On-chip sub-terahertz surface plasmon polariton transmission lines with mode converter in CMOS

Abstract

An on-chip low-loss and high conversion efficiency plasmonic waveguide converter is demonstrated at sub-THz in CMOS. By introducing a subwavelength periodic corrugated structure onto the transmission line (T-line) implemented by a top-layer metal, surface plasmon polaritons (SPP) are established to propagate signals with strongly localized surface-wave. To match both impedance and momentum of other on-chip components with TEM-wave propagation, a mode converter structure featured by a smooth bridge between the Ground coplanar waveguide (GCPW) with 50 Ω impedance and SPP T-line is proposed. To further reduce area, the converter is ultimately simplified to a gradual increment of groove with smooth gradient. The proposed SPP T-lines with the converter is designed and fabricated in the standard 65 nm CMOS process. Both near-field simulation and measurement results show excellent conversion efficiency from quasi-TEM to SPP modes in a broadband frequency range. The converter achieves wideband impedance matching (<−9 dB) with excellent transmission efficiency (averagely −1.9 dB) from 110 GHz–325 GHz. The demonstrated compact and wideband SPP T-lines with mode converter have shown great potentials to replace existing waveguides as future on-chip THz interconnects. To the best of the author’s knowledge, this is the first time to demonstrate the (sub)-THz surface mode conversion on-chip in CMOS technology.

Properties of spoof plasmon in thin structures

“…This discovery immediately broadened the scope of constructing truly subwavelength structure which can be bent and twisted to lend the signal routing through them in a flexible way [17]. Yu et al demonstrated that subwavelength size standalone interconnect can be implemented in thin, planar CMOS-compatible SSPP metamaterial to operate at sub-terahertz range having strong immunity to interference [18][19][20]. This unravels the potential of the SSPP interconnect to serve as a reliable way of transferring data at terahertz speed with reduced crosstalk.…”

Terahertz Spoof Surface Plasmon Polariton Waveguides: A Comprehensive Model with Experimental Verification

“…Above all, the dielectric thicknesses in this study, as well as all above-mentioned studies, are significantly lower than the free-space wavelength at their corresponding operation frequencies, which address a totally different problem compared to proposed model. Although few sSPP waveguides are also presented for the terahertz integrated circuits 39,40 , they also follow a similar approximation to that of the studies presented in the microwave bands, and neither an effective dielectric constant model, nor its experimental verification is presented so far for the terahertz band. In particular, the effective dielectric constants in these studies are extracted from a limited set of physical dimensions and no model that governs the effects of the variations in all the physical parameters is presented.…”

Integrated spoof plasmonic circuits

“…One challenge of applying the spoof SPP TLs in circuit design lies in the feeding of the TLs and the conversion from conventional circuits to spoof SPP devices so that the efficiency and bandwidth can be maximized. Extensive studies have been performed on this topic, and different techniques have been proposed at both microwave [23][24][25][26][27] and sub-terahertz [28] frequencies. Owing to the high field confinement property, the conformal spoof SPs do not suffer from the compactness limitations of traditional circuits.…”