Recent studies showed that conventional approaches being used to solve problems imposed by hard-wired metal interconnects will eventually encounter fundamental limits and may impede the advance of future ultralarge-scale integrated circuits (ULSIs). To surpass these fundamental limits, we introduce a novel RF/wireless interconnect concept for future inter-and intra-ULSI communications. Unlike the traditional "passive" metal interconnect, the "active" RF/wireless interconnect is based on low loss and dispersion-free microwave signal transmission, near-field capacitive coupling, and modern multiple-access algorithms. In this paper, we address issues relevant to the signal channeling of the RF/wireless interconnect and discuss its advantages in speed, signal integrity, and channel reconfiguration. The electronic overhead required in the RF/wireless-interconnect system and its compatibility with the future ULSI and MCM (multi-chip-module) will be discussed as well.

This work presents a Butler matrix based four-directional switched beamforming antenna system realized in a two-layer hybrid stackup substrate for 28-GHz mm-Wave 5G wireless applications. The hybrid stackup substrate is composed of two layers with different electrical and thermal properties. It is formed by attaching two layers by using prepreg, in which the circuit components are placed in both outer planes and the ground layers are placed in the middle. The upper layer that is used as antenna substrate has εr = 2.17, tanδ = 0.0009 and h = 0.254 mm. The lower layer that is used as a Butler matrix substrate has εr = 6.15, tanδ = 0.0028 and h = 0.254 mm. By realizing the antenna array on the lower-εr layer while the Butler matrix on the higher-εr layer, the Butler matrix dimension is significantly reduced without sacrificing the array antenna performance, leading to significant overall antenna system size reduction. The two-layer substrate approach also significantly suppresses parasitic radiation leaking from the Butler matrix toward the antenna side, allowing overall radiation pattern improvement. The fabricated beamforming antenna is composed of 1 × 4 patch antenna array and a 4 × 4 Butler matrix. The measured return loss is lower than −8 dB at all ports in 28-GHz. It demonstrates the switched beam steering toward four distinct angles of—16°, +36°, −39°, and +7°, with the sidelobe levels of −12, −11.7, −6, and −13.8 dB, respectively. Antenna gain is found to be about 10 dBi. Due to the two-layer hybrid stackup substrate, the total antenna system is realized only in 1.7λ × 2.1λ, which shows the smallest form factor compared to similar other works.

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