Gravimetric biosensor based on a 1.3 GHz AlN shear-mode solidly mounted resonator

We investigate the performance of solidly mounted resonators based on Ir/tilted-AlN/Ir piezoelectric stacks as biosensors. These films are deposited by varying the pressure, the cathode power and the temperature of a two-step process based on depositing (00·2)-tilted AlN active layers over an (10·3)-oriented AlN seed layer. To minimize the influence of the temperature coefficient of frequency on the stability of the biosensor, we use insulating acoustic mirrors made of layers of SiO2 and amorphous TaOx with non-λ/4 thicknesses, which enables to reduce the TCF to −14 ppm/°C. The mass loading of the resonators with SiO2 thin films results in a sensitivity of 1800 kHz/pg·cm2. Surface functionalization consists on the binding of silane groups on plasma oxidized SiO2 surfaces. After a glutaraldehyde link, streptavidin is bonded to the surface to receive biotinylated receptors for several species. We test thrombin-binding aptamer (TBA29 against thrombin, and IgG antibody against immunoglobulin). The sensors response to species of different molecular weight like TBA-29 (9.75 kDa) or IgG antibody (150 kDa) is monitored. Finally, we assess the response of the biosensors to different thrombin concentrations (ranging from 4 nM to 270 nM) on surfaces functionalized with the TBA29 aptamer.