Study of the Electrical Contact in a Fully Inkjet Printed Membrane Switch

Inkjet printing technology is a direct writing fabrication process which demonstrated its ability to pattern a large variety of materials (metals, dielectrics and ceramics) on different substrates. This paper introduces a membrane switch fully fabricated by inkjet printing of silver nanoparticles on polyimide and polyethylene terephthalate substrates. It focuses on electrical measurements of the contact resistance between two inkjet printed silver layers. Low temperature annealing is necessary to prevent substrate damaging and to enable nanoparticles coalescence resulting in a high conductive layer. Best achieved resistivity of the printed silver layer for 150°C annealing temperature is 6 μΩ.cm, disregarding the granular microstructure and an average thickness of 570 nm. Contact resistance is probed with a four point measurement and has a value lower than 1 Ω for an actuation force of 5N. A geometrical model has been developed for a better understanding of the electrical contact in the membrane switch. The device has been tested under cold and hot switching at 5V and 10 mA. For low power applications, the membrane switch proves to be reliable for 105 mechanical actuation cycles. This work validates inkjet technology potential for electrical contact applications.