Electric Double Layer Transistor Research Articles

Low voltage electric-double-layer transistor nonenzymic erythromycin sensors based on molecularly imprinted polymers

Erythromycin (Ery) is a commonly used antibiotic that can be found ubiquitously in water bodies. The increasing apprehension over the adverse effects of antibiotic remnants in aquatic environments necessitates the prompt advancement of erythromycin detection techniques that are both highly sensitive and compact. Here, we propose a non-enzyme Ery sensor that integrates a mesoporous SiO2-based low-voltage oxide electric-double-layer transistor (EDLT) with a molecular imprinting technique, featuring a molecularly imprinted polymers (MIP) functionalized gate electrode. The mesoporous SiO2-based oxide transistor exhibits excellent electrical characteristics, including an operating voltage of small than 1.0 V, an on/off ratio exceeding 106 and a mobility of 14.95 cm2V−1s−1. At an ultra-low operating voltage within 0.5 V, the sensor exhibits a linear response to the concentration range of 1 nM–10 μM of Ery, with a detection limit of 0.22 nM and a sensitivity of 23.3 mV dec−1. Besides, the single-spike dynamic sensing mode effectively reduces the power consumption of the detection. The proposed sensor provides a rapid and convenient approach to detect Ery in aqueous environments, with benefits such as miniaturization, high sensitivity, and simplicity.

Enhancement of the Synaptic Performance of Phosphorus-Enriched, Electric Double-Layer, Thin-Film Transistors

The primary objective of neuromorphic electronic devices is the implementation of neural networks that replicate the memory and learning functions of biological synapses. To exploit the advantages of electrolyte gate synaptic transistors operating like biological synapses, we engineered electric double-layer transistors (EDLTs) using phosphorus-doped silicate glass (PSG). To investigate the effects of phosphorus on the EDL and synaptic behavior, undoped silicate spin-on-glass-based transistors were fabricated as a control group. Initially, we measured the frequency-dependent capacitance and double-sweep transfer curves for the metal-oxide-semiconductor (MOS) capacitors and MOS field-effect transistors. Subsequently, we analyzed the excitatory post-synaptic currents (EPSCs), including pre-synaptic single spikes, double spikes, and frequency variations. The capacitance and hysteresis window characteristics of the PSG for synaptic operations were verified. To assess the specific synaptic operational characteristics of PSG-EDLTs, we examined EPSCs based on the spike number and established synaptic weights in potentiation and depression (P/D) in relation to pre-synaptic variables. Normalizing the P/D results, we extracted the parameter values for the nonlinearity factor, asymmetric ratio, and dynamic range based on the pre-synaptic variables, revealing the trade-off relationships among them. Finally, based on artificial neural network simulations, we verified the high-recognition rate of PSG-EDLTs for handwritten digits. These results suggest that phosphorus-based EDLTs are beneficial for implementing high-performance artificial synaptic hardware.

Molecular dynamics simulations of electrochemical interfaces.

Molecular dynamics (MD) simulations have become a powerful tool for investigating electrical double layers (EDLs), which play a crucial role in various electrochemical devices. In this Review, we provide a comprehensive overview of the techniques used in MD simulations for EDL studies, with a particular focus on methods for describing electrode polarization, and examine the principle behind these methods and their varying applicability. The applications of these approaches in supercapacitors, capacitive deionization, batteries, and electric double-layer transistors are explored, highlighting recent advancements and insights in each field. Finally, we emphasize the challenges and potential directions for future developments in MD simulations of EDLs, such as considering movable electrodes, improving electrode property representation, incorporating chemical reactions, and enhancing computational efficiency to deepen our understanding of complex electrochemical processes and contribute to the progress in the field involving EDLs.

