Dynamic scattering modes

Thermotropic cholesterics have several practical applications, some of which are very widespread. Most of the liquid crystal displays produced use either the twisted nematic (see Figure 7.3) or the supertwisted nematic electrooptical effects.6 The liquid crystal materials used in these cells contain a chiral component (effectively a cholesteric phase) which determines the twisting direction. Cholesteric LCs can also be used for storage displays utilizing the dynamic scattering mode.7 Short-pitch cholesterics with temperature-dependent selective reflection in the visible region show different colors at different temperatures and are used for popular digital thermometers.8... 

Dynamic Scattering Mode Liquid Crystal Displays... 

Figure 3.2 Schematic representation of a dynamic scattering mode (DSM) LCDJ...

We should also note that the visualization of defects by a nematic liquid crystal, based on the flexoelectric effect in a spatially nonuniform field, is significantly more efiicient than in the dynamic scattering mode [81, 82], because of the higher contrast, the lower visualization voltages (3 to 4 times), and the lower leakage current (about 10 times) [84-86]. 

The turn-on time of presently available liquid crystals operating in the dynamic scattering mode is relatively long. According to Kochlman and Felici [101] the turn-on time of a nematic layer is given by the expression... 

Figure 41. Turn-on time of the dynamic scattering mode versus voltage U with the layer thickness d as parameter dj = 6pm, = 12pm, dj = 25 pm (after reference [69]).

Figure 61. Granulation free liquid crystal picture screen. Comparison of a test picture projected onto a conventional ground glass plate (a) and a liquid crystal layer in the dynamic scattering mode (b).

For driving matrix liquid crystal display panels, the silicon metal-oxide semiconductor field effect transistor (MOSFET) fabricated on a silicon monolithic wafer has been investigated by several groups [134-150]. The MOS transistor circuit fabrication techniques are well developed and have been used to produce various LSI devices. A dynamic scattering mode, a planar type GH mode or a polymer dispersed (PD) mode are used in these displays because the silicon wafer is intrinsically opaque. The circuit configuration of the panel is essentially the same as that of the p-Si TFT switch matrix addressed liquid crystal display panel as shown its equivalent circuit in Fig. 18(a). 

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