Modeling of Thermal Processes in Thin-Film BAW Resonators

Abstract

Thermal processes in three type of thin-film bulk acoustic wave resonator, such as a resonator with an air gap, a membrane-type resonator and a resonator with a Bragg acoustic reflector, are considered. In the structures of the resonators the 2D domains of modeling are marked out. For the resonator with an air gap and the membrane-type resonator the 2D domain of modeling is in the plane of its piezoelectric transducer. For the resonator with a Bragg acoustic reflector the 2D domain of modeling is in the plane perpendicular to that of the piezoelectric transducer. The domains of modeling of the resonators are divided into the regions. For each region, the stationary heat deferential equation and the boundary conditions are defined and then this equation is solved using eigenfunction method. The heat flux densities between the regions included in the solution are presented as the sums of orthogonal functions with unknown weighting coefficients. These coefficients are found using the adjoint boundary conditions. The presented approach was used to analyze the thermal processes in the above mentioned three types of the thin-film bulk acoustic wave resonators with piezoelectric transducers based on aluminum nitride. The overheating temperature distribution in the piezoelectric transducer of each resonator and the dependence of the weighted average overheating temperature of this transducer on the dissipated power are determined.