Water stability of organic and electrolyte-gated field-effect transistors

Abstract

Organic bioelectronics is an emerging field that utilizes electronic devices made from a large family of aromatic compounds (conjugated polymers and small molecules) for biological applications. Organic materials seem ideal candidates for bioelectronics due to their softness, biocompatibility, stretchability, and their ability to conduct both electrons and ions. Many fundamental studies have been conducted, utilizing devices such as the Organic Field Effect Transistor (OFET), the Electrolyte-Gated OFET (EG-OFET), and the Organic Electro-Chemical Transistor (OECT). However, water constitutes a key factor in charge trapping and device degradation in organic materials, due to its strong dipole moment, high dielectric constant, and its omnipresence in almost all processing, environmental, and operational conditions. In this dissertation, we used an additives-based approach to stabilize OFETs immersed in DI water and saline solution, for periods up to a month, making the first high-performance water-stable OFETs reported in the literature. We then repeated the long-term water stability experiments on EG-OFETs, and demonstrated that cleanly fabricated EG-OFETs can remain stable within the course of an overnight measurement (16 hours), without needing the additive stabilization process. By comparing the water stability of OFETs and EG-OFETs, we highlighted the different requirements involved in stabilizing these two architectures, challenging the notion that organic materials are intrinsically unstable in water.