Polarity control of (0001) oriented AlN films by Si doping and applications to polarity inverted SiAlN/AlN film bulk acoustic wave resonators

It has been reported that 1-15% of Si doping into AIN films induce polarity inversion from Al-polarity to N-polarity. We fabricated SiAlN monolayer film with Si concentration of 5% and two-layer polarity inverted Si0.05Al0.95N/AlN and AlN/Si0.05Al0.95N films by RF magnetron sputtering deposition. Si concentration in the films were controlled by adjusting the amount of the Si grains on the Al target. Polarity directions of the AlN and SiAlN films, estimated by a press test, were Al-polarity and N-polarity, respectively. The kt² of the SiAlN films were determined from the frequency characteristics of conversion loss in SiAlN film HBARs. The crystalline orientation and the kt² of the Si0.05Al0.95N film degraded from those of the pure AIN thin film. Moreover, we investigated the longitudinal wave conversion loss of two layered polarity inverted HBARs. They resonated in a 2nd mode and agreed with theoretical results by a Mason's equivalent circuit model. From these results, two layered polarity inverted structures can be obtained.