Research On R_on,sp-BV Optimization Model And Structure Of Partial Super-junction VDMOS Devices

With the increasing development of electronic products,the competition is becoming more and more fierce,and the requirement of power device products is getting higher and higher.High quality and low cost are the core competitiveness in the current electronic product market.As an important part of power devices,superjunction VDMOS devices are also developing rapidly.It has great advantages in automotive electronics,lighting driver,power switch and so on.In the application of switching power supply,switching devices need not only to withstand high voltage,but also to have low on-resistance,so as to reduce on-state power loss as much as possible.Superjunction VDMOS,as a kind of unipolar device breaking the traditional"silicon limit",can withstand both high voltage and very low specific on resistance.The withstanding voltage depends on the depth of PN strip in its drift region.For the traditional superjunction process,the deeper the PN strip is,the more difficult the process is.Therefore,in the actual product,Semi-superjunction VDMOS is used instead of the traditional superjunction VDMOS device to obtain the relationship between process cost and product performance.In this paper,the relationship between specific on-resistance and blocking withstand voltage of semi-superjunction VDMOS devices is studied.The main contents are as follows:?1?Solution of Electric Field Interpretation Model for Semi-Superjunction VDMOS DevicesThe electric field of semi-superjunction VDMOS devices is decomposed into three parts:superjunction charge field,Nbuffer charge field and potential field.The distribution expressions of superjunction charge field and Nbuffer charge field are solved by piecewise solving two-dimensional Poisson equation and Laplace equation.Then the electric field of semi-superjunction devices is compared by simulation results of software Medici.The simulation results are in good agreement with the interpretation results.In the longitudinal direction of semi-superjunction devices,the electric field is uniformly distributed in the superjunction region and linearly distributed in the Nbuffer region,which is reflected in the rectangular electric field plus trapezoidal electric field in the coordinates.We obtain that the optimized electric field in the Nbuffer region satisfies one third of the ratio of the top to bottom of the trapezoidal electric field.?2?Optimizing the Minimum Specific on Resistance of Semi-Superjunction VDMOS DevicesUnder the conditions of given device blocking voltage BV,half cell width W and length of superjunction region,the specific on resistance optimization of semi-superjunction VDMOS devices can be divided into two steps.Firstly,the specific on resistance of Nbuffer region is optimized under given superjunction doping concentration.It is obtained that the specific on resistance optimization of Nbuffer region satisfies the ratio of electric field?=E_P/E_pB=1/3,and then the doping of superjunction region is optimized based on the Nbuffer optimization condition.Based on this optimization result,we discussed the relationship between the specific on resistance of semi superjunction devices,the doping concentration in superjunction region,length and concentration of Nbuffer region with the length of superjunction region.?3?Optimization of unbalanced termination for semi-superjunction VDMOS devicesWhen the dose of P-strip in the termination region is larger than that of N-strip,the peak surface electric field of PN junction in the termination region can be reduced and the voltage withstand of the terminal can be improved.The relationship between terminal withstand voltage and unbalanced dose of PN strip in terminal area is studied in this paper.