Deposition parameters were found to have a marked effect on piezoelectric response of reactive radio frequency (RF) sputtered AlN thin films. We observed piezoelectric response values ranging from -3.5 to +4.2 pm/V for 1 mu m thick AlN films deposited onto Ti//Ru electrode stacks. This substantial variation in piezoelectric response occurred despite the fact that all of the AIN thin films exhibited the correct crystallographic orientation for piezoelectric activity ((0002) crystallographic planes parallel to the substrate). An investigation of the effects of deposition parameters, in particular the nature of the Ru//AlN interface, was conducted. The lag time between deposition of adjacent thin film layers appeared to have the greatest affect on the value of the piezoelectric response. This result suggests that a chemical reaction occurring on the Ru thin film surface is responsible for changing an important thin film property such as dipole orientation within the overlying AlN thin film.