Compact InP HBT Power Amplifiers Using Integrated Thick BCB Dielectrics

An indium-phosphide (InP) double-heterojunction bipolar transistor (DHBT) process for compact millimeter-wave power amplifier MMICs has been developed with integrated 15 mum thick layers of BCB dielectric. The thick BCB layers provide low-loss millimeter-wave transmission lines with much smaller dimensions compared to conventional microstrip placed directly on the semiconductor substrate. A single layer BCB process with two metal layers is used for microstrip circuits, and a two-layer BCB process (30 mum total thickness) with three metal layers is used for stripline MMICs. The stripline MMICs inherent shielding enables new MMIC packaging concepts such as three dimensional embedded circuits that are enabling for low-cost phased array antennas architectures. A two-stage cascode power amplifier has been fabricated and characterized using microstrip lines on a single thick layer of BCB. The compact 6 mm² Ka-band PA demonstrated 1.1 Watts of saturated output power at 38 GHz, a dc power added efficiency (PAE) was 28.6%, and a small signal gain of 14.9 dB. The measured die area power density is 18.3 W/cm². These results demonstrate the potential of thick BCB microstrip and stripline MMICs to enable compact power amplifiers for space constrained millimeter-wave applications.