Optical Clock Distribution To Silicon Chips

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Abstract
Timing constraints for state-of-the-art very large scale integrated circuits (VLSI) in silicon are rapidly approaching communication limits available with layered two-dimensional metal and polysilicon wiring approaches. For such communication-limited systems, reliable clock distribution is a key concern. The range of finite differences in signal delays over clock wires of various lengths for large chips creates a timing skew that is significant when compared to the switching time of transistors in the circuit. The high bandwidth and three-dimensionality of imaging optical systems suggest that optical clock distribution systems have the potential to overcome the timing barriers presented by planar wiring. Clock signals can be holographically mapped to detector sites within small functional cells on a chip surface. Within each functional cell, the clock is distributed via surface wires with negligible delays, reducing skew effects to the variation in reaction times of the photodetectors on the chip. Experiments simulating the response of optical clock detection circuits in standard 4 micron CMOS technology have been performed.

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