Lithography-free, fully-printed lithium phosphate-based humidity sensors on paper as zero-waste, sustainable electronic solution

Abstract

Electronic waste management is becoming an increasing concern for the planet, especially because it is increasing at a staggering rate of twenty percent per year. Therefore, various green, reusable, sustainable, and decomposable electronic technologies are being sought after in recent times. Among these, biodegradable paper electronics have emerged as one of the most preferred and affordable solutions. Here, in this study, we demonstrate a flexible and biodegradable humidity sensor based on lithium phosphate with titanium carbide on a photo paper substrate using lithography-free, all-printing technology that combines screen printing and inkjet printing. The local acidic environment created by the addition of acetic acid to the inkjet-printable lithium phosphate ink helps in absorbing and desorbing humidity on the surface of the printed lithium phosphate film. The paper-based humidity sensor leverages excellent sensing performance for a wide range of relative humidity values, with a substantially low response time and recovery time when the relative humidity changes by an approximate amount of fifteen percent. This study paves the way for a new generation of environment-friendly, sustainable, flexible, inexpensive sensors to provide sustainable sensing solutions in various applications, such as agriculture, environment monitoring, healthcare, weather prediction, etc. © 2025 IEEE.