AlN/ScAlN composite films-based spurious free A1 mode lamb wave resonator with adjustable effective electromechanical coupling coefficient

Abstract Narrow-band filters are widely applied in the narrow-band Internet of Things (NB-IoT). To meet the diverse bandwidth requirements of NB-IoT applications, this work presents the first antisymmetric (A1) mode Lamb wave resonators (LWRs) based on aluminum nitride (AlN) and AlN/ScAlN composite films. The impact of structural parameters, including pitch ( P ) and duty factor (DF), on main mode excitation and suppression of spurious modes is investigated. The optimal P and DF are found to be 10 μ m and 0.05, respectively. Based on spurious-free A1 LWRs, an AlN/Sc 0.096 Al 0.904 N composite film is utilized to adjust the effective electromechanical coupling coefficient <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>k</mml:mi> <mml:mrow> <mml:mrow> <mml:mtext>eff</mml:mtext> </mml:mrow> </mml:mrow> <mml:mrow> <mml:mtext>2</mml:mtext> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> . The experiment results demonstrate a tunable <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>k</mml:mi> <mml:mrow> <mml:mrow> <mml:mtext>eff</mml:mtext> </mml:mrow> </mml:mrow> <mml:mrow> <mml:mtext>2</mml:mtext> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> from 0.40% (5 MHz) to 0.25% (3 MHz), realizing a 37.5% adjustment range of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>k</mml:mi> <mml:mrow> <mml:mrow> <mml:mtext>eff</mml:mtext> </mml:mrow> </mml:mrow> <mml:mrow> <mml:mtext>2</mml:mtext> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> , which establishes a foundation for narrow-band tunable filters.