FET mobility degradation and device mismatch due to packaging induced die stress

CMOS FETs exhibit a stress sensitivity that is similar to classical piezoresistors in which mechanical stress induces changes in the FET transconductance through device mobility changes. Transconductance changes are a function of channel orientation, transistor location, and channel length. In plastic encapsulated die, it is demonstrated that NMOS transistors exhibit fairly uniform transconductance degradation, whereas PMOS devices can exhibit both degradation and enhancement. These changes can result in both degradation and increased spread of analog and digital circuit performance.