Electric conductivity of remotely heated Cu nanofilaments in Cu/TaO_x/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 R on , 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 R off state to the original on state or very close to the initial R on 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.

Nanoscale-Resistive Switching in Forming-Free Zinc Oxide Memristive Structures

“…The resistive switching effect is exhibited in many classes of materials, such as chalcogenides, perovskites, organic compounds, solid state electrolytes, graphene, and metal oxides [ 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 ]. Among the latter are binary oxides such as ZnO, HfO 2 , ZrO 2 , NiO, TiO 2 , WO 3 , TaO x , and Gd 2 O 3 , which is of particular interest due to its compatibility with CMOS technology, multi-bit switching, and simple chemistry [ 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 ].…”

Analysis of the Electrical ReRAM Device Degradation Induced by Thermal Cross‐Talk

“…The Joule heat density in commercial cutting edge memory arrays is much more severe, about two orders of magnitude higher than in our memory arrays. [ 19 ] Hence, the presented thermal analysis may serve as reliable guide in material selection in an effort to mitigate ReRAM degradation and reliability issues caused by thermal‐cross‐talk. The question as to what may be the optimum choices for the inert electrode is still not satisfactorily resolved.…”

“…For comparison the variations of R on and R off in Pt devices are less than 10% as discussed in more detail. [26] As described in more detail, [8,19] a frequent switching of a cell led to a deposition of Joules heat in that cell that can spread to neighboring cells disposed along one of the electrodes shared with the heated cell. Even those cells that do not share any of the two electrodes with the heated cell can be affected by the thermal cross-talk provided the intermediate cells are set in the ON-state whereby the Cu filament provides a thermal conduit for the heat transport.…”

“…Therefore, several cycles are needed to accumulate enough heat in the device to reach a certain temperature. It has been recently shown [18,19] that the Joules heat is transported along the shared electrode metal lines, which affects the neighboring cells and causes the deterioration of their electrical properties. [19] The heat generated in the heated memory cell can be controlled by the voltage ramp rate, rr, applied during the reset operation and by the number, N, of consecutive set-reset cycles, and by the R on resistance of the Cu CF.…”

“…It has been shown [18,19] that the Joules heat is transported preferentially along the electrode metal lines affecting the neighboring cells disposed along the same electrode lines and causing the deterioration of their electrical properties. Moreover, it has been shown [19,20] that the thermal cross-talk can erase a programmed neighboring cell, if the nanofilament in the cell is fragile enough and sufficient amount of heat has been transferred to it from the heated cell. For some combinations of specific amount of heat transfer and the strength of the Cu filament, the bit of the cell may be erased temporarily by remote heating.…”