A study of strain effect on stretchable carbon nanotube gas sensors

Wearable electronics and sensors are drawing much attention with the emergence of the internet of things (IoT) and point-of-care testing (POTC) applications. Such wearable devices should be flexible and stretchable to account rather dynamic human motions. Recently, flexible and stretchable gas sensors have emerged as promising technologies to protect workers from exposure to toxic gases. This work presents a detailed study of the impact of strain on the morphology and performance of multi-walled carbon nanotube (MWCNT) based nitrogen dioxide (NO₂) gas sensors. To localize the strain effect on the CNT sensing region, rather than electrodes and support structures, we have developed a CNT gas sensor on dog-bone-shaped polydimethylsiloxane (PDMS) substrate. A tensile strain of up to 50% is applied, inducing cracks on the CNT sensing layer and thus altering the electrical resistance of sensors. In addition, a significant shift in the temperature coefficient of resistance (TCR) is observed. Under the assumption that thermally activated carriers overwhelm charge carrier scattering, the TCR of CNTs is altered when strained. Such a strain effect on NO₂ gas sensing performance is analyzed in detail. Our study could be applied to developing high-performance flexible and stretchable gas sensors.