Miniature high-frequency longitudinal wave mass sensors in liquid

In this paper, micromachined longitudinal wave resonant mass sensors operating near 1 GHz in a liquid environment are investigated and characterized. Mass sensitivities of the film bulk acoustic resonator (FBAR) and high-tone bulk acoustic resonator (HBAR) microbalances with small size are measured to be 782.7 cm²/g (50 times larger than that of conventional bulky quartz crystal microbalance) and 9.3 cm²/g, respectively. Based on the mass sensitivities and frequency noise floor, the minimum detectable mass of the FBAR and HBAR are estimated to be 2.8 ng/cm² and 11.9 ng/cm² in liquid, respectively.