Complementary symmetric MOSFET pair - has gradual doping profiles at junctions with guard ring to raise permissible load voltage

摘要

The complementary symmetric MOSFET pair is not restricted to low voltages despite high packing density. It avoids abrupt PN junctions between the guard ring and the source and drain zones that it surrounds. A compensation region is formed at each junction so that the doping profile of the junction between the first drain and source zones (14, 16) and the first guard ring (20) has an intermediate region whose conduction type is the same as that of the substrate (18) and whose doping concentration is not much greater than that of the substrate. An intermediate region is also formed between the second drain and source zones (22, 24) and the second guard ring (28) and has the same conduction type as the centre zone (26).