mm-Wave and sub-THz Chip-to-Package Transitions for Communications Systems

TL;DR

Addresses the problem of achieving low-loss, broadband chip-to-package transitions for mm-Wave and sub-THz systems in low-cost packaging. The authors analyze the limitations of standard GSG transitions, develop alternative structures, and implement a stripline-based transition in two CMOS-to-organic-substrate configurations with integrated/external matching. Using a link-budget framework, including $SNR$ and $C = B \log_2(1+SNR)$, they show that insertion losses at the interface dominate capacity in wideband links and that sub-dB IL is achievable. Simulations and measured results demonstrate sub-1 dB losses across broad bandwidths (e.g., $1.03\,\text{dB}$ at 140 GHz with 85 GHz bandwidth and $0.41\,\text{dB}$ from DC to 339 GHz), validating the approach and highlighting potential for scalable, heterogeneous integration in future communications systems.

Abstract

This work presents mm-Wave and sub-THz chip-to-package transitions for communications systems. To date, reported transitions either have high loss, typically 3 to 4 dB, or require high cost packages to support very fine bump pitches and low loss materials. We analyze the impact of transitions on a high frequency, wide bandwidth communication system and present the design of a chip-to-package transition in two different commercial packaging technologies. The proposed transitions achieve <1 dB loss in both technologies, validating the design methodology.

Figures (16)

• Figure 1: A flip-chip CMOS chip-to-package transition on a low-cost organic substrate interposer for mm-Wave and sub-THz communication systems.
• Figure 2: The impact of chip-to-package transition losses on link capacity for a proposed wideband systems. Here $f_0=140GHz$, $B=20GHz$, $N_{ant}=16$, $N_{beams} = 8$, $N_{pol}=2$, $P_{tx} = +4\dBm$ after back-off, $G_r = G_t = 5dB$, $d = 5m$, and $F = 10dB$.
• Figure 3: Conventional microstrip GSG transition (a) structure, (b) cross section, (c) schematic model and (d) simulated Poynting vector at 400GHz.
• Figure 4: GSG simulation showing (a) notches in $G_{\text{max}}$ for different pitches and (b) the loop antenna radiation model for the notch frequency.
• Figure 5: Comparison between metal and dielectric materials losses and radiation losses in a back-shielded microstrip to chip transition.