Highly stretchable wrinkled gold thin film wires

Abstract

With the growing prominence of wearable electronic technology, there is a need to improve the mechanical reliability of electronics for more demanding applications. Conductive wires represent a vital component present in all electronics. Unlike traditional planar and rigid electronics, these new wearable electrical components must conform to curvilinear surfaces, stretch with the body, and remain unobtrusive and low profile. In this paper, the piezoresistive response of shrink induced wrinkled gold thin films under strain demonstrates robust conductive performance in excess of 200% strain. Importantly, the wrinkled metallic thin films displayed negligible change in resistance of up to 100% strain. The wrinkled metallic wires exhibited consistent performance after repetitive strain. Importantly, these wrinkled thin films are inexpensive to fabricate and are compatible with roll to roll manufacturing processes. We propose that these wrinkled metal thin film wires are an attractive alternative to conventional wires for wearable applications. Rapid growth in the fields of flexible electronics and wearable technology has created a surge of research into new materials and component designs in an effort to create electronics better suited for the human body.1-6 Therefore, there is a critical need to develop wires that can withstand repeated large strains and can be manufactured into discreet, low cost, and dense arrays. Unlike traditional electronics which are planar and rigid, these new electrical components must conform to curvilinear surfaces and stretch with the body. These components, especially for body-worn consumer and medical applications, must also endure frequent exposure to moisture as well as large strains while maintaining favorable electronic properties. Conductive wires that exhibit constant conductivity under high dynamic strains are of great interest.5 Such a stretchable wire would find application in many wearable systems because they would be used to electronically interface multiple components. Additionally, stretchable conductive wires can provide mechanical isolation for rigid components worn on the body where there is not yet a stretchable substitute. Active areas of research for creating these wires can be categorized into developing new composite materials, liquid metals, and mechanical design optimization of metal thin films.In developing stretchable wires, one of the active areas of research has been in developing new electronic materials that are able to withstand strains greater than that of metal thin films, which are known to have fracture limits of around 1% strain.7 For example, Chun et al. have shown that by mixing a silver nanoparticle and multi-walled carbon nanotube composite (Ag-MWNT) with polyvinylidenefluoride (PVDF), they were able to develop an elastic conductor with conductivities of up to 5710 S cm À1 at 0% strain and 20 S cm À1 at 140% strain. 8 Lee et al. have developed a highly transparent graphene and silver nanowire hybrid structure with a sheet resistance of 33 X/sq th...

Highly Flexible Wrinkled Carbon Nanotube Thin Film Strain Sensor to Monitor Human Movement

“…As deposited planar CNT thin film on PS is shown in Figure a. After heat induced shrinkage, the CNT thin film buckled and created self‐similar wrinkled structures similar to those previously shown in metal thin films . The CNT thin films wrinkle because each individual CNT is entangled and weakly adhered to each other via van der Waal forces resulting in one thin film as opposed to an assortment of individual CNTs.…”

Flexible Piezoresistive Pressure Sensor Using Wrinkled Carbon Nanotube Thin Films for Human Physiological Signals

“…In addition to being robust and unobstrusive, they must be mechanically flexible and stretchable while maintaining high pressure sensitivities and quick response times. Much effort to date have been directed toward developing novel materials and design configurations to improve mechanical robustness and performance in wearable sensors . Researchers have reported various transduction mechanisms to detect physical pressure changes including: piezoelectric, capacitance, and piezoresistive .…”

“…As shown in Figure , a CNT thin film was deposited onto a polystyrene (PS) substrate using a spray gun deposition method. PS is a shape memory polymer that is able to shrink (≈67% in area) back to its original shape when induced with an external stimulus such as heat . When the PS was heated pass its glass transition temperature (100 °C), the PS shrunk causing the CNT thin film to buckle and form highly self‐similar wrinkled structures.…”

Stint

“…We deployed a soft flexible capacitive pressure sensor that utilizes nano-structured wrinkled Au thin films (similar to Kim et al [12] [13]). The wrinkled Au structures provide robust integration with the underlying polymeric substrate allowing the thin film to withstand mechanical deformation, while maintaining electrical performance.…”