A 5.3 GHz Al0.76Sc0.24N Two-Dimensional Resonant Rods Resonator With a kt2 of 23.9%

This work reports on the measured performance of an Aluminum Scandium Nitride (AlScN) Two-Dimensional Resonant Rods resonator (2DRR), fabricated by using a Sc-doping concentration of 24% , characterized by a low off-resonance impedance ( $\sim $ 25 $\Omega $ ) and exhibiting a record electromechanical coupling coefficient ( ${k}_{t}^{\textit {2}}$ ) of 23.9% for AlScN resonators. In order to achieve such performance, we identified and relied on optimized deposition and etching processes for highly-doped AlScN films, aiming at achieving high crystalline quality, low density of abnormally oriented grains in the 2DRR's active region and sharp lateral sidewalls. Also, the 2DRR's unit-cell has been acoustically engineered to maximize the piezo-generated mechanical energy within each rod and to ensure a low transduction of spurious modes around resonance. Due to its unprecedented ${k}_{t}^{\textit {2}}$ , the reported 2DRR opens exciting scenarios towards the development of next generation monolithic integrated radio-frequency (RF) filtering components. In fact, we show that $5^{th}$ -order 2DRR-based ladder filters with fractional bandwidths (BW) of $\sim $ 11% , insertion-loss (I.L) values of $\sim $ 2.5 dB and with $>$ 30 dB out-of-band rejections can now be envisioned, paving an unprecedented path towards the development of ultra-wide band (UWB) filters for next-generation Super-High-Frequency (SHF) radio front-ends. [2022-0024]