Modeling and Design of Integrated Iontronic Circuits Based on Ionic Bipolar Junction Transistors

TL;DR

This paper models and designs complex iontronic circuits, such as flip-flops and oscillators, using ionic bipolar junction transistors, advancing the development of bio-inspired ionic information processing devices.

Contribution

It introduces the first modeling and design of complex ionic circuits with IBJTs, including bistable flip-flops and ring oscillators, demonstrating dynamic ionic signal processing capabilities.

Findings

IBJTs modeled with good agreement between 1D and 2D models

Reducing base width enhances current amplification

Ionic flip-flop retains memory, ring oscillator self-oscillates

Abstract

Biological systems rely on ions and molecules as information carriers rather than electrons, motivating the development of devices that interface with biochemical systems for sensing, information processing, and actuation via spatiotemporal control of ions and molecules. Iontronics aims to achieve this vision by constructing devices composed of ion-conducting materials such as polyelectrolyte hydrogels, but advancing beyond simple single-stage circuit configurations that operate under steady-state conditions is a challenge. Here, we propose and model more complex ionic circuits, namely bistable flip-flop and ring oscillators, consisting of multiple ionic bipolar junction transistors (IBJTs). We begin by modeling and characterizing single IBJTs using both a simplified one-dimensional Nernst-Planck model and a more-detailed two-dimensional Poisson-Nernst-Planck model, elucidating the effects of geometry, size, and fixed charge on the IBJT performance and response time. The one- and two-dimensional models exhibit good agreement, indicating negligible transverse inhomogeneities. Additionally, these models show that reducing the base width improves current amplification, a behavior analogous to electronic BJTs. Building on this understanding, by using the IBJTs as voltage inverters and buffers, we design and model more complex ionic circuits that dynamically change their states in response to ionic signals. Specifically, we demonstrate that the ionic flip-flop retains one-bit memory and that the ring oscillator achieves autonomous periodic self-oscillation without an external clock. Our work provides a foundation for designing dynamic iontronic circuitry using ionic conductors, enabling biochemical signal processing and logic operations based on ionic transport.