Piezoelectric AlScN thin films: A semiconductor compatible solution for mechanical energy harvesting and sensors

The transverse piezoelectric coefficient e31,f of Al1-xScxN thin films was investigated as a function of composition. It increased nearly 50% from x = 0 to x = 0.17. As the increase of the dielectric constant was only moderate, these films are very suitable for energy harvesting, giving a 60% higher transformation yield (x = 0.17) as compared to pure AlN. A higher doping might even lead to a 100% augmentation. The thickness strain response (d33,f) was found to increase proportionally to the ionic part of the dielectric constant. The e-type coefficients (stress response), however, did not augment so much as the structure becomes softer. As a result, the transverse voltage/strain response (h31,f-coefficient) was raised only slightly with Sc doping. The low dielectric loss obtained at all compositions suggests also the use of Al1xScxN thin films in sensors.