Flexible electrical circuits printed on polymers using graphene-cellulose inks

A graphene based ink for printing passive electrical components (conductive traces, resistors, capacitors, inductors) and circuitry on mechanically flexible polymer substrates is described in this paper. The ink is synthesized by using carboxymethyl cellulose (CMC), a hydrophilic cellulose derivative, to suspend the naturally hydrophobic graphene (G) sheets in an aqueous solvent composed of 70% DI water and 30% 2-butoxyethanol. Once deposited on the functionalized substrate the conductivity of the printed electrical components can be optimized by decomposing the cellulose stabilizer using thermal reduction. Several printed passive electrical circuits are fabricated and tested including an interdigitated capacitive chemical sensor and a low-pass electrical filter. The measured characteristics of the printed circuits are compared with theoretical values for performance validation. Mechanical bending tests were also performed to demonstrate that the thermally modified G-CMC films can absorb large levels of strain without fracturing or degrading the electrical properties.