Novel superjunction collector design of power SiGe HBTs for high fT×BVCEO×β product

It is well known that there is a fundamental tradeoff among the breakdown voltage (including BV_CBO and BV_CEO), the cutoff frequency (f_T), and the current gain (β) for standard collector SiGe HBTs. In order to enhance the breakdown voltage at a fixed f_T and β, the superjunction collector design is proposed and the model of NPN SiGe HBT with a superjunction P-type doping layer inside the collector-base (CB) space charge region (SCR) is established with SILVACO TCAD. It is shown that the inserted P-type layer provides a reverse electric field to change electric field distribution, reduce the peak ionization coefficient, and hence enhance the breakdown voltage with a slight decrease off and β. Furthermore, a novel composite of double P-type layers inside the CB SCR is proposed for further improvement of the breakdown voltage at a minor expense of f_T and β It is shown that SiGe HBT with double P-type layers has the lowest peak electric field, the lowest peak ionization coefficient and consequently the highest breakdown voltage when compared with standard collector and one P-type layer collector SiGe HBTs. As a result, the figure of merit f_T×BV_CEO×β is improved from 65945GHz-V to 83729GHz-V, which effectively develops the high frequency and high power application of SiGe HBTs.