Device structures and related fabrication methods for asymmetric MOSFETs that exhibit high BVDSS and low HCl characteristics while substantially improving the poor sub-threshold slope and output resistance ROUT characteristics common to conventional asymmetric
MOSFET devices. Embodiments are fabricated by implanting halo and / or LDD dopants on the source-side of an asymmetric
MOSFET using at least two different non-90° twist angles, each in a different quadrant. By implanting
dopant at different twist angles,
dopant is implanted within otherwise shadowed corners, thus essentially eliminating the parasitic transistors within such corners. Optionally, an extra implantation of halo / LDD dopants may be performed at a 90° twist angle. As a result, a non-90°, multi-twist implanted asymmetric
MOSFET exhibits improved
linearity and an essentially equivalent
gain characteristic compared to conventional asymmetric MOSFETs. Optionally, thick spacers may be used. The asymmetric MOSFETs are quite suitable for applications, such as power amplifiers, which require good
linearity and
gain characteristics.