Probing of Polarization Reversal in Ferroelectric (Al,Sc)N Films Using Single- and Tri-Layered Structures With Different Sc/(Al+Sc) Ratio

Abstract

Wurtzite-(Al,Sc)N films are promising candidates for ferroelectric memory devices owing to their outstanding properties. However, there are many challenges on the way to practical applications, including lowering an electric field required for polarization switching. Understanding the switching kinetics, especially the starting point of polarization reversal, is key to designing materials with desired properties. Here, the impact of Sc concentration and segregation on the switching kinetics for (Al,Sc)N capacitors is investigated by evaluating time- and field-dependences of the switching polarization for the tri-layered (Al,Sc)N films with various Sc/(Al+Sc) ratios. The remanent polarization of stacked films slightly decreased compared to those of the single-layered films with the same average Sc/(Al+Sc) ratio, while their coercive fields depended on the average Sc content in (Al,Sc)N. The ferroelectric switching behavior suggests the possibility of nucleation originating from the Sc-rich region and the sequential switching mechanism for individual layers, which is unique to multilayered films. This shows a possibility that nucleations of the polarization switching start not from the interface between the (Al,Sc)N films and the electrodes. The unique switching kinetics in tri-layered (Al,Sc)N films have provided new insights into the field of ferroelectric switching in wurtzite-nitrides.