Electrolyte-gated Transistors Research Articles

Influence of Surface Treatments on Urea Detection Using Si Electrolyte-Gated Transistors with Different Gate Electrodes.

We investigated the impact of surface treatments on Si-based electrolyte-gated transistors (EGTs) for detecting urea. Three types of EGTs were fabricated with distinct gate electrodes (Ag, Au, Pt) using a top-down method. These EGTs exhibited exceptional intrinsic electrical properties, including a low subthreshold swing of 80 mV/dec, a high on/off current ratio of 106, and negligible hysteresis. Three surface treatment methods ((3-amino-propyl) triethoxysilane (APTES) and glutaraldehyde (GA), 11-mercaptoundecanoic acid (11-MUA), 3-mercaptopropionic acid (3-MPA)) were individually applied to the EGTs with different gate electrodes (Ag, Au, Pt). Gold nanoparticle binding tests were performed to validate the surface functionalization. We compared their detection performance of urea and found that APTES and GA exhibited the most superior detection characteristics, followed by 11-MUA and 3-MPA, regardless of the gate metal. APTES and GA, with the highest pKa among the three surface treatment methods, did not compromise the activity of urease, making it the most suitable surface treatment method for urea sensing.

Increasing the Stability of Electrolyte-gated Organic Synaptic Transistors for Neuromorphic Implants

Electrolyte-gated organic synaptic transistors (EGOSTs) can have versatile synaptic plasticity in a single device, so they are promising as components of neuromorphic implants that are intended for use in neuroprosthetic electronic nerves that are energy-efficient and have simple system structure. With the advancement in transistor properties of EGOSTs, the commercialization of neuromorphic implants for practical long-term use requires consistent operation, so they must be stable in vivo. This requirement demands strategies that maintain electronic and ionic transport in the devices while implanted in the human body, and that are mechanically, environmentally, and operationally stable. Here, we cover the structure, working mechanisms, and electrical responses of EGOSTs. We then focus on strategies to ensure their stability to maintain these characteristics and prevent adverse effects on biological tissues. We also highlight state-of-the-art neuromorphic implants that incorporate these strategies. We conclude by presenting a perspective on improvements that are needed in EGOSTs to develop practical, neuromorphic implants that are long-term usable.

Reconfigurable optoelectronic transistors for multimodal recognition

Biological nervous system outperforms in both dynamic and static information perception due to their capability to integrate the sensing, memory and processing functions. Reconfigurable neuromorphic transistors, which can be used to emulate different types of biological analogues in a single device, are important for creating compact and efficient neuromorphic computing networks, but their design remains challenging due to the need for opposing physical mechanisms to achieve different functions. Here we report a neuromorphic electrolyte-gated transistor that can be reconfigured to perform physical reservoir and synaptic functions. The device exhibits dynamics with tunable time-scales under optical and electrical stimuli. The nonlinear volatile property is suitable for reservoir computing, which can be used for multimodal pre-processing. The nonvolatility and programmability of the device through ion insertion/extraction achieved via electrolyte gating, which are required to realize synaptic functions, are verified. The device’s superior performance in mimicking human perception of dynamic and static multisensory information based on the reconfigurable neuromorphic functions is also demonstrated. The present study provides an exciting paradigm for the realization of multimodal reconfigurable devices and opens an avenue for mimicking biological multisensory fusion.

An Enhanced Synaptic Plasticity of Electrolyte-Gated Transistors through the Tungsten Doping of an Oxide Semiconductor

Oxide electrolyte-gated transistors have shown the ability to emulate various synaptic functions, but they still require a high gate voltage to form long-term plasticity. Here, we studied electrolyte-gated transistors based on InOx with tungsten doping (W-InOx). When the tungsten-to-indium ratio increased from 0% to 7.6%, the memory window of the transfer curve increased from 0.2 V to 2 V over a small sweep range of −2 V to 2.5 V. Under 50 pulses with a duty cycle of 2%, the conductance of the transistor increased from 40-fold to 30,000-fold. Furthermore, the W-InOx transistor exhibited improved paired pulse facilitation and successfully passed the Pavlovian test after training. The formation of WO3 within InOx and its ion intercalation into the channel may account for the enhanced synaptic plasticity.

