Analysis and modeling of liquid-crystal tunable capacitors

Abstract

Three different configurations of liquid-crystal tunable capacitors were investigated, including fractal structures, comb structures, and square structures. The tuning ranges of the fractal structures, the comb structures, and the square structures at 4 GHz from 0 to 5 V were found to be 8.81%, 7.17%, and 11.85%, respectively. The square structures have the largest tuning ranges mostly because of the uniform electric fields dominated. The Q-values of the fractal structures, the comb structures, and the square structures at 4 GHz with an operation voltage of 5 V were 68.2, 98.3, and 31.0, respectively. Compared to the other two structures, the square structures perform the highest inductive effects, leading to the lowest Q-values. In addition, the liquid crystals with different chiral doping concentrations were injected into the capacitor structures to investigate the impact of different liquid crystals on the tunable capacitors. The threshold voltages (Vth) increase as the chiral doping concentrations enlarge. The steepness of the C-V curves increases as the chiral doping concentrations reduce. Furthermore, a liquid-crystal capacitor model was developed to qualitatively illustrate the performance of the liquid-crystal tunable capacitors. The model prediction and the measurement results were highly correlated. © 2006 IEEE.