Temperature characteristics of ZnO-based thin film bulk acoustic wave resonators

In the past few years, thin film bulk acoustic wave (BAW) devices have caught the attention of many RF researchers and developers primarily for their potential utilization in wireless applications. Some of the major advantages BAW devices present over other filter technologies in use today include size reduction and the possibility of on-chip integration. As the technology matures, it becomes necessary to more fully characterize the performance of the devices and to develop more accurate models describing their behavior. In this investigation, the effects that temperature variations have on 1.8 GHz zinc oxide (ZnO)-based solidly mounted BAW resonators (SMRs) are studied. The average temperature coefficients of the series and parallel resonant frequencies of the fabricated devices were found to be -30.5 ppm/1/spl deg/C and -32.5 ppm//spl deg/C, respectively. The slight decrease in separation between the two resonant frequencies with temperature implies there is slightly less effective coupling with increased temperature. With little temperature coefficient data for thin film ZnO available in the literature, the importance of an accurate model is evident. The resonator device performance was simulated using Ballato's electronic circuit model for acoustic devices on a SPICE-based platform. By virtue of the comparison between the predicted and measured device response, various material parameters were extracted.