Aptamer-Based Electric-Double -Layer (EDL) Extended-Gated FET Biosensor for Detection of Cadmium Ion

Cadmium ion (Cd2+) is a highly toxic heavy metal pollutant. It causes irreversible damage to human health even at low doses due to a long biological half-life and strong bioaccumulation. Common heavy metal detection includes Inductively Coupled Plasma with Atomic Emission, Spectroscopy (ICP-AES), Inductively coupled plasma mass spectrometry (ICP-MS), Flame Atomic Absorption Spectrophotometry (FAAS), and Graphite Furnace Atomic Absorption Spectrometry (GFAAS), and. However, these technologies are high-cost, time-consuming, complicated operations, and can't be detected immediately and accurately.In this study, we developed an electric double-layer (EDL) extended-gate field effect transistor sensor based on aptamers to detect cadmium ions (Cd2+). Use N-channel enhanced-mode MOSFETs to connect the extended-gate array chips with aptamer modified. The aptamers were self-assembled on the gold electrode surface through Au-S bonds. Since the aptamer has a specific binding ability to cadmium ions, it will bind to the aptamer to form a stem-loop structure. The gate voltage changes caused by the structure change and then amplify the electrical signal through the transconductance of the field effect transistor. The linear detection range of this sensor for cadmium ions is from 1nM to 10uM. The Cd2+ calibration curve is shown a high correlation coefficient (R2 = 0.99001) and an excellent detection limit as low as 99.5 nＭ. Importantly, it responds to Cd2+ within 10 seconds. The sensor exhibits high selectivity in the presence of other heavy metals such as arsenic, chromium, lead, and mercury for electrical signal measurements. It also can be reused without significant signal attenuation.The advantages of this method are convenient portability, short detection time, high sensitivity, and simple operation. It has a good prospect for detection in the daily life of cadmium environmental pollution. Figure 1

Electrical properties and parameter analysis of all-solid-state LaZrO/InO electric double-layer transistors

All-solid-state electric double-layer (EDL) thin-film transistors (TFTs) consisting of solution-processed LaZrO gate insulators and sputtered InO channels with thicknesses of 10–200 nm were prepared, and their microstructures and electrical properties were investigated. In addition, mobility, carrier concentration, and their gate-voltage dependence in the InO layer were analyzed during a transistor operation to clarify the electron transport properties. It was confirmed that LaZrO was amorphous and that InO crystallized and had an In2O3 bixbyite structure. The transfer conductance increased with the InO thickness, and its normalized value was maximized (3.6 mS/V) at an InO thickness of 200 nm. The maximum capacitance of LaZrO was 31 μF/cm2, strongly suggesting the formation of an EDL. Solid EDL-TFTs operated stably without deterioration at gate voltages up to 5 V, which usually degrade liquid-electrolyte EDL transistors via electrolysis. Assuming the formation of a 1-nm-thick EDL, the concentration of carrier electrons induced during the transistor operation was estimated to be 1019–1021 cm−3. Moreover, the mobility increased with the InO thickness and reached a maximum value of 68 cm2/(V s) at an InO thickness of 120 nm. The conduction electrons were significantly affected by grain boundary scattering and surface scattering, in addition to scattering within the crystal grain. An increase in the InO thickness, which improved the crystallinity in the crystal grain, reduced the barrier height and the effect of grain boundary scattering.

A tunable leaky integrate-and-fire neuron based on one neuromorphic transistor and one memristor

Artificial leaky integrate-and-fire (LIF) neurons have attracted significant attention for building brain-like computing and neuromorphic systems. However, previous artificial LIF neurons have primarily focused on implementing integrate-and-fire function, and the function of dendritic modulation has rarely been reported. In this Letter, a tunable artificial LIF neuron based on an IGZO electric-double-layer (EDL) transistor and a TaOx memristor is fabricated, and dendritic modulation is investigated. An IGZO-based EDL transistor with a modulatory terminal is used to realize dendritic nonlinear integration and filtering capability, as well as the tunable neural excitability. An Ag/TaOx/ITO threshold switching memristor mimics the all-or-nothing spiking and threshold switching of the soma. By incorporating these two components in a customized way, such artificial LIF neuron can emulate the key function of biological neuron with rich computational flexibility. Our artificial LIF neurons with rich nonlinear dynamics have great potential to perform more complex tasks in future spiking neuromorphic systems.

Revisiting the Hetero-Interface of Electrolyte/2D Materials in an Electric Double Layer Device.

