Polyelectrolyte-gated organic complementary circuits operating at low power and voltage

Ultrathin Ambipolar Polyelectrolyte Capacitors Prepared via Layer-by-Layer Assembling

Miniaturized solid state capacitors leveraging migration of unipolar ions in a single polyelectrolyte layer sandwiched between metal electrodes, namely, polyelectrolyte capacitors (PECs), have been recently reported with areal capacitance up to 100-200 nF mm-2. Nonetheless, application of PECs in consumer and industrial electronics has been hindered so far by their small operational frequency range, up to a few kHz, due to the resistive behavior (phase angle >-45°) of PECs in the range kHz-to-MHz. Here, it is reported on multilayer polyelectrolyte capacitors (mPECs) that leverage as dielectric an ambipolar nanometer-thick (down to 10 nm) stack of anionic and cationic polyelectrolytes assembled layer-by-layer between metal electrodes to eliminate the resistive behavior at frequencies from kHz to MHz. This significantly extends the operational range of mPECs over PECs. mPECs with areal capacitance as high as 25 nF mm-2 at 20 Hz and full capacitive behavior from 100 mHz to 10 MHz are demonstrated using different assembling conditions and anionic/cationic polyelectrolyte pairs. The mPECs reliably operate over time for >300 million cycles, at different biasing voltages up to 3 V, and temperatures up to 80 °C, showing a reversible capacitive behavior without significant hysteresis. Application of mPECs in flexible electronics, also operating at high frequency, is envisaged.

Fully-Solution-Processed Enhancement-Mode Complementary Metal-Oxide-Semiconductor Carbon Nanotube Thin Film Transistors Based on BiI3 -Doped Crosslinked Poly(4-Vinylphenol) Dielectrics for Ultralow-Power Flexible Electronics

The threshold voltage (V_th ) adjustment of complementary metal-oxide-semiconductor (CMOS) thin film transistors (TFTs) is one of the research hotspots due to its key role in energy consumption control of CMOS circuits. Here, ultralow-power flexible CMOS circuits based on well-matched enhancement-mode (E-mode) CMOS single-walled carbon nanotube (SWCNT) TFTs are successfully achieved through tuning the work function of gate electrodes, electron doping, and printing techniques. E-mode P-type CMOS SWCNT TFTs with the full-solution procedure are first obtained through decreasing the work function of Ag gate electrodes directly caused by the deposition of bismuth iodide (BiI₃ )-doped solid-state electrolyte dielectrics. After synthetic optimization of dielectric compositions and semiconductor printing process, the flexible printed E-mode SWCNT TFTs show the high I_on /I_off ratios of ≈10⁶ , small subthreshold swing (SS) of 70-85 mV dec^-1 , low operating voltages of ≈0.5 to -1.5 V, good stability and excellent mechanical flexibility during 10 000 bending cycles. E-mode N-type SWCNT TFTs are then selectively achieved via printing the polarity conversion ink (2-Amino-2-methyl-1-propanol (AMP)  as electron  doping agent) in P- type TFT channels. Last, printed SWCNT CMOS inverters are successfully constructed with full rail-to-rail output characteristics and the record unit static power consumption of 6.75 fW µm^-1 at V_DD of 0.2 V.

Optically modulated ionic conductivity in a hydrogel for emulating synaptic functions

Ion-conductive hydrogels, with ions as signal carriers, have become promising candidates to construct functional ionotronics for sensing, actuating, and robotics engineering. However, rational modulation of ionic migration to mimic biological information processing, including learning and memory, remains challenging to be realized in hydrogel materials. Here, we develop a hybrid hydrogel with optically modulated ionic conductivity to emulate the functions of a biological synapse. Through a responsive supramolecular approach, optical stimuli can trigger the release of mobile ions for tuning the conductivity of the hydrogel, which is analogous to the modulation of synaptic plasticity. As a proof of concept, this hydrogel can be used as an information processing unit to perceive different optical stimuli and regulate the grasping motion of a robotic hand, performing logical motion feedback with "learning-experience" function. Our ionic hydrogel provides a valuable strategy toward developing bioinspired ionotronic systems and pushes forward the functional applications of hydrogel materials.

