Multiphysikalische Modellierung und Optimierung von HF-BAW-Komponenten

Description

Nowadays primarily acoustic wave devices are used for filtering in front ends of modern mobile transceivers. No competitive technology providing the same performance at the same size and costs exists at the moment. At higher frequencies mainly BAW filters are used. At these frequencies BAW resonators are superior to SAW resonators. They have a higher quality factor and show a better power durability.

Changes in ambient temperature of BAW filters lead to frequency shifts of the filter skirts and increase in the insertion loss. Furthermore, the TX filters are usually used at high power levels of up to 29 dBm. A part of the applied power will dissipate and cause a temperature increase within the filter. Both effects can lead to situations where the filter will not meet the required performance anymore. On the one hand, the steepness of the filter skirts can become insufficient so the filter will not switch from transmission to rejection within the specified band gap or the specified insertion loss will not be hold anymore. On the other hand, the live time of each device exponentially depends on the temperature and, therefore, will be significantly reduced by the self-heating effect. Furthermore, BAW filters show a nonlinear behavior at higher power levels. Specially for devices using Carrier Aggregation where several bands are used simultaneously to transmit and receive data problems in the receiver path can arise.

In this work methods for multi-physical modeling of BAW components have been developed. An approach for modeling the changes in the transfer functions of BAW filters due to homogeneous heating has been implemented. Also, a technique for the determination of the temperature coefficients of the thin film layers used in BAW filters which are required for modeling BAW components at different temperatures has been exposed and realized. An accurate and at the same time highly efficient method for modeling the self-heating and the changes in the transfer function of BAW filters due to the self-heating has been developed. Additionally, a novel and accurate method for modeling the nonlinear behavior of BAW components has been invented. The new realized methods have been verified by experiments. By using the developed methods it is now possible for the designers of BAW components to evaluate and optimize the BAW components at different temperatures and power levels. Moreover, the developed methods have been used to explore different compensation methods in order to improve the thermal behavior of BAW components, to reduce the self-heating and to optimize the nonlinear behavior.