Low Loss Al0.7Sc0.3N Thin Film Acoustic Delay Lines

reports novel aluminum scandium nitride (Al
_0.7
Sc
_0.3
N) thin film acoustic delay lines (ADLs). Low loss ADLs are implemented on sputtered Al
_0.7
Sc
_0.3
N thin film using cross-field excited single-phase unidirectional transducers (SPUDT), which generate S0 mode Lamb wave between two ports. ADLs are fabricated with up to 300
$\mu \text{m}$
flat delay gap by optimized low stress Al
_0.7
Sc
_0.3
N thin film. A large electromechanical coupling factor (
$K^{ {2}}$
) of 7.8% provided by approximately 1
$\mu \text{m}$
Al
_0.7
Sc
_0.3
N thin film allows for an overall improvement. Compared to implemented aluminum nitride (AlN) thin film counterparts, Al
_0.7
Sc
_0.3
N ADLs achieve remarkably lower insertion loss (IL), wide fractional bandwidth (FBW), and better impedance matching, featuring a minimum IL of 2.27 dB and a 3-dB FBW of 7.1% at approximately 780 MHz. The increase in relative permittivity due to Sc doping reduces the imaginary part of the matched network by 40%. For fundamental symmetric (S0) Lamb waves, a high group velocity of 8532 m/s, a propagation loss of 0.07 dB/
$ {\lambda }$
, and a propagation quality factor (Q) of 338 are extracted. Upon further development, scandium (Sc) doped AlScN thin films could enable CMOS-compatible piezoelectric acoustic platform for signal processing, sensing, and computing applications.