the invention is not limited to this moreover the source 141 and the drain 142 can be provided respectively along the inner and outer sides of the channel 143 or along the outer and inner sides respectively since the source 141 and the drain 142 are separated by the channel 143 the shapes of the source 141 and the drain 142 need to match the shape of the channel 143 in this embodiment the shape of the channel 143 is so to enclose a peninsula region the shape of the source 141 also has a peninsula shape as shown in fig6 a to 6 c the peninsula regions defined by the channels 143 a 143 b 143 c are roughly in the shapes of a u a rectangle and a polygon the profile of the gate layer 120 corresponds to that of the peninsula region the area of the gate layer 120 can be either smaller or bigger than the peninsula region alternatively as shown in fig7 a and 7b the gate layer 120 has an opening region 121 a or 121 b their shapes correspond to the peninsula region the area of the opening region 121 a or 121 b can be smaller fig7 a or bigger fig7 b than the peninsula region.