Understanding of multi-level resistive switching mechanism in GeO_x through redox reaction in H₂O₂/sarcosine prostate cancer biomarker detection

Formation-free multi-level resistive switching characteristics by using 10 nm-thick polycrystalline GeO_x film in a simple W/GeO_x/W structure and understanding of switching mechanism through redox reaction in H₂O₂/sarcosine sensing (or changing Ge°/Ge⁴⁺ oxidation states under external bias) have been reported for the first time. Oxidation states of Ge⁰/Ge⁴⁺ are confirmed by both XPS and H₂O₂ sensing of GeO_x membrane in electrolyte-insulator-semiconductor structure. Highly repeatable 1000 dc cycles and stable program/erase (P/E) endurance of >10⁶ cycles at a small pulse width of 100 ns are achieved at a low operation current of 0.1 μA. The thickness of GeO_x layer is found to be increased to 12.5 nm with the reduction of polycrystalline grain size of <7 nm after P/E of 10⁶ cycles, which is observed by high-resolution TEM. The switching mechanism is explored through redox reaction in GeO_x membrane by sensing 1 nM H₂O₂, which is owing to the change of oxidation states from Ge⁰ to Ge⁴⁺ because of the enhanced O^2- ions migration in memory device under external bias. In addition, sarcosine as a prostate cancer biomarker with low concentration of 50 pM to 10 μM is also detected.