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

John Damiano - TECHCON 2000 / SRC Copper ChallengeJohn Damiano - TECHCON 2000 / SRC Copper Challenge

A High-Speed and High-Capacity A High-Speed and High-Capacity Single-Chip Copper CrossbarSingle-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 #38North Carolina State University

Raleigh, NC


The Copper CrossbarThe Copper Crossbar

Why a crossbar? The inherently long interconnects can best

demonstrate the benefits of advanced interconnect technology

Function Crosspoint switch with

programmable, non-blocking connections between sets of input and output lines


Cell DesignCell Design Programmed through input lines

Cell Schematic

Cell LayoutReset & Pre-Configures provide fast erase & write

Cell size (W x L) = 5.68 m x 19.50 m

two cells shown at right)

I/O connection set by writing “1” to latch

Latch outputs along output column combined OR-tree


Interconnect StrategiesInterconnect Strategies

Input lines on M5, Output OR-tree on M3

M4/M6 used as GND planes

Interconnect Al (fF) Cu (fF) % red.Input lines 1478 705 52%Reset lines 112 77 34%

Pre-configure lines 56 38 32%Write-enable lines 56 38 32%

OR-tree, final stage 112 77 34%OR-tree, int. stage 56 38 32%

Global Strategy: Maintain R and Decrease Linewidth to Reduce C

Reduced RC load drops => Higher Performance

Reliability of Cu not an issue

Capacitance Values for Crossbar Interconnect


SimulationSimulation

Metric #1 - Data Ratemaximum input signal frequency for the crossbar

Reduced RC load using Copper interconnect enables higher data rate vs. Aluminum

Copper: 5.3 Gb/sAluminum: 4.0 Gb/s

Copper

Aluminum

Output for 2.0GHz square wave input


SimulationSimulation

Metric #2 - LatencyDelay of signal from crossbar input to output

Faster edge rate with Copper interconnect enables lower latency vs. Aluminum

Copper: 370 psAluminum: 425 ps

Copper

Aluminum

Output for 2.0GHz square wave input


Advantages of Copper InterconnectAdvantages 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 ResultsElectrical Results

Input

VDD-VDD & VSS -VSS VDD -VSS

Input NOT passed to Output for all I/O configurations

VDD/VSS Diode characteristics NOT observed

Output


Failure AnalysisFailure AnalysisDie 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

How could this happen?

Detail of pad cell

Detail of crossbar array


Generating Fill ShapesGenerating Fill Shapes

AB B’

A-B’(A-B’)+B


Silicon vs. Layout DataSilicon vs. Layout Data

pad cell layout

array layout

pad cell silicon

array silicon


Failure AnalysisFailure 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


ConclusionsConclusions 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

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