An InGaP/GaAs collector-up tunnelling-collector HBT and subtransistor via-hole structure for small and highly efficient power amplifiers

A novel structure of InGaP/GaAs collector-up tunneling-collector heterojunction bipolar transistors (C-up TC-HBTs) with sub-transistor via-holes, for use in small power amplifiers, is presented. Having the via-holes directly under the C-up UBTs is convenient in terms of thermal conduction; power amplifiers composed of multi-finger HBTs in this configuration take up dramatically less area than those with devices in the conventional configuration. The result was the demonstration of thermally stable operation for a 4-finger C-up TC-HBT at up to 0.9 mW//spl mu/m/sup 2/, in spite of the low finger pitch of only 15 /spl mu/m. Moreover, a small 32-finger C-up TC-HBT, with a total area of 0.25 /spl times/ 0.31 mm, was capable of delivering a power-added efficiency of 52% at 24.4 dBm in wide-band CDMA operation. These results show the strong potential for microwave application of high-efficiency power amplifiers composed of C-up TC-HBTs.