Impact of the forming and cycling processes on the electrical and physical degradation characteristics of HfO₂-based resistive switching devices

In this work, electrical and physical analysis of filamentary-type Ni/HfO₂/n⁺-Si resistive random access memory devices were carried out with the aim of evaluating the microstructural changes occurring in the oxide layer and metal electrode after the initial forming step and subsequent switching cycles. To this end, Scanning Electron Microscopy analysis of the top oxide surface after Ni removal was performed. The obtained images show the generation of small hillocks and defects in the active area of the device caused by current-induced Joule heating effects. Material analysis of these hillocks reveals that they are a Ni-based compound. The size and morphology of the generated damage is shown to depend both on the switching polarity and compliance used to limit the current flow during the formation of the conductive filament. In addition, the damage induced in the structure not only depends on the current magnitude reached in the set process, but also on the maximum current reached during the reset phase, with both current levels severely affecting the long-term switching capability of the devices.