Plasma-beam alignment technique for ferroelectric liquid crystals Gurumurthy Hegde Oleg Yaroshchuk (SID Member) Ruslan Kravchuk Anatoli Murauski Vladimir Chigrinov (SID Fellow) Hoi Sing Kwok (SID Fellow) Abstract — The plasma-beam alignment procedure earlier developed for the alignment of nematic liquid crystals is successfully extended to ferroelectric liquid crystals (FLC). The highly uniform align- ment of the “chevron” structure (before electrical treatment of FLC cells) and “quasi bookshelf” struc- ture (after the electrical treatment) are realized. The contrast of bistable switching larger than 350:1 is achieved. This makes the non-contact plasma-beam alignment procedure especially attractive for high-contrast bistable LCDs on an LCOS base, particularly used in PDA and e-books. Fast switching and realization of gray scale in the plasma-beam aligned FLC cells makes this technique also promising for full-color displays including color LCD TV. Keywords — Feroelectric liquid crystal, FLC LCD, FLC alignment, plasma-beam alignment, ion-beam alignment. DOI # 10.1889/JSID16.10.1075 1 Introduction The discovery of ferroelectricity of the chiral smectic-C phase (SmC*) by Mayer et al. 1 in 1975 and the practical realization of bistable electrical switching in these phases by Clark and Lagerwall 2 in 1980 were very influencial in the development of liquid-crystal displays (LCDs). The bistable switching in these materials, coined as ferroelectric liquid crystals (FLC), was realized in thin cells in which the helical structure was suppressed. The FLC-display prototypes excel in wide viewing angle, fast response time, and ultra- low power consumption, showing revolutionary improve- ments compared with present-day TN-LCDs. Because of this, FLC-LCDs are recognized as one of the most promis- ing devices for future displays. Their potential is especially high for high-contrast LCDs used in portable devices and color television. Despite their very high potential, FLC devices are still not commercialized mainly because of alignment problem. Good alignment of FLC cannot be easily attained, as in the case of nematic LC because of the layered helical structure. The alignment force will not only provide uniform align- ment of the FLC layers, but also suppress the helix of the vector of spontaneous polarization. In practice, this prob- lem is solved either by the introduction of aligned polymer networks (polymer-stabilized FLC) 3 or by proper treatment of the boundary substrates confining FLC film (surface-sta- bilized FLC). In the latter case, in parallel with traditional rubbing, 2 alternative alignment processes have been consid- ered. Among them are photoalignment, 4,5 vapor deposi- tion, 6,7 and ion-beam sputtering deposition 8 of the SiO x layers. Special treatment of FLC cells, such as low-fre- quency ac field treatment 9 and treatment based on the tem- perature gradient, 10 are additionally used to improve alignment generated by these methods. In the present paper, we consider a novel approach for the surface stabilization of FLC films. It consists of aniso- tropic etching of the alignment substrates by the obliquely incident beam of accelerated ions or plasma. Recently, this process was successfully applied for the alignment of con- ventional nematic LC 11–13 and “passive” LC such as reac- tive mesogens and semiconducting LC used in optical films and surface electronics. 14 This technique provides excellent alignment uniformity of LC on a macroscopic and micro- scopic scale, wide range variation in pretilt angle and anchoring energy, and good electro-optic performance. Two types of alignment of nematic LC were observed: easy axis in the plane of the plasma-beam incidence and perpendicu- lar to this plane. These types of alignment were coined as the first and second alignment modes. The transition from the first to the second alignment mode was observed with increasing exposure dose. 15 The present paper shows that plasma-beam alignment can also be successfully extended for the alignment of FLC. Alignment by this method results in FLC films having excel- lent uniformity and demonstrating high electro-optic contrast. The most effective applications of plasma-beam-aligned FLC layers are discussed. 2 Experimental details 2.1 Preparation of substrates We used films of polyimide AL3046 from JSR for the bounding substrates. The polymer layers were spin-coated at 3000 rpm on glass slides (2 × 3 cm) containing patterned ITO electrodes and subsequently baked at 80°C for 5 min and then at 180°C for 1 hour. In the following, the substrates were processed by the plasma-beam alignment technique. G. Hegde, A. Murauski, V. Chigrinov, amd H-S. Kwok are with the Hong Kong University of Science and Technology, Dept. of ECE, Clear Water Bay, Kowloon, Hong Kong; telephone +852-2358-8528, fax –8520, e-mail: murthyhegde@gmail.com. O. Yaroshchuk is with the Hong Kong University of Science and Technology, Kowloon, Hong Kong, and The Institute of Physics, National Academy of Sciences, Ukraine. R. Kravchuk is with The Institute of Physics, National Academy of Sciences, Ukraine. © Copyright 2008 Society for Information Display 1071-0922/08/1610-1075$1.00 Journal of the SID 16/10, 2008 1075