Capacitive frequency tuning of ALN micromechanical resonators

Frequency tuning of aluminum nitride (AlN) micromechanical resonators has been demonstrated by reactance manipulation via termination with variable capacitors. Shunting one electrode with a variable capacitor in a 13 MHz fourth overtone length-extensional mode resonator effected resonator stiffening to yield a ~600 ppm frequency shift. Tunability could be further increased by dedicating two electrodes for tuning doubling the frequency tuning range to ~1500 ppm. A tunable bandwidth balun filter has been constructed by parallel coupling of independently tunable resonators demonstrating almost three-fold increase in the bandwidth from 12 kHz to 33 kHz. Also a voltage-controlled frequency tuning printed circuit board (PCB) was implemented.