An Electrochemical-Electret Coupled Organic Synapse with Single-Polarity Driven Reversible Facilitation-to-Depression Switching

Neuromorphic engineering and artificial intelligence demands hardware elements that emulates synapse algorithms. During the last decade electrolyte-gated organic conjugated materials have been explored as a platform for artificial synapses for neuromorphic computing. Unlike biological synapses, in current devices the synaptic facilitation and depression are triggered by voltages with opposite polarity. To enhance the reliability and simplify the operation of the synapse without lowering its sophisticated functionality, here, an electrochemical-electret coupled organic synapse (EECS) possessing a reversible facilitation-to-depression switch, is devised. Electret charging counterbalances channel conductance changes due to electrochemical doping, inducing depression without inverting the gate polarity. Overall, EECS functions as a threshold-controlled synaptic switch ruled by its amplitude-dependent, dual-modal operation, which can well emulate information storage and erase as in real synapses. By varying the energy level offset between the channel material and the electret, the EECS's transition threshold can be adjusted for specific applications, e.g., imparting additional light responsiveness to the device operation. The novel device architecture represents a major step forward in the development of artificial organic synapses with increased functional complexity and it opens new perspectives toward the fabrication of abiotic neural networks with higher reliability, efficiency, and endurance.

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.

Ambipolar Deep-Subthreshold Printed-Carbon-Nanotube Transistors for Ultralow-Voltage and Ultralow-Power Electronics

The development of ultralow-power and easy-to-fabricate electronics with potential for large-scale circuit integration (i.e., complementary or complementary-like) is an outstanding challenge for emerging off-the-grid applications, e.g., remote sensing, "place-and-forget", and the Internet of Things. Herein we address this challenge through the development of ambipolar transistors relying on solution-processed polymer-sorted semiconducting carbon nanotube networks (sc-SWCNTNs) operating in the deep-subthreshold regime. Application of self-assembled monolayers at the active channel interface enables the fine-tuning of sc-SWCNTN transistors toward well-balanced ambipolar deep-subthreshold characteristics. The significance of these features is assessed by exploring the applicability of such transistors to complementary-like integrated circuits, with respect to which the impact of the subthreshold slope and flatband voltage on voltage and power requirements is studied experimentally and theoretically. As demonstrated with inverter and NAND gates, the ambipolar deep-subthreshold sc-SWCNTN approach enables digital circuits with complementary-like operation and characteristics including wide noise margins and ultralow operational voltages (≤0.5 V), while exhibiting record-low power consumption (≤1 pW/μm). Among thin-film transistor technologies with minimal material complexity, our approach achieves the lowest energy and power dissipation figures reported to date, which are compatible with and highly attractive for emerging off-the-grid applications.

Single- versus Dual-Ion Conductors for Electric Double Layer Gating: Finite Element Modeling and Hall-Effect Measurements

Electric double layer (EDL) gating using a single-ion conductor is compared to a dual-ion conductor using both finite element modeling and Hall-effect measurements. Modified Nernst-Planck Poisson (mNPP) equations are used to calculate the ion density per unit area in a parallel plate capacitor geometry with a bulk ion concentration of 215 ≤ c_bulk ≤ 1782 mol/m³. With electrodes of equal size at a 2 V potential difference, the EDL ion density of the single-ion conductor is ∼7 × 10¹³ ions/cm², which is approximately 50% of the ion density induced in the dual-ion conductor. However, this difference is reduced to 8% when the electrode at which the cationic EDL forms is 10 times smaller than the counter electrode. Thus, for a field-effect transistor gated by a single-ion conductor, it is especially important to have a large gate-to-channel size ratio to achieve strong ion doping. The modeled ion densities are validated by Hall-effect measurements on graphene Hall bars gated by a polyethylene oxide (PEO)-based single-ion conductor. The sheet carrier density, n_S, is ∼2 × 10¹³ cm^-2 at V_g = 2 V, which is 3.5 times smaller than the predicted value and has the same order of magnitude as the n_s measured for a PEO-based, dual-ion conductor on the same graphene. The numerical modeling results can be approximated by a simple analysis of capacitors in series, where the EDLs are modeled as capacitors with thickness estimated by the sum of the Debye screening length and the Stern layer. The series of capacitor estimate agrees with the numerical modeling of the dual-ion conductor to within 10% and the single-ion conductor to within 30% from 0.25 to 2 V (c_bulk = 925 mol/m³); similar agreement is observed in the concentration range of 353-1650 mol/m³ for both single- and dual-ion conductors.

