Research And Optimized Design Of Sic Superjunction VDMOS

With the development of SiC technology,the performance improvement of SiC power device will reach the theoretical limit as Si poower devices in the near future.The super junction structure used to break the Si limit can be applied in the SiC device to further enhance the performance,which has important significance of promoting the social development and device application.This thesis mainly designs and optimizes a 1400V 4H-SiC VDMOS cell with super junction structure and the main work and results are summarized as follows:First,the basic structure and working principle of SiC VDMOS is researched.And the main static parameters are given such as threshold voltage,breakdown voltage and on-resistance.Moreover,the influence of design parameters on static electrical characteristics is analyzed.Meanwhile.the basic theory of super junction is researched and the influence of its design parameters on breakdown voltage and on-resistance is analyzed too.Second,the thesis designs a 1400V SiC super junction VDMOS by designing and optimizing the basic parameters such as the drift region,JFET region,channel region,P-type barrier layer and P well.Aimed at the breakdown voltage of 1400V.the specific on-resistance and device reliability are both considered.Based on the theoretical analysis,the influence of the doping concentration and size of these regions on the MOSFET device characteristics is analyzed through TCAD software.According to the influence curve,the tradeoff is made among the breakdown voltage,on-resistance,the gate oxide breakdown in the JFET region,the punch through of the P well and the threshold voltage.In this way.the parameters of the VDMOS cell are determined.The drift region was 9um-thick with a doping concentration of 1.9 ×1016cm-3.JFET region is 0.5um*2 long.Channel length is 0.5um.P-type barrier is 0.3um deep with a doping concentration of 1.5×1018cm-3.The doping concentration of P well is 5×1016cm-3.Finally,the thesis proposes a super junction structure with local charge imbalance,where the doping concentrations of PN columns are locally imbalanced but overall balanced.VDMOS with proposed super junction is compared with conventional VDMOS with N-type drift region and super junction VDMOS.With same thickness and doping concentration,the change of their breakdown voltage shows that the VDMOS with proposed structure has the highest breakdown voltage.Besides,the on-resistance and quality factor(VB2/R)are also considered.The quality factor of the MOSFET with the proposed structure is higher than the conventional MOSFET and lower than the super junction MOSEFT.In summary,the main work of this paper is designing and optimizing a 4H-SiC VDMOS cell with super junction structure with blocking voltage of 1400V and proposing a super junction structure with local charge imbalance.The simulation results show that the super junction structure can effectively improve power performance of SiC VDMOS and the proposed structure with local charge imbalance can improve the blocking voltage further of SiC VDMOS.The proposed structure is an effective way to improve breakdown behavior of SiC VDMOS.