uniform, continuous and dense layers and is thus more suitable for printed TFTs with larger channel dimensions. Several precursor routes for solution-processed metal-oxide semiconductor layers based on metal alkoxides, [ 14,15 ] and on metal salts such as acetates, nitrates, and chlorides have been reported. [ 16,17 ] Precursors based on metal nitrates have been shown to convert into metal oxides generally at lower temperatures than acetateor chloride-based precursors. [ 17,18 ] In contrast to metal alkoxides, metal nitrates are less sensitive to air humidity and can be processed via an aqueous precursor route. [ 7 ] Based on these advantages, metal nitrates show promise as potential precursor materials for printed low-temperature-processed metal-oxide semiconductors. A large amount of work has concentrated on lowering the conversion temperature of the precursor solutions to semiconducting metal-oxide layers. Functional TFTs have been obtained at ≈200 °C or below (1) via the careful design of precursor chemistry utilizing metal alkoxides with controlled hydrolysis, [ 14,15 ] combustion process, [ 11,19 ] or the addition of oxidizing agents, [ 20 ] (2) via the use of additional energy in conversion such as various wavelengths of UV light, [ 8,15,21 ] or microwaves, [ 22 ] or (3) by employing conditions during annealing that promote effi cient precursor conversion such as ozone or vacuum. [ 6,7,20 ] After the fi rst report on inkjet-printed metal oxide layers from metal chloride precursors by Lee et al. in 2007, [ 16 ] the deposition of metal-oxide semiconductor layers for TFTs has been successfully performed via several printing techniques. [ 4 ] In addition to inkjet-printing, [ 12,16,17,19,23 ] metaloxide TFTs have been fabricated with electrodynamic-jet, [ 24 ] spray pyrolysis, [ 9 ] gravure (glass substrate, 550 °C annealing), [ 25 ] and fl exographic printing (Si wafer, 450 °C annealing). [ 26 ] The inkjet, electrodynamic jet, and spray pyrolysis techniques are typically utilized in noncontact sheet-to-sheet batch processes while the contact gravure and fl exographic printing are readily available also as continuous high-throughput roll-to-roll processes. Also novel combinations of conventional vacuum processes and techniques well known from the fi eld of printing have been proposed to prepare metal-oxide TFTs on fl exible substrates such as inkjet-printed growth inhibitors for the patterning of atomic-layer-deposited (ALD) metal-oxide layers, [ 27 ] and transferring of vacuum-processed functional TFTs from rigid to fl exible substrates by a roll-transfer method. [ 28 ] The previous results clearly indicate the challenges in the processability of materials that need to be overcome to enable large-area electronics fabrication using the industrial high-throughput additive printing processes on fl exible low-cost substrates.In this work, for the fi rst time, the metal-oxide TFT fabrication process was performed on fl exible substrate using process technologies that are roll-to-roll-compatible and industrially...

We propose a combined far ultraviolet (FUV) and thermal annealing method of metal-nitrate-based precursor solutions that allows efficient conversion of the precursor to metal-oxide semiconductor (indium zinc oxide, IZO, and indium oxide, In2O3) both at low-temperature and in short processing time. The combined annealing method enables a reduction of more than 100 °C in annealing temperature when compared to thermally annealed reference thin-film transistor (TFT) devices of similar performance. Amorphous IZO films annealed at 250 °C with FUV for 5 min yield enhancement-mode TFTs with saturation mobility of ∼1 cm2/(V·s). Amorphous In2O3 films annealed for 15 min with FUV at temperatures of 180 °C and 200 °C yield TFTs with low-hysteresis and saturation mobility of 3.2 cm2/(V·s) and 7.5 cm2/(V·s), respectively. The precursor condensation process is clarified with x-ray photoelectron spectroscopy measurements. Introducing the FUV irradiation at 160 nm expedites the condensation process via in situ hydroxyl radical generation that results in the rapid formation of a continuous metal-oxygen-metal structure in the film. The results of this paper are relevant in order to upscale printed electronics fabrication to production-scale roll-to-roll environments.

