Dual-gate Thin-film Transistors Research Articles

Construction and Application of a Neuromorphic Circuit With Excitatory and Inhibitory Post-Synaptic Conduction Channels Implemented Using Dual-Gate Thin-Film Transistors

Construction and Application of a Neuromorphic Circuit With Excitatory and Inhibitory Post-Synaptic Conduction Channels Implemented Using Dual-Gate Thin-Film Transistors

Rapid and simultaneous multiple detection of a tripledemic using a dual-gate oxide semiconductor thin-film transistor-based immunosensor

The simultaneous infection with a tripledemic—simultaneous infection with influenza A pH1N1 virus (Flu), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), and respiratory syncytial virus (RSV)—necessitates the development of accurate and fast multiplex diagnostic tests. The coronavirus disease 2019 (COVID-19) pandemic has emphasized the importance of virus detection. Field-effect transistor (FET)-based immuno-biosensors have a short detection time and do not require labeling or polymerase chain reaction. This study demonstrates the rapid, sensitive detection of influenza A pH1N1, SARS-CoV-2, and RSV using a multiplex immunosensor based on a dual-gate oxide semiconductor thin-film transistor (TFT), a type of FET. The dual-gate oxide TFT was modified by adjusting both top and bottom gate insulators to improve capacitive coupling to approximately 120-fold amplification, exhibiting a high pH sensitivity of about 10 V/pH. The dual-gate oxide TFT-based immunosensor detected the target proteins (hemagglutinin (HA) protein of Flu, spike 1 (S1) protein of SARS-CoV-2, and fusion protein of RSV) of each virus, with a limit of detection of approximately 1 fg/mL. Cultured viruses in phosphate-buffered saline or artificial saliva and clinical nasopharynx samples were detected in 1-μL sample volumes within 60 s. This promising diagnosis could be potentially as point-of-care tests to facilitate a prompt response to future pandemics with high sensitivity and multiplexed detection without pretreatment.

Fully Transparent and Highly Sensitive pH Sensor Based on an a-IGZO Thin-Film Transistor with Coplanar Dual-Gate on Flexible Polyimide Substrates

In this paper, we propose a fully transparent and flexible high-performance pH sensor based on an amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) transducer with a coplanar dual-gate structure on polyimide substrates. The proposed pH sensor system features a transducer unit consisting of a floating gate (FG), sensing gate (SG), and control gate (CG) on a polyimide (PI), and an extended gate (EG) sensing unit on a separate glass substrate. We designed a capacitive coupling between (SG) and (CG) through the FG of an a-IGZO TFT transducer to contribute to sensitivity amplification. The capacitance ratio (CSG/CCG) increases linearly with the area ratio; therefore, the amplification ratio of the pH sensitivity was easily controlled using the area ratio of SG/CG. The proposed sensor system improved the pH sensitivity by up to 359.28 mV/pH (CSG/CCG = 6.16) at room temperature (300 K), which is significantly larger than the Nernstian limit of 59.14 mV/pH. In addition, the non-ideal behavior, including hysteresis and drift effects, was evaluated to ensure stability and reliability. The amplification of sensitivity based on capacitive coupling was much higher than the increase in the hysteresis voltage and drift rate. Furthermore, we verified the flexibility of the a-IGZO coplanar dual-gate TFT transducer through a bending test, and the electrical properties were maintained without mechanical damage, even after repeated bending. Therefore, the proposed fully transparent and highly sensitive a-IGZO coplanar dual-gate TFT-based pH sensor could be a promising wearable and portable high-performance chemical sensor platform.

Dual-gate thin film transistor lactate sensors operating in the subthreshold regime

Organic thin-film transistors (TFTs) with an electrochemically functionalized sensing gate are promising platforms for wearable health-monitoring technologies because they are light, flexible, and cheap. Achieving both high sensitivity and low power is highly demanding for portable or wearable devices. In this work, we present flexible printed dual-gate (DG) organic TFTs operating in the subthreshold regime with ultralow power and high sensitivity. The subthreshold operation of the gate-modulated TFT-based sensors not only increases the sensitivity but also reduces the power consumption. The DG configuration has deeper depletion and stronger accumulation, thereby further making the subthreshold slope sharper. We integrate an enzymatic lactate-sensing extended-gate electrode into the printed DG TFT and achieve exceptionally high sensitivity (0.77) and ultralow static power consumption (10 nW). Our sensors are successfully demonstrated in physiological lactate monitoring with human saliva. The accuracy of the DG TFT sensing system is as good as that of a high-cost conventional assay. The developed platform can be readily extended to various materials and technologies for high performance wearable sensing applications.

