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