Large-Range MEMS Motion Detection With Subangström Noise Level Using an Integrated Piezoresistive Silicon Nanowire

Electrostatically actuated microelectromechanical systems (MEMS) devices integrating a surface micromachined silicon nanowire were batch processed to investigate motion detection with a nanowire piezoresistive gauge. In the proposed implementation, the nanogauge is indirectly coupled to the MEMS structure through an intermediate coupling spring. This design allows an arbitrary choice of MEMS motion detection range and a resolution improvement of in situ nanowire gauge factor measurements. Using this approach, it is demonstrated that an in-plane MEMS displacements up to 180 nm with a noise level down to 0.7 Å/Hz^1/2 can be achieved. MEMS resonance measurement in air and in vacuum by this method is also demonstrated. Results are compared with ex situ measurements of MEMS displacement by optical microscopy and by integrated capacitive detection.