Current through Si O 2 gate oxide and its low frequency fluctuations: Trapping on charged dangling bonds with negative Hubbard U

An estimate of Hubbard U supports instability of neutral one-electron Si dangling bonds in Si O 2 and the formation of charged two-electron and two-hole negative U centers through the reaction Si *  + Si *  → Si + + Si − * * . The trapping on these negative U centers creates and annihilates "dents" in the thin barrier for electron and hole tunneling through the gate oxide. Such dents are visible as gate current low frequency fluctuations ( 1 ∕ f noise). The longer trapping time of holes causes irreversible Si − * * → Si + conversion, which leads to stress-induced leakage current and accumulation of positive charge in the oxide under voltage stress.