Organic-based inverters: basic concepts, materials, novel architectures and applications

The review article covers the materials and techniques employed to fabricate organic-based inverter circuits and highlights their novel architectures, ground-breaking performances and potential applications.

Electric Double-Layer Gating of Two-Dimensional Field-Effect Transistors Using a Single-Ion Conductor

Electric double-layer (EDL) gating using a custom-synthesized polyester single-ion conductor (PE400-Li) is demonstrated on two-dimensional (2D) crystals for the first time. The electronic properties of graphene and MoTe₂ field-effect transistors (FETs) gated with the single-ion conductor are directly compared to a poly(ethylene oxide) dual-ion conductor (PEO:CsClO₄). The anions in the single-ion conductor are covalently bound to the backbone of the polymer, leaving only the cations free to form an EDL at the negative electrode and a corresponding cationic depletion layer at the positive electrode. Because the cations are mobile in both the single- and dual-ion conductors, a similar enhancement of the n-branch is observed in both graphene and MoTe₂. Specifically, the single-ion conductor decreases the subthreshold swing in the n-branch of the bare MoTe₂ FET from 5000 to 250 mV/dec and increases the current density and on/off ratio by two orders of magnitude. However, the single-ion conductor suppressed the p-branch in both the graphene and the MoTe₂ FETs, and finite element modeling of ion transport shows that this result is unique to single-ion conductor gating in combination with an asymmetric gate/channel geometry. Both the experiments and modeling suggest that single-ion conductor-gated FETs can achieve sheet densities up to 10¹⁴ cm^-2, which corresponds to a charge density that would theoretically be sufficient to induce several percent strain in monolayer 2D crystals and potentially induce a semiconductor-to-metal phase transition in MoTe₂.

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.

Gelatin Hydrogel-Based Organic Electrochemical Transistors and Their Integrated Logic Circuits

We suggest gelatin hydrogel as an electrolyte and demonstrate organic electrochemical transistors (OECTs) based on a sheet of gelatin. We also modulate electrical characteristics of the OECT with respect to pH condition of the gelatin hydrogel from acid to base and analyze its characteristics based on the electrochemical theory. Moreover, we extend the gelatin-based OECT to electrochemical logic circuits, for example, NOT, NOR, and NAND gates.

A Ferroelectric/Electrochemical Modulated Organic Synapse for Ultraflexible, Artificial Visual-Perception System

Human eyes undertake the majority of information assimilation for learning and memory. Transduction of the color and intensity of the incident light into neural signals is the main process for visual perception. Besides light-sensitive elements that function as rods and cones, artificial retinal systems require neuromorphic devices to transform light stimuli into post-synaptic signals. In terms of plasticity timescale, synapses with short-term plasticity (STP) and long-term potentiation (LTP) represent the neural foundation for experience acquisition and memory formation. Currently, electrochemical transistors are being researched as STP-LTP devices. However, their LTP timescale is confined to a second-to-minute level to give unreliable non-volatile memory. This issue limits multiple-plasticity synapses with tunable temporal characteristics and efficient sensory-memory systems. Herein, a ferroelectric/electrochemical modulated organic synapse is proposed, attaining three prototypes of plasticity: STP/LTP by electrochemical doping/de-doping and ferroelectric-LTP from dipole switching. The device supplements conventional electrochemical transistors with 10000-second-persistent non-volatile plasticity and unique threshold switching properties. As a proof-of-concept for an artificial visual-perception system, an ultraflexible, light-triggered organic neuromorphic device (LOND) is constructed by this synapse. The LOND transduces incident light signals with different frequency, intensity, and wavelength into synaptic signals, both volatile and non-volatile.

Intrinsically ionic conductive cellulose nanopapers applied as all solid dielectrics for low voltage organic transistors

Biodegradability, low-voltage operation, and flexibility are important trends for the future organic electronics. High-capacitance dielectrics are essential for low-voltage organic field-effect transistors. Here we report the application of environmental-friendly cellulose nanopapers as high-capacitance dielectrics with intrinsic ionic conductivity. Different with the previously reported liquid/electrolyte-gated dielectrics, cellulose nanopapers can be applied as all-solid dielectrics without any liquid or gel. Organic field-effect transistors fabricated with cellulose nanopaper dielectrics exhibit good transistor performances under operation voltage below 2 V, and no discernible drain current change is observed when the device is under bending with radius down to 1 mm. Interesting properties of the cellulose nanopapers, such as ionic conductivity, ultra-smooth surface (~0.59 nm), high transparency (above 80%) and flexibility make them excellent candidates as high-capacitance dielectrics for flexible, transparent and low-voltage electronics.