Tuning Gate Potential Profiles and Current-Voltage Characteristics of Polymer Electrolyte-Gated Transistors by Capacitance Engineering.

We demonstrate that the transfer characteristics of electrolyte-gated transistors (EGTs) with polythiophene semiconductor channels are a strong function of gate/electrolyte interfacial contact area, i.e., gate size. Polythiophene EGTs with gate/electrolyte areas much larger than the channel/electrolyte areas show a clear peak in the drain current vs gate voltage (ID-VG) behavior, as well as peak voltage hysteresis between the forward and reverse VG sweeps. Polythiophene EGTs with small gate/electrolyte areas, on the other hand, exhibit current plateaus in the ID-VG behavior and a gate-size-dependent hysteresis loop between turn on and off. The qualitatively different transport behaviors are attributed to the relative sizes of the gate/electrolyte and channel/electrolyte interface capacitances, which are proportional to interfacial area. These interfacial capacitances are in series with each other such that the total capacitance of the full gate/electrolyte/channel stack is dominated by the interface with the smallest capacitance or area. For EGTs with large gates, most of the applied VG is dropped at the channel/electrolyte interface, leading to very high charge accumulations, up to ∼0.3 holes per ring (hpr) in the case of polythiophene semiconductors. The large charge density results in sub-band-filling and a marked decrease in hole mobility, giving rise to the peak in ID-VG. For EGTs with small gates, hole accumulation saturates near 0.15 hpr, band-filling does not occur, and hole mobility is maintained at a fixed value, which leads to the ID plateau. Potential drops at the interfaces are confirmed by in situ potential measurements inside a gate/electrolyte/polymer semiconductor stack. Hole accumulations are measured with gate current-gate voltage (IG-VG) measurements acquired simultaneously with the ID-VG characteristics. Overall, our measurements demonstrate that remarkably different ID behavior can be obtained for polythiophene EGTs by controlling the magnitude of the gate-electrolyte interfacial capacitance.

One Memristor-One Electrolyte-Gated Transistor based High Energy-Efficient Dropout Neuronal Units

Abstract Artificial neural networks (ANN) have been extensively researched due to their significant energy-saving benefits. Hardware implementations of ANN with dropout function would be able to avoid the overfitting problem. This letter reports a dropout neuronal unit (1R1T-DNU) based on one memristor-one electrolyte-gated transistor with an ultralow energy consumption of 25 pJ/spike. A dropout neural network is constructed based on such device and has been verified by MNIST dataset, demonstrating high recognition accuracies (>90%) within a large range of dropout probabilities up to 40%. The running time can be reduced by increasing dropout probability without a significant loss in accuracy. Our results indicate the great potential of introducing such 1R1T-DNUs in full-hardware neural networks to enhance energy efficiency and to solve the overfitting problem.

Ultrathin All-Solid-State MoS2-Based Electrolyte Gated Synaptic Transistor with Tunable Organic-Inorganic Hybrid Film.

Electrolyte-gated synaptic transistors (EGSTs) have attracted considerable attention as synaptic devices owing to their adjustable conductance, low power consumption, and multi-state storage capabilities. To demonstrate high-density EGST arrays, 2D materials are recommended owing to their excellent electrical properties and ultrathin profile. However, widespread implementation of 2D-based EGSTs has challenges in achieving large-area channel growth and finding compatible nanoscale solid electrolytes. This study demonstrates large-scale process-compatible, all-solid-state EGSTs utilizing molybdenum disulfide (MoS2) channels grown through chemical vapor deposition (CVD) and sub-30nm organic-inorganic hybrid electrolyte polymers synthesized via initiated chemical vapor deposition (iCVD). The iCVD technique enables precise modulation of the hydroxyl group density in the hybrid matrix, allowing the modulation of proton conduction, resulting in adjustable synaptic performance. By leveraging the tunable iCVD-based hybrid electrolyte, the fabricated EGSTs achieve remarkable attributes: a wide on/off ratio of 109, state retention exceeding 103, and linear conductance updates. Additionally, the device exhibits endurance surpassing 5 × 104 cycles, while maintaining a low energy consumption of 200 fJ/spike. To evaluate the practicality of these EGSTs, a subset of devices is employed in system-level simulations of MNIST handwritten digit recognition, yielding a recognition rate of 93.2%.

