E-Paper Displays

5Bistable Cholesteric Liquid Crystal Displays – Review and Writing Tablets

Clinton Braganza and Mauricio Echeverri

Kent Displays Inc., Portage Blvd, Kent, OH, USA

5.1 Introduction

Cholesteric liquid crystals (ChLC) were the beginning of this incredible phase of matter – discovered in the late nineteenth century. It was not till the late twentieth century that researchers at the Liquid Crystal Institute at Kent State University exploit their true applications and usefulness. Today, ChLCs are well suited for ePaper and more. They have multiyear bistability and do not require any polarizers or color filters to produce images [1]. ChLCs can be encapsulated for integration into flexible substrates (Figure 5.1a), are easily electrically driven (Figure 5.1b), and can also be optically addressed to create images [2].

In the last three decades, they have been developed into formidable display architectures from direct driven signage to large area passive matrix displays for signs, instrumentation, and more. They have been developed into flexible embodiments for electronic skins, eReaders, and, most recently, writing tablets (Figure 5.1c).

More fundamentally, they can be used to create full‐color images by either photo addressing, stacking layers, placing side‐by‐side ChLC tuned to primary colors or electrical tuning of each pixel. Displays made of ChLCs also lend themselves well to transparent modes. This permits the display to be used as a tracing paper or a form. The simplicity and ...