Sub-0.5 V Highly Stable Aqueous Salt Gated Metal Oxide Electronics

Novel solution-gated transistor sensor-based SnO2 epitaxial thin films grown by pulsed laser deposition for nitrite detection

A solution-gate controlled thin-film transistor with SnO2 epitaxial thin films (SnO2-SGTFT) is successfully utilized for highly sensitive detection of nitrite. The SnO2 films are deposited as channel materials on a c-plane sapphire (c-Al2O3) substrate through pulsed laser deposition (PLD), with superior crystal quality and out-of-plane atomic ordering. PtAu NPs/rGO nanocomposites are electrodeposited on a gold electrode to function as a transistor gate to further enhance the nitrite catalytic performance of the device. The change in effective gate voltage due to the electrooxidation of nitrite on the gate electrode is the primary sensing mechanism of the device. Based on the inherent amplification effect of transistors, the superior electrical properties of SnO2, and the high electrocatalytic activity of PtAu NPs/rGO, the SnO2-SGTFT sensor has a low detection limit of 0.1 nM and a wide linear detection range of 0.1 nM ~ 50 mM at VGS = 1.0 V. Furthermore, the sensor has excellent characteristics such as rapid response time, selectivity, and stability. The practicability of the device has been confirmed by the quantitative detection of nitrite in natural lake water. SnO2 epitaxial films grown by PLD provide a simple and efficient way to fabricate nitrite SnO2-SGTFT sensors in environmental monitoring and food safety, among others. It also provides a reference for the construction of other high-performance thin-film transistor sensors.

Wide-range and selective detection of SARS-CoV-2 DNA via surface modification of electrolyte-gated IGZO thin-film transistors

The 2019 coronavirus pandemic resulted in a massive global healthcare crisis, highlighting the necessity to develop effective and reproducible platforms capable of rapidly and accurately detecting SARS-CoV-2. In this study, we developed an electrolyte-gated indium-gallium-zinc-oxide (IGZO) thin-film transistor with sequential surface modification to realize the low limit of detection (LoD <50 fM) and a wide detection range from 50 fM to 5 μM with good linearity (R2 = 0.9965), and recyclability. The surface chemical modification was achieved to anchor the single strand of SARS-CoV-2 DNA via selective hybridization. Moreover, the minute electrical signal change following the chemical modification was investigated by in-depth physicochemical analytical techniques. Finally, we demonstrate fully recyclable biosensors based on oxygen plasma treatment. Owing to its cost-effective fabrication, rapid detection at the single-molecule level, and low detection limit, the proposed biosensor can be used as a point-of-care platform to perform timely and effective SARS-CoV-2 detection.

Bimodal Gating Mechanism in Hybrid Thin-Film Transistors Based on Dynamically Reconfigurable Nanoscale Biopolymer Interfaces

In recent years, increased control over naturally derived structural protein formulations and their self-assembly has enabled the application of high-resolution manufacturing techniques to silk-based materials, leading to bioactive interfaces with unprecedented miniaturized formats and functionalities. Here, a hybrid biopolymer-semiconductor device, obtained by integrating nanoscale silk layers in a well-established class of inorganic field-effect transistors (silk-FETs), is presented. The devices offer two distinct modes of operation-either traditional field-effect or electrolyte-gated-enabled by the precisely controlled thickness, morphology, and biochemistry of the integrated silk layers. The different operational modes are selectively accessed by dynamically modulating the free-water content within the nanoscale protein layer from the vapor phase. The utility of these hybrid devices is illustrated in a highly sensitive and ultrafast breath sensor, highlighting the opportunities offered by the integration of nanoscale biomaterial interfaces in conjunction with traditional semiconductor devices, enabling functional outcomes at the intersection between the worlds of microelectronics and biology.

