Research On New Structures Of Two-dimensional Super-Junction Like LDMOS

Due to the advantages of surface distributed electrode, simple production process, Lateral double-diffused-metal-oxide-semiconductor (LDMOS) has been widely applied in power integrated circuits. As the key performances index of LDMOS, how to improve the trade-off between the breakdown voltage and on-resistance are therefore becoming a popular researching area. The thought of Super-junction(SJ) imparts power devices the abilities of supporting high breakdown voltage and low on-resistance in the meantime; however, because of the issues of substrate-assisted-depletion-effect, Super-junction applied in LDMOS causes the performance degradation of the device. This phenomenon deeply hinders the development of LDMOS power devices.Based on the idea of the charge balance,this thesis proposes two new Two-dimensional SJ-LDMOS structures, which compromise the LDMOS performance in both breakdown voltage and on-resistance; And then, by comparing with the conventional structures, it analyzes the new structures of LDMOS on both breakdown voltage and on-resistance through the two-dimensional simulation software MEDICI; Meanwhile, the main parameters, which affecting the performance of high voltage LDMOS, also have been simulated and analyzed. Specific findings are as follows:1) Two-dimensional SJ/RESURF LDMOS device designSubstrate assisted depletion effect is the most serious in drain side; therefore, the new structure introduces RESURF area near the drain side in drift region, which compensates the charge excess in P pillar caused by the longitudinal electric field. Simulation results show that under the same doping density in super-junction and the same length of the drift region (25 microns), the breakdown voltage of the new structure is 407V, while the conventional two-dimensional super-junction LDMOS is 202V.2) Two-dimensional SJ/RESURF device with step-doping P pillars designWhen the device reverses the voltage, the substrate-assisted-depletion caused by longitudinal electric field will lead to superfluous charge in the P pillars, and the concentration of the excess charge is gradually increased from the source to the drain. Based on this, the new structure stepped doping the P pillars in the super junction, and the doping concentration gradually decreases from the source to the drain side. On one hand, the layer distributed design of charge doping at P pillar utilizes the new electric field generated by the graded junction to regulate the surface electric field of the device, which makes the electric filed in drift region evenly distributed. On the other hand, when compared with the conventional N column ladder-doped, the new structure with P pillars step doping layer improves the doping concentration of N columns, and the on-resistance at on-state is further reduced. According to the simulation result, it showed that with the same doping conditions and same drift region length (45 microns), the breakdown voltage of the two-dimensional SJ/RESURF LDMOS device with step-doping P pillars reached 743V, while the conventional type is only 528V.