Microstructure and piezoelectric properties of c-axis ScAlN films on the Y-128° LiNbO₃ substrate

Highly c-axis preferred orientation ScAlN films were deposited on Y-128° lithium niobate using the co-sputtering technique. The substitution of Sc atoms at Al positions causes a lattice distortion and induces a large piezoelectric response. X-ray diffraction patterns indicated that most of the films showed (002) peaks and the best crystallinity appeared at the Sc content of 9.0 at%. The cross-section of TEM results showed that the higher c-axis orientation columnar structure formed as the film thickness increased, and the structure transforms from wurtzite to cubical structure from the nano-beam diffraction analysis. Then the piezoelectric coefficient would be enhanced obviously at the Sc content of 18.1 at% and the value is nearly two times larger than pure AlN. After rapid thermal annealing treatment, the crystal quality could be improved and the highest value of piezoelectric coefficient was achieved at 18.26 pC/N.