Highly Effective and Efficient Self-Assembled Multilayer-Based Electrode Passivation for Operationally Stable and Reproducible Electrolyte-Gated Transistor Biosensors

To ensure the operational stability of transistor-based biosensors in aqueous electrolytes during multiple measurements, effective electrode passivation is crucially important for reliable and reproducible device performances. This paper presents a highly effective and efficient electrode passivation method using a facile solution-processed self-assembled multilayer (SAML) with excellent insulation property to achieve operational stability and reproducibility of electrolyte-gated transistor (EGT) biosensors. The SAML is created by the consecutive self-assembly of three different molecular layers of 1,10-decanedithiol, vinyl-polyhedral oligomeric silsesquioxane, and 1-octadecanethiol. This passivation enables EGT to operate stably in phosphate-buffered saline (PBS) during repeated measurements over multiple cycles without short-circuiting. The SAML-passivated EGT biosensor is fabricated with a solution-processed In2O3 thin film as an amorphous oxide semiconductor working both as a semiconducting channel in the transistor and as a functionalizable biological interface for a bioreceptor. The SAML-passivated EGT including In2O3 thin film is demonstrated for the detection of Tau protein as a biomarker of Alzheimer's disease while employing a Tau-specific DNA aptamer as a bioreceptor and a PBS solution with a low ionic strength to diminish the charge-screening (Debye length) effect. The SAML-passivated EGT biosensor functionalized with the Tau-specific DNA aptamer exhibits ultrasensitive, quantitative, and reliable detection of Tau protein from 1 × 10-15 to 1 × 10-10 M, covering a much larger range than clinical needs, via changes in different transistor parameters. Therefore, the SAML-based passivation method can be effectively and efficiently utilized for operationally stable and reproducible transistor-based biosensors. Furthermore, this presented strategy can be extensively adapted for advanced biomedical devices and bioelectronics in aqueous or physiological environments.

Aqueous electrolyte-gated solution-processed metal oxide transistors for direct cellular interfaces

Biocompatible field-effect-transistor-based biosensors have drawn attention for the development of next-generation human-friendly electronics. High-performance electronic devices must achieve low-voltage operation, long-term operational stability, and biocompatibility. Herein, we propose an electrolyte-gated thin-film transistor made of large-area solution-processed indium-gallium-zinc oxide (IGZO) semiconductors capable of directly interacting with live cells at physiological conditions. The fabricated transistors exhibit good electrical performance operating under sub-0.5 V conditions with high on-/off-current ratios (>107) and transconductance (>1.0 mS) over an extended operational lifetime. Furthermore, we verified the biocompatibility of the IGZO surface to various types of mammalian cells in terms of cell viability, proliferation, morphology, and drug responsiveness. Finally, the prolonged stable operation of electrolyte-gated transistor devices directly integrated with live cells provides the proof-of-concept for solution-processed metal oxide material-based direct cellular interfaces.

Fully Transparent, Ultrathin Flexible Organic Electrochemical Transistors with Additive Integration for Bioelectronic Applications

Optical transparency is highly desirable in bioelectronic sensors because it enables multimodal optical assessment during electronic sensing. Ultrathin (<5 µm) organic electrochemical transistors (OECTs) can be potentially used as a highly efficient bioelectronic transducer because they demonstrate high transconductance during low-voltage operation and close conformability to biological tissues. However, the fabrication of fully transparent ultrathin OECTs remains a challenge owing to the harsh etching processes of nanomaterials. In this study, fully transparent, ultrathin, and flexible OECTs are developed using additive integration processes of selective-wetting deposition and thermally bonded lamination. These processes are compatible with Ag nanowire electrodes and conducting polymer channels and realize unprecedented flexible OECTs with high visible transmittance (>90%) and high transconductance (≈1 mS) in low-voltage operations (<0.6 V). Further, electroencephalogram acquisition and nitrate ion sensing are demonstrated in addition to the compatibility of simultaneous assessments of optical blood flowmetry when the transparent OECTs are worn, owing to the transparency. These feasibility demonstrations show promise in contributing to human stress monitoring in bioelectronics.

