ASHRAE Journal - November 2013 - 85

Column Data centers

Module Heat Flux in W/in.2

that, in turn, consumed more power.
Figure 2 Bipolar versus CMOS heat flux graphs.
Despite being published back in 1965,
91
Moore's Law is still considered to be the
blueprint of predicting technology growth.
78
Moore's Law effectively predicted a technology rate of growth as a doubling of the
65
number of transistors on integrated circuits
every two years (Figure 1), and this trend has
52
been proven approximately true ever since
39
that time.
The success of Moore's Law was not as
26
much about predicting the actual technology advances but more about an informal
13
roadmap/performance target.
The increase in demand for more process0
ing created a compounded cooling prob1950
1960
1970
1980
1990
2000
2010
Year of Announcement
lem since the advent of bipolar technology
also meant that devices could, and were
tAble 1 Table C.1 From ASHRAE's Datacom Power Trends & Cooling Applications (2nd Edition).
miniaturized to be more efficient in their
operation.
iNDeX
(iNstitute For
sWAN
MiND
This led to the introduction of liquid
WiN
NANoelectroNics
(soutHWest
(MiDWest iNstitute For
cooling for mainframes around the 1960s
(WesterN iNstitute oF
DiscoverY &
AcADeMY For
NANoelectroNics
NANoelectrics)
eXplorAtioN) NANoelectroNics)
DiscoverY)
and liquid cooling remained the de-facto
UT-Austin, UTindustry standard until the late 1980s,
UCLA, UCSB, UC-Irvine, SUNY-Albany, GIT, RPI,
UT-Austin, UT-Dallas, TX
Dallas, TX A&M,
Berkeley, Stanford, U Harvard, MIT, Purdue,
A&M, Rice, ASU, Notre
at which time bipolar technology was
Rice, ASU, Notre
Denver, Iowa, Portland
Yale, Columbia,
Dame, Maryland, NCSU,
Dame, Maryland,
approaching the end of its useful life
State
Caltech, NCSU, UVA NCSU, Illinois-UC
Illinois-UC
with unit module heat flux approaching
Logic Devices
Novel State-Variable
Graphene Devices:
the very limits of cooling methods at that
Spin Devices
with New StateDevices
Thermal, Tunnel, & Spin
Variables
time.
With technology demand showing
Fabrication & SelfMaterials & Interband Tunnel Devices
Spin Circuits
Assembly
Structures
no signs of slowdown, and continued
shrinking of transistors required in
Modeling & Nanoscale Thermal Non-equilibrium Systems
Benchmarks & Metrics
Architecture
Management
Model/Measurement
order to continue performance gains, the
Interconnect &
slower but more efficient complemenSpin Metrology
Theory & Simulation
Nanoarchitecture
Arch
tary metal-oxide-semiconductor (CMOS)
Nanoscale
technology was adopted for CPUs. CMOS
Roadmap
Characterization
technology itself was not new, but its
Metrology
high density application was enabled by
improvements in manufacturing and lithography.
Compared to its bipolar equivalent, CMOS was a
crossroads of approaching an end of life for a semiconfar more efficient technology and the liquid cooling ductor technology.
needed for the last of the bipolar devices was no lonFigure 2 shows how the bipolar and CMOS techger a necessity.
nologies have followed a similar path in terms of
As a result, beginning around 1990, the technolincrease in module heat flux and although more
ogy industry underwent a radical change from liquid
precise and efficient ways to provide air cooling
cooling to a more simple air-cooling interface for elecin data centers have been developed, the industry
tronic equipment. However, we are once again at the
is faced with potential reaching the performance
N OVEM BER 2013

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