Subthreshold measurements can reveal key device parameters. We present a method to identify the region of the transfer characteristic where the drain current is affected by neither parasitic off-state leakage nor strong inversion current. Then we employ this method to obtain the conduction band edge shift for FinFETs with various fin widths using temperature dependent transfer characteristics. The results indicate lowering of the conduction band edge up to 40 meV, and hence threshold voltage, for fin widths down to 5 nm. This is explained by the combination of quantum confinement and strain effect on the band edges. We demonstrate a qualitative agreement between measurements, theory and simulation.
