Low motional impedance distributed Lamé mode resonators for high frequency timing applications

This paper presents a novel high-Q silicon distributed Lame mode resonator (DLR) for VHF timing reference applications. The DLR employs the nature of shear wave propagation to enable a cascade of small square Lame modes in beam or frame configurations with increased transduction area. Combined with high efficiency nano-gap capacitive transduction, it enables low motional impedances while scaling the frequency to VHF range. The DLR designs are robust against common process variations and demonstrate high manufacturability across different silicon substrates and process specifications. Fabricated DLRs in beam and frame configurations demonstrate high performance scalability with high Q-factors ranging from 50 to 250 k, motional impedances 90 °C in the VHF range, and are fabricated using a wafer-level-packaged HARPSS process. Packaged devices show excellent robustness against temperature cycling, device thinning, and aging effects, which makes them a great candidate for stable high frequency references in size-sensitive and power-sensitive 5 G and other IoT applications. Timing resonators are crucial components in a range of electronic devices, where they provide a time-based reference, commonly used in consumer electronics, automotive and industrial settings. Square Lame mode resonators enable a silicon-based timing resonator with high Q-factor and high-temperature stability. However, they have certain limitations, primarily at VHF ranges. Now, a team from Georgia Institute of Technology, USA, led by Farrokh Ayazi have designed and fabricated timing resonators that utilize the in-plane shear nature of the Lame mode to create distributed resonance which overcome the limitations of conventional timing resonators. Combined with high efficiency nano-gap capacitive transduction, they enable low motional impedances with increased transduction area, while scaling the frequency to VHF range. These DLR designs are robust against common process variations and demonstrate high manufacturability across different silicon substrates and process specifications.