Research On The Mechanism And Characteristics Of BRT With Buried Layer

In the field of power semiconductor devices,MOS gate control devices are widely used in locomotive traction,wind power generation,and new energy vehicles,because of their advantages of high input impedance and easy driving.They IGBT is a typical MOS gate controlled composite device.The main problem in high power applications is how to solve the contradiction between its on state voltage drop and turn-off loss.This thesis proposes two new structures of base resistance controlled thyristor(BRT)with buried layers,a BRT structure with buried n-type carrier storage layer(BN-CS-BRT)and a BRT structure with SiO2 buried oxygen layer(BOX-BRT)are presented.The new structures introduce the electron injection enhancement(IE)effect in the IGBT into the traditional BRT structure.The new structures can completely suppress the snapback phenomenon of the traditional BRT and improve the trade-off relationship between the on-state voltage drop and the turn-off loss.The main research contents and results are as follows:Firstly,The structural characteristics and working principle of BN-CS-BRT and BOX-BRT are studied.The 6.5kV voltage level structure models are established by T-CAD simulation software,and the working mechanism of the devices are studied.The results show that the new structures need to apply a negative gate bias voltage to meet the withstand voltage requirements during forward blocking;Positive gate voltage is applied during turn-on,and the device mainly work in IGBT mode at low current density.As the current density increases,The device is mainly work in the thyristor mode;When it is turned off,a negative gate bias is applied to make the P-channel MOSFET turn on to extract hole current,and the positive feedback of the PNPN thyristor is destroyed;Due to the regeneration mechanism of the thyristor,the positive gate voltage is removed after the device is turned on,the device can still be turned on.Secondly,The mechanism of the IE effect of the new structures is studied,and the maximum turn-off current density analysis model is established.The results show that the n-type buried layer and the buried oxide layer can form a hole barrier to hinder the outflow of holes,and cause the IE effect.Thereby accelerating the opening of the thyristor mode,completely suppressing the snapback phenomenon,and reducing the on-state voltage drop of the device;The maximum turn-off current density is a function of the gate bias and increases with the increase of the gate bias.Thirdly,The static and dynamic characteristics of BN-CS-BRT,BOX-BRT and traditional BRT are compared and analyzed,and key structural parameters are extracted.The results show that the concentration and thickness of the n-type buried layer and the position of the buried oxide layer have an effect on the static characteristics of the device.Lastly,The influence of carrier lifetime on the static and dynamic characteristics of the new structure is analyzed,and the technical curves of the on-state voltage drop and turn-off loss of the new structure and the traditional BRT are compared.The results show that both BN-CS-BRT and BOX-BRT improve the trade-off relationship between on-state voltage drop and turn-off loss,and BOX-BRT has a better trade-off relationship;The influence of high and low temperature on the static and dynamic characteristics of the new structure is analyzed.BN-CS-BRT is more sensitive to temperature changes.The research results have certain reference value for the research and development of high voltage MOS gate control devices.