There is a frequent demand for smaller devices with more memory. Some efforts have been initiated in using a resistance variable as a mechanism for creating more memory in less space. Resistive random access memory (RRAM) is a memory structure including an array of RRAM cells, each of which can change and maintain the value of its resistivity based on applied electrical conditions. Particularly, each of the RRAM cells includes a resistance variable layer, the resistance of which can be adjusted to represent logic “0” or logic “1”.
From an application point of view, RRAM has many advantages. RRAM has a simple cell structure and CMOS logic compatible processes which result in a reduction of manufacturing complexity and cost in comparison with non-volatile memory structures. In addition, RRAM can be used in lower power conditions and has a faster timescale than other non-volatile memory structures. In order to replace the current NAND flash memories, which have a high stack density in a 3D array, RRAM array has been eagerly developing.