Enhanced electromagnetic modeling of bulk acoustic wave resonators and filters

With the rapid miniaturization and increasing performance demands of bulk acoustic wave (BAW) devices, more accurate and sophisticated design and modeling methods are required. Accurate simulation results and appropriate software tools as well as their correct application are essential for a precise characterization of BAW devices. Depending on the simulated device, its complexity, required accuracy and available computational resources, different modeling and simulation methods have to be applied. For this modeling task it is important to know what details to model, how to model them and at what extent. In order to capture all relevant effects that are important to characterize the device with high accuracy, deep knowledge of the simulation software´s working principles as well as its computational limits and capabilities are necessary. This paper presents different enhanced electromagnetic models of mirror-type BAW resonators that are simulated with a 3D electromagnetic solver, whereas the acoustic effects are computed with a 1D solver. The electromagnetic effects of different resonator models are analyzed by fitting the simulated resonator admittance to an equivalent lumped circuit and comparing the fitted values. Further, the effects of the electromagnetic mesh-cell-density in simulations for the different resonator models are analyzed. The computational costs for these resonator models are shortly discussed by comparing mesh size, required memory and computational time. With the understanding of the model and electromagnetic mesh properties from the resonator simulations, an enhanced electromagnetic BAW duplexer model is simulated and compared to a measurement. The simulations of BAW resonators and duplexers can be improved by appropriate electromagnetic modeling and specific knowledge about the simulated device.