Patent
1987-06-15
1990-02-27
Miller, Stanley D.
350333, 350340, G02F 113
Patent
active
049040642
DESCRIPTION:
BRIEF SUMMARY
INTRODUCTION
The present invention relates to the art of electronic driving of liquid crystal devices, more precisely those devices containing a liquid crystal medium that, at least partly, shows a linear response to an applied electric field. Examples of such liquid crystal media are ferroelectric and flexoelectric liquid crystal configurations. All chiral tilted smectic liquid crystals are ferroelectric and also have the potential of showing a flexoelectric response in a number of deformed configurations. Nematic liquid crystals behave flexoelectric in certain deformed configurations. Presently, great expectations are being attached to the ferroelectric liquid crystals (FLC) due to some valuable and long sought for properties that can hardly be found in the other kinds of liquid crystals. This is particularly true for the so-called surface-stabilized ferroelectric liquid crystals (SSFLC) which have been made polarizable by surface interactions and in which any inherent helix, even if present in the bulk, would nevertheless not appear as a result of the same surface interactions. SSFLC cells are easily polarizable and are capable of high speed, bistability, grey scale and colour performance. These properties are, however, very sensitive to, and interrelated with, the design and alignment of the cell, and with the design of the addressing scheme required for the electric pulse driving circuitry. A small number of operating ferroelectric devices have been demonstrated but so far no really satisfactory driving schemes have been proposed and applied to the ferroelectric case. This is due to the fact that not all the important differences between FLC and nematic driving characteristics have been recognized and thus the addressing requirements not fully analyzed. Driving schemes proposed so far can be found in the European patent application 0 092 181 (Hitachi, filing date Apr. 14, 1983), in the German patent application DE 3 414 704 Al (Canon Inc, filing date Apr. 18, 1984), in the German patent application DE 3 443 011 Al (Canon Inc., filing date Nov. 26, 1984) and in the European patent application 0 149 899 (Seiko Instruments and Electronics, filing date Dec. 7, 1984).
The prior art devices and methods might work more or less well under certain conditions, but in view of our analysis of the prevailing conditions, particularly in SSFLC devices, the prior art propositions will not be able to solve the problems of electrical addressing, especially with respect to good optical contrast. The problems are accentuated by the physical dimensions and properties of SSFLC devices, where the liquid crystal is confined in a very small space between two plates. This means, among other things, that charge accumulation on the plate surfaces will create substantial electrical fields, which are objectional in several ways.
It is an object of the present invention to design a method for electrically addressing liquid crystal devices, which takes into account those difficulties, in order to fully utilize the intrinsic advantages of bistability and fastness, particularly in FLC devices.
For the FLC addressing, which has to be considerably different from conventional liquid crystal addressing, general requirements will now first be identified and then, finally, examples will be given for well-performing multiplex addressing schemes.
The present invention will now be elucidated by reference to the drawings.
FIG. 1 is a schematic sketch showing in cross-section a ferroelectric liquid crystal configuration.
FIG. 2 shows modular orientation corresponding to FIG. 1 in a perspective view.
FIG. 3 is a diagram demonstrating typical time-voltage dependence of switching in ferroelectric liquid crystals.
FIG. 4 shows the optical response for electrical pulses of different duration.
FIGS. 5 and 6 illustrate basic polar driving of one pixel or linear array devices.
FIG. 7 shows several examples of DC compensated switching waveforms.
FIG. 8 gives an example for DC compensated driving of a linear array.
FIG. 9 explains DC and AC-stabilization
REFERENCES:
patent: 4367924 (1983-01-01), Clark et al.
patent: 4508429 (1985-04-01), Nagai et al.
patent: 4563059 (1986-01-01), Clark et al.
patent: 4564266 (1986-01-01), Durand et al.
patent: 4591886 (1986-05-01), Umeda et al.
patent: 4625204 (1986-11-01), Clerc
patent: 4712877 (1987-12-01), Okada et al.
patent: 4715688 (1987-12-01), Harada et al.
Kondo et al., "A Practical Method of Preparing Thin Homogeneous Ferroelectric Smectic Cells for Electro-Optical Microsecond Switches", Japanese J. of Appl. Phys., vol. 22, No. 2, 2/1983, pp. L85-L87.
Blinov, "Electro Optical and Magneto-Optical Properties of Liquid Crystals", John Wiley & Sons Ltd., N.Y., pp. 134-145, 1983.
Lagerwall Sven T.
Wahl Jurgen
Mai Huy K.
Miller Stanley D.
S.A.R.L. S T Lagerwall
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