On Organic Field-effect Transistors Research Articles

Highly Sensitive, Low-Energy-Consumption Biomimetic Olfactory Synaptic Transistors Based on the Aggregation of the Semiconductor Films.

Artificial olfactory synaptic devices with low energy consumption and low detection limits are important for the further development of neuromorphic computing and intelligent robotics. In this work, an ultralow energy consumption and low detection limit imitation olfactory synaptic device based on organic field-effect transistors (OFETs) was prepared. The aggregation state of poly(diketopyrrolopyrrole-selenophene) (PTDPP) semiconductor films is modulated by adding unfavorable solvents and annealing treatments to obtain excellent charge transfer and gas synaptic properties. The regulated OFET device can execute basic biological synaptic functions, including excitatory postsynaptic currents (EPSCs), paired-pulse facilitation (PPF), and the transition from short-term to long-term plasticity, at an ultralow operating voltage of -0.0005 V. The ultralow energy consumption during the biomimetic simulation is in the range of 8.94-88 fJ per spike. Noteworthily, the gas detection limit of the device is as low as 50 ppb, well below normal human NO2 gas perception limits (100-1000 ppb). Additionally, high-pass filtering, Pavlovian conditioned reflexes, and decoding of "Morse code" were simulated. Finally, a grid-free conformal device with outstanding flexibility and stability was fabricated. In conclusion, the control of semiconductor thin-film aggregation provides effective guidance for preparing low-energy-consumption, highly sensitive olfactory nerve-mimicking devices and promoting the development of wearable electronics.

Hydrogel-Gated FETs in Neuromorphic Computing to Mimic Biological Signal: A Review.

Hydrogel-gated synaptic transistors offer unique advantages, including biocompatibility, tunable electrical properties, being biodegradable, and having an ability to mimic biological synaptic plasticity. For processing massive data with ultralow power consumption due to high parallelism and human brain-like processing abilities, synaptic transistors have been widely considered for replacing von Neumann architecture-based traditional computers due to the parting of memory and control units. The crucial components mimic the complex biological signal, synaptic, and sensing systems. Hydrogel, as a gate dielectric, is the key factor for ionotropic devices owing to the excellent stability, ultra-high linearity, and extremely low operating voltage of the biodegradable and biocompatible polymers. Moreover, hydrogel exhibits ionotronic functions through a hybrid circuit of mobile ions and mobile electrons that can easily interface between machines and humans. To determine the high-efficiency neuromorphic chips, the development of synaptic devices based on organic field effect transistors (OFETs) with ultra-low power dissipation and very large-scale integration, including bio-friendly devices, is needed. This review highlights the latest advancements in neuromorphic computing by exploring synaptic transistor developments. Here, we focus on hydrogel-based ionic-gated three-terminal (3T) synaptic devices, their essential components, and their working principle, and summarize the essential neurodegenerative applications published recently. In addition, because hydrogel-gated FETs are the crucial members of neuromorphic devices in terms of cutting-edge synaptic progress and performances, the review will also summarize the biodegradable and biocompatible polymers with which such devices can be implemented. It is expected that neuromorphic devices might provide potential solutions for the future generation of interactive sensation, memory, and computation to facilitate the development of multimodal, large-scale, ultralow-power intelligent systems.

Molecular Electronics: From Nanostructure Assembly to Device Integration.

Integrated electronics and optoelectronics based on organic semiconductors have attracted considerable interest in displays, photovoltaics, and biosensing owing to their designable electronic properties, solution processability, and flexibility. Miniaturization and integration of devices are growing trends in molecular electronics and optoelectronics for practical applications, which requires large-scale and versatile assembly strategies for patterning organic micro/nano-structures with simultaneously long-range order, pure orientation, and high resolution. Although various integration methods have been developed in past decades, molecular electronics still needs a versatile platform to avoid defects and disorders due to weak intermolecular interactions in organic materials. In this perspective, a roadmap of organic integration technologies in recent three decades is provided to review the history of molecular electronics. First, we highlight the importance of long-range-ordered molecular packing for achieving exotic electronic and photophysical properties. Second, we classify the strategies for large-scale integration of molecular electronics through the control of nucleation and crystallographic orientation, and evaluate them based on factors of resolution, crystallinity, orientation, scalability, and versatility. Third, we discuss the multifunctional devices and integrated circuits based on organic field-effect transistors (OFETs) and photodetectors. Finally, we explore future research directions and outlines the need for further development of molecular electronics, including assembly of doped organic semiconductors and heterostructures, biological interfaces in molecular electronics and integrated organic logics based on complementary FETs.