Multisensors based on electrolyte-gated organic field-effect transistors (EGOFETs) with aptamers as recognition elements: current state of research

The review gives a systematic account of published data devoted to multisensor technologies for manufacturing effective miniature devices capable of simultaneous accurate determination of several analytes and/or characteristics of biological fluids. The use of electrolyte-gated field-effect transistors as a biosensing platform is considered in detail. The devices based on these transistors demonstrate record-low limits of detection and are easy for mass production. The use of electrolyte-gated field-effect transistors in combination with aptamers capable of specifically binding to various analytes forms the grounds for innovations in early medical diagnosis (label-free biomarker detection). The most successful examples of multisensor devices using these transistors are presented, and the prospects of using aptamers as a recognition element in these devices are demonstrated.<br>Bibliography — 154 references.

Dynamic studies of antibody-antigen interactions with an electrolyte-gated organic transistor

Dynamic studies of antibody-antigen interactions with an electrolyte-gated organic transistor

Electrolyte-Gated Flexible MoS₂ Synaptic Transistors With Short-Term Plasticity

Electrolyte-Gated Flexible MoS₂ Synaptic Transistors With Short-Term Plasticity

Oxide Ionic Neuro-Transistors for Bio-inspired Computing.

Current computing systems rely on Boolean logic and von Neumann architecture, where computing cells are based on high-speed electron-conducting complementary metal-oxide-semiconductor (CMOS) transistors. In contrast, ions play an essential role in biological neural computing. Compared with CMOS units, the synapse/neuron computing speed is much lower, but the human brain performs much better in many tasks such as pattern recognition and decision-making. Recently, ionic dynamics in oxide electrolyte-gated transistors have attracted increasing attention in the field of neuromorphic computing, which is more similar to the computing modality in the biological brain. In this review article, we start with the introduction of some ionic processes in biological brain computing. Then, electrolyte-gated ionic transistors, especially oxide ionic transistors, are briefly introduced. Later, we review the state-of-the-art progress in oxide electrolyte-gated transistors for ionic neuromorphic computing including dynamic synaptic plasticity emulation, spatiotemporal information processing, and artificial sensory neuron function implementation. Finally, we will address the current challenges and offer recommendations along with potential research directions.

Electrolyte‐Gated Transistor Array (20 × 20) with Low‐Programming Interference Based on Coplanar Gate Structure for Unsupervised Learning

Compute‐in‐memory (CIM) is a pioneering approach using parallel data processing to eliminate traditional data transmission bottlenecks for faster, energy‐efficient data handling. Crossbar arrays with two‐terminal devices such as memristors and phase‐change memory are commonly employed in CIM, but they encounter challenges such as leakage current and increased power usage. Three‐terminal transistor arrays have potential solutions, yet large‐scale electrolyte‐gated transistors (EGTs) demonstrations are uncommon due to compatibility issues with existing photolithography processes. Herein, a 20 × 20 EGTs array is designed using indium‐gallium‐zinc‐oxide as the semiconductor channel and polyacrylonitrile (PAN) doped with C2F6LiNO4S2 as the electrolyte. Each transistor unit in the array can serve as a synapse, exhibiting a large conductance range, low energy consumption (6.984 fJ) for read–write operations, excellent repeatability, and quasilinear update characteristics. It has been confirmed that the EGTs array not only enables precise device programming but also virtually eliminates signal interference between neighboring devices during the programming process. Using 54 transistors in the EGTs array, unsupervised learning with a winner‐takes‐all neural network is successfully demonstrated. After 50 training iterations, the neural network achieves perfect 100% accuracy in classifying test‐set letters. The work demonstrates the potential of EGTs for constructing large‐scale integration synaptic array toward efficient computing architectures.

Sensing Characteristics of SARS-CoV-2 Spike Protein Using Aptamer-Functionalized Si-Based Electrolyte-Gated Field-Effect Transistor (EGT).

