| Ferroelectric memory, as a novel candidate for the traditional memory, has gained broad attention and study for a long time. In ferroelectric memory, ferroelectric resistive switching effects based on polarization reversal are particularly attractive and popular, since polarization reversal does not induce a chemical alteration and is an intrinsically fast phenomenon. Depending on the transport property, ferroelectric resistive switching effects can be categorized into two types. One is the tunnel electroresistance effect based on the tunneling behaviors in ferroelectric ultrathin film. The other is the ferroelectric diode relied on the interface barrier potential modified by polarization switching. The tunnel electroresistance effect usually appears in ferroelectric tunnel junctions, and it relies on a change of tunneling barrier height modulated by polarization switching. As for ferroelectric diodes, a Schottky barrier or p-n junction exists at the interface between the ferroelectric thin film and electrode layer, and the potential profile of the barrier or junction is changed by the polarization reversal. No matter what transport mechanism functions in ferroelectric film, both two mechanisms are induced by polarization reversal in ferroelectric material. It is of great importance to study different ferroelectric materials and domain switching, and analyze the conductance behaviors.In this work, based on the two different transport properties, we adopt two kinds of representative materials such as BaTiO2 and (K,Na)NbO3 respectively, and study the polarization switching of the ferroelectric domains. Beside, we measure the conductance and transport property for each kind of material. The results have been achieved as below,1) We fabricate epitaxial BaTiO3 ultrathin film with thickness of 1.2 nm by pulsed laser deposition. The cross-sectional structure is observed by high-resolution transmission electron microscopy. Combining atomic force microscopy, piezoresponse force microscopy and conductive-tip atomic force microscopy, we have studied the surface topography, domain switching and tunneling conductance behavior.2) The tunnel electroresistance effect is observed in ferroelectric tunnel junctions based on the BaTi03/Lao.67Sr0.33MnO3 heterostructure, and the resistance ratio between ON and OFF can reach up to 100. The proportion of upward or downward polarization domains can be controlled by the amplitude and direction of the poling bias, and it will lead to several local regions with different conductivities. The multi-resistance states under different poling biases with stable retention contribute to researches of the multi-resistance states storage in ferroelectric materials.3) Highly (001) oriented (K,Na)NbO3 lead-free piezoelectric film was deposited on LaNiO3 coated silicon substrate by RF magnetron sputtering. Through the measurement by piezoelectric force microscopy, the phase loops and amplitude loops show good stability and repeatability in (K,Na)NbO3 thin film. Besides, the ferroelectric domains can be switched for many times and keep the polarization direction for a long time.4) The resistive switching behavior in Pt/(K,Na)NbO3/LaNiO3 devices can be achieved by controlling the polarization direction of the (K,Na)NbO3 film. The change of resistance states is attributed to the polarization reversal which modulates the interface potential barrier height and the depletion layer width. In addition, the fact that the resistance ratio can keep for a long time indicates good stability and anti-fatigued ability. The promising result shows potential application of our devices as non-volatile memories. |
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