Session: 06-04 Neuromorphic Computing

Paper Number: 171324

171324 - Enhancement-Mode Bioionic Transistor Architecture With a Fully Ionic Gating Mechanism 

This study presents the design, fabrication, and characterization of a new class of ion-gated organic electrochemical transistors (IGTs) that utilize an entirely ionic gating mechanism, enabling stable and reversible switching behavior within physiologically relevant voltage ranges. The IGT architecture operates by mobilizing ionic species to dynamically form and dissolve ionic double layers (IDLs), which act as tunable conductive pathways between the source and drain terminals. This mechanism allows for rapid switching while maintaining electrochemical isolation between all terminals, thereby avoiding undesirable faradaic reactions or material degradation. The design introduces a fundamental shift from traditional electrolyte-gated or organic electrochemical transistor (OECT) architectures by fully decoupling the gating function from the environment, enabling integration into bioelectronic applications with improved longevity and signal fidelity.

The gating behavior, validated through chronoamperometric analysis, demonstrated sub-millisecond response times, with a measured time constant of 100 µs. This performance exceeds conventional OECTs, whose response times are often hindered by sluggish ion diffusion into the bulk channel. To further enhance the performance and reliability of the system, an ionomeric Nafion membrane impregnated with 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIM⁺ Otf⁻) ionic liquid was integrated into the device. This solid-state design offered a substantial increase in both baseline and peak current levels while preserving switching speed, indicating its effectiveness as an ion reservoir and gating medium. The membrane also mitigated ionic leakage and reduced the risk of contamination, which is critical for in vivo or long-term operation in bioelectronic platforms.

Drain current-voltage characteristics revealed a distinctive multi-stage response, unlike conventional field-effect transistors, with multiple ohmic and saturation regions emerging at different gate voltages (25–2500 mV). These behaviors are attributed to the ionic nature of the gating mechanism, ion mass disparity, and field-dependent clustering and declustering of ions within the device. At physiologically relevant gating voltages (25–300 mV), the IGT demonstrated excellent performance, maintaining a consistent output conductance of approximately 1 µS and a nearly constant transconductance. These features are especially valuable for biosensing and neural interfacing applications where analog signal amplification and low-voltage operation are essential.

This proof-of-concept study establishes the feasibility of a stable, fast-switching, low-voltage ionic transistor based on reversible IDL formation. By avoiding chemical doping or irreversible interactions with analytes, the IGT ensures operational longevity and minimizes cross-contamination risks. The architecture is scalable and adaptable to flexible or biocompatible substrates such as hydrogels or polyimide films, opening avenues for future applications in biointegrated electronics, soft robotics, and electrophysiological recording systems. Overall, this work introduces a robust bioionic transistor platform with enhanced functional versatility for the next generation of solid-state bioelectronics.

Presenting Author: Fatemeh Hassanpour Iowa State University

Presenting Author Biography: Fatemeh Hassanpour is a Graduate Research Assistant in the Department of Mechanical Engineering at Iowa State University. She received her B.S. in Chemical Engineering and M.S. in Polymer Engineering from Sharif University of Science and Technology (2017) and Sahand University (2020), respectively.