Time dependent oxide SiO/sub 2/ breakdown in MOSFET: a consequence of quantum mechanical tunneling of electrons

Abstract

Considering the quantum mechanical tunneling of electrons as a leakage current through the thin oxide of a MOSFET, a mathematical model of time dependent dielectric (SiO/sub 2/) breakdown (TDDB) process under high field and current conditions, is developed here. The proposed model involves hole generation, trapping and most importantly high electric field. Impact ionization, occurring by electron tunneling under high field, has been considered as a cause of hole generation. It is believed that the accumulation of positive charges, due to impact ionization within the oxide, results in a decrease in the oxide potential barrier. This provides easy access of excited electrons to the oxide, and thus accelerates the positive charge buildup process. This charge buildup process is time dependent and consequently breaks the oxide potential barrier. In this model, the required time is shown as indicative of the successful operational life time of oxide in digital circuits.