Positive and negative charging of thermally grown SiO2 induced by Fowler-Nordheim emission

Abstract

Charging properties of thermally grown SiO₂ associated with Fowler‐Nordheim (F‐N) emission have been investigated using a metal‐oxide‐silicon structure. Shifts in flatband voltage are induced by the F‐N current with positive or negative dc gate voltage. The number (N_trapped) of charges trapped in the SiO₂ film is calculated from the flatband voltage shift. The number (N_injected) of electrons injected into the SiO₂ film is calculated from the F‐N current. The relationship between N_trapped and N_injected is discussed. Charge trapping is marked when current density through the SiO₂ film is more than 1×10⁻⁶ A/cm², regardless of the polarity of gate voltage. Both positive charges, trapped under negative gate voltage, and negative charges, trapped under positive gate voltage, are found to depend basically on N_injected and not on the gate voltage. These trapped charges are located near or at the Si‐SiO₂ interface, Charge trapping efficiency η, defined as η = ∂N_trapped/∂N_injected, is found to decrease with increasing N_injected and to vary inversely with N_injected for values of N_injected over 10¹⁸ /cm². The trapping efficiency of negative charge is found to be lower than that of positive charge. A simple quantitative model derived from the F‐N characteristic is presented to account for these behaviors. Relatively good agreement between this model and experimental findings is shown.