Electric double layer (EDL) devices based on 2D materials have made great achievements for versatile electronic and opto-electronic applications; however, the ion dynamics and electric field distribution of theEDL at the electrolyte/2D material interface and their influence on the physical properties of 2D materials have not been clearly clarified. In this work, by using Kelvin probe force microscope and steady/transient optical techniques, the character of the EDL and its influence on the optical properties of monolayer transition metal dichalcogenides (TMDs) are probed. The potential drop, unscreened EDL potential distribution, and accumulated carriers at the electrolyte/TMD interface arerevealed, which can be explained by nonlinear Thomas-Fermi theory. By monitoring the potential distribution along the channel, the evolution of the electric field-induced lateral junction in the TMD EDL transistor isaccessed, giving rise to the better exploration of EDL device physics. More importantly, EDL gate-dependent carrier recombination and exciton-exciton annihilation in monolayer TMDs on lithium-ion solid state electrolyte (Li2 Al2 SiP2 TiO13 ) areevaluated for the first time, benefiting from the understanding of the interaction between ions, carriers, and excitons. Thework will deepen the understanding of the EDL for the exploitation of functional device applications.

Ultrafast-switching of an all-solid-state electric double layer transistor with a porous yttria-stabilized zirconia proton conductor and the application to neuromorphic computing

All-solid-state electric double layer transistors (ASS-EDLTs) have recently been attracting attention because of their huge potential for use in neuromorphic device applications. However, their low switching response speed is a significant drawback to their practical application. Here, we demonstrate ultrafast-switching of ASS-EDLTs, which was achieved by an excellent combination of hydrogenated diamond single crystal and a porous yttria stabilized zirconia thin film with extremely high proton conductivity. The switching response speed was investigated in response to gate voltage pulses. We achieved the ASS-EDLT that can operate at a very short response time of less than a hundred μs (i.e., 27 μs), even at room temperature. This is a far shorter time than that found in typical conventional ASS-EDLTs, which characteristically have response times measured in milliseconds or longer. Furthermore, the subject ASS-EDLT possessed characteristics that are similar to those of volatile memory devices. To demonstrate neuromorphic computing capability of the device, waveform transformation task has been performed. The results indicated that the ASS-EDLT, with its high operating speed, can contribute to the development of high-speed neuromorphic systems.

Aptamer-Based Electric-Double -Layer (EDL) Extended-Gated FET Biosensor for Detection of Cadmium Ion

In this study, we developed an electric double-layer (EDL) extended-gate field effect transistor sensor based on aptamers to detect cadmium ions (Cd2+). Since the aptamer has a specific binding ability to cadmium ions. The signal is amplified through the transconductance of the FET. The linear detection range of this sensor for cadmium ions is from 1 nM to 10 uM. The Cd2+ calibration curve is shown a high correlation coefficient (R2 = 0.981) and an excellent detection limit as low as 0.094 nM. Importantly, it responds to Cd2+ within 10 seconds. The sensor exhibits high selectivity in the presence of other heavy metals. It also can be reused without significant signal attenuation. The advantages of this method are convenient portability, short detection time, high sensitivity, and simple operation. It has a good prospect for detection in the daily life of cadmium environmental pollution.

Planar Multi-Gate Artificial Synaptic Transistor with Solution-Processed AlOx Solid Electric Double Layer Dielectric and InOx Channel

Multi-terminal artificial synaptic devices are promising for building neural morphological networks and manufacturing neural chips. In this study, planar multi-gate InOx-based artificial synaptic transistor was demonstrated by using solution-processed AlOx as an electric double layer (EDL) dielectric with mobile hydrogen protons. The excitatory postsynaptic current (EPSC) was successfully controlled by adjusting amplitude, duration, and interval of the stimulating voltage pulses applied on the planar gates. The EPSC stimulated by multiple inputs shows the property of sublinear summation. As spatial resolution function of the artificial synaptic transistor, the EPSC depends on the presynaptic (planar gate) area and distance to the channel, nonlinearly. The paired-pulse facilitation (PPF), depending on time sequence, demonstrates the temporal resolution function of the multi-gate artificial synaptic transistor. The study shows the potential of planar multi-gate AlOx/InOx EDL transistor as multi-terminal artificial synaptic device.

Analysis of capacitance and charge accumulation for an electric double layer on porous electrode

The configuration of an electric double layer transistor (EDLT) allows for a very high surface charge density that cannot be achieved by solid dielectrics. Novel phases and superconductivity have been explored using the EDLT technique. The channel in an EDLT typically consists of single crystals or two-dimensional materials. When polycrystalline materials with porous surfaces are used as channel materials in an EDLT, it may not be easy to prepare gate electrodes that have a larger surface area than that of the channel to accumulate significant charge on the channel. Based on the impedance measurements, we estimated the electric double layer (EDL) capacitance on porous YBa2Cu3Oy (YBCO), which can be used as a gate electrode. The ratio of the EDL capacitances on YBCO and Au per unit area was found to be larger than 10, implying that the large surface area is associated with the YBCO porosity. The accumulated electrostatic charge on the YBCO electrodes estimated from double-step chronocoulometry is consistent with the EDL capacitance obtained from impedance measurements. Our work should broaden the applicability of EDLT to a wide range of materials, including porous materials.

