The temperature dependence of dc characteristics and its implication in microwave power Si/SiGe/Si HBTs

Si/SiGe/Si HBTs provide excellent microwave power performance within the context of homo-junction silicon BJT. Applications of the technology, however, will require the performance specifications with regard to the temperature range of operation. In this paper, we have measured the temperature dependence of properties such as the Gummel plots, ideality factors, the base-emitter voltage V_BE at various base current levels, current gain, common emitter characteristics and early voltage from 23 °C to 260 °C. Our data show the current gain decreases with increasing current and temperature in normal operating ranges, and that the variation of V_BE with temperature in SiGe HBT is smaller than that of homo-junction silicon BJT. The negative differential resistance (NDR) characteristics of Si/SiGe/Si HBT at high collector-emitter voltage and high current is observed also. These are important in preventing thermal runaway in power transistors, and may decrease or remove the necessity of emitter ballast resistors and provide higher power-added efficiency in an amplifier block. We also show that the gain-early voltage product is roughly linear with 1/T above ambient temperature, this result are important and useful for circuit applications.