A method for activating a backup unit includes providing a fuse element connected to the backup unit. The fuse element includes an active area, which includes a source region and a drain region beside the source region, a gate region disposed on the active area, and a shallow trench isolation (STI) structure surrounding the active area. The method also includes applying a stress voltage on the drain region of the fuse element; accumulating electrons in a portion of the STI structure adjacent to the drain region; generating a conductive path through the drain region and the source region so that the fuse element is conductive; and activating the backup unit through the fuse element.