Testing and characterization of different papers as substrate material for printed electronics and application in humidity sensor

The use of papers as substrates in the process of manufacturing flexible electronic components is urgently required to obtain cost-effective products as well as to expand the potential applications of such components. This study aimed to examine the suitability of three different types of paper for sensor applications using an inkjet printing process. Three types of paper (denoted as Types 1, 2, and 3) designed for specific applications in printed electronics were selected and entirely characterized in terms of microscopic and macroscopic properties, such as internal fibers structure, cross-sectional layer structure, surface roughness, and hardness. Dot arrays were printed on these three types of paper to determine how the papers absorb silver ink and which one is the best substrate for manufacturing printed electronic components. After a comprehensive analysis, the paper that exhibited the best feature was further studied as a substrate for printing interdigitated electrodes to develop a humidity sensor. The Type 2 paper-based sensor demonstrated the variation in capacitance in the range from 9.4 to 10.6 pF while changing the relative humidity (RH) from 40 to 90%. Thus, Type 2 has the great potential for application in flexible sensors, suggesting the possibility of industrial scalability and mass production of inexpensive, biodegradable, and conformable electronic components.