SiGe HBTs for ultra-high speed applications

Although the first transistors were made of Ge, the role of this semiconductor material soon faded away. During the last few years, however, we witnessed a renaissance of Ge in semiconductor electronics. Alloyed with Si, it forms SiGe which is currently widely used in SiGe HBTs. Recently, the improvement of nanoscale MOSFET performance by applying SiGe has been intensively investigated. This paper describes the evolution of SiGe HBTs over the last 15 years and provides an overview on the current state of the art of these devices. The impact of SiGe in other fields of semiconductor electronics is briefly discussed.