Experimental improvement of birefringence and response time in Liquid Crystals using surface preparation of polyimide at 20GHz

This paper presents an experimental study analyzing the effects of surface treated Polyimide (PI) on dielectric anisotropy and response time of Liquid Crystal (LC) in an In-Plane Switching (IPS) cell design. A Co-Planar Waveguide (CPW) transmission line is used as an in-plane interrogation architecture, with a layer of LC enclosed on top of the CPW. By applying different surface preparations of PI, we are able to derive an optimum condition to maximize birefringence and minimize response times at 20 GHz. Measured phase change is increased from 28 deg to 72 deg for the same length of the CPW line. At the same time, measurement results show that fall time is decreased from 9.32 s down to 4.1 s. These improvements will facilitate realization of LC in microwave devices in need of fast and tunable materials.