Phase transition kinetics and sublayer optimization of HfO2/ZrO2 superlattice ferroelectric thin films

Abstract

The sublayer thickness of superlattices, as a key factor affecting lattice integrity, interface defects, and strain, deserves in-depth studies about its impact on improving ferroelectric properties. This study described and analyzed the performance of HfO2/ZrO2 superlattices with various sublayer thicknesses. It can be concluded that the structure of the thicker layers will guide the trend of the phase composition of the entire device: when ZrO2 layers are thicker, the superlattices will exhibit antiferroelectricity due to the higher content of the tetragonal phase (t-phase); when HfO2 layers become thicker, the fraction of the monoclinic phase (m-phase) will increase, leading to a decrease in ferroelectricity and an increase in leakage current. In this way, the device with a 1:1 HfO2/ZrO2 thickness ratio was optimized to have the largest remanent polarization and the lowest leakage current. Maintaining the same thickness ratio of the HfO2/ZrO2 superlattices, it was found that HfO2/ZrO2 superlattices with thinner sublayers exhibited a larger remanent polarization (Pr) value due to increased interlayer distortion. On the contrary, the thicker sublayers reduced leakage current, which was beneficial for improving the device lifespan.