Stretchable Transistor-Structured Artificial Synapses for Neuromorphic Electronics.

Stretchable synaptic transistors, a core technology in neuromorphic electronics, have functions and structures similar to biological synapses and can concurrently transmit signals and learn. Stretchable synaptic transistors are usually soft and stretchy and can accommodate various mechanical deformations, which presents significant prospects in soft machines, electronic skin, human-brain interfaces, and wearable electronics. Considerable efforts have been devoted to developing stretchable synaptic transistors to implement electronic device neuromorphic functions, and remarkable advances have been achieved. Here, this review introduces the basic concept of artificial synaptic transistors and summarizes the recent progress in device structures, functional-layer materials, and fabrication processes. Classical stretchable synaptic transistors, including electric double-layer synaptic transistors, electrochemical synaptic transistors, and optoelectronic synaptic transistors, as well as the applications of stretchable synaptic transistors in light-sensory systems, tactile-sensory systems, and multisensory artificial-nerves systems, are discussed. Finally, the current challenges and potential directions of stretchable synaptic transistors are analyzed. This review presents a detailed introduction to the recent progress in stretchable synaptic transistors from basic concept to applications, providing a reference for the development of stretchable synaptic transistors in the future.

Accelerated/decelerated dynamics of the electric double layer at hydrogen-terminated diamond/Li+ solid electrolyte interface

The electrical response of the electric double layer (EDL) effect at the interface between a hydrogen-terminated diamond (H-diamond) and a Li+-conducting solid electrolyte [i.e., LiNbO3 and Li3PO4] was investigated by using an all-solid-state H-diamond-based EDL transistor (EDLT). A 5-nm-thick LiNbO3 or Li3PO4 interlayer was inserted between a H-diamond and a Li–Si–Zr–O (700 nm) Li+ solid electrolyte. We performed Hall measurements and pulse response measurements to investigate the EDL charging characteristics exhibited. The Hall measurements evidenced that all EDLTs exhibited EDL-induced hole density modulation, with a large EDL capacitance (CEDL) to 15 μF/cm2 in the Li + -deficient region (negative VG side). On the other hand, in the pulse response measurement, insertion of an LiNbO3 or Li3PO4 interlayer caused significant acceleration/deceleration of the switching response speed, ranging from τ = 61.4 ms to 229 μs? CEDL at the LiNbO3/H-diamond and Li3PO4/H-diamond interface, particularly on the Li+ rich side, was indicated as determining the switching response speed. The results indicate that the very thin EDL (i.e., 5 Å) can be formed at the solid/solid electrolyte interface, even when inorganic solid electrolytes are used instead of liquid electrolytes, and CEDL at the solid/solid electrolyte can be controlled by electrolyte compositions within a thickness of several Å from the interface.

Enhanced Synaptic Properties in Biocompatible Casein Electrolyte via Microwave-Assisted Efficient Solution Synthesis

In this study, we fabricated an electric double-layer transistor (EDLT), a synaptic device, by preparing a casein biopolymer electrolyte solution using an efficient microwave-assisted synthesis to replace the conventional heating (heat stirrer) synthesis. Microwave irradiation (MWI) is more efficient in transferring energy to materials than heat stirrer, which significantly reduces the preparation time for casein electrolytes. The capacitance-frequency characteristics of metal-insulator-metal configurations applying the casein electrolyte prepared through MWI or a heat stirrer were measured. The capacitance of the MWI synthetic casein was 3.58 μF/cm2 at 1 Hz, which was higher than that of the heat stirrer (1.78 μF/cm2), confirming a stronger EDL gating effect. Electrolyte-gated EDLTs using two different casein electrolytes as gate-insulating films were fabricated. The MWI synthetic casein exhibited superior EDLT electrical characteristics compared to the heat stirrer. Meanwhile, essential synaptic functions, including excitatory post-synaptic current, paired-pulse facilitation, signal filtering, and potentiation/depression, were successfully demonstrated in both EDLTs. However, MWI synthetic casein electrolyte-gated EDLT showed higher synaptic facilitation than the heat stirrer. Furthermore, we performed an MNIST handwritten-digit-recognition task using a multilayer artificial neural network and MWI synthetic casein EDLT achieved a higher recognition rate of 91.24%. The results suggest that microwave-assisted casein solution synthesis is an effective method for realizing biocompatible neuromorphic systems.

