Behavior of BAW devices at high power levels

Bulk acoustic wave (BAW) and FBAR technologies offer key advantages for transmit filters which are used between the power amplifier and antenna in cell phone applications. The classical challenge for Tx filters in duplexers is to achieve low insertion loss, high return loss, high Rx-Tx isolation and good wideband performance at the same time. The trade-offs between those parameters can be modeled in a straightforward approach is briefly described. The main section of this paper discusses 2nd order effects which become relevant at high power levels. The energy loss in each individual BAW resonator generates a shift and spread of resonance frequencies in the filter elements by self-heating effects. These effects can cause unexpected performance issues and may even lead to thermal instability. A concept for modeling of self-heating effects is presented in detail. The role of self-heating with regard to power-handling capability of a filter is pointed out. As a consequence of extreme energy density at high power levels a certain degree of nonlinear effects can be observed in BAW/FBAR filters. The origin of these effects is discussed as well as a modeling strategy. This is in particular important for emerging W-CDMA applications of BAW and FBAR filters.