The thermodynamic parameters of domain relaxation process in the absence of external electric fields are related to the intrinsic electrostatic and stress/strain conditions inside the materials, such as the states at surface, states at interface with the electrode, and the atomic defects in the bulk. In order to perform systematical studies of these intrinsic effects, we investigated domain relaxation in a monodomain environment, which was obtained in strained epitaxial BiFeO 3 (BFO)(111) films. Without as-grown domain walls and grain boundaries, the epitaxial BFO (111) film provided an ideal system for the dynamic observation of 180-degree domain wall motion. Nano-domains were initially created by writing voltage pulses under the tip of a scanning force microscope and then relaxed through time. The downward polarized domains exhibited much better retention behaviors than the upward domains. A two-step backswitching process was observed, and the behaviors varied with the initial domain sizes. Surface potential measurement showed the dissipation of surface screen charges with time, which was strongly coupled with the 1st step relaxation. The asymmetry behaviors for upward and downward backswitchings, and the two-stage relaxation processes can be explained by the mobile vacancies and the redistribution of surface charges. This study provides the basic understanding of the role of surface charges during the ferroelectric domain relaxation. V

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In this study,MFIS (Metal/Ferroelectric/Insulator/Semiconductor) capacitors whose structure is Al/BFO+Nb/HfO2/p-Si are investigatedby using Taguchi Method. The effects of leakage current, memory window, and signal-to-noise ratio (S/N ratio) are discussed by different process conditions. As a result, the leakage current and memory window indicate the better performance on th same process condition. The better conditions of this MFIS capacitoroccur in rapid thermal annealing (RTA) at 700°C, 5W direct current (DC) power of Nb sputtering and 15 of argon-to-oxygen ratio for laekage current and memory window.Oxygen vacancies were reduced bydoping niobium (Nb) that Nb ions replace ferrum (Fe) ions with RTA at 700°C. The more Nb dopesthe more Nb ions replace Fe ions. Butthe excessive Nb induces to increase the leakage current and reduce the memory widow.