interpreted memristance as a hysteresis relationship (one in which effect
lags cause) between voltage and current, when in fact it is based on flux
and charge, the time integrals of voltage and current, says Chua. He likens
the pre-1971 view of memristance to
Aristotle’s belief that force is proportional to velocity and not, as Newton
correctly demonstrated 2,000 years
later, as proportional to the change in
velocity, or acceleration.
In 2006, HP designed and built a
titanium memristor that worked pre-
dictably and retained its state when
powered off, based on the mathemati-
cal framework proposed by Chua. “For
years people built [memristance] de-
vices almost by accident. It’s to the
great credit of HP that they finally fig-
ured it out,” he says. Figuring it out,
according to HP’s Stanley Williams,
the chief architect of the company’s
memristor, meant “understanding
the mathematical framework for
memristors.”
Almost 40 years seems a long time
between the emergence of Chau’s
framework and the ability to reli-
ably produce memristors, but enor-
mous engineering hurdles had to be
overcome. It required methods and
tools, such as scanning tunneling mi-
croscopy, that could work at atomic
scales. HP says it experimented with
an enormous number of device types,
many based on exotic materials and
structures, but the results were often
inconsistent and unexplainable. It was
not until 2006 that HP developed equa-
tions that explained just what was oc-
curring in its titanium memristors.
More speed, Less Power
The breakthrough achieved by HP
in 2006 could revolutionize memory
technology, the company says. “
Memristor memory chips promise to run at
least 10 times faster and use 10 times
less power than an equivalent flash
memory chip,” according to Williams,
director of HP’s Information and
Quantum Systems Lab. “Experiments
in our lab also suggest that memristor memory can be erased and written over many more times than flash
memory. We believe we can create
memristor ReRAM products that, at
any price point, will have twice the capacity of flash memory.”
the memristor could
enable computation
to be performed in
chips where data is
stored, rather than
on a specialized
cPu, says Gilberto
Medeiros Ribeiro.
However, not everyone has been im-
pressed by the recent announcements
from HP and Rice. “The memristor is
only one of several interesting [recent]
flash technologies, and by no means
the most interesting,” says Justin Rat-
tner, Intel’s chief technology officer.
“Any time someone hypes a particular
memory technology before building a
large memory chip, you should be sus-
picious, very suspicious. It’s one thing
to demonstrate a storage device in the
lab, but it’s an entirely different thing
to demonstrate it can be built in high
volume at low cost and with exception-
al reliability.”
Rattner acknowledges that flash
memory, which is a $20 billion-plus
market, is rapidly approaching its scal-
ing limit. But rather than memristors,
Intel is concentrating on nonvola-
tile phase-change memory, by which
certain types of glass can be made to
switch between two states by the ap-
plication of heat. In the amorphous
state, the atomic structure of the glass
is highly disordered and has high re-
sistivity. But when switched to its crys-
talline state, the glass has a regular
atomic structure and low resistivity.
“We built commercial-grade, phase-
change memories of sufficient size to
fully understand the pros and cons of
the technology in a high-volume envi-
ronment,” Rattner says. Intel is look-
ing at additional novel approaches to
nonvolatile memories such as the spin
torque transfer memory, which ex-
ploits magnetic spin states to electri-
cally change the magnetic orientation
of a material.
Society
Women
and
Tenure
Over the last couple of decades,
women have played an
increasingly important role in
the research sciences. however,
according to Keeping Women
in the Science Pipeline, a recent
study by university of California,
Berkeley researchers, there’s
trouble brewing. Women,
who now receive more than
50% of the Ph.D.s granted by
institutions, are more likely to
leave the profession than men.
this, combined with growing
demand for talent in europe
and asia, puts u. S. preeminence
in the sciences at risk.
The authors, who collected
data from multiple sources
and surveyed 62 academic
institutions, found considerable
differences in men and women
attaining tenure track positions.
Married women with young
children are 35% less likely than
their male counterparts to enter
a tenure-track position after
receiving a Ph. D. in science.
What’s more, married women
with children are 27% less likely
than men with children to
receive tenure after entering a
tenure-track job in the sciences.
On the other hand, single
women without young children
are about as successful as
married men with children in
attaining tenure-track jobs.
According to the report, both
men and women view tenure-track positions in research-intensive universities as less
than a family-friendly career
choice. Only 46% of the men
and 29% of the women rate their
institutions “somewhat” or
“very” family friendly. Numerous
work hours and maternity leave
of less than six weeks were cited
as common problems.
The upshot? The academic
world needs to adopt more
family-friendly policies and
provide greater opportunities
for female tenure-track
candidates. “America’s
researchers do not receive
enough family-responsive
benefits,” the report concludes.
“Academia needs to be more
flexible… research universities
should look to build a family-
friendly package of policies and
resources.”
—Samuel Greengard