Low‐Temperature‐Processed Printed Metal Oxide Transistors Based on Pure Aqueous Inks

Additive patterning of transparent conducting metal oxides at low temperatures is a critical step in realizing low‐cost transparent electronics for display technology and photovoltaics. In this work, inkjet‐printed metal oxide transistors based on pure aqueous chemistries are presented. These inks readily convert to functional thin films at lower processing temperatures (T ≤ 250 °C) relative to organic solvent‐based oxide inks, facilitating the fabrication of high‐performance transistors with both inkjet‐printed transparent electrodes of aluminum‐doped cadmium oxide (ACO) and semiconductor (InO_x ). The intrinsic fluid properties of these water‐based solutions enable the printing of fine features with coffee‐ring free line profiles and smoother line edges than those formed from organic solvent‐based inks. The influence of low‐temperature annealing on the optical, electrical, and crystallographic properties of the ACO electrodes is investigated, as well as the role of aluminum doping in improving these properties. Finally, the all‐aqueous‐printed thin film transistors (TFTs) with inkjet‐patterned semiconductor (InO_x ) and source/drain (ACO) layers are characterized, which show ideal low contact resistance (R _c < 160 Ω cm) and competitive transistor performance (µ _lin up to 19 cm² V^?1 s^?1, Subthreshold Slope (SS) ≤150 mV dec^?1) with only low‐temperature processing (T ≤ 250 °C).     

High‐Speed,Low‐Voltage,and Environmentally Stable Operation of Electrochemically Gated Zinc Oxide Nanowire Field‐Effect Transistors

Single‐crystal, 1D nanostructures are well known for their high mobility electronic transport properties. Oxide‐nanowire field‐effect transistors (FETs) offer both high optical transparency and large mechanical conformability which are essential for flexible and transparent display applications. Whereas the “on‐currents” achieved with nanowire channel transistors are already sufficient to drive active matrix organic light emitting diode (AMOLED) displays; it is shown here that incorporation of electrochemical‐gating (EG) to nanowire electronics reduces the operation voltage to ≤2 V. This opens up new possibilities of realizing flexible, portable, transparent displays that are powered by thin film batteries. A composite solid polymer electrolyte (CSPE) is used to obtain all‐solid‐state FETs with outstanding performance; the field‐effect mobility, on/off current ratio, transconductance, and subthreshold slope of a typical ZnO single‐nanowire transistor are 62 cm²/Vs, 10⁷, 155 μS/μm and 115 mV/dec, respectively. Practical use of such electrochemically‐gated field‐effect transistor (EG FET) devices is supported by their long‐term stability in air. Moreover, due to the good conductivity (≈10^?2 S/cm) of the CSPE, sufficiently high switching speed of such EG FETs is attainable; a cut‐off frequency in excess of 100 kHz is measured for in‐plane FETs with large gate‐channel distance of >10 μm. Consequently, operation speeds above MHz can be envisaged for top‐gate transistor geometries with insulator thicknesses of a few hundreds of nanometers. The solid polymer electrolyte developed in this study has great potential in future device fabrication using all‐solution processed and high throughput techniques.     

Three‐Dimensional Inkjet‐Printed Interconnects using Functional Metallic Nanoparticle Inks

Inkjet‐printed gold nanoparticle pillars are investigated as a high‐performance alternative to conventional flip‐chip interconnects for electronic packages, with significant advantages in terms of mechanical/chemical robustness and conductivity. The process parameters critical to pillar fabrication are described and highly uniform pillar arrays are demonstrated. More generally, this work underscores the impact of sintering on the electrical, mechanical, structural, and compositional properties of three‐dimensional nanoparticle‐based structures. Using heat treatments as low as 200 °C, electrical and mechanical performance that outcompetes conventional lead‐tin eutectic solder materials is achieved. With sintering conditions reaching 300 °C it is possible to achieve pillars with properties comparable to bulk gold. This work demonstrates the immense potential for both inkjet printing and metal nanoparticles to become a viable and cost‐saving alternative to both conventional electronic packaging processes and application‐specific integration schemes.     

