Example acoustic bandgap devices provided that can be fabricated in a semiconductor fabrication tool based on design check rules. An example device includes a substrate lying in an x-y plane and defining an x-direction and a y-direction, an acoustic resonant cavity over the substrate, and a phononic crystal disposed over the acoustic resonant cavity by generating the phononic crystal as a plurality of unit cells disposed in a periodic arrangement. Each unit cell include: (a) at least one higher acoustic impedance structure having a longitudinal axis oriented in the y-direction and a thickness in the x-direction greater than or about equal to a minimal feature thickness of the semiconductor fabrication tool, and (b) at least one lower acoustic impedance material bordering at least a portion of the at least one higher acoustic impedance structure and forming at least a portion of a remainder of the respective unit cell.