| The transferred-substrate HBT technology developed at UCSB has demonstrated the ability to realize extremely high bandwidth bipolar transistors. Record values of fmax over 1 THz have been attained, promising levels of performance in distributed and tuned amplifier circuitry far beyond the current state of the art. In order to fabricate fast digital circuitry as well as analog circuitry of more conventional topologies, it is absolutely necessary to have simultaneously high f tau as well as fmax. It is of paramount importance to improve the ftau figure of merit in transferred-substrate HBTs via improved MBE growth of the HBT semiconductor, bandgap engineering techniques, and lateral as well as vertical scaling of the transistor structure. An ftau of 275 GHz has been achieved in transferred---substrate HBT technology; this is the highest ftau achieved to date for a bipolar transistor.;The high fmax values achieved at UCSB so far are the result of aggressive lithographic scaling of the collector dimension and space---charge screening effects in the collector (capacitance cancellation). Achieving high ftau is more difficult. To minimize the various components of the HBT forward delay (proportional to the inverse of ftau) quickly requires a combination of lithographic scaling, reduction of contact and access resistances, and reduction of parasitic layout capacitances.;Development of the basic HBT technology has continued in this work. A gas carbon source is now operational in the MBE system, and is able to dope the bases of future HBTs well into the 1020/cm3 range without worry of dopant diffusion. A phosphorous source also has been installed in the MBE system and will soon be operational, giving transferred-substrate HBTs improvement in breakdown voltage and hence output power performance.;This work also demonstrates the highest gain-bandwidth single-stage amplifiers, implemented in the common-collector, common-emitter configuration. These wide bandwidth amplifiers have very low power consumption of tens of milliwatts, and are further evidence of the frequency performance of transferred substrate HBTs. |
