Body Bias

The threshold voltage varies somewhat with the bias between Source and Bulk, VSB.

VT = VT0 + GAMMA [ (2 PHIF + VSB)1/2 - (2 PHIF)1/2 ]

where VT0 is the zero-bias threshold voltage, GAMMA is the body-bias factor

PHIF is the bulk Fermi potential

Na is the acceptor, boron, doping density, usually on the order of 1015 cm-3.