Mass effects of quartz resonant sensors with different surface microstructures in liquids

Liquid trapped by the rough surface of a quartz resonator vibrating in thickness-shear mode (TSM) will act as a mass effect to the crystal. It has been proven that this mass effect not only depends on the liquid mass enclosed in the surface cavities, but also the liquid properties and the crystal surface features. Based on a series of experiments, this paper introduces "trapping factor" to analyze the mechanism of the liquid mass effect. Influences of different surface microstructures, including structure dimension and orientation, on the liquid mass effect have been studied on 10 MHz fundamental mode AT-cut resonators. The result indicates that the trapping factor of a chess-board structure has no advantage compared to a line-structure. For the same structure height of 0.4 microm, the mass effect of a crystal with about 3 microm distance line-structure is bigger than that of a 7.5 microm distance line-structure. With a similar surface roughness value (R (a)), the crystal with a line structured surface has a much bigger mass effect than that with a randomly rough surface.