A micro-electrical-mechanical system, MEMS, resonator device comprising: a substrate; and a bulk acoustic wave resonator structure arranged over at least a portion of the substrate, the bulk acoustic wave resonator structure including a piezoelectric material comprising a c-axis having an orientation distribution that is predominantly non-parallel to normal of a face of the substrate, a top side electrode arranged over the piezoelectric material, and a bottom side electrode arranged between the piezoelectric material and the substrate, wherein at least a portion of the piezoelectric material is arranged between the top side electrode and the bottom side electrode to form an active region; characterized in that: the active region is laterally surrounded by an inactive region, and a thickness of piezoelectric material of at least a portion of the inactive region is less than a thickness of piezoelectric material of the active region, such that at least an upper portion of the inactive region along a boundary of the active region is devoid of piezoelectric material, defining at least one discontinuity along at least upper portions of opposing lateral edges of piezoelectric material of the active region; the at least one discontinuity is configured to reduce mechanical clamping of the active region in a direction of maximum lateral displacement in shear mode operation of the bulk acoustic wave resonator structure; the active region comprises a length parallel to the direction of maximum lateral displacement in shear mode operation of the bulk acoustic wave resonator structure, the length extending between a first lengthwise end and a second lengthwise end of the active region; and the at least one discontinuity is bounded at least in part by the first lengthwise end and the second lengthwise end. a substrate; and a bulk acoustic wave resonator structure arranged over at least a portion of the substrate, the bulk acoustic wave resonator structure including a piezoelectric material comprising a c-axis having an orientation distribution that is predominantly non-parallel to normal of a face of the substrate, a top side electrode arranged over the piezoelectric material, and a bottom side electrode arranged between the piezoelectric material and the substrate, wherein at least a portion of the piezoelectric material is arranged between the top side electrode and the bottom side electrode to form an active region; characterized in that: the active region is laterally surrounded by an inactive region, and a thickness of piezoelectric material of at least a portion of the inactive region is less than a thickness of piezoelectric material of the active region, such that at least an upper portion of the inactive region along a boundary of the active region is devoid of piezoelectric material, defining at least one discontinuity along at least upper portions of opposing lateral edges of piezoelectric material of the active region; the at least one discontinuity is configured to reduce mechanical clamping of the active region in a direction of maximum lateral displacement in shear mode operation of the bulk acoustic wave resonator structure; the active region comprises a length parallel to the direction of maximum lateral displacement in shear mode operation of the bulk acoustic wave resonator structure, the length extending between a first lengthwise end and a second lengthwise end of the active region; and the at least one discontinuity is bounded at least in part by the first lengthwise end and the second lengthwise end. the active region is laterally surrounded by an inactive region, and a thickness of piezoelectric material of at least a portion of the inactive region is less than a thickness of piezoelectric material of the active region, such that at least an upper portion of the inactive region along a boundary of the active region is devoid of piezoelectric material, defining at least one discontinuity along at least upper portions of opposing lateral edges of piezoelectric material of the active region; the at least one discontinuity is configured to reduce mechanical clamping of the active region in a direction of maximum lateral displacement in shear mode operation of the bulk acoustic wave resonator structure; the active region comprises a length parallel to the direction of maximum lateral displacement in shear mode operation of the bulk acoustic wave resonator structure, the length extending between a first lengthwise end and a second lengthwise end of the active region; and the at least one discontinuity is bounded at least in part by the first lengthwise end and the second lengthwise end.