The Nature of Defects Responsible for Transport in a Hafnia-Based Resistive Random Access Memory Element

A promising candidate for universal memory, which would involve combining the most favorable properties of both high-speed dynamic random access memory and nonvolatile flash memory, is resistive random access memory (ReRAM). ReRAM is based on switching back and forth from a high resistance state to a low resistance state. ReRAM cells are small, allowing for the creation of memory on the scale of terabits. One of the most promising materials for use as an active medium in resistive memory is hafnia (HfO₂). However, unresolved in physics is the nature of defects and traps that are responsible for charge transport in different states of resistive memory. In this study, we demonstrated experimentally and theoretically that oxygen vacancies are responsible for charge transport in resistive memory elements based on HfO₂. We also demonstrated that transport in the low resistance state occurs through a mechanism described according to percolation theory. Based on the model of phonon-assisted tunneling between traps, and assuming that the electron traps are oxygen vacancies, a good quantitative agreement between the experimental and theoretical data of current-voltage characteristics was achieved. The thermal excitation energy of the traps in hafnia was determined based on the excitation spectrum and luminescence of the oxygen vacancies. The findings of this study demonstrate that oxygen vacancies play the key role in charge transport in hafnia-based resistive memory elements.