Electrical Characterization of Traditional and Aerosol Jet Printed Conductors Under Tensile Strain

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.

Materials, Mechanics, and Patterning Techniques for Elastomer-Based Stretchable Conductors

“…Besides, stencil printing and screen printing are employed to pattern features that do not require high complexity and superfine resolution [ 19 , 20 , 21 ]. With the development of additive manufacturing, direct printing emerges as an alternative to the conventional subtractive patterning method [ 14 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ]. Transfer printing generally means to transfer functional materials from one substrate to another.…”

“…Owing to the development of additive manufacturing, conductive inks can be directly printed on various substrates without physical contact. Various printing techniques, including laser-aided direct writing [ 22 ], ink-jet printing [ 23 , 24 , 25 , 26 ], and aerosol-jet printing [ 14 , 27 , 28 , 29 , 30 ] have been developed for printed electronics. The maskless processes are well suited for rapid prototyping.…”

“…Besides the adhesion issue, many other problems, such as the swelling [ 62 ], thermal hardening, and large thermal expansion of the elastomers, still exist in the direct printing of conductive inks [ 26 ], resulting in poor performance of printed stretchable conductors. Cracking [ 26 , 31 ] and low stretchability are some of the resulting issues found in printed stretchable conductors [ 14 ]. As an example, Figure 6 d shows the morphologies of ink-jet-printed silver track on PDMS before and after sintering, after bending, and after re-sintering [ 26 ], in which the silver track cracked as a result of the thermal expansion problem.…”

“…Due to their high stretchability, elastomeric materials are commonly chosen as the supporting substrate or matrix for stretchable conductors and integrated device systems. Along with the traditional metallic conductors [ 1 , 12 , 13 , 14 ], several research groups have focused on developing conductive nanomaterials, including silver nanowires (AgNWs) [ 15 ], carbon nanotubes (CNTs) [ 16 ], etc. A substantial amount of work has been done to combine the rigid, brittle conductors with the flexible and soft elastomers, and overcoming the mismatches between their elastic behaviors.…”

“…Patterning the conductors is one of the key techniques for the successful fabrication of stretchable electronic devices. The common patterning techniques for stretchable conductors include lithography [ 17 , 18 ], screen/stencil printing [ 19 , 20 , 21 ], direct printing [ 14 , 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 , 30 , 31 ], and transfer printing [ 32 , 33 , 34 ]. The patterning methods used in wafer-based electronics have also been adopted in stretchable electronics.…”