Electrothermal Modeling of Surface Acoustic Wave Resonators and Filters

In this article, an electrothermal modeling approach of surface acoustic wave (SAW) resonators and filters is presented. The starting point for the model is a preliminary design that has to be assessed for thermal aspects. Due to the high geometrical complexity of SAW components, simplifications are elaborated and qualified on resonator and filter levels to prepare the design for thermal simulation. A thermal model is created and simulated in a finite-element method environment. The simulated behavior is exported as a thermal impedance and implemented in a circuit model of a SAW filter. The layout's electromagnetic behavior is taken into account. Electrothermal models of the SAW resonators and the bus bars are developed. The interface to the thermal impedance is achieved by the use of electrothermal ports. The dynamic effect of the frequency shift is included. Verification is done by a comparison of the temperature increase of a resonator in a filter test structure to a corresponding simulation model. The filter is excited by a radio frequency large signal, and the temperature is detected by the use of a resistive temperature sensor. A simulation that shows the impact of mutual heating between the resonators in a filter environment is performed.