Phase noise of nanoelectromechancial systems

Abstract

Nanoelectromechanical systems (NEMS) are microelectromechanical systems (MEMS) scaled down to nanometer range. As the size of the NEMS resonators is scaled downward, some fundamental and nonfundamental noise processes will impose sensitivity limits to their performance. In this work, we first present theory of phase noise mechanism of NEMS to examine both fundamental and nonfundamental noise processes. Fundamental noise processes considered here include thermomechanical noise, momentum-exchange noise, adsorption-desorption noise, diffusion noise, and temperature-fluctuation noise. For nonfundamental noise processes, we develop a formalism to consider the Nyquist-Johnson noise from transducer-amplifier implementations. As an initial step to experimental exploration of these noise processes, we describe and analyze several phase-locked loop schemes based on NEMS at very high frequency and ultrahigh frequency bands. In particular, we measure diffusion noise of NEMS arising from xenon atoms adsorbed on the device surface using the frequency modulation phase-locked loop. The observed spectra of fractional frequency noise and Allan deviation agree well with the prediction from diffusion noise theory. Finally, NEMS resonators also provide unprecedented sensitivity for inertial mass sensing. We demonstrate in situ measurement in real time with mass floor of ~20 zg. Our best mass sensitivity corresponds to ~7 zeptograms, equivalent to ~30 xenon atoms or the mass of an individual 4 kDa molecule. Detailed analysis of the ultimate sensitivity of such devices based on these experimental results indicates that NEMS can ultimately provide inertial mass sensing of individual intact, electrically neutral macromolecules with single-Dalton sensitivity.