Technology | DOI: 10.1145/1897852.1897859
Gary Anthes
Memristors:
Pass or fail?
The device may revolutionize data storage, replacing flash memory
and perhaps even disks. Whether they can be reliably and cheaply
manufactured, though, is an open question.
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A FunDaMental eleC- tROniC device, whose xistence was postulat- ed five decades ago but which proved hard to
understand, let alone build, is ready
to emerge from the lab, corporate and
university researchers say. If so, the
memristor (or memory resistor), as it
is called, may arrive just in time to save
the information storage industry from
the transistor’s collision with the scaling wall at the end of Moore’s Law.
Hewlett-Packard announced last
August that it would team with the
South Korean computer memory
maker Hynix Semiconductor to develop memristor-based memory chips,
called resistive RAM (ReRAM), which
they say will be on the market in about
three years. The companies say their
titanium-based chips could replace
flash memory—which has become
nearly ubiquitous in mobile applications—and would be 10 times faster
and 10 times more energy efficient.
Meanwhile, Rice University has joined
with Austin, TX-based PrivaTran, a
semiconductor design company specializing in custom integrated systems, to develop an all-silicon ReRAM
chip that could be a substitute for flash
memory. But a senior research official
at Intel says it is far from certain that
either effort will succeed.
A memristor is a tiny two-terminal
electronic component that can be
made from a variety of materials—
including polymers, metal oxides, and
conventional semiconductors like silicon— whose resistance varies with the
voltage applied across it and with the
length of time the voltage is applied.
Its initial applications are likely to be
as binary memory devices, but it could
work in an analog fashion and could
eventually become the basis for cer-
an image of a circuit with 17 memristors captured by an atomic force microscope at
hewlett-Packard’s information and Quantum systems Lab.
tain types of logic circuits. “That [logic
ability] could change the standard paradigm of computing, by enabling computation to one day be performed in
chips where data is stored, rather than
on a specialized CPU,” says Gilberto
Medeiros Ribeiro, a senior scientist at
HP Labs.
The memristor has several quali-
ties that make it attractive for memory
chips. First, it is nonvolatile, so that
it remembers its state after electrical
current is switched off. Second, it can
be scaled to a single nanometer (nm)
in size, researchers believe, whereas
the one-bit flash memory cell is expect-
ed to reach its scaling limit at about
20 nm. And Leon Chua, a professor of
electrical engineering and computer
science at the University of California,
Berkeley, says the memristor’s size ad-
vantage isn’t its sole advantage. “You
can not only build them smaller, but
use fewer of them,” he says. “Ten mem-
ristors might do the same thing as 50
transistors, so it’s a new ball game.”
In 1971, Chua published a paper,
“Memristor—The Missing Circuit Ele-
ment,” in IEEE Transactions on Circuit
Theory, which outlined the mathemat-
ical underpinnings of memristors,
which he called the fourth fundamen-
tal building block of electronics (along
with resistors, capacitors, and induc-
tors). The existence of memristance
had been reported earlier—in 1960 by
Bernard Widrow at Stanford Univer-
sity, for example—but it was not well
understood.