Mass production of flexible printed temperature sensors

Abstract

In this report we describe a material set and method for the fabrication of all-printed thermistors on flexible substrates. The development of these devices has been driven by concern around eventual mass production, and as such we demonstrate both scale up of the active temperature sensitive ink, and fabrication of the thermistors in an industrial environment using production class equipment. The temperature sensitive material used is a paste made from a blend of metal oxide particles and a eutectic alloy. This ink can be reliably printed using screen-printing and is processed at temperatures lower than 150 C, making it compatible with low-cost plastic substrates. Complete devices, fabricated in air on a PET film using screen-printed conductive silver contacts, show a resistivity of about 100 k cm, and a greater than 1% change in resistance per degree Celsius between 20 and 70 C. Encapsulation of these devices with a flexible film was necessary in order to prevent moisture absorption which causes the resistance values to drift over time. Remaining issues for the commercialization of such printed sensors will also be discussed, as will the incorporation of these thermistors into more complex integrated systems containing other printed electronic components.