Study On LDMOS With Trench And Super-junction Buried Layer

Lateral Double-diffused MOS?LDMOS?,whose electrodes are concentrated on the surface of the device,are more compatible with the integrated circuit process than Vertical Double-diffused MOS?VDMOS?.As a result,with the development of PIC?Power Integrated Circuit?,LDMOS with high impedance input and high slew rate will occupy a more important position in the field of power devices.However,there is a contradictory relationship between on-resistance and breakdown voltage in LDMOS,seriously restricting the development of LDMOS devices.In addition,when applied to high and low voltage integration,LDMOS requires a very thin epitaxial layer,which will limit the vertical breakdown voltage.When the drift region reaches a certain length,even if the length is increased,breakdown voltage of LDMOS is not significantly improved.In order to solve the above problems,the paper proposes OT-DGLDMOS structure which can alleviate the contradictory relationship and SJBL-LDMOS structure which can increase the vertical breakdown voltage.The detail contributions of the dissertation are listed as followings:Firstly,a new double-gate LDMOS with oxide trench?OT-DGLDMOS?is proposed.In this new structure,the drift region adds a SiO₂ dielectric trench while increasing a gate electrode in the vertical direction of the device.The Si O₂ dielectric trenche fold the drift region in the longitudinal direction,which will increase the effective total length of the drift region and increase the withstand voltage of the structure.According to the RESURF effect,the concentration of the drift region is optimized and the on-resistance of the structure is reduced because the trench occupies a part of the drift region.Besides,a gate electrode is added in the vertical direction of the structure,that is forming a conductive channel in the vertical direction.Compared to the one-gate LDMOS,the electron injection capability of double-gate structure is significantly better.When the device is turned on,the gate of the current control is stronger in the double-gate structure,which will reduce the on-resistance.The simulation results of the ISE-TCAD show that,when the length of drift region is 3.5?m,the breakdown voltage of OT-DGLDMOS is 128V and the on-resistance is 2.30m?.cm².Compared with the conventional LDMOS,the breakdown voltage is increased by 47%,and the on-resistance is decreased by 15%.Compared to the same size one-gate trench LDMOS,the on-resistance of OT-DGLDMOS is decreased by 50%.Secondly,a new structure of LDMOS with a super junction buried layer?SJBL-LDMOS?is proposed.Compared to conventional RESURF LDMOS,a super junction buried layer?SJBL?is introduced under the drain electrode of SJBL-LDMOS.In one aspect,the PN junction formed by the P-pillar and the drain extends the depleted layer of the drift region.On the other hand,the N-pillar and the P-pillar are depleted with each other,which also can extend the depleted layer of the drift region.So the SJBL can greatly improve the vertical breakdown voltage of the SJBL-LDMOS.In the SJBL-LDMOS,the breakdown characteristic of the device would be influenced by the SJBL in three ways.Firstly,the vertical depleted region would be expanded for the introduced SJBL and the vertical breakdown voltage would be increased;secondly,the surface electric field would also be affected and modulated for the charge-coupled effect introduced by the SJBL and the lateral breakdown voltage would be increased;thirdly,due to the electric field modulation effect introduced by the SJBL,the vertical bulk electric field distribution would also be modulated to be more uniform.The simulation results of the ISE-TCAD show that,with the same 70?m drift region length,the breakdown voltage is increased from 465V for the conventional LDMOS to 812V for SJBL-LDMOS.