Simulation Of Quantum Transport Effects In Nano-scaled Double-Gate MOSFETs

The design and fabrication technology of integrated circuits have been developedat very fast speed. When the feature size of devices is reduced to several tens ofnanometers, it is necessary to simulate devices using quantum transport models. Atpresent, device simulation faces a new challenge. The research on the transport ofcarriers is mostly based on the Schr?dinger equation with effective massapproximation and Quantum Boltzmann equation, and many quantum transportmodels have been developed and used in the simulation of devices. Theself-consistent solution of 2D coupled effective-mass Schr?dinger equation andPoisson equation can not only be used to resolve carriers' wave characteristicsmicroscopically, but also be used to calculate electrical characteristics of devicemacroscopically. It is the main objective of this dissertation to implement the 2Dself-consistent solution of effective-mass Schr?dinger equation and Poisson equationin DG(double-gate) MOSFETs. In this dissertation, first, the QTBM (Quantum Transmitting Boundary Method)[i] for solving 2D effective-mass Schr?dinger equation is described in detail. Then theQDAME (Quantum Device Analysis by Modal Evaluation) [ii] is introduced,including several important issues such as sampling standing wave function,establishment of energy eigen-equation, decomposition of traveling wave functions,the introduction of drift wavevector, calculation of individual occupancy probability,the introduction of quantum current continuity equation nd the Broyden method inNewton iteration. Based on QTBM and QDAME, programming using MATLAB,firstly 1D self-consistent result in closed boundary, including potential energy andcarrier density, is analyzed at different widths. The convergence behavior of Broydenmethod is validated. Secondly, using the 1D solution as boundary conditions anddiscretization using finite element method, 2D coupled effective-mass Schr?dingerequation and Poisson equation are solved self-consistently under roomtemperature(300K) in DG MOSFET with channel lengths of 5nm to 20nm. Deviceoutput characteristics and the internal distribution of potential energy and carriers areprovided. The short channel effects and lost of charge neutrality at open boundariesare thought over. Further more, considering device practice, lateral diffusion areaswhich obey Gaussian Distribution are included. The influence of lateral diffusionlength on the threshold voltage is analyzed. Comparing with quasi-2D simulationresult of nanoMOS, the simulation result of this paper manifests device quantumtransport mechanism well.