The Study Of Novel Trench LDMOS With High Breakdown Voltage

Many novel device structures come up with the development of power semiconductor device technology.Laterally double-diffused metal-oxide semiconductor(LDMOS)has been widely used in equipment manufacturing,rail transport,national defense and other important field because of its high power,high linearity,good thermal performance and ideal compatibility in very large scale integrated circuits.However,due to the technology progress,the performance requirements of semiconductor devices also increase,i.e.higher breakdown voltage,higher working current and faster switching speed.Therefore,in order to meet the growing demand,researchers explore to study from devices material,structure,fabrication for improving the device performance.In this thesis,based on the field plate,the trench structure and other terminal technologies,two novel trench LDMOS are proposed to achieve the higher breakdown voltage(BV)and the lower on-resistance(Ron).The first proposed novel structure is L-shaped vertical field plate trench LDMOS device.In this device,L-shaped vertical field plate(LVFP)connected with gate electrode is inserted into the trench.The LVFP introduces four peaks in the drift region,which can ajust the electric field distribution and the RESURF effect in the device.Thus,the breakdown voltage of the device is enhanced.Moerover,the LVFP can assist to deplete the drift region more effectively,which means that the drift doping concentration is improved.Thus,the on-resistance decrease.The influence of the key parameters on the device performance are analysed comprehensively including the position of the LVFP,the profile of trench and the drift doping concentration.Compared with the conventional vertical field plate LDMOS,the breakdown voltage of LVFP LDMOS is increase from 710 V to 833 V and the onresistance is reduced by 48.19%.Its figure-of-merit(FOM,=BV2/Ron)is the highest and its performance has been greatly improved.Based on Silicon-On-Insulator(SOI)technology,the second device named trapezoidal trench SOI LDMOS is presented.The trapezoidal trench can effectively adjust the electric field and potential distribution in the device,due to the fact that two higher electric field peaks occur near the corners of the trapezoidal trench.Compared with the Conventional trench LDMOS,for the prosposed device,the breakdown voltage is increased by 13.35%,although the on-resistance is not significantly deceased.Thus,the trapezoidal trench SOI LDMOS can still achieve a larger FOM,which means the higher device performance.