Tunable resistivity in ink-jet printed electrical structures on paper by plasma conversion of particle-free, stabilizer-free silver inks

Printable metal inks are typically composed of premade nanoparticles that require postdeposition thermal sintering to produce crystalline, electrically conductive features. In this paper, it is shown that particle-free Ag inks made from simple, water-soluble metal salts such as silver nitrate can be ink-jet printed and converted into electrical features with tunable resistivity at low temperature (<100 °C) by exposure to a pure argon plasma. X-ray diffraction confirms that the converted inks are crystalline, and four-point probe electrical measurements show that the sheet resistances are a function of the pressure and power in the plasma. From cross-sectional scanning electron microscopy analysis, it is found that the morphology of the converted silver layer becomes increasingly dense with increasing plasma treatment time, which explains the measured changes in sheet resistance, and that the thickness of the layer is ∼1.5 μm, which yields a minimum resistivity of ∼6 × 10⁻⁸ Ω m, approximately 3.8 times higher than bulk resistivity of silver. Interestingly, the resistivity can be varied over a span of 6 orders of magnitude which allows resistor-capacitor filter devices to be fabricated exhibiting varying cut-off frequencies from a single material and geometry.