On the profile design and optimization of epitaxial Si- and SiGe-base bipolar technology for 77 K applications. II. Circuit performance issues

For pt.I see ibid., vol.40, no.3, p.525-41 (1993). The circuit performance issues associated with optimizing epitaxial Si- and SiGe-base bipolar technology for the liquid-nitrogen temperature environment are examined in detail. It is conclusively demonstrated that the notion that silicon-based bipolar circuits perform poorly at low temperatures is untrue. Transistor frequency response is examined both theoretically and experimentally, with particular attention given to the differences between SiGe and Si devices as a function of temperature. ECL and NTL ring oscillator circuits were fabricated for each of the four profiles described in pt.I. The minimum ECL gate delay for a SiGe base is essentially unchanged from its room-temperature value. ASTAP models were used to explore circuit operation under typical wire loading. The results indicate that epitaxial-base bipolar technology offers significant leverage for future cryogenic applications.<
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