A multi-step ICTS method for analyzing time-dependent changes of interface states in Pt/Nb-doped SrTiO₃ junction

Pt/Nb:SrTiO₃ is a good candidate for interface-type resistance random-access memory, which is highly anticipated for use in next-generation memory and neuromorphic computing. The current relaxation phenomenon after resistive switching is a key property for time-series data processing in machine learning. However, the mechanisms of such phenomena remain puzzling, leading to difficulties in practical applications. Here, we proposed multi-step Isothermal Capacitance Transient Spectroscopy (MS-ICTS) to obtain detailed information about interface states and their temporal changes after resistance switching in low Nb concentration (0.05 wt%) devices, and how the interface states affect device properties. We found that in the initial state before high voltage application, there are no interface states above Fermi-energy. However, shallow interface states were generated after applying high voltage for resistance switching, which decreased the Schottky barrier height and the resistance to a low resistance state. Furthermore, such voltage-induced interface states were found to naturally decrease over time.