Electrothermally Actuated Silicon Carbide Tunable MEMS Resonators

This paper presents the fabrication and characterization of silicon carbide (SiC) flexural-mode structures able to operate as electrothermomechanical tunable resonators. Single- and double-clamped beams, as well as circular structures, have been fabricated with aluminium and platinum (Pt) top electrodes. Electrothermal excitation has been used for device actuation and resonant-frequency tuning and mixing. Circular structures (i.e., disks) have been shown to possess higher resonant frequencies and Q factors (up to ~23 000) compared to beams having similar dimensions. The tuning of the resonant frequency has been performed by varying the dc and ac components of the actuating voltage on SiC beams with u-shaped and slab Pt electrodes. When increasing the dc bias, the frequency-shift rates of about -11 000 and -1100 ppm/V are measured for the u-shaped and slab electrodes, respectively. When increasing the amplitude of the ac input, shift rates of about -1800 and -800 ppm/V are measured. In addition, measurements have shown that the frequency-shift rate increases with the ambient temperature. Electrothermal mixing has been performed by applying two actuating voltages with the sum or difference of their frequencies matching the fundamental resonance of the SiC structure. The tuning of the electrothermally mixed output signal has been demonstrated on a disk resonator.