Self-assembled peptides-modified flexible field-effect transistors for tyrosinase detection

Flexible biosensors have received intensive attention for real-time, non-invasive monitoring of cancer biomarkers. Highly sensitive tyrosinase biosensors, which are important for melanoma screening, remained a hurdle. Herein, high-performance tyrosinase-sensing field-effect transistor-based biosensors (bio-FETs) have been successfully achieved by self-assembling nanostructured tetrapeptide tryptophan-valine-phenylalanine-tyrosine (WVFY) on n-type metal oxide transistors. In the presence of target tyrosinase, the phenolic hydroxyl groups in WVFY are rapidly converted to benzoquinone with the consumption of protons, which could be detected potentiometrically by bio-FETs. As a result, the WVFY-modified bio-FETs exhibited an ultra-low detection limit of 1.9 fM and an optimal detection range of 10 fM to 1 nM toward tyrosinase sensing. Furthermore, flexible devices fabricated on ∼2.9-μm-thick polyimide (PI) substrates illustrated robust mechanical flexibility, which could be attached to human skin conformally. These achievements hold promise for wearable melanoma screening and provide designing guidelines for detecting other important cancer biomarkers with bio-FETs.

Flexible complementary circuits operating at sub-0.5 V via hybrid organic-inorganic electrolyte-gated transistors

Electrolyte-gated transistors (EGTs) hold great promise for next-generation printed logic circuitry, biocompatible integrated sensors, and neuromorphic devices. However, EGT-based complementary circuits with high voltage gain and ultralow driving voltage (<0.5 V) are currently unrealized, because achieving balanced electrical output for both the p- and n-type EGT components has not been possible with current materials. Here we report high-performance EGT complementary circuits containing p-type organic electrochemical transistors (OECTs) fabricated with an ion-permeable organic semiconducting polymer (DPP-g2T) and an n-type electrical double-layer transistor (EDLT) fabricated with an ion-impermeable inorganic indium-gallium-zinc oxide (IGZO) semiconductor. Adjusting the IGZO composition enables tunable EDLT output which, for In:Ga:Zn = 10:1:1 at%, balances that of the DPP-g2T OECT. The resulting hybrid electrolyte-gated inverter (HCIN) achieves ultrahigh voltage gains (>110) under a supply voltage of only 0.7 V. Furthermore, NAND and NOR logic circuits on both rigid and flexible substrates are realized, enabling not only excellent logic response with driving voltages as low as 0.2 V but also impressive mechanical flexibility down to 1-mm bending radii. Finally, the HCIN was applied in electrooculographic (EOG) signal monitoring for recording eye movement, which is critical for the development of wearable medical sensors and also interfaces for human-computer interaction; the high voltage amplification of the present HCIN enables EOG signal amplification and monitoring in which a small ∼1.5 mV signal is amplified to ∼30 mV.

Ionic Conductive Cellulose Mats by Solution Blow Spinning as Substrate and a Dielectric Interstrate Layer for Flexible Electronics

Renewable cellulose substrates with submicron- and nanoscale structures have revived interest in paper electronics. However, the processes behind their production are still complex and time- and energy-consuming. Besides, the weak electrolytic properties of cellulose with submicron- and nanoscale structures have hindered its application in transistors and integrated circuits with low-voltage operation. Here, we report a simple, low-cost approach to produce flexible ionic conductive cellulose mats using solution blow spinning, which are used both as dielectric interstrate and substrate in low-voltage devices. The electrochemical properties of the cellulose mats are tuned through infiltration with alkali hydroxides (LiOH, NaOH, or KOH), enabling their application as dielectric and substrate in flexible, low-voltage, oxide-based field-effect transistors and pencil-drawn resistor-loaded inverters. The transistors exhibit good transistor performances under operation voltage below 2.5 V, and their electrical performance is strictly related to the type of alkali ionic specie incorporated. Devices fabricated on K⁺-infiltrated cellulose mats present the best characteristics, indicating pure capacitive charging of the semiconductor. The pencil-drawn load resistor inverter presents good dynamic performance. These findings may pave the way for a new generation of low-power, wearable electronics, enabling concepts such as the "Internet of Things".

