Recovery of negative and positive bias temperature stress in pMOSFETs

Based on the asymmetric recovery behavior observed following negative and positive bias temperature stress in pMOSFETs, various stress tests with different stress times, oxide electric fields, and oxide thicknesses were performed. In contrast to NBTI, where the relaxation of the threshold voltage often follows a logarithmic behavior, PBTI stress reveals no logarithmic recovery. Notable relaxation after PBTI stress instead appears to happen later but faster. This asymmetry is more pronounced at harsher stress conditions, e.g. increasing stress time and oxide electric field. This can be explained by the different relative measurement windows for NBTI and PBTI, which depend on the stress time and the oxide electric field. A closer analysis of the recovery yields the spectra of capture and emission time constants of the underlying defects. We analyze the dependence of these spectra on the stress time and the oxide electric field, where the emission times of the defects are shifted towards smaller times for higher oxide electric field.