ZnO/Al:ZnO Transparent Resistive Switching Devices Grown by Atomic Layer Deposition for Memristor Applications.

ZnO has intrinsic semiconductor conductivity because of an unintentional doping mechanism resulting from the growth process that is mainly attributable to oxygen vacancies (VO) positioned in the bandgap. ZnO has multiple electronic states that depend on the number of vacancies and the charge state of each vacancy. In addition to the individual electron states, the vacancies have different vibrational states. We developed a high-temperature precursor vapor mask technique using Al2O3 to pattern the atomic layer deposition of ZnO and Al:ZnO layers on ZnO-based substrates. This technique was used to create a memristor device based on Al:ZnO thin films having metallic and semiconducting and insulating transport properties ZnO. We demonstrated that adding combination of Al2O3 and TiO2 barrier layers improved the resistive switching behavior. The change in the resistance between the high- and low-resistivity states of the memristor with a combination of Al2O3 and TiO2 was approximately 157%. The devices were exposed to laser light from three different laser diodes. The 450 nm laser diode noticeably affected the combined Al2O3 and TiO2 barrier, creating a high-resistivity state with a 2.9% shift under illumination. The high-resistivity state shift under laser illumination indicates defect shifts and the thermodynamic transition of ZnO defects.