Improvements in electrical properties of piezoelectric microcantilever sensors by reducing parasitic effects

Piezoelectric microcantilever sensors (PEMSs) are very highly sensitive label-free sensors, and silicon-based PEMSs have parasitic elements such as parasitic capacitances and resistances between the electrodes through their substrate; they affect the coupling coefficient and leakage current and thereby the accuracy of the sensor. In this study, we have experimentally analyzed the parasitic effects that affect these PEMSs. Further, we have developed a method to reduce the parasitic effects and fabricated a PEMS on this basis; we have successfully demonstrated that its electrical properties improved. The parasitic effects were reduced by employing a deep trench structure near the electrodes and a highly resistive (>10 kΩ cm) silicon-on-insulator (SOI) wafer and by reducing the electrode pad areas. The coupling coefficient and leakage current were analyzed from the experimental data of admittance spectra and velocity spectra. The coupling coefficient increased by approximately 42%, the leakage current at resonance decreased by approximately 76%, the parasitic conductance decreased and the transformation factor increased. Moreover, the electrical power loss decreased as the leakage current decreased, whereas the motional conductance increased with the coupling coefficient. In this manner, we could enable more accurate electrical readouts of the PEMS by reducing the parasitic effects