Designing Polymeric Mixed Conductors and Their Application to Electrochemical-Transistor-Based Biosensors

Organic electrochemical transistors that employ polymeric mixed conductors as their active channels are one of the most prominent biosensor platforms because of their signal amplification capability, low fabrication cost, mechanical flexibility, and various properties tunable through molecular design. For application to biomedical devices, polymeric mixed conductors should fulfill several requirements, such as excellent conductivities of both holes/electrons and ions, long-term operation stability, and decent biocompatibility. However, trade-offs may exist, for instance, one between ionic conduction and overall device stability. In this report, the fundamental understanding of polymeric mixed conductors, the recent advance in enhancing their ionic and electrical conductivity, and their practical applications as biosensors based on organic electrochemical transistors are reviewed. Finally, key strategies are suggested for developing novel polymeric mixed conductors that may exceed the trade-off between device performance and stability.

Experimental and theoretical evidence for hydrogen doping in polymer solution-processed indium gallium oxide

The field-effect electron mobility of aqueous solution-processed indium gallium oxide (IGO) thin-film transistors (TFTs) is significantly enhanced by polyvinyl alcohol (PVA) addition to the precursor solution, a >70-fold increase to 7.9 cm²/Vs. To understand the origin of this remarkable phenomenon, microstructure, electronic structure, and charge transport of IGO:PVA film are investigated by a battery of experimental and theoretical techniques, including In K-edge and Ga K-edge extended X-ray absorption fine structure (EXAFS); resonant soft X-ray scattering (R-SoXS); ultraviolet photoelectron spectroscopy (UPS); Fourier transform-infrared (FT-IR) spectroscopy; time-of-flight secondary-ion mass spectrometry (ToF-SIMS); composition-/processing-dependent TFT properties; high-resolution solid-state ¹H, ⁷¹Ga, and ¹¹⁵In NMR spectroscopy; and discrete Fourier transform (DFT) analysis with ab initio molecular dynamics (MD) liquid-quench simulations. The ⁷¹Ga{¹H} rotational-echo double-resonance (REDOR) NMR and other data indicate that PVA achieves optimal H doping with a Ga···H distance of ∼3.4 Å and conversion from six- to four-coordinate Ga, which together suppress deep trap defect localization. This reduces metal-oxide polyhedral distortion, thereby increasing the electron mobility. Hydroxyl polymer doping thus offers a pathway for efficient H doping in green solvent-processed metal oxide films and the promise of high-performance, ultra-stable metal oxide semiconductor electronics with simple binary compositions.

High performance indium oxide nanoribbon FETs: mitigating devices signal variation from batch fabrication

Nanostructured field effect transistor (FET) based sensors have emerged as a powerful bioanalytical technology. However, performance variations across multiple devices and between fabrication batches inevitably exist and present a significant challenge holding back the translation of this cutting-edge technology. We report an optimized and cost-effective fabrication process for high-performance indium oxide nanoribbon FET with a steep subthreshold swing of 80 mV per decade. Through systematic electrical characterizations of 57 indium oxide nanoribbon FETs from different batches, we demonstrate an optimal operation point within the subthreshold regime that mitigates the issue of device-to-device performance variation. A non-linear pH sensing of the fabricated indium oxide nanoribbon FETs is also presented.

Ion buffering and interface charge enable high performance electronics with organic electrochemical transistors

Organic electrochemical transistors rely on ionic-electronic volumetric interaction to provide a seamless interface between biology and electronics with outstanding signal amplification. Despite their huge potential, further progress is limited owing to the lack of understanding of the device fundamentals. Here, we investigate organic electrochemical transistors in a wide range of experimental conditions by combining electrical analyses and device modeling. We show that the measurements can be quantitatively explained by nanoscale ionic-electronic charge interaction, giving rise to ion buffering and interface charge compensation. The investigation systematically explains and unifies a wide range of experiments, providing the rationale for the development of high-performance electronics. Unipolar inverters — universal building blocks for electronics — with gain larger than 100 are demonstrated. This is the highest gain ever reported, enabling the design of devices and circuits with enhanced performance and opening opportunities for the next-generation integrated bioelectronics and neuromorphic computing.

