Solidly mounted bulk acoustic wave filters for the GHz frequency range

Abstract

Small sized, highly selective solidly mounted bulk acoustic wave (BAW) band pass filters are suitable for mobile and wireless systems operating in the frequency range 0.8 and 10 GHz. Both lattice and ladder BAW resonator filters have been designed and fabricated on 6" wafers using multilayer Bragg type acoustic reflectors. For the piezoelectric film highly oriented AlN has been deposited using an optimised sputter process. Resonators and filters were made and measured both on glass and silicon wafers. Resonators on glass and Si show different substrate loss. Dielectric loss in the AlN piezo-layer is small. The acoustic loss is found to be small in all the materials. The properties of the acoustic reflector can be monitored by a thorough examination of small details of the resonator's frequency response. Resonator and filter examples are shown for 2 GHz, 2.8 GHz, and 8 GHz.