Design And Electro-thermal Characteristics Of LDMOS With Separated N-type Buried Layer And Tripple Gates

LDMOS devices,which have the advantages of good voltage resistance,strong driving ability and easy integration,are widely used in the power circuit of electronic automobile,smart home and other fields.LDMOS devices have several important key parameters such as breakdown voltage（BV）,specific on-resistance(R_on,sp).For a long time,researchers are committed to improving the contradictory relationship between BV and R_on,sp in order to break through the ideal"silicon limit".On the other hand,the reliability of devices is also one of the concerns.The internal self-heating effect of devices is significant during operation,which will lead to the degradation of key performance parameters and result in the deterioration of device performance.In addition,the buried oxide layer becomes a barrier of device heat dissipation in the SOI devices,and the self-heating effect is more prominent.Therefore,it is of great practical significance to obtain better BV,R_on,sp and reliable LDMOS devices.In this paper,a SNTG-LDMOS structure is proposed which can realize the compromise optimization of electrical characteristics.Using bulk silicon SNTG-LDMOS and SOI SNTG-LDMOS as carriers,the electric heating characteristics are simulated and analyzed to achieve the comprehensive performance improvement of the device.The main research contents and achievements of this paper are as follows:1.A LDMOS device with Seperated N-type Buried Layer and Tripple Gates（SNTG-LDMOS）is proposed,which has low R_on,sp and high conducting current I_DS while maintaining a certain BV.Compared with Double gates LDMOS（DG-LDMOS）devices,the G_m of SNTG-LDMOS increases about 205%.When BV is 182 V,the R_on,sp is 30.5mΩ·cm²,which decreases by 14.6%.The compromise optimization of electrical characteristics is realized and the device performance is improved.2.The optimal parameters are determined to achieve the compromise optimization of the electrical characteristics of the device.The influence of key doping concentration and structure parameters on SNTG-LDMOS devices was studied and the principle was analyzed.The optimized device power was 1.191 MW/cm².In addition,common media（Hf O₂,Si₃N₄,Ga As）are introduced into the grid oxide film and simulated.When the grid oxide film medium is Hf O₂,the device performance is excellent.After optimization,the BV is 189 V,R_on,sp is 25 mΩ·cm²,which is decreased by 16.7%,FOM is 1.428 MW/cm²,and the comprehensive performance of SNTG-LDMOS devices is improved.3.The self-heating effect of bulk silicon and SOI SNTG-LDMOS was studied,the temperature distribution and thermal resistance distribution caused by self-heating effect were simulated,the mechanism was explained and the performance was compared.Compared with bulk silicon devices,the thermal characteristics of SOI SNTG-LDMOS devices are slightly worse that R_th increased by 14.3%and I_DS degraded by 6.2%.Secondly,a silicon window is made and a silicon column structure is added to improve the reliability of SOI SNTG-LDMOS devices.Compared with SOI SNTG-LDMOS,the thermal characteristics of SOI SNTG-LDMOS with silicon windows are effectively improved.Finally,the number and size of silicon windows were optimized and improved in order to further alleviate the self-heating effect of SOI SNTG-LDMOS devices with silicon windows.The simulation results show that the thermal characteristics of the device are improved by 20%without affecting the electrical characteristics.In conclusion,the SNTG-LDMOS device proposed in this paper has better comprehensive performance,realizes the compromise optimization of BV and R_on,sp,and improves the thermal reliability of the device,which can be considered for use in the field of medium and low voltage automotive electronics and communication base stations within 200V.