The inkjet-printing process of precursor solutions containing In nitrate dissolved in 2-methoxyethanol is optimized using ethylene glycol as a cosolvent that allows the stabilization of the droplet formation, leading to a robust, repeatable printing process. The inkjet-printed precursor films are then converted to InO semiconductors at flexible-substrate-compatible low temperatures (150-200 °C) using combined far-ultraviolet (FUV) exposure at ∼160 nm and thermal treatment. The compositional nature of the precursor-to-metal oxide conversion is studied using grazing incidence X-ray diffraction (GIXRD), X-ray reflectivity (XRR), and Fourier transform infrared (FTIR) spectroscopy that indicate that amorphous, high density (up to 5.87 g/cm), and low impurity InO films can be obtained using the combined annealing technique. Prolonged annealing (180 min) at 150 °C yields enhancement-mode TFTs with saturation mobility of 4.3 cm/(Vs) and ∼1 cm/(Vs) on rigid Si/SiO and flexible plastic PEN substrates, respectively. This paves the way for manufacturing relatively high-performance, printed metal-oxide TFT arrays on cheap, flexible substrate for commercial applications.

Lately, printed oxide electronics have advanced in the performance and low‐temperature solution processability that are required for the dawn of low‐cost flexible applications. However, some of the remaining limitations need to be surpassed without compromising the device electronic performance and operational stability. The printing of a highly stable ultra‐thin high‐κ aluminum‐oxide dielectric with a high‐throughput (50 m min−1) flexographic printing is accomplished while simultaneously demonstrating low‐temperature processing (≤200 °C). Thermal annealing is combined with low‐wavelength far‐ultraviolet exposure and the electrical, chemical, and morphological properties of the printed dielectric films are studied. The high‐κ dielectric exhibits a very low leakage‐current density (10−10 A cm−2) at 1 MV cm−1, a breakdown field higher than 1.75 MV cm−1, and a dielectric constant of 8.2 (at 1 Hz frequency). Printed indium oxide transistors are fabricated using the optimized dielectric and they achieve a mobility up to 2.83 ± 0.59 cm2 V−1 s−1, a subthreshold slope <80 mV dec−1, and a current ON/OFF ratio >106. The flexible devices reveal enhanced operational stability with a negligible shift in the electrical parameters after ageing, bias, and bending stresses. The present work lifts printed oxide thin film transistors a step closer to the flexible applications of future electronics.

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Reverse‐offset printing (ROP) is a novel printing technique capable of forming electronics‐industry‐relevant linewidths (≈1 µm) with good thickness control and sharp edge definition. It is demonstrated that through a controlled oxygen‐plasma treatment, the energy of the surfaces related to the process steps of ROP can be optimized to allow the patterning of metal‐oxide semiconductor layers using a simple printing ink based on metal nitrates dissolved in an organic solvent. The steps of the ROP process are analyzed using surface‐energy measurements and Fourier transform infrared spectra of the ink during drying. Thin‐film transistors (TFTs) fabricated using a roll‐to‐plate ROP of In2O3 semiconductor and evaporated Al source/drain (S/D) contacts show, on average, mobilities of 3.1 and 3.5 cm2 V−1 s−1, and ON/OFF‐ratios up to 108 and 107 on a Si/SiO2 substrate and on a flexible polyimide‐type substrate, respectively. TFTs on the flexible substrate with also the S/D‐contacts printed with ROP using Ag nanoparticle ink exhibit a 1.4 cm2 V−1 s−1 mobility. To demonstrate the scalability of the process, continuous lines of In2O3 are printed using a roll‐to‐roll‐compatible (R2R) ROP with linewidths down to ≈2 µm. This process is expected to lead to miniaturized metal‐oxide circuits as required by flexible high‐resolution sensor arrays and displays.

Room temperature substrate-facilitated sintering of nanoparticles is demonstrated using commercially available silver nanoparticle ink and inkjet printing substrates. The sintering mechanism is based on the chemical removal of the nanoparticle stabilizing ligand and is shown to provide conductivity above one-fourth that of bulk silver. A novel approach to attach discrete components to printed conductors is presented, where the sintered silver provides the metallic interconnects with good electrical and mechanical properties. A process for printing and chip-on-demand assembly is suggested.

Engineering of an In2O3 semiconductor and Ag source/drain interface in inkjet-printed thin-film transistors enhances the saturation mobility by two orders of magnitude.