BAW multiplexers for 5G: Visualizing the source of perturbed nonlinear cancellation by interferometry

Nonlinear (NL) performance requirements on BAW filters and modules highly increased in the past years. Next generation 5G BAW modules will serve many new frequency bands, where superior NL performance of BAW filters is indispensable. Whereas the prediction accuracy on the purely electromagnetic (EM) contributions of BAW simulation reached an impressive level, there is still a lack of predicting all acoustic phenomena that can impact the final response of a real device precisely. Regarding harmonics specifications of a filter, this manifests in acoustic spurious modes showing up as pronounced ripples for example in the second harmonic (H2) response. In this article the main contributions to imperfect cancellation in a real BAW device are summarized and a novel way to visualize harmonics cancellation using interferometry is presented. This new approach allows for an indirect detection of the strains present in the resonator’s piezo layer over frequency and thus makes it possible to analyze and gain a deeper understanding of the final electrical nonlinear performance.