SiGe heterojunction bipolar transistor issues towards high cryogenic performances

The performances increase at low temperature make the SiGe HBT a masterpiece for cryogenic circuits. The time-progressive enhancement of fT and fMAX toward the THz frequency at room and at cryogenic temperatures is presented along with STMicroelectronics and IBM successive HBTs generations. The influence of the Ge content and graduality into the base is discussed, highlighting the keys for best high-frequency cryogenic operation. This is shown with eight different cases and addressed on fT, fMAX, the transit time, the minimum noise figure and the equivalent noise resistance.