High crystal quality and low residual stress composite piezoelectric films prepared by a two-step method

The crystal quality and residual stress of piezoelectric films are critical factors that limit the performance of acoustic wave devices. To overcome this challenge, a new two-step method integrating metal-organic chemical vapor deposition (MOCVD) and physical vapor deposition (PVD) was presented. The lower part of the composite film was first grown by MOCVD, exhibiting monocrystalline quality and high residual stress. Subsequently, the upper part of the composite film deposited by PVD effectively compensates for the residual stress in the lower part of the composite film. The new two-step method was validated on the growth of AlN and AlScN on sapphire substrate. A composite film Al0.8Sc0.2 N/AlN was obtained with a full width at half maximum of 0.047° for AlN (002) of rocking curve, exhibiting a residual stress of +381 MPa and a surface roughness of 1.12 nm. It demonstrates the feasibility of preparing high-quality composite piezoelectric films for further acoustic applications.