Flexible Electronics and Manufacturing
This area covers aspects related to both fundamental and applied research to develop innovative, efficient, and sustainable manufacturing processes using emerging micro- and nanoscale materials for flexible electronics. Flexible and printed electronics using additive manufacturing techniques that are material-conserving and sustainable, is an important area of focus which is also well-aligned with the broader aspects of manufacturing research. These techniques are used to form devices on light-weight, conformable substrates using environmentally-friendly materials and processes, which can enable advances in areas such as wearable electronics, transparent electronics, sensors, among other things.
As an example, in work conducted in PACCAR Director’s lab, The Nanoscale Materials and Devices Lab (NMDL), Prof. Kaul’s group is conducting studies on how nozzle number, printing passes, and annealing conditions determine printed line resolution and electronic transport characteristics of the printed features. Ink-jet printing is poised to impact device manufacturing for flexible electronics, as more suitable and printable fluids become available. An important step in the preparation of an ink is the successful exfoliation and dispersion of the bulk material using chemical solvents. Commonly used solvents include N-methyl-2-pyrrolidone (NMP), N,N-dimethylacetamide (DMA) and dimethylformamide (DMF) to exfoliate layered materials such as graphene and the transition metal dichalcogenides that are well-suited for printed and flexible electronics.
Prof. Kaul’s group has successfully utilized these inks to fabricate devices such as high power resistive structures or high-performance photodetectors. Here the inks are dispersed drop-by-drop in pico-liter volumes using drop-on-demand ink-jet printing to construct macro-scale device architectures on a wide range of substrates from rigid, to flexible and transparent.
Shown above is the current versus probe distance data for a printed device illustrated in the top inset, where the 80 μm line widths span lateral lengths of more than 200 mm, validating the potential scalability of ink-jet printing compared to other approaches such as bottom-up, vapor-based synthesis techniques. Arrays of 80 μm lines are shown in the optical microscopy image on the right, where the magnified image on the far right indicates good line resolution.
In many cases, the solvents commonly used in creating dispersions for ink-jet printing are toxic, and so there is an impetus for producing more environmentally friendly options of solution dispersions for sustainability. In Prof. Kaul’s research group, efforts have been underway to successfully formulate suitable inks derived from a mixture of terpineol (T) in cyclohexanone (C) as a more environmentally friendly option for the exfoliation of bulk graphite. The image on the right shows an I–V Characteristic of graphene dispersed in different ratios of C/T that were drop-casted onto SiO2/Si substrates.
M. Michel, C. Biswas, and A. B. Kaul, “High-performance ink-jet printed graphene resistors formed with environmentally-friendly, surfactant-free inks for extreme thermal environments,” Applied Materials Today 6, 16 (2017)
M. Michel, C. Biswas, R. Hossain, C. Tiwary, P. M. Ajayan, and A. B. Kaul, “A thermally-invariant, high-power graphite resistor for flexible electronics formed using additive manufacturing,” 2D Materials Journal (IOP) 4(2), 025076 (2017).
D. Fadil, R. F. Hossain, G. A. Saenz, and A. B. Kaul, “On the chemically-assisted excitonic enhancement in environmentally-friendly solution dispersions of two-dimensional MoS2 and WS2,” Journal of Materials Chemistry C 5, 5323 (2017); DOI: 10.1039/C7TC01001J; Article selected for back cover image
Faculty Affiliated with Focus Area 1
Please note, some activities in Focus Area 2 (e.g. Sensing and Biomedical Devices) and Focus Area 3 (Energy Harvesting and Solar Cells) are also well aligned with the activities of Focus Area 1.