A High-Speed and High-Capacity Single-Chip Copper Crossbar

A High-Speed and High-Capacity Single-Chip Copper Crossbar • Outline • Circuit Design and Simulation • Advantages of Copper Interconnect • Electrical and Physical Characterization John Damiano, Bruce Duewer, Alan Glaser, Toby Schaffer, John Wilson, and Paul Franzon Copper Challenge Team #38 North Carolina State University Raleigh, NC

The Copper Crossbar • Function • Crosspoint switch with programmable, non-blocking connections between sets of input and output lines • Why a crossbar? • The inherently long interconnects can best demonstrate the benefits of advanced interconnect technology

Cell Design • Programmed through input lines • I/O connection set by writing “1” to latch • Latch outputs along output column combined OR-tree Cell Schematic Cell Layout • Reset & Pre-Configures provide fast erase & write Cell size (W x L) = 5.68 mm x 19.50 mm (two cells shown at right)

Interconnect Strategies • Input lines on M5, Output OR-tree on M3 • M4/M6 used as GND planes Global Strategy:Maintain R and Decrease Linewidth to Reduce C Capacitance Values for Crossbar Interconnect • Reduced RC load drops => Higher Performance • Reliability of Cu not an issue

Simulation Output for 2.0GHz square wave input Metric #1 - Data Rate maximum input signal frequency for the crossbar Reduced RC load using Copper interconnect enables higher data rate vs. Aluminum Copper: 5.3 Gb/s Aluminum: 4.0 Gb/s Aluminum Copper

Simulation Output for 2.0GHz square wave input Metric #2 - Latency Delay of signal from crossbar input to output Faster edge rate with Copper interconnect enables lower latency vs. Aluminum Copper: 370 ps Aluminum: 425 ps Aluminum Copper

Advantages of Copper Interconnect • Performance • Copper Interconnect enables 30% higher Data Rate and 15% lower Latency vs. Aluminum • Cell Size • Tighter metal pitch with same resistivity available with Copper Interconnect • Aluminum cell with equivalent performance would be 64% larger due to wider lines, increased pitch, and/or larger drivers • Significant for arrayed / SOC applications

Electrical Results • Input NOT passed to Output for all I/O configurations Input Output • VDD/VSS Diode characteristics NOT observed VDD-VDD & VSS -VSS VDD -VSS

Failure Analysis • Die stripped to substrate using HF to investigate VDD-VSS opens • Diffusion pattern, created by P20 reticle, discovered to be absent! • Only Diffusion pattern visible on die consists of Fill Shapes around original diffusion data Detail of pad cell How could this happen? Detail of crossbar array

Generating Fill Shapes A B’ B (A-B’)+B A-B’

Silicon vs. Layout Data pad cell layout pad cell silicon array layout array silicon

Failure Analysis • Crossbar pad cells compared to NCSU Team #16 - the diffusion pattern was dropped only for our die • Explains unusual electrical data - no active devices present • Only solution - new P20 (diffusion) reticle must be generated • Good News! UMC has agreed to re-order P20 reticle and start new Copper Challenge lot Team #38 pad cell Team #16 pad cell

Conclusions • Copper Crossbar circuit developed to exploit the advantages of copper interconnect technology • Crossbar design using copper interconnect achieved a higher data rate and reduced latency, with a smaller cell size vs. equivalent aluminum circuit • Puzzling Electrical Results from fabricated chips led to discovery of missing diffusion pattern • UMC re-run of Copper Challenge designs promises to yield functional die with advanced interconnect & high performance

A High-Speed and High-Capacity Single-Chip Copper Crossbar