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

Abstract

It is well known that there is a fundamental tradeoff among the breakdown voltage (including BVCBO and BVceo), the cutoff frequency (fT), and the current gain (β) for standard collector SiGe HBTs. In order to enhance the breakdown voltage at a fixed fT 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 fT 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 fT×BVCEO×β is improved from 65945GHz-V to 83729GHz-V, which effectively develops the high frequency and high power application of SiGe HBTs.