Abstract: A bulk acoustic resonator includes a stack structures, including a piezoelectric layer having a first side and an opposing second side; a first electrode disposed under the first side of the piezoelectric layer; a second electrode disposed over the second side of the piezoelectric layer; and a multistep structure with a bottom part having first dimensions disposed between the piezoelectric layer and second electrode and a second part having second dimensions, different from the first dimensions, disposed between the bottom part of the multistep structure and the second electrode. An active region of the stack is configured to resonate in response to an electrical signal applied between the first electrode and the second electrode, and the multistep structure is arranged to provide destructive interference of lateral acoustic waves within the bulk acoustic resonator.