Permeable Thermistor Temperature Sensors Based on Porous Melamine Foam

Abstract

Flexible sensors and electronics have gained much attention in recent years. They are especially interesting due to their abilities to conform to static and dynamic surfaces while keeping their functionality. These characteristics make them relevant for a wide range of applications, from health care and fitness monitoring to soft robotics. In this work, we go beyond simple mechanical flexibility and present a lightweight and permeable flexible sensor utilizing melamine foam as a substrate. The foam is coated with metallic copper (Cu) and semiconductive Indium-Gallium-Zinc-Oxide (InGaZnO) to form a thermistor-type temperature sensor. The sensor showed a very stable response when cycling the temperature between 25 °C and 51 °C, exhibiting a maximum sensitivity of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-01.6 \%^{\circ }\mathrm{C}^{-1}$</tex-math></inline-formula> , a permeability of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$366.6\,{\rm g\,m^{-2}\,h^{-1}}$</tex-math></inline-formula> at 24 °C, and a maximum resistance variation of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$-2.9\%\mathrm{RH}^{-1}$</tex-math></inline-formula> when varying the relative humidity from 40% to 70%. The device also remained fully functional even after being bent to a radius of 5 mm.