Effects of high-temperature thermal annealing on the crystal structure and phase separation in sputtered ScAlN thin films

• Published in: Journal of alloys and compounds 2024-08, Vol.997, p.174997, Article 174997
• Main Authors: Deng, Liqiong, Meng, Fanping, Li, Ji, Ye, Fang, Guo, Wei, Ye, Jichun
• Format: Article
• Language: English
• Subjects: High temperature thermal annealing; Phase separation; Piezoelectric thin films; Scandium Aluminum Nitride; Sputter deposition
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2024.174997

Doping scandium in aluminum nitride (AlN) can effectively enhance the piezoelectric properties of the material, herein making ScAlN a research hotspot for the application of high-frequency and wide-bandwidth RF devices. However, there has been limited investigations into the evolution of crystal structure and composition stability under thermal annealing, especially at high temperatures. In this work, the crystal quality, surface morphology, phase and elemental distribution of sputter-deposited ScxAl1−xN thin films with various Sc contents were comprehensively investigated before and after high-temperature thermal annealing. It is found that the full-width-half-maximum values of the (002) diffraction peaks of ScxAl1−xN thin films increase with higher Sc contents, while appropriate annealing condition can enhance crystal quality. It is also revealed that Sc segregation leads to the formation of cubic-phase ScN grains, and Sc atoms diffuse towards the sapphire substrate and surface, forming a Sc2O3 layer on two sides of the ScAlN core layer. These findings provide important insights into the preparation of wurtzite ScAlN films under thermal annealing and offer valuable references for the development of novel ScAlN-based devices. •ScxAl1−xN films with 0-20% Sc component were deposited.•Incorporating Sc into the AlN crystal lattice induces lattice strain and distortion.•The FWHM values of the XRD rocking curve of Sc0.05Al0.95N thin films is improved from 1.5° to 0.85° after annealing at 1550℃ for 30 min.•Cubic-phase ScN grains were formed inside the Al-rich ScAlN matrix after thermal annealing.•Sc atoms diffuse towards the sapphire substrate and surface, forming Sc2O3 layer due to the stronger oxygen affinity of Sc compared to Al.