Inkjet Printed Strain Gauges Fabricated Using AgNO3/Ethylene Glycol-Based Inks

The development of inkjet printed silver (Ag) strain gauges using particle-free inks composed of silver nitrate (AgNO3) and an ethylene glycol (EG) solvent is presented. As an alternative to thermal annealing, the fabrication process incorporates low-temperature, low-pressure Ar plasma exposure to form Ag structures from the printed ink. The effect of plasma exposure time on the gauge factor (GF) for inks composed of three forms of ethylene glycol (monoEG, diEG and triEG) that differ significantly in vapor pressure is investigated. For each solvent, the GF decreases with increasing plasma exposure time, providing a mechanism to tune the GF. With respect to solvent, the GF, surface roughness and porosity increase with decreasing solvent vapor pressure, providing a second mechanism to tune the GF. And while the highest gauge factors were observed in structures printed using inks with the lowest vapor pressure solvent (triEG), these structures lack the electrical stability required for sensing applications. However, electrically stable structures with an average gauge factor of
$\sim 6$
were produced using the diEG ink.