Investigation of chemical distribution in the oxide bulk layer in Ti/HfO2/Pt memory devices using x-ray photoelectron spectroscopy

Resistive switching (RS) of Ti/HfO2/Pt memory devices was studied using X-ray photoelectron spectroscopy. Hf4+ monotonously decreases with depth increasing towards to HfO2/Pt interface in low resistance state, while a fluctuation distribution of Hf4+ is shown in high resistance state (HRS) and in the pristine Ti/HfO2/Pt devices (without any SET or RESET process). It is explained by the existence of locally accumulated oxygen vacancies (clusters) in the oxide bulk layer in HRS and pristine states. A dynamic model of RS processes was proposed that the oxygen vacancy clusters dominantly determines the resistivity by the connecting/rupture between the neighbor cluster sites in the bulk.