Micromechanical Piezoelectric-on-silicon BAW Resonators for Sensing in Liquid Environments

This paper reports micromachined piezoelectric-on-silicon bulk acoustic wave resonators operating at a nominal frequency of approximately 3.15 MHz in fluidic media. Electrical measurements of the open-loop response of the resonators when one of the resonator surfaces is submerged in water indicate high quality factors in the range of 110-190. These values of quality factor are at least an order of magnitude higher than the flexural mode counterparts. The resonators are further exposed to Glycerol-Water mixtures of varying viscosity-density resulting in characteristic negative resonant frequency shifts. Experimental values are compared with a simplified liquid loading model and an agreement of up to 13% for highest and within 3-4% for lowest glycerol concentrations is established. These devices due to the relative ease of operation in liquid environments, scalability, high quality-factors and high mass-sensitivity have the potential for integration with microfluidics and electronics in order to realize an integrated platform for biochemical sensing and analysis