Gate tunneling currents in ultrathin oxide metal-oxide-silicon transistors

Abstract

Carrier tunneling through ultrathin (1-3 nm) SiO2 layers in MOS (metal-oxide-silicon) structures is investigated using the Bardeen-Harrison transition probability method. Quantum mechanical wave function matching at the two abrupt potential boundaries of a trapezoidal Si/SiO2/Si barrier gives an electric-field dependent preexponential factor in the Wentzel-Kramers-Brillouin tunneling probability, which significantly affects the current-voltage characteristic at low fields. An analytical theory is employed to predict the relative importance of three elastic tunneling pathways (electrons, valence electrons, and holes) and two geometrical tunneling locations (channel region and source or drain overlap regions) in MOS transistors (MOSTs), showing (1) hole tunneling dominant in p + gate pMOST (p-channel MOST) at low gate voltages, and (2) overlap regions dominant prior to base-region inversion in both p+gate pMOST and n+ gate nMOST (n-channel MOST). The analytic theory is used to analyze the experimental tunneling currents measured at the gate, source, well, and substrate terminals of sourced MOS capacitors to give the oxide thickness and impurity doping concentrations in the base and source regions. © 2001 American Institute of Physics.