Single device on-chip feedthrough cancellation for enhanced electrical characterization of piezoelectric-on-silicon resonators in liquid

Even though piezoelectric MEMS resonators are known to possess substantially stronger electromechanical transduction efficiencies than the more traditional capacitive MEMS resonators, parasitic feedthrough remains an impediment for electrical characterization of resonators in liquids. The increase in parasitic feedthrough is particularly pertinent in liquids with high dielectric constants like water. In this paper, a previously proposed pseudo-differential parasitic feedthrough cancellation technique involving only a single capacitive MEMS resonator operating in vacuum is here adapted for a Thin-film Piezoelectric-on-Silicon (TPoS) MEMS resonator that is fully immersed in deionized (DI) water. The proposed technique targets parasitics on the package level rather than parasitics intrinsic to the device. We have tested the proposed technique on three different resonator designs to investigate its scalability, and have found that the method is most beneficial when the resonators are smaller. The proposed technique is thus highly relevant to resonant mass sensing applications. We experimentally demonstrate a reduction in feedthrough by as much as a factor 90 using the proposed method, which results in a corresponding increase in the signal to background ratio from 3.45 dB to 25 dB despite a quality factor of 221 in water.