Devices and manufacturing methods thereof are presented. The device includes a substrate and a fin-type transistor disposed on the substrate. The transistor includes a fin structure that protrudes from the substrate to serve as a source of the transistor. The fin structure is doped with dopants of a first polarity. The transistor also includes a gate layer formed over and around a first end of the fin structure to serve as a gate of the transistor. A drain layer is disposed over the fin structure and adjacent to the gate layer to serve as a drain of the transistor. The drain layer is doped with dopants of a second polarity opposite the first polarity.