Electrical Characterization of Traditional and Aerosol Jet Printed Conductors Under Tensile Strain
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Electrical Characterization of Traditional and Aerosol Jet Printed Conductors Under Tensile Strain Jake Rabinowitz1,2, Gregory Fritz1, Parshant Kumar1, Peter Lewis1, Mikel Miller1, Andrew Dineen1, Caprice Gray1 1 – C. S. Draper Laboratory, Cambridge MA 2 – Northeastern University Dpt. Chemical Engineering, Boston MA ABSTRACT In this work, we propose a model to quantify strain induced conductor discontinuities based on measuring electrical resistance while applying tensile strain to metal-polymer systems. Under strain, changing conductor geometry and induced conductor discontinuity increase electrical resistance. On Kapton substrates strained to ε = .07, evaporated gold films did not deform and resistance increase was only caused by geometry change. Conversely, discontinuity caused 31% and 72% of the resistance increase in evaporated and printed silver films at the same strain. On PDMS substrates, the same magnitude of discontinuity, causing 31% of the resistance increase, occurred at only ε = .024 in evaporated silver films. At the same strain, discontinuity caused 86% of the resistance increase in evaporated gold films. Printed silver films were inelastic. The results suggest that traditional fabrication techniques may be more suitable to flexible hybrid electronics applications than additively manufactured conductors. INTRODUCTION Soft materials integration into electronic systems can lead to many new applications. Vapor-based conductor deposition requires conditions that are generally incompatible with soft materials, spurring the development of additive manufacturing techniques that hope to enable realization of flexible hybrid electronics (FHE) [1]. Aerosol jet printing is of particular interest to FHE because it enables precise deposition of any aerosolized materials onto a variety of surfaces – rigid, curved, non-uniform, flexible, elastic, and hybrid [2,3]. In order to determine their viability for many potential applications, aerosol jet printed materials must be characterized under mechanical strain that will be intrinsically present in future FHE systems. Extant research has characterized a variety of conductors on non-silicon substrates under single strain conditions. A number of studies have quantified resistance increase in metal films deposited over polymer substrates using traditional evaporation and sputtering methods [4-6]. Silver has been the most heavily characterized nontraditional material under strain, as researchers have demonstrated stretchable silver nanoparticle, microparticle, flake, and reactive inks, as well as nanowire networks [2,3,7,8]. THEORY Resistance increase as a function of strain, R(ε), is the sum of the geometric resistance increase as the conductor maintains its continuity and the resistance increase due to induced conductor discontinuities, such as cracks, buckles, or losses of adhesion. Throughout tensile
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strain, changing geometry and the rise of discontinuities alter the conductive path. The dual mechanisms are expressed below in the following equation
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