BAW Filters for 5G: Lead Geometry Impact on Current Distribution in Resonators

Thermal performance and power handling of BAW filters in modern 5G capable handsets is an ever-increasing challenge. Higher integration densities - e. g. more communication bands and other functionality - and smaller form factor PCBs - e. g. slim phones with larger, long-lasting batteries - dictate the trend for smaller BAW filter modules [1]. The higher frequency bands included in 5G with operating frequencies above 3GHz intensify this challenge due to smaller resonators inherent to the BAW technology at these frequencies. As a result, the power density in Tx filters increases, which is unfavorable for power handling and thermal management. Thus, a better understanding of the heat generating mechanism in BAW resonators is of utmost importance to be able to create filter designs that are up to the task. In this paper we will focus on the impact of connection lead geometry on the electrode currents and their distribution in single and cascaded resonator stages. An overview of the mathematical background in means of network theory and the corresponding methodology is presented. To reveal the layout dependent impact on the current distribution, which can drive unwanted localization of joule heating, interferometric surface deflection measurement of BAW resonators on wafer were performed.