Oral:Role of Oxygen vacancies in resistive switching in ZnO

The resistance of the metal oxides under external bias has been observed to show brain-like synapses with suitable metal-metal oxide-metal configuration.It is paving the way for Resistive-Random Access Memories with faster switching time and low power consumption. Under low resistance state point defects like Oxygen vacancies segregate to form a conductive filament and when it gets ruptured a high resistive state is achieved. The physical nature and electrical properties of conductive filament formation have been studied using transport measurement, TEM and AFM. However, the nature of electron distribution and relative contribution from atomic orbitals remain tricky. In this regard, we have explored the resistive switching phenomena of ZnO by creating and removing a series of vacancies along [010] direction using density functional theory. Oxygen vacancies can exist in three different states V_o⁰,V_o⁺¹ and V_o⁺². The V_o⁰ found to be stable at higher energy than V_o⁺².For the V_o⁰state, the Zn nearest neighbours are displaced inward by 12 % of the equilibrium Zn–O bond length and for the V_o⁺¹ and V_o⁺² states, the displacements are outward by 2 % and 23 %, respectively.Electron localisation and band decomposed charge density calculations have confirmed the observation of conductive filament. A better insight into the nature of resistive switching will help in the development of ReRAMs and neuromorphic electronic devices.