Evolution of resistive switching mechanism through H2O2 sensing by using TaOx-based material in W/Al2O3/TaOx/TiN structure

Highlights: • Simulated resistive switching mechanism is due to the change in oxidation states between Ta²⁺ and Ta⁵⁺. • The oxidation states are evidenced by X-ray photo-electron spectroscopy and H₂O₂ sensing. • Al₂O₃ layer restricts the formation of WO_x layer, hence longer 10⁸ program/erase cycles are achieved with 100 ns pulse width at current of 30 μA. • TaO_x as a sensing membrane shows detection of H₂O₂ with a low concentration of 1 nM. Understanding of resistive switching mechanism through H₂O₂ sensing and improvement of switching characteristics by using TaO_x-based material in W/Al₂O₃/TaO_x/TiN structure have been reported for the first time. Existence of amorphous Al₂O₃/TaO_x layer in the RRAM devices has been confirmed by transmission electron microscopy. By analyzing the oxidation states of Ta²⁺/Ta⁵⁺ for TaO_x switching material and W⁰/W⁶⁺ for WO_x layer at the W/TaO_x interface through X-ray photoelectron spectroscopy and H₂O₂ sensing, the reduction-oxidation mechanism under Set/Reset occurs only in the TaO_x layer for the W/Al₂O₃/TaO_x/TiN structures. This leads to higher Schottky barrier height at the W/Al₂O₃ interface (0.54 eV vs. 0.46 eV), higher resistance ratio, and long program/erase endurance of >10⁸ cycles with 100 ns pulse width at a low operation current of 30 μA. Stable retention of more than 10⁴ s at 85 °C is also obtained. Using conduction mechanism and reduction-oxidation reaction, current-voltage characteristic has been simulated. Both TaO_x and WO_x membranes have high pH sensitivity values of 47.65 mV/pH and 49.25 mV/pH, respectively. Those membranes can also sense H₂O₂ with a low concentration of 1 nM in an electrolyte-insulator-semiconductor structure because of catalytic activity, while the Al₂O₃ membrane does not show sensing. The TaO_x material in W/Al₂O₃/TaO_x/TiN structure does not show only a path towards high dense, small size memory application with understanding of switching mechanism but also can be used for H₂O₂ sensors.