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)-til ted AIN active layers over an (10 3)-oriented AIN 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 Si0 2 and amorphous TaO x with non-\/4 thicknesses, which enables to reduce the TCF to-14 ppm/°C. The mass loading of the resonators with SÍO2 thin films results in a sensitivity of 1800 kHz/pg cm 2. Surface functionalization consists on the binding of silane groups on plasma oxidized SÍO2 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.

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Film bulk acoustic resonators (FBAR) are promising candidates to replace surface acoustic wave devices as filters or delay lines, but also offer exciting opportunities as biological or gas sensors. In this work, solidly mounted FBARs were manufactured by substituting commonly used pure aluminium nitride (AlN) by scandium doped aluminium nitride (ScAlN) thin films as the piezoelectric layer. The ScAlN-based resonators feature a significant improvement of the electromechanical coupling factor from ~3% to ~12% compared to the pure AlN, while the decreased stiffness of ScAlN results in a decrease of the quality factor from ~300 to ~100 due to increased damping losses in the piezoelectric material.

ZnO films with a c-axis significantly inclined away from the surface normal were grown by a remote plasma sputtering technique at room temperature. The films were used to make solidly mounted resonators (SMRs) operating in shear mode at a resonant frequency of 1.35 GHz. Control of the ZnO microstructure was achieved using a polycrystalline AlN seed layer which can be added on top of a sputtered acoustic mirror to give a complete SMR device. The ZnO was reactively sputtered in an atmosphere of argon and oxygen from a zinc target. The c-axis of the ZnO was estimated to be at an angle of ~ 45° to the surface normal. SMRs were measured to have quality factors (Q) of up to 140 and effective electromechanical coupling coefficients of up to 2.2% in air. Although an inclined c-axis can be achieved with direct growth onto the acoustic mirror, it is shown that the AlN seed layer provides higher coupling coefficients and narrower inclination angular distribution. The responses of the devices in liquids of different viscosities (acetone, water and AZ5214E photoresist) were measured. The shear mode Q decreased by 45% in acetone, 72% in water and 92% in AZ5214E.