Study Of High Voltageand Low Specific On-resistance SOI Lateral Power Device

The key goals of power device are high thebreakdown voltage （BV） and low thespecific on-resistance(R_on,sp). However,high Breakdown voltage demands lowerdrift-contration and longer drift-length, so acontradictory relationship of R_on,sp∝BV^2.5forpower devices exists between BV and R_on,sp.That is the Si-limit. Many scholars relatedpropose many improvements of the main issue, so three novel devices structures areproposed in the thesis.（1） A low specific on-resistance (R_on,sp) Triple RESURF MOSFET with double gates（DG-T-RESURF MOSFET） is proposed. The features for the MOSFET are dual-gateand a P-type buried layer in the drift region. On one hand, the P buried layer and a MISstructure（substrate/buried oxide layer/the N-drift region）form a Triple RESURF, soit notonly enhances the drift concentration, but also optimizes the electric field. On the otherhand, the double gates with trench gateand planar gate form double current conductionchannels, and then the trench gate increases the current conduction area and optimizesthe electric field.Thereby all above reduce R_on,spgreatlyand enhance the breakdownvoltage （BV）.By the software simulation, BV of336.8V and R_on,spof8.7m·mm²areobtained for the DG-T-RESURF MOSFET. Compared with the planar gateTripleRESURF（PG-T-RESURF） MOSFET, R_on,spand BVof the DG-T-RESURF MOSFETdecreaseby63%and increase14%, respectively. The trench gate alsoplays an importantpart of an isolation trench simplifying the fabrication processes and saves the cost.（2） A low specific on-resistance(R_on,sp) MOSFET with double gates and recesseddrain is proposed. The features forthe device structrure are a recessed drain and dualgates which is formed a trench gate reachedthe buried oxide layerand a planargate（DGRD MOSFET）.On one hand, the double gates form doublecurrent conductionchannels, and the recessed drain combines with the trench gate to increase the currentconduction area and reduce the current path.On the other hand,the P-type top layer notonly increases the drift optimized doping concentration but also optimizes the lateralelectric field.All of these forthe DGRD MOSFET maintain a high breakdown voltage（BV） and significantly reduce R_on,sp. So R_on,spof4.151m·cm²and the BV of233Vare obtained.With the same BV, itsR_on,spis reduced respectively by36%and33%, incomparison with those of the trench gate LDMOS and the conventional LDMOS.（3） A low specific on-resistance (R_on,sp) and high voltage silicon-on-insulator （SOI）trench-typepower device is proposed.The featuresfor the device structure are multipletrenches（MT）, which consists of a trench gate reached the buried oxide and two oxidetrenches in the drift region.On one hand,the double oxide trenchesfolded the N-driftregionresulting in a device cell pitch, and optimizes the electric field with the trenchgate; on the other hand, thetrench gate not only increases the current conduction areabut also plays an important part of an isolation trench simplifying the fabricationprocesses and saving the cost.Withthe same21.5μm half device cell pitch,the R_on,spofthe MT SOI LDMOSreduces from419m·cm²for the conventional LDMOS to36.6m·cm²and BVenhances from309V to632V.Bythe simulation software MEDICI and TSUPREM4, thestructure mechanism andsome keydevice parameters are analyzed. According to the fabrication level in ourcountry, some feasible processes are formulated.