Next-generation organic electronics require flexible organic field effect transistors that show low-voltage operation and are biodegradable. Here, Huang and co-workers demonstrate high-performance transistors that utilize solid-state ionic conductive cellulose nanopaper as the dielectric.

Printed Electronics Based on Inorganic Semiconductors: From Processes and Materials to Devices

Following the ever-expanding technological demands, printed electronics has shown palpable potential to create new and commercially viable technologies that will benefit from its unique characteristics, such as, large-area and wide range of substrate compatibility, conformability and low-cost. Through the last few decades, printed/solution-processed field-effect transistors (FETs) and circuits have witnessed immense research efforts, technological growth and increased commercial interests. Although printing of functional inks comprising organic semiconductors has already been initiated in early 1990s, gradually the attention, at least partially, has been shifted to various forms of inorganic semiconductors, starting from metal chalcogenides, oxides, carbon nanotubes and very recently to graphene and other 2D semiconductors. In this review, the entire domain of printable inorganic semiconductors is considered. In fact, thanks to the continuous development of materials/functional inks and novel design/printing strategies, the inorganic printed semiconductor-based circuits today have reached an operation frequency up to several hundreds of kilohertz with only a few nanosecond time delays at the individual FET/inverter levels; in this regard, often circuits based on hybrid material systems have been found to be advantageous. At the end, a comparison of relative successes of various printable inorganic semiconductor materials, the remaining challenges and the available future opportunities are summarized.

High performance printed oxide field-effect transistors processed using photonic curing

Oxide semiconductors are highly promising candidates for the most awaited, next-generation electronics, namely, printed electronics. As a fabrication route for the solution-processed/printed oxide semiconductors, photonic curing is becoming increasingly popular, as compared to the conventional thermal curing method; the former offers numerous advantages over the latter, such as low process temperatures and short exposure time and thereby, high throughput compatibility. Here, using dissimilar photonic curing concepts (UV-visible light and UV-laser), we demonstrate facile fabrication of high performance In₂O₃ field-effect transistors (FETs). Beside the processing related issues (temperature, time etc.), the other known limitation of oxide electronics is the lack of high performance p-type semiconductors, which can be bypassed using unipolar logics from high mobility n-type semiconductors alone. Interestingly, here we have found that our chosen distinct photonic curing methods can offer a large variation in threshold voltage, when they are fabricated from the same precursor ink. Consequently, both depletion and enhancement-mode devices have been achieved which can be used as the pull-up and pull-down transistors in unipolar inverters. The present device fabrication recipe demonstrates fast processing of low operation voltage, high performance FETs with large threshold voltage tunability.

Complementary Logic Circuits Based on High-Performance n-Type Organic Electrochemical Transistors

Organic electrochemical transistors (OECTs) have been the subject of intense research in recent years. To date, however, most of the reported OECTs rely entirely on p-type (hole transport) operation, while electron transporting (n-type) OECTs are rare. The combination of efficient and stable p-type and n-type OECTs would allow for the development of complementary circuits, dramatically advancing the sophistication of OECT-based technologies. Poor stability in air and aqueous electrolyte media, low electron mobility, and/or a lack of electrochemical reversibility, of available high-electron affinity conjugated polymers, has made the development of n-type OECTs troublesome. Here, it is shown that ladder-type polymers such as poly(benzimidazobenzophenanthroline) (BBL) can successfully work as stable and efficient n-channel material for OECTs. These devices can be easily fabricated by means of facile spray-coating techniques. BBL-based OECTs show high transconductance (up to 9.7 mS) and excellent stability in ambient and aqueous media. It is demonstrated that BBL-based n-type OECTs can be successfully integrated with p-type OECTs to form electrochemical complementary inverters. The latter show high gains and large worst-case noise margin at a supply voltage below 0.6 V.

