P‐125: Optimisation of the Mechanical Stability and Rewriting Speed of Optically Rwritable e‐Paper

Abstract

Process optimization for increasing the response speed of liquid crystal optical rewritable e-paper was investigated. It is demonstrated that by filling LC in atmosphere condition rewriting time could be decreased to 6 seconds with good repeatability. Increasing the spin coating speed and time could also decrease the azimuthal anchoring energy, but it will cause non-continuous film form of alignment layer which causes large speed dispersion that is not good for practical use. Serial experiments show that with smaller azimuthal anchoring energy the rewriting time could be smaller. The results demonstrate that with proper fabrication process of alignment layer for liquid crystal optical rewritable e-paper, azimuthal anchoring energy could be adjusted to an optimal value which is beneficial for achieving fastest rewriting speed and at the same time strong enough to well align LC. Keywords: optical rewritable; anchoring energy; rewriting speed; azo-dye; Oral/Poster Preference: Either oral or poster presentation; Symposium Topic: Liquid Crystal Technology; Background and ObjectivesE-paper is one type of display device designed to mimic the ordinary paper, which requires ultra low or zero power consumption. It should use no backlight and is capable of holding text and images without applying any electricity, while allows the image to be changed later. High level complexity of driving electronics often causes problems of insufficient durability of flexible conductor and contact bonding to the epaper application of nematic liquid crystal (NLC) [1][2][3][4][5][6][7][8][9][10][11]. We developed an optically rewritable (ORW) display [12][13][14][15][16][17][18][19][20][21] by separating e-paper display unit from driving electronics, significantly reducing the complexity of the ORW e-paper structure. This separation makes the ORW e-paper much more durable and cheaper and ready for the flexible challenge. By using ORW technique, text or images of LC e-paper can be obtained in a one-mask step exposure process. First, uniform alignment over the entire substrate surface is created. Then, exposure process was done again using one mask with text or image information shadowed in desired regions, and finally the alignment in the non-shadowed area is simply rewritten to desired orientation. The process is fully compatible with standard photolithography exposure equipped with adjustable polarizer. ORW technology is still limited to laboratory application field mainly due to long rewriting time. Previous paper shows that the operational time of the ORW e-paper using E7 LC was about 11 seconds exposed by 125 mW/cm 2 polarized light from a highpressure Hg lamp filtered with a peak at 450 nm [15]. We have investigated the effect of LC type on the rewriting speed of ORW e-paper and demonstrated that the rewriting speed can be increased by selecting 5CB LC [22]. However, phase transformation point for 5CB from nematic to isotropic state is as low as 35°C, which makes it impossible to be used in hot environment.In this study, we inve...