Influence of process parameters on properties of piezoelectric AlN and AlScN thin films for sensor and energy harvesting applications

This paper reports on the deposition of AlN and Al X Sc 1-X N films by pulse magnetron sputtering. The influence of process parameters on the film properties and the evaluation of the films for micro energy harvesting are presented. For AlN it is shown, that film stress can be varied in a considerable range between compressive and tensile stress while maintaining good piezoelectric properties. Additionally, the effect of doping AlN with Sc regarding piezoelectric and mechanical properties is presented. The films show the expected increase of piezoelectric properties as well as the softening of the material with higher Sc concentrations. Above a threshold concentration of around 40% Sc in the Al X Sc 1-X N films, there exists a separation into two phases, an Al-rich and a Sc-rich wurtzite phase, which is shown by XRD. At Sc concentrations higher than 50%, the films are not piezoelectric, as the films are composed primarily of the cubic ScN phase. Sc doping allows to significantly increase the energy generated in test setup. Up to 350 μW power have been generated under optimum conditions.