| With the development of integrate circle,the integration of device is improving rapidly,and transistor,as the basic unit of integrated circuits,its size is shrinking.The reduction of the size of MOSFET lead to the decrease in device volume and power consumption of system and the improvement in performance and integration of device,and it can also affect the physical characteristics of the device.When the size of MOSFET is scaled down to the nanometer,the size of drain/source region is not conform to the Scaling Down,the resistance of the drain/source region plays a more important role in the total resistance.The calculation of MOSFET drain/source resistance has become one of the hot topics in device research.Modeling method can build a concise and accurate calculation model and obtained explicit analytical expressions of the physical parameters,these models play an important role in reducing the drain/source resistance and improving the device performance.Main works of this thesis are to establish the shallow junctions MOSFET model by semi-analytical method,and to study factors which affect the potential and resistance of the MOSFET drain/source region.Main works of this thesis are as follows.Firstly,this thesis summarizes recent research methods of resistance in drain/source region in detail,and analyzes the advantages and disadvantages through concrete examples.Secondly,in order to avoid shortcomings of these methods,a semi-analytical method is proposed for the modeling of MOSFET with shallow junctions in this thesis.The integral equations and the generalized Fourier series are used to solve out the drain/source resistance.According to the normal workling characteristics of MOSFET,the drain/source region is divided into the sensing channel region and the extended resistance region,the doping concentration in these two regions is discontinuous.The resistance of the sensing channel region is calculated as the lumped resistance,and the resistance of the extension region is modeled by semi-analytical method.According to the theory of rectangular equivalent source,this thesis establishes a two-dimensional potential model for each regions,lists boundary value problems and convergence conditions of this model Using the separation variable method to solve out boundary value problems,and potential integral expressions of each region can be obtained.After convergence conditions are been substituted,a set of equations with unknown functions can be obtained.Expanding unknown functions by using the Fourier series,the matrix equation with unknown coefficients can also be obtained.Unknown coefficients of matrix equation can be solved out by MATLAB,after that,these coefficients can be substituted into the potential equations,and analytical expressions of the two-dimensional potential is obtained,and then the resistance of the MOSFET in drain/source extension region can be found out.Finally,the two-dimensional semi-analytical model of MOSFET with shallow junctions is verified.The PDE toolbox is used to verify the potential distribution curve of this model under the same doping concentration in the extended resistance region The correctness of the theory and calculation of the model is proved by comparisons with different physical parameters,the accuracy of the model is proved by analyzing the error of the model calculation results and the ATLAS simulation results.And this thesis also analyzes the influences of various physical parameters to the resistance of MOSFET in drain/source regio.In order to eliminate the exponential term in the calculation,this thesis uses the generalized Fourier series expansion method so that infinite series of equations can be calculatted to any term,that greatly improves the accuracy of the calculation results.Compared with other modeling methods,the most outstanding advantage of this model is that it can be used to solve the resistance of the drain/source region with non-homogeneous and complex structure. |
PDF Full Text Request