Laser sintering of printed silver thin films for fabrication of strain sensors directly on a structure

Abstract

Piezoresistive strain sensors, commonly known as resistance strain gauge, have many important applications. In this work, an alternative method to fabricate piezoresistive strain sensors directly on the structure of interest is demonstrated using a particle-free silver ink as the sensing material. The sensing material is first printed as a rectangular film on the structure of interest and a conductive serpentine pattern is generated by selective laser sintering. Only the material exposed to the focused laser is sintered and becomes conductive. The rest is washed-off by 1-dodecene solvent, leaving only the serpentine pattern, which serves as the piezoresistive strain sensor. This alternative method eliminates the need for a carrier or backing substrate and thus improves the mechanical coupling between the sensing material and the structure of interest. It also removes reinforcement effect due to the stiffness of the carrier substrate. Results from electrical characterization revealed that laser sintering power is a crucial parameter that influences fundamental properties of the sensing material such as electrical conductivity and work function. In addition, it was observed that there exists an optimum laser sintering power that results in a maximum gauge factor (GF). For strain sensors, the GF is the most important parameter because it is the measure of sensor sensitivity. When the particle-free silver ink was printed as a serpentine pattern followed by thermal sintering on a hot plate, a lower GF was measured. This shows that the alternative method to fabricate piezoresistive strain sensors is more attractive than printing the serpentine pattern then thermally sintering it.