Microstructure and piezoelectric properties of reactively sputtered highly C-axis ScxAl1-xN thin films on diamond-like carbon/Si substrate

We report deposition of pure AlN and ScxAl1-xN thin films with different Sc concentration on DLC/Si substrate by RF and DC reactive magnetron co-sputtering method by using Al and Sc as targets. The X-ray diffraction (XRD) results showed that the films have high c-axis-orientation. Electron probe microanalyzer (EPMA) analysis reveals the presence of scandium atoms reduce the space occupied by aluminum atoms, leading to lattice distortion during the phase transition. The SEM cross-section results showed that the ScxAl1-xN films are highly aligned along c-axis and have columnar like morphology. The top view of SEM results indicated that the new phase formation above Sc 30.33%, however no new peak appeared in the XRD pattern. The piezoelectric coefficient (d33) of ScxAl1-xN thin films are measured and the highest value (11.54 pC/N) is achieved at x = 30.33% increasing 14 times, as that with AlN/DLC/Si, 0.73 pC/N. ScxAl1-xN films on DLC/Si substrate have a great potential to be applied on high frequency SAW devices in the future.