Fabrication of Releasable Single‐Crystal Silicon–Metal Oxide Field‐Effect Devices and Their Deterministic Assembly on Foreign Substrates

A new class of thin, releasable single‐crystal silicon semiconductor device is presented that enables integration of high‐performance electronics on nearly any type of substrate. Fully formed metal oxide–semiconductor field–effect transistors with thermally grown gate oxides and integrated circuits constructed with them demonstrate the ideas in devices mounted on substrates ranging from flexible sheets of plastic, to plates of glass and pieces of aluminum foil. Systematic study of the electrical properties indicates field‐effect mobilities of ≈710 cm² V^?1 s^?1, subthreshold slopes of less than 0.2 V decade^?1 and minimal hysteresis, all with little to no dependence on the properties of the substrate due to bottom silicon surfaces that are passivated with thermal oxide. The schemes reported here require only interconnect metallization to be performed on the final device substrate, which thereby minimizes the need for any specialized processing technology, with important consequences in large‐area electronics for display systems, flexible/stretchable electronics, or other non‐wafer‐based devices.     

Tailoring Morphology and Structure of Inkjet‐Printed Liquid‐Crystalline Semiconductor/Insulating Polymer Blends for High‐Stability Organic Transistors

Inkjet printing of semiconducting polymers is desirable for realizing low‐cost, large‐area printed electronics. However, sequential inkjet printing methods often suffer from nozzle clogging because the solubility of semiconducting polymers in organic solvents is limited. Here, it is demonstrated that the addition of an insulating polymer to a semiconducting polymer ink greatly enhances the solubility and stability of the ink, leading to the stable ejection of ink droplets. This bicomponent blend comprising a liquid‐crystalline semiconducting copolymer, poly(didodecylquaterthiophene‐alt‐didodecylbithiazole) (PQTBTz‐C12), and an insulating commodity polymer, polystyrene, is extremely useful as a semiconducting layer in organic field‐effect transistors (OFETs), providing fine control over the phase‐separated morphology and structure of the inkjet‐printed film. Tailoring the solubility‐induced phase separation of the two components leads to a bilayer structure consisting of a polystyrene layer on the top and a highly crystalline PQTBTz‐C12 layer on the bottom. The blend film is used as the semiconducting layer in OFETs, reducing the semiconductor content to several tens of pictograms in a single device without degrading the device performance. Furthermore, OFETs based on the PQTBTz‐C12/polystyrene film exhibit much greater environmental and electrical stabilities compared to the films prepared from homo PQTBTz‐C12, mainly due to the self‐encapsulated structure of the blend film.     

Paper with Power: Engraving 2D Materials on 3D Structures for Printed,High‐Performance,Binder‐Free,and All‐Solid‐State Supercapacitors

The prevalence of the Internet of Things (IoT) and wearable electronics create an unprecedented demand for new power sources which are low cost, high performance, and flexible in many application settings. In this paper, a strategy for the scalable fabrication of high‐performance, all‐solid‐state supercapacitors (SCs) is demonstrated using conventional paper and an inkjet printer. Emerging printed electronics technology and low‐cost chemical engraving methods are bridged for the first time to construct Cu_xO nanosheets, in situ, on the 3D metallized fiber structures. Benefitting from both the “2D Materials on 3D Structures” design and the binder‐free nature of the fabricated electrodes, substantial improvements to electrical conductivity, aerial capacitance, and electrochemical performance of the resulting SCs are observed. With the proposed strategy, the fabricated SCs can be seamlessly integrated into any printed circuit, sensors, or artwork; the properties of these SCs can be easily tuned by simple pattern design, fulfilling the increasing demand of highly customized power systems in the IoT and flexible/wearable electronics industries.     

An Inkjet‐Printed Field‐Effect Transistor for Label‐Free Biosensing

A flexible, biological field‐effect transistor (BioFET) for use in biosensing is reported. The BioFET is based on an organic thin‐film transistor (OTFT) fabricated mainly by inkjet printing and subsequently functionalized with antibodies for protein recognition. The BioFET is assessed for label‐free detection of a model protein, human immunoglobulin G (HIgG). It is characterized electrically to evaluate the contribution of each step in the functionalization of the OTFT and to detect the presence of the target protein. The fabrication, structure, materials optimization, electrical characteristics, and functionality of the starting OTFT and final BioFET are also discussed. Different materials are evaluated for the top insulator layer, with the aim of protecting the lower layers from the electrolyte and preserving the BioFET electrical performance.     

