Tristable switching

Antiferroelectric LC s with tristable switching have been known for the last ten years120,121. The chemistry of ferroelectric and antiferroelectric liquid crystals follows the rules valid for calamitic LC s, but with some additional constraints ... 

A.D.L. Chandani, E. Gorecka, Y. Ouchi, H. Takezoe and A. Fukuda, Anti-ferroelectric chiral smectic phases responsible for the tristable switching in MHPOBC, Jpn. J. Appl. Phys. 28(7), L1265-L1268, (1989). 

In conclusion of this chapter it should be stated that bistable and tristable switching of ferro- and antiferroelectric liquid crystals is very fast and provides long memory states. The latter allows one to design displays without semiconductor... 

Chandani, A.D.L., Gorecka, E., Ouchi, Y., Takezoe, H., Firkuda, A. Novel phases exhibiting tristable switching. Jprt J. Appl. Phys. 28, L1261-L1264 (1989)... 

In 1988, Fukuda and co-workers discovered the existence of liquid crystalline materials showing antiferroelectric properties [1], exhibiting tristable switching, as shown in Fig. 6.2.1. The alignment structure of these materials was concluded to be the one depicted in Fig. 6.2.2. 

Fig. 6.2.3 Concept for the driving method to realize grey scale expression using AFLC tristable switching.

The most important observation of AFLCs was made in 1988 before the identification of the antiferroelectric phase i.e., tristable switching with a sharp threshold and a double hysteresis [10], The tristable switching is observable by two methods, i.e., the electro-optic effect and the switching current measurements. These results are shown in Figure 9.2 [10], in which... 

So far, four display modes have been proposed in ferroelectric and antiferroelectric display applications, as shown in Figure 9.34. A bistable switching in surface stabilized ferroelectric liquid crystals (SSFLCs) has been manufactured as a passive matrix liquid crystal display (PM-LCD). The counterpart of AFLC is a tristable switching, which is also a promising candidate for PM-LCD. In addition to these PM-LCDs, active matrix displays (AM-LCDs) are also proposed in FLC and AFLC materials, i.e., deformed helix FLCD (DHFLC) and V-shaped LCD (VLCD). In this section, PM-AFLCD and AM-VLCD will be described. 

In the search for novel materials, particularly new ferroelectric materials, new phase types were also discovered, notably the antiferroelectric phase [56] which, with tristable switching characteristics, also has potential for display use, possibly overcoming some of the difficulties with ferroelectric systems and providing a further display device of high quality. 

Figure 16. Ordinary tristable switching (a) apparent tilt angle versus applied electric field (b) optical transmittance versus applied electric field (c) molecular tilt directions during the pretransitional effect and in the antiferroelectric (AF) and ferroelectric (F) states.

Note added in proof Quite recently, Itoh et al. reported that the phase in these pyrimidine host mixtures is not antiferroelectric but ferroelectric and that the typical tristable switching results from an ultra-short pitch of about 50 nm. (K. Itoh, Y. Takanishi, J. Yokoyama, K. Ishikawa, H. Takezoe and A. Fu-kuda, Jpn. J. Appl. Phys. 1997, 36, L784). 

Despite this circumstantial evidence and in the absence of a final model for the phase stmeture, we went into applied research to develop display devices. The basic principle of the device, as reported in the Japanese Journal of Applied Physics [48], is an electro-optical response that is based on a tristable switching, as shown in Fig. 9.1. As shown in Fig. 9.2 the tilt angle of the molecules led to a tristable state with two threshold values that show a double hysteresis. As shown in Fig. 9.3 it is possible to switch to either of the bistable states from the third state by applying... 

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