In this study, polarity dependent and multilevel resistive switching characteristics of the Ta/TaO x /Pt device are investigated. The resistive switching polarity is decisively associated with the location of the Ta/ TaO x interface while at a specific switching polarity, and multiple (four) resistance states in the Ta/TaO x /Pt device are achieved by controlling the stop voltage during the reset process and are stable for more than 10 4 s under continuous readout testing. X-ray photoelectron spectroscopy reveals that the Ta/TaO x interface is rich in oxygen vacancies. A schematic on the configurations of oxygen-vacancy aggregated conducting paths is proposed, where the Ta/TaO x interface acts as an oxygen vacancy reservoir, and the migration of vacancies can be driven by the applied electric field as well as the vacancy concentration gradient emanated from the Ta/TaO x interface. The polarity-dependent and multilevel resistive switching behaviors are then discussed in terms of filament configuration variation, and their interrelationship is visibly unveiled.

A distinct unipolar but single-polarity resistive switching behavior is observed in a TiO(x)/Pt/TiO(x) trilayer structure, formed by thermal oxidation of a Ti/Pt/Ti stack. As a comparison, a memory device with a single TiO(x) active layer (without addition of Pt midlayer) is also fabricated but it cannot perform resistive switching. Energy band diagrams are illustrated to realize the modulation of Schottky barrier junctions and current conduction in TiO(x)-based devices under various biasing polarities. Introduction of the Pt midlayer creates two additional Schottky barriers, which mediate the band bending potential at each metal-oxide interface and attains a rectifying current conduction at the high-resistance state. The rectifying conduction behavior is also observed with an AFM-tip as the top electrode, which implies the rectifying property is still valid when miniaturizing the device to nanometer scale. The current rectification consequently leads to a single-polarity, unipolar resistive switching and electrically rewritable performance for the TiO(x)/Pt/TiO(x) device.

In general, the conventional sliding mode control design is assumed that the upper boundary of parameter variations and external disturbances is known, it causes high frequency chattering and high gain phenomenon by using sign function, else steady-state error by using sat function. Immune-Fuzzy theorem simplifies the complexity of humor system, as well as introducing fuzzy control. This paper presents an Immune-Fuzzy sliding mode controller (FISMC) not only eliminate the system uncertainty but also overcomes the drawback of sign function and sat function. Finally, the performance of the proposed method is verified by simulation. The proposed FISMC shows the robustness for the motor parameters variation and the improvement of chattering phenomenon.