Impact of Deposition Temperature on Crystal Structure and Ferroelectric Properties of (Al1−xScx)N Films Prepared by Sputtering Method

Abstract

The deposition temperature dependence of the crystal structure and ferroelectricity for Sc‐doped AlN [(Al0.78Sc0.22)N] films is investigated. (Al0.78Sc0.22)N films 120–190 nm thick are deposited at various deposition temperatures between 500 °C and ambient temperature without heating on (111)Pt/TiO x /SiO2/(100)Si substrates. Crystalline films are obtained for all films, but its (001) orientation decreases with decreasing deposition temperature below 300 °C. Crystal anisotropy increases with decreasing deposition temperature due to the decrease in the thermal strain that originates from the larger thermal expansion coefficient of (Al0.78Sc0.22)N than Si. Ferroelectricity is observed by both of the polarization–electric field (P–E) curves and the positive‐up–negative‐down (PUND) measurement for all films. The ferroelectric polarization switching of the films deposited without heating is ascertained not only by P–E curves but also by the phase change of the piezoresponse. Slight increase in the coercive field with decreasing deposition temperature can be explained by the increase in crystal anisotropy.