An Artificial Neural Network Implemented Using Parallel Dual-Gate Thin-Film Transistors

Implementing in-memory computation, an artificial neural network (ANN) consisting of thin-film transistors (TFTs) monolithically integrated in each unit of an array of capacitors is constructed. Both single-gate and parallel, dual-gate (DG) TFTs are deployed. The capacitors and the DG TFTs serve as the respective memory and computational elements. The DG TFT offers the capability of amplifying a weak but relevant input signal and suppressing a strong but irrelevant input signal across a synaptic gap, and the storage of charge on the capacitor is pseudostatic because of the exceptionally low OFF-state leakage current of the accompanying address TFT built on a metal–oxide semiconductor. The feasibility of such an ANN is demonstrated using a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4\times6$ </tex-math></inline-formula> array for classifying a specific set of Tetris patterns.

Neuromorphic Implementation of Logic Functions Based on Parallel Dual-Gate Thin-Film Transistors

Composed of computation units each containing a parallel, dual-gate (DG) thin-film transistor (TFT) and a memory capacitor addressed by an access TFT, a neuromorphic circuit implementing fundamental AND and OR logic functions is realized and characterized. The exceptionally low leakage current of a TFT built on indium-gallium-zinc oxide (IGZO) allows the capacitor to be used as a quasi-static memory element. Appropriate weight signals for the realization of the two logic functions are obtained using a gradient-descent training algorithm. The circuit can be configured to execute one of the two functions by the setting of the weight signals.

Tensile-Force-Resilient Biomedical Front-End Circuits Employing Auto-Calibrated Omni-Directional Thin-Film Transistors

Flexible electronics based on thin film transistors (TFTs) are expected to deliver important benefits in the mobile healthcare field. Nevertheless, the mechanical strain caused by the respiration or movement of organisms seriously affects the characteristics of the TFTs, and thus deteriorates the performance of TFT-based circuits and systems. Taking indium-gallium-zinc-oxide (IGZO) TFT as an example, this paper proposes a tensile-force-resilient biomedical front-end system based on omni-directional thin film transistors (OD TFTs). The proposed OD TFT is a combination of dual gate TFTs with optimized layout, whose force-insensitive axis can be adjusted by the biasing of top gate. Based on this, an auto calibration technique in front-end system is introduced, which can automatically adjust the top gate biasing of OD TFTs according to the Poisson's ratio of substrate and the direction of external force, so as to align the force-insensitive axis along the direction of external force. Employing the OD TFTs in circuits and the auto calibration technique, the force resilience of the flexible electronic system is significantly improved in practical applications. The simulations of front-end system on acquiring electrocardiogram (ECG) and electromyogram (EMG) signals are performed. The results show that the proposed front-end system with auto calibration provides an increase of SNR from initial -19.91 dB and -25.89 dB without calibration to 17.53 dB and 1.32 dB in two cases, respectively.

A System-Level Approach towards a Hybrid Energy Harvesting Glove.

This paper presents a novel wearable hybrid harvester system as a glove that contains four distinct scavenging modules of flexible transducer film, photosensitive 3D dual-gate thin-film transistor, and a particular power management box. Each single module is formed by a piezoelectric-charge-gated TFT (PCGTFT). The reported system is capable of scavenging energy from two various free of charge energy sources (Piezoelectric plus Photoelectric). Aforesaid system unlike other state-of-the-arts overcomes several key challenges in interfacing, storage and power management. Harvested energy which is administered through power and storage management system ultimately lightens a typical light emitting diode (LED), testifies capability of such glove to power up some low-power electronic devices.

An Analytical Model for Dual Gate Piezoelectrically Sensitive ZnO Thin Film Transistors.

