Intra- and Inter-Chip Transmission of Millimeter-Wave Interconnects in NoC-Based Multi-Chip Systems

The primary objective of this paper is to investigate the communication capabilities of short-range millimeter-wave (mmWave) communication among network-on-chip (NoC)-based multi-core processors integrated on a substrate board. This paper presents the characterization of transmission between on-chip antennas for both intra- and inter-chip communication in multi-chip computing systems, such as server blades or embedded systems. Through simulation at 30 GHz, we have characterized the inter-chip transmission and studied the electric field distribution to explain the transmission characteristics. It is shown that the antenna radiation efficiency reduces with a decrease in the resistivity of silicon. The simulation results have been validated with fabricated antennas in different orientations on silicon dies that can communicate with inter-chip transmission coefficients ranging from -45 to -60 dB while sustaining bandwidths up to 7 GHz. Using measurements, a large-scale log-normal channel model is derived, which can be used for system-level architecture design. Using the same simulation environment, we perform design and analysis at 60 GHz to provide another non-interfering frequency channel for inter-chip communication in order to increase the physical bandwidth of the interconnection architecture. Furthermore, densely packed multilayer copper wires in NoCs have been modeled in this paper to study their impact on the wireless transmission for both intra- and inter-chip links. The dense orthogonal multilayer wires are shown to be equivalent to copper sheets. In addition, we have shown that the antenna radiation efficiency reduces in the presence of these densely packed wires placed in the close proximity of the antenna elements. Using this model, the reduction of inter-chip transmission is quantified to be about 20 dB compared with a system with no wires. Furthermore, the transmission characteristics of the antennas resonating at 60 GHz in a flip-chip packaging environment are also presented.