Response to "comment on real-time observation on dynamic growth/dissolution of conductive filaments in oxide-electrolyte-based ReRAM".

In our recently published paper, [ 1 ] we achieved direct visualization of the dynamic growth and dissolution of conductive fi laments (CFs) in Ag (or Cu)/ZrO 2 /Pt systems based on in situ transmission electron microscope (TEM) observations. Furthermore, continuous TEM images clearly showed that the CFs start to grow at the Cu/ZrO 2 (or Ag/ZrO 2 ) interface and begin to dissolve at the ZrO 2 /Pt interface, which is in contrast to the prediction from the electrochemical metallization (ECM) theory developed for the solid-electrolyte-based ReRAM (also referred to a the ECM cell). [ 2 , 3 ] The same direction of CF growth/dissolution had been demonstrated in other ECM cells, including Ag/ α -Si/Pt, [ 4 ] Cu/ZnO/Pt, [ 5 ] and Cu/P3HT:PCBM/ ITO devices. [ 6 ] In our paper, [ 1 ] we suggested that the differences in cation solubility and diffusion coeffi cient between traditional solid-electrolyte and oxide-electrolyte materials accounts for this discrepancy, and based on our suggestion, the metal ions would be reduced and crystallized inside the ZrO 2 -electrolyte system in order to explain the observed results. Valov and Waser made a comment to dispute our explanation based on the following arguments. (1) The EDX analysis presented in our paper cannot identify the chemical valence of Ag (Cu) species inside the CF region. They suggested that the resistive switching (RS) behavior in our device cannot rule out valence change memory (VCM) effects due to oxide materials like ZrO 2 , TiO 2 , HfO 2 , and Ta 2 O 5 which are often used for ECM and VCM cells. (2) The large amount of electrons in the solid materials is not a suffi cient condition to reduce the incoming metal ions inside the solid electrolyte materials. (3) Considering the electric potential distribution, the Cu or Ag CFs should not start to grow at the Cu/ZrO 2 (or Ag/ZrO 2 ) interface and begin to dissolve at the ZrO 2 /Pt interface. At the end of their comment, they presented a hypothesis in which the growth and dissolution of CF in ZrO 2 result from the metal ion doping/