Low-interference on-chip millimeter-wave transmission using silicon integrated coding metamaterials

Abstract

On-chip millimeter-wave interconnects based on surface wave propagation present a promising alternative to conventional wired interconnects, addressing scalability challenges associated with increasing latency and interconnect complexity. However, most existing surface wave systems rely on the natural fan-out of electromagnetic waves on silicon substrates launched by low-directivity on-chip antennas, resulting in limited beam control and poor interference resilience. These limitations make wireless channels highly vulnerable to co-channel interference and external electromagnetic noise, constraining communication reliability and integration density. Based on a detailed analysis of surface wave propagation mechanisms on silicon substrate at millimeter-wave frequencies. This thesis presents the design, fabrication, and experimental validation of various silicon-compatible on-chip metamaterials to mitigate interference in surface wave interconnect through direct signal blocking, enhanced beam control and directional signal modulation. The proposed metamaterials enable low-interference, reconfigurable TE-mode surface wave propagation for intra-chip wireless communications.

Firstly, a cost-effective, sub-wavelength, and silicon-compatible metamaterial absorber is presented, designed to suppress interference by directly attenuating TE-mode surface wave propagation on silicon substrates. The absorber employs a bloom-shaped unit cell that induces strong electromagnetic resonance with surface waves excited by on-chip antennas in multiple directions. Fabricated using standard silicon microfabrication processes. The proposed metamaterial can exhibit a maximum energy absorption over 99\% at the target frequency. Consistent absorption performance can be achieved under a large range of signal incident angles from 0° to 60°.

Secondly, enhanced metamaterial unit cells are designed through topology optimisation. Innovative unit cell designs are generated using metal pixel maps encoded from binary strings. Automatic optimisation, driven by a genetic algorithm targeting user-defined objectives and fitness functions, yields unit cells that outperform conventional designs. These optimised cells demonstrate a 4.5 times improvement in 90\% absorption bandwidth and a 7.5 times improvement in absorption consistency at incident angles ranging from 0 to 45°.

Thirdly, we present the design of an integrated 1-bit digital-coding metamaterial with numerous beam control and steering capabilities. By controlling the refractive index distributions in the unit cell array through different binary coding sequences, the metamaterial can realise various functions, including beamsteering in the range of $\pm$ 40°, 3.3 dB transmission gain enhancement, 90° beam splitting, and efficient energy attenuation. The proposed digital-coding metamaterial enables precise and reconfigurable management of wireless signal propagation across the chip, significantly enhancing the flexibility, efficiency, and scalability of on-chip millimeter-wave communications.

Lastly, we engineered an on-chip digital-coding metamaterial with integrated modulation functionalities, building the foundation for a novel on-chip wireless transmission architecture based on metamaterial direct modulation. The modulation metamaterial can support various phase shift keying (PSK) schemes, including BPSK, QPSK, and 8-PSK, as well as a hybrid modulation and beam steering mode offering a beam steering range of up to $\pm$28°. Multiple modulation metamateiral in collaboration with a central broadcast antenna, the system enables multi-directional modulation with distinct data streams to different spatial regions from a single transmitter. The proposed metamateiral presents an innovative method for information routing in intra-chip millimeter-wave transmission, helps to reduce the signal crosstalk under parallel transmission, and expands the wireless channel capacity and spectral efficiency.

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Identifiers

ORCID for Jize Yan: orcid.org/0000-0002-2886-2847

ORCID for Sajjad Taravati: orcid.org/0000-0003-3992-0050

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