Retina-inspired organic neuromorphic vision sensor with polarity modulation for decoding light information

The neuromorphic vision sensor (NeuVS), which is based on organic field-effect transistors (OFETs), uses polar functional groups (PFGs) in polymer dielectrics as interfacial units to control charge carriers. However, the mechanism of modulating charge transport on basis of PFGs in devices is unclear. Here, the carboxyl group is introduced into polymer dielectrics in this study, and it can induce the charge transfer process at the semiconductor/dielectric interfaces for effective carrier transport, giving rise to the best device mobility up to 20 cm2 V−1 s−1 at a low operating voltage of −1 V. Furthermore, the polarity modulation effect could further increase the optical figures of merit in NeuVS devices by at least an order of magnitude more than the devices using carboxyl group-free polymer dielectrics. Additionally, devices containing carboxyl groups improved image sensing for light information decoding with 52 grayscale signals and memory capabilities at an incredibly low power consumption of 1.25 fJ/spike. Our findings provide insight into the production of high-performance polymer dielectrics for NeuVS devices.

Food Freshness Measurements and Product Distinguishing by a Portable Electronic Nose Based on Organic Field-Effect Transistors.

Determination of food freshness, which is the most ancient role of the human sense of smell, is still a challenge for compact and inexpensive electronic nose devices. Fast, sensitive, and reusable sensors are long-awaited in the food industry to replace slow, labor-intensive, and expensive bacteriological methods. In this work, we present microbiological verification of a novel approach to food quality monitoring and spoilage detection using an electronic nose based on organic field-effect transistors (OFETs) and its application for distinguishing products. The compact device presented is able to detect spoilage-related gases as early as at the 4 × 104 CFU g-1 bacteria count level, which is 2 orders of magnitude below the safe consumption threshold. Cross-selective sensor array based on OFETs with metalloporphyrin receptors were made on a single substrate using solution processing leading to a low production cost. Moreover, machine learning methods applied to the sensor array response allowed us to compare spoilage profiles and separate them by the type of food: pork, chicken, fish, or milk. The approach presented can be used to monitor food spoilage and distinguish different products with an affordable and portable device.

Organic small molecule semiconductor materials for OFET-based biosensors

Biosensors is an advanced detection and monitoring device for the development of biotechnology, and is also a rapid and microanalytical device at the molecular level. Demands for high sensitivity, high flexibility, good biocompatibility, easy chemical modification and low cost offer incentive for exploring new materials to develop the next-generation biosensors. With the vigorous development of organic electronics, the performances of organic devices have been effectively improved, leading to organic semiconductor materials with low cost, good flexibility, easy chemical modification and good biocompatibility for biosensors. Biosensors based on organic field-effect transistors (OFETs) have become one of the most advanced biosensor platforms because of their inherent ability to amplify received signals. Furthermore, OFET-based biosensors have been widely used in the detection of DNA, protein, cell, glucose and other biological substances due to its high sensitivity, fast analysis speed, label-free detection, small size and simple operation. This mini review briefly discusses the organic small molecule semiconductor materials, device configurations, basic principles and application fields of OFETs-based biosensors.

Facile Strategy for Modulating the Nanoporous Structure of Ultrathin π-Conjugated Polymer Films for High-Performance Gas Sensors.

