Electrolyte-gated Organic Transistors Research Articles

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 useable.

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

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

Investigation of transcription factor–DNA binding with electrolyte-gated organic transistors

The first electrolyte-gated organic transistor biosensor for the detection of a transcription factor (NF-Y) in buffer and cell lysate.

Distinctive Behavior of Field-Effect and Redox Electrolyte-Gated Organic Transistors

Distinctive Behavior of Field-Effect and Redox Electrolyte-Gated Organic Transistors

Single-Molecule Bioelectronic Portable Array for Early-Diagnosis of Pancreatic Cancer Precursors.

A cohort of 47 patients is screened for pancreatic cancer-precursors with a portable 96-well bioelectronic sensing-array for single-molecule assay in cysts fluid and blood plasma deployable at point-of-care (POC). Pancreatic cancer precursors are mucinous cysts diagnosed with a sensitivity of at most 80% by state-of-the-art cytopathological molecular analyses (e.g., KRASmut DNA). Adding the simultaneous assay of proteins related to malignant transformation (e.g., MUC1 and CD55) is deemed essential to enhance diagnostic accuracy. The bioelectronic array here proposed, based on the SiMoT (Single-Molecule-with-a-large-Transistor) technology, can assay both nucleic acids and proteins at the single-molecule Limit-Of-Identification, LOI (<1% of false-positives and false-negatives). It comprises an ELISA-like 8×12-array organic-electronics disposable cartridge with an electrolyte-gated organic transistor sensor array, and a reusable reader, integrating a custom Si-IC chip, operating via software installed on a USB-connected smart device. The cartridge is complemented by a 3D-printed sensing gate cover plate. KRASmut , MUC1, and CD55 biomarkers either in plasma or cysts-fluid from 5-6 patients at a time, are multiplexed at single-molecule LOI in 1.5 hours. The pancreatic cancer precursors are classified via a machine-learning analysis resulting in at least 96% diagnostic-sensitivity and 100% diagnostic-specificity. This preliminary study opens the way to POC liquid-biopsy-based early diagnosis of pancreatic-cancer precursors in plasma. This article is protected by copyright. All rights reserved.

Physically defined long-term and short-term synapses for the development of reconfigurable analog-type operators capable of performing health care tasks.

Extracting valuable information from the overflowing data is a critical yet challenging task. Dealing with high volumes of biometric data, which are often unstructured, nonstatic, and ambiguous, requires extensive computer resources and data specialists. Emerging neuromorphic computing technologies that mimic the data processing properties of biological neural networks offer a promising solution for handling overflowing data. Here, the development of an electrolyte-gated organic transistor featuring a selective transition from short-term to long-term plasticity of the biological synapse is presented. The memory behaviors of the synaptic device were precisely modulated by restricting ion penetration through an organic channel via photochemical reactions of the cross-linking molecules. Furthermore, the applicability of the memory-controlled synaptic device was verified by constructing a reconfigurable synaptic logic gate for implementing a medical algorithm without further weight-update process. Last, the presented neuromorphic device demonstrated feasibility to handle biometric information with various update periods and perform health care tasks.

Pre-synaptic DC bias controls the plasticity and dynamics of three-terminal neuromorphic electrolyte-gated organic transistors

The role of pre-synaptic DC bias is investigated in three-terminal organic neuromorphic architectures based on electrolyte-gated organic transistors—EGOTs. By means of pre-synaptic offset it is possible to finely control the number of discrete conductance states in short-term plasticity experiments, to obtain, at will, both depressive and facilitating response in the same neuromorphic device and to set the ratio between two subsequent pulses in paired-pulse experiments. The charge dynamics leading to these important features are discussed in relationship with macroscopic device figures of merit such as conductivity and transconductance, establishing a novel key enabling parameter in devising the operation of neuromorphic organic electronics.

Electrical and mechanical stability of flexible, organic electrolyte-gated transistors based on iongel and hydrogels

Mechanical and operational stability of electrolyte-gated transistors were studied using iongels and hydrogels. Iongel-based devices showed long-term stability in ambient condition. Addition of glycerol to the formulation of hydrogels improved the operational stability.

A continuum theory of organic mixed ionic-electronic conductors of phase separation

Organic mixed ionic-electronic conductors (OMIECs) are the core functioning component in the emerging flexible, bio-, and optoelectronics owning to their unique capability of mixed conduction. Of all types, two-phase OMIECs exhibit exceptional performance due to their high stretchability and balanced ionic-electronic conduction. However, the electron-conducting phase may segregate from the ion-conducting phase in a two-phase OMIEC, changing the conducting path and eventually leading to degraded performance and dysfunction of the devices. In this work, we formulate a continuum theory following the thermodynamics framework of a two-phase OMIEC undergoing phase separation. The free energy consists of contributions from the deformation of the polymer chains, the mixing of the polymer with salts and solvents, the electrostatic field, and the two-phase interfaces. The equilibrium conditions and kinetics equations are derived with the constraint of mass conservation, thermodynamics laws, and electrostatics. We implement the theory into a finite element model and study the mechanics and electrochemistry of the OMIEC channel in an electrolyte-gated organic electrochemical transistor (OECT) device. The computational model captures the concurrent transport of charge carriers, mechanical swelling, and phase separation in the OMIEC and replicates the transfer curves of an OECT which agree well with the experiments. More specifically, we reveal the origin of the volumetric capacitance as the accumulation of charge carriers at the two-phase interfaces. We examine the parametric space to elucidate experimental observations such as molecular size-dependent conductivity and substrate-dependent phase separation. The swelling behavior and the transfer curves of OECTs under stretched, free, and constrained states are compared, demonstrating the effects of deformation on the phase dynamics and the electron-conducting behavior. We show that, for volumetric swelling and the electrochemical transfer curves, the effect of stress-transport coupling dominates while the effect of the Maxwell stress is negligible. This work provides a theoretical basis for the mechanics and electrochemistry of two-phase OMIECs.

