Efficiency of Nanoelectrothermal Actuators in Fluids

Electrothermal actuation relies on non-uniform thermal expansion of a bilayer structure that consist of materials with different thermal expansion coefficients. Typically, a small metallic electrode on a suspended semiconductor structure is heated by a periodic voltage, which excites mechanical oscillations of the structure. Electrothermal actuators have recently been scaled into the NEMS domain, thanks to advances in nanofabrication methods. To date, most electrothermally-actuated devices have been operated in vacuum; however, future NEMS applications are in fluids. Here, we characterized the efficiency of nanoelectrothermal actuation in different fluids, such as air and water. We fabricated doubly-clamped silicon nitride nanomechanical beam resonators with gold actuation and detection loops. We then measured the displacement amplitudes of the beams as a function of the excitation power using optical interferometry. With data from devices and actuators of different linear dimensions, we developed a model for nanoelectrothermal actuation in fluids.