Tuning oxygen vacancies and resistive switching properties in ultra-thin HfO2 RRAM via TiN bottom electrode and interface engineering

Highlights: • Two OxRRAM stacks -TiN bottom metal electrode were fabricated by PVD and ALD. • The HfO_x layer in HfO_x/PVD-TiN is found to be more oxygen deficient. • Higher oxygen deficiency leads to larger band bending at HfO_x/PVD-TiN interface. • Higher oxygen deficiency results in a higher Schottky barrier at the interface. • ALD-TiN O xRRAM shows low voltage switching - 10⁶ switches with 10 μA ± 1.0 V pulses. Resistive random access memory (RRAM) technologies based on non-volatile resistive filament redox switching oxides have the potential of drastically improving the performance of future mass-storage solutions. However, the physico-chemical properties of the TiN bottom metal electrode (BME) can significantly alter the resistive switching (RS) behavior of the oxygen-vacancy RRAM devices, yet the correlation between RS and the physico-chemical properties of TiN and HfO_x/TiN interface remains unclear. Here, we establish this particular correlation via detailed material and electrical characterization for the purpose of achieving further performance enhancement of the stack integration. Two types of RRAM stacks were fabricated where the TiN BME was fabricated by physical vapor deposition (PVD) and atomic layer deposition (ALD), respectively. The HfO_x layer in HfO_x/PVD-TiN is more oxygen deficient than that of the HfO_x/ALD-TiN because of more defective PVD-TiN and probably because pristine ALD-TiN has a thicker TiO₂ overlayer. Higher concentration of oxygen vacancies induces a larger magnitude of band bending at the HfO_x/PVD-TiN interface and leads to the formation of a higher Schottky barrier. Pulsed endurance measurements of up to 10⁶ switches, with 10 μA ± 1.0 V pulses, demonstrate the potential of the studied ultra-thin-HfO_x/TiN device stack for dense, large scale, and low-power memory integration.