the dissipation mechanisms in these systems in an effort to control and reduce them. In the light of the experimental results, we discuss the primary dissipation mechanisms, including both DC and AC losses. The major contribution to the losses in these materials comes from the liquid crystal conductivity. Quantitative interpretation of the results can be clouded by a number of factors including incomplete phase separation of the liquid crystal and polymer, percolation effects and a frequency-dependent conductivity due to charge-carrier depletion in the liquid crystal droplets. Using simple two-phase composite formuli to model the dielectric behavior, the contributions of the real and imaginary parts of the dielectric constant to the field inside a droplet are discussed. The model agrees quantitatively with capacitance experiments, indicating that for frequencies below 100 Hz the field inside of a droplet is strongly modified by charge built up at the droplet/polymer interface.
Droplet size and shape effects in nematic droplet/polymer films
Paul S. Drzaic
Control over the operating voltage of nematic droplet/polymer films continues to be an important area of development in this class of devices. Our recent work in this area has included both materials modifications in order to alter the reorientation voltages of these films, as well as efforts to tie theory to experimental results. Here, we present evidence which shows that the shape of nematic droplets in these films is important in determining the operating voltage of a film. Specifically, we show two film systems in which the nematic droplets adopt the shape of oblate spheroids, but differ in the amount of eccentricity of the droplets. The more distorted droplets require higher reorientation fields, consistent with the model of the volume elastic deformation free energy as a major factor affecting the reorientation fields of these films. We also demonstrate that the apparent operating voltage of a film depends on which property of the film is being measured. Measurements based on film scattering, dichroism, and capacitance are presented, and the implications of these measurements with regards to apparent film operating voltages discussed.
Liquid crystal mixtures for polymer matrix displays
David Coates, S. Greenfield, I. C. Sage, et al.
Chemically stable , wide temperature range nematic liquid crystal mixtures with birefringence values up to almost 0 .3 are described . For applications where high ultra-violet stability is required a range of mixtures optirnised for this application have been developed. Chemically stable mixtures with a lc*i threshold voltage have also been developed and are compared with standard mixtures.
Reverse-mode microdroplet liquid crystal display
Yao-Dong Ma, Bao Gang Wu, Gang Xu
This paper presents the production of the a reverse-mode microdroplet liquid crystal (RMLC) light shutter display. In this unit, the display is formed by a thin polymer film with dispersed liquid crystal microdroplets. The display is light transmissive in the absence of an applied electrical field. The display is converted to a non-transmissive state (i.e. absorbing or scattering) when an electrical field is applied. The "off' and "on" state. of this display are thus exactly opposite to that encountered in "normal-mode" microdroplet liquid crystal display devices such as polymer dispersed liquid crystals (PDLC)15 or Nematic Curvilinear Aligned Phase (NCAP)6. The Reverse Mode Microdroplet Liquid Crystal is obtained by modification of the surface energy of the polymer which encases liquid crystals via reaction of a dopant incorporated inside of the microdroplet during the droplet formation within the inside polymer layer. The liquid crystal used in RMLC is of negative dielectric anisotropy.
Optical Elements Using Liquid Crystal Materials
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Textures of polymer-dispersed chiral liquid crystal microdroplets
Deng Ke Yang, Peter P. Crooker
We have microscopically observed the texture of very large droplets of chiral liquid crystal in a polymer matrix under the influence of an electric field. The dielectric anisotropy of the liquid crystal is negative and the pitch is made very long so that a fingerprint-like texture can be observed within the droplet. Without the field, the droplets appear to be in a spherulite texture: the helical axis lies everywhere along a radius and a disclination line extends from the center to the periphery of the droplet. As an electric field is applied, the droplet undergoes a transition to the planar texture, the texture first occurring near the center of the droplet and increasing in radius as the field is increased. The zero-field texture will be discussed in terms of the Frank-Pryce spherulite model. Implication for a polymer-dispersed chiral liquid crystal (PDCLC) display will be reviewed.
Director configurations and configuration transitions in PDLC material
John H. Erdmann, Slobodan Zumer, Brian G. Wagner, et al.
The molecular anchoring strength for the liquid crystal E7 (EM Chemicals) confined to spherical cavities dispersed in the polyurethane TU5OA (CONAP) is measured. The anchoring strength values result from a study of the radial-to-axial configuration transition when perpendicular anchoring conditions exist at the polymer/liquid crystal interface. This transition is also a function of droplet radius, temperature, and the strength of any external fields present. A study of field-induced configuration transitions provides values for the reduced local electric fields inside droplets. Computer simulated pictures of nematic droplets are formed to identify director configurations.
Dichroic dye containing polymer-dispersed liquid crystal films
John L. West, Renate Ondris-Crawford, Meg A. Erdmann
Polymer dispersed liquid crystal (PDLC) devices modulate light through electrically controlled light scattering. Colored PDLCs are formed by incorporation ofdichroic dyes. The efficiency ofthe dichroic dye, PDLC films depend on the scattering efficiency of the films, the dichroic ratio of the dichroic dye, the order parameter ofthe dichroic dye in the liquid crystal used, and the fraction ofdye dissolved in the liquid crystal droplets. The efficiency of these films can be measured using a UV/visible spectrometer. Incorporation of dichroic dye in the PDLC film increases the refractive indices of the liquid crystal droplet affecting the scattering efficiency ofthe PDLC film.
Synthesis and properties of liquid crystalline materials with high optical anisotropy
Volker Reiffenrath, Ulrich Finkenzeller, Eike Poetsch, et al.
