Bimaterial electromechanical systems for a biomimetical acoustic sensor

Bimaterial planarized micromechanical beams have been designed, simulated, and fabricated with lengths in the range 800–5800 μm and distance to substrate 0.8–4.0 μm. The beams are to be used as vertical-mode resonant gates on p-type field-effect transistors for implementing an adaptable MEMS acoustic sensor inspired by the human ear. A process for fabricating planar bilayer double-clamped beams made of silicon nitride (SiN) and aluminum (Al(1%Si)) has been developed. The planar design and bimaterial approach allow the fabrication of relatively straight beams with length up to 5800 μm with the possibility of controlling the degree of static deflection of the beams. The fabricated beams have shown a maximum deflection of ∼300 nm and a transverse concave shape with respect to the substrate due to the bilayer nature of the structure. From wafer curvature measurements, the stress in the SiN and Al(1%Si) is 200 and 280 MPa, respectively. Finite element simulations and analysis of the profile of the beams have demonstrated that the films’ stress magnitude influences the longitudinal and transverse profile of the beams. The fabricated devices resonate mechanically in the range 15–160 kHz. Preliminary electrical characterization of the devices has shown drain currents in the μA range for gate voltages of −20 to −25 V and drain voltages of -5V.