Common ground inductance effect in combined acoustic-electromagnetic simulation of bulk acoustic wave filter

Aiming at the phenomenon that left transmission zero of bulk acoustic wave(BAW) filter has a leftward deviation in combined acoustic-electromagnetic simulation, we verified the existence of common inductance effect in simulation and analyzed the influence of common ground inductance on filter performance. We changed positions of parallel thin-film bulk acoustic resonators(FBARs) P1 and P4 to ground in the original layout of the BAW filter(shortening paths to the ground), respectively. Then combined acoustic-electromagnetic simulation of filter was done. The results show that: common ground inductance effect existed between parallel FBAR to ground and input port and output port in combined acoustic-electromagnetic simulation. When the paths of parallel FBARs to ground were shortened, the common ground inductance effect was reduced in combined acoustic-electromagnetic simulation, and out of band rejection was better. The influence of common ground inductance effect on the smaller area parallel FBAR was more obvious. So the influence of common inductance effect on left transmission zero and left out of band rejection should be considered in combined acoustic-electromagnetic simulation of BAW filter.