AlScN films prepared by alloy targets and SAW device characteristics

In this paper, we reported a surface acoustic wave (SAW) device prepared and optimized by piezoelectric films containing AlN, AlScN (Sc-20 at%) and AlScN (Sc-30 at%) by reactive magnetron sputtering using Al and AlSc alloy targets. We calculated the material intrinsic electromechanical coupling coefficient kt2 of AlScN (Sc-20 at%) and AlScN (Sc-30 at%) which are much better than AlN. It can be explained by the lattice softening. Furtherly, the results were confirmed by transmission electron microscopy (TEM) observation of the microstructure. Then the SAW devices based on three thin films were tested by vector network analysis obtaining the device equivalent electromechanical coupling coefficient keff2. The value of AlScN (Sc-20 at%) keff2, which equals to 1.94%, is higher than that of AlN and AlScN (Sc-30 at%) while the value of AlScN (Sc-30 at%) kt2 is higher than that of others. It is shown in our study that the crystallinity and orientation of the material still have a greater impact on keff2 but it does not have influence on kt2 in the actual device preparation process.