Microfluidic Lateral Flow Cytochrome P450 Assay on a Novel Printed Functionalized Calcium Carbonate‐Based Platform for Rapid Screening of Human Xenobiotic Metabolism

Cytochrome P450 (CYP) is a superfamily of enzymes in charge of elimination of the majority of clinically used drugs and other xenobiotics. This study focuses on the development of a rapid microfluidic lateral flow assay to study human phase I metabolism reactions mediated by CYP2A6 isoenzyme, the major detoxification route for many known carcinogens and drugs, with coumarin 7‐hydroxylation, as the prototype model reaction. Assay fabrication utilizes custom‐designed porous functionalized calcium carbonate (FCC) coatings and inkjet‐printed fluid barriers. All materials used are novel and carefully chosen to preserve biocompatibility. The design comprises separate zones for reaction, separation and detection, and an absorbent pad to keep the assay wet for extended periods (up to 10 min) even when heated to physiological temperature. The concept enables CYP assays to be made at lower cost than conventional well‐plate assays, while providing increased selectivity at equally high speed, owing to the possibility for simultaneous chromatographic separation of the reaction products from the reactants on the FCC coating. The developed concept provides a viable rapid prediction of the interaction risks related to metabolic clearance of drugs and other xenobiotics, and exemplifies a novel coating technology illustrating the opportunity to broaden application functionality.     

Inkjet‐Printed Flexible Gold Electrode Arrays for Bioelectronic Interfaces

Bioelectronic interfaces require electrodes that are mechanically flexible and chemically inert. Flexibility allows pristine electrode contact to skin and tissue, and chemical inertness prevents electrodes from reacting with biological fluids and living tissues. Therefore, flexible gold electrodes are ideal for bioimpedance and biopotential measurements such as bioimpedance tomography, electrocardiography (ECG), electroencephalography (EEG), and electromyography (EMG). However, a manufacturing process to fabricate gold electrode arrays on plastic substrates is still elusive. In this work, a fabrication and low‐temperature sintering (≈200 °C) technique is demonstrated to fabricate gold electrodes. At low‐temperature sintering conditions, lines of different widths demonstrate different sintering speeds. Therefore, the sintering condition is targeted toward the widest feature in the design layout. Manufactured electrodes show minimum feature size of 62 μm and conductivity values of 5 × 10 ⁶ S m^?1. Utilizing the versatility of printing and plastic electronic processes, electrode arrays consisting of 31 electrodes with electrode‐to‐electrode spacing ranging from 2 to 7 mm are fabricated and used for impedance mapping of conformal surfaces at 15 kHz. Overall, the fabrication process of an inkjet‐printed gold electrode array that is electrically reproducible, mechanically robust, and promising for bioimpedance and biopotential measurements is demonstrated.     

Self‐Organization of Inkjet‐Printed Organic Semiconductor Films Prepared in Inkjet‐Etched Microwells

The high‐precision deposition of highly crystalline organic semiconductors by inkjet printing is important for the production of printed organic transistors. Herein, a facile nonconventional lithographic patterning technique is developed for fabricating banks with microwell structures by inkjet printing solvent droplets onto a polymer layer, thereby locally dissolving the polymer to form microwells. The semiconductor ink is then inkjet‐printed into the microwells. In addition to confining the inkjet‐printed organic semiconductor droplets, the microwells provide a platform onto which organic semiconductor molecules crystallize during solvent evaporation. When printed onto the hydrophilic microwells, the inkjet‐printed 6,13‐bis(triisopropylsilylethynyl) pentacene (TIPS_PEN) molecules undergo self‐organization to form highly ordered crystalline structures as a result of contact line pinning at the top corner of the bank and the outward hydrodynamic flow within the drying droplet. By contrast, small crystallites form with relatively poor molecular ordering in the hydrophobic microwells as a result of depinning of the contact line along the walls of the microwells. Because pinning in the hydrophilic microwells occurred at the top corner of the bank, treating the surfaces of the dielectric layer with a hydrophobic organic layer does not disturb the formation of the highly ordered TIPS_PEN crystals. Transistors fabricated on the hydrophilic microwells and the hydrophobic dielectric layer exhibit the best electrical properties, which is explained by the solvent evaporation and crystallization characteristics of the organic semiconductor droplets in the microwell. These results indicate that this technique is suitable for patterning organic semiconductor deposits on large‐area flexible substrates for the direct‐write fabrication of high‐performance organic transistors.     

