A new optically controlled CDS-polymer capacitor for tunable microwave components

For the first time, we show that a new optically sensitive MIM CdS-polymer capacitor can provide sufficiently large capacitance variation to be useful for tunable microwave components. The new capacitor, based on photoconductive particle inclusions that cause dielectric permittivity change with light, is demonstrated in a coplanar circuit operating over the 1 to 10 GHz band. Upon illumination through the lower ITO electrode, its capacitance varied from 0.16pF to 0.18pF, a 13% change. A complete equivalent model of the capacitor is given. The basic CPW circuit could easily be modified to overcome present material limitations associated with the optically transparent ITO metal and the CdS polymer mix, leading to future low cost, simply processed, integrated, tunable components such as filters and phase shifters. This new technology allows for the elimination of performance degrading electronic circuitry that has traditionally plagued reconfigurable components.