Multiplexed operation of nanoelectromechanical systems (NEMS) arrays

Nanoelectromechanical systems (NEMS) are rapidly being developed for a variety of applications as well as for exploring interesting regimes in fundamental physics. In most of these endeavors, operation of a NEMS device involves actuating the device harmonically around its fundamental resonance and detecting the subsequent motion, while the device interacts with its environment. Up to date, with few notable exceptions, most NEMS work has been done on single devices. Even though a single NEMS resonator is exceptionally sensitive, a typical application, be it nanomechanical sensing or signal processing, requires the detection of signals from many resonators distributed over the surface of a chip. Therefore, one of the key technological challenges in the field of NEMS is the development of multiplexed measurement techniques to simultaneously detect the motion of a large number of NEMS resonators. The main objective of this project is to address this important and difficult problem of interfacing with a large number of NEMS devices and facilitating the use of such arrays in, for example, sensing and signal processing applications.;In preparatory work, photothermal/optical operation of high frequency NEMS at ambient conditions is carried out. The flexural resonances of bi-layered doubly clamped beams are actuated using a tightly focused modulated laser source and the resulting out-of-plane displacements are measured at a single point using a path-stabilized interferometer. The signal from the interferometer is coupled to a radiofrequency (RF) lock-in amplifier allowing for narrowband phase-sensitive detection. The optical measurements have enabled the determination of beam resonance parameters such as resonance frequencies, mechanical quality (Q) factors and mode shapes. Experimental results show that the all-optical excitation-detection technique is well suited for the non-destructive testing and remote interrogation of NEMS with exquisite spatial and temporal resolution.;In subsequent work, a full-field multiplexed system is developed for the excitation and detection of vibration in arrays of nanomechanical beams. Parallel detection of the motion of array devices is achieved through a full-field optical interferometry system making use of a photorefractive crystal. In this system, a coherent imaging approach using an adaptive photorefractive holography technique and a parallel detection scheme employing a charge-coupled device (CCD) is used to obtain full-field displacement images of the entire NEMS array. Two techniques for the excitation of vibrations in nanomechanical resonators are used. First, an ultrasonic transducer-based excitation, where the ultrasound couples to the beams through the array substrate material, is described. In the second approach, an optical excitation technique, where a modulated laser source is used to heat the beams, is described. Here, actuation is produced through the thermoelastic effect. Full-field out-of-plane displacement images of an array of 60 nanomechanical beams excited using ultrasonic and optical transduction schemes are presented. Experimental results obtained in these transduction schemes are compared in terms of amplitude of displacement, uniformity of displacement across the array, and potential effects on the resonance frequency. The full-field system is characterized in terms of both efficiency of excitation of nanomechanical vibration and sensitivity of the interferometric displacement detection and is found to be well suited for the measurement of vibrations in large-scale NEMS arrays.