53 GHz-f/sub max/ Si/SiGe heterojunction bipolar transistors

The authors report Si/SiGe HBTs (heterojunction bipolar transistors) with a base sheet resistance of only 680 Omega / Square Operator , leading to a measured f/sub max/ of 53 GHz. The complete layer structure was grown by MBE (molecular beam epitaxy), including the single-crystal emitter with no need for a poly-drive-in anneal. Devices were built on high-resistivity substrates with As-implanted and diffused buried layers. A double-mesa structure using a self-aligned base metallization with respect to the emitters was employed. On-wafer high-frequency measurements from 0.5 to 26 GHz showed transit frequencies between 40 and 50 GHz for devices with 1-3 mu m wide emitter fingers. The reduced base sheet resistance compared to earlier devices led to a maximum available gain at 26 GHz for a 1*16 mu m device of 6.3 dB corresponding to a record f/sub max/=53 GHz.