Comparison of resistive switching characteristics by using e-gun/sputter deposited SiO_x film in W/SiO_x/TiN structure and pH/creatinine sensing through iridium electrode

Effects of two deposition techniques like e-gun evaporation and RF sputtering for the SiO_x films have been evaluated, and a long program/erase (P/E) endurance of >10⁹ cycles with small pulse width of 100 ns and lower P/E current of <50 μA has been achieved for the e-gun deposited SiO_x film in a simple W/SiO_x/TiN structure for the first time. However, the RF sputtering deposited SiO_x switching material has shown higher operation current of >200 μA. Resistive switching characteristics by using tungsten (W) and iridium (Ir) electrodes in a metal/SiO_x/TiN structure have been also investigated. Memory device with amorphous SiO_x film is observed by transmission electron microscope image. E-gun deposited films show more defective SiO_x than the sputtering and the mixture of Si⁰ and Si⁴⁺ oxidation states are observed, which is confirmed by X-ray photoelectron spectroscopy. Schottky barrier height modulation is responsible for changing the high and low resistance states (0.55 eV vs, 0.46 eV) under external bias at low current of 10 μA. Similarly, the pH sensing occurs in Ir/SiO_x/TiN structure due to Schottky barrier height changing at the Ir/SiO_x interface. Under external bias, reduction-oxidation (redox) occurs at the SiO_x/TiN interface for the W/SiO_x/TiN structure and Ir/SiO_x interface by changing of Si⁰/Si⁴⁺ oxidations states as well as Schottky barrier height is modulated owing to O²⁻ ions migration. This switching mechanism is also understood by pH sensing. Creatinine with a low concentration of 100 nM has been detected through Ir electrode using Ir/SiO_x/TiN structure for the first time, which will be useful for healthcare unit in near future.