The Wake-Up Behavior in Bi1/2(Na0.8K0.2)1/2TiO3 Thin Films by Nb Doping

Abstract

In ferroelectric thin films, the remanent polarization intensity commonly decreases with electric field cycling, known as fatigue behavior. However, there is an interesting phenomenon where the remanent polarization intensity increases with electric field cycling, called wake-up behavior. This phenomenon was first discovered in HfO₂-based ferroelectric thin films, and the mechanism of the wake-up behavior has not been fully studied. In this work, we adopted Nb doping to enhance the relaxor characteristics of the Bi_1/2(Na_0.8K_0.2)_1/2TiO₃ (BNKT) thin films. The BNKT-0.6%Nb thin film shows a maximum P_r value of 31.49 μC/cm² after 10⁸ cycles and better fatigue resistance of more than 10⁹ cycles. By an appropriate amount of Nb doping, there are more ergodic relaxor phases in the thin film, which is the key to the wake-up behavior. The disorderly nanodomains in the ergodic relaxor could be slowly expanded to larger range domain structures under electric field cycling, which is the nonpolar to polar phase transition. Moreover, this slow transition could only happen under a certain amplitude, and the full transition requires a certain number of cycling. This wake-up behavior in BNKT-based thin films provides a potential approach to solve fatigue problems and is beneficial for application in ferroelectric memory.