Metric- and Geometry-Dependent Mechanical Stress Effects on Hot-Carrier Degradation in nMOSFETs

Abstract

This work investigates the effect of externally applied uniaxial mechanical stress (MS) on hot-carrier degradation (HCD) in nMOSFETs. Uniaxial tensile and compressive MS of ±300 MPa are applied via four-point bending to investigate purely mechanical effects. Among the monitored parameters, including threshold voltage shift, saturation current degradation, and linear current degradation, only linear current degradation shows a clear order of tensile > unstressed > compressive. The impact ionization rate and power-law time exponents remain unchanged across the applied MS range, indicating that MS barely alters the trap generation kinetics. The apparent MS separation in linear current degradation is attributed to the MS-dependent initial resistance and the MS-proportional hot-carrier flux. It is also shown that the MS-induced separation decreases at high gate voltage and in devices with shorter and narrower channels. These findings demonstrate that when assessing HCD reliability under MS, the choice of degradation metric, sensing gate voltage, and device geometry must be carefully considered.