 The tunneling current is described by a modified Fowler-Nordheim tunneling equation, i.e.a tunneling equation that takes into account that the shape of the tunneling barrrier is not triangular (as assumed for the Fowler-Nordheim formula derivation), but composed of the series of a trapezoidal barrier in the oxide, and a triangular barrier in the nitride.The Poole-Frenkel process is the limiting mechanism of conduction at the beginning of the memory programming regime due to the higher current provided by tunneling.