Localized and distributed mass detectors with high sensitivity based on thin-film bulk acoustic resonators

A mass sensor based on thin-film bulk acoustic resonator, intended for biomolecular applications, is presented. The thin film is a (002) AlN membrane, sputtered over Ti∕Pt on a (001) Si wafer, and released by surface micromachining of silicon. Two experiments are proposed to test the mass sensing performance of the resonators: (a) distributed loading with a MgF2 film by means of physical vapor deposition and (b) localized mass growing of a C∕Pt∕Ga composite using focused-ion-beam-assisted deposition, both on the top electrode. For the distributed and localized cases, the minimum detectable mass changes are 1.58×10−8g∕cm2 and 7×10−15g, respectively.