Heterogeneous CFs induced unipolar and bipolar resistive switching behaviors in InGaZnO thin films

This paper investigates resistive switching behaviors of amorphous InGaZnO (a-IGZO) thin films for non-volatile resistive random access memory applications. Reversible transition process between bipolar and unipolar modes in Ag/InGaZnO/Pt memory cell takes place through changing the polarities of sweeping voltages, whereas the reset process cannot be operated by applying a positive voltage. The dominant conduction mechanisms in both modes are Ohmic conduction for the low resistance state, but different for the high resistance state, that is, Poole-Frenkel emission in the unipolar mode and trap-controlled space charge limited conduction in the bipolar mode. Temperature dependence of low resistance state and transmission electron microscopy analysis further indicate that the dominant conductive filaments (CFs) are composed of Ag atoms for the bipolar mode and oxygen vacancies for the unipolar mode, respectively. These two kinds of conductive filaments play a coordination role in resistive switching transition between bipolar and unipolar modes in Ag/InGaZnO/Pt memory devices. Based on the conductive filament model, the physical mechanisms for resistive switching are discussed.