Current transport mechanism in trapped oxides: A generalized trap-assistedtunneling model

A generalized trap-assisted tunneling (GTAT) model is proposed in this work , where an effective tunneling barrier of trapezoidal shape is considered, instead of the triangular barrier utilized in the conventional trap-assiste d tunneling (TAT) model. It is demonstrated that trapezoidal barrier tunnel ing dominates at low electric fields (E<4 MV/cm), while triangular barrier tunneling contributes the main part of the tunneling current at high electr ic fields (E = 6-8 MV/cm). The comparisons of this improved model and the r esults of the conventional TAT model at high and low electric fields are di scussed. It is concluded that GTAT can more accurately model the current de nsity-electric field (J-E) curves for the conduction enhancement of a trapp ed oxide film under various deposition conditions over a wider range of ele ctric fields. This is confirmed by the comparative use of both TAT and GTAT models on experimental data obtained from existing reports. Furthermore, a simple method for determining the trap energy level is derived from the J- E relationship. This method provides a convenient way to characterize the t rap levels inside the oxide layers, without the need of other complicated m easurements. The developed GTAT model can be applied to the investigations of gate oxide reliability, especially the stress-related effects and impuri ty incorporated oxide films (i.e., SiOF or SiON). (C) 1999 American Institu te of Physics. [S0021-8979(99)01615-1].