Engineering Silver Nanostructures for Surface Acoustic Wave Humidity Sensors Sensitivity Enhancement

Abstract

In this paper, the sensitivity of the LiNbO3 surface acoustic wave (SAW) based humidity
\nsensors has been enhanced with various nanostructured Ag materials, including thermally evaporated
\nor chemically synthesized, and then thermally annealed ones. The results showed that the humidity
\nsensitivity of the SAW devices increases with the surface roughness (porosity) of the film, and can be
\nfurther improved when Ag NPs are used. Smooth Ag film deposited by evaporation onto the SAW
\ndevices did not change the humidity sensitivity noticeably, but those with chemically deposited high
\nporosity Ag films have a good sensitivity of 80 kHz/75%RH. The SAW sensors with the Ag NPs have
\nthe highest sensitivity up to about 800 kHz/75%RH, at least one order of magnitude higher than that
\nreported before. The SAW sensors with Ag nano-particles showed a strong non-linearity, and
\nexplained by the different chemisorption capabilities of Ag and LiNbO3 surface.