(a) Schematic of the TS mode FBAR with c-axis tilted AlN film with the SEM image of AlN showing the tilted angle [175]. Reproduced with permission from I. Katardjiev et al., Vacuum; published by Elsevier, 2012. (b) Optical image and schematic of the TS mode FBAR with lateral filed excitation on the c-axis oriented piezo film [49]. Reproduced with permission from Da Chen et al., Biosensors and Bioelectronics; published by Elsevier, 2017. (c) Optical image and schematic of the LE or contour mode FBAR sensor for the liquid medium [177]. Reproduced with permission from A. Ali et al., Sensors and Actuators A: Physical; published by Elsevier, 2016.