Ionic thermoelectric gating organic transistors

Temperature is one of the most important environmental stimuli to record and amplify. While traditional thermoelectric materials are attractive for temperature/heat flow sensing applications, their sensitivity is limited by their low Seebeck coefficient (∼100 μV K⁻¹). Here we take advantage of the large ionic thermoelectric Seebeck coefficient found in polymer electrolytes (∼10,000 μV K⁻¹) to introduce the concept of ionic thermoelectric gating a low-voltage organic transistor. The temperature sensing amplification of such ionic thermoelectric-gated devices is thousands of times superior to that of a single thermoelectric leg in traditional thermopiles. This suggests that ionic thermoelectric sensors offer a way to go beyond the limitations of traditional thermopiles and pyroelectric detectors. These findings pave the way for new infrared-gated electronic circuits with potential applications in photonics, thermography and electronic-skins.

The design of electronic skin for medical imaging or robotics applications calls for high capability of temperature sensing. Here, Zhao et al. integrate ionic thermoelectric gating to an organic thin-field transistor to detect temperature at sensitivity comparable to that of pyroelectric materials.

Sub-50 nm Channel Vertical Field-Effect Transistors using Conventional Ink-Jet Printing

A printed vertical field-effect transistor is demonstrated, which decouples critical device dimensions from printing resolution. A printed mesoporous semiconductor layer, sandwiched between vertically stacked drive electrodes, provides <50 nm channel lengths. A polymer-electrolyte-based gate insulator infiltrates the percolating pores of the mesoporous channel to accumulate charge carriers at every semiconductor domain, thereby, resulting in an unprecedented current density of MA cm^-2 .

Flexible, High-Speed CdSe Nanocrystal Integrated Circuits

We report large-area, flexible, high-speed analog and digital colloidal CdSe nanocrystal integrated circuits operating at low voltages. Using photolithography and a newly developed process to fabricate vertical interconnect access holes, we scale down device dimensions, reducing parasitic capacitances and increasing the frequency of circuit operation, and scale up device fabrication over 4 in. flexible substrates. We demonstrate amplifiers with ∼7 kHz bandwidth, ring oscillators with <10 μs stage delays, and NAND and NOR logic gates.

Single ion conducting, polymerized ionic liquid triblock copolymer films: high capacitance electrolyte gates for n-type transistors

There has been impressive progress in the fabrication and characterization of p-type organic electrolyte-gated transistors (EGTs). Unfortunately, despite the importance of n-type organic transistors for complementary circuits, fewer investigations have focused on developing electrolytes as gate dielectrics for n-type organic semiconductors. Here, we present a novel single ion conductor, a polymerized ionic liquid (PIL) triblock copolymer (PS-PIL-PS) composed of styrene (PS) and 1-[(2-acryloyloxy)ethyl]-3-butylimidazolium bis(trifluoromethylsulfonyl)imide (PIL), that conducts only the TFSI anion. This triblock copolymer acts as a gate dielectric to allow low-voltage n-type organic EGT operation. Impedance characterization of PS-PIL-PS reveals that there are three polarization regions: (1) dipolar relaxation, (2) ion migration, and (3) electric double layer (EDL) formation. These polarization regions are controlled by film thickness, and rapid EDL formation can be obtained in thinner polyelectrolyte films. In particular, a 500 nm-thick polyelectrolyte film exhibits a large capacitance of ∼1 μF/cm(2) at 10 kHz. Employing this single ion conducting PIL triblock copolymer as the gate insulator, we achieved low voltage operation (<1 V supply) of poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-bithiophene)} (P(NDI2OD-T2)) n-type organic EGTs (electron mobility of ∼0.008 cm(2)/(V·s) and ON/OFF current ratio of ∼2 × 10(3)) by preventing electrochemical doping. Furthermore, the recognition that the performance of n-type organic EGTs is diminished by 3D electrochemical doping suggests that it may be necessary to have a unipolar electrolyte to gate n-type organic semiconductors. Finally, we highlight that the use of PIL block copolymer electrolytes as gate insulators opens unique opportunities to explore the role of ion penetration in n-type organic EGTs by tuning the extent of electrochemical doping.

