Xianwen Sun

Coexistence of the bipolar and unipolar resistive switching behaviours in Au/SrTiO3/Pt cells

The bipolar and unipolar resistive switching (BRS and URS) modes are first observed to coexist in the Au/SrTiO3/Pt cell fabricated by pulsed laser deposition. These two switching modes can be activated separately depending on the different current compliance (CC) during the electroforming process: with a lower CC (1 mA) the asymmetric BRS behaviour is measured in the voltage range −1.2 to +1 V, while the URS behaviour is observed with a higher CC (10 mA). On the basis of current–voltage characteristics, the switching mechanisms for the BRS and URS modes are considered as a change in Schottky-like barrier height and/or width at the Au/SrTiO3 interface and the formation and disruption of conduction filaments, respectively. The conversion between BRS and URS is reversible. Because each switching mode has a specific advantage, selecting the desired switching mode can broaden the application scope of the cell and enable large flexibility in terms of memory architecture.

Bipolar resistance switching characteristics with opposite polarity of Au/SrTiO3/Ti memory cells

Two types of bipolar resistance switching with eightwise and counter eightwise polarities are observed to coexist in Au/SrTiO3/Ti memory cells. These two types of switching can be induced by different defect distributions which are activated by controlling the electric process. The analyses of I-V and C-V data reveal that the resistance switching with eightwise polarity originates from the change of Schottky barrier at the Au/SrTiO3 interface caused by trapping/detrapping effects at interface defect states, while the switching with counter eightwise polarity is caused by oxygen-vacancy migration.

Unipolar memristors enable “stateful” logic operations via material implication

The realization of material implication (IMP) in a simple circuit combining two bipolar memristors with a conventional resistor was reported and published on Nature recently. The key to IMP is the memristors which are used as digital switches and perform “stateful” logic operations. Here we report that the IMP circuit composed of the unipolar memristors of Au/SrTiO3/Pt devices, which have large switching ratio (over 1000) and linear I-V correlation in low-resistance states, enables logic operations. In the IMP circuit, a small modulation factor of 1.2 is obtained. These results indicate that the robustness of IMP operation is effectively increased.

Study on the Multi-level Resistance-Switching Memory and Memory-State-Dependent Photovoltage in Pt/Nd:SrTiO 3 Junctions

Pt/Nd:SrTiO3 (STO)/In devices were fabricated by depositing Schottky-contact Pt and Ohmic-contact In electrodes on a single crystal STO with Nd doping. The Pt/Nd:STO/In devices show multi-level resistance-switching (RS) memory and memory-state-dependent photovoltage (PV) effects, which can be controlled by the applied pulse width or magnitude. Both the RS and PV are related to the bias-induced modulation of the interface barrier, both in height and width, at the Pt/Nd:STO interface. The results establish a strong connection between the RS/PV effects and the modulation of the Nd:STO interface triggered by applied electric field and provide a new route by using an open-circuit voltage for non-destructively sensing multiple non-volatile memory states.