Preparation Of BaTiO₃-based Ferroelectric Diode And Its Non-volatile Storage Performance

As a promising candidate for next-generation non-volatilememory technology,ferroelectric-induced resistanceswitching has attracted considerable attention owing to theadvantages of high-density data storage,fast write/readspeed,and non-destructive readout.In general,a ferroelectric resistive memory is composed of a ferroelectric thin film sandwiched between two metallic electrodes.One ofthe ferroelectric resistive memory is the ferroelectricdiodes which utilizethe polarization to tune the interface Schottky barriers and the resistive switching properties.Nowadays,the ferroelectric diodeshave achieved great progress since itisfirst proposed by Blom et al.in 1994.However,ferroelectric diodes have low ON/OFF current ratio which has severely limit their development.Therefore,how to improve ON/OFF current ratiohas become a hot topic inthis research community.In order to solve these problems,weadopt ionic doping tochange the distribution of charged defects inside the ferroelectric layer and the profile of Schottky barriersat the ferroelectric/electrode interface,which in turn modulates ferroelectricity and resistive memory performance of the ferroelectric diodes.Three research topics are involved in this thesis.1.The fabrication and resistance switching properties of BaTiO₃ ferroelectric diodes was explored.Bottom electrodes and ferroelectric thin films were fabricated by using pulsed laser deposition,besidesthe growth conditionof high quality thin films was optimized.X-ray diffraction and atomic force microscopywere performed to ensure quality of the thin films.The thickness of the epitaxial thin films was confirmed by X-ray reflectivity.2.The electricalperformance of Ba TiO₃ ferroelectric diodes was tested.Resistance switchingperformance and ferroelectricity are two typical categoriesof theelectricity testing.Different thickness gradient of the Ba TiO₃ ferroelectric diodes was fabricated by controlling the laser pulse number.We got the relationshipbetween resistive switching performance andthickness.Moreover,we got the optimum thickness of resistive switching performance.3.The electrical performance in BaTiO3-basedferroelectric diodes due tothedoping was tested.A large ON/OFF current ratio is achieved in a Au/Nb:Ba TiO₃/SrRuO₃ diode at room temperature.This can be ascribed to the enhanced ferroelectric-modulation on potential barrier at the Nb:Ba TiO₃/SrRuO₃ interface associated with the Nb⁵⁺donors.In contrast,the resistance switching is suppressed in a Au/Fe:Ba TiO₃/SrRuO₃ device since the Fe³⁺acceptors suppresssemiconductingcharacter of the Ba TiO₃ thin film and makethe polarization-modulation of band diagram negligible.The substitution-dependent resistance switching behaviors are discussed in terms of the modulation of band diagrams with polarization reversal and the transport analysis for the ON and the OFF state at various temperatures.