Egg shell membrane based electrolyte gated oxide neuromorphic transistor

In recent years, the study of neuromorphic devices has received extensive attention. It is becoming an important branch of the development of artificial intelligence technology. At the same time, natural biomaterials have several priorities, such as biodegradability, good biocompatibility, and non-toxicity, and have important value in novel portable intelligent systems. The egg shell membrane (ESM) is a fiber scaffold composed of highly crosslinked collagen, glycoprotein and cysteine-rich eggshell membrane proteins. It has porous morphology, thermal stability, mechanical strength, etc. Therefore, these protein-based fiber membranes have several potential applications, including nanocatalysts, microbial fuel cells, and adsorption of toxic dyes. This study adopts ESM as electrolyte, exhibiting extremely high proton conductivity of about 6.4×10<sup>–3</sup> S/cm and extremely high electric-double-layer (EDL) capacitance of about 2.8 µF/cm<sup>2</sup> at room temperature. Thus, it has extremely strong interfacial EDL electrostatic modulation capability. Then, indium tin oxide EDL transistor is fabricated by using a single step masking processing and magnetron sputtering deposition technology. The device exhibits typical n-type output curves and transfer curves at low operating voltage. In addition, transfer curves are scanned twice. It is observed that the curves approach to each other quite well, indicating the good stabilities. Owing to the extremely strong proton gating effects, the device exhibits excellent electrical performances. Specifically, ON/OFF ratio, mobility and sub-threshold swing are estimated to be about 2.5×10<sup>6</sup>, about 3.2 cm<sup>2</sup>/(V·s), and about 213 mV/dec, respectively. With the unique interfacial EDL modulation activities of ESM, the transistor can mimic some important synaptic plasticity behaviors, such as excitatory postsynaptic current (EPSC) and paired pulse facilitation (PPF). With the increase of pre-synaptic spike amplitude, the EPSC value increases correspondingly. With the increase of pre-synaptic spike frequency, the EPSC grain increases, indicating the potentials in high-pass synaptic filtering. By loading 64 potentiation spikes and 64 depression spikes, multi-level synaptic weight can be updated, demonstrating potentiation activity and depression activity. Again, with the same potentiation spikes and depression spikes, synaptic weight value curves approach to each other quite well, indicating that the present ESM gated oxide neuromorphic transistor has good stability. Then, an artificial neural network is adopted to perform supervised learning with Modified National Institute of Standards and Technology (MNIST) database. For simulation, a two-layer multilayer perceptron (MLP) neural network with 400 input neurons, 100 hidden neurons and 10 output neurons is adopted. The best recognition accuracy is as high as 92.59%. The proposed ESM gated oxide neuromorphic transistors have certain potentials in low-cost biodegradable neuromorphic systems.

Flexible Floating-Gate Electric-Double-Layer Organic Transistor for Neuromorphic Computing

The key to the study of flexible neuromorphic computing is the excellent weight update characteristic of neuromorphic devices. Electric-double-layer transistors (EDLTs) include high transconductance, excellent stability of threshold voltage, linear weight updates, and repetitive ion-concentration-dependent switching properties. However, up to now, there is no report on a flexible EDLT that provides all the aforementioned performance characteristics. Here, a planar flexible floating-gate EDLT including an excellent linear/symmetric weight update, a large number (>800) of conductance states, repetitive switching endurance (>100 cycles), and low variation in weight update is reported. After 800 signal stimulations, it is found that the nonlinearity values of LTP are between 0.20 and 0.85, those of LTD fall between 0.66 and 1.55, the symmetricity values are between 120.7 and 639.8, and the dynamic range is between 150 and 352 nS. The study of 8 × 8 flexible floating-gate EDLT arrays shows that the average deviation and standard deviation between the experimental and theoretical values are 1.36 and 1.93, respectively, indicating that the conductance regulation in the array has a relatively small deviation. The different bending angles and the mechanical stability of the floating-gate EDLT are also studied, which exhibit the excellent bending properties. Furthermore, we studied the recognition of MNIST handwritten digit images by a three-layer perceptron artificial neural network with the experimental weight update, and the maximal recognition accuracy is up to 87.8%.

