An Ultra-Low Impedance 4.8 GHz Al72Sc28N Resonant Rods Resonator With a Record kt2 of 21.2%

This work reports on the measured performance of the first Aluminum Scandium Nitride Two-Dimensional Resonant Rods resonator (2DRR) fabricated using a Sc-doping concentration of 28% (i.e. Al72Sc28N), characterized by an ultra-low impedance (~12 Ω), and exhibiting an all-time record electromechanical coupling coefficient ($k_t^2$) of 21.2%. Due to its unprecedented $k_t^2$, enabled by its unique dispersion characteristics, the reported 2DRR opens exciting scenarios towards the development of next generation monolithic integrated radio-frequency (RF) filtering components. In particular, given the demonstrated electromechanical performance of the reported 2DRR device, we show that 2DRR-based ladder filters with ~9.2% of fractional bandwidth, ~2.5 dB insertion-loss (I.L) and a >40 dB out-of-band rejection can be envisioned in the short-term, providing unprecedented means to extend the commercial and military use of acoustic filters up to the mm-wave frequency range.