We report the experimental realization of piezoelectric ZnO dual-gate thin film transistors (TFTs) as highly sensitive force sensors and discuss the physical origins of its electrically tunable piezoelectric response using a simple analytical model. A dual gate TFT is fabricated on a polyimide substrate using radio-frequency (RF) magnetron sputtering of piezoelectric ZnO thin film as a channel. The ZnO TFTs exhibited a field effect mobility of ~ 5 cm2/Vs, I max to I min ratio of 107, and a subthreshold slope of 700 mV/dec. Notably, the TFT exhibited static and transient current changes under external force stimuli, with varying amplitude and polarity for different gate bias regimes. To understand the current modulation of the dual-gate TFT with independently biased top and bottom gates, an analytical model is developed. The model includes accumulation channels at both surfaces and a bulk channel within the film and accounts for the force-induced piezoelectric charge density. The microscopic piezoelectric response that modulates the energy-band edges and correspondent current-voltage characteristics are accurately portrayed by our model. Finally, the field-tunable force response in single TFT is demonstrated as a function of independent bias for the top and bottom gates with a force response range from -0.29 nA/mN to 22.7 nA/mN. This work utilizes intuitive analytical models to shed light on the correlation between the material properties with the force response in piezoelectric TFTs.

Programmable a-InGaZnO gate array with laser-induced forward transfer

Here, we present a pseudo-CMOS NOR gate array based on dual-gate amorphous indium-gallium-zinc oxide thin-film transistors (TFTs) on plastic. We fabricated a 14 12 array of NOR gates which was programmed using laser-induced forward transfer printing technology to realize a negative-edge-triggered D flip-flop. Two drive transistors in a conventional NOR gate configuration were replaced by a single independently gate-controlled dual-gate transistor, which enabled us to design and fabricate a gate array with much reduced number of transistors and interconnects. We anticipate that programmable gate arrays based on dual-gate oxide TFTs can be a new route to design and fabrication of digital circuitry that will be essential for emerging applications Internet-of-Things and wearable electronics.

MgZnO Dual Gate Thin Film Transistor for the Sensitive Determination of Modified Folic Acid

Folate receptor (FR) is a typical tumor-associated antigen that has been widely used as a biomarker for the determination of cancer. A biosensing platform functionalized with folic acid (FA) is essential to FR detection because FA specifically binds FR. We demonstrate an MgZnO dual-gate thin-film transistor (MZO DGTFT) based biosensor for the sensitive determination of FA derivative, hexadecyl alkynated folic acid (HAFA). The receptor is an MZO nanostructure (MZO $_{\mathrm {nano}}$ ) modified sensing pad which electrically connects to the top gate of DGTFT. The bottom gate of DGTFT is used to bias the device to its optimum operation point, enabling high sensitivity. First, 11-azidoundecanoic acid (AA) was bond onto the MZO $_{\mathrm {nano}}$ surface as the linker layer, resulting in negative charges to MZO $_{\mathrm {nano}}$ due to carboxylic acid binding chemistry. HAFA was then immobilized on MZO $_{\mathrm {nano}}$ via click reaction with AA. HAFA is a polar molecule with the positive end adjacent to AA/MZO $_{\mathrm {nano}}$ , and therefore, the electrostatic condition of MZO $_{\mathrm {nano}}$ is impacted again. Such changes were detected by DGTFT that displayed significant drain current variations. Fourier-transform infrared spectroscopy (FTIR) imaging confirms such successful chemical processes. This MZO DGTFT biosensor with HAFA is promising for potential applications in the detection of FR overexpressed cancer cells.

A Piezoelectric-Transducer-Biased 3-D Photosensitive Thin-Film Transistor as a Dual-Mode Wearable Energy Harvester

This letter reports on a dual-mode wearable energy harvester that utilizes both piezoelectric and photoelectric effects. It integrates a piezoelectric transducer with a 3-D photosensitive dual-gate thin-film transistor (DGTFT) as a rectifier and a buffer. The energy conversion efficiency is enhanced by reducing the internal resistance of the 3-D photosensitive DGTFT upon light illumination. Such a dual-mode energy harvester is promising for wearable electronics.

P‐5: Compact Modeling of Independent Dual Gate TFTs and OLED for Display Panel Circuit Simulations

This work presents a universal and comprehensive compact model for three‐ and four‐terminal thin‐film transistors (TFTs). The DC and AC behaviors of TFTs with independent bottom gate or light shield layer are modeled. A threshold‐voltage‐based capacitance model is built to meet the requirements of charge conservation and Gummel capacitance symmetry in order to illuminate spurious voltage shift and current discontinuity that are found in conventional TFT models such as RPI. Stress models are implemented in a stretched‐exponential form. In addition, a compact model for OLED is included in the build.

