SiGe Heterojunction Bipolar Transistors

ABSTRACTStrained layer growth of SiGe on Si by either Molecular Beam Epitaxy (MBE) or various methods of Chemical Vapor Deposition (CVD), including Limited Reaction Processing (LRP) and Ultra High Vacuum CVD (UHV/CVD) have been used to realize narrow bandgap base double heterojunction bipolar transistors (HBTs). This review paper will focus on the fabrication of high performance transistors, and on the material and process challenges facing the implementation of SiGe HBT technology. In particular, the use of SiGe alloys for bandgap engineering of bipolar devices and the development of self-aligned, epitaxial base bipolar device structures will be discussed, including the most recent accomplishment of 75 GHz ƒr heterojunction bipolar transistors, and the record sub-25 ps EC L ring oscillator delay. The design flexibility and trade-offs offered by SiGe heterojunction technology, like junction field/capacitance control, liquid nitrogen operation and complementary processes, arc also reviewed, to assess the leverage of a SiGe base bipolar technology in high speed circuits.