Molecular Orientations and Display Performance in FLC Displays

In typical FLC (Ferroelectric Liquid Crystal) displays, the FLC material is sandwiched between two substrates separated by around 2 pm. A number of molecular orientations have been found to be suitable for use in FLC displays and investigated. Some of these are summarized in Fig. 6.1.1. 

The orientations of the molecules of the FLC materials are classified by the presence or absence of a helical structure. The most famous FLC device is the SSFLC (Surface Stabilized FLC) [1], in which the helical structure of the FLC material is unwound. While a variety of molecular orientations have been applied in SSFLC devices, three molecular orientations appear to be the most useful in practical FLC displays.These are the bookshelf-layered structure and the Cl-uniform (CIU) and the C2-uniform (C2U) orientations [2]. Each of these structures shows monostability or bistability, depending on the material and its alignment properties. The monostable orientations are applicable to active matrix FLC displays while the bistable orientations are applicable to passive matrix FLC displays. FLC displays with a helical orientation have also been investigated. One useful FLC mode with the helical orientation is the DHF (deformed-helix ferroelectric) mode [3]. This mode is monostable and is thus suitable for an active matrix drive method. 

Molecular orientation is a very important factor in determining the performance of a display and thus in the development of practical FLC displays. The situation is more complex than with nematic liquid crystal displays because FLC displays require consideration of additional properties. These are the layered 

Several typical molecular orientations used in FLC displaj and the relationship between molecular orientation and display performance will be described in this chapter. This chapter will also describe how to realize a desired molecular orientation by optimizing material parameters, alignment parameters, etc. 

Section 2 covers the DHF mode with a helical structure. The bookshelf structure, the Cl-uniform (CIU) orientation, and the C2-uniform (C2U) orientation are described in Sections 3, 4, and 5, respectively. Section 6 covers the stability of the molecular orientations in FLC devices exposed to shock. Weakness in this respect is one of the intrinsic problems of FLC displays. The layer rotation behaviour, an intrinsic behaviour of FLC displays, is described in Section 7. 

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