Fully printed field-effect transistor humidity sensor with chitosan/polyvinyl alcohol/nano carbon powder for enhanced moisture sensitivity.

With the advancement of flexible electronics, the demand for low-cost, high-performance flexible humidity sensors for wearable devices has increased significantly. However, commercial humidity sensors require complex preparation methods and are expensive. Therefore, we report polyvinyl alcohol/chitosan/nano carbon powder (PVA/CS/NCP) humidity-sensitive composite materials, which were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and contact angle measurements. A resistive humidity sensor was fabricated using screen printing, and the device showed a good response at 33%RH-98%RH humidity, and at 98 % RH, the sensor achieved a response of 1.74. A fully printed field-effect transistor (FET) humidity sensor was prepared by integrating an ion gel transistor with a CS/PVA/NCP humidity-sensitive resistor to improve the response. The comparison reveals a significant improvement in the FET humidity sensor's response, reaching 6.27 at 98 % RH. In addition, both types of sensors exhibit less hysteresis and good repeatability. Lastly, we tested the constructed humidity sensors under non-contact and variable breathing conditions, laying the groundwork for future wearable applications.