Isolated emitter AlGaAs/GaAs HBT integrated with emitter-down HI/sup 2/L technology

A process that integrates isolated-emitter heterojunction bipolar transistors (HBTs) with common-emitter HBTs in the emitter-down epi structure on n/sup +/ substrates is discussed. Overgrowth of the epi onto a p/sup -/ implanted region results in back-to-back diodes for approximately 12-V vertical isolation. Isolated transistors are used in emitter-follower output buffers for heterojunction injection logic (HI/sup 2/L) ring oscillators, demonstrating the integration of the two transistor types.<
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