Hf Cap Thickness Dependence in Bipolar-Switching TiN\HfO2\Hf\TiN RRAM Device

In this work, the influence of Hf cap thickness of bipolar resistive switching in TiNHfO2HfTiN resistive random access memory (RRAM) stack was investigated. More stable bipolar switching and longer endurance were achieved by increasing the Hf cap thickness from 2nm to 10nm. First-principlesimulation suggested more oxygen vacancies (Vox) generation for thicker Hf cap. Lower FORMING voltage from thicker Hf cap devices confirms more Voxgeneration in the stack. X-ray photoelectron spectroscopy (XPS) also physically detected more oxygen scavenge from HfO2bulk by thicker Hf cap. The more generated Voxin thicker Hf cap stack probably accounted for the improved bipolar switching properties.