Conventional conjugated polymer (CP) films based on organic field-effect transistors (OFETs) tend to limit the performance of gas sensors owing to restricted analyte diffusion and limited interactions with the charge carriers that accumulate in the first few monolayers of the CP film in contact with the dielectric layer. Herein, a facile strategy is presented for modulating the morphology and charge-transport properties of nanoporous CP films using shearing-assisted phase separation of polymer blends for fabricating OFET-based chemical sensors. This approach enables the formation of nanoporous films with pore size and thickness in the ranges of 90-550 and 7-27 nm, respectively, which can be controlled simply by varying the shear rate. The resulting OFET sensors exhibit excellent sensing performance when exposed to NH3 gas, demonstrating a high responsivity (≈70.7%) at 10 ppm and good selectivity toward NH3 over various organic solvent vapors. After a comprehensive analysis of the morphology and electrical properties of the CP films, it is concluded that morphological features, such as film thickness and surface area, affect the sensing performance of nanoporous-film-based OFET sensors more significantly compared to the charge-transport characteristics of the films.

Temperature Sensors Based on Organic Field-Effect Transistors

The rapid growth of wearable electronics, Internet of Things, smart packaging, and advanced healthcare technologies demand a large number of flexible, thin, lightweight, and ultralow-cost sensors. The accurate and precise determination of temperature in a narrow range (~0–50 °C) around ambient temperatures and near-body temperatures is critical for most of these applications. Temperature sensors based on organic field-effect transistors (OFETs) have the advantages of low manufacturing cost, excellent mechanical flexibility, easy integration with other devices, low cross-sensitivity, and multi-stimuli detectability and, therefore, are very suitable for the above applications. This article provides a timely overview of research progress in the development of OFET-based temperature sensors. First, the working mechanism of OFETs, the fundamental theories of charge transport in organic semiconductors, and common types of OFET temperature sensors based on the sensing element are briefly introduced. Next, notable advances in the development of OFET temperature sensors using small-molecule and polymer semiconductors are discussed separately. Finally, the progress of OFET temperature sensors is summarized, and the challenges associated with OFET temperature sensors and the perspectives of research directions in this field are presented.

Modulation Doping for Threshold Voltage Control in Organic Field-Effect Transistors.

Organic electronics is the technology enabling truly flexible electronic devices. However, despite continuous improvements in the charge-carrier mobility, devices used for digital circuits based on organic field-effect transistors (OFETs) have still not achieved a commercial breakthrough. A substantial hurdle to the realization of effective digital circuitry is the proper control of the threshold voltage Vth. Previous approaches include doping or self-assembled monolayers to provide the threshold voltage control. However, while self-assembled monolayers-modified OFETs often do not show the level of reproducibility which is required in digital circuit engineering, direct doping of the channel material results in a poor on/off ratio leading to unfavorable power dissipation. Furthermore, direct doping of the channel material in organic semiconductors could cause the formation of trap states impeding the charge-carrier transport. Employing the concept of modulation-doped field-effect transistors (MODFETs), which is well established in inorganic electronics, the semiconductor-dopant interaction is significantly reduced, thereby solving the above-described problems. Here, we present the concept of an organic semiconductor MODFET which is composed of an organic-organic heterostructure between a highly doped wide-energy-gap material and an undoped narrow-energy-gap material. The effectiveness of charge transfer across the interface is controlled by the doping concentration and thickness of an undoped buffer layer. A complete picture of the energy landscape of this heterostructure is drawn using impedance spectroscopy and ultraviolet photoelectron spectroscopy. Furthermore, we analyze the effect of the dopant density on the charge-carrier transport properties. The incorporation of these heterostructures into OFETs enables a precise adjustment of the threshold voltage by using the modulation doping concept.

Dual-functional optoelectronic memories based on ternary hybrid floating gate layers.

Optoelectronic memories based on organic field-effect transistors (OFETs) have been extensively investigated, and great progress has been made in improving memory performance and reducing operating power consumption. Despite these achievements, optoelectronic memories reported so far have only a single storage function, such as light-assisted memory, light writing memory, or light-erasing memory, which may not meet the requirements of multi-functional storage in the future. Here, the dual-functional optoelectronic memories are demonstrated by employing ternary hybrid films as floating gate layers. Integrating the advantages of hole trapping in [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and photoinduced electron trapping in CsPbBr3 quantum dots (QDs), the dual-functional storages including electric programming holes and light programming electrons can be realized in one device. Owing to the complementary charge trapping advantages in CsPbBr3 QDs and PCBM, the devices also show a short light erasing time of 0.05 s and low erasing gate bias within -35 V. In addition, the devices exhibit decent endurance for 500 continuous light programming-reading-electric programming-reading cycling tests and admirable electron and hole retention time of 10 000 s with negligible charge leakage. This study may offer a feasible path for the development of new-generation memory.

