Micro-electro-mechanical transducer having an optimized non-flat surface

A method for a capacitive micromachined ultrasound transducer (cMUT), the method comprising:

• growing and patterning a diffusion barrier layer over a surface of a base layer, the patterned diffusion barrier layer having a first area and a second area, the first area allowing more diffusion penetration therethrough than the second area;
• performing a diffusion process over the diffusion barrier layer such that a diffusion reactivated material reaches a first depth into the base layer below the first area;
• a second depth into the base layer below the second area, the first depth being greater than the second depth;
• forming an anchor using a second diffusion reactivated material, the anchor having a top portion higher than the surface of the base layer;
• and
• forming a cover layer over the anchor and the base layer, wherein the base layer has a first electrode, the cover layer has a second electrode opposing the first electrode to define a gap width therebetween, and at least one of the cover layer and the base layer includes a flexible layer, such that the first electrode and the second electrode are movable relative to each other to cause a change of the gap width.