Frequency Stabilization of Nanomechanical Resonators Using Thermally Invariant Strain Engineering

• Published in: Nano letters 2020-05, Vol.20 (5), p.3050-3057
• Main Authors: Wang, Mingkang, Zhang, Rui, Ilic, Robert, Aksyuk, Vladimir, Liu, Yuxiang
• Format: Article
• Language: English
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.9b04995

Microfabricated mechanical resonators enable precision measurement techniques from atomic force microscopy to emerging quantum applications. The resonance frequency-based physical sensing combines high precision with long-term stability. However, widely used Si3N4 resonators suffer from frequency sensitivity to temperature due to the differential thermal expansion vs the Si substrates. Here we experimentally demonstrate temperature- and residual stress-insensitive 16.51 MHz tuning fork nanobeam resonators with nonlinear clamps defining the stress and frequency by design, achieving a low fractional frequency sensitivity of (2.5 ± 0.8) × 10–6 K–1, a 72× reduction. On-chip optical readout of resonator thermomechanical fluctuations allows precision frequency measurement without any external excitation at the thermodynamically limited frequency Allan deviation of ≈7 Hz/Hz1/2 and (relative) bias stability of ≈10 Hz (≈ 0.6 × 10–6) above 1 s averaging, remarkably, on par with state-of-the-art driven devices of similar mass. Both the resonator stabilization and the passive frequency readout can benefit a wide variety of micromechanical sensors.