Buckling in serpentine microstructures and applications in elastomer-supported ultra-stretchable electronics with high areal coverage

Abstract

Lithographically defined electrical interconnects with thin, filamentary serpentine layouts have been widely explored for use in stretchable electronics supported by elastomeric substrates. We present a systematic and thorough study of buckling physics in such stretchable serpentine microstructures, and a strategic design of serpentine layout for ultra-stretchable electrode, via analytical models, finite element method (FEM) computations, and quantitative experiments. Both the onset of buckling and the postbuckling behaviors are examined, to determine scaling laws for the critical buckling strain and the limits of elastic behavior. Two buckling modes, namely the symmetric and anti-symmetric modes, are identified and analyzed, with experimental images and numerical results that show remarkable levels of agreement for the associated postbuckling processes. Based on these studies and an optimization in design layout, we demonstrate routes for application of serpentine interconnects in an ultra-stretchable electrode that offer, simultaneously, an areal coverage as high as 81%, and a biaxial stretchability as large as ~170%.

Rugged and breathable forms of stretchable electronics with adherent composite substrates for transcutaneous monitoring

“…ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms5779 systems. For a representative yield strain of 0.3% for the copper 16,17 , FEA predicts an elastic-stretchability of B60% for the electronics/UL-Sil/fabric system, which is B15 times larger than that (B4%) of an otherwise equivalent electronics/PDMS/ fabric system. Techniques based on prestrain, previously demonstrated on conventional PDMS substrates 18 , can further enhance the stretchability.…”

Toward Soft Skin‐Like Wearable and Implantable Energy Devices

“…[30] Many identical parallelogram faces were connected by 'mountain' and 'valley' creases. Depending on the difference in [24] Copyright 2013, The Royal Society of Chemistry. c) Optical images of the LIB pads and self-similar interconnects on a Si wafer.…”

“…[5] Such serpentine interconnects have much lower effective stiffness when compared to rigid active "bridge" components, which could undertake most of deformation upon stretching to ensure the functionality of the whole device. [3g] Similar to the buckling design, the serpentine interconnect can be coplanar [23] or non-coplanar [5,24] to the elastomeric substrate. Coplanar configuration enables fully bonded serpentine interconnects with stretchable substrates.…”

“…This configuration could lead to ultra-stretchable electrodes that offer biaxial stretchability up to ≈170% (Figure 3a,b). [24] In the non-coplanar bridge-island system, mechanics models of both bridge and island can guide and optimize the design of patterns. [26] For the bridge, the maximum strain ( bridge max ε ) is given by: …”

Elastic instability induced mechano-responsive luminescence for super-flexible strain sensing

“…For the emerging stretchable/super-flexible devices [1][2][3][4], substrate deformation strain could be much higher than the fracture strains of rigid materials during compressing and stretching. To avoid compromising local features such as metal interconnects and integrated transducers, different strategies have been developed, such as island-bridge and serpentine shaped interconnects [1,5] and competing growth of elastic instabilities [4,6]. This paper presents a concept in which large mechanical strain change (up to ~60% or 0.6) is transduced to optical signals switching by elastomeric substrates with microengineered materials and structural characteristics.…”