Noble-Metal-Free Memristive Devices Based on IGZO for Neuromorphic Applications

Amorphous indium-gallium-zinc-oxide (a-IGZO) based memristive devices with molybdenum contacts as both top and bottom electrodes are presented aiming to be used in neuromorphic applications. Devices down to 4 µm² are fabricated using conventional photolithography processes, with an extraordinary yield of 100%. X-ray photoelectron spectroscopy and transmission electron microscopy performed on the developed structures confirm the presence of a thin intermixed oxide layer (4–5 nm) containing Mo⁶⁺ oxidation state at the interface with the bottom contact. This results in Schottky diode-like characteristics at the pristine state with a rectification ratio of 3 orders of magnitude. The devices have electroforming-free and area-dependent analog resistive switching properties. Temperature analysis of resistive switching I–V data reveals barrier height variations of the junction. Several synaptic functions, such as synaptic potentiation and depression as response to programmed pulses, short- to long-term plasticity transition (STP to LTP) and “learning experience” properties are presented. The Mo/IGZO/Mo memristive device shows potential application of an electronic synapse for brain-inspired computing application. Integration in System-on-Panel architectures is possible at negligible cost, because all materials are used in commercial IGZO thin-film transistor fabrication.