Characterization of the Piezoelectric Response of Aluminum Nitride Grown by dc Magnetron Sputtering for Applications in Thin-Film Resonators

Aluminum nitride is a promising material for use in thin-film bulk acoustic wave resonators for applications in RF bandpass filters. This paper discusses the requirements needed for a dc magnetron sputtering system to grow piezoelectrically active films with x-ray diffraction rocking curves of 3.3° on silicon substrates, 5° on aluminum substrates and oxygen concentrations of l at.%. For applications in integrated resonators, a materials characterization is insufficient in predicting the subsequent device performance. A simple acoustic device structure which allows a quick measurement of the device performance is used to extract maximum effective coupling coefficients keff2 of 0.009% at 3.4GHz and 0.002% at 2.4GHz for two different films with rocking curves of 5.7° and 9.0° respectively. This parameter extraction technique may be used to make relative comparisons between films grown under different deposition conditions.