Electroforming effects on the composition, structure, and electrical resistance of Pt/ TiO 2 / Pt switching cells are investigated. The correlation between the electroforming procedure and the resulting bipolar switching behavior is discussed. The dependence of electroforming behavior on atmosphere is also identified, from which we define symmetric or asymmetric electroforming. The symmetry of electroforming is a key factor determining the resulting bipolar switching characteristics. From the experimental results we suggest a possible mechanism for electroforming in Pt/ TiO 2 / Pt in terms of the formation of oxygen gas and vacancies in the vicinity of the anode.

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Metal/insulator/metal thin film stacks showing stable resistive switching are promising candidates for future use as a nonvolatile resistive random access memory, competitive to FLASH and DRAM. Although the switching mechanisms are not completely understood a lot of theories and models try to describe the effects. One of them postulates the trapping and detrapping of electronic charge in immobile traps as the reason for the resistance changes, also known as Simmons & Verderber model. This contribution shows that this “pure electronic” switching mechanism will face a voltage-time dilemma—general to all switching insulators—at conditions competitive to the state-of-the-art FLASH. There is an incompatibility between the long retention time (10 years) and the short READ/WRITE current pulses (tREAD/WRITE≤100 ns) at high densities (area≤100×100 nm2) at low applied voltages (≤1 V). This general dilemma is exemplified in two detailed scenarios with different electronic band and defect properties.