Toward ultraviolet solution processed ZrOx/IZO transistors with top-gate and dual-gate operation: Selection of solvents, precursors, stabilizers, and additive elements

Low-temperature processed oxide thin-film transistors (TFTs) have been developed by the process of solution-processed metal oxide films using deep ultraviolet (UV) irradiation, although they still suffer from relatively poor electrical performance and severe electrical and chemical instability. This UV coating solution essentially involves chemical damage from acidic or basic precursor ligands; therefore, the top-gate and dual-gate TFTs suffer structurally inherent chemical damage, which limits the freedom of process design. An engineering concept solution using the four functional components of solvent, precursor, stabilizer, and additive was suggested for UV solution coating of high-k zirconium oxide (ZrOx). Here the proposed solvent, stabilizer, precursor, and additive include polar-aprotic N,N-methylformamide, zirconium acetylacetonate, ethanolamine, and oleic acid for polar-aprotic solution, effective photolysis, complete precursor dissolution, and high densification, respectively. The ultrathin ZrOx (15 nm) revealed a low leakage current density of <10−11 mA/cm2 at 1 MV/cm, good breakdown voltage, and a constant capacitance of approximately 260 nF/cm2 at 1 MHz. Similar transfer characteristics of both the bottom and top gates, and a field-effect mobility of 24 cm2/V, without degradation of subthreshold swing and threshold voltage values in the dual-gate, were involved in the chemically durable process and the dense coating conditions of ZrOx, regardless of the IZO and ZrOx stacking sequence.

Performance dependence of self-aligned dual-gate poly-Si TFTs on localized defective regions

This study investigates effects of localized defect regions on electrical characteristics of self-aligned dual-gate poly-Si thin-film transistors (TFTs). The thickness of the poly-Si channel layer ranges from 20 nm to 140 nm. The threshold voltage, subthreshold swing, and mobility are found to be sensitive to the defect position. The localized defects in the left channel (source side) exhibit a significant impact while those in the right channel (drain side) show a lower influence on the TFT performance. In addition, the performance variation caused by the localized defects in the right channel is highly sensitive to the magnitude of the applied drain bias. A higher drain bias can observably reduce the performance degradation. Effects of multiple defect regions on the electrical behavior of the TFTs are also explored. We found that the upper width of the defect regions dominates the TFT performance deterioration. The hole transport, hole concentration distributions, and current flowlines are analyzed to study the physical mechanisms.

Surface potential-based analytical model for InGaZnO thin-film transistors with independent dual-gates**Project supported by the National Key Research and Development Program of China (Grant No. 2017YFA0204600) and the Fundamental Research Funds for the Central Universities of Central South University, China (Grant No. 2019zzts424).

An analytical drain current model on the basis of the surface potential is proposed for indium–gallium zinc oxide (InGaZnO) thin-film transistors (TFTs) with an independent dual-gate (IDG) structure. For a unified expression of carriers’ distribution for the sub-threshold region and the conduction region, the concept of equivalent flat-band voltage and the Lambert W function are introduced to solve the Poisson equation, and to derive the potential distribution of the active layer. In addition, the regional integration approach is used to develop a compact analytical current–voltage model. Although only two fitting parameters are required, a good agreement is obtained between the calculated results by the proposed model and the simulation results by TCAD. The proposed current–voltage model is then implemented by using Verilog-A for SPICE simulations of a dual-gate InGaZnO TFT integrated inverter circuit.