Sensitive Detection of Glyphosate by a Water-Gated Organic Transistor

Introduction Glyphosate (GlyP), a widely used herbicide in the agricultural field, was classified as a probable carcinogenic compound (Group 2A) by the International Agency for Research of Cancer (IARS) in 2015. Since then, the importance of the GlyP detection in aqueous media has increased in the field of environmental chemistry and clinical research. The concentration of GlyP in ground and tap water is strictly regulated. For example, the permissible limit for the GlyP concentration in drinking water set at 0.7 ppm in the United States. To-this-date, liquid chromatography (LC) is a common method to sensitively detect GlyP. However, the apparatuses of LC are expensive and require trained personnel, requesting the development of affordable, simple and sensitive sensors for the on-site GlyP detection. Thus, our research has focused on organic field-effect transistors (OFETs) as chemical sensing platforms, because of their low-cost and solution-processability, compact size, and mechanical flexibility[1]. Here, we report an OFET-based chemical sensor for the detection of GlyP in water. Design of the OFET sensor Polythiophene derivatives (PTs) have been widely studied and applied as organic semiconductors in OFET devices. Moreover, PTs has been employed for materials in chemical sensors because their optical and electrical properties can be tuned by introducing artificial receptors into their 3- and/or 4-positions as side chains. However, such OFET-based sensors based on PT attached with artificial receptors are still rare due to the typical high applied voltage (>|20V|) of the OFET which causes materials degradation. Thus we designed a water-gated OFET (WG-OFET) for chemical sensing applications, which could be operated at an ultra-low voltage (<|0.3| V) derived from an electrical double-layer capacitor. For the detection of GlyP, we employed a carboxy side-chain attached to PT (poly{3-(5-carboxypentyl)thiophene-2,5-diyl}, P3CPT) [2] as the semiconductor layer. Due to the molecular wire effect of the π conjugated polymer [3], the sensitive detection of GlyP is expected based on the competitive binding among the carboxylate terminals of P3CPT, copper(II) ions and GlyP in an aqueous solution. Fabrication Method For the fabrication of the WG-OFET sensor device, we applied the side-gate structure (Figure 1). Compared to the conventional multi-stacked OFETs, the planar structure enables easy fabrication process. First, Au electrodes were selected as gate, source and drain, and were deposited on the same substrate. Then, an amorphous perfluoropolymer (Cytop) was used as the hydrophobic bank and patterned with oxygen plasma etching. Finally, a semiconducting polymer P3CPT was deposited onto the channel region by a drop-cast method. In order to prepare the dielectric layer made of aqueous media, 50 µL of 100 mM HEPES (4-(2-Hydroxyethyl)piperazine-1-ethanesulfonic acid) buffer solution containing 100 mM NaCl was dropped onto the channel region and the gate terminal. After dropping the solution, 40 μM of a copper (II) ion was added into the HEPES buffer solution. The fabricated device was then allowed to stand for 10 minutes to stabilize the transistor characteristics. Results and Conclusions Figure 2 shows the transfer characteristics of the fabricated WG-OFET with the addition of the increasing amount of GlyP from 10 µM to 300 µM in a HEPES buffer solution at pH 7.4 at r.t. As expected, the changes of transfer characteristics were observed by increasing the concentration of GlyP, indicating that the GlyP removed the copper ion from the side-chain of P3CPT. From the low concentration part range of the titration isotherm, the limit of detection (LOD) was estimated to be 0.26 ppm. Notably, the obtained LOD value meets the criteria for the detection of GlyP in drinking water. Furthermore, the selectivity study as shown in Figure 3 demonstrated the highest response of the WG-OFET device to GlyP among the structurally similar carboxylates and phosphates, because of the strong binding affinity of GlyP for copper(Ⅱ) ions. We expect that this study is one step forward in the development of the OFET-based GlyP sensors for environmental and clinical assessment.

