Design and performance of metal conductors for stretchable electronic circuits

Abstract

PurposeThe purpose of this paper is to present an update on the progress of the design and reliability of stretchable interconnections for electronic circuits.Design/methodology/approachFinite element modelling (FEM) is used to analyse the physical behaviour of stretchable interconnects under different loading conditions. The fatigue life of a copper interconnect embedded into a silicone matrix has been evaluated using the Coffin‐Manson relation and FEM.FindingsThe mechanical properties of the substrate and the design of the metal interconnection play an important role on the fatigue lifetime of circuit. In the case of copper embedded into a PDMS Sylgard 186, more than 2,500 tensile cycles have been observed for a periodic deformation of 10 per cent.Research limitations/implicationsReliability results are limited and need further work to create a more accurate empirical model to estimate the lifetime of stretchable interconnections.Originality/valueThe combined use of FEM and experimental analysis enable a more reliable design of the stretchable metal interconnections. The proposed horseshoe design offers the benefit of reduced permanent damage during elongation.

Indium Tin Oxide (ITO) serpentine ribbons on soft substrates stretched beyond 100%

“…Cracks are also expected to first appear near the crest based on the FEM results of substratebonded serpentines [23,36,41]. If we differentiate the strain-to-rupture before delamination and after delamination to be bonded and debonded strain-to-rupture, it can be concluded that for narrow serpentines, strain-to-debond is smaller than bonded strain-to-rupture but wide ribbons exhibit smaller bonded strain-to-rupture than strain-to-debond.…”

“…For example, a filamentary serpentine network of gold with vanishing rigid islands has enabled mechanically invisible electronic tattoos to be intimately integrated with human skin for non-invasive electrophysiological, thermal, and hydration sensing [14][15][16][17], as well as wearable soft antenna for wireless communication [18]. The mechanics of metallic serpentines has also been studied extensively through both experimental [8,[19][20][21] and theoretical/numerical means [22][23][24][25][26].…”

Elastomeric substrates with embedded stiff platforms for stretchable electronics

“…Despite the latest demonstrations of stretchable circuits, this hard-onsoft, pixelated design suffers from large strain concentration at the rigid-to-elastic transition zones, which often limits the long-term performance of the stretchable circuit. 8 Here we introduce an alternative approach where the pixelated circuits are manufactured directly onto a planar but mechanically engineered heterogeneous elastic substrate. We further present the associated design rules to produce stretchable circuitry.…”

“…Active device materials are first deposited and patterned on a rigid or plastic substrate, which in turn is machined into a thin mesh defining the rigid nodes, and subsequently transferred onto the elastic matrix. Complex wiring technology, based on thick composite elastomers, 7 2D, 8 or 3D 10 meandering structures, is required to interconnect electromechanically the stiff nodes. Despite the latest demonstrations of stretchable circuits, this hard-onsoft, pixelated design suffers from large strain concentration at the rigid-to-elastic transition zones, which often limits the long-term performance of the stretchable circuit.…”

Three-dimensionally deformable, highly stretchable, permeable, durable and washable fabric circuit boards

“…Microcracked gold film on the PDMS substrate, created by thermal expansion mismatch, endured 25 000 cycles at 20% strain, while increasing its electrical resistance by 300% [100]. Horseshoe copper film embedded in the PDMS substrate, with a fatigue life of 2500 cycles at 10% strain, was capable of being stretched up to 56% strain with an increment of 2.1% in its electrical resistance [101]. Controlled wrinkling semiconductor nanoribbons on the PDMS substrates, from thin silicon ribbon with a wavy shape [84,85], to a pop-up pattern [83,102,103], non-coplanar mesh [86,89], as well as non-coplanar mesh with serpentine bridges [90][91][92], have increased their stretchability from 10% to 140% owing to the outof-plane deflection in thin layers, thereby accommodating strains applied in the plane.…”