Fabrication of Elastomeric Wires by Selective Electroless Metallization of Poly(dimethylsiloxane)

Abstract

This Communication describes a simple, low-cost method of fabricating mechanically flexible, patterned metal films for use in lightweight, flexible electronic devices such as conformal displays and wearable electronics, and in bioelectronic devices such as sensors and artificial nerves, skins and muscles. Our method uses microcontact printing to define a chemical pattern on an elastomeric substrate (poly(dimethylsiloxane) (PDMS)); this pattern directs the deposition of metal on the PDMS surface from an electroless deposition (ELD) solution. Using microcontact printing for pattern formation instead of conventional photolithography and selective ELD to deposit the metal films instead of physical vapour deposition (PVD) simplifies the fabrication procedure and significantly reduces fabrication costs. We demonstrate the process by fabricating patterned copper films on PDMS surfaces with minimum feature sizes of 2 lm over substrates that are 2-3 cm 2 . These metal-elastomer composites can withstand linear strains of up to 52 % without a loss of conductivity and function as conformable electrical contacts in an organic lightemitting device (OLED).Integrating metals with elastomers is an effective way to create flexible conductors. PDMS is often the elastomer of choice because it is commercially available, electrically insulating, durable, and biocompatible. Embedding conductive particles such as carbon nanotubes or carbon black in PDMS is a simple method to make conductive, flexible interconnects, but these composites suffer from low conductivity relative to metal.[1] Both high conductivity and mechanical flexibility result from microfabricating metal wires on the surface of PDMS or enclosing electroplated wires in PDMS. Stretching these composites fractures the metal films and interrupts the flow of current. The conductivity returns with the resumption of metal-metal contact at the fracture site when the strain is released. [2,3] The amount of linear strain that the metal-elastomer composite can withstand before a loss of conductivity depends on the shape of the metal film: Lacour et al. reported that stretching the PDMS substrate by 25 % before depositing the metal wires caused undulations perpendicular to the PDMS surface to form in the gold film and yielded wires that remained conductive when stretched up to 100 % linear strain; [2a] PDMS substrates that had not been prestretched failed at 23 % linear strain.[2b] Gray et al. used tortuous wire geometries to maximize the strain: whereas linear wires lost their conductivity at 2.4 % strain, tortuous wires remained conductive at strains up to 54 %.[3]The unresolved problem with patterned metal-elastomer composites is the cost and complexity associated with depositing and patterning the metal films. Fabrication strategies generally rely on PVD of metals and photolithography, both of which are slow processes that bear high capital and operating expenses and require specialized equipment. For example, Gray et al. [3] and Maghribi et al. [4] both used electroplating to f...

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