Ultrathin and Ultrasensitive Printed Carbon Nanotube-Based Temperature Sensors Capable of Repeated Uses on Surfaces of Widely Varying Curvatures and Wettabilities

In this paper, we demonstrate the ability to fabricate temperature sensors by using our newly developed carbon nanotube–graphene oxide (CNT-GO) ink to print temperature-sensitive traces on highly flexible, thin, and adhesive PET (polyethylene terephthalate) tapes, which in turn are integrated on surfaces of different curvatures and wettabilities. Therefore, the strategy provides a facile, low-cost, and environmentally friendly method to deploy printed temperature sensors on surfaces of widely varying curvatures and wettabilities. The temperature sensing occurs through a thermally induced change in the resistance of the printed traces and we quantify the corresponding negative temperature coefficient of resistance (α) for different conditions of curvatures and wettabilities. In addition, we identify that at low temperatures (below 15 °C), the printed traces show an α value that can be as large (in magnitude) as 60 × 10–3/°C, which is several times higher than the typical α values reported for temperature sensors fabricated with CNT or other materials. Furthermore, we achieve the printing of traces that are only 1–3 μm thick on a 50 μm-thick PET film: therefore, our design represents an ultrathin additively fabricated temperature sensor that can be easily integrated for wearable electronic applications. Finally, we show that despite being subjected to repeated temperature cycling, there is little degradation of the CNT-GO microarchitectures, making these printed traces capable of repeated uses as potential temperature sensors.