Low-Cost and Fast-Response Resistive Humidity Sensor Comprising Biopolymer-Derived Carbon Thin Film and Carbon Microelectrodes

In this study, we present a highly responsive room-temperature resistive humidity sensor based on a shellac-derived carbon (SDC) active film deposited on sub-micrometer-sized carbon interdigitated electrodes (cIDEs). This monolithic carbon-based sensor demonstrates excellent linear relationship with humidity and ohmic contact between the active carbon film and carbon electrodes, which results in low noise and low power consumption (similar to 1 mW). The active SDC film is synthesized by a single-step thermal process, wherein the temperature is found to control the amount of oxygen functional moieties of the SDC film, thereby providing an efficient means to optimize the sensor response time, recovery time, and sensitivity. This SDC-cIDEs-based humidity sensor exhibits an excellent dynamic range (0%-90% RH), a large dynamic response (50%), and high sensitivity (0.54/% RH). In addition, the two-dimensional feature (thickness similar to 10 nm) of the SDC film enables a swift absorption/desorption equilibrium, leading to fast response (similar to 0.14 s) and recovery (similar to 1.7 s) under a humidity range of 0%-70% RH. Furthermore, the thin SDC-based sensor exhibited excellent selectivity to humidity from various gases, which in combination with its fast response/recovery promises it application for an instant calibration tool for gas sensors.