A retrospective on the SiGe HBT: What we do know, what we don´t know, and what we would like to know better

By any reasonable reckoning, SiGe HBT BiCMOS technology has “come of age,” as evidenced by a robust set of sources for SiGe fabrication around the world (including open foundries in the USA, Europe and Asia), multiple generational scaling nodes in production (3, soon to be 4), significant market penetration in a diverse set of performance-constrained analog, digital and RF systems, and recognized appeal for use in emerging mm-wave through near-THz electronic systems. In this retrospective on the SiGe HBT, I share a personal view of what we do know, what we don´t know, and what we would like to know better, from the perspective of materials, devices, technology, circuits, and applications.