Anomalous random telegraph noise in nanoscale transistors as direct evidence of two metastable states of oxide traps

In this paper, a new pattern of anomalous random telegraph noise (RTN), named “reversal RTN” (rRTN) induced by single oxide trap, is observed in the drain current of nanoscale metal-oxide-semiconductor field-effect transistors (MOSFETs) with high-k gate dielectrics. Under each gate voltage, the rRTN data exhibit two zones with identical amplitudes but reversal time constants. This abnormal switching behavior can be explained by the theory of complete 4-state trap model (with two stable states and two metastable states), rather than the simple 2-state or improved 3-state trap model. The results provide a direct experimental evidence of the existence of two metastable states in a single oxide trap, contributing to the comprehensive understanding of trap-related reliability and variability issues in nanoscale transistors.