Low-Loss Single-Band, Dual-Band, and Broadband mm-Wave and (Sub-)THz Interconnects for THz SoP Heterogeneous System Integration

Abstract

Low-loss single-band, dual-band, and broadband terahertz (THz) interconnects for THz system-on-package heterogeneous system integration are proposed in this article. Transmission lines deployed on a 0.18- <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> m Complementary Metal-Oxide-Semiconductor (CMOS) chip and an integrated-passive-devices carrier, respectively, are coupled electromagnetically as the chip is flip-chip packaged onto the carrier using low-cost gold stud bumps. By doing this, two pairs of quarter-wave coupled lines can be formed to realize a low-loss THz interconnect for transiting a signal from the chip to the carrier. Moreover, single-band and dual-band operations can be acquired by designing the coupled lines to have a length of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\lambda}$</tex-math></inline-formula> /4 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\lambda}$</tex-math></inline-formula> /4 and 3 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\lambda}$</tex-math></inline-formula> /4 at the frequencies of interest, respectively. The gold stud bumps are also employed to realize a broadband directly-connected THz interconnect which transfers a signal from an on-chip microstrip line to an on-carrier microstrip line in a low-loss and broadband manner. A theoretical analysis using signal flow graphs and Mason's rule is conducted to provide design guidelines. Experimental results show that the proposed single-band, dual-band, and broadband THz interconnects can provide the insertion losses of 1.7, 2.7 and 2.9 dB, and lower than 3.3 dB at 306.5, 140 and 324.5 GHz, and from 140 to 330 GHz, with the return loss better than 10 dB from 256.5 to 330, 140 to 182 and 280 to 330, and 140 to 330 GHz, respectively. To the best of the authors’ knowledge, the proposed THz interconnect demonstrates the first dual-band operation reported thus far.