History and Future Directions in SiGe HBT BiCMOS Technology and Its Applications

The development of SiGe BiCMOS has mirrored silicon semiconductor development as the technology transitioned from Ge transistors, to silicon transistors, to ion-implanted base, to polysilicon emitter transistors, and finally to SiGe HBTs and SiGe BiCMOS. While the physics of the graded base SiGe HBT transistor was established early on in 1954 by Herb Kroemer it was not until the 1980s that SiGe HBTs were first realized. At the core of the SiGe Heterojunction Bipolar transistor development is the SiGe Epitaxy. In fact the SiGe HBT drove the development of the SiGe: B S/D processes now used for stressors in advanced CMOS since it was the first commercial technology with SiGe layers. SiGe HBT BiCMOS continues to find large volume production opportunities in applications that require mostly RF/Analog and less digital content (Big-A/little-D). Scaling has driven the speed performance (f(MAX)) towards terahertz levels to open up yet more applications. Many challenges still exist in the technology.