High‐Performance Flexible Organic Nonvolatile Memories with Outstanding Stability Using Nickel Oxide Nanofloating Gate and Polymer Electret

AbstractOrganic nonvolatile memory devices based on organic field‐effect transistors (OFETs) have attracted attention as promising memory components in flexible organic integrated circuits. OFET‐based organic memories can be fabricated using solution processes with high portability and flexibility. However, many challenges still remain, such as achieving high levels of transparency and data storage while maintaining device reliability. In this study, the high‐performance of flexible organic nonvolatile memory devices is demonstrated through the synergistic effect of using a combination of polymer electret (poly(2‐vinyl naphthalene), PVN) and nanofloating gates (nickel oxide nanoparticles (NiOx NPs)). The PVN/NiOx NPs bilayer successfully acts as a charge storage medium with high transparency in the visible range. This system greatly improves memory performance including high data storage capacity, stable cyclic endurance, and quasi‐permanent retention characteristics (&gt;10 years). Furthermore, these devices also show excellent charge storage characteristics after 1000 bending cycles and even under the sharply bent state (bending radius 3 mm). This enhanced mechanical stability of flexible synergistic memory devices demonstrates that NiOx NPs can play an important role as a reliable data storage material for next‐generation wearable electronic devices.

Organic-based field effect transistors for protein detection fabricated by inkjet-printing

Abstract Biosensors based on Organic Field-Effect Transistors (OFETs) have attracted increasing attention due to the possibility of rapid, label-free, and inexpensive detection. Among all the different possibilities, inkjet-printed top-gate organic Field Effect Transistors-Based Biosensors (BioFETs) using a polymeric gate insulator have been seldom reported. In this work, a systematic investigation in terms of topographical and electrical characterization was carried out in order to find the optimal fabrication process for obtaining a reliable polymer insulator. Previous studies have demonstrated that the best electrical performance arises from the use of the perfluoropolymer Cytop™[12,13,14]. Consequently, a simple immobilization protocol was used to ensure the proper attachment of a model biomolecule onto the Cytop's hydrophobic surface whilst keeping its remarkable insulating properties with gate current in the range of dozens of pico-amperes. The top-gate inkjet-printed BioFETs presented in this study operate at threshold voltages in the range of 1–2 V and show durability even when exposed to oxygen plasma, wet amine functionalization treatments, and aqueous media. As a preliminary application, the inkjet-printed top-gate BioFETs is used for monitoring an immunoreaction by measuring changes in the drain current, paving the way for further use of this device in the immunosensing field.

