8 GHz microwave filters based on bulk acoustic waves in piezoelectric AlN thin films

Bulk acoustic wave (BAW) resonators and filters have been fabricated in the frequency range between 7 and 8 GHz. Resonators with quality factors of 550, and coupling factors k² of 5.5 % have been achieved. The obtained resonator characteristics theoretically yield filters of 3.5 % 3dB bandwidths with flat channel characteristics, and insertion losses of -6 dB. The tradeoffs related to the use of aluminum or platinum bottom electrodes is investigated theoretically. While aluminum is expected to yield filters with lower insertion loss, Pt is expected to yield larger bandwidths.