Phase Noise and Frequency Stability of Very-High Frequency Silicon Nanowire Nanomechanical Resonators

We report measurements and analyses of noise characteristics of very-high frequency (VHF) silicon nanowire (SiNW) nanoelectromechanical systems (NEMS). VHF SiNW resonators vibrating at ~200MHz typically have displacement sensitivity of ~5fm/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1/2</sup> and force sensitivity of 50~250aN/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">½</sup> , set by thermomechanical fluctuations. They have ~1nm critical amplitude and intrinsic dynamic range of 90~110 dB. Amplifier noise and resistor thermal noise dominate the resonance detection, resulting in in compromised displacement noise floor (typically ≥30fm/Hz <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">½</sup> ), dynamic range (reduced to 70~90dB), and phase noise (≥20~30dB degradation). We develop SiNW-NEMS-based phase-locking techniques to investigate the phase noise and frequency stability performance. Frequency stability of ~0.1ppm and 71 resonant mass sensitivity of ~10zg(1zg=10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-21</sup> g) have been achieved.