Ultra-sensitive low-frequency dual-mode humidity sensor using a methyl red-PVA-graphene oxide composite

In this study, a novel ternary composite (MPG), composed of methyl red (MR), polyvinyl alcohol (PVA), and graphene oxide (GO), is synthesized and employed for the fabrication of a humidity sensor. To explore its potential for humidity sensing applications, the structural and morphological characteristics of the MPG composite were analyzed using SEM, XRD, FTIR, and UV-visible spectroscopy. The composite demonstrated a well-integrated, crosslinked microstructure enriched with functional groups and carbon-based elements, which are highly conducive to water molecule adsorption. A 678 nm thick MPG film was deposited onto an interdigitated electrode via spin coating, followed by thermal annealing at 100 °C. The sensor exhibited stable and reliable performance across a wide humidity range (32-92% RH) at 25 °C, featuring a high capacitive sensitivity of 11 nF/%RH at 100 Hz, rapid response and recovery times of 6 and 8 seconds, respectively, and a low hysteresis of 17.3%. Additionally, the electrical performance of the MPG composite film was evaluated over a voltage range of -5 to 5 V at various temperatures. Results revealed enhanced conductivity with increasing temperature, attributed to increased lattice vibrations and the generation of thermally activated charge carriers. This temperature-dependent behavior highlights the composite's suitability for use in electronic devices that operate under diverse thermal conditions. This cost-effective ternary composite-based humidity sensor shows promise for use in hygrometers and real-time relative humidity monitoring in electronic devices.