Optimization of piezoresistive motion detection for ambient NEMS applications

Electrical readout of nanomechanical motion in ambient pressure and temperature imposes an important challenge for emerging applications of nanoelectromechanical systems (NEMS). Here, we optimize a metallic piezoresistive motion transducer for NEMS resonators in air. The nanomechanical motion of the NEMS resonator serves as a signal down-mixer and enables the detection of the motional signal by a low-frequency circuit. A balanced circuit in the detection loop reduces some of the unwanted background and allows for detection without significant losses. We explore the detection parameter space and use an optimized parameter set to detect the fundamental, second and third harmonic resonances of a NEMS doubly-clamped beam resonator. Our simple circuit model agrees with experimental observations and points the way for further optimization.