Transient conduction in multidielectric silicon-oxide-nitride-oxide semiconductor structures

The voltage- and time-dependence of the tunneling currents in polysilicon-oxide-nitride-oxide semiconductor structures have been investigated. Electron and hole contributions were separated using a shallow junction technique. The standard tunneling model for charge injection was successfully applied to describe the observed threshold voltage shifts. For both positive and negative gate voltages, the time-dependence of the current density through the tunneling oxide is given by a simple analytical equation. This equation is characterized by an initial time constant and an asymptotic t(-1)-dependence. At large programming times the current density follows the t(-1)-dependence, independent of the tunneling oxide thickness and applied voltage. Under positive polarity (write) electrons are injected from the substrate. Under negative polarity (erase) and previous injection electron back-tunneling rather than hole injection is dominant at the beginning of erasing. At the end of erasing, steady-state conduction can be dominated either by electrons or holes, depending on the applied voltage. (C) 2001 American Institute of Physics.