Accelerating the Screening of Perovskite Compositions for Photovoltaic Applications through High‐Throughput Inkjet Printing

The exploration and optimization of numerous mixed perovskite compositions are causing a strong demand for high‐throughput synthesis. Nevertheless high‐throughput fabrication of perovskite films with representative film properties, which can efficiently screen the perovskite compositions for photovoltaic applications, has rarely been explored. A high‐throughput inkjet printing approach that can automatically fabricate perovskite films with various compositions with high reproducibility and high speed is developed. The automatic sequential printing of four precursors forms 25 mixed films in a fast and reproducible manner. The obtained bandgaps, photoluminescence (PL) peak positions, and PL lifetimes allow for the efficient screening of perovskite compositions for photovoltaic applications. To exemplify this concept, among 25 tested films, two compositions CH₃NH₃PbBr_0.75I_2.25 (MA) and (HC(NH₂)₂)_0.75(CH₃NH₃)_0.25PbBr_0.75I_2.25 (FA_0.75MA_0.25) with a long (237 ns) and short (49.0 ns) PL lifetime, respectively, are screened out for device investigations. As expected, the MA‐based device exhibits a much higher efficiency (19.0%) than that (15.3%) of the FA_0.75MA_0.25 counterpart. This efficiency improvement is mainly ascribed to a smaller dark saturate current density, a lower level of energetic disorder, more efficient charge transfer and decreased charge recombination losses, which are consistent with the much longer PL lifetime in the database.     

High‐Mobility Air‐Stable Solution‐Shear‐Processed n‐Channel Organic Transistors Based on Core‐Chlorinated Naphthalene Diimides

High charge carrier mobility solution‐processed n‐channel organic thin‐film transistors (OTFTs) based on core‐chlorinated naphthalene tetracarboxylic diimides (NDIs) with fluoroalkyl chains are demonstrated. These OTFTs were prepared through a solution shearing method. Core‐chlorination of NDIs not only increases the electron mobilities of OTFTs, but also enhances their air stability, since the chlorination in the NDI core lowers the lowest unoccupied molecular orbital (LUMO) levels. The air‐stability of dichlorinated NDI was better than that of the tetrachlorinated NDIs, presumably due to the fact that dichlorinated NDIs have a denser packing of the fluoroalkyl chains and less grain boundaries on the surface, reducing the invasion pathway of ambient oxygen and moisture. The devices of dichlorinated NDIs exhibit good OTFT performance, even after storage in air for one and a half months. Charge transport anisotropy is observed from the dichlorinated NDI. A dichlorinated NDI with ?CH₂C₃F₇ side chains reveals high mobilities of up to 0.22 and 0.57 cm² V^?1 s^?1 in parallel and perpendicular direction, respectively, with regard to the shearing direction. This mobility anisotropy is related to the grain morphology. In addition, we find that the solution‐shearing deposition affects the molecular orientation in the crystalline thin films and lowers the d(001)‐spacing (the out‐of‐plane interlayer spacing), compared to the vapor‐deposited thin films. Core‐chlorinated NDI derivatives are found to be highly suitable for n‐channel active materials in low‐cost solution‐processed organic electronics.     

High‐Performance Top‐Gated Organic Field‐Effect Transistor Memory using Electrets for Monolithic Printed Flexible NAND Flash Memory

High‐performance top‐gated organic field‐effect transistor (OFET) memory devices using electrets and their applications to flexible printed organic NAND flash are reported. The OFETs based on an inkjet‐printed p‐type polymer semiconductor with efficiently chargeable dielectric poly(2‐vinylnaphthalene) (PVN) and high‐k blocking gate dielectric poly(vinylidenefluoride‐trifluoroethylene) (P(VDF‐TrFE)) shows excellent non‐volatile memory characteristics. The superior memory characteristics originate mainly from reversible charge trapping and detrapping in the PVN electret layer efficiently in low‐k/high‐k bilayered dielectrics. A strategy is devised for the successful development of monolithically inkjet‐printed flexible organic NAND flash memory through the proper selection of the polymer electrets (PVN or PS), where PVN/‐ and PS/P(VDF‐TrFE) devices are used as non‐volatile memory cells and ground‐ and bit‐line select transistors, respectively. Electrical simulations reveal that the flexible printed organic NAND flash can be possible to program, read, and erase all memory cells in the memory array repeatedly without affecting the non‐selected memory cells.     

