8/6/2019 Berkeley Science Review 20 - Smart Circuits

1/212 Berkeley Science Review Spring 2011

Smart circuits

Making electronics thatremember

Electrical engineering is on the cusp of a

breakthroughone that will al low engineers

to create circuits that drastically increasethe speed of processing, use far less power

than modern computers, and even mimic

the kind of computations carried out by the

human brain. This shift comes in the form

of the memristor, a long-theorized but only

recently constructed electrical component

that stores information about its past activity

and uses this information to influence its

behavior. First theorized nearly 40 years ago,

and finally built by Hewlett-Packard Labs

in 2008, it promises to redefine the abilities

and applications of computers of the future.While memristors have only recently

been constructed, they have existed in theo-

retical electronics for many years. Leon Chua,

a longstanding member of the Department

of Electrical Engineering and Computer

Sciences at UC Berkeley, laid out the original

theory in 1971. In his paper, Chua addressed

a hole that existed in our knowledge of elec-

trical engineering.

The world of electronics is largely built

around devices that carry out interactions

between the basic variables in any circuit:

charge, resistance, voltage, and flux. For

example, a capacitor creates a voltage by

maintaining an imbalance of electrons (or

charge) on either side of a gap. At the time

of the theorys publication, there was a clearexplanation for how a real-world device

could connect each combination of these

elements but one: charge and flux.

Chua theorized a new circuit element

to carry out the missing interaction. This

element would behave very similarly to a

resistor, but with one key difference: the

amount that it impeded the flow of electricity

would depend on the current that had already

passed through. In essence, this electrical

element would have a memory, combining

information about the past with its input inthe present. For this reason, Chua dubbed

this new element the memristor.

Though it made a splash in theoreti-

cal electronics, it would be nearly 40 years

until the memristor would be realized in the

laboratory. Up to that point, Chuas depiction

of the properties of memristors had been

likened to the elusive Higgs boson of theo-

retical physics: a particle that exists in theory

but has not yet been observed. Then, in 2008,

HP Labs announced that they had created a

nano-scale circuit that showed exactly the

same properties that Chua had theorized.

Memristors were real.

Although memristors have yet to

be successfully integrated into standard

electronics, the ability to engineer circuitswith memristors is improving rapidly, and

hybrid memristor/traditional computers are

expected to make their first appearance in

consumer technology in the next few years.

Your next computer could have memristors

that allow for faster booting and processing.

These early successes bode well for a para-

digm shift in the future of electronics. While

most modern computers perform calcula-

tions using dynamic random access memory

(DRAM) that must be wiped clean every time

a computer loses power, a new memristor-equipped computer could remember the

state from when it was last turned off and

boot up nearly instantaneously.

Memristors could also decrease comput-

ers power consumption, which has increased

exponentially as demands on processors

continue to rise. Currently, this power

consumption poses a significant challenge

to increasing the complexity and power of

processing chips. Memristors, however, con-

sume relatively little power because storing

memory within small units, rather than ina separate system, allows designers to use

fewer and shorter wires, and thus less power.

Memristor systems bring data close to com-

putation, much as biological systems do,

explains Massimiliano Versace, a researcher

at Boston University who is using memristors

to study, and possibly create, models that are

inspired by human cognition.

The potential to create highly intercon-

nected systems that are eerily similar to the

way our own brains are structured is one of

the most exciting potential applications formemristors. For many years, scientists have

tried to model human cognition, but have

often fallen short due to the limitations of

our current hardware. Such systems are built

with specific locations for computations (cen-

tral processing units, or CPUs), short-term

memory (dynamic random-access memory,

or DRAM), and long-term memory (the hard

BriefsMemristors

An image of an array of memristors formed at the

intersection of crossed microscopic wires. Each is

approximately 150 atoms wide.

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