Liquid crystalline materials with high optical anisotropy are of great interest for many electrooptical devices, such as STN and 2'-Mithmum Active Matrix Displays. Use of these materials leads to improved response times by using smaller cell gaps as well as enhanced contrast. As standard materials for achieving high optical anisotropy cyanobiphenyls and cyanoterphenyls are used at present. The demand for materials with lower viscosity as well as improved stability and resistivity has led us to develop new materials to meet these requirements. Introduction offluorine and fluorine containing substituents (CF3, OCF3, OCHF2) in terminal position ofhigh nstructures leads to new liquid crystals with high positive dielectiic anisotropy and good stability. Also liquid crystals with negative dielectñ anisotropy can be obtained by the incorporation of an 2,3-difluoro-l,4-phenylene moiety.
Full-color subtractive light valve for display applications
J. Robert Trimmier, Ronald S. Gold, Karen E. Jachimowicz, et al.
A full-color miniature light valve is being investigated for display applications. The light valve is based on a subtractive rather than an additive approach to color mixture. In utilizing a subtractive color approach, a full-color information display is created using a single broadband light source whose energy passes through a stack of three thin liquid crystal cells. Each cell contains a different dichroic dye (e.g. cyan, magenta, and yellow) in a guest/host arrangement with the liquid crystal medium. Each dichroic guest/host liquid crystal cell constitutes an electronic color filter, switchable by the application of an appropriate voltage across the two plates of the cell. In one extreme state, the cells simply pass all spectral components of the light, while in the other extreme state the spectral composition of light passing through the cells is altered by the particular dichroic dye so that the complementary color of the dye is blocked or subtracted from passage through the cell. Voltages between the extremes produce the gradations in spectral throughput required for fullcolor operation. The achievable color gamut will be approximately equal to a shadow-mask color CRT. With a pixel addressing mechanism in each of the cells, a full color information display is created with complete color control at each individual pixel.
Liquid Crystal Materials and Display Applications
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Gray-scale ferroelectric liquid crystal devices
David Armitage
Ferroelectric liquid-crystal gray-scale effects are reviewed. The experimental behavior of a charge-controlled surfacestabilized ferroelectric liquid crystal pixel of area 1 mm2 is reported. Obliquely evaporated silicon-oxide alignment is compared with rubbed-nylon alignment. The experimental behavior of a deformable helix ferroelectric liquid crystal cell is reported.
Automated equipment considerations for liquid crystal display production
John C. Varney
The recent development of large multiplex and active matrix liquid crystal displays (LCD's) has increased the need for efficient automation. Spacing and plate-to-plate alignment control both have to be improved and cost effective production of these high information content systems requires efficient processing and high yields. Yield is dependent on process and contamination control and can only be effectively improved by process development and automation. While automation is necessary, a key problem is designing the production facility to be cost effective. This has been achieved in the past by producing large quantities of the same product in order to avoid costs associated with changing machine set-ups. The array process for standard LCD's was developed to minimise handling costs and to minimise investment by designing the production line to work with one substrate size. This system allows production of different sizes and styles of product within the line substrate size limitation, the major constraint being efficiency of fit. Substrate handling problems and tighter process control requirements now require the development of standardised systems to cope with the large substrate sizes. The design of automated LCD production equipment is discussed in relation to the problems of automating in a cost effective manner.
Variable parameters for bonding heat seal connectors to flat panel displays
James R. Bouldin, Roger R. Reinke
This paper reports on a study of the three basic parameters involved in bonding heat seal connectors to flat panel displays. Those parameters are: temperature. at the bond, pressure at the bond, and the time that the temperature and pressure are applied to the bond.
Thickness and angular dependency of color change in TN LCDs
Shui-Chih A. Lien, S. Suzuki
The background color of a TN LCD is one of the important issues of the liquid crystal flat panel display technology, especially as the panel size gets bigger and the displayed information content gets larger. Therefore, in the first part of this paper, we carried out (1) a theoretical calculation of the color coordinates as a function of And for the range of the ind from 0. 1 jm to 2.0 jtm, which cover the first, second, and third Gooch and Tarry minima; and (2) theoretical calculations for the color coordinates as a function of viewing angle near the first, second and third Gooch and Tarry minima. Our experimental results corresponding to the above two cases will also be presented for cornparison. Our data shows that our theoretical results agree reasonably well with the experimental ones. In the second part of this paper, we will use the above experimentally verified theoretical method to study and compare the color quality of the single-gap NB mode, the multi-gap NB mode, and the NW mode LCDs. The result will provide important information for LCD design and the selection of a mode of operation.
Optical Elements Using Liquid Crystal Materials
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Collective and molecular processes in ferroelectric liquid crystals and their application aspects
Wolfgang Haase, S. Wrobel, Matthias Pfeiffer
In tilted smectic phases C Sm C, Sm 1, Sm F and Sm / ) consisting of polar non-centrosymmetric molecules, a pronounced contribution to the dielectric permittivity is observed, which can be assigned to the Goldstone mode. It is a collective process showing a non-Arrhenius type behaviour in the temperature dependence of the relaxation time . By applying a bias electrical field, which is strong enough to unwind the helix, the Goldstone mode contribution can be suppressed . In all smectic phases there are high frequency relaxations arising from the principal molecular motions, i. e. from the reorientations about the long and short molecular axes. In the vicinity of the Sm A* Sm C* phase transition the so-called soft mode appears obeying Curie-Weiss behavior of the dielectric increment. Application aspects of different chiral smectics will be discussed in view of the different relaxation mechanisms by taking the recent experimental studies into account.