Cutoff: definition · Chip Field Guide

Beginner

The off state: the gate voltage is too low to open the switch, so only a tiny trickle gets through.

Novice

The region where $V_{\mathrm{GS}}$ is below the threshold voltage. No channel forms, so the drain current is close to zero. In a simple model it is exactly zero; in a real device a small subthreshold current still flows.

Expert

$V_{\mathrm{GS}} < V_{\mathrm{t}}$ . The square law sets $I_{\mathrm{D}} = 0$ here, but the real current falls exponentially with $V_{\mathrm{GS}}$ at the subthreshold slope, which sets the device’s off-current.