Non-destructive piezoelectric characterisation of Sc doped aluminium nitride thin films at wafer level

Scandium doped aluminium nitride (ScAlN) gained much attention during last years, since its piezoelectric response is much enlarged as compared to pure AlN films. Above 30% Sc the films are of high interest for piezoMEMS sensing and actuation, ultrasound generation, as well as energy harvesting applications. In this work, piezo-performance uniformity maps are presented for 20% and 33% Sc containing films, sputter deposited on 200-mm wafers. Furthermore, we employ a new method to determine the electro-mechanical coupling k(t)(2). Coupling results for various Sc/(Sc+Al) concentration (0, 6, 20, 26, 33%) are shown. In addition, the dielectric constant epsilon(r) and dielectric loss tan delta, and the transversal and the longitudinal piezoelectric coefficients, e(31,f) and d(33,f,) were measured. The wafers show a high with-in-wafer uniformity (1 sigma uniformity < 2% for Sc20Al80N and < 1% for Sc33Al67N). The highest coupling k(t)(2) = 21.2% was achieved for a 33% Sc film. The presented Al-Sc property-uniformity maps provide a good foundation for ScAlN based MEMS device design and manufacturing.