The rationale design of optimized organic electrochemical transistors (OECTs) for next-generation bioelectronics requires further exploration of the underlying device physics. Here, the authors report the role of ionic-electronic charge interactions on OECTs and high-performance unipolar inverters.

Silicon Nanoribbon pH Sensors Protected by a Barrier Membrane with Carbon Nanotube Porins

Limited biocompatibility and fouling propensity can restrict real-world applications of a large variety of biosensors. Biological systems are adept at protecting and separating vital components of biological machinery with semipermeable membranes that often contain defined pores and gates to restrict transmembrane transport only to specific species. Here we use a similar approach for creating fouling-resistant pH sensors. We integrate silicon nanoribbon transistor sensors with an antifouling lipid bilayer coating that contains proton-permeable carbon nanotube porin (CNTP) channels and demonstrate robust pH detection in a variety of complex biological fluids.

Fully Printed Zinc Oxide Electrolyte-Gated Transistors on Paper

Fully printed and flexible inorganic electrolyte gated transistors (EGTs) on paper with a channel layer based on an interconnected zinc oxide (ZnO) nanoparticle matrix are reported in this work. The required rheological properties and good layer formation after printing are obtained using an eco-friendly binder such as ethyl cellulose (EC) to disperse the ZnO nanoparticles. Fully printed devices on glass substrates using a composite solid polymer electrolyte as gate dielectric exhibit saturation mobility above 5 cm² V⁻¹ s⁻¹ after annealing at 350 °C. Proper optimization of the nanoparticle content in the ink allows for the formation of a ZnO channel layer at a maximum annealing temperature of 150 °C, compatible with paper substrates. These devices show low operation voltages, with a subthreshold slope of 0.21 V dec⁻¹, a turn on voltage of 1.90 V, a saturation mobility of 0.07 cm² V⁻¹ s⁻¹ and an I_on/I_off ratio of more than three orders of magnitude.

Understanding Electric Double-Layer Gating Based on Ionic Liquids: from Nanoscale to Macroscale

In electric double-layer transistors (EDLTs), it is well known that the EDL formed by ionic liquids (ILs) can induce an ultrahigh carrier density at the semiconductor surface, compared to solid dielectric. However, the mechanism of device performance is still not fully understood, especially at a molecular level. Here, we evaluate the gating performance of amorphous indium gallium zinc oxide (a-IGZO) transistor coupled with a series of imidazolium-based ILs, using an approach combining of molecular dynamics simulation and finite element modeling. Results reveal that the EDL with different ion structures could produce inhomogeneous electric fields at the solid-electrolyte interface, and the heterogeneity of electric field-induced charge distributions at semiconductor surface could reduce the electrical conductance of a-IGZO during gating process. Meanwhile, a resistance network analysis was adopted to bridge the nanoscopic data with the macroscopic transfer characteristics of IL-gated transistor, and showed that our theoretical results could well estimate the gating performance of practical devices. Thereby, our findings could provide both new concepts and modeling techniques for IL-gated transistors.

High-Performance All-Printed Amorphous Oxide FETs and Logics with Electronically Compatible Electrode/Channel Interface

Oxide semiconductors typically show superior device performance compared to amorphous silicon or organic counterparts, especially when they are physical vapor deposited. However, it is not easy to reproduce identical device characteristics when the oxide field-effect transistors (FETs) are solution-processed/printed; the level of complexity further intensifies with the need to print the passive elements as well. Here, we developed a protocol for designing the most electronically compatible electrode/channel interface based on the judicious material selection. Exploiting this newly developed fabrication schemes, we are now able to demonstrate high-performance all-printed FETs and logic circuits using amorphous indium-gallium-zinc oxide (a-IGZO) semiconductor, indium tin oxide (ITO) as electrodes, and composite solid polymer electrolyte as the gate insulator. Interestingly, all-printed FETs demonstrate an optimal electrical performance in terms of threshold voltages and device mobility and may very well be compared with devices fabricated using sputtered ITO electrodes. This observation originates from the selection of electrode/channel materials from the same transparent semiconductor oxide family, resulting in the formation of In-Sn-Zn-O (ITZO)-based-diffused a-IGZO-ITO interface that controls doping density while ensuring high electrical performance. Compressive spectroscopic studies reveal that Sn doping-mediated excellent band alignment of IGZO with ITO electrodes is responsible for the excellent device performance observed. All-printed n-MOS-based logic circuits have also been demonstrated toward new-generation portable electronics.

