In a method for manufacturing a micromechanical structure, first a two-dimensional structure is formed in a substrate. The transistor may also comprise an insulated gate formed above the source and pocket regions, the insulated gate being configured to generate electron tunneling between the source and pocket regions if a voltage is applied to the insulated gate. The proof mass includes a first portion, a second portion separated from the first portion and a third portion connecting the first portion to the second portion.