Sol-gel/drop-coated micro-thick TiO₂ memristors for γ-ray sensing

Abstract

Sol-gel/drop-coated micro-thick TiO₂ memristors were investigated and developed for low-power radiation sensing. Devices constructed with coated aluminum (Al) electrodes exhibited unipolar I-V characteristics with dynamic turn-on voltage, and progressive R_OFF/R_ON ratio loss under applied bias. Endurance failure of micro-thick Al/Al stacks is ascribed to gradual passivation of Al surface resulting from an electrically-enhanced oxygen-ion diffusion. By exchanging a single Al contact with higher work function copper (Cu) metal, two distinct superimposed TiO₂ phases were formed. The TiO₂ coating on Al surface was carbon-contaminated and amorphous, while that on Cu was found to be additionally doped with Cu^(I/II) ions resulting from the corrosion of the surface of the electrode by the amine-based gelation agent. After initial forming, the hybrid stack could achieve a bipolar memristance, with high R_OFF/R_ON (up to 10⁶), and over 10 switching cycles at low-operating voltages (±1 V). The enhanced memristive switching properties of Al/Cu devices are explained via cooperative valence-change/electrochemical-metallization processes, involving migration of oxygen and copper species. The advanced micro-thick TiO₂ memristors were exposed to Cs-137 γ-rays, providing for the first time initial insights into their radiation detection capabilities. The sensing mechanism through these devices could be actuated by synergistic radiation-induced and field-driven photo-electric effects.