Liquid crystal display (LCD) industry is among the most rapidly growing and innovating industries in the world. Here continuously much effort is devoted towards developing and implementing new types of LCDs for various applications. Some types of LCDs require relatively high voltages for their operation. For example, bistable displays, in which an altering field at different frequencies is used for switching from clear to scattering states and vice versa, require electric fields at around 10 V/μm for operation. When operated at such high voltages an electrical breakdown is very likely to occur in the liquid crystal (LC) cell. This has been one of the limiting factors for such displays to reach market.
In the present paper, we will report on the results of electrical breakdown investigations in high-voltage LC cells. An electrical breakdown in the cell is observed when current in the liquid crystal layer is above a specific threshold value. The threshold current is determined by conductivity of the liquid crystal as well as point defects, such as dust particles in LC layer, pinholes in coatings and electrode hillocks. In order to reduce the currents flowing through the liquid crystal layer several approaches, such as electrode patterning and adding of various buffer layers in the series with LC layer, have been tested. We demonstrate that the breakdown voltages can be significantly improved by means of adding insulating thin films.
If the inline PDF is not rendering correctly, you can download the PDF file here.
1. Chen J. Cranton W. and Fihn M. (2012). Handbook of Visual Display Technology 1st ed. Springer-Verlag Berlin Heidelberg.
2. Geis M. W. Lyszczarz T. M. Osgood R. M. and Kimball B. R. (2010). 30 to 50 ns liquid-crystal optical switches. Opt. Express 18 (18) 18886-18893.
3. Lu Y. Guo J. Wang H. and Wei J. (2012). Flexible bistable smectic-A liquid crystal device using photolithography and photoinduced phase separation. Adv. Condens. Matter Phys. 2012 1-9.
4. Coates D. Crossland W. A. Morrissy J. H. and Needham B. (1978). Electrically induced scattering textures in smectic A phases and their electrical reversal. Journal of Physics D: Applied Physics 11 (14) 2025-2034.
5. Neusel C. and Schneider G. A. (2014). Size-dependence of the dielectric breakdown strength from nano- to millimeter scale. J. Mech. Phys. Solids 63(1) 201-213.
6. Palmer S. (2005). Fast Optical Shutter. US 2005/0206820 A1 2005.
7. Grote J. G. (2001). Effect of conductivity and dielectric constant on the modulation voltage for optoelectronic devices based on nonlinear optical polymers. Opt. Eng. 40(11) 2464-2473.
8. Scharf T. (2006). Polarized Light in Liquid Crystals and Polymers 1st ed. Wiley-Interscience.
9. Dierking I. (2001). Dielectric breakdown in liquid crystals. J. Phys. D. Appl. Phys. 34 (5) 806-813.
10. Nandi S. K. Llewellyn D. J. Belay K. D. Venkatachalam K. Liu X. and Elliman R. G. (2014). Effect of microstructure on dielectric breakdown in amorphous HfO2 films. Microsc. Microanal. 20(3) 1984-1985.
11. Mahdy A. M. Anis H. I. and Ward S. A. (1998). Electrode roughness effects on the breakdown of air-insulated apparatus. IEEE Trans. Dielectr. Electr. Insul. 5(4) 612-617.
12. Wetz D. Mankowski J. and Kristiansen M. (2005). The impact of electrode area and surface roughness on the pulsed breakdown strength water. 2005 IEEE Pulsed Power Conference 1163-1166.
13. Li T.-C. and Chang R.-C. (2014). Improving the performance of ITO thin films by coating PEDOT:PSS. Int. J. Precis. Eng. Manuf. Technol. 1(4) 329-334.