Preparation, Characterization, and Application of AlN/ScAlN Composite Thin Films

Piezoelectric aluminum nitride (AlN) thin film, as a commonly used material for high-frequency acoustic resonators, has been a research hotspot in the RF field. Doping Sc elements in AlN is one of most effective methods to improve the piezoelectricity of the material. In this work, the first principal calculation and Mori-Tanaka model are used to obtain the piezoelectric constants of AlN, ScAlN, and AlN/ScAlN composites. Then, five types of AlN/ScAlN thin films are prepared on 8 inch silicon substrates. The crystal quality, roughness, and stress distribution are measured to characterize the film quality. The results show that composite film can effectively solve the problem of abnormal grains and reduce the roughness. Finally, a lamb wave resonator with an AlN/Sc0.2Al0.8N composite working at 2.33 GHz is fabricated. The effective electromechanical coupling coefficient K-eff(2) is calculated to be 6.19%, which has the potential to design high-frequency broadband filters.

Automated summary

The piezoelectric constants of AlN, ScAlN, and AlN/ScAlN composites were obtained through first-principles calculation and Mori-Tanaka model. Five types of AlN/ScAlN thin films were prepared on 8-inch silicon substrates, and the film quality was characterized by measuring crystal quality, roughness, and stress distribution. The results showed that the composite film effectively addressed the problem of abnormal grains and reduced roughness. A lamb wave resonator with an AlN/Sc0.2Al0.8N composite was fabricated, which had an effective electromechanical coupling coefficient K-eff(2) of 6.19% and potential for designing high-frequency broadband filters.