Sensitive Detection of Glyphosate By a Water-Gated Organic Transistor

Introduction Glyphosate (GlyP), a widely used herbicide in the agricultural field, was classified as a probable carcinogenic compound (Group 2A) by the International Agency for Research of Cancer (IARS) in 2015. Since then, the importance of the GlyP detection in aqueous media has increased in the field of environmental chemistry and clinical research. The concentration of GlyP in ground and tap water is strictly regulated. For example, the permissible limit for the GlyP concentration in drinking water set at 0.7 ppm in the United States. To-this-date, liquid chromatography (LC) is a common method to sensitively detect GlyP. However, the apparatuses of LC are expensive and require trained personnel, requesting the development of affordable, simple and sensitive sensors for the on-site GlyP detection. Thus, our research has focused on organic field-effect transistors (OFETs) as chemical sensing platforms, because of their low-cost and solution-processability, compact size, and mechanical flexibility[1]. Here, we report an OFET-based chemical sensor for the detection of GlyP in water. Design of the OFET sensor Polythiophene derivatives (PTs) have been widely studied and applied as organic semiconductors in OFET devices. Moreover, PTs has been employed for materials in chemical sensors because their optical and electrical properties can be tuned by introducing artificial receptors into their 3- and/or 4-positions as side chains. However, such OFET-based sensors based on PT attached with artificial receptors are still rare due to the typical high applied voltage (>|20V|) of the OFET which causes materials degradation. Thus we designed a water-gated OFET (WG-OFET) for chemical sensing applications, which could be operated at an ultra-low voltage (<|0.3| V) derived from an electrical double-layer capacitor. For the detection of GlyP, we employed a carboxy side-chain attached to PT (poly{3-(5-carboxypentyl)thiophene-2,5-diyl}, P3CPT) [2] as the semiconductor layer. Due to the molecular wire effect of the π conjugated polymer [3], the sensitive detection of GlyP is expected based on the competitive binding among the carboxylate terminals of P3CPT, copper(II) ions and GlyP in an aqueous solution. Fabrication Method For the fabrication of the WG-OFET sensor device, we applied the side-gate structure (Figure 1). Compared to the conventional multi-stacked OFETs, the planar structure enables easy fabrication process. First, Au electrodes were selected as gate, source and drain, and were deposited on the same substrate. Then, an amorphous perfluoropolymer (Cytop) was used as the hydrophobic bank and patterned with oxygen plasma etching. Finally, a semiconducting polymer P3CPT was deposited onto the channel region by a drop-cast method. In order to prepare the dielectric layer made of aqueous media, 50 µL of 100 mM HEPES (4-(2-Hydroxyethyl)piperazine-1-ethanesulfonic acid) buffer solution containing 100 mM NaCl was dropped onto the channel region and the gate terminal. After dropping the solution, 40 μM of a copper (II) ion was added into the HEPES buffer solution. The fabricated device was then allowed to stand for 10 minutes to stabilize the transistor characteristics. Results and Conclusions Figure 2 shows the transfer characteristics of the fabricated WG-OFET with the addition of the increasing amount of GlyP from 10 µM to 300 µM in a HEPES buffer solution at pH 7.4 at r.t. As expected, the changes of transfer characteristics were observed by increasing the concentration of GlyP, indicating that the GlyP removed the copper ion from the side-chain of P3CPT. From the low concentration part range of the titration isotherm, the limit of detection (LOD) was estimated to be 0.26 ppm. Notably, the obtained LOD value meets the criteria for the detection of GlyP in drinking water. Furthermore, the selectivity study as shown in Figure 3 demonstrated the highest response of the WG-OFET device to GlyP among the structurally similar carboxylates and phosphates, because of the strong binding affinity of GlyP for copper(Ⅱ) ions. We expect that this study is one step forward in the development of the OFET-based GlyP sensors for environmental and clinical assessment.

Highly sensitive OFET-based gas sensors using fluorinated naphthalenediimide semiconductor films

Naphthalene diimide bearing fluorinated alkyl side chains (FNDI) was synthesized and characterized by NMR spectroscopy. FNDI demonstrated good semiconductor characteristics and was used to fabricate gas sensors based on organic field-effect transistors (OFETs). The designed sensor devices exhibited fast response to low concentrations (1 ppm and less) of ammonia and some aliphatic amines. The revealed high sensitivity of the sensors in combination with the group-selectivity (with respect to amines) and good operational stability makes promising their practical application for food (e.g. fish) quality control or for medical diagnostics.

Highly sensitive NO2 sensors based on organic field effect transistors with Al2O3/PMMA bilayer dielectrics by sol-spin coating

Abstract NO2 gas sensors based on organic field effect transistors (OFETs) with alumina/poly(methyl methacrylate) (Al2O3/PMMA) bilayer dielectrics were prepared by sol-spin coating method. The sensors with 0.8 mol/L Al2O3-sol dielectric layer show a high NO2 response, low baseline drift, stable sensing performance, and fast response/recovery time at room temperature. The sensitivity is over 129%/ppm and the limit of detection is below 1 ppm (134%). The results are comparable to most organic devices. The high sensor properties were attributed to the more ordered films on the dielectric layer and better electrical properties with bilayer dielectric devices than those with single dielectric devices. Compared to OFETs with PMMA single dielectric, the mobility was improved above 23 times, threshold voltage was reduced by 32.47 V, and both on-off current radio and saturation current were improved above an order of magnitude for OFETs with Al2O3/PMMA bilayer dielectrics at 0.8 mol/L Al2O3-sol. Moreover, the mechanism of organic film growth and the effect of bilayer dielectrics on sensing properties were analyzed. It is revealed that the highly electrical and NO2 sensing properties are closely relate. A simple and effective method, the sol-spin coating method, was provided to obtain high performance NO2 gas sensors based on OFETs.

