Electrothermally Actuated Silicon Carbide Tunable MEMS Resonators

Abstract

This paper presents the fabrication and characterisation of SiC flexural-mode structures able to operate as electro-thermo-mechanical tunable resonators. Single and double clamped beams, as well as circular structures, have been fabricated with aluminium (Al) and platinum (Pt) top electrodes. Electro-thermal excitation has been used for device actuation, 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. Tuning of the resonant frequency has been performed by varying the DC and AC component of the actuating voltage on SiC beams with u-shaped and slab Pt electrodes. When increasing the DC bias, frequency shift rates of about-11,000 ppm/V and-1,100 ppm/V are measured for the ushaped and slab electrodes, respectively. When increasing the amplitude of the AC input, shift rates of about-1,800 ppm/V and-800 ppm/V are measured. In addition, measurements have shown that the frequency shift rate increases with the ambient temperature. Electro-thermal 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. Tuning of the electro-thermally mixed output singal has been demonstrated on a disk resonator.

Tuning Performance of Silicon Carbide Micro-Resonators

“…As reported previously [5], it is expected that, for similar dimensions, the resonant frequency of a cantilever will be lower than a bridge, which has been confirmed in this work. The larger dimension (400 µm diameter) as well as the electrode configuration in the ring compared to the cantilever (200 µm length) may have contributed to the relatively similar resonant frequencies measured.…”

Piezoelectric sensing of electrothermally actuated silicon carbide MEMS resonators

“…The resonant frequency tuning range of ~300,000 ppm has been achieved using relatively low DC input bias voltage (2 V -6 V). The decrease in resonant frequency detected as the DC bias voltage increases can be attributed to the increase of compressive stress in the beam, caused by the increase in thermal expansion of the structure as the temperature increases [14,15].…”

Tunable MEMS cantilever resonators electrothermally actuated and piezoelectrically sensed

“…The bilayer structure of materials with different thermal expansion coefficients (Pt and 3C-SiC) allows enhanced mechanical strain of the structure [18]. As the dissipated power depends on the squared value of actuation voltage, a device can be driven into resonance if the frequency f AC of an actuating voltage containing an AC component that is equal to half of the structure's natural frequency f 0 (f AC = f 0 /2) [14]. However, a device can be driven into resonance using the actuation frequency equal to the structure's natural frequency (f AC = f 0 ), so far as actuation signal contains both AC and DC component.…”

“…Although cantilever structures have been driven into resonance electrothermally successfully, the resonant operation has been detected optically [14], capacitively [15] and piezoresistively [16]. This paper reports on design, fabrication, simulation and testing of two-port cantilever MEMS resonators with electrothermal actuation and piezoelectric sensing.…”