Study On Characteristics Of SiC Bipolar Integrated Transister

As the demand for sensing applications in high-temperature environment is increasing,SiC bipolar integrated circuits have attracted more and more attention due to their excellent high temperature tolerance.As the core device of SiC bipolar integrated circuits,low-voltage SiC integrated bipolar transistor has important research value.Therefore,in this thesis,software simulation has been used to take the npn SiC integrated transistor as an example to carry out the structural design and optimization,the influence mechanism of the structural parameters of each region on the DC and frequency characteristics of the transistor,as well as the influence of minority carrier lifetime,temperature and SiO₂/SiC interface traps of the external base region on the device performance are studied.The main research contents and conclusions are as follows:1.The design and optimization of npn SiC integrated transistor are carried out.The n+/p/n-/n+device structure on semi-insulating substrate is used for optimization,the influence of the structural parameters of transistor on the DC and frequency characteristics is studied,and a optimized structural parameter is determined by compromise,the maximum current gain ?max is 93.7 and the unity current gain frequency fT is 2.2GHz at room temperature.Results show that the doping concentration and thickness of the base layer have the greatest impact on the DC and frequency characteristics of the transistor.The length of the external base mainly affects the base current by changing the electron concentration reaching the base electrode,thereby affecting the current gain ?.When the collector doping concentration is increased,the current gain of the transistor at high current density can be effectively improved.2.The analysis of the influence of minority carrier lifetime and temperature on transistor characteristics has been completed.The results show that when the minority carrier lifetime in the emitter and base layer is greater than 20ns and 60ns,respectively,the effect on gain ? is ignorable,and the minority carrier lifetimes in each region have an ignorable effect on the frequency characteristics when the forward bias voltage of the base-emitter junction is small,and when VBE is larger,the minority carrier lifetime has a obvious influence on the frequency characteristic.As temperature rises from 27? to 500?,the current gain ? and the unity current gain frequency fT both decrease significantly,and the downward trend of ? at higher collector current density becomes gentle as the temperature increases.The knee current IKF decreases at higher temperature.3.The effect of the SiO₂/SiC interface traps at the external base on the current gain ? has been studied.The results show that the variation of interface-trap density can significantly affect the base current,thereby affecting the current gain,and when the interface-trap density is lower than 1×10¹¹cm^-2eV^-1,the effect on the transistor current gain can be ignored.Finally,it is proposed that when the interface quality of the external base is poor,a multi-base epitaxial structure is introduced to increase the current gain of the transistor,thereby reducing the strict requirements for the passivation process.