ROMJIST Volume 29, No. 2, 2026, pp. 191-200, DOI: 10.59277/ROMJIST.2026.2.08
Monica NEDELCU, Dan VASILACHE, Florin NASTASE, Alexandra NICOLOIU, Claudia NASTASE, Ioana ZDRU, George BOLDEIU, Adrian DINESCU, Alexandru MÜLLER Sensing Performance of Dual-Mode SAW Humidity Sensors on ScAlN/Si Using HfO2 and SiO2 Functionalization Layers
ABSTRACT: This paper presents a comparative study of surface acoustic wave (SAW) humidity sensors fabricated on Sc0.3Al0.7N/Si, functionalized with HfO2 and SiO2 thin films, operating in both Rayleigh and Sezawa propagation modes. The paper describes the manufacturing of SAW humidity sensors by advanced nanolithographic processing tools and deposition methods of two different functionalization layers. The effect of HfO2 and SiO2 films on the resonance frequencies of the devices is analyzed for both propagation modes. The devices were characterized under controlled relative humidity conditions (20. . . 90 %) by monitoring the resonance frequency shifts of both acoustic modes. Depending on the type of functionalization layer, the analyzed sensors exhibit distinct responses to humidity: the SAW sensors covered with HfO2 show an increase of the resonance frequency with the relative humidity, while the SAW sensor having SiO2 layer has an opposite response, the resonance frequency decreases with the increase of the humidity. This contrasting behavior is explained by the sensing mechanism that becomes dominant in each case: the stiffening effect for HfO2 and the mass loading effect for SiO2. The high values obtained for the humidity sensitivities confirm the advantage of SAW sensors manufacturing on III-Nitride/Si layered structures, allowing an increase of the resonance frequencies above 5 GHz.KEYWORDS: HfO2 thin films, humidity sensing, SAW, ScAlN, SiO2 functionalization layerRead full text (pdf)