Multiscale fabrication and characterization of a NEMS force sensor

Abstract

This study investigates the fabrication and characterization of an innovative nanoelectromechanical system force sensor that utilizes suspended submicron silicon nanowires for detecting multi-axis forces in the micro-newton range. The sensor combines microscale shuttle platforms with nanowire piezoresistors along with retaining springs. Its fabrication involves a rather involved set of Si deep etching, doping, metallization, release, and encapsulation processes on silicon-on-insulator wafers. Electromechanical characterization demonstrates sensor reliability under mechanical strains up to the level of 10% as well as gauge factor measurements. Dynamic response analysis confirms a high resonant frequency of 12.34 MHz with a quality factor of 700 in air, closely matching simulation results. Thermal characterization of the sensor reveals a Temperature Coefficient of Resistance of 6.4 × 10⁻⁴ °C⁻¹. Sensor characterization under jet flow reveals its ability to detect strong flows demonstrating a resistance change of as much as 2.02% under sustained gas flow through a nozzle. Sensor integration into the gas flow measurement setup demonstrates its versatility in detecting small forces, paving the way for further exploration of thermomechanical factors. Combined with its miniature footprint, the sensor's electromechanical performance hints at applications in the analysis of velocity gradients in microscale flows including micro/nano diffusers and nozzles in small satellite propulsion.