A High-Speed

1
A High-Speed High-Capacity Single-Chip Copper
Crossbar John Damiano, Bruce Duewer, Alan Glaser,
Toby Schaffer,John Wilson, and Paul
Franzon North Carolina State University
RC values for interconnects were calculated for
the design and inserted into the crossbar HSPICE
netlist as passive components. Critical
interconnect RC values
are shown at left, and HSPICE simulation
waveforms are shown below.
Simulation Results
Copper
Aluminum
Cell size advantages
The design advantages resulting from the use of
copper interconnects in this circuit extend
beyond a basic performance improvement. The use
of copper allows interconnect scaling (and
improved performance) while maintaining excellent
reliability due to copper's lower resistivity and
enhanced electromigration properties. Embedded
applications benefit even more. Achieving the
performance of copper using aluminum interconnect
for an arrayed circuit would require some or all
of the following (1) use of larger drivers
within the crossbar cell (2) use of wider
interconnect to ensure that reliability specs are
met (3) increasing cell size to reduce coupling
capacitance between I/O lines. Modifications
required to achieve equivalent performance for
aluminum interconnect would increase cell size
substantially. Modifying the crossbar cell to
make RC equivalent to the copper cell would
require increase cell (and circuit) area by 64.
Moreover, these figures do not include further
changes to aluminum line width required to
compensate for the larger cell size and
subsequently longer interconnects. Achieving
significant die size reduction with improved
performance, as demonstrated by the copper
crossbar, is critical for SOC or embedded
applications and therefore aligns copper process
technology with future design needs.
The copper crossbar (left) functions for a
square-wave input signals with f2.67GHz while
the aluminum crossbar (right) functions up to
f2.0GHz. Use of copper interconnect improved
the maximum data rate more than 30, from 4.0Gb/s
to 5.33Gb/s.
Total delay through the the copper crossbar
(left) is 370ps vs. 425ps for the aluminum
crossbar (right) - a reduction of 15. Delays
through the input lines, the crossbar cell, and
the OR tree were all lower using copper
interconnect.
Above and Below Tracing 2.0GHz signals through
the copper (left) and aluminum (right) crossbar.
Signal integrity is improved for the circuit
using copper interconnect, with better OR tree
performance the most notable feature. These
performance advantages are the result of copper
interconnects lower capacitive load while
maintaining low resistance.
Performance Summary
The crossbar circuit demonstrates that the use of
copper interconnect provides strong performance
enhancements in a state-of-the-art circuit, while
design trade-offs make copper technology
attractive for embedded applications. Speed and
latency are improved through the use of copper
interconnect. We have also demonstrated that
copper interconnect can allow for the use of a
smaller crossbar cell, offering higher
performance with a substantially smaller die
size. Features such as high performance and
smaller die size make copper technology
particularly attractive for future design
solutions.
Full Report available on the web at
http//www.ece.ncsu.edu/erl/copper