A general route toward complete room temperature processing of printed and high performance oxide electronics

Critical prerequisites for solution-processed/printed field-effect transistors (FETs) and logics are excellent electrical performance including high charge carrier mobility, reliability, high environmental stability and low/preferably room temperature processing. Oxide semiconductors can often fulfill all the above criteria, sometimes even with better promise than their organic counterparts, except for their high process temperature requirement. The need for high annealing/curing temperatures renders oxide FETs rather incompatible to inexpensive, flexible substrates, which are commonly used for high-throughput and roll-to-roll additive manufacturing techniques, such as printing. To overcome this serious limitation, here we demonstrate an alternative approach that enables completely room-temperature processing of printed oxide FETs with device mobility as large as 12.5 cm(2)/(V s). The key aspect of the present concept is a chemically controlled curing process of the printed nanoparticle ink that provides surprisingly dense thin films and excellent interparticle electrical contacts. In order to demonstrate the versatility of this approach, both n-type (In2O3) and p-type (Cu2O) oxide semiconductor nanoparticle dispersions are prepared to fabricate, inkjet printed and completely room temperature processed, all-oxide complementary metal oxide semiconductor (CMOS) invertors that can display significant signal gain (∼18) at a supply voltage of only 1.5 V.

High-resolution patterning of graphene by screen printing with a silicon stencil for highly flexible printed electronics

High-resolution screen printing of pristine graphene is introduced for the rapid fabrication of conductive lines on flexible substrates. Well-defined silicon stencils and viscosity-controlled inks facilitate the preparation of high-quality graphene patterns as narrow as 40 μm. This strategy provides an efficient method to produce highly flexible graphene electrodes for printed electronics.

High capacitance, photo-patternable ion gel gate insulators compatible with vapor deposition of metal gate electrodes

A facile fabrication route to pattern high-capacitance electrolyte thin films in electrolyte-gated transistors (EGTs) was demonstrated using a photoinitiated cross-linkable ABA-triblock copolymer ion gel. The azide groups of poly(styrene-r-vinylbenzylazide) (PS-N3) end-blocks can be chemically cross-linked via UV irradiation (λ = 254 nm) in the self-assembly of poly[(styrene-r-vinylbenzylazide)-b-ethylene oxide-b-(styrene-r-vinylbenzylazide)] (SOS-N3) triblock copolymer in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]). Impedance spectroscopy and small-angle X-ray scattering revealed that ion transport and microstructure of the ion gel are not affected by UV cross-linking. Using a photoinduced cross-linking strategy, photopatterning of ion gels through a patterned mask was achieved. Employing a photopatterned ion gel as the high-capacitance gate insulator in thin film transistors (TFTs), arrays of TFTs exhibited uniform and high device performance. Specifically, both p-type (poly(3-hexylthiophene)) (P3HT) and n-type (ZnO) transistors displayed high carrier mobility (hole mobility of ∼ 1.4 cm(2)/ (V s) and electron mobility of ∼ 0.7 cm(2)/ (V s) and ON/OFF current ratio (∼ 10(5)) at supply voltages below 2 V. This study suggests that photopatterning is a promising candidate to conveniently incorporate high-capacitance ion gels into TFTs in the fabrication of printed electronics.

Aerosol jet printed, sub-2 V complementary circuits constructed from P- and N-type electrolyte gated transistors

Printed low-voltage complementary inverters based on electrolyte gated transistors are demonstrated. The printed complementary inverters showed gain of 18 and power dissipation below 10 nW. 5-stage ring oscillators operate at 2 V with an oscillation frequency of 2.2 kHz, corresponding to stage delays of less than 50 μs. The printed circuits exhibit good stability under continuous dynamic operation.

A multifunctional ionic iridium complex for field-effect and light-emitting devices

We synthesized a multifunctional ionic iridium complex used for field-effect and light-emitting devices.

Toward printed integrated circuits based on unipolar or ambipolar polymer semiconductors

