Sub-6dB Aluminum Scandium Nitride Acoustic Delay Lines

This work reports an acoustic delay line (ADL) based on aluminum scandium nitride. In order to reduce the fabrication difficulty and AlScN defects at the bottom electrode edges, a floating bottom electrode is utilized in this acoustic delay line design. ADLs are fabricated with up to 200 µm flat delay gap by Al
0.7
Sc
0.3
N and AlN thin film. The increase of piezoelectric coefficient resulting from the 30% Sc doping enhances the electromechanical coupling by more than a factor of 2, compared to AlN. This design achieves an insertion loss of sub-6db without patterned bottom electrodes. With Al
0.7
Sc
0.3
N thin film, an insertion loss of 5.8 dB and a fractional bandwidth (FBW) of 6.0% are obtained at 650 MHz. Compared to the same design AlN device, insertion loss reduced by 27% and fractional bandwidth increased by 9%. This design gives an alternative to low-loss ADLs which does not require consideration of alignment between top and bottom layers.