Off-current (Ioff): definition

Beginner

The tiny current a transistor leaks when it is off. Billions of tiny leaks add up to wasted power.

Novice

The drain current with the gate at 0 V and the drain at the supply voltage. It is mostly subthreshold current, so it rises steeply as the threshold voltage is lowered or the chip gets hotter.

Expert

$I_{\mathrm{DS}}$ at $V_{\mathrm{GS}} = 0$ , $V_{\mathrm{DS}} = V_{\mathrm{DD}}$ . Dominated by subthreshold conduction (plus gate and junction leakage), raised by DIBL at full $V_{\mathrm{DS}}$ and roughly tenfold for each $S$ of $V_{\mathrm{t}}$ reduction. The ratio $I_{\mathrm{on}}/I_{\mathrm{off}}$ summarizes a device’s switch quality.