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This paper reports the first heterojunction bipolar transistors (HBTs) with significant power gain at 10 GHz or above, and describes measured and simulated characteristics of their performance. Highlights of our results include the following: ft up to 40 GHz has been measured. This is the highest ever reported for a bipolar transistor. fmax above 25 GHz has been measured. This is comparable to the hightest attained with Si bipolar transistors (fabricated with electron-beam lithography).Narrowband gain of 11 dB at 12 GHz has been measured in an amplifier configuration. RF noise has been measured for the first time on HBTs. A noise figure of 6 . 5 dB has been measured at 12 GHz, with associated gain of 7.5 dB.An equivalent circuit for the device (including noise sources) has been analyzed. The agreement with measured noise performance is excellent. The model indicates the principal cause of the high noise figure to date is high parasitic resistance, and that noise figures significantly lower may be obtained in the future.. Low frequency noise (in the l/f regime) has been measured for these devices. Equivalent l/f noise input currents on the order of ~x~O -~O A/ f i z at 100 HZ have been obtained at Ic=lmA, corresponding to extrapolated noise corner frequencies below 1MHz. This result is better than has typically been obtained with GaAs FETs, and indicates that HBTs may be worthwhile in low phase-noise oscillators.The current gain of the devices decreases with increasing temperature. it is argued that this may ease the requirement of emitter ballasting typically used to prevent current hogging in power transistors.The microwave HBTs were fabricated using processing similar to that previously reported for digital integrated circuits. In brief, an MBE grown epilayer structure on a semi-insulating GaAs substrate was used. Contacts to the base were made with the u s e of ion-implanted, rapidly annealed extrinsic base regions. Oxygen implants were used to decrease the extrinsic base-collector capacitance. Oxygen implants were used to decrease the extrinsic based-collector capacitance. Optical contact lithography was used, and emitter widths were on the order of 1 . 2 pm. Current gain at dc was on the order of 40-50. For the most part, testing was carried out on HBTs mounted in commercial 70 mil stripline packages in common emitter configuration.These first HBT resulte at X band are of particular significance since they contribute to clarifying the future role of HBTs in microwave circuits. Our projections suggest that HBTs will be particularly important in oscillators and power amplifiers.

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