Photolithographic structuring of stretchable conductors and sub-kPa pressure sensors

Abstract

This paper presents a novel method to prepare stretchable conductors and pressure sensors based on the gold/polydimethylsiloxane (PDMS) system. The gold films were sputtered onto structured PDMS surfaces produced with a photolithographic surface treatment with the aim of reducing tensile strains in the gold film. Scanning electron microscopy (SEM) and atomic force microscopy analyses showed that these 3D patterns reduce cracks and delaminations in the gold film. Electrical measurements indicate that the patterns also protect the films against repeated tensile cycling, although the un-patterned samples remained conducting as well after the completion of 120 cycles. The extrapolated resistivity value of the patterned sample (4.5 × 10−5 Ωcm) compares well with previously published data. SEM micrographs indicate that the pattern features deflect the cracks and therefore toughen the gold film. However, x-ray photoelectron spectroscopy and contact angle analyses indicate that the patterning process also slightly modifies the surface chemistry. This patterning method was used to prepare capacitive strain gauges with pressure sensitivity (ΔZ/Z)/P of 0.14 kPa−1 in the sub-kPa regime. Such stretchable and potentially conformal low-pressure sensors have not been produced before and could prove advantageous for many smart fabric applications.