Research On Novel Lateral Power Device With A Polysilicon Voltage Sustaining Layer

As a noval power electronics technology applied to the field of power,the research and development of power semiconductor devices play a key role in promoting the development of power electronics technology.Because the electrodes of the lateral power device are located on the surface of the chip and are easy to be integrated,they have been widely used in power integrated circuits.Among lateral power semiconductor devices,lateral double-diffused field effect transistors(LDMOS)and lateral insulated gate bipolar transistors(LIGBT)have become two widely used mainstream devices because of their many advantages.In this thesis,after briefly explain the optimization technology of lateral voltage sustaining region,and based on the convention LDMOS and LIGBT,two noval LDMOS and LIGBT power devices with polysilicon voltage sustaining layers are proposed,and the device structures,opetrating principles and performances are analyzed in detail:1)Although LDMOS has many advantages such as easy driving and fast switching speed,it also has outstanding problems:its specific on-resistance increases significantly with the increase of breakdown voltage.Junction termination technology and RESURF(Reduced RURface Field)technology improve the breakdown voltage of the device without increasing the specific on-resistance by optimizing the electric field on the surface drift region of the device.And the accumulation layer technology reduces the specific on-resistance of the device without affecting the breakdown voltage of the device by introducing an additional electron accumulation layer.Based on these technologies,this thesis analyzes the characteristics of a noval LDMOS(AG LDMOS)device with a polysilicon voltage-sustaining layer.The AG(accumulated-extension modeed gate)structure not only increases the charge density on the surface of the drift region when the device is turned on,but also optimizes the electric field distribution on the surface of the drift region when the device is turned off.The simulation results show that,compared with RESURF LDMOS with the same size,the AG LDMOS device's specific on-resistance is reduced by nearly 80%at the same 500 V breakdown voltage.2)LIGBT has gradually become the core component of automatic control and power transformation because of its advantages such as high input impedance and low on-state voltage drop.RC-LIGBT is a LIGBT with reverse conduction function.By introducing an inverse parallel freewheeling diode consisting of N⁺collector region,drift region and P base in the structure to realize the reverse conduction ability.Due to the influence of the freewheeling diode,the device operates in MOS mode with large body resistance during forward conduction state,and then in IGBT mode with small body resistance,which causes the phenomenon of voltage snap-back.This thesis proposes a new reverse-conducting lateral insulated gate bipolar transistor(RC-LIGBT)device with a polysilicon voltage-sustaining layer,which eliminates the phenomenon of voltage snap-back by isolating LIGBT and freewheeling diode,and the device only operates in IGBT mode during forward conduction state.At the same time,the polysilicon voltage-sustaining layer can be used to optimize the surface electric field in the drift region.The simulation results show that,compared with the convention RC-LIGBT with the same device parameters,the on-state voltage drop of the RC-LIGBT device proposed in this thesis is reduced by 33.5%(@E_off=2.17 mJ/cm²)and the E_off is reduced by 87.5%(@V_on=1.98V)at the same 500 V breakdown voltage,and the reverse recovery time has been reduced by 85.5%.