A Comparison Between Tunable Fbars with an Integrated and with a Discrete Variable MEMS Capacitor

A comparison between two types of frequency tunable film bulk acoustic resonators (FBARs) is presented in this paper. In both types, the frequency tuning is based on a variable MEMS capacitor connected in series with the piezoelectric resonating layer. The difference is in the embodiment of the capacitor, which can be either a discrete element or an integrated part of the device. It is shown that the integrated approach not only reduces the device area by about half, but also gives better fabrication compatibility, and renders on average a quality factor more than 30% higher than the discrete approach.