Wide-Band and High-Rejection RF Filters for 5G Applications Using BAW-on-Insulator Technology

This paper introduces a novel BAW-on-insulator (BOI) structure for high-performance, miniaturized filters targeting 5G applications. Leveraging a wafer transfer process to create suspended thin films on an insulating layer, this technology effectively suppresses substrate parasitic, leading to superior resonator performance. This is demonstrably showcased by a scandium-doped aluminum nitride (Al0.8Sc0.2N) film resonator boasting a remarkable figure of merit with an effective coupling coefficient of 13.6% and a Q factor of 1470. Further underscoring the potential of BOI, a compact N41 band filter is designed and fabricated with a footprint of only <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1.1\ mm × 0.9\ mm</tex> This filter exhibits an impressive insertion loss of 2.5 dB and robust rejection in other key 5G bands. Beyond immediate filter applications, BOI technology opens exciting avenues for RF MEMS manufacturing and monolithic integration within RF front-end systems.