SiGe HBT for application in BiCMOStechnology: II. Design, technology and performance

Abstract

SiGe technology has acquired great importance in recent years. Recent advances made in the SiGe HBT technologyfor analogue applications are discussed in this two-part reviewpaper. Strain, stability, reliability, mobility of chargecarriers, bandgap narrowing and effective density of states ofSiGe layers have beendiscussed in part I. This paper (part II)is devoted to the HBTs: their design and performance. The twodesigns of the HBTs developed by IBM and by Daimler-Benz arediscussed. Their relative merits and constraints imposed by thestability criterion on each design are described. Thetechnology used for implementing the two designs is alsodescribed. The dc and ac characteristics and Ge profiles needed tooptimize different figures of merit are discussed in detail.The parasitic barriers created by outdiffusion of B and alsoon operating the HBT at high current densities are explained.High injection barriers can be suppressed by a special design ofthe Ge profiles. Introduction of C in the base suppressesoutdiffusion of B. HBTs with SiGeC base layers are discussed.Issues involved in simultaneous optimization of fT,fmax and BVCEO are addressed. Values of fT,fmax and BVCEO of high-performance HBTs arecompiled and given in a table. The noise characteristics ofthe SiGe HBTs are far superior to those of III-V devices.Noise in SiGe HBTs is discussed in detail. Finally, a summary ofselected circuits that have been fabricated using SiGe HBTs isgiven.