*Taiwan Semiconductor Manufacturing Company, Science-based Industrial Park,

Abstract — The high-frequency behavior and power capability of SiGe HBTs with selectively implanted collector structure have been measured at temperature between 77 and 350 K. Detailed analyses of temperature dependence on dc, high-frequency parameters, and power performances are presented. An HBT transit-time analysis is also described to find out the factors causing the increase in cutoff frequency (fT) at low temperature operation of different functionality of devices. In addition, the power capability of enhanced- breakdown device at liquid-nitrogen temperature is severely degraded. Index Terms — SiGe HBT, transit time, power capability, liquid-nitrogen temperature