I-V measurement of NiO nanoregion during observation by transmission electron microscopy

Abstract

Conduction measurements with simultaneous observations by transmission electron microscopy (TEM) were performed on a thin NiO film, which is a candidate material for resistance random access memories (ReRAMs). To conduct nanoscale experiments, a piezo-controlled TEM holder was used, where a fixed NiO sample and a movable Pt-Ir counter electrode were placed. After the counter electrode was moved to make contact with NiO, I-V measurements were carried out from any selected nanoregions. By applying a voltage of 2 V, the insulating NiO film was converted to a low resistance film. This phenomenon may be the "forming process" required to initialize ReRAMs. The corresponding TEM image indicated a structural change in the NiO layer generating a conductive bridge with a width of 30-40 nm. This finding supports the "breakdown" type forming in the so-called "filament model" of operation by ReRAMs. The inhomogeneity of resistance in the NiO film was also investigated.

Analysis of resistance switching and conductive filaments inside Cu-Ge-S using in situ transmission electron microscopy

“…For example, studies have been done on the appearance and disappearance of superstructures in PCMO by applying voltage, 30 I-V hysteresis of PCMO in TEM, 31 filament-like structural changes in TiO 2 , 32 and dynamical forming processes in NiO. 33 More detailed experimental results that would confirm the conduction mechanism during the switching process are required to enable the switching mechanism to be better understood.…”

“…In situ transmission electron microscopy (TEM), where TEM observations and physical (e.g., electrical) measurements have been simultaneously performed, [27][28][29][30][31][32][33][34][35][36][37] has attracted a great deal of attention to satisfy this demand. The numbers of such studies using piezo-controlled TEM holders have been increasing in the past few years.…”

In-situ transmission electron microscopy of conductive filaments in NiO resistance random access memory and its analysis

“…2 MX). As reported earlier, 42 the bridge may work as a conductive filament contributing to the ReRAM switching.…”

“…22 The resistivity around the grain boundary is expected to be low, and this was experimentally confirmed by means of in-situ TEM. 42 Formation of conductive filaments and further ReRAM switching would preferentially occur around the grain boundaries. 11,43 Because of the less insulating property at the grain boundary, soft forming is expected, and possibility of permanent breakdown must be reduced.…”

“…By using a serial resistor in the measurement circuit to suppress current overshoot during the forming process, 8,40 Fujii et al performed a real-time observation of the forming process of NiO. 42 A tiny conductive region called the "bridge" was formed during the abrupt decrease in resistance. The bridge region had a much lower level of resistance than those of the adjacent regions, and the bridge was clarified to contain the conductive filament contributing to the ReRAM switching.…”