An acoustic transducer includes: substrate including first silicon layer, first oxide layer and second silicon layer, back chamber is formed therethrough; second oxide layer on the substrate; piezoelectric unit on the second oxide layer and including first electrode layer, piezoelectric layer and second electrode layer; slit and opening formed in the second electrode layer; metal pad stacked on the first electrode layer at the opening; and additional film layer including first, second and third parts, the first part is in the slit, side wall and bottom wall of the first part form groove, and through slot is formed in the third part to expose metal pad.