Compared with BVceo,BVces is more related to collector optimization and more practical significance,so that BVces×fT rather than BVceO×fT is employed in representing the limit of the product of the breakdown voltage-cutoff frequency in SiGe HBT for collector engineering design.Instead of a single decrease in collector doping to improve BVces×fT and BVceo×fT,a novel thin composite of N- and P~+ doping layers inside the CB SCR is presented to improve the well-known tradeoff between the breakdown voltage and cut-off frequency in SiGe HBT,and BVces and BVceo are improved respectively with slight degradation in fT.As a result,the BVces×fT product is improved from 537.57 to 556.4 GHz·V,and the BVceo×fT product is improved from309.51 to 326.35 GHz·V. Compared with BVceo, BVces is more related to collector optimization and more practical significance, so that BVces × fT rather than BVceO × fT is employed in representing the product of the product of the breakdown voltage-cutoff frequency in SiGe HBT for collector engineering design. Instead of a single decrease in collector doping to improve BVces × fT and BVceo × fT, a novel thin composite of N- and P ~ + doping layers inside the CB SCR is presented to improve the well-known tradeoff between the breakdown voltage and cut -off frequency in SiGe HBT, and BVces and BVceo are improved respectively with slight degradation in fT.As a result, the BVces × fT product is improved from 537.57 to 556.4 GHz · V, and BVceo × fT product is improved from 309.51 to 326.35 GHz · V.