Low-Loss and Compact Millimeter-Wave Silicon-Based Filters: Overview, New Developments in Silicon-on-Insulator Technology, and Future Trends

This paper presents an overview of Silicon-based millimeter-wave (mm-wave) passive devices for bandpass and bandstop filtering applications, while also reporting originally-conceived filter developments and future trends. First of all, the state-of-the-art on mm-wave low-loss bandpass filters (BPFs) is covered, and new BPF designs are shown. The engineered BPFs employ a center-tapped ring architecture with shunt-connected capacitors to realize a standard 2(nd)-order baseline BPF design, which is subsequently scaled to 30-GHz and 60-GHz operational frequencies. To increase the selectivity as well as the stopband rejection levels of this baseline BPF, the in-series cascade connection of the baseline BPF units is used for a higher-order BPF realization. For experimental-validation purposes, a total of four mm-wave BPFs based on these design strategies are implemented, fabricated in 45-nm Silicon-on-Insulator (SOI) complementary-metal-oxide-semiconductor-(CMOS) technology, and tested. Afterward, a review of Silicon-based-integrated bandstop filters (BSFs) operating in the mm-wave region is provided, which includes both reflective-type and reflectionless/absorptive filter realizations for RF-interference-suppression in highly-congested electromagnetic (EM) environments. Finally, future research trends in the Silicon-based-integrated filter area are discussed. They are expected to play a key role in the development of modern radio-frequency (RF) front-ends for emerging beyond 5G and EM-sensing scenarios.