US Patent 7989878 Cathode cell design

An n-channel insulated gate semiconductor device with an active cell (5) comprising a p channel well region (6) surrounded by an n type third layer (8), the device further comprising additional well regions (11) formed adjacent to the channel well region (6) outside the active semiconductor cell (5) has enhanced safe operating are capability. The additional well regions (11) outside the active cell (5) do not affect the active cell design in terms of cell pitch, i.e. the design rules for cell spacing, and hole drainage between the cells, hence resulting in optimum carrier profile at the emitter side for low on-state losses.