Hydrophilicity modulation of surface acoustic wave resonators for high-performance humidity sensing

Humidity sensing is of great importance in monitoring moisture levels in the air, which directly impacts health, safety, comfort, and industrial processes. However, current humidity detection technologies still fall short in meeting the requirements of higher-end applications. In this work, high-performance humidity sensors were developed by tuning the hydrophilicity and hydrophobicity of polymer blends composed of PVP, PEG, and PVDF, which were integrated onto the surface of surface acoustic wave (SAW) resonators. By carefully adjusting the blend ratio, a porous and layered nanostructure was achieved, significantly enhancing humidity sensing performance. The optimized sensors exhibited a rapid response time of 2.2 s, a short recovery time of approximately 1.2 s, and a large frequency shift of up to 14 MHz under 15-98% RH. In addition, the devices maintained stable operation for over 2000 seconds with negligible hysteresis, outperforming commercial counterparts in both sensitivity and response speed. These results demonstrate the great potential of the proposed sensor design for future applications requiring fast, accurate, and reliable humidity sensing.