Coexistence of Urbach-Tail-Like Localized States and Metallic Conduction Channels in Nitrogen-Doped 3D Curved Graphene.

Nitrogen (N) doping is one of the most effective approaches to tailor the chemical and physical properties of graphene. By the interplay between N dopants and 3D curvature of graphene lattices, N-doped 3D graphene displays superior performance in electrocatalysis and solar-energy harvesting for energy and environmental applications. However, the electrical transport properties and the electronic states, which are the key factors to understand the origins of the N-doping effect in 3D graphene, are still missing. The electronic properties of N-doped 3D graphene are systematically investigated by an electric-double-layer transistor method. It is demonstrated that Urbach-tail-like localized states are located around the neutral point of N-doped 3D graphene with the background metallic transport channels. The dual nature of electronic states, generated by the synergistic effect of N dopants and 3D curvature of graphene, can be the electronic origin of the high electrocatalysis, enhanced molecular adsorption, and light absorption of N-doped 3D graphene.

Design and Functional Test of Transistor Inverter Based on Polyvinyl Alcohol and Graphene Oxide Electrolyte

Eco‐friendly “green” electronics are attracting increasing interest in recent years. For example, neural prostheses, nerve implants, drug delivery devices, and diagnostic electronics, as well as some green materials (paper, silk, and polysaccharides) with bioabsorbable and biocompatible transistors, load inverters, and other devices. Here, biodegradable polyvinyl alcohol (PVA)/graphene oxide (GO) electric double‐layer (EDL) transistors are prepared on glass substrates. PVA film treated with GO solution is used as a gate dielectric. Oxide EDL transistors show good performance. A resistive load inverter is also constructed, which shows full swing characteristics and high voltage gain at low operating voltage. The waveform conversion is realized, including the conversion from sine wave to rectangular wave, and the conversion from noise signal to two‐bit output. In addition, PVA/GO transistors can be easily dissolved in water. The proposed PVA/GO oxide transistors may have potential applications in “green” portable devices.

Time-Dependent Sensitivity Tunable pH Sensors Based on the Organic-Inorganic Hybrid Electric-Double-Layer Transistor.

In this study, we propose tunable pH sensors based on the electric-double-layer transistor (EDLT) with time-dependent sensitivity characteristics. The EDLT is able to modulate the drain current by using the mobile ions inside the electrolytic gate dielectric. This property allows the implementation of a device with sensitivity characteristics that are simply adjusted according to the measurement time. An extended gate-type, ion-sensitive, field-effect transistor consisting of a chitosan/Ta2O5 hybrid dielectric EDLT transducer, and an SnO2 sensing membrane, were fabricated to evaluate the sensing behavior at different buffer pH levels. As a result, we were able to achieve tunable sensitivity by only adjusting the measurement time by using a single EDLT and without additional gate electrodes. In addition, to demonstrate the unique sensing behavior of the time-dependent tunable pH sensors based on organic–inorganic hybrid EDLT, comparative sensors consisting of a normal FET with a SiO2 gate dielectric were prepared. It was found that the proposed pH sensors exhibit repeatable and stable sensing operations with drain current deviations <1%. Therefore, pH sensors using a chitosan electrolytic EDLT are suitable for biosensor platforms, possessing tunable sensitivity and high-reliability characteristics.

Strong temperature dependence of transfer characteristics and time constants near freezing point of ionic liquid in an ambipolar electric double layer transistor

The gating operation of electric double layer transistors (EDLTs) is typically conducted at low temperatures to prevent possible damage due to electrochemical reactions. We studied the temperature dependence of the transport properties of an EDLT with a molybdenum disulfide channel at low temperatures approaching the freezing point of the ionic liquid used for gating. The strong temperature dependence of the ambipolar transfer characteristics was attributed to the Arrhenius-type temperature dependence of the time constants of the drain current at a fixed gate voltage, which were estimated for both p- and n-channels. The time constants are explained in terms of the resistance and capacitance associated with the ionic liquid and electric double layer.