Frequency Stability and Noise Characteristics of Ultra-High Frequency (UHF) Nanoelectromechanical Resonators
X.L. Feng and M.L. Roukes
California Institute of Technology, US
NEMS, resonator, mass sensor, oscillator, frequency stability
Nanoelectromechanical systems (NEMS) are emerging as great candidates for a variety of technological applications ranging from sensors and actuators to signal processing and communications . Nanofabricated high-frequency (often in the VHF/UHF bands) electromechanical resonators (i.e., NEMS resonators) are promising to be the future on-chip high-Q resonators for frequency generation and conversion in wireless communication systems . NEMS resonators’ high operating frequencies, small mass, and high-Q, also make them natural choices for resonant mass and force sensors with unprecedented sensitivities [3, 4]. However, new and elaborate engineering is crucial to realize the above projected applications. In particular, it is desirable to attain comprehensive understanding of the frequency stability  and noise processes  of NEMS resonators, the key factors that determine the ultimate performance and sensitivities of the systems. In this work, we present the initial experimental study of frequency stability and phase noise of UHF NEMS resonators. Generations of NEMS resonators with operating frequencies in the UHF band have been fabricated from high quality SiC epilayer grown on Si which is proven to be suitable for making RF and microwave resonators . A low-noise frequency locking and tracking scheme has been developed to lock to the device resonance and perform real-time frequency tracking which is generic for oscillator and resonant mass sensor applications. This scheme allows us to characterize frequency stability and phase noise of the device with controlled environmental parameters. Allan deviation [5, 6], a standard measure of frequency stability, of generations of UHF NEMS resonators, are plotted and compared in Figure 4. Successful characterization of frequency stability and noise behavior of UHF NEMS resonators clearly illustrates the ultimate performance of NEMS resonant sensors and will lay the foundations for NEMS engineering.
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Nanotech 2005 Conference Program Abstract