(Well Proximity Effect简称为WPE)

（自己找的一些WPE的资料，如有不对的地方请指正）

NMOS or PMOS that are close to the edge of a well will exhibit a difference inthreshold and Id from that of the device located remotely from the edge.

The WPE effect occurs to every MOS: standard V t , high V t , low V t , thick/thin oxideMOS. 

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At front-end stages of CMOS wafer process，P and N types of ions are implanted to form. wells.During the implantations，lateral scattering(横向散射)of the ions nearby edges of hte photo-resist(光刻胶) causes well doping concentration，as shown in Fig.1 . The well doping concentration mainly drifts the threshold voltage of Mos transisitors.We call it "well edge proximity effect"(WPE).As advanced deep well implants with high-energy implanters are introduced to suppress parasitic bipolar gail for latch-up protection,WPE becomes severer.In circuit design ,WPE can be suppressed by making a large separation between gate poly and enclosing well edge.