A method of forming a semiconductor device includes providing a semiconductor substrate; forming a gate stack on the semiconductor substrate; forming a gate spacer adjacent to a sidewall of the gate stack; thinning the gate spacer; and forming a secondary gate spacer on a sidewall of the gate spacer after the step of thinning the gate spacer. The electro-mechanical energy conversion element generates in the vibration element at least one of a plurality of vibration modes. An elongate strip is arranged on the peripheral surface of the felt covering in the top region, extending along the front and back regions to points beyond the hammer equator. The solvent is allowed to react and is then removed from the polymer work piece, whereby at least a part of the waterproofing agent remains bound in the surface of the polymer work piece. An adder circuit is coupled to the receiver circuit and the plurality of antennas.