Design, fabrication and characterization of capacitive humidity sensors based on emerging flexible technologies

Abstract

This work presents a case-based comparison between two emerging fabrication techniques for the development of conductive patterns for flexible electronics: inkjet-printing and nanographene production by laser-scribing. In particular, these two methods are used to fabricate planar interdigitated electrode (IDE) capacitors with Kapton® HN polyimide as supporting flexible substrate. Silver-based electrodes are manufactured by inkjet-printing, while a laser-scribing technique is used to obtain laser-reduced graphene oxide (laser-rGO) patterns from deposited graphene oxide (GO) and laser-induced graphene (LIG) layouts from the bare polyimide substrate. The comparison is focused on the application of these IDE capacitors as relative humidity (RH) sensors. The different sensors are benchmarked in terms of sensitivities to RH as well as thermal drift and linearity considering frequency dependencies. The results show that the manufactured capacitors exhibit a very competitive performance as capacitive structures when compared with other similar capacitive sensors from the literature. Furthermore, inkjet-printed and LIG-based capacitors stand out for its thermal stability and linearity.