SiGe HBT compact modeling for circuit design at cryogenic temperatures

Silicon-Germanium (SiGe) heterojunction bipolar transistors (HBTs) have shown high current gain and high cut-off frequencies at cryogenic temperatures. These features can be traded for low noise and low power dissipation and thus make SiGe HBTs attractive for different types of qubit readout circuits as well as for space-based applications. However, the design of such integrated circuits is significantly impeded by the present lack of compact models that are able to accurately describe HBT characteristics over a range of cryogenic temperatures. This presentation provides an overview on the present status of physics-based SiGe HBT compact modeling for low temperature applications. Starting with the low temperature behavior of important material parameters and the relevant physical effects, the resulting modifications and extensions of a widely available industry standard HBT model are discussed. The temperature and bias dependent characteristics of the extended model and important transistor parameters are compared to experimental data. Finally, still existing open questions regarding SiGe HBT device physics at cryogenic temperatures are indicated.