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.