Body Effect

The body effect explains the changes in the threshold voltage through the change in the source-bulk voltage, approximated by the subsequent equation:

In which V_TN is the threshold voltage with substrate bias present, and V_TO is the zero-V_SB value of threshold voltage, γ is the body effect parameter, and 2φ is the surface potential parameter.

Figure: Ohmic contact to body to ensure no body bias; top left: sub threshold, top right: Ohmic mode, bottom left: Active mode at onset of pinch-off, bottom right: Active mode well into pinch-off - channel length modulation evident

The body can be functioned as a second gate, and is sometimes considered to as the "back gate"; the body effect is sometimes known as the "back-gate effect".