Resistivity study of inkjet-printed structures and electrical interfacing on flexible substrates

Development and evaluation of electronics with printing techniques such as inkjet printing is currently an active subject of research with various outstanding results in sensing applications. Printing technologies have shown high efficiency and compatibility with various types of inks and substrates, enhancing the opportunity for scientific innovation and research in this field. The present work reports on the evaluation of the resistivity and the sheet resistance of inkjet-printed conductive commercial Ag-nanoparticle ink, graphene ink and a custom functionalized reduced graphene oxide (f-rGO) ink on Kapton substrate using the Van-der-Pauw method. Two different approximations have been used to determine the sheet resistance (Rs) and the corresponding resistivity (ρ). The results showed differences in the extracted sheet resistance value, which emphasizes the importance of the adopted calculation method. Furthermore, in order to demonstrate the ability to fabricate printed structures with efficient electrical connection to external devices, we have evaluated standard methods for interfacing two inkjet-printed materials on Kapton substrate, namely: commercial Ag-nanoparticle ink and graphene ink. Two standard connection techniques implementing a 4-pin Flexible Printed Circuit (FPC) connector and an Amphenol Clincher connector were evaluated, along with a custom direct interconnection approach. Direct interconnection between Cu patterned tracks and printed structures attracts special interest because it addresses one of the main problems in printed electronics, which is the interfacing of the printed structure with other electronic or read-out components. Thus, the printed Ag-Graphene/Cu direct interconnection case was further investigated. Two-point [2p] and four-point [4p] measurements were performed in order to study the effect of the various probe locations of engagement to the extracted resistance. The results acquired for this interconnection method revealed the importance of the measurement probe location. To support these experimental results, FEA simulations were performed and the outcomes were consistent with the experimental findings.