Electric conductivity of remotely heated Cu nanofilaments in Cu/TaOx/Pt ReRAM cells

Abstract

A memory cell, initially set to a conductive state, of a resistive resistive random access memory array is heated remotely and controllably by a neighboring heat source cell, both cells having either a common active or an inert electrode. Upon switching off the heating of the heat source cell, the conductivity of the filament of the investigated cell is characterized by sufficiently small voltages to make sure that the filament does not suffer any structural reconstruction such as removal, addition, or permanent displacement of Cu atoms. One observes that immediately after the heating of the neighboring heat source device is switched off, the cell, initially set to an on state and characterized by a low resistance Ron, is found to be reset by remote heating to an off state, characterized by R off ≫ R on. In some instances, after a cooling off time of approximately 2 min or more, one observes the cell's spontaneous recovery from the Roff state to the original on state or very close to the initial Ron value. The process of the spontaneous recovery of the electric conductivity of the filament is interpreted as an attenuation of Cu atom vibrations in the filament with the attendant increase of electron tunneling effects for which the variation of the average tunneling distance between the vibrating Cu atoms is roughly proportional to the square root of the absolute temperature. At high temperatures, the average tunneling distance increases, leading to a sharp decrease of the tunneling probability and, consequently, to a sharp increase in transient resistance.