Low Loss Al<sub>0.7</sub>Sc<sub>0.3</sub>N Thin Film Acoustic Delay Lines
Shuai Shao, Zhifang Luo, Yuan Lu, Andrea Mazzalai, C. Tosi, Tao Wu
Abstract
reports novel aluminum scandium nitride (Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> N) thin film acoustic delay lines (ADLs). Low loss ADLs are implemented on sputtered Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> flat delay gap by optimized low stress Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> N thin film. A large electromechanical coupling factor ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$K^{ {2}}$ </tex-math></inline-formula> ) of 7.8% provided by approximately 1 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> N thin film allows for an overall improvement. Compared to implemented aluminum nitride (AlN) thin film counterparts, Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.7</sub> Sc <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> 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/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$ {\lambda }$ </tex-math></inline-formula> , 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.