Heterojunction Transistors Printed via Instantaneous Oxidation of Liquid Metals.

Semiconducting transparent metal oxides are critical high mobility materials for flexible optoelectronic devices such as displays. We introduce the continuous liquid metal printing (CLMP) technique to enable rapid roll-to-roll compatible deposition of semiconducting two-dimensional (2D) metal oxide heterostructures. We leverage CLMP to deposit 10 cm2-scale nanosheets of InOx and GaOx in seconds at a low process temperature (T < 200 °C) in air, fabricating heterojunction thin film transistors with 100× greater Ion/Ioff, 4× steeper subthreshold slope, and a 50% increase in mobility over pure InOx channels. Detailed nanoscale characterization of the heterointerface by X-ray photoelectron spectroscopy, UV-vis, and Kelvin probe elucidates the origins of enhanced electronic transport in these 2D heterojunctions. This combination of CLMP with the electrostatic control induced by the heterostructure architecture leads to high performance (µlin up to 22.6 cm2/(V s)) while reducing the process time for metal oxide transistors by greater than 100× compared with sol-gels and vacuum deposition methods.

Protocol for deposition of conductive oxides onto 3D-printed materials for electronic device applications.

Additively manufactured (AM) three-dimensional (3D) mesostructures can be designed to enhance mechanical, thermal, or optical properties, driving future device applications at the micron to millimeter scale. We present a protocol for transforming AM mesostructures into 3D electronics by growing nanoscale conducting films on 3D-printed polymers. In this generalizable approach, we describe steps to utilize precision thermal atomic layer deposition (ALD) of conducting, semiconducting, and dielectric metal oxides. This can be applied to ultrasmooth, customizable photopolymer lattices printed by high-resolution microstereolithography. For complete details on the use and execution of this protocol, please refer to Huddy et al. (2022).

Scalable, High-Performance Printed InO x Transistors Enabled by Ultraviolet-Annealed Printed High- k AlO x Gate Dielectrics.

Inorganic transparent metal oxides represent one of the highest performing material systems for thin-film flexible electronics. Integrating these materials with low-temperature processing and printing technologies could fuel the next generation of ubiquitous transparent devices. In this work, we investigate the integration of UV-annealing with inkjet printing, demonstrating how UV-annealing of high- k AlO x dielectrics facilitates the fabrication of high-performance InO x transistors at low processing temperatures and improves bias-stress stability of devices with all-printed dielectrics, semiconductors, and source/drain electrodes. First, the influence of UV-annealing on printed metal-insulator-metal capacitors is explored, illustrating the effects of UV-annealing on the electrical, chemical, and morphological properties of the printed gate dielectrics. Utilizing these dielectrics, printed InO x transistors were fabricated which achieved exceptional performance at low process temperatures (<250 °C), with linear mobility µlin ≈ 12 ± 1.6 cm2/V s, subthreshold slope <150 mV/dec, Ion/ Ioff > 107, and minimal hysteresis (<50 mV). Importantly, detailed characterization of these UV-annealed printed devices reveals enhanced operational stability, with reduced threshold voltage ( Vt) shifts and more stable on-current. This work highlights a unique, synergistic interaction between low-temperature-processed high- k dielectrics and printed metal oxide semiconductors.

Gravure-Printed Sol-Gels on Flexible Glass: A Scalable Route to Additively Patterned Transparent Conductors.

Gravure printing is an attractive technique for patterning high-resolution features (<5 µm) at high speeds (>1 m/s), but its electronic applications have largely been limited to depositing nanoparticle inks and polymer solutions on plastic. Here, we extend the scope of gravure to a new class of materials and on to new substrates by developing viscous sol-gel precursors for printing fine lines and films of leading transparent conducting oxides (TCOs) on flexible glass. We explore two strategies for controlling sol-gel rheology: tuning the precursor concentration and tuning the content of viscous stabilizing agents. The sol-gel chemistries studied yield printable inks with viscosities of 20-160 cP. The morphology of printed lines of antimony-doped tin oxide (ATO) and tin-doped indium oxide (ITO) is studied as a function of ink formulation for lines as narrow as 35 µm, showing that concentrated inks form thicker lines with smoother edge morphologies. The electrical and optical properties of printed TCOs are characterized as a function of ink formulation and printed film thickness. XRD studies were also performed to understand the dependence of electrical performance on ink composition. Printed ITO lines and films achieve sheet resistance (Rs) as low as 200 and 100 Ω/□, respectively (ρ≈2×10(-3) Ω-cm) for single layers. Similarly, ATO lines and films have Rs as low as 700 and 400 Ω/□ with ρ≈7×10(-3) Ω-cm. High visible range transparency is observed for ITO (86-88%) and ATO (86-89%). Finally, the influence of moderate bending stress on ATO films is investigated, showing the potential for this work to scale to roll-to-roll (R2R) systems.