Various bioreceptor immobilizations for the different configurations of FBAR biosensors. (a) SMR with the top electrode as an active sensing area for bioreceptors [182]. Reproduced with permission from Martin Nirschl et al., Sensors and Actuators A: Physical; published by Elsevier, 2009. (b) Back cavity FBAR with the top electrode for the immobilization of bioreceptors [183]. Reproduced with permission from Tae Yong Lee et al., Thin Solid Films; published by Elsevier, 2010. (c) Back cavity FBAR with the backside Si3N4 membrane in the cavity coated with Au and used for the immobilization of bioreceptors [184]. Reproduced with permission from Hao Zhang et al., Applied Physics Letters; published by AIP Publishing, 2010.