A mm-Wave Stub-Loaded ECPW Wilkinson Power Divider/Combiner in 90 nm CMOS

This letter presents a millimeter-wave (mm-wave) slow-wave elevated coplanar waveguide (ECPW) power divider/combiner fabricated in the back-end-of-the-line (BEOL) of a 90 nm CMOS technology. Design techniques using periodical loading stubs and elevated signal conductors are applied toward the CPWs that enable i) an aggressive size-reduction by increasing the artificial effective dielectric constant $(\varepsilon _{{\rm eff}})$ ii) realization of high-impedance transmission lines at mm-wave. The measurement results reveal that the insertion loss is 2.3 and 2.4 dB at 60 and 67 GHz, respectively. The measured isolation of over 13 dB is observed from 59 GHz to at least 110 GHz. The divider also achieves an excellent amplitude imbalance and phase imbalance of less than 0.16 dB and less than 0.45 $^{\circ}$ , respectively, up to 67 GHz (limited by test setup). The core size of the proposed divider is only 205 $\mu$ m ${\times}$ 250 $\mu$ m (0.051 mm $^{{{2}}}$ ) equivalent to a size-reduction of over 70% compared to a conventional Wilkinson power divider. To the best of authors\´ knowledge, this is the first Wilkinson power divider/combiner that has demonstrated the highest operating frequency characterized among all other known semiconductor technologies reported.