High- k Gate Dielectrics for Emerging Flexible and Stretchable Electronics

Recent advances in flexible and stretchable electronics (FSE), a technology diverging from the conventional rigid silicon technology, have stimulated fundamental scientific and technological research efforts. FSE aims at enabling disruptive applications such as flexible displays, wearable sensors, printed RFID tags on packaging, electronics on skin/organs, and Internet-of-things as well as possibly reducing the cost of electronic device fabrication. Thus, the key materials components of electronics, the semiconductor, the dielectric, and the conductor as well as the passive (substrate, planarization, passivation, and encapsulation layers) must exhibit electrical performance and mechanical properties compatible with FSE components and products. In this review, we summarize and analyze recent advances in materials concepts as well as in thin-film fabrication techniques for high- k (or high-capacitance) gate dielectrics when integrated with FSE-compatible semiconductors such as organics, metal oxides, quantum dot arrays, carbon nanotubes, graphene, and other 2D semiconductors. Since thin-film transistors (TFTs) are the key enablers of FSE devices, we discuss TFT structures and operation mechanisms after a discussion on the needs and general requirements of gate dielectrics. Also, the advantages of high- k dielectrics over low- k ones in TFT applications were elaborated. Next, after presenting the design and properties of high- k polymers and inorganic, electrolyte, and hybrid dielectric families, we focus on the most important fabrication methodologies for their deposition as TFT gate dielectric thin films. Furthermore, we provide a detailed summary of recent progress in performance of FSE TFTs based on these high- k dielectrics, focusing primarily on emerging semiconductor types. Finally, we conclude with an outlook and challenges section.

Nanostructured Graphene: An Active Component in Optoelectronic Devices

Nanostructured and chemically modified graphene-based nanomaterials possess intriguing properties for their incorporation as an active component in a wide spectrum of optoelectronic architectures. From a technological point of view, this aspect brings many new opportunities to the now well-known atomically thin carbon sheet, multiplying its application areas beyond transparent electrodes. This article gives an overview of fundamental concepts, theoretical backgrounds, design principles, technological implications, and recent advances in semiconductor devices that integrate nanostructured graphene materials into their active region. Starting from the unique electronic nature of graphene, a physical understanding of finite-size effects, non-idealities, and functionalizing mechanisms is established. This is followed by the conceptualization of hybridized films, addressing how the insertion of graphene can modulate or improve material properties. Importantly, it provides general guidelines for designing new materials and devices with specific characteristics. Next, a number of notable devices found in the literature are highlighted. It provides practical information on material preparation, device fabrication, and optimization for high-performance optoelectronics with a graphene hybrid channel. Finally, concluding remarks are made with the summary of the current status, scientific issues, and meaningful approaches to realizing next-generation technologies.

Highly Sensitive and Wearable In2O3 Nanoribbon Transistor Biosensors with Integrated On-Chip Gate for Glucose Monitoring in Body Fluids

