Evolution of growth/dissolution conductive filaments (CFs) in oxide-electrolyte-based resistive switching memories are studied by in situ transmission electron microscopy. Contrary to what is commonly believed, CFs are found to start growing from the anode (Ag or Cu) rather than having to reach the cathode (Pt) and grow backwards. A new mechanism based on local redox reactions inside the oxide-electrolyte is proposed.

In this paper, the resistive switching characteristics in a Cu/HfO(2):Cu/Pt sandwiched structure is investigated for multilevel non-volatile memory applications. The device shows excellent resistive switching performance, including good endurance, long retention time, fast operation speed and a large storage window (R(OFF)/R(ON)>10(7)). Based on the temperature-dependent test results, the formation of Cu conducting filaments is believed to be the reason for the resistance switching from the OFF state to the ON state. By integrating the resistive switching mechanism study and the device fabrication, different resistance values are achieved using different compliance currents in the program process. These resistance values can be easily distinguished in a large temperature range, and can be maintained over 10 years by extrapolating retention data at room temperature. The integrated experiment and mechanism studies set up the foundation for the development of high-performance multilevel RRAM.