Fully Printed Ag/a-TiO2/Ag electronic synapse for biomimetic applications

"Biological synapses constitute a basis of information processing and adaptive learning in the human brain. Ultimately, the brain wondrous computation abilities arise from synaptic plasticity, that is the modification of the synaptic weight, and thus the strength of interneural communication according to the history of past events.As such, the emulation of synaptic plasticity in electronic synapses is vital for brain-inspired computing and biomimetic applications. With developing applications demanding low-cost and rapid prototyping of electronic devices, there are significant incentives toward finding solutions for straightforward deposition techniques utiliz-ing low-cost and eco-friendly materials.In this project, fully inkjet printed Ag/a-TiO2/Ag nanoelectronic synapses are designed, developed and proposed as computational nodes for neuromorphic applications, building on recent advances in both two-terminal electronic synapses and alternative emerging applications. Specifically, the present work is concentrated onthe functionalization of custom-made TiO2 ink through simple routes of synthesis, showcasing the feasibility of jettable and printable ink in functional electronic synapses production. The developed fully-printed prototypes consist of nanoscale uniform a-TiO2 layers with functional thickness in the range of 80 nm - 350 nm andare free from the cracks and deformations that routinely form in solution-processed derived layers.A significant attribute of these simple-structured nanoelectronic devices is an intrinsic mechanism that adjusts their resistance state according to the history of applied voltage triggers; adhering to biological synaptic plasticity dynamics that are responsible for memorisation and learning. In this project, the devices’ plasticity features are investigated by adjusting the duty cycle α of voltage triggers. By changing α from low (10 %) to high (90 %) values, short-term to long-term adjustment in conductance is achieved that also occurred in a stepwise manned, phenomenologically similar to that found in Ca2+ transients during biological cells depolarisation.Due to the demonstrated rich biomimetic attributes, energy-efficiency and versatility of the developed printed devices, such electronic elements are perceived as promising candidates in future soft electronics with a wide area of applications in neuromorphic systems , sensing and prosthetic applications. Out of the large range of such applications, this work used tactile sensing as a case study for the realization of bio-inspired electronic skin.