Profile scaling constraints for ion-implanted and epitaxial bipolartechnology designed for 77 K operation

摘要

The scaling constraints on vertical profile design which areunique to liquid nitrogen temperature operation (LNT≅77 K) ofion-implanted and epitaxial Si and SiGe bipolar technologies areinvestigated experimentally. While conventional on-implantationtechniques can yield transistors with cutoff frequencies as high as 36GHz at LNT, these devices have limited extendibility for circuitapplications due to excessive base freeze-out. A more advanced epitaxialSiGe technology can be used to simultaneously achieve anf_T for 59 GHz and superior base freeze-outproperties at low temperatures, yielding a very aggressive ECL (emittercoupled logic) gate delay of 28 ps at LNT. For SiGe devices, however,the optimum collector profile design is constrained by a barrier inducedat the SiGe-Si heterojunction under high injection which limits thedevice transconductance and f_T at LNT