SiGe transistors have been mainstream in RF electronics for decades.
I’ve always wondered why there wasn’t more germanium in my computer. I’m sort of wondering if that will change with chiplets. Say for instance a germanium MMU or cache.
SiGe bipolar transistors are fabricated on top of old CMOS processes and are relatively cheap from a fixed-cost perspective but not highly integrated and only cost/power-efficient for niche PHY layer applications.