Gate Capacitance‐Dependent Field‐Effect Mobility in Solution‐Processed Oxide Semiconductor Thin‐Film Transistors

Solution‐processed oxide semiconductors (OSs) used as channel layer have been presented as a solution to the demand for flexible, cheap, and transparent thin‐film transistors (TFTs). In order to produce high‐performance and long‐sustainable portable devices with the solution‐processed OS TFTs, the low‐operational voltage driving current is a key issue. Experimentally, increasing the gate‐insulator capacitances by high‐k dielectrics in the OS TFTs has significantly improved the field‐effect mobility of the OS TFTs. But, methodical examinations of how the field‐effect mobility depends on gate capacitance have not been presented yet. Here, a systematic analysis of the field‐effect mobility on the gate capacitances in the solution‐processed OS TFTs is presented, where the multiple‐trapping‐and‐release and hopping percolation mechanism are used to describe the electrical conductivity of the nanocrystalline and amorphous OSs, respectively. An intuitive single‐piece expression showing how the field‐effect mobility depends on gate capacitance is developed based on the aforementioned mechanisms. The field‐effect mobility, depending on the gate capacitances, of the fabricated ZnO and ZnSnO TFTs clearly follows the theoretical prediction. In addition, the way in which the gate insulator properties (e.g., gate capacitance or dielectric constant) affect the field‐effect mobility maximum in the nanocrystalline ZnO and amorphous ZnSnO TFTs are investigated.     

Polymer Dielectrics and Orthogonal Solvent Effects for High‐Performance Inkjet‐Printed Top‐Gated P‐Channel Polymer Field‐Effect Transistors

We investigated the effects of a gate dielectric and its solvent on the characteristics of top‐gated organic field‐effect transistors (OFETs). Despite the rough top surface of the inkjet‐printed active features, the charge transport in an OFET is still favorable, with no significant degradation in performance. Moreover, the characteristics of the OFETs showed a strong dependency on the gate dielectrics used and its orthogonal solvents. Poly(3‐hexylthiophene) OFETs with a poly(methyl methacrylate) dielectric showed typical p‐type OFET characteristics. The selection of gate dielectric and solvent is very important to achieve high‐performance organic electronic circuits.     

High‐Mobility n‐Type Organic Transistors Based on a Crystallized Diketopyrrolopyrrole Derivative

A new high‐performing small molecule n‐channel semiconductor based on diketopyrrolopyrrole (DPP), 2,2′‐(5,5′‐(2,5‐bis(2‐ethylhexyl)‐3,6‐dioxo‐2,3,5,6‐tetrahydropyrrolo[3,4‐c]pyrrole‐1,4‐diyl)bis(thiophene‐5,2‐diyl))bis(methan‐1‐yl‐1‐ylidene)dimalononitrile (DPP‐T‐DCV), is successfully synthesized. The frontier molecular orbitals in this designed structure are elaborately tuned by introducing a strong electron‐accepting functionality (dicyanovinyl). The well‐defined lamellar structures of the crystals display a uniform terrace step height corresponding to a molecular monolayer in the solid‐state. As a result of this tuning and the remarkable crystallinity derived from the conformational planarity, organic field‐effect transistors (OFETs) based on dense‐packed solution‐processed single‐crystals of DPP‐T‐DCV exhibit an electron mobility (μ_e) up to 0.96 cm² V^?1 s^?1, one of the highest values yet obtained for DPP derivative‐based n‐channel OFETs. Polycrystalline OFETs show promise (with an μ_e up to 0.64 cm² V^?1 s^?1) for practical utility in organic device applications.     

Inkjet Printed Negative Supercapacitors: Synthesis of Polyaniline‐Based Inks,Doping Agent Effect,and Advanced Electronic Devices Applications

Low frequency negative supercapacitors and high frequency negative capacitors are realized developing a polyaniline (PANI) based ink for piezoelectric inkjet printers, water based. PANI is synthesized by oxidation polymerization starting from the aniline dimer, thus avoiding the use of a toxic/mutagen substance such as aniline. In order to work in aqueous phase, the reverse addition of the dimer in the oxidative solution is made. The chlorinated emeraldine salt of PANI is produced and emeraldine base is prepared by dedoping. Two different doped PANI solutions are produced by solubilization of the emeraldine salt in dimethylsulphoxide and addition of respectively trifluorosulfonic acid and camporsulfonic acid, and then used as inks for the fabrication of inkjet‐printed tracks of different geometries. The properties of inkjet‐printed devices are characterized both in DC and AC regimes, showing very good performances under specific measurement conditions in terms of conductivity, as well as extremely interesting phenomena whose origin is still under debate, such as low frequency negative supercapacitance, high frequency negative capacitance and negative resistance. The realization of the highest negative supercapacitance realized so far, of –2.3 mF @ 30 Hz, corresponding to a specific mass capacity of –799 F g^?1, is reported.