Frequency Stabilization of Nanomechanical Resonators Using Thermally Invariant Strain Engineering.
basic_science · Level V
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- Record sourced from PubMed, PMID 32250636.
- Also identified by DOI 10.1021/acs.nanolett.9b04995 and PMC identifier 7558603.
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Abstract
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 Si<sub>3</sub>N<sub>4</sub> 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<sup>-6</sup> K<sup>-1</sup>, 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/Hz<sup>1/2</sup> and (relative) bias stability of ≈10 Hz (≈ 0.6 × 10<sup>-6</sup>) 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.