“…There are two main types of acoustic wave resonators: surface acoustic wave (SAW) resonators [ 4 , 5 , 6 ], in which the propagation of acoustic waves is on the surface of the substrate, and bulk acoustic wave (BAW) resonators [ 4 , 7 , 8 ], where the acoustic waves propagate through the bulk of the substrate. BAW resonators normally feature high bulk moduli [ 9 ], high operating frequencies, as well as high quality (Q) factors [ 10 ] and thus are widely used as filters [ 3 , 11 , 12 , 13 , 14 , 15 ], oscillators [ 3 , 13 , 16 , 17 , 18 ] as well as sensors [ 3 , 15 , 19 , 20 , 21 , 22 ].…”