Electroforming-Free and Multilevel Resistance Switching Properties in Al/TiOx/Cu Structure

Resistance random access memory (RRAM) in various oxide materials,especiallybinaryoxidematerialssuchasTiO2, 1 ZrO2, 2 HfO2, 3 and ZnO, 4 has attracted considerable attention as one of the promising applications in next-generation nonvolatile semiconductor memory devices. Although the resistance switching (RS) materials can be classified into several groups according to switching mechanisms, this study focuses on combined different mechanisms effects on the RS performance in Al/TiOx/Cu. As Cu is an active metal in the electrochemical metallization memory (ECM), 5 adopting Cu as electrode may induce Cu conductive filaments (CFs). Meanwhile, because of the higher oxidation potential of Al compared with Ti, 6 adopting Al onTiOx mayinducetheoxygenvacancy (Vo)relatedRSmechanisms, such as electronic switching related with the trapping and detrapping of carriers along the Vo channels. 7 Particularly, when RRAM devices is programmed, a filament with trap-controlled space charge limited current (SCLC) could be formed, while a metallic CFs could also be formed. Therefore, multilevel resistance states may be obtained by forming different filaments inside the device. However, research on combining these two mechanisms remains to be clarified. During the resistance switching process, the “electroforming” process is usually needed to obtain the resistance switching. However, this process often results in the random fluctuations of switching parameters and needs a much higher bias, which are generally unfavorable for the device fabrication and operation. 8 In this paper, the characteristics of multilevel resistance switching, electroforming-free and low Ireset (the maximum current level changes from LRS to HRS) were investigated through Al/TiOx/Cu structure. The relationship between electroforming-free and low Ireset will be elucidated in this paper, as well as the multilevel resistance switching mechanism.