Nanoribbon- and nanowire-based field-effect transistor (FET) biosensors have stimulated a lot of interest. However, most FET biosensors were achieved by using bulky Ag/AgCl electrodes or metal wire gates, which have prevented the biosensors from becoming truly wearable. Here, we demonstrate highly sensitive and conformal In₂O₃ nanoribbon FET biosensors with a fully integrated on-chip gold side gate, which have been laminated onto various surfaces, such as artificial arms and watches, and have enabled glucose detection in various body fluids, such as sweat and saliva. The shadow-mask-fabricated devices show good electrical performance with gate voltage applied using a gold side gate electrode and through an aqueous electrolyte. The resulting transistors show mobilities of ∼22 cm² V^-1 s^-1 in 0.1× phosphate-buffered saline, a high on-off ratio (10⁵), and good mechanical robustness. With the electrodes functionalized with glucose oxidase, chitosan, and single-walled carbon nanotubes, the glucose sensors show a very wide detection range spanning at least 5 orders of magnitude and a detection limit down to 10 nM. Therefore, our high-performance In₂O₃ nanoribbon sensing platform has great potential to work as indispensable components for wearable healthcare electronics.

Role of Electrical Double Layer Structure in Ionic Liquid Gated Devices

Ionic liquid gating of transition metal oxides has enabled new states (magnetic, electronic, metal-insulator), providing fundamental insights into the physics of strongly correlated oxides. However, despite much research activity, little is known about the correlation of the structure of the liquids in contact with the transition metal oxide surface, its evolution with the applied electric potential, and its correlation with the measured electronic properties of the oxide. Here, we investigate the structure of an ionic liquid at a semiconducting oxide interface during the operation of a thin film transistor where the electrical double layer gates the device using experiment and theory. We show that the transition between the ON and OFF states of the amorphous indium gallium zinc oxide transistor is accompanied by a densification and preferential spatial orientation of counterions at the oxide channel surface. This process occurs in three distinct steps, corresponding to ion orientations, and consequently, regimes of different electrical conductivity. The reason for this can be found in the surface charge densities on the oxide surface when different ion arrangements are present. Overall, the field-effect gating process is elucidated in terms of the interfacial ionic liquid structure, and this provides unprecedented insight into the working of a liquid gated transistor linking the nanoscopic structure to the functional properties. This knowledge will enable both new ionic liquid design as well as advanced device concepts.

Recent Progress in the Development of Printed Thin-Film Transistors and Circuits with High-Resolution Printing Technology

Printed electronics enable the fabrication of large-scale, low-cost electronic devices and systems, and thus offer significant possibilities in terms of developing new electronics/optics applications in various fields. Almost all electronic applications require information processing using logic circuits. Hence, realizing the high-speed operation of logic circuits is also important for printed devices. This report summarizes recent progress in the development of printed thin-film transistors (TFTs) and integrated circuits in terms of materials, printing technologies, and applications. The first part of this report gives an overview of the development of functional inks such as semiconductors, electrodes, and dielectrics. The second part discusses high-resolution printing technologies and strategies to enable high-resolution patterning. The main focus of this report is on obtaining printed electrodes with high-resolution patterning and the electrical performance of printed TFTs using such printed electrodes. In the final part, some applications of printed electronics are introduced to exemplify their potential.

Quasi-Two-Dimensional Metal Oxide Semiconductors Based Ultrasensitive Potentiometric Biosensors

Ultrasensitive field-effect transistor-based biosensors using quasi-two-dimensional metal oxide semiconductors were demonstrated. Quasi-two-dimensional low-dimensional metal oxide semiconductors were highly sensitive to electrical perturbations at the semiconductor-bio interface and showed competitive sensitivity compared with other nanomaterial-based biosensors. Also, the solution process made our platform simple and highly reproducible, which was favorable compared with other nanobioelectronics. A quasi-two-dimensional In₂O₃-based pH sensor showed a small detection limit of 0.0005 pH and detected the glucose concentration at femtomolar levels. Detailed electrical characterization unveiled how the device's parameters affect the biosensor sensitivity, and lowest detectable charge was extrapolated, which was consistent with the experimental data.

Enhanced pH sensitivity over the Nernst limit of electrolyte gated a-IGZO thin film transistor using branched polyethylenimine

a-IGZO based EGTFT with 4.6-fold enhanced pH sensitivity of ∼110 mV pH⁻¹ using thin film coating of branched polyethylenimine (BPEI).