Oscillator far-from-carrier phase noise reduction via nano-scale gap tuning of micromechanical resonators

Substantial improvements in the far-from-carrier phase noise of oscillators referenced to stand-alone (as opposed to arrayed) capacitively transduced micromechanical disk resonators have been attained via the use of atomic layer deposition (ALD) to tune the electrode-to-resonator capacitive gaps. Specifically, ALD of about 30 nm of hafnia (HfO₂) onto the surface of a released 60-MHz micromechanical disk resonator to reduce its effective resonator-to electrode gap size from 92 nm to 32 nm provides an increase in power handling leading to more than 15-20 dB reduction in the far-from-carrier phase noise of an oscillator referenced to this resonator. This ALD-enabled nano-scale gap tuning provides a simple and effective method to satisfy increasing demands for higher short-term stability in frequency references for electronic applications.