A novel compact three-dimensional CMOS branch-line coupler using the meandering ECPW, TFMS, and buried micro coaxial technologies at 60 GHz

This paper proposes a new approach for realizing a compact 3-D 90° hybrid coupler incorporating compact meandered elevated coplanar waveguides (ECPW), thin-film microstrip (TFMS) transmission lines, and micro coaxial shunt stub loading. The design technique has been successfully demonstrated using a multi-layer 90 nm CMOS process. The proposed coupler takes advantage of the multi-level metallization processes offered in CMOS technology. The intrinsic area of the fabricated 3-D hybrid coupler is significantly reduced with a size reduction of 81% in circuit area at 60 GHz as compared to that of a conventional hybrid coupler using the ECPW/TFMS configuration. Simulated and experimental results are presented in support of the novel miniature coupler.