Analysis and modeling of liquid-crystal tunable capacitors

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 (V_th) 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