Anthony V. Mule

Electrical and optical clock distribution networks for gigascale microprocessors

A summary of electrical and optical approaches to clock distribution within high-performance microprocessors is presented. System-level properties of intrachip electrical clock distribution networks corresponding to three microprocessor families are summarized. It is found that global clock interconnect performance and short-term jitter present the greatest challenges to the continued use of conventional clock distribution methodologies. An extrapolation of trends describing the percentage of clock period consumed by global skew and short-term jitter identifies the 32-nm technology generation of the 2002 International Technology Roadmap for Semiconductors (ITRS) as the first technology generation within which alternate methods of clock distribution may be warranted. Research efforts investigating interboard through intrachip optical clock distribution are also summarized. An optical distribution network compatible with high volume manufacturing in conjunction with a suitable means of providing optical-to-electrical signal conversion comprise the two fundamental challenges facing successful implementation of an optical clock distribution network. It is found that a global guided-wave distribution capable of efficient input and output coupling of optical power is required to meet the first challenge. The identification of a suitable means of optical-to-electrical conversion, however, remains an active topic of research.

Optical and electrical interconnect partition length based on chip-to-chip bandwidth maximization

The lengths beyond which board-level optical waveguides are capable of transferring a larger number of bits per second than electrical interconnects are found for various technology generations. As technology scales from the 130-nm technology node to the 45-nm technology node, the partition length falls from 29 to 8.3 cm due to seven times larger driver-switching frequency and 40% finer waveguide pitches.

Sea of dual mode polymer pillar I/O interconnections for gigascale integration

The Sea of Polymer Pillars offers highly compliant electrical, optical, and RF wafer-level I/O interconnects at an I/O density larger than 10/sup 5//cm/sup 2/. Dual mode I/O pillars function simultaneously as both electrical and optical interconnects to offer circuit/system designers essentially unlimited I/O bandwidth at potentially the lowest cost.

Polylithic integration of electrical and optical interconnect technologies for gigascale fiber-to-the-chip communication

Polylithic integration of electrical and optical interconnect technologies is presented as a solution for merging silicon CMOS and compound semiconductor optoelectronics. In contrast to monolithic and hybrid integration technologies, polylithic integration allows for the elimination of optoelectronic and integrated optic device-related processing from silicon CMOS manufacturing. Printed wiring board-level and compound semiconductor chip-level waveguides terminated with volume grating couplers facilitate bidirectional optical communication, where fiber-to-board and board-to-chip optical coupling occurs through a two-grating (or grating-to-grating) coupling path. A 27% increase in the electrical signal I/O projected by and 33% increase in the number of substrate-level electrical signal interconnect layers implied by the International Technology Roadmap for Semiconductors (ITRS) projections for the 32-nm technology generation are required to facilitate 10 Tb/s aggregate bidirectional fiber-to-the-chip communication. Buried air-gap channels provide for the routing of chip or board-level encapsulated air-clad waveguides for minimum crosstalk and maximum interconnect density. Optical signals routed on-board communicate with on-chip volume grating couplers embedded as part of a wafer-level batch package technology exhibiting compatible electrical and optical input/output interconnects. Measurements of grating-to-grating coupling reveal 31% coupling efficiency between two slab, nonoptimized, nonfocusing volume grating couplers.

Photopolymer-based diffractive and MMI waveguide couplers

Diffractive and multimode-interference waveguide couplers constructed from photopolymer materials are presented. Two-material grating-in-the-waveguide optical interconnects are fabricated and tested with respect to waveguide propagation loss and grating out-coupling. Waveguide/grating interconnects have been constructed with both index-defined and air-clad waveguide channel regions, where air-clad channels exhibit measured propagation losses of /spl alpha//sub wg/=0.47-3 dB/cm. Measurements of output coupling coefficients of volume grating couplers terminating various waveguide channels range from /spl alpha//sub g/=1.4-5.3 mm/sup -1/. A 1 /spl times/ 4 photopolymer-based multimode-interference power-splitting coupler fabricated and tested for the provision of in-plane optical coupling is found to demonstrate 0.3-0.6-dB output power uniformity.

Input coupling and guided-wave distribution schemes for board-level intra-chip guided-wave optical clock distribution network using volume grating coupler technology

The input coupling and guided-wave distribution schemes for a novel board-level guided wave optical clock distribution network using volume grating coupler technology are described. Volume grating coupler technology is employed to couple light into the optical waveguide distribution with high efficiency, allowing for compact packaging of the entire optical system and reduced optical input power requirements. A novel single-split-region waveguide distribution network is proposed to allow for larger radii of curvature in the final, smallest-radii levels for reduced bending loss in comparison to a conventional multiple-split-region topology.

Quasi-free-space optical coupling between diffraction grating couplers fabricated on independent substrates

Optical coupling between preferential-order volume diffraction grating couplers fabricated on independent substrates is demonstrated. The coupling efficiency between gratings is quantified as a function of both grating and waveguide fabrication technology and relative angular position of the two substrates. A maximum grating-to-grating coupling efficiency of 31% is reported for coupling between two nonoptimized, nonfocusing, unpatterned volume grating couplers.

An optical clock distribution network for gigascale integration

A novel system-level model describing a printed wiring board-level, high-fanout, curved aperture optical waveguide H-tree network using volume grating focusing couplers is presented. The intra-chip optical network globally distributes an optical signal to monolithic CMOS receivers for local clock distribution. An estimation for the available optical output power as a function of distribution fanout is presented. Assuming -2 dB optical loss per y-junction, a distribution fanout of 256 can be achieved for an optical input power of 1.23 W.

Partition length between board-level electrical and optical interconnects

The lengths beyond which board-level optical interconnects are capable of transferring a larger number of bits per second in comparison with electrical interconnects are found for different technology generations. At the 130 nm node, the partition length is 29 cm which reduces to 8.3 cm at the 45 nm because of 7 times faster drivers and 40% finer waveguide pitch.

Polymer optical interconnect technologies for polylithic gigascale integration

Polymer optical waveguides embedded within buried air-gap cladding regions are presented as part of a wafer-level packaging technology for polylithic integration of optical interconnection with CMOS microelectronics. Functional 5 /spl mu/m wide/25 /spl mu/m pitch optical channels with dielectric/air core/cladding regions exhibit 0.43-1.22 dB/cm. scattering losses for unpassivated and passivated channels. A 1/spl times/4 multimode interference (MMI) power splitter constructed from the same polymer material exhibits 0.23-1.3 dB output power non-uniformity. Volume grating couplers constructed from a second photopolymer material exhibit /spl sim/72% input coupling efficiency.