Abstract: There is provided a piston assembly configured to include: a hollow cylinder-shaped magnet sleeve having a magnet(s) bonded on external circumferential surface thereof; a hollow cylinder-shaped piston inserted into a hollow space of the magnet sleeve; and a hollow disc-shaped ring fixed to the piston by a shrink fitting process, and welded to the magnet sleeve which is made of the same material as the ring so as to obtain a configuration of the piston assembly in which the magnet sleeve and the piston are coupled to each other.

Abstract: Provided is a method of manufacturing a flash memory device. In accordance with the present invention, an undoped polysilicon layer is formed over a semiconductor substrate where a floating gate and a dielectric layer are formed. By performing N2 plasma process with respect to the undoped polysilicon layer, a heavily doped polysilicon layer is formed to form a control gate. Due to N2 plasma process, a nitrogen layer is formed at the interfaces between the dielectric layer and the undoped polysilicon layer. As a result, during a re-oxidization process, it is possible to prevent a thickness of the dielectric layer from being increased by reducing diffusion speed phosphorous and oxygen. Additionally, phosphorous of the heavily doped polysilicon layer is diffused into the undoped polysilicon layer in a subsequent process, thereby increasing a phosphorous concentration of the undoped polysilicon layer.