  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
(~25 Ohm) and exhibiting a record electromechanical coupling coefficient (kt2)
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
kt2, the reported 2DRR opens exciting scenarios towards the development of next
generation monolithic integrated radio-frequency (RF) filtering components. In
fact, we show that 5th-order 2DRR-based ladder filters with fractional
bandwidths (BW) of ~11%, insertion-loss (I.L) values of ~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.

Signal Processing