Ab initio modeling of resistive switching mechanism in binary metal oxides

Binary transition metal oxides TiO_x, NiO_x, HfO_x, AlO_x, TaO_x have been recently proposed as possible materials for resistance change based non-volatile memory devices. Currently, a major bottleneck in determining the scalability, retention and endurance of these devices, is the lack of detailed understanding of the resistive switching mechanism. To explain the observed device characteristics the so-called filamentary models have been widely adopted and also extensively investigated theoretically. First, in order to control the forming voltage in these devices the formation energy implications of possible conductive channels has to be evaluated. Ab initio techniques have recently been applied to study conductive filamentary structures characteristic to the “ON” state (or LRS - low resistance state). Next, the atomistic descriptions of the rupturing/dissolution process into the “OFF” state of the memory operation (HRS - high resistance state) needed to be addressed. Based on quantum mechanical calculations, electron and hole trapping effects were shown to have a significant role in the switching process under applied electrical field. While hole injection into oxygen reduced transition metal oxide with a formed filament can favor the dissolution process, electron injection induces filament formation. Then, as possible ways to achieve desired device characteristics, preferential impurity doping in these types of systems has been proposed to favorably affect and control the “ON” - “OFF” transition process.