William Scheideler

The minimum flow rate scaling of Taylor cone-jets issued from a nozzle

A minimum flow rate is required to maintain steady Taylor cone-jets issued from an electrified nozzle. This letter reports that the well-known scaling law proportional to the charge relaxation time and independent of the nozzle diameter is only applicable to lowly viscous systems. For highly viscous systems with rapid viscous diffusion, the cone-jet transitional region spans a length scale comparable to the nozzle diameter; the minimum flow rate appears to be proportional to the capillary-viscous velocity and the cross-sectional area of the nozzle, but independent of the liquid conductivity.

A robust, gravure-printed, silver nanowire/metal oxide hybrid electrode for high-throughput patterned transparent conductors

High-throughput patterning and enhanced mechanical stability are key to enabling large-area applications of metal nanowire mesh transparent electrodes. In this work, hybrid transparent conductors based on silver nanowires embedded in an indium zinc oxide matrix were prepared by high-speed gravure-printing (1.0 m s−1) from a single, stable liquid precursor. These gravure-printed films demonstrate excellent conductivity (9.3 Ω □−1) and transparency (T550nm ∼ 91%), as well as robust mechanical properties. The encapsulating indium zinc oxide matrix dramatically improves adhesion, surface roughness (Rq < 5 nm), film uniformity, and thermal stability (up to 350 °C) of the embedded silver nanowires. These properties of the hybrid films make them a suitable electrode material for a variety of printed electronic devices, such as flexible OLEDs and solar cells.

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.

Understanding Thickness-Dependent Charge Transport in Pentacene Transistors by Low-Frequency Noise

Close correlation between low-frequency noise and charge transport in pentacene transistors is observed. The trap density evolving with pentacene deposition reveals transformation of growth phase and different transport mechanisms. It explains the greatly altered mobility and contact resistance in which the upper surfaces trapping plays an important role. Inspecting contact noise shows high density of traps at contacts that result possibly from pyramid like growth of pentacene or contact damage or both.

Contact Thickness Effects in Bottom-Contact Coplanar Organic Field-Effect Transistors

Influences of contact thickness on bottom-contact and bottom-gate coplanar organic transistors are studied. In transistors with poor-quality pentacene films, thick contacts improve mobility and lower contact resistance. However, in transistors with high-quality pentacene films, thick contacts significantly degrade performance by disrupting molecular self-organization at the contact edge. These results highlight the importance of contact thickness to such organic transistors and reveal that semiconductor morphology should be considered in designing devices with minimal contact effects.

High-resolution gravure printed lines: proximity effects and design rules

Gravure printing is a very promising method for printed electronics because it combines high throughput with high resolution. Recently, printed lines with 2μm resolution have been demonstrated at printing speeds on the order of 1m/s. Here we build on these results to study how more complex patterns can be printed that will ultimately lead to printed circuits. We study how the drag-out effect leads to proximity effects in gravure when multiple lines are printed close to each other. Drag-out occurs as the doctor blade passes over the roll surface to remove excess ink from the land areas in between the cells that make up the pattern. In addition to this desirable removal of excess ink, some ink from the cells also wicks up the doctor blade and is removed from the cells. This ink is subsequently deposited on the land area behind the cells leading to characteristic drag-out tails. If multiple lines, oriented perpendicular to the print direction, are printed close to each other, the ink that has wicked up the doctor blade from the first line will affect the drag-out process for subsequent lines. Here we show how this effect can be used to enhance print quality of lines as well as how it can deteriorate print quality. Important variables that will determine the regime for printing optimization are ink viscosity, printing speed, cell size, cell spacing and relative placement of lines. Considering these factors carefully allows one to determine design rules for optimal printing results.

Scalable, High-Performance Printed InOx Transistors Enabled by Ultraviolet-Annealed Printed High-k AlOx 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.

UV-annealing-enhanced stability in high-performance printed InO x transistors

We report on low-temperature additive processing methods for fabrication of high-performance InOx thin film transistors (TFTs) based on UV-annealed, printed high-k AlOx gate dielectrics. The impact of UV annealing on dielectric properties, TFT performance, and bias-stress stability is studied.

Engineering high-k La x Zr 1−x O y dielectrics for high-performance fully-solution-processed transparent transistors

Summary form only given. Metal oxide thin-film transistors based on high-k dielectrics (ZrOx, HfOx, Al2Ox) are a promising technology with attractive performance (μeff ~ 10 -100 cm2/Vs, On/Off > 107) and high transparency (80 - 90%). Solution-processed routes to oxide TFTs can potentially leverage printing technologies to enhance material utilization and throughput. However, realizing the true benefits of solution-processed oxide TFTs requires integrating dielectrics, semiconductors, and conductors that are printable and transparent. To date, there have been few reports of fully solution-processed, transparent oxide TFTs. Full oxide integration is difficult because solution-processed transparent conducting oxides (TCO), such as ITO (Tin-doped indium oxide) and ATO (Antimony-doped tin oxide), reach acceptable conductivity (100 - 1000 S/cm) only after annealing at 400°C - 500°C, while promising high-k dielectrics, such as ZrOx, crystallize at these temperatures, resulting in high leakage and poor reliability. Here, we demonstrate that doping zirconia with lanthanum can reduce leakage and improve low-frequency dispersion, resulting in a robust dielectric for printed oxide TFTs. We apply these dielectrics in ZnO TFTs, achieving mobilities > 6 cm2/Vs and On/Off ratios > 106.