High-linearity and small-chip AlGaAs/GaAs power HBTs for L-band personal digital cellular applications

A high-linearity AlGaAs/GaAs power heterojunction bipolar transistor (HBT) is developed for personal digital cellular phones. For compact chip layout, thermal design was considered. To improve power performance, proton implantation, optimum alloy condition for collector electrodes, and multiple via holes were used. A 2400-μm
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-emitter-area HBT fabricated on a 0.5×0.67 mm
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substrate exhibits adjacent channel leakage powers below -53 dBc for 0.95- and 1.5-GHz /spl pi//4-shifted QPSK modulated input signals at a low collector-emitter voltage of 3.4 V. The HBT produces a 31.7-dBm output power, 50% power-added efficiency, and 15-dB linear power gain at 0.95 GHz, and produced a 31.3-dBm output power, 52% power-added efficiency, and 11.5-dB linear power gain at 1.5 GHz. These results were achieved on about one-fifth of the substrate area of conventional GaAs FETs.