Research On Physics Characteristics And Device Modeling Simulation Of Multiple-gate MOSFET

Scaling of the classical planar Metal-Oxide-Semiconductor Field-Effect Transistors(MOSFETs) below20nm gate length is facing not only technological difficulties but alsolimitations imposed by short channel effects(SCE), gate and junction leakage current due toquantum tunneling, high body doping induced threshold voltage variation, and carrier mobilitydegradation. Non-classical multiple-gate (MG) structures such as double-gate (DG) MOSFETsand surrounding-gate (SG) MOSFETs have a good control of channel charge and reduce SCE.They are also capable of improving sub-threshold slope degradation and drain induced barrierlowering (DIBL) effect. Therefore,3D multiple-gate MOSFET is an alternatives to planarMOSFET for the below20nm technology nodes. This dissertation focuses on the modeling andTechnology Computer Aided Design (TCAD) simulation of two categories of non-classicalMOSFETs, namely DG MOSFETs and SG MOSFETs.In order to fully understand the modeling and simulation of semiconductor devices, SCEinduced by scaled down and inversion layer capacitance in multiple-gate MOSFETs areintroduced here. The charge sheet approximation is no longer suitable for MG MOSFETs due tothe so-called “volume inversion” effect. As a result, the complete non-charge-sheet-basedanalytic models of drain current for long channel symmetric DG and SG MOSFETs issummarized. The DG and SG models can be generalized to a unified analytic drain currentmodel for all kinds of MG MOSFETs, with some reasonable approximations. The electricalcharacteristics of DG and SG MOSFETs with various device parameters are simulated usingSilvaco TCAD numerical simulation tools, and simulation results are obtained and discussed.An expression for electrostatic surface potentials in the long-channel symmetric doped DGMOSFETs is deduced. Also, an accurate inversion charge implicit expression derived from thesurface potentials is proposed for the long-channel DG MOSFETs. Based on the inversioncharge solution, a charge-based drain-current model for symmetric DG MOSFETs with dopingconcentration from1014cm3to1018cm3is derived, and further verified by the2D numericalsimulation. Finally, the validity of the developed proposed model is verified by comparisonswith numerical simulations. The simulation results show that the proposed model is in goodagreement with the numerical simulation results under various conditions. Therefore, theproposed model can be served as a basis for the physics analysis of DG and SG MOSFETs, andit is also suitable for circuit simulators.