Hybrid integration of BAW resonators with an on‐chip inductor to improve the stopband rejection of the N78 band filter

Abstract This paper demonstrates a 3.4 GHz micro‐acoustic filter with excellent in‐band insertion loss, rectangle coefficient, and out‐of‐band rejection. The proposed filter was based on a novel topology by integrating the bulk acoustic wave (BAW) resonators with an on‐chip clamping inductor, the introduction of the lumped components is beneficial for improving the filters' stopband rejection while having minimal influence on the rectangle coefficient and in‐band insertion loss. Al 0.8 Sc 0.2 N material was selected as the piezoelectric film of the BAW device and the inductor was fabricated on the same wafer with BAW devices. The manufactured filter has a minimum in‐band insertion loss of ~ 1.5 dB, a 3 dB bandwidth of about 170 MHz, and a stopband rejection of nearly ‐30 dB. The experimental results verify the design and show great applications for 5G communication and beyond.