Feedthrough cancellation in micromechanical square resonators via differential transduction

Due to the limited transduction capacitances stemming from their small form factor, micromechanical resonators typically exhibit large feedthrough. The parasitic feedthrough is caused by the direct coupling between the drive and sense ports, interfering with the electrical characterization by distorting the bandpass. In this paper, through adopting a fully-differential configuration, we show that the feedthrough level can be greatly reduced by 3 orders of magnitude relative to the more common single-ended transduction configurations. The measurements have been respectively carried out for 25 μm and 10 μm thick SOI square-plate resonators with lengths of 360 μm, each excited in the bulk square wine-glass mode. The 25 μm device shows a Q-factor of 1.27×10⁶ measured at the resonator frequency of 11.492MHz, corresponding to a Q-f product of 1.45 × 10¹³, close to the limit for silicon. To quantify the impact of differential transduction at the drive and sense ports, the feedthrough levels at each sense electrode were measured and compared against the results where both outputs were differentially combined. We show that feedthrough suppression is achieved most significantly through differential drive at the input port, while differential sensing provides comparatively a smaller enhancement in the suppression of feedthrough.