Design and Fabrication of ZnO-Based SAW Sensor Using Low Power Homo-Buffer Layer for Enhanced Humidity Sensing

Zinc oxide (ZnO) nanostructures were proven to enhance the sensitivity performance of nanoscale ZnO-based surface acoustic wave (SAW) sensor greatly. Here, we developed ZnO sensitive layer-based SAW sensors by low power homo-buffer layer (LPHBL) method and focused on the quality of preparation, their mass sensitivity and humidity sensing applications. ZnO films were prepared on the surface of the SAW devices by radio frequency magnetron sputte ring method by employing different sputtering power. Island-shape ZnO nanostructures were successfully prepared by the simple LPHBL method. The mass sensitivities of these sensor devices based on Rayleigh wave mode and Sezawa wave mode were increased dramatically by increasing ZnO top layer thickness. To evaluate the humidity sensing performance, the humidity testing experiments were conducted for a range of moisture concentrations between 1% and 95%. The ZnO/quartz sensor without LPHBL frequency response magnitudes varied between 0-19.25 kHz and insertion loss (IL) shifts changed between 0-0.815 dB for 1%-95% RH while the ZnO/ZnO/quartz SAW sensor with LPHBL showed 0-26.25 kHz response magnitudes and 0-1.878 dB IL shifts at the same conditions. The Love-SAW sensor with LPHBL exhibited more than 36% greater humidity response sensitivity compared to its no intermediate layer counterpart. In addition, the recovery of the ZnO/ZnO/quartz humidity sensing device could reach 91.5%. Overall, the ZnO-based Love-SAW sensor fabricated by the LPHBL method may hold promise for chemical and biological detection applications.