In collaboration with:
Dr. M. P. Anantram, Dr. T. R. Govindan, and
Dr. Bryan Biegel

Quantum mechanical features that are of importance to ultra small MOSFETs are the quantized energy levels in the inversion layer and the ballistic nature of charge transport. While the qualitative effects of these features are reasonably well understood, a comprehensive study of device physics in two dimensions that is capable of providing quantitative answers has been lacking (SIA roadmap). The major strengths of our approach is that it provides a: (a) frame work to explore device physics issues such as the source-drain and gate leakage currents, DIBL, and threshold voltage shift due to quantization, and (b) way to benchmark empirical modifications to semiclassical methods that aim to simulate characteristics of ultra small channel MOSFETs (such as the density gradient method, quantum corrected MEDICI). As traditional device simulation is rooted in semiclassical methods, an effort to build expertise in quantum mechanical analysis of 2D MOSFET physics has been an open problem.

Our typical device of interest to benchmark our code is the MIT (25nm, 50nm and 90nm) "well tempered" MOSFET, which is used by the device modeling community as a common basis to compare different simulation tools. The model is based on a self consistent solution of Poisson and Non-Equilibrium Green's Function equations, which in the absence of scattering are equivalent to Schroedinger equation with open boundaries. Anisotropic effective mass Hamiltonian is used throughout the calculations. Oxide leakage and quantum effects in poly-Si gate are taken into account by either including the gate region in the 2D domain or using 1D approximations within the context of non-equilibrium Green's function method. Phase-breaking scattering is treated within self-consistent Born approximation.

A recursive algorithm is used to solve for the density of states, electron and current densities (diagonal and first off-diagonal elements of Gr and G<). A nonuniform spatial grid is must to resolve electron confinement in the inversion layer and the decay of the electron density into the oxide. A nonuniform energy grid can be used to better resolve resonances in the channel. A non-linear Poisson equation is solved self-consistently with NEGF, using predictor-corrector scheme. The code is parallelized on SGI Origin 2000 using OpenMP directives.