US Patent 7129546 Electrostatic discharge protection device

An ESD protection device. The ESD protection device has a substrate; a channel region, a source region, and a drain region. The channel region is formed on a predetermined area of a surface of the substrate, the channel region has a first side and a second side. The source region is formed adjacent to the first side. The drain region which has a heavily doped region and a lightly doped region formed below the heavily doped region is formed adjacent to the second side. The width along a longitudinal axis of the heavily doped region has variable length and thus the length between one side of the heavily doped region to the second side has variable length.