Grain boundary-driven leakage path formation in HfO2 dielectrics

The time evolution of the leakage current in HfO₂ based MIM capacitors under constant voltage stress applied either continuously or with periodic interruptions was studied for a range of stress voltages and temperatures. The data analysis was performed based on the results of the conductive AFM measurements demonstrating preferential current flow along grain boundaries (GB) in the HfO₂ dielectric and ab initio calculations, which show the formation of a conductive sub-band due to oxygen vacancy precipitation at GBs. The proposed model suggests that the observed reversible increase in leakage current is caused by the defects segregation at GBs and electron trapping/detrapping at these defects. The energy characteristics of the electrically active defects extracted from the electrical measurements match well with those calculated for neutral oxygen vacancies in hafnia.