Bistable switching effect

In solid state all the 10 pyroelectric crystal groups allow in principle for bistable switching behaviour. This is the proper ferroelectricity. Under certain conditions ferroelectricity (improper) can be realized in liquid crystals. This was shown by Meyer and coworkers115 in 1975. Since that time intense activities have been initiated, applying this property for flat-panel devices, switches, light modulators etc. In principle, three effects can be observed and used ... 

Let us mention the case of tetrakis(methyltelluro)TTF [76]. This material is (already) in the quasi-ionic phase at 300 K and it undergoes dimerization below 240 K. Some measured values of the threshold field Eth above which jumps of current density occur are = 300 V/cm at 200 K, = 600 V/cm at 180 K, and = 1100 V/cm at 160 K. Crystals have typical dimensions of 0.8 x 0.8 x 0.2 mm3. This material was also chosen to build a prototype bistable device which utilized the switching effect [76]. 

Figure 1. The property displayed by an active subunit may depend according to a sigmoidal mode upon an external parameter by means of an appended bistable control unit. A dramatic variation of the property features a switch effect.

The existence of two or more thermodynamically stable states with different optical transmission is a very important feature of FLC cells. As mentioned above, bistable switching or bistability is realized in the Clark-Lagerwall effect. In this section, we will consider the influence of physical parameters and cell configuration on the appearance of the phenomenon. Reliable reproduction of bistability conditions is very crucial for technological applications. 

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