Structure of semiconductor device and method for fabricating the same

A method for fabricating a semiconductor device, comprising:

• providing a circuit substrate;
• forming a first metal layer on the circuit substrate;
• forming a buffer layer on the first metal layer;
• forming an absorbing layer on the buffer layer;
• forming a first electrode layer on the absorbing layer;
• forming a piezoelectric material unit on the first electrode layer;
• forming a protection layer, covering an entirety of a sidewall of the piezoelectric material unit directly connected to a topmost surface and a bottommost surface of the piezoelectric material unit;
• and
• forming a second metal layer over the piezoelectric material unit, the second metal layer comprising:
• a first part, disposed on the piezoelectric material unit through the protection layer, serving as a second electrode layer;
• and
• a second part, at a same level of the first part, and at least electrically connecting to the first electrode layer,
• wherein the step of forming the absorbing layer comprises:
• forming a dielectric layer containing a sacrificial material layer embedded in the dielectric layer;
• and
• removing the sacrificial material layer after forming the protection layer on the piezoelectric material unit to form an air-gap region surrounded by the dielectric layer,
• wherein the air-gap region corresponds to the piezoelectric material unit, and the dielectric layer is disposed between the air-gap region and the first electrode layer.