Noncovalent conformational locks in organic semiconductors

Highly planar conformation is considered to be one of the most important properties for high performance organic semiconductors. Among all kinds strategies for designing highly performing materials, noncovalent conformational locks (NCLs) have been widely used to increase the planarity and rigidity for π-conjugated systems. This review summarizes π-conjugated small molecules and polymers by employing various NCLs for controlling molecular conformation in the past two years. The optoelectronic properties of the conjugated materials, together with their applications on organic field-effect transistors (OFETs) and organic photovoltaics (OPVs) are discussed. Besides, the outlook and challenges in this field are also presented. It is obvious that NCLs play an important role in the design and synthesis of high-performance organic semiconductors.

Fabrication of a Flexible Biosensor Based on an Organic Field-effect Transistor for Lactate Detection.

A novel flexible lactate sensor based on organic field-effect transistors (OFETs) is demonstrated. Because lactate is known as a biomarker for assessing our physical performance, wearable lactate sensors could contribute to the monitoring of human health conditions. The flexible and low-voltage operatable OFET possesses an extended-gate modified with enzymes and an osmium-redox polymer for the lactate detection, meaning that the continuous measurement of lactate levels (0 - 10 mM) has been successfully achieved. We believe that insight obtained will open up opportunities for applying OFETs in wearable biosensors.

Solution-Processed Bilayer Dielectrics for Flexible Low-Voltage Organic Field-Effect Transistors in Pressure-Sensing Applications.

Flexible pressure sensors based on organic field‐effect transistors (OFETs) have emerged as promising candidates for electronic‐skin applications. However, it remains a challenge to achieve low operating voltages of hysteresis‐free flexible pressure sensors. Interface engineering of polymer dielectrics is a feasible strategy toward sensitive pressure sensors based on low‐voltage OFETs. Here, a novel type of solution‐processed bilayer dielectrics is developed by combining a thick polyelectrolyte layer of polyacrylic acid (PAA) with a thin poly(methyl methacrylate) (PMMA) layer. This bilayer dielectric can provide a vertical phase separation structure from hydrophilic interface to hydrophobic interface which adjoins well to organic semiconductors, leading to improved stability and remarkably reduced leakage currents. Consequently, OFETs using the PMMA/PAA dielectrics reveal greatly suppressed hysteresis and improved mobility compared to those with a pure PAA dielectric. Using the optimized PMMA/PAA dielectric, flexible OFET‐based pressure sensors that show a record high sensitivity of 56.15 kPa−1 at a low operating voltage of −5 V, a fast response time of less than 20 ms, and good flexibility are further demonstrated. The salient features of high capacitance, good dielectric performance, and excellent reliability of the bilayer dielectrics promise a bright future of flexible sensors based on low‐voltage OFETs for wearable electronic applications.

Multi-Valued Logic Circuits Based on Organic Anti-ambipolar Transistors.

Multivalued logic circuits, which can handle more information than conventional binary logic circuits, have attracted much attention as a promising way to improve the data-processing capabilities of integrated circuits. In this study, we developed a ternary inverter based on organic field-effect transistors (OFET) as a potential component of high-performance and flexible integrated circuits. Key elements are anti-ambipolar and n-type OFETs connected in series. First, we demonstrate an organic ternary inverter that exhibits three distinct logic states. Second, the operating voltage was greatly reduced by taking advantage of an Al2O3 gate dielectric. Finally, the operating voltage was finely tuned by the designing of the device geometry. These results are achievable owing to the flexible controllability of the device configuration, suggesting that the organic ternary inverter plays an important role with regard to high-performance organic integrated circuits.