Magnesium Zinc Oxide Nanostructure-Modified Multifunctional Sensors for Full-Scale Dynamic Monitoring of Pseudomonas aeruginosa Biofilm Formation

We demonstrate magnesium zinc oxide nanostructure (MZOnano) modified multifunctional devices for the full-scale dynamic monitoring of Pseudomonas aeruginosa (P. aeruginosa) biofilm formation: the dual-gate thin film transistor (DGTFT) as an electrical sensor for early stage detection and the quartz crystal microbalance (QCM) as an acoustic sensor for long-term monitoring. The sensing surfaces of both devices were modified with MZOnano to enhance their sensitivity and biocompatibility. P. aeruginosa bacteria were cultured in vitro on both sensing surfaces. The early stage detection is realized by sensing the charge transfer from cell membrane to the MZOnano during bacterial adhesion using the DGTFT biosensor while the monitoring of the long-term evolution is achieved through the sensing of mass loading and viscoelastic transition during biofilm development using the MZOnano QCM. The drain current of DGTFT starts to change at the beginning of the test and levels off after ∼6.5 h of bacterial inoculation, whereas the signals of MZOnano QCM become detectable after ∼5 h and then lasts for 24 h. The full-scale process of biofilm development covering from bacterial adhesion to maturation is thus dynamically monitored using this MZOnano modified multifunctional sensing technology.

Oxide semiconductor thin-film transistors with nano-splitting and field-surrounding channels fabricated by subwavelength photolithography

Oxide semiconductors feature high tunability of carrier concentrations under the control of electric field. In thin film transistors (TFTs), applying dual gate has been reported to be efficient in enhancing the coupling between the gate field and the channel accumulation. In this work, we demonstrate nano-splitting and field-surrounding semiconducting channels (based on InGaZnO) in TFTs, which is fabricated by facile subwavelength photolithography. In such TFTs, semiconducting channels have 200 nm gaps parallel to the drain field, are wrapped by oxide insulators and thus the gate field. The devices show enhanced performance as compared with dual-gate and single gate TFTs, exhibiting higher drain current and steeper subthreshold swing. The maximum transconductance gm is 27.9% higher than dual gate TFT and 73.1% higher than single gate TFT. According to device simulation, the improvement of the wrapping insulators device correlates with the three-dimensional accumulation of carriers and increased gate electric field near the semiconductor-dielectric interface. These surrounded-channel effects become noticeable in the device with the gap distance less than 1 μm, with gate electric field squeezing in the submicron gaps. The proposed approach offers an alternative way to take advantage of the oxide semiconductors and their application in TFTs with related circuits.

Early stage detection of Staphylococcus epidermidis biofilm formation using MgZnO dual-gate TFT biosensor

Early stage detection of biofilm formation is an important aspect of microbial research because once formed, biofilms show serious tolerance to antibiotics in contrast to the free-floating bacteria, which significantly increases the difficulty for clinical treatment of bacterial infections. The early stage detection technology is desired to improve the efficiency of medical treatments. In this work, we present a biosensor consisting of a magnesium zinc oxide (MZO) dual gate thin-film transistor (DGTFT) as the actuator and an MZO nanostructure (MZOnano) array coated conducting pad as the extended sensing gate for the early stage detection of Staphylococcus epidermidis (S. epidermidis) biofilm formation. S. epidermidis bacteria were cultured in vitro on the nanostructure modified sensing pad. Charge transfer occurs between microbial cells and the MZOnano during the initial bacterial adhesion stage. Such electrical signals, which represent the onset of biofilm formation, were dynamically detected by the DGTFT where the top gate electrode was connected to the extended MZOnano sensing pad and the bottom gate was used for biasing the device into the optimum characteristic region for high sensitivity and stable operation. The testing results show that a current change of ~80% is achieved after ~200 min of bacterial culturing. A crystal violet staining-based assay shows that tiny bacterial microcolonies just start to form at 200 min, and that it would take approximately 24 h to form matured biofilms. This technology enables medical professionals to act promptly on bacterial infection before biofilms get fully established.

Junctionless Dual In-Plane-Gate Thin-Film Transistors with AND Logic Function on Paper Substrates.

Dual-gate thin-film transistors (DGTFTs) have attracted increasing attention in the past few years because of threshold voltage modulation and device logic functionality. Here, solution-processed chitosan-based proton conductors are used as the gate dielectric. The threshold voltage shift depends on the ratio of the capacitances of the two gate dielectrics. The second interesting application of DGTFTs is logic functionality. This device demonstrates AND logic function controlled by applying either 0 or −1 V to each of the gate electrodes. When both gates were simultaneously applied to be 0 V, the current flows (ON). Otherwise, the current is blocked (OFF). In order to provide a comprehensive overview of these paper devices, the planarization of paper surface and switching stability of such DGTFTs are all discussed.