The sensing responses of SARS-CoV-2 spike protein using top-down-fabricated Si-based electrolyte-gated transistors (EGTs) have been investigated. An aptamer was employed as a receptor for the SARS-CoV-2 spike protein. The EGT demonstrated excellent intrinsic characteristics and higher sensitivity in the subthreshold regime compared to the linear regime. The limit of detection (LOD) was achieved as low as 0.94 pg/mL and 20 pg/mL for the current and voltage sensitivity, respectively. To analyze the sensing responses of EGT in detecting the aptamer-SARS-CoV-2 spike protein conjugate, a lumped-capacitive model with the presence of an effective dipole potential and an effective capacitance of the functionalized layer component was employed. The aptamer-functionalized EGT showed high sensitivity even in 10 mM phosphate-buffered saline (PBS) solution. These results suggest that Si-based EGTs are a highly promising method for detecting SARS-CoV-2 spike proteins.

Electrochemical Analysis of Ion Effects on Electrolyte-Gated Synaptic Transistor Characteristics.

Electrolyte-gated transistors (EGTs) are promising candidates as artificial synapses owing to their precise conductance controllability, quick response times, and especially their low operating voltages resulting from ion-assisted signal transmission. However, it is still vague how ion-related physiochemical elements and working mechanisms impact synaptic performance. Here, to address the unclear correlations, we suggest a methodical approach based on electrochemical analysis using poly(ethylene oxide) EGTs with three alkali ions: Li+, Na+, and K+. Cyclic voltammetry is employed to identify the kind of electrochemical reactions taking place at the channel/electrolyte interface, which determines the nonvolatile memory functionality of the EGTs. Additionally, using electrochemical impedance spectroscopy and qualitative analysis of electrolytes, we confirm that the intrinsic properties of electrolytes (such as crystallinity, solubility, and ion conductivity) and ion dynamics ultimately define the linearity/symmetricity of conductance modulation. Through simple but systematic electrochemical analysis, these results offer useful insights for the selection of components for high-performing artificial synapses.

Microfluidic electrolyte-gated TiS3 nanoribbons-based field-effect transistor as ultrasensitive label-free immunosensor for prostate cancer marker analysis

Early detection of prostate cancer, the second main cause of death in men, with robust assay platforms by using the appropriate biomarkers is of great importance for diagnosis and follow-up of disease under treatment. The aim of this research is to investigate how novel TiS3 nanoribbons can be used as a channel material in the microfluidic electrolyte-gated field-effect transistor (FET), with the goal of developing a label-free immunosensor for the sensitive, selective, and rapid detection of PSA as a cancer marker in both PBS and human serum samples. To create an active channel material, the TiS3 nanoribbons were deposited onto the FET surface through a drop-casting process, and the surface of the channel was subsequently modified with an anti-PSA monoclonal antibody. The electrical properties of the microfluidic electrolyte-gated TiS3 nanoribbon-based FET were characterized, and the results showed that it exhibited a depletion-mode n-type behavior with a field-effect mobility of 2.3 × 10−3 cm2/Vs, an Ion/Ioff current ratio of 4.12, and a subthreshold swing (SS) of 914.1 mV/decade. As the concentration of PSA increased from 0.1 fg/mL to 10 pg/mL, there was a corresponding increase in the drain current with a high sensitivity of 2.2665 nA/decade and a detection limit of 0.04 fg/mL. Integrating the electrolyte-gated FET with the microfluidic channel resulted in improved performance of the microfluidic electrolyte-gated FET immunosensor. The combination of these two components led to better control and delivery of small sample volumes to the surface of the electrolyte-gated FET, which improved the repeatability of the obtained data. Based on the results obtained from the microfluidic immunosensor, it can be inferred that the developed platform has the potential to be an excellent candidate for point-of-care cancer diagnosis and therapeutic monitoring.

Comparing Charge Dynamics in Organo-Inorganic Halide Perovskite: Solid-State versus Solid-Liquid Junctions

In this study, we explore the dynamics of a perovskite-electrolyte photoelectrochemical cell, pivotal for advancing electrolyte-gated field effect transistors, water-splitting photoelectrochemical and photocatalytic cells, supercapacitors, and CO2 capture and reduction technologies. The instability of hybrid perovskite materials in aqueous electrolytes presents a significant challenge, yet recent breakthroughs have been achieved in stabilizing organo-inorganic halide perovskite films. This stabilization is facilitated by employing liquid electrolytes, specifically those formed by dissolving tetrabutylammoniumperchlorate in dichloromethane. A critical aspect of this research is the comparative analysis of charge and ion kinetics at the perovskite/liquid electrolyte interface versus the perovskite/solid charge transport layer interface. Employing Intensity Modulated Photocurrent Spectroscopy (IMPS), Open-Circuit Voltage Decay (OCVD), and Capacitance-Frequency (C-F) methods, the study scrutinizes charge dynamics in both perovskite/electrolyte and perovskite/solid interfaces. Furthermore, the investigation extends to contrasting the properties of solid–liquid and solid-state junctions, focusing on mobile ions, electric field impacts, and electron-hole transport. The research also examines variations in recombination resistance and ionic double layer charging in perovskite-based devices, aiming to elucidate the operational mechanisms and kinetic complexities at the hybrid perovskite/electrolyte interface.

