leakage power

Leakage power is the energy a chip wastes just by being powered on — even when nothing is switching and the clock is stopped. Think of a garden hose with a closed nozzle: ideally no water flows, but a tired old hose still weeps a slow drip at the seams. A transistor that is 'off' is that leaky hose; a thin trickle of current sneaks through it all the time, and across billions of transistors those trickles add up to real watts.

Leakage exploded as transistors shrank below ~90 nm, because thinner gate oxides and lower threshold voltages let more current sneak through. The two main culprits are subthreshold leakage (current through a barely-closed channel) and gate leakage (current tunnelling straight through the ultra-thin gate insulator). Leakage roughly doubles for every 10 °C of temperature rise, so a hot phone leaks far more than a cool one. The cure is to physically cut power to idle blocks (power gating) and to use high-threshold 'slow-but-tight' transistors where speed isn't needed (multi-Vt).