Charge trapping mechanism leading to sub-60-mV/decade-Swing FETs

In this work, we present a novel method to reduce the subthreshold swing of field-effect transistors below 60 mV/dec. Through modeling, we directly relate trap charge movement between the gate electrode and the gate dielectric to subthreshold swing 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 de-trapping, the subthreshold swing diminishes to a minimum value of 46 mV/dec at room temperature. Furthermore, we relate the charge trapping/de-trapping effects to a negative capacitance behavior of the Cu/Al2O3 metal-insulator structure.