Liquid–Solid Interface Engineering of Ultrathin and Solution-Processed Indium Oxide-Based Electrolyte-Gated Transistors by Gallium Doping

Liquid–Solid Interface Engineering of Ultrathin and Solution-Processed Indium Oxide-Based Electrolyte-Gated Transistors by Gallium Doping

Improved dynamic characteristics of oxide electrolyte-gated transistor for time-delayed reservoir computing

Time-delayed reservoir computing (RC) equipped with prominent superiorities such as easy training and friendly hardware implementation is identified as a high-efficient answer to complex temporal tasks, and thereby draws increasing attention. Oxygen ion-based oxide electrolyte-gated transistor (Ox-EGT) with rich ion dynamic characteristics is deemed as a promising candidate for RC. However, it is still a challenge to produce the required dynamic characteristics for RC implementation. Herein, we develop an Ox-EGT with an oxygen vacancy-electron-coupled electric-double-layer at the electrolyte/channel interface to implement time-delayed RC. Effects of oxygen vacancy concentration on the short-term plasticity are investigated, revealing the optimal concentration range of oxygen vacancies for the dynamic characteristics improvement. The underlying physical mechanism is demonstrated by TCAD simulations. Simulations using the waveform classification and handwritten-digit recognition tasks validate the good information processing ability of the Ox-EGT RC system. These results provide a promising approach to exploit Ox-EGT dynamics for large-scale and energy-efficient neuromorphic computing hardware.

Synaptic devices with sodium alginate ionic gel gating for global regulation

Information processing and memorizing in the brain take place in a neural network consisting of neurons connected with each other by synapses. Meanwhile, the neural network is immersed in a common electrochemical environment with global parameters regulating the overall functions, which is barely discussed in neuromorphic devices. In this study, organic/inorganic hybrid transistors with sodium alginate as the gate dielectric layer and indium tin oxide as the channel were successfully prepared. We have not only simulated the basic properties of synapses in a single device, but, on top of that, also simulated the global regulation of information processing in the brain due to the incorporation of global grids, achieving excitatory and inhibitory synaptic weight. Moreover, the construction of a 3 × 3 synaptic array enables image learning and memorizing functions. These results demonstrate the significant advantages of electrolyte-gated transistors in enabling complex neural network connectivity and offer a promising opportunity for future artificial synapses.

How Biorecognition Affects the Electronic Properties of Reduced Graphene Oxide in Electrolyte‐Gated Transistor Immunosensors

AbstractAmbipolar electrolyte‐gated transistors (EGTs) based on reduced graphene oxide (rGO) have been demonstrated as ultra‐sensitive and highly specific immunosensors. However, the physics and chemistry ruling the device operation are still not fully unraveled. In this work, the aim is to elucidate the nature of the observed sensitivity of the device. Toward this aim, a physical–chemical model that, coupled with the experimental characterization of the rGO‐EGT, allows one to quantitatively correlate the biorecognition events at the gate electrode and the electronic properties of rGO‐EGT is proposed. The equilibrium of biorecognition occurring at the gate electrode is shown to determine the apparent charge neutrality point (CNP) of the rGO channel. The multiparametric analysis of the experimental transfer characteristics of rGO‐EGT reveals that the recognition events modulate the CNP voltage, the excess carrier density Δn, and the quantum capacitance of rGO. This analysis also explains why hole and electron carrier mobilities, interfacial capacitance, the curvature of the transfer curve, and the transconductances are insensitive to the target concentration. The understanding of the mechanisms underlying the transistor transduction of the biorecognition events is key for the interpretation of the response of the rGO‐EGT immunosensors and to guide the design of novel and more sensitive devices.