Thickness and temperature dependence of the leakage current in hafnium-based Si SOI MOSFETs

The dependence on oxide thickness and temperature of the gate-leakage current density (Jg) in metal-gate/hafnium-based-oxide/Si SOI n-channel and p-channel MOSFETs has been investigated both experimentally and theoretically to identify the leakage mechanism(s). Fowler–Nordheim (FN) tunneling is found to be the dominant leakage mechanism at high bias (Vg > 1.5 V) at all measured temperatures, the slope of the FN plot corresponding to an oxide barrier-height decreasing almost linearly with increasing temperature. This ‘effective’ barrier lowering is caused by the thermal heating of the Fermi–Dirac source distribution function in the cathode. On the contrary, around the operating bias (Vg ≈ 0.5–1 V for nFETs, 1–1.5 V for pFETs), Poole–Frenkel (PF) emission is dominant, especially at high temperatures. However, strong nonlinearities seen in the In (Jg)−1/T-plots at low Vg (<1 V) indicate the existence of multiple temperature-dependent leakage mechanisms.

► Fowler–Nordheim tunneling at high gate voltages.
► Effective barrier lowering with increasing temperature.
► Poole–Frenkel emission around operating voltages at high temperatures.
► Multiple leakage mechanisms (direct tunneling and hoping conduction) at low gate voltages.