Grain boundaries as preferential sites for resistive switching in the HfO2 resistive random access memory structures

Resistive switching (RS) phenomenon in the HfO2 dielectric has been indirectly observed at device level in previous studies using metal-insulator-metal structures, but its origin remains unclear. In this work, using the enhanced conductive atomic force microscope (ECAFM), we have been able to obtain in situ direct observation of RS with nanometric resolution. The ECAFM measurements reveal that the conductive filaments exhibiting the RS are primarily formed at the grain boundaries, which were shown exhibiting especially low breakdown voltage due to their intrinsic high density of the oxygen vacancies.