Linghong Ding

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.

Study on Resistance Switching Properties of Na0.5Bi0.5TiO3Thin Films Using Impedance Spectroscopy

The Na0.5Bi0.5TiO3(NBT) thin films sandwiched between Au electrodes and fluorine-doped tin oxide (FTO) conducting glass were deposited using a sol–gel method. Based on electrochemical workstation measurements, reproducible resistance switching characteristics and negative differential resistances were obtained at room temperature. A local impedance spectroscopy measurement of Au/NBT was performed to reveal the interface-related electrical characteristics. The DC-bias-dependent impedance spectra suggested the occurrence of charge and mass transfer at the interface of the Au/NBT/FTO device. It was proposed that the first and the second ionization of oxygen vacancies are responsible for the conduction in the low- and high-resistance states, respectively. The experimental results showed high potential for nonvolatile memory applications in NBT thin films.

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.

Resistance switching properties of sol-gel derived La0.67Ca0.33MnO3 thin films on F-doped SnO2 conducting glass

The electric-pulse-induced resistance switching of the Au–La0.67Ca0.33MnO3(LCMO)-FTO (fluorine-doped tin oxide) heterostructures was studied by electrochemical workstation. A distinct current-voltage characteristic of the device with pronounced reproducible nonlinearity, asymmetry, and hysteresis was observed at room temperature. The current-voltage characteristics suggest a Poole–Frenkel and space-charge-limited current type mechanism controlled by Au/LCMO interface traps. The resistance switching behavior shows obvious multilevel resistance switching. The present results suggest a possible application of Ag-LCMO-FTO system as multilevel memory devices.

Bottom-gate amorphous In2O3 thin film transistors fabricated by magnetron sputtering

In this letter, bottom-gate thin film transistors using amorphous In2O3 as the n-channel active layer were fabricated on SiO2/Si substrates by direct current magnetron sputtering at room temperature. By controlling the sputtering time, In2O3 can be grown into the amorphous phase. Compare to its crystalline counterpart, amorphous In2O3 offer distinctive attractions such as smoother surfaces, better film uniformity, while maintaining comparable or greater carrier mobility. The device with amorphous channel layer shows good performance with the mobility of 15 cm2/Vs and the current on-off ratio of 106. The device operates in enhancement mode with the threshold voltage of 1.4 V. Excellent device performance and low fabrication temperature make the In2O3-TFTs suitable for the potential applications in the large-area electronics.