Submicron Vertical Channel Organic Electrochemical Transistors with Ultrahigh Transconductance

AbstractOrganic electrochemical transistors (OECTs) belong to the class of electrolyte gated organic transistors (EGOTs) that offer a smooth interface with biology in combination with high transconductance values of typically a few mS. Fabrication‐wise, though, most of the up‐to‐date reported devices are limited to two dimensional structures, where the transistor channel is patterned on the same plane as the source and drain electrodes. Here, a method is introduced for the fabrication of integrated vertical channel OECTs (vOECTs) with submicron channel length. By employing electrodeposition, a vertical channel sandwiched between the source and drain electrodes is created. Channel lengths down to 60 nm are demonstrated, giving rise to ultrahigh transconductance of up to 275 mS. Accounting for the voltage loss on the device connection tracks, an intrinsic transconductance of vOECTs of 500 mS is found. The vOECTs are three‐dimensional transistors finding relevant application in “organ‐on‐a‐chip” and implantable devices, where high amplification and small footprint are demanded.

Cationic effects on solid polymer electrolyte-gated organic transistors

Unlike the conventional organic field effect transistors using traditional gate dielectric layer, the electrolyte-gated organic transistors (EGOTs) use electrolytes as gate media, resulting in a tunable highly conductive channel. Due to their unique advantages, such as: higher gate-capacitance and lower operating voltages, the EGOTs are subject to extensive research. In a solid polymer electrolyte gate, the solvated cations and anions are initially evenly distributed in the ion-conducting polymer, under gate bias, the counter ions then drift towards the electrolyte/active layer interface and under high enough bias they might insert into the active layer and dope the polymer. Given the above mechanism, the anions and cations play the crucial role for gate operation in EGOTs. Although how the anions significantly affect the organic electrochemical transistors using the liquid electrolyte media was investigated, the ionic effect in the solid electrolyte-gated transistors has been barely reported. In this work, the effects of cation on the device performance of solid polymer electrolyte-gated organic transistors have been systematically studied. In the devices made with alkali perchlorates, a systematic shift in threshold voltage, current hysteresis, and response time with increasing cation size/mass has been observed. A lower threshold voltage is obtained with the smaller cation which also displays smaller hysteresis and faster response due to faster migration of smaller cations in polymer electrolyte. This study suggests the smaller cations should be used in the fabrication of solid polymer EGOTs. • Cationic effects on the solid electrolyte (PEO:alkali perchlorate salt)-gated organic transistors (EGOTs) are studied. • The smaller cation based device displays lower threshold voltage, smaller hysteresis, and faster response. • The cation motion in polymer electrolyte is key for performances of EGOTs.

Influence of Gate Voltage Operation on Effective Mobility of Electrolyte-Gated Organic Transistors

Influence of Gate Voltage Operation on Effective Mobility of Electrolyte-Gated Organic Transistors

Aqueous-processable, naphthalene diimide-based polymers for eco-friendly fabrication of high-performance, n-type organic electrolyte-gated transistors

Aqueous-processable, naphthalene diimide-based polymers for eco-friendly fabrication of high-performance, n-type organic electrolyte-gated transistors

Design of a Portable Microfluidic Platform for EGOT-Based in Liquid Biosensing.

In biosensing applications, the exploitation of organic transistors gated via a liquid electrolyte has increased in the last years thanks to their enormous advantages in terms of sensitivity, low cost and power consumption. However, a practical aspect limiting the use of these devices in real applications is the contamination of the organic material, which represents an obstacle for the realization of a portable sensing platform based on electrolyte-gated organic transistors (EGOTs). In this work, a novel contamination-free microfluidic platform allowing differential measurements is presented and validated through finite element modeling simulations. The proposed design allows the exposure of the sensing electrode without contaminating the EGOT device during the whole sensing tests protocol. Furthermore, the platform is exploited to perform the detection of bovine serum albumin (BSA) as a validation test for the introduced differential protocol, demonstrating the capability to detect BSA at 1 pM concentration. The lack of contamination and the differential measurements provided in this work can be the first steps towards the realization of a reliable EGOT-based portable sensing instrument.

Nanoscopic Electrolyte-Gated Vertical Organic Transistors with Low Operation Voltage and Five Orders of Magnitude Switching Range for Neuromorphic Systems.

