Resistance switching in metal oxides could form the basis for next-generation non-volatile memory. It has been argued that the current in the high-conductivity state of several technologically relevant oxide materials flows through localized filaments, but these filaments have been characterized only indirectly, limiting our understanding of the switching mechanism. Here, we use high-resolution transmission electron microscopy to probe directly the nanofilaments in a Pt/TiO(2)/Pt system during resistive switching. In situ current-voltage and low-temperature (approximately 130 K) conductivity measurements confirm that switching occurs by the formation and disruption of Ti(n)O(2n-1) (or so-called Magnéli phase) filaments. Knowledge of the composition, structure and dimensions of these filaments will provide a foundation for unravelling the full mechanism of resistance switching in oxide thin films, and help guide research into the stability and scalability of such films for applications.

The detailed mechanism of electronic bipolar resistance switching (BRS) in the Pt/TiO(2)/Pt structure was examined. The conduction mechanism analysis showed that the trap-free and trap-mediated space-charge-limited conduction (SCLC) governs the low and high resistance state of BRS, respectively. The SCLC was confirmed by fitting the current-voltage characteristics of low and high resistance states at various temperatures. The BRS behavior originated from the asymmetric potential barrier for electrons escaping from, and trapping into, the trap sites with respect to the bias polarity. This asymmetric potential barrier was formed at the interface between the trap layer and trap-free layer. The detailed parameters such as trap density, and trap layer and trap-free layer thicknesses in the electronic BRS were evaluated. This showed that the degradation in the switching performance could be understood from the decrease and modified distribution of the trap densities in the trap layer.

Limiting the location where electron injection occurs at the cathode interface to a narrower region is the key factor for achieving a highly improved RS performance, which can be achieved by including Ru Nanodots. The development of a memory cell structure truly at the nanoscale with such a limiting factor for the electric-field distribution can solve the non-uniformity issue of future ReRAM.

The role of grain boundaries on oxygen surface exchange in an oxide ion conductor is reported. Atomic‐scale characterization of the microstructure and chemical composition near the grain boundaries of gadolinia‐doped ceria (GDC) thin films show the segregation of dopants and oxygen vacancies along the grain boundaries using the energy dispersive spectroscopy in scanning transmission electron microscopy (STEM‐EDS). Kelvin probe microscopy is employed to verify the charge distribution near grain boundaries and shows that the grain boundary is positively charged, indicating a high concentration of oxygen vacancies. AC impedance spectroscopy on polycrystalline GDC membranes with thin interfacial layers with different grain boundary densities at the cathodes demonstrated that the cells with higher grain boundary density result in lower electrode impedance and higher exchange current density. These experimental evidences clearly show that grain boundaries on the surface provide preferential reaction sites for facilitated oxygen incorporation into the GDC electrolyte.

This study examined the effects of electrical forming methods on the bipolar resistance switching (BRS) behavior in Pt/TiO(2)/Pt sandwich structures. The BRS is confined to a region near the ruptured end of conducting nanofilaments, which are composed of a Ti(n)O(2n-1) Magnéli phase formed by electroforming. The intermediate phase with an oxygen vacancy concentration between the insulating TiO(2) and the residual conducting filament that formed at the interface region was considered to be the switching layer (SL). The change in filament shape caused by a variation in the compliance current during filament formation resulted in a different filament rupture location and SL configuration. Precise control of the filament formation and rupture process resulted in SLs connected in an anti-parallel configuration. It was possible to reconfigure the SLs in the same fashion without any restraints, which allowed an unlimited memristive operation to be achieved. This paper presents a new technique in voltage sweep mode that applies a compliance current as a tool to achieve a memristor with unlimited operation.