Detailed Study on Filamentary Bipolar EPIR Switching in Copper Oxide and Amorphous Silicon RRAM

Electric pulse-induced resistance change in oxide films has generated much interest in RRAM devices due to the promise of low operating voltage, short set, and reset time. CuXO oxide and alpha-Si systems are promising candidates for RRAM. We address here highly stable bipolar resistance switching in thin CuXO and alpha-Si films.;In the case of alpha-Si RRAM, alpha-Si films were grown using e-beam evaporation of undoped and doped silicon on different substrates. The alpha-Si films were sandwiched between different types of electrodes (W and Cu) to form the RRAM device. The alpha-Si films exhibited electrical forming when subjected to high voltage/current signals. The effects of doping and electrode material on the forming process have been investigated. Migration of metal electrodes ions during the forming process was confirmed. The forming process was related to the formation of bulk metallic filament due to the diffusion of the electrode material into alpha-Si. The alpha-Si films also show bipolar switching, where the switching characteristics (stability, EPIR ratio, and switching polarity) were independent on the doping, but clearly depended on the electrode material. The change in the EBIR switching polarity was related to the change in the diffusion direction of the electrode material. The switching mechanisms were related to filament rupturing and formation under the action of the applied pulse.;The CuXO films were grown using RF sputtering of several different copper targets: Cu, Cu2O, CuO, on Pt/TiN/SiO2/Si substrates in Ar:O2 atm. The Cu4O3 phase the major content in the films mixed with some free Cu was found to exhibit stable bipolar switching. CuXO films exhibits both forming and bipolar switching. Strong evidences for a metallic bulk filament formation in the CuXO films under application of an initial 'forming' electric pulse have been seen. After forming, two distinct resistance change regions were seen: (i) resistance states from 20 O to 40 O with reversed polarity (highly stable); and (ii) resistance states from 150 O to 8K O with regular polarity. A model for the switching mechanisms based on Cu+ ion motion in the interface region between the metallic filament and the top electrode was developed.