Forming-free bipolar memristive switching of ZnO films deposited by cyclic-voltammetry

Cyclic voltammetry deposition (CV-D) was applied to deposit ZnO films on indium-tin-oxide (ITO) glass. Delineated in details are the optimizations of CV-D parameters which bestow enhanced nucleation of ZnO grains. The result is much superior coverage of the CV-D thin films as compared to those obtained by conventional electrochemical deposition. Memristive devices in the stacks of Pt/ZnO/ITO were prepared and tested. The devices in which ZnO prepared by CV-sweeping within ±0.9 V for 6 cycles then fix-potential-deposited at −0.75 V for 300 s show reproducible forming-free bipolar switching operation at voltages ≤±1 V. The cycle-life in DC sweeping mode is at least 200 cycles. The electrical conduction belongs to space-charge-limited-current conduction mechanism, which is fitted to extract carrier mobility 0.97 cm2/V s and carrier concentration 8.6 × 1018 cm−3. Chemical bonding status and concentration profiles of oxygen and zinc were examined by electron spectroscopy and an Auger electron nanoscope. Gradient oxygen bonding status in ZnO film, typical of cyclic voltammetry deposition, facilitates the electrical switching at low voltages.

► Memristive property of cyclic voltammetry deposited ZnO thin films is investigated.
► The stacks of Pt/ZnO/ITO were operated within ±1 V and cycled over 200 cycles.
► The electrical conduction is based on space-charge-limited-current conduction.
► Carrier mobility 0.97 cm2/V s and carrier concentration 8.6 × 1018 cm−3 are extracted.
► Chemical bonding and concentration profiles are analyzed by electron spectroscope.