Sven T. Lagerwall

Submicrosecond bistable electro‐optic switching in liquid crystals

Ferroelectric smectic C (FSC) liquid crystals are used in a simple new geometry that allows the spontaneous formation of either of two surface‐stabilized smectic C monodomains of opposite ferroelectric polarization. These domains are separated by well‐defined walls which may be manipulated with an applied electric field. The resulting electro‐optic effects exhibit a unique combination of properties: microsecond dynamics, threshold behavior, symmetric bistability, and a large electro‐optic response.

Ferroelectric Liquid Crystal Electro-Optics Using the Surface Stabilized Structure

Abstract The strong linear coupling of the director ň to electric field E in ferroelectric liquid crystals can be utilized to perform high-speed electro-optic switching suitable for device applications. In this article we summarize the current understanding of the high-speed, bistable, threshold-sensitive electro-optic effects obtained in planar structures using surface interactions to suppress the spontaneous director helix characteristic of the bulk ferroelectric liquid crystal.

Solution of the dark state problem in antiferroelectric liquid crystal displays

So far, it has proven impossible to achieve an acceptable dark state between crossed polarizers for antiferroelectric liquid crystals (AFLCs), which otherwise would have an enormous potential for electro-optic applications, in particular for high-resolution full color displays. The reason lies in static and dynamic spatial fluctuations of the optic axis. As both have intrinsic causes it is not likely that the problem is ever going to be solved by improvement in alignment and addressing methods. We show that if the directors in alternating layers are orthogonal to each other, the AFLC acquires new optical properties such that the problem is eliminated, and a dark state extinction is achieved which is only limited by the quality of the polarizers. After having synthesized such a material, we have been able to demonstrate the predicted unique electro-optical properties of this new class of AFLC materials.

Ferroelectric Liquid Crystals

Abstract A review of the ferroelectricity in liquid crystals is given, beginning with a discussion of the symmetry properties allowing a macroscopic polarization in some of the more ordered liquid crystal phases. The fundamental mechanisms behind the dipolar ordering are discussed in some detail. The two linear electric effects, ferro- and flexo-electricity, give rise to completely different phenomena. In the smectic C phase there is one ferroelectric coefficient and nine flexoelectric ones, giving independent contributions to the polarization of the medium. We further discuss helical and non-helical structures, doped and intrinsic infinite-pitch ferroelectrics and, finally, the rich potential of liquid crystal ferroelectrics aligned in the »book-shelfgeometry» for fast electro-optic devices.

The molecular aspect of the double absorption peak in the dielectric spectrum of the antiferroelectric liquid crystal phase

Abstract The dielectric spectrum of the antiferroelectric smectic C∗ phase exhibits a low and a high frequency absorption peak (Pl, Ph) which have been studied as a function of temperature and bias electric field. Measurements from 10 Hz to 10 MHz were carried out with smectic layers parallel and quasi-perpendicular to the cell plates for the multicomponent mixture CS-4000 (Chisso). In addition to the orthogonal smectic A∗ phase, this material has four tilted phases, three narrow phases with a dielectric behaviour permitting us to classify two of them as C∗α (82·80° to 81·91°C) and C∗γ (80·10° to 79.17°C), and one broad antiferroelectric phase (79.17° to −10°C). On applying an increasing bias field, Δ∊ for both processes first increases by about a factor of two, then exhibits a maximum at a threshold field E c corresponding to the antiferroelectric-ferroelectric transition at which it decreases by almost one order of magnitude. In fact, at E c the PH peak vanishes and the PL peak shows up at a frequency s...

Material Properties of Ferroelectric Liquid Crystals and Their Relevance for Applications and Devices

Abstract Recent developments in understanding structural and material properties of ferroelectric liquid crystals are reviewed with emphasis on their relevance for electro-optic effects and device applications. In only a few years the material situation has changed from one characterized by an almost complete lack of technically useful materials to one, not yet adapted to technical needs, but beginning to offer interesting, commercially available ferroelectric mixtures. The present device limitations can, however, be tracked down, not so much to the principal non-availability of materials as to the lack of understanding of which material properties are desirable and needed, in particular to permit simple and efficient matrix addressing. Thus we have centered our discussion to properties of prime importance for device dynamics in this review, which also contains a general discussion of material properties based on the molecular structure, as well as an assessment of the present industrial development.

Electro-optic characteristics of de Vries tilted smectic liquid crystals: Analog behavior in the smectic A* and smectic C* phases

Chiral smectic A liquid crystal materials of the de Vries type (with molecules tilted relative to the layer normal) exhibit analog field-induced (electroclinic) optic axis rotation accompanied by an increase in birefringence. We identify two such de Vries smectic A* materials and use them to develop and test models for these characteristic electro-optic effects. These materials also exhibit colossal analog field-induced optic axis rotation in the lower temperature smectic C* phase, a consequence of polarization charge stabilization, and of polarization screening of the applied field in the liquid crystal.

Ferroelectric liquid crystals: The development of devices

Abstract The discovery of ferroelectric liquid crystals (1974) together with the subsequent discovery of the surface-stabilized liquid crystals (1980) have enriched the family of ferroelectrics with a new, different and powerful member. At the same time it has considerably raised the performance level of liquid crystals as general electro-optic media and opened up new opportunities in domains where fast processing is necessary, for instance in optical computing. The last few years have seen an important development in the technology of surface-stabilized ferroelectric liquid crystal (SSFLC) devices, which today offers solutions for full dynamic grey scale, full color, high speed, high resolution and high information processing and storage. An example of a very demanding industrial application now attracting the SSFLC approach and where the full range of the SSFLC potential will be required, is the large and flat screen high definition television (HDTV). In this paper we review some key events in the resea...

The case of thresholdless antiferroelectricity: polarization-stabilized twisted SmC* liquid crystals give V-shaped electro-optic response

We have studied the three-component liquid crystal mixture reported to exhibit ‘thresholdless antiferroelectricity’ [Inui et al., J. Mater. Chem., 1996, 6, 671]. We find that the thresholdless or V-shaped switching is obtained in the absence of antiferroelectricity. This analog electro-optic response is due to the field-induced switching of a twisted smectic C* structure stabilized by polar surface interactions and by electrostatic bulk polarization charge interactions. The latter confine the director twist to thin surface regions leaving the bulk of the cell uniform, which gives good extinction at zero field. In sufficiently thin cells, such thresholdless switching can in fact be followed down to much lower temperatures, where the bulk would be antiferroelectric, but is maintained in the cells in the ferroelectric state by hysteresis from surface action.

A Family of Ferroelectric Liquid Crystals with Very High Spontaneous Polarization

Abstract A new family of ferroelectric liquid crystals is presented. In particular, some mixtures of compounds from this family show an interesting combination of high spontaneous polarization, good alignment properties and room temperature smectic C* phase. Measurements are presented for transition enthalpies, refractive indices, X-ray tilt angle, electro-optic tilt angle and spontaneous polarization. The electro-optic response is described as measured in 2 micron thick shear-aligned cells.