Abstract
Most formulations of metal inks comprise of a suspension of nanoparticles however, these suffer when printed by the formation of unwanted agglomeration. The exploration and optimisation of particle-free silver-complex ink is causing a strong demand for inkjet printing of these formulations over nanoparticle-based suspension inks. This is due to the enhanced printability and rapid conversion via thermal reduction into a conductive material, which can be utilised in electronics manufacture. We developed a silver-complex ink for ‘smart-clothing’ through inkjet printing. The high-quality printing - characterised by no satellite droplet formation and fast speed - is demonstrated upon polyester fabric by the formation of electrical circuitry using a thermal reduction process. Fabric printing is limited by good metal coverage and adhesion, which we demonstrate and improve on in the work by the application of a low temperature, atmospheric air plasma pre-treatment to the polyester surface, which improves printed silver density and coverage using a plasma device which is easy to operate and economic. Printed silver layer reduction and film crystallinity is characterised from high resolution scanning electron microscopy, and spectroscopy (Ultraviolet-visible and Raman) detailing growth mechanisms for high track feature conductivity, producing a low sheet resistivity of 1.378 ± 0.001 Ω/□ and by the lighting of a 1.9 V, 250 mA Light Emitting Device, highlighting its application for conductive features processing. • Conductive films on PET fabric. • Ink jet printing particle-free silver-complex ink. • Conductive thin Ag films, 1.378 ± 0.001 Ω/□. • Enhancement of printed density and coverage by atmospheric plasma pre-treatment.
Highlights
Within the last decade considerable developments have occurred in the fabrication of wearable electronics
Before printing the properties of the ink were evaluated from measurements of a droplet of ink of area 10 ± 0.5 mm2 suspended from a syringe including its surface tension, as see Fig. 1A
The viscosity and density of the ink was measured as 12 mPa.s and 1.1415 g/mL, respectively and using these values the Z number of the ink was evaluated as 2.14, which is within an acceptable range for inkjet printing (1− 10) [20]
Summary
Within the last decade considerable developments have occurred in the fabrication of wearable electronics. The formation of Ag metal features from printed ink is possible by reduction, which can be achieved either chemically, optically, by high energy radiation, or thermally [4,7]. Air plasma has been shown to be more efficient at wetting PET than oxygen-containing argon or helium plasma treatments, due to the more rapid reactions occurring between the oxygen species and the created radicals on the surface [17] For these reasons, an investigation was performed looking to improve the wettability of the reduced particle-free Ag printed ink using an at mospheric air plasma treatment of the PET fabrics. The evaluation of thermally reduced printed Ag quality and crystallinity on different thickness PET samples was conducted using electron and optical microscopes, and spectro scopic techniques (Ultraviolet-visible (UV–vis), Raman); and deposit composition and uniformity by Energy Dispersive X-ray (EDX). The deposit adhesive and electrical properties due to the application of plasma treatment were evaluated using the so-called “Scotch tape” test [16], four-point probe measurements and the demonstration of the lighting of a light emitting device (LED) using the printed features
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