Study On Resistance Switching Characters Of Nb:SrTiO₃Film, Al₂O₃Film And The Stacked Structure Composed Of The Two Films

With benefits of high switching speed, reliable stability, high storage density, low power consumption,well scalability and the compatible fabrication process with CMOS, resistance random access memory（RRAM） is considered to be a most potential candidate for the next-generation nonvolatile memory（NVM）. But the mechanism of RRAM is still not well understood, which is the biggest trouble for furtherdevelopment and application. With typical perovskite structure Nb: SrTiO₃（NSTO） film and highinsulation Al₂O₃film demonstrate as interfacial effect and the mechanism of conductive filaments,respectively. It is beneficial to discuss the mechanisms of electrical resistance characters with researchingon the resistance switching （RS） characters of NSTO and Al₂O₃. Based on this situation0.7wt%Nb-dopedSrTiO₃film and Al₂O₃high insulation film are fabricated though pulse laser deposition （PLD） and directcurrent reactive magnetron sputtering technology. By means of changing the metal electrode and stackingthe dielectric layer, RS properties are investigated and the mechanisms of the two films are discussed.Several aspects are included in this thesis.1. The fabrication and RS properties of Pt/NSTO/Pt cellBoth anticlockwise bipolar and unipolar RS coexist in Pt/NSTO/Pt device. The bipolar RS characters aregradually stable with the sweeping cycles. The unipolar RS characters are stable relatively. There are twointerfaces in this device which introduces Schottky barriers and hence bipolar RS characters come out. Theunipolar RS characters are produced by the forming and rupture of conductive filaments which are mainlycomposed of carriers, oxygen vacancy or other defects.2. The fabrication and RS properties of Al/NSTO/Pt cell At the initial state In/Al/NSTO/Pt device has two interfaces which introduced Schottky barriers. Theheight of Schottky barrier at the Al/NSTO interface is higher than that at the NSTO/Pt interface. Multilevelbipolar RS characters appear with the increasing of sweeping voltages. And the Schottky barrier at theNSTO/Pt interface dominates the bipolar RS. A new device is obtained under a proper breakdown. Thisnew cell had more stable and reliable anticlockwise RS characters. Different resistive hyteresises polarityimplies that proper breakdown impacts the Schottky barrier and the distribution of oxygen vacancy andother defects in the device. A thin Al₂O₃film introduced between NSTO film and Al electrode plays animportant role for the improvement of RS properties. The existence of multilevel RS characters depends onthe Schottky barrier at the NSTO/Pt interface.3. The influence of NSTO insert layer to the RS properties of Al/Al₂O₃/NSTO/Pt cellWith the inserting NSTO film the RS properties has been improved such as stability, switching voltagesand power dissipation. The traditional electroforming process was replaced by a lubrication process. Theswitching voltages VONand VOFFof this device are0.35V and-0.4V respectively. The device has relativelow power consumption. Both high resistance state （HRS） and low resistance state （LRS） have goodstability. A mass of oxygen vacancy, carriers or other defects are existed in the polycrystalline NSTO film,so there is no electroforming process. According to fitting results of I-V curves, the conductionmechanisms of the ON and OFF states are demonstrated as ohmic conduction and Frankel-Poole emission,severally. The switching mechanisms are formation and rupture of the conducting paths. The mainlycomposition of the conducting paths are injection carriers, which come from the interface between NSTO insert layer and Al2O3layer. The interface barriers also play some roles in resistive switching but not theimportant composition.