Designing with Iontronic Logic Gates─From a Single Polyelectrolyte Diode to an Integrated Ionic Circuit

Abstract

This article presents the implementation of on-chip iontronic circuits via small-scale integration of multiple ionic logic gates made of bipolar polyelectrolyte diodes. These ionic circuits are analogous to solid-state electronic circuits, with ions as the charge carriers instead of electrons/holes. We experimentally characterize the responses of a single fluidic diode made of a junction of oppositely charged polyelectrolytes (i.e., anion and cation exchange membranes), with a similar underlying mechanism as a solid-state p- and n-type junction. This served to carry out predesigned logical computations in various architectures by integrating multiple diode-based logic gates, where the electrical signal between the integrated gates was transmitted entirely through ions. The findings shed light on the limitations affecting the number of logic gates that can be integrated, the degradation of the electrical signal, their transient response, and the design rules that can improve the performance of iontronic circuits.

Study on the Rectification of Ionic Diode Based on Cross-Linked Nanocellulose Bipolar Membranes

“…To compare equally and parallelly, all curves in Figure were selected from curves that were swept in the same direction as the red curve in Figure b, which means the back sweep from +3 to −3 V after the first sweep from −3 to +3 V. The rectification ratio was calculated by the ratio of the current at +3 V to the current at −3 V. Figure a shows that the bipolar membrane with thickness ratio of around 1:1 (50 μm ACNF + 55 μm CCNF) exhibits the optimal rectification ratio compared to the thickness ratios of 2:1 (70 μm ACNF + 35 μm CCNF) and 1:2 (35 μm ACNF + 70 μm CCNF). This could have two causes: one is that when the ions need to go through a longer distance, this results in increased resistance when a forward bias is applied; another is that it is easier for the ions to pass through a thinner layer which leads to higher conductivity under a reverse bias. , Therefore, if the total thickness of the bipolar membrane is fixed, when the thickness of the two sublayers is similar, then the diode shows a higher rectification ratio. The influence of scan rate on the rectification ratio of the bipolar membrane with 50 μm ACNF + 55 μm CCNF is illustrated in Figure b.…”

“…The junction between p-type and n-type semiconductors is a critical part of many electronic devices due to the asymmetric charge transport at the interface which only enables the transport of electrons/holes in one direction, known as rectification. , These electronics are the building blocks of modern digital technology due to their unique junction structure, such as diodes, photovoltaic cells, and transistors. − In biology, it is the ions in liquids rather than the electrons in solids that are the charge carrying particles used for different functions. For this reason, ions as signal carriers play essential roles in bioelectronic devices for applications such as ionic circuitry, sensory systems, and smart gating. , …”

Logic gating of low-abundance molecules using polyelectrolyte-based diodes

“…Yet, when considering more complex computational processes, the number of diode-based logic gates that can be integrated is severely limited due to the degradation of the electrical potential signal and leakage currents associated with each sequential logic gate. 42 To extend the functionality and integration level of ionic circuits, future iontronic circuits should also incorporate ion-based transistors into the circuit in order to compensate for voltage drops. Such a future direction in iontronic circuits, which has tremendous potential in terms of functionality and integration level, is reminiscent of the technological revolution that integrated electronic circuits have undergone since the invention of the solid-state transistor.…”

“…The entire procedure closely followed previously reported works. 42 The polyelectrolyte indicator spots were similarly synthesized after forming the diodes, wherein each spot contained only a single type of polyelectrolyte, tailored to accommodate the net charge of the target molecule that needed to be adsorbed and visualized. A bright-field microscopy image of the interface formed between the two oppositely charged polyelectrolytes can be seen in Fig.…”

Geometrically Scalable Iontronic Memristors: Employing Bipolar Polyelectrolyte Gels for Neuromorphic Systems

“…Furthermore, their integration in small-scale fluidic circuits for handling complex tasks has hardly been achieved, 38 limiting their potential applications in advanced computing systems. 16 This work reports on iontronic memristors featuring a threelayer bipolar ion-selective hydrogel structure that enhances the control of ion transport. These memristors demonstrate scalability of memory timescales from seconds to hours, controlled by ICP within polyelectrolyte gels in a microfluidic channel architecture.…”