Body Bias

The threshold voltage varies somewhat with the bias between Source and
Bulk, V_{SB}.

V_{T} = V_{T0} + GAMMA [ (2 PHI_{F} + V_{SB})^{1/2}
- (2 PHI_{F})^{1/2} ]

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

GAMMA = (2 q *EPSILON*_{Si} N_{a})^{1/2}
/ C_{ox}.

*PHI _{F} *is the bulk Fermi potential

PHI_{F} = (kT/q) ln(N_{a}/n_{i}).

N_{a} is the acceptor, boron, doping density, usually on the
order of 10^{15} cm^{-3}.