The fellow has worked at the Northeastern University in Boston, USA and University of Sheffield, Sheffield, UK during the outgoing phase of the fellowship. At Northeastern University, the fellow focused on both experimental and simulation studies. At the experimental front, the fellow performed nanowire synthesis, its contact printing, transistor fabrication using printed nanowires, interconnecting the transistors, selective doping of nanowire channel, and eventually the circuit (inverter) realisation. The fellow has characterised the transistors and inverter circuits based on nanowire ensembles, systematically compared their performance, and optimised the whole fabrication process. Particularly, the bottom-gated nanowire transistor exhibits synaptic behaviour, which mimics the response of the biological synapse including long- and short-term potentiation and depression, spiking rate dependent plasticity, etc.
At the simulation front, the fellow has built a Monte Carlo simulation framework to quantify the stochasticity of the nanowire ensemble-based transistors. The fellow also has developed a mathematical equation set to describe the synaptic behaviours observed from the bottom-gated nanowire-based transistors. Using the equations, the fellow has developed a SPICE simulation framework that allows the simulation of transistor and circuit behaviours which can serve as biomimetic mechanoreceptors. At the University of Sheffield, the fellow built on the TouchSim model developed in the Active Touch Lab [1] and interfaced it with the SPICE simulation, enabling the simulation of touch in the electronic skin context.
The main achievements are:
1) Developed the fabrication scheme to fabricate ZnO nanowire ensemble-based transistors and circuits controlled by localised bottom gate.
2) Characterised the nanowire-ensemble based transistors and inverters, and explored their synaptic behaviours.
3) Built a theoretical framework to simulate the touch process in electronic skin.
[1] Saal, H. P., Delhaye, B. P., Rayhaun, B. C., & Bensmaia, S. J. Simulating tactile signals from the whole hand with millisecond precision. Proceedings of the National Academy of Sciences, 114(28), E5693-E5702, 2017.
