Materials Approach to Control The Properties of Electrochemical Artificial Neurons and Synapses

Memristive devices have significantly developed in the last decade, expanding their application horizon much beyond memory applications. Especially important is their functionalities as artificial neurons and synapses, making them promising building units for the next generation bio-inspired neuromorphic hardware. Despite a lot has been learned about materials design and the operation principles of memristors, recent research has shown that fundamentals can still be significantly amended, demonstrating new operation principles and functionalities.<br/>In this contribution, the common electrochemical fundamentals of biological and memristive artificial neurons and synapses will be discussed as well as new aspects on materials design and its influence on the physicochemical processes and resulting functionalities of both ECM (CBRAM) and VCM (OxRAM) devices. The effects of the materials and thicknesses of the capping layer appear of special importance and as well the thicknesses and combination of thicknesses of all involved layers. The selection of different materials is changing the electrochemical nanoionics processes and as well the performance of the memrsitors. For reliable performance the device stack should be considered as a whole, and materials used in the stack and their thicknesses should be coordinated and harmonised.<br/>A special attention will be paid on controlling the energy barriers at the interface electrode / switching film, where Schottky barrier competes with the energy barrier of the redox reactions. A new switching mechanism will be presented, relying entirely on electrochemical processes of oxidation and reduction and depends on the valence state and thickness of filament. The ohmic memritsive devices, demonstrate a number of advantages compared to Schottky-based devices, such as combination of digital and analogue switching in same devices, higher voltage window of stability, lower operating currents, higher OFF to ON ratio, high endurance and retention, high temperature stability. The importance of fundamental research will be highlighted, allowing for new functionalities and opportunities for applications.