“…By applying appropriate SET/RESET voltage (V SET =V RESET ) between top and bottom electrodes, the connecting and rupture of conducting filaments are triggered by three major physical mechanisms and results in different bipolar RS (BRS) and unipolar RS (URS) modes, namely electrochemical metallization of metal filaments for BRS, valance change effect of oxygen-vacancy filaments for BRS, and thermochemical effect for URS when Joule heating is predominant at RESET. 2) Among a wide range of materials showing RS phenomena, such as perovskite oxides, ferromagnets, chalcogenides, and binary metal oxides, [3][4][5][6][7][8][9] the binary metal oxides such as HfO 2 have been the most interesting because of their compatibility with advanced CMOS technology. 10,11) Furthermore, the RS modes in RRAM had been shown to depend strongly on the metal electrodes using an identical binary oxide.…”