Bistable twisted nematic

T. Tanaka, Y. Sato, A. Inoue, et al., A bistable twisted nematic (BTN) LCD driven by a passive-matrix addressing, Proc. Asia Display 95, 259 (1995). 

Z. L. Xie and H. S. Kwok, New bistable twisted nematic liquid crystal displays, J. Appl. Phys. Lett, 84, 77 (1998). 

H. Cheng and H. Gao, Optical properties of reflective bistable twisted nematic liquid crystal display,... 

F. Zhou and D.-K. Yang, Analytical solution of film compensated bistable twisted nematic liquid crystal displays, J. Display Tech., 1, 217 (2005). 

There are two types of matrix addressing schemes— passive and active. The passive matrix (PM) addressing scheme requires the row and coluiim electrodes to address each individual pixel. This scheme still promises well in the area of bistable device such as ferroelectric liquid crystal (FLC) display and bistable twisted nematic (BTN) display because they do not need a control unit for gray-scale capability. The active matrix (AM) addressing scheme is the most developed and widely adopted one in cmrent LC displays. In this scheme, each pixel is cormected to a small electronic switch or TFT made with o-Si, poly-Si, or CdSe. This switch not only enables the pixel to hold the video information until it can be refreshed, but also prevents cross talk among neighboring addressed pixels. 

Figure 4.12 Switching behavior of the jr-BTN bistable LC cell with asymmetrical anchoring conditions [46]. Top optical response bottom switching pulse train. Reproduced from F. Yeung and H.-S. Kwok, Truly bistable twisted nematic liquid crystal display using photoalignment technology. Applied Physics Letters 83, 4291 (2003), American Institute of Physics...

F. Yeung and H.-S. Kwok, Truly bistable twisted nematic bquid crystal display using photoaUgnment technology. Applied Physics Letters 83, 4291 (2003). 

The degree of stability of supertwisted bistable twisted nematic (SBTN) displays is shown to improve considerably in nematic twist configurations generated by photoaligned and domain-stabilized bias tilt angle patterns on one or both display substrates. Incorporation of uniaxial optical retarders into SBTN-LCD was shown to result in black and white display operation. 

Figure 6.1 Optically bistable, photoaligned, supertwisted nematic LCD [1]. Reproduced from M. Stalder and M. Schadt, Photoaligned bistable twisted nematic liquid crystal displays. Liquid Crystals 30, 285 (2003)...

Fig. I. Schematic diagrams of the contrast versus the applied field for (a) a twisted nematic, (b) a cholesteric guest-host bistable display (Wysocki ei al., 1972 Ohtsuka and Sukamoto, 1973), and (c) a bistable LCD (Boyd et al., 1982).

The concept of defects came about from crystallography. Defects are dismptions of ideal crystal lattice such as vacancies (point defects) or dislocations (linear defects). In numerous liquid crystalline phases, there is variety of defects and many of them are not observed in the solid crystals. A study of defects in liquid crystals is very important from both the academic and practical points of view [7,8]. Defects in liquid crystals are very useful for (i) identification of different phases by microscopic observation of the characteristic defects (ii) study of the elastic properties by observation of defect interactions (iii) understanding of the three-dimensional periodic structures (e.g., the blue phase in cholesterics) using a new concept of lattices of defects (iv) modelling of fundamental physical phenomena such as magnetic monopoles, interaction of quarks, etc. In the optical technology, defects usually play the detrimental role examples are defect walls in the twist nematic cells, shock instability in ferroelectric smectics, Grandjean disclinations in cholesteric cells used in dye microlasers, etc. However, more recently, defect structures find their applications in three-dimensional photonic crystals (e.g. blue phases), the bistable displays and smart memory cards. 

Fig. 12.16 Bistable twist cell. Right- and left-handed twist-structures of a nematic liquid crystal with the same elastic energy (a) and the angular dependence of total free energy (b)...

When a bistable TN display is optimized, the transmittance of one of the stable states should be 0 and the transmittance of the other stable state should be 1. The parameters of the display are the twist angles (f). In + (p) of the stable states, the angle a,- of the entrance polarizer, the angle of the exit polarizer, and the retardation F of the liquid crystal. As discussed in Chapter 3, the transmittance of a uniformly twisted nematic display in the geometry shown in Figure 3.3 is... 

A bistable photoswitchable reflective liquid crystal display (PRLCD) based on azo-dye doped liquid crystal (DDLC), which can be written, erased, and rewritten by changing the polarization of a writing laser beam has been demonstrated [2], The mechanism is primarily due to thephotoinduced adsorption of azo-dyes doped in the LC cell. Linearly polarized diode-pumped solid-state laser light with X = 532 nm and an intensity of 150 mW/cm was employed as a writing beam to switch the DDLC sample from a homogeneous texture to a 45° twisted nematic (TN) one (Figure 6.2). 

There are several types of bistable nematic LCDs that have good performance characteristics. They are twisted-untwisted bistable nematic LCD [9-13], zenithal bistable nematic LCD [14,15], surface-induced bistable nematic LCD [16-19], mechanically bistable nematic LCD and bistable STN-LCD [20-24], A bistable nematic material has two bistable states with... 

The effects of bistability and hysteresis in supertwisted nematic layers were first investigated in [122]. To obtain twist angles larger than 90 , nematics were doped with a small amount of an optically active material. Thus a cholesteric (or chiral nematic) with a large pitch P was created, so that the pitch value had to adjust the boundary conditions for the directors on the substrates. The corresponding texture was first discovered by Grandjean and is discussed in Chapter 6. In 1984 the display based on the Supertwist Birefringent Effect (SBE) was proposed [123]. 

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