Comparison of 5-GHz Quadrature Couplers Using GaAs and Silicon-Based IPD Technologies

The 5-GHz quadrature couplers implemented in GaAs and silicon-based integrated passive device (IPD) technologies are presented. Although GaAs technology is superior to silicon-based technology in terms of substrate resistivity and back-side vias, the quadrature coupler using a silicon IPD process achieved better insertion loss due to thick metal traces and comparable substrate resistivity. While the coupler using the GaAs process employed 4-μm-thick metal traces, the coupler using silicon IPD technology employed 10.8-μm-thick traces realized with via connections between a top metal of 5.3-μm thickness and a bottom metal of 5.5-μm thickness. The couplers using the silicon and GaAs IPD process technologies showed 0.15 and 0.27 dB of insertion loss, respectively. Also, the silicon IPD design uses a slightly different topology which splits a coupled inductor into two coupled inductors with shunt capacitors to achieve a broader distributed bandwidth.