Feasibility of Printing Woven Humidity and Temperature Sensors for the Integration into Electronic Textiles

We demonstrate a woven textile with an integrated humidity and temperature sensor on flexible PI substrates. We discuss the fabrication process of the smart textile and compare two methods of sensor fabrication, first conventional photo lithography and second printing using ink jet. The humidity sensor is based on a capacitive interdigitated transducer covered with a sensing layer while the temperature sensor is made of a resistive metallic meander. An encapsulation method protecting the sensors during dicing, weaving and operation has been successfully implemented. The fabricated structures are tested to bending strain, a main source of failure during the fabrication of textiles. We were able to bend bare electrodes and complete sensors down to a minimal bending radius of 100 μm without loss of functionality. The woven temperature sensor has a temperature coefficient of 0.0027 /°C for lithography made and 0.0029 /°C for printed sensors. The humidity sensor shows a repeatable behaviour in the tested humidity range between 20 to 70 %RH. The weaving process does not damage or change the behaviour of the fabricated sensors. This contribution will highlight the challenges and promises of printing and laminating processes for the large scale fabrication of smart polymeric stripes to be woven into textiles.