Multidimensional Simulation of Threshold Switching in NbO₂ Based on an Electric Field Triggered Thermal Runaway Model

Abstract

Volatile threshold switching devices have attracted great attention for use as selectors in passive crossbar arrays. These devices show an abrupt hysteretic jump in the current–voltage characteristic and thus offer very high selectivity. As this nonlinearity appears for either voltage polarity, threshold switches are an ideal selector for bipolar‐switching redox‐based resistive memories. To date, the predominant explanation of the threshold‐switching phenomenon in NbO 2 and related materials is the insulator‐to‐metal transition that occurs at a certain temperature and is connected to a phase transition. However, some essential experimental findings are not satisfactorily explained. Here, a multidimensional simulation of the threshold switching in NbO 2 is presented that overcomes these shortcomings. The model is based on an electric field‐induced thermal runaway that increases the amount of mobile charge carriers in the device. Applying this model in a simulation correctly predicts the experimentally observed threshold‐type current–voltage characteristic, inclusive of important features like the narrow opening of the hysteresis and the magnitude of the current jump. Furthermore, the simulation enables to discuss different influencing parameters independently at spatial resolution. The model is also applicable to a wider class of materials showing the threshold switching, but does not show a temperature‐induced insulator‐to‐metal transition.