Subbreakdown drain leakage current in MOSFET

Significant drain leakage current can be detected at drain voltages much lower than the breakdown voltage. This subbreakdown leakage can dominate the drain leakage current at zero V G in thin-oxide MOSFET's. The mechanism is shown to be band-to-band tunneling in Si in the drain/gate overlap region. In order to limit the leakage current to 0.1 pA/µm, the oxide field in the gate-to-drain overlap region must be limited to 2.2 MV/cm. This may set another constraint for oxide thickness or power supply voltage.