Enhancement of the Dynamic Performance of Electrolyte-Gated Transistors: Toward Fast-Switching, Low-Operating Voltage Printed Electronics

Abstract

A transistor is an electrical circuit element which acts as a switch, can tune the current in an electrical circuit, and can amplify input signals. Fast switching with low-operating voltage and high amplification are desired characteristics for transistors but are not readily achieved by printed electronics. Electrolyte-gated transistors (EGTs) are a specific class of transistors with an electrolyte as the gate dielectric. Using electrolyte as the gate dielectric enables low-operating voltage, high amplification (gain), and relaxed fabrication requirements. Electrolytes have a huge capacitance which is thickness independent thanks to the formation of electrical double layers (EDL) at the interfaces of the electrolyte with the electrodes. Ion gel is a type of electrolyte consisting of an ionic liquid and a triblock copolymer. The polymer is responsible for providing mechanical integrity, whereas the ionic liquid is responsible for the gating mechanism with great electrical, physical, chemical, and electrochemical properties. Ion gels pave the way for miniaturizing EGTs and their use in printed electronics. Despite all the promising properties of printed EGTs including low-operating voltage, ease of printing, flexibility, and low-toxicity, fast EGTs have not yet been demonstrated. Similarly, higher EGT gain is also required to improve the sensitivity and computational power of devices. In this thesis, the EGT working principles have been investigated, as well as the effects of EGT architectures, materials, components, printing resolution, and precision on the EGT operating speed and gain. New architectures have been designed to produce fast and high-performance EGTs. Modification of EGT architectures and components enabled us to achieve 5 MHz operation with an order of magnitude increase in gain and amplification. In order to fabricate different architectures, a variety of techniques including inkjet, aerosol-jet, and screen printing have been employed. Screen-printed, UV-cured ion gels with a line width resolution of 10 µm have been demonstrated. In conclusion, in this thesis, the performance of printed ion gel-based electrolyte-gated transistors has been investigated and improved by relating the device dynamic and static characteristics to its material components and architecture.