Resistive switching in hafnium dioxide layers: Local phenomenon at grain boundaries

Abstract

Overcoming challenges associated with implementation of resistive random access memory technology for non-volatile information storage requires identifying the material characteristics responsible for resistive switching. In order to connect the switching phenomenon to the nano-scale morphological features of the dielectrics employed in memory cells, we applied the enhanced conductive atomic force microscopy technique for in situ analysis of the simultaneously collected electrical and topographical data on HfO2 stacks of various degrees of crystallinity. We demonstrate that the resistive switching is a local phenomenon associated with the formation of a conductive filament with a sufficiently small cross-section, which is determined by the maximum passing current. Switchable filament is found to be formed at the dielectric sites where the forming voltages were sufficiently small, which, in the case of the stoichiometric HfO2, is observed exclusively at the grain boundary regions representing low resistant conductive paths through the dielectric film.

Role and Optimization of the Active Oxide Layer in TiO2‐Based RRAM

“…The effects of grain boundaries on the behavior of RRAM devices has previously been reported for devices based on HfO 2 thin fi lms. [ 27,28 ] Furthermore, the concave-up nonlinearity in the I -V characteristics below switching threshold is signifi cantly more pronounced in annealed devices, whilst quasi-Ohmic I -V s are readily obtained in unannealed samples. This, in combination with the lower current draw at similar voltages renders annealed devices more suitable for use in crossbar arrays.…”

Optimal stoichiometry for nucleation and growth of conductive filaments in HfOx

“…This can be achieved either by deliberately growing a substoichiometric oxide film or by inserting an oxygen scavenging metal layer such as Ti or Hf [9]. There is evidence that in polycrystalline HfO x films oxygen deficiency is enhanced near extended defects, such as grain boundaries, which subsequently serve as precursors for filament growth [11,12,19,20]. This observation is also supported by theoretical predictions which show that oxygen vacancies can be up to 0.8 eV more stable at m-HfO 2 grain boundaries relative to the bulk crystal [21].…”

Light assisted irreversible resistive switching in ultra thin hafnium oxide

“…These small variations in switching elds may be due to inhomogeneous distribution of grain boundaries in large device area. 12,31 Please note that we have not mentioned the energy density of light source in present investigation, because during illumination of light on devices, large portion of silicon wafer which hold the devices also received light and contribute in transport properties. Interestingly it has been found that once the device switched under light, it never recover the original high resistance, charge injection may permanently changed the band off set and create new impurities charge/trap levels as shown in the band diagram and breakdown mechanism of devices under light ( Fig.…”