Quantum mechanical calculation of hole tunneling gate leakage current in nanoscale pMOSFETs

Abstract

To achieve higher integration density and enhanced performance of metal-oxide-semiconductor field-effect-transistors (MOSFETs), scaling down device dimensions has been the major breakthrough for over 30 years. In order to maintain the strong gate control over the channel region, along with shortening physical lengths of the gate pitch and the junction depth, gate dielectric thickness has shrunk to be less than 2 nanometers in cutting edge devices. The low dimension of the nanoscale MOSFETs unveil growing quantum mechanical effects, which were negligible before. These no longer ignorable quantum effects include tunneling currents through the gate dielectric. This gate leakage current adversely affects the MOSFET device`s performance and greatly increases the power consumption of highly integrated circuits. It is thus an essential work to assess these currents accurately quantum mechanically. The non-equilibrium Green`s function (NEGF) method is a powerful tool that can take into account these quantum mechanical effects and make an accurate estimation of the leakage current. However, unlike the 3-D continuous state tunneling currents, the standard NEGF formalism does not provide coverage of quasi-bound state (QBS) tunneling currents. Quasi-bound states are formed beneath the gate oxide in the case of inversion operation of the MOS capacitor. Since transistors that are in the ON-state are as well operating in the inversion regime, tunneling currents through these QBSs are important in assessing ON-state gate leakage and power consumption. Others made effort developing methods to determine this QBS tunneling current by introducing artificial factors such as escape time or life time, which requires less computational cost than the NEGF method and works well enough but unfortunately are not applicable to non-bounded state tunneling currents. In this thesis we introduce a method to calculate hole tunneling gate leakage currents including QBS tunneling...