An epitaxial emitter cap, SiGe-base bipolar technology with 22 ps ECL gate delay at liquid nitrogen temperature

We have presented a SiGc-basc bipolar technology which has faster circuit speed at liquid nitrogen temperature than at room temperature. Transistors were fabricated using a reduced-temperature process employing a novel in-situ doped polysilicon emitter contact, a lightly doped epitaxial emitter cap layer, and a graded SiGe base. Transistors have a current gain as high as 500 with a cutoff frequency (fT) of 61 GHz, up from 43 GHz at 300 K. ECL circuits switch at a record 21.9 ps at 84 K at Jcs=1.0 mA/μm2 (25.4 ps at 310 K). For completeness the low-temperature properties of this technology are compared with more conventional ipi and pi SiGe-base designs.