Charge Trapping Mechanism Leading to Sub-60-mV/decade-Swing FETs

In this paper, we present a novel method to reduce the subthreshold swing (SS) of FETs below 60 mV/decade. Through modeling, we directly relate trap charge movement between the gate electrode and the gate dielectric to SS reduction. We experimentally investigate the impact of charge exchange between a Cu gate electrode and a 5-nm-thick amorphous Al2O3 gate dielectric in an InGaZnO4 thin-film transistor. Positive trap charges are generated inside the gate dielectric while the semiconductor is in accumulation. During the subsequent detrapping, the SS diminishes to a minimum value of 46 mV/decade at room temperature. Furthermore, we relate the charge trapping/detrapping effects to a negative capacitance behavior of the Cu/Al2O3 metal-insulator structure.