For at least the past ten years printed electronics has promised to revolutionize our daily life by making cost-effective electronic circuits and sensors available through mass production techniques, for their ubiquitous applications in wearable components, rollable and conformable devices, and point-of-care applications. While passive components, such as conductors, resistors and capacitors, had already been fabricated by printing techniques at industrial scale, printing processes have been struggling to meet the requirements for mass-produced electronics and optoelectronics applications despite their great potential. In the case of logic integrated circuits (ICs), which constitute the focus of this Progress Report, the main limitations have been represented by the need of suitable functional inks, mainly high-mobility printable semiconductors and low sintering temperature conducting inks, and evoluted printing tools capable of higher resolution, registration and uniformity than needed in the conventional graphic arts printing sector. Solution-processable polymeric semiconductors are the best candidates to fulfill the requirements for printed logic ICs on flexible substrates, due to their superior processability, ease of tuning of their rheology parameters, and mechanical properties. One of the strongest limitations has been mainly represented by the low charge carrier mobility (μ) achievable with polymeric, organic field-effect transistors (OFETs). However, recently unprecedented values of μ ∼ 10 cm(2) /Vs have been achieved with solution-processed polymer based OFETs, a value competing with mobilities reported in organic single-crystals and exceeding the performances enabled by amorphous silicon (a-Si). Interestingly these values were achieved thanks to the design and synthesis of donor-acceptor copolymers, showing limited degree of order when processed in thin films and therefore fostering further studies on the reason leading to such improved charge transport properties. Among this class of materials, various polymers can show well balanced electrons and holes mobility, therefore being indicated as ambipolar semiconductors, good environmental stability, and a small band-gap, which simplifies the tuning of charge injection. This opened up the possibility of taking advantage of the superior performances offered by complementary "CMOS-like" logic for the design of digital ICs, easing the scaling down of critical geometrical features, and achieving higher complexity from robust single gates (e.g., inverters) and test circuits (e.g., ring oscillators) to more complete circuits. Here, we review the recent progress in the development of printed ICs based on polymeric semiconductors suitable for large-volume micro- and nano-electronics applications. Particular attention is paid to the strategies proposed in the literature to design and synthesize high mobility polymers and to develop suitable printing tools and techniques to allow for improved patterning capability required for the down-scaling of devices in order to achieve the operation frequencies needed for applications, such as flexible radio-frequency identification (RFID) tags, near-field communication (NFC) devices, ambient electronics, and portable flexible displays.

Flexible low-voltage organic transistors with high thermal stability at 250 °C

Low-operating-voltage flexible organic thin-film transistors with high thermal stability using DPh-DNTT and SAM gate dielectrics are reported. The mobility of the transistors are decreased by 23% after heating to 250 °C for 30 min. Furthermore, flexible organic pseudo-CMOS inverter circuits, which are functional after heating to 200 °C, are demonstrated.

Electrolyte-gated transistors for organic and printed electronics

Here we summarize recent progress in the development of electrolyte-gated transistors (EGTs) for organic and printed electronics. EGTs employ a high capacitance electrolyte as the gate insulator; the high capacitance increases drive current, lowers operating voltages, and enables new transistor architectures. Although the use of electrolytes in electronics is an old concept going back to the early days of the silicon transistor, new printable, fast-response polymer electrolytes are expanding the potential applications of EGTs in flexible, printed digital circuits, rollable displays, and conformal bioelectronic sensors. This report introduces the structure and operation mechanisms of EGTs and reviews key developments in electrolyte materials for use in printed electronics. The bulk of the article is devoted to electrical characterization of EGTs and emerging applications.

Tetrachlorinated tetraazaperopyrenes (TAPPs): highly fluorescent dyes and semiconductors for air-stable organic n-channel transistors and complementary circuits

A range of 2,9-perfluoroalkyl-substituted tetraazaperopyrene (TAPP) derivatives (1-5) was synthesised by reacting 4,9-diamino-3,10-perylenequinone diimine (DPDI) with the corresponding carboxylic acid chloride or anhydride in the presence of a base. The reaction of compounds 1-4 with dichloroisocyanuric acid (DIC) in concentrated sulphuric acid resulted in the fourfold substitution of the tetraazaperopyrene core, yielding the 2,9-bisperfluoroalkyl-4,7,11,14-tetrachloro-1,3,8,10-tetraazaperopyrenes 6-9, respectively. The optical and electrochemical data demonstrate the drastic influence of the core substitution on the properties. All compounds are highly luminescent (fluorescence quantum yields of up to Φ=0.8). The LUMO energies of the tetrachlorinated TAPP derivatives (determined by cyclic voltammetry and computed by DFT calulations) were found to be below -4 eV. In the course of this work the performance of TAPP derivatives in organic thin-film transistors (TFTs) was investigated, and their n-channel characteristics with field-effect mobilities of up to 0.14 cm(2)  V(-1)  s(-1) and an on/off current ratio of >10(6) were confirmed. Long-term stabilities of 3-4 months under ambient conditions of the devices were established. Complementary inverters and ring oscillators with n-channel TFTs based on compound 8 and p-channel TFTs based on dinaphtho-[2,3-b:2',3'-f]thieno[3,2-b]thiophene (DNTT) were fabricated on a glass substrate.