Enhanced Piezoelectric $\mathrm{AL}_{1-\mathrm{X}}\mathrm{SC}_{\mathrm{X}}\mathrm{N}$ RF-MEMS Resonators for Sub-6 GHz RF-Filter Applications: Design, Fabrication and Characterization

This paper reports the design, fabrication and characterization of bulk acoustic wave (BAW) resonators of the SMR-type (surface mounted resonator) with highly c-axis oriented Al
_0.8
Sc
_0.2
N thin-films. Various filter topologies have been demonstrated for high frequencies with sharp roll-off, wide bandwidth BW and low insertion loss IL (rel. 3dB-BW up to 9% and min. IL of 0.9 dB to 1.5 dB at 2350 to 2550 MHz). Furthermore, the challenges regarding the integration of Al
_1-x
Sc
_x
N for n79 applications (4400 to 5000 MHz) are indicated. The demonstrations show promising results regarding acoustic-only filters at 5G frequencies.