Electrolyte-gated organic transistors (EGOTs) are promising candidates as a new class of neuromorphic devices in hardware-based artificial neural networks that can outperform their complementary metal oxide semiconductor (CMOS) counterparts regarding processing speed and energy consumption. Several ways in which to implement such networks exist, two prominent methods of which can be implemented by nanoscopic vertical EGOTs, as we show here. First, nanoscopic vertical electrolyte-gated transistors with a donor-acceptor diketopyrrolopyrrole-terthiophene polymer as an active material can be used to reversibly switch the channel conductivity over five orders of magnitude (3.8 nS to 392 μS) and perform switching at low operation voltages down to -1 mV. Second, nanoscopic EGOTs can also mimic fundamental synaptic functions, and we show an interconnection of up to three transistors, highlighting the possibility to emulate biological nerve cells.

A Simple Approach to Fabrication of Highly Efficient Electrolyte-Gated Organic Transistors by Phase Microsegregation of 2,7-Dioctyl [1]benzothieno[3,2-b]benzothiophene and Polystyrene Mixtures

Electrolyte-gated organic transistors represent a promising platform for the design of fluid biosensors. The paper presents a simple and easily scalable approach to the manufacture of high-performance stable electrolyte-gated organic transistors with reproducible electrical characteristics, based on phase microsegregation in mixtures of an organic semiconductor, 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene, with a dielectric polymer, polystyrene.

Solid-State Organic Electrolyte-Gated Transistors Based on Doping-Controlled Polymer Composites with a Confined Two-Dimensional Channel in Dry Conditions.

We report comprehensive and comparative studies on chemical and electrochemical controls of doping characteristics of various poly(3,4-ethylenedioxythiophene) (PEDOT) composites complexed with sulfonates. Chemical treatment of PEDOT composites was conducted with a dedoping agent, tetrakis(dimethylamino)ethylene (TDAE), resulting in the changes in conformation and bulk charge-carrier density. Electrochemical control of doping states was done with a solid-state ionogel based on an ionic liquid dispersed in a polymer matrix. With this approach, we can fabricate solid-state organic electrolyte-gated transistors (OEGTs) with a large current modulation, a high mobility of holes, and a low driving voltage. Our OEGTs are operational in a dry environment and, surprisingly, form the two-dimensional channel of the interfacial charge carriers modulating the conductance under gate bias, unlike conventional liquid-based OEGTs. The charge-carrier mobility and the on-to-off current ratio reach up to ∼7 cm2 V-1 s-1 and over 104, respectively, from the chemically dedoped PEDOT composites. The ionogel-based gating of the layer of TDAE-treated PEDOT composites induces a reversible transition between a highly doped bipolaronic state and neutral/polaronic states, as revealed by the absorption profiles under gate bias. We also demonstrate in-plane OEGTs, in which the dedoped channel and the conductive source/drain electrodes are made of a single PEDOT composite layer.

Tunable Short-Term Plasticity Response in Three-Terminal Organic Neuromorphic Devices

Reversibly tunable short-term plasticity (STP) of the channel current in organic neuromorphic devices is demonstrated with a three-terminal architecture. Electrolyte-gated organic transistors—EGOTs...

Flexible Organic Electrolyte-Gated Transistors Based on Thin Polymer Blend Films of Crystalline C8-BTBT and Amorphous PTAA

Thin films of polymer blends consisting of a crystalline small-molecular semiconductor, 2,7-dioctyl[1]benzothieno[3,2-b][1]benzothiophene (C8-BTBT), and an amorphous polymer semiconductor, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA), are studied and applied to organic electrolyte-gated transistors (OEGTs). The compositions can be easily controlled by adjusting the mixing ratios of the solutions in chloroform. In the thin-film state, PTAA acts as a structural matrix and a charge-transport bridge for C8-BTBT grains. The C8-BTBT:PTAA blends have a compositional effect on the thin-film properties and performance of OEGTs. As a result, the C8-BTBT:PTAA blend films with weight ratios of 8:2 exhibit a hole mobility twice that of pristine C8-BTBT films. Moreover, OEGTs based on the C8-BTBT:PTAA blend exhibit better charge-transport properties on flexible plastic substrates under bending conditions, compared to flat devices.

Photovoltage generation in enzymatic bio-hybrid architectures

Most of the photochemical activity of bacterial photosynthetic apparatuses occurs in the reaction center, a transmembrane protein complex which converts photons into chargeseparated states across the membrane with a quantum yield close to unity, fuelling the metabolism of the organism. Integrating the reaction center from the bacterium Rhodobacter sphaeroides onto electroactive surfaces, it is possible to technologically exploit the efficiency of this natural machinery to generate a photovoltage upon Near Infra-Red illumination, which can be used in electronic architectures working in the electrolytic environment such as electrolyte-gated organic transistors and bio-photonic power cells. Here, photovoltage generation in reaction center-based bio-hybrid architectures is investigated by means of chronopotentiometry, isolating the contribution of the functionalisation layers and defining novel surface functionalization strategies for photovoltage tuning.