Resistive Switchings in Transition Metal Oxides

Promising candidates for the next-generation memory devices have emerged one after another for the last decade. Ferroelectric random access memories (FeRAM), magnetoresistive random access memories (MRAM), phase change memories (PCM) are indeed at the dawn of the international development races. Along with those three fascinating memories, we focus here on probably the most seminal candidate of the future device — resistive random access memory (RRAM® or ReRAM). ReRAM consists of a simple metal/oxide/metal sandwich structure as shown schematically in Fig. 1 with myriad combinations of the metals and oxides. The sandwich shows reversible and non-volatile changes of the electric resistance by applications of ordinary electric pulses (see the right panel of Fig. 1). This phenomenon is called “resistance change” or “resistive switching”. Because of the