Effects of Bottom Electrode Materials on the Resistive Switching Characteristics of HfO2-Based RRAM Devices

In this paper, we present the results of our systematic investigations of the resistive switching characteristics of HfO2-based metal–insulator–metal structures using four different metal bottom electrode (BE) materials, namely Au, Al, Pt and Cu. Ag is used as the top electrode for all these resistive random access memory devices. On one hand, Au and Pt show lower set and reset voltages, whereas the Pt electrode has a higher resistance ratio (Roff/Ron) ~ 105). On the other hand, Al and Cu exhibit multilevel switching during the reset process. Thus, the oxygen affinity of the BE is expected to result in the formation of an interfacial layer with the active (HfO2) layer. Furthermore, conduction mechanisms have been studied for the various regions in the high resistance state (HRS) curves of all these devices. It is found that the Poole–Frenkel effect is more dominant at higher voltages (> 1 V) in the HRS curve. Therefore, it is essential to elucidate the appropriate BE material and optimum active switching layer to understand the conduction mechanisms for the resistive switching phenomenon.