An electron conduction model of resistive memory for resistance dispersion, fluctuation, filament structures, and Set/Reset mechanism

Abstract

A model of electron conduction in a nonvolatile resistive memory is presented. The model is based on a charge transport by hopping between localized electric states and/or metal ions in insulator. A concept of dual-level electronic energy for a hopping has been introduced. This is the first physical model which explains the dispersion, distribution tail and fluctuation of the cell resistance, and random telegraph signal noise simultaneously. All of these characteristics are represented by a random combination of hopping that is described by a simple formulation of electron hopping of a stochastic process. Main parameters causing the resistance dispersion are the distance between ions and the energy gap in hopping. Current fluctuation of cells is attributed to the variation of the hopping probability. Structures of the conduction filament are discussed with relation to the conduction model. A minimum size of the conduction filament is estimated at ∼4 nm in diameter for a stable low resistive state. A Set/Reset model is presented in which the main driving force of Set/Reset is attributed to the ion drift. A Set-process is initiated by the threshold switching of the insulator. An increased electric field in the vicinity of an electrode by the threshold switching drives the ion flow along the current path. A drift diffusion model applied to the Reset-process shows that the main driving force of the Reset process is also the ion drift rather than diffusion by Joule heating.