SiGeHBT for application in BiCMOS technology: II. Design, technology and performance

SiGe technology has acquired great importance in recent years. Recent advan ces made in the SiGe HBT technology for analogue applications are discussed in this two-part review paper. Strain, stability, reliability, mobility of charge carriers, bandgap narrowing and effective density of states of SiGe layers have been discussed in part I. This paper (part II) is devoted to t he HBTs: their design and performance. The two designs of the HBTs develope d by IBM and by Daimler-Benz are discussed. Their relative merits and const raints imposed by the stability criterion on each design are described. The technology used for implementing the two designs is also described. The de and ac characteristics and Ge profiles needed to optimize different figure s of merit are discussed in detail. The parasitic barriers created by outdi ffusion of B and also on operating the HBT at high current densities are ex plained. High injection barriers can be suppressed by a special design of t he Ge profiles. Introduction of C in the base suppresses outdiffusion of B. HBTs with SiGeC base layers are discussed. Issues involved in simultaneous optimization of f(T), f(max) and B V-CEO are addressed. Values of f(T), f( max) and B V-CEO Of high-performance HBTs are compiled and given in a table . The noise characteristics of the SiGe HBTs are far superior to those of I II-V devices. Noise in SiGe HBTs is discussed in detail. Finally, a summary of selected circuits that have been fabricated using SiGe HBTs is given.