Design of Low-Loss Transmission Lines in Scaled CMOS by Accurate Electromagnetic Simulations

Transmission lines are becoming of common use at mm-wave to implement on-chip functions as impedance matching, filtering and interconnects. Lack of an accurate and fast simulation method is nonetheless evident for transmission lines in scaled CMOS where metal dummies inserted for IC planarization make their physical structure extremely complicate. Although lines are not uniform due to displacement of small dummies, they are still periodic. In this paper, we describe an analytical procedure, leveraging lines periodicity and based on Floquet's theorem, in order to derive electromagnetic parameters from simulations. Conventional, slow-wave and shielded CPWs have been realized in a 65 nm CMOS technology. Thanks to the developed method, an optimum line design has been made possible. The lossy CMOS substrate, responsible for a significant performance degradation, can be effectively shielded and achieved performances are comparable with other technologies considered better suited to implement low-loss, high frequency passive components. Shielded CPW lines show attenuation as low as 0.65 dB/mm at 60 GHz, a record in scaled CMOS.

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