Fully Printed High-Performance Flexible OECTs with Sub-Micron Channel Length for Bioelectronics

Organic Electrochemical Transistors (OECTs) modulate the electrical conductivity of an organic channel through ion movements from an electrolyte to the channel, making it suitable for applications in bioelectronics and chemical sensing. Due to high conformality, high transconductance, inherent signal amplification, and stable operation in the aqueous environment, OECTs have gained interest in applications of in-vivo bioelectronics. Most wearable bioelectronics applications require a flexible platform. The printed fabrication process paves the way for implementing OECTs on a flexible substrate. Since the channel volumetric capacitance of OECTs is inversely proportional to the operating frequency, geometry scaling of OECTs is needed for high-frequency applications. However, miniaturization of the planar OECT remains a challenge, which hinders the application of these devices in fast biological events like neuronal signaling and neuromorphic application. In this work, we present a fully printed fabrication method of high-performance OECTs with sub-micron channel length on a flexible substrate. We fabricate the OECT source and drain contacts using gold (Au) nanoparticle ink. After inkjet printing the source electrode, we modify the metal surface with a hydrophobic surface coating, and then inkjet-print the drain metal electrode. Hence, the drain electrode self-aligns with the previously printed source electrode with sub-micron resolution. Next, we use direct 3D printing to fabricate silver/silver chloride (Ag/AgCl) gate electrodes. After that, we inkjet print the organic poly(3,4-ethylene dioxythiophene): poly(styrene sulfonic acid) (PEDOT: PSS) as the channel material for this sub-micron channel length OECTs. We conclude the fabrication process by inkjet printing a protective dielectric layer on the metal electrodes to prevent direct contact of the liquid electrolyte with the metal electrodes. Reducing the volumetric capacitance increases the cut-off frequency of these OECTs, improving their performance and making them suitable for high-frequency bioelectronics.