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-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula>-thick metal traces, the coupler using silicon IPD technology employed 10.8-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula>-thick traces realized with via connections between a top metal of 5.3-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> thickness and a bottom metal of 5.5-<inline-formula> <tex-math notation="LaTeX">$\mu \text{m}$ </tex-math></inline-formula> 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.