A piezoelectric microelectromechanical structure, comprising a piezoelectric stack having a main extension in a horizontal plane (xy) and a variable section in a plane transverse to said horizontal plane (xy) and formed by stacked arrangement of a bottom-electrode region; a piezoelectric material region, constituted by a film of PZT, arranged on the bottom-electrode region; and a top-electrode region arranged on the piezoelectric material region, wherein the piezoelectric material region has, as a result of said variable section, a first thickness along a vertical axis (z) transverse to said horizontal plane (xy) at a first area thereof, and a second thickness along the vertical axis (z) at a second area (14") thereof, the second thickness being smaller than the first thickness; wherein the piezoelectric material region has projections with the first thickness jointly defining said first area and recesses with the second thickness jointly defining said second area (14"), said projections being interposed between the recesses along a first horizontal axis (x) of the horizontal plane (xy); and wherein said piezoelectric stack is arranged, with the corresponding bottom-electrode region, on an underlying patterned structure having respective projections, at the recesses of the overlying piezoelectric material region and respective recesses at the projections of the overlying piezoelectric material region; wherein said piezoelectric stack is arranged on a supporting element, designed to undergo deformation along the vertical axis (z) via the piezoelectric effect, suspended above an underlying opening and separated from the piezoelectric stack by a dielectric region, interposed between said supporting element and the bottom-electrode region; wherein said patterned structure is defined by said dielectric region, either exclusively or jointly with a surface portion of said supporting element. wherein the piezoelectric material region has, as a result of said variable section, a first thickness along a vertical axis (z) transverse to said horizontal plane (xy) at a first area thereof, and a second thickness along the vertical axis (z) at a second area (14") thereof, the second thickness being smaller than the first thickness; wherein the piezoelectric material region has projections with the first thickness jointly defining said first area and recesses with the second thickness jointly defining said second area (14"), said projections being interposed between the recesses along a first horizontal axis (x) of the horizontal plane (xy); and wherein said piezoelectric stack is arranged, with the corresponding bottom-electrode region, on an underlying patterned structure having respective projections, at the recesses of the overlying piezoelectric material region and respective recesses at the projections of the overlying piezoelectric material region; wherein said piezoelectric stack is arranged on a supporting element, designed to undergo deformation along the vertical axis (z) via the piezoelectric effect, suspended above an underlying opening and separated from the piezoelectric stack by a dielectric region, interposed between said supporting element and the bottom-electrode region; wherein said patterned structure is defined by said dielectric region, either exclusively or jointly with a surface portion of said supporting element.