Three-Stage Suspended Frames for Quality Factor Improvement in Lamb Wave Resonators

Recently, aluminum nitride (AlN) lamb wave resonators (LWRs) have gained considerable attention due to their unique advantages, including multifrequency operation on a single chip and moderate electromechanical coupling coefficient (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</i><sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>2</roman></sup>). A major challenge in the practical application of LWRs is the need for further enhancement of their quality factors (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i>). This study presents a novel approach to improving the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> factor of LWRs through the implementation of a three-stage suspended frame structure. By incorporating three-stage suspended frames between the resonator body and the substrate, anchor loss is significantly mitigated, resulting in an enhanced <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> factor. The design of the three-stage suspended frame, as well as its influence on energy dissipation, is analyzed in detail. Experimental results demonstrate that a conventional LWR achieves a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> factor <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>3dB</roman></sub> of 1366 at the resonant frequency of 49.76 MHz, and the three-stage suspended frame LWR achieves a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> factor of 2924 at the resonant frequency of 49.71 MHz, indicating that the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> factor <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>3dB</roman></sub> was enhanced by approximately 2.14×, thereby effectively reducing insertion loss. These findings underscore the potential of the proposed approach for developing low-loss LWR filters and other advanced acoustic devices.