Maximizing Q at mmWave Frequencies: Material and Mirror Engineering in Overmoded Bulk Acoustic Resonator

This work presents a major advancement in mmWave Bulk Acoustic Wave (BAW) resonator technology by achieving a record-high Quality factor <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$(Q)$</tex> of 184 at 51 GHz using a 35% Scandium alloyed Aluminum Nitride Overmoded Bulk Acoustic Resonator (ScAlN OBAR). Achieving high <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Q$</tex> at such elevated frequencies is extremely challenging due to intrinsic material losses and energy leakage. To address this major bottleneck for radio frequency (RF) front-end filter applications, we isolate and mitigate key loss contributors through a systematic design and fabrication of four OBAR variants. The final design not only demonstrates superior <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Q$</tex> performance but also maintains fabrication simplicity, standing out against competing technologies which require significantly more complex architectures to achieve comparable <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$Q$</tex>.