Ultra-High Frequency Nanoelectromechanical Systems with Low-Noise Technologies for Single-Molecule Mass Sensing

Citation

Feng, Philip Xiao-Li (2007) Ultra-High Frequency Nanoelectromechanical Systems with Low-Noise Technologies for Single-Molecule Mass Sensing. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/Z9NC5Z62. https://resolver.caltech.edu/CaltechETD:etd-05292007-002034

Abstract

Advancing today's very rudimentary nanodevices toward functional nanosystems with considerable complexity and advanced performance imposes enormous challenges. This thesis presents the research on ultra-high frequency (UHF) nanoelectromechanical systems (NEMS) in combination with low-noise technologies that enable single-molecule mass sensing and offer promises for NEMS-based mass spectrometry (MS) with single-Dalton sensitivity. The generic protocol for NEMS resonant mass sensing is based on real-time locking and tracking of the resonance frequency as it is shifted by the mass-loading effect. This has been implemented in two modes: (i) creating an active self-sustaining oscillator based on the NEMS resonator, and (ii) a higher-precision external oscillator phase-locking to and tracking the NEMS resonance.

The first UHF low-noise self-sustaining NEMS oscillator has been demonstrated by using a 428MHz vibrating NEMS resonator as the frequency reference. This stable UHF NEMS oscillator exhibits ~0.3ppm frequency stability and ~50zg (1zg = 10^-21 g) mass resolution with its excellent wideband-operation (~0.2MHz) capability. Given its promising phase noise performance, the active NEMS oscillator technology also offers important potentials for realizing NEMS-based radio-frequency (RF) local oscillators, voltage-controlled oscillators (VCOs), and synchronized oscillators and arrays that could lead to nanomechanical signal processing and communication. The demonstrated NEMS oscillator operates at much higher frequency than conventional crystal oscillators and their overtones do, which opens new possibilities for the ultimate miniaturization of advanced crystal oscillators.

Low-noise phase-locked loop (PLL) techniques have been developed and engineered to integrate with the resonance detection circuitry for the passive UHF NEMS resonators. Implementations of the NEMS-PLL mode with generations of low-loss UHF NEMS resonators demonstrate improving performance, namely, reduced noise and enhanced dynamic range. Very compelling frequency stability of ~0.02ppm and unprecedented mass sensitivity approaching 1zg has been achieved with a typical 500MHz device in the narrow-band NEMS-PLL operation.

Retaining high quality factors (Q's) while scaling up frequency has become crucial for UHF NEMS resonators. Extensive measurements, together with theoretical modeling, have been performed to investigate various energy loss mechanisms and their effects on UHF devices. This leads to important insights and guidelines for device Q-engineering.

The first VHF/UHF silicon nanowire (NW) resonators have been demonstrated based on single-crystal Si NWs made by bottom-up chemical synthesis nanofabrication. Pristine Si NWs have well-faceted surfaces and exhibit high Q's (Q ≈ 13100 at 80MHz and Q ≈ 5750 at 215MHz). Given their ultra-small active mass and very high mass responsivity, these Si NWs also offer excellent mass sensitivity in the ~10?50zg range.

These UHF NEMS and electronic control technologies have demonstrated promising mass sensitivity for kilo-Dalton-range single-biomolecule mass sensing. The achieved performance roadmap, and that extended by next generations of devices, clearly indicates realistic and viable paths toward the single-Dalton mass sensitivity. With further elaborate engineering, prototype NEMS-MS is optimistically within reach.

Thesis Files