Localized-mass detection based on thin-film bulk acoustic wave resonators (FBAR): Area and mass location aspects

Localized-mass sensors using thin-film bulk acoustic resonators (FBAR) have been implemented for the study of sensitivity and possible configurations in biological applications. In a first experiment, a group of resonators are loaded with the same amount of mass but different contact areas, achieving responsivities as high as 10−19 g/Hz, and potential sensitivities in the order of 10−14 g. These numbers are at least one order of magnitude higher than those obtained for uniform thin-film loadings, although it is clear that sensitivity decreases with the area of the localized-mass. The current phase-noise levels and the quality factor of resonators would allow measuring frequency changes of 30 kHz – the minimum measured frequency shifting has been 500 kHz so far – due to a mass deposition of 9.0 × 10−15 g. In a second experiment, localized-loadings with the same mass are located in different positions of the top electrodes of the corresponding FBARs. It was found out that a location change of the mass in the electrode causes different magnitudes of frequency shifting. A discussion on these topics is opened, in order to define future applications and research lines concerning localized-mass sensing in FBARs.