Doping Dependent Subthreshold Swing Modelling of Quadruple Gate MOSFETs

Abstract

MOSFET scaling has undergone a drastic change in the size and packing density in the recent years and new methods of improvising the performance of the device being introduced every year. Many ingenious techniques have been used to model the device and its properties. There are many to model the same device parameter. So it is upto the designer's requirement to choose the method that is suitable for him. Some methods give more accuracy but take very large computational time where as some may provide results with less accuracy but provide results faster. Here in this thesis we have brought a balance between the two, i.e. the methodology used here is simple but very ecient in providing results to very satisfactory levels. A potential function has been developed for a quadruple gate MOSFET by introducing the concept of eective number of gates (ENGs). In this ENGs concept the quadruple gate MOSFET is broken into 2 double gate MOSFETs and so the need to solve large 3-D equations nullies. The 2-D potential function in the channel is assumed to be parabolic in nature and the 2-D Poission's equation has been solved to obtain the channel potential function. After introducing the concept of ENGs the 3-D structure has been successfully modelled into a 2-D structure. This is the main advantage of this technique. Then the subthreshold swing parameter is obtained by the concept of eective conduction path. Finally after the device has been modelled the eect of variation of device parameters on subthreshold swing is analysed. The device parameters that have been considered for variation are device channel length, oxide thickness, channel thickness, drain to source voltage, channel doping. ATLASTM has been used for obtaining the simulation results and validated against the modelling results obtained with the help of MATLABTM. Both the results have been plotted together and their level of matching in observed and analysed.