On the Physical Meaning of Single-Value Activation Energies for BTI in Si and SiC MOSFET Devices

Bias temperature instability (BTI) has been shown to be the collective response of an ensemble of defects to a gate voltage signal. Each defect can be described using first-order reactions for either charge trapping or defect creation with a broad distribution of time constants. Consequently, the temperature dependence of BTI has to be determined by a distribution of activation energies reflecting the variety of available defects. Commonly employed single-value apparent activation energy-based modeling of BTI can therefore be at best a very rough approximation and its apparent activation energy is consequently a model parameter without physical justification. This study investigates the impact of measurement parameters, such as the extraction point in the drift curve and the recovery time, on these apparent activation energies that can be extracted either by threshold voltage shift increase (vertical method) or by stress time acceleration (horizontal method). The framework of activation energy maps enables an analytical mathematical approach to calculate the dependence of extracted apparent activation energies on the measurement parameters. A comparison between Si and SiC MOSFET devices is employed, and nonphysical negative apparent activation energies are explained. Since apparent activation energies have been repeatedly employed to justify physics-based descriptions of BTI, their physical (in)significance is discussed.