THz Interconnect


Continuous scaling of semiconductor devices allows more processor cores and integrated functionalities into a single chip to support the growing computation demands of scientific and commercial workloads in both increasing speed and volume. This trend mandates an ever increasing inter-/intra-chip communication bandwidth, which has been a big challenge over decades. This challenge has motivated active research to improve interconnect capacities, characterized by two key specs: bandwidth density, defined as gigabits per second per square millimeter, determining the aggregate throughput; and energy efficiency, defined as Joules per bit, indicating the overall power consumption. The required off-chip I/O bandwidth doubles about every two years, significantly exceeding the growth rate of the I/O pin number due to packaging/assembly limitations. The gap between the interconnect requirement and the supporting capability forms the “interconnect gap.” With the projecting trend, the power consumption and chip size to support interconnect only will be intolerable for most high performance computers and data centers in the near future . In addition, cost, defined as dollars per gigabit per second, also needs to scale down inversely proportional to the interconnect bandwidth to be sustainable. To support the continuous demands for inter-/intra- chip interconnect, the “interconnect gap” must be filled.

Our Approach: THz Interconnect

To ultimately solve the problem and close the gap, bandwidth density, energy efficiency and cost should be all be significantly improved. THz Interconnect (TI), utilizing the frequency spectrum sandwiched between microwave and optical frequencies, holds high potential to complement Electrical Interconnect (EI) and Optical Interconnect (OI) by leveraging the advantages of both electronics and optics, as shown in Figure 1. Continuous scaling of mainstream silicon technologies enables terahertz electronics in silicon, which favors low cost and high reliability. On the other hand, terahertz waveguides, similar to their optical counterparts, have small dimensions and present low loss, which alleviates the TI link budget to allow low transmission output power and improves the energy efficiency. In addition, TI favors technology scaling because the increasing frequency supports higher communication data rates and reduces channel dimensions, thus resulting in a larger bandwidth density. These unique features equip TI with high energy efficiency, high bandwidth density, low cost, and high resilience with the potential to ultimately fill the
interconnect gap.


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  17. Q. J. Gu, Z. Xu, and M.-C. F. Chang, “Millimeter Wave and Sub-millimeter Wave Circuits for Integrated System-On-a-Chip,” 2011 IEEE International Symposium on Radio-Frequency Integration Technology(RFIT), Best Paper Award

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