Effects of deposition conditions on the ferroelectric properties of (Al1-xScx)N thin films

The ferroelectricity of (Al1-xScx)N (x=0-0.34) thin films with various thicknesses was investigated. (Al1-xScx)N films were prepared at 400 degrees C on (111)Pt/TiOx/SiO2/(001)Si substrates by the radio frequency dual-source reactive magnetron sputtering method using Al and Sc targets under pure N-2 gas or a mixture of N-2 and Ar gases. The film deposited under N-2 gas showed larger remanent polarization than those under N-2 + Ar mixture. Ferroelectricity was observed for films with x=0.10-0.34 for about 140-nm-thick films deposited under N-2 gas. The x=0.22 films showed ferroelectricity down to 48nm in thickness from the polarization-electric field curves and the positive-up-negative-down measurement. The ferroelectricity of the 9nm-thick film also was ascertained from scanning nonlinear dielectric microscopy measurement. These results reveal that ferroelectric polarization can switch for films with much broader compositions and thicknesses than those in the previous study.