An Investigation of the Printing of Circuits using Organic Field-Effect Transistors that Mimic the Function of Spiking Neurons

Abstract

This thesis presents an investigation into the use of organic field-effect transistors (OFETs) in neuromorphic circuits. These are electric circuits that mimic the behaviour of biological neurons. Transistors are the smallest switch within electric circuits and OFETs are an alternative to the standard silicon technology with some attractive features that arise from the solution processability and mechanical flexibility of the involved materials. This allows (among other things) for large area applications, interesting for neuromorphic circuits, as these tend to require a significant number of transistors and with that wider areas. (It should be noted that some artificial neuronal networks have already been realised with traditional silicon transistors.) A general overview of OFET principles, materials and applications will be given in Chapter 1, alongside a brief introduction into neuromorphic circuits. Printing a neuromorphic circuit with OFETs has several distinct advantages, one of them being that OFETs and biological neurons function on the same timescales (a few milliseconds), while traditional silicon transistors are much faster. This can lead to a significant mismatch between the two systems. OFETs are a versatile technology, as they can also be utilised in gas sensors, in the Bottom-Gate Bottom-Contact structures and printing of these devices will be briefly discussed in Chapter 2. However, different device architectures, namely the Top-Gate Bottom-Contact, would provide a more stable device operation for use in electric circuits. An investigation in the change in structure will be presented in Chapter 3, with a significant portion of it dedicated to finding a suitable dielectric that can be deposited from solution. This work leads to Chapter 4 that discusses the use of fabrication procedures developed by Tokito et al. to print a proof-of-concept neuromorphic circuit. This circuit is very small, but functions as a simple integrate-and-fire neuron, meaning that after several ingoing voltage spike the circuit will react with an outgoing voltage spike.

Date of Award	4 Mar 2021
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Michael Turner (Main Supervisor) & Leszek Majewski (Co Supervisor)