A 3D Finite Element Model of H2 Emissions in Apodized BAW Devices

As nonlinear emissions requirements for RF filtering solutions continue to tighten, there is a need to accurately model the general nonlinear behavior of bulk acoustic wave (BAW) devices. In particular, it is necessary to predict H2 emissions due to spurious resonances, as well as the level to which they cancel in resonators connected in anti-series or anti-parallel configurations, for example. In this case the celebrated 1D nonlinear Mason model is no longer sufficient and must be supplemented by methods that account for the bounded resonator geometry. Here we present a 3D finite element model that accurately predicts such nonlinear effects in arbitrarily shaped BAW devices, with a special focus on second harmonic emissions. Additionally, we show that the FEM model can be combined with a rational approximation method to predict nonlinear emissions based on a single linear FEM simulation, drastically reducing solve time.