A MEMS structure includes a substrate, a structural dielectric layer, and a diaphragm. A structural dielectric layer is disposed over the substrate. The diaphragm is held by the structural dielectric layer at a peripheral end. The diaphragm includes multiple trench/ridge rings at a peripheral region surrounding a central region of the diaphragm. A corrugated structure is located at the central region of the diaphragm, surrounded by the trench/indent rings.