SiC/Si and AlN/Si heterostructures for microelectromechanical RF sensors

Micromechanical SiC and AlN resonators with resonant frequencies between 170 kHz and 1.8 MHz have been prepared on silicon substrates by heteroepitaxial deposition of thin layers (/spl sim/200 nm) and subsequent dry etching. The resonators were operated by magnetomotive actuation and detection using a thin (/spl sim/50 nm) metallisation on top of the resonant beams. The strong RF driving signal masked the much weaker response of the resonators at resonance. Different methods to overcome this problem are proposed, namely (i) differential measurements, (ii) separation of excitation and detection by using coupled resonators, or an additional (e.g., capacitive) read-out electrode, and (iii) piezoelectric actuation.