Substrate current-a device and process monitor

Typical characteristics of an n-channel, enhancement mode, insulated-gate field effect transistor (IGFET). The drain current is plotted against the drain voltage for different values of the gate voltage. It can be seen from the figure that, after saturation is reached, the drain current increases again as the drain voltage is further increased. This additional current is attributed to the substrate current and can be measured simultaneously in the substrate lead.