Abstract
The advantages of using thin epitaxial layers for bipolar integrated circuits are discussed in this paper. Using epitaxial layer thicknesses of ~ 1 /spl mu/ and a low-voltage form of transistor-transistor logic, packing densities of 10/SUP 5/ logic gates/in/SUP 2/ have been achieved. The power x delay product of the circuits was 5 pJ. The transistors were formed in 1 /spl mu/ thick epitaxial layers and have inverse common-emitter current gains of 2 to 3. These high inverse gains make practical some new circuit configurations, including a dual-emitter inverter with reduced storage time. The thin epitaxial layer may be p type, rather than the usual n type, and this makes possible a new isolation scheme that allows the fabrication of bipolar integrated circuits using only five photolithographic steps.

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