Degradation and time dependent breakdown of SiO2 gate oxides were discussed based upon the Anderson–Mott theory of amorphous solids with dangling bonds as diamagnetic so-called negative Hubbard U centers. Negative-U dangling bonds in the oxide were either positive D+ centers or two-electron negative D– centers. Due to a large difference in mobility between electrons and holes, hopping current in SiO2 was mainly electron current on D+ centers. Degradation of isolation properties and time dependent breakdown of SiO2 gate oxide under voltage stress were due to the conversion of D– into D+ centers caused by the hole-hopping current in SiO2. The reaction of conversion was stress polarity dependent. Thermal conductivity of Si was approximately 100 times higher than thermal conductivity of SiO2. Heat dissipation and accumulation of D+ centers inside the oxide were important in understanding the time dependent breakdown of the oxide.

Understanding Degradation and Breakdown of SiO2 Gate Dielectric with “Negative Hubbard U” Dangling Bonds. J.Karp, D.Gitlin, S.Jeong, B.Moyzhes: Journal of Applied Physics, 2004, 95[5], 2490-4