Investigation of Optical and Flexible Characteristics for Organic-Based Cholesteric Liquid Crystal Display by Utilizing Bending and Torsion Loadings

Given that the induced stress resulting from fatigue bending or torsional loads increases with increasing display thickness, the long-term mechanical reliability of display modules in soft electronics has attracted considerable attention. Therefore, understanding the related failure mechanism and stress contour distribution in the display structure is important and necessary, particularly in torsional load application. This study introduces two important types of testing loads (i.e., entire reverse of bend and torsion with several cycles) to investigate the optical and flexible characteristics of film-type cholesteric liquid crystal displays (ChLCDs). The bending radius and the torsion angle used are 20 mm and ±10^°, respectively. The stress contour and possible failure location of the testing specimens are obtained by using non-linear finite element analysis (FEA). Results indicate that a significant optical characteristic decay occurs beyond 1000 testing times. In 11,000 cycles of fatigue bending and torsion tests, 45% and 55% decay change rates, respectively, are obtained for the National Television System Committee. Accordingly, a worse situation occurs at the torsion test. This phenomenon is attributed to a two-direction bend torsion exerted on the tested ChLCD. The foregoing behavior is validated by using FEA.