Characterization and Reliability Analysis of Direct-Write Additively Printed Flexible Humidity Sensor With Super Capacitive Material for Wearable Astronaut Sensor in Harsh Environments

Using additive technologies to fabricate printed circuit boards eliminates the need for expensive manufacturing - software-based design and production permit production flexibility, as well as quicker tool modifications and design evolution. In addition, additive printing techniques can be applied to various surfaces and shapes. This adaptability to a wide range of applications enables the construction of novel applications, such as biosensors, by designers. Several previous studies have focused on developing additively printed humidity sensors because of their potential for flexibility and integration. Flexure in the operating environment has been known to cause performance degradation in prior generations of temperature and humidity sensor technologies. This study uses the direct write printing method with a nScrypt printer to print the humidity sensor. Characterization of the sensor has been done by studying the process-performance interactions of temperature coefficient to resistance and sensitivity to humidity. Sensor accuracy, hysteresis, repeatability, linearity, and stability have been quantified concerning printing recipe and encapsulation. A folding reliability test has been conducted to assess the viability of the sensor in operation to mimic real-life use conditions. The cyclic folding motions are administered every 13 seconds with the same folding diameter and travel distance on every three samples, with single trace and multi-trace sensing materials and trace with polyimide encapsulation. Furthermore, chemo-electrical measurement with cyclic voltammetry method has been conducted to assess water possession under high humidity conditions. It is found that encapsulation might help improve the humid and mechanical reliability of the additively printed humidity sensor.