[LINK] Memristors: 'logic, signal routing, AND memory'
stephen at melbpc.org.au
stephen at melbpc.org.au
Thu Mar 5 02:06:21 EST 2009
PhysOrg.com) -- http://www.physorg.com/news154865950.html
As researchers strive to increase the density and functionality of
circuit elements onto computer chips, one newer option they have is
a 'memory resistor' or 'memristor' the fourth passive-circuit element.
First predicted to exist in 1971 and fabricated in 2008, memristors are
two-terminal devices that change their resistance in response to the
total amount of current flowing through them.
Dynamically changing the doping profile inside memristive materials can
control the current-voltage relationship of the device, thus controlling
Since they dont lose their state when the electrical power is turned
off, memristors also have nonvolatile memory.
In a recent study, a team of researchers from Hewlett-Packard
Laboratories in Palo Alto, California, have fabricated and demonstrated a
hybrid memristor/transistor circuit for the first time.
The team demonstrated conditional programming of a nanomemristor by the
hybrid circuit, showing that the same elements in a circuit can be
configured to act as logic, signal routing, and memory.
By routing a logic operations output signal back onto a memristor, the
circuit could even reconfigure itself, opening the doors to a variety of
The HP teams memristor design (was) tested by performing a basic logic
function (AB + CD) from four voltage inputs representing the four values.
The operations were performed on two different rows of the memristor
crossbar, and the results were routed through the transistors, which
amplified the signals and fed the corresponding signal back to the
memristor crossbars for programming purposes.
In other words, the output signal from the simple logic function of the
memristor circuits could be used to reprogram new operations.
'Self-programming is a form of learning,' Williams explained.
'Thus, circuits with memristors may have the capacity to learn how to
perform a task, rather than have to be programmed to do it.'
As the researchers explained, the basis of the memristor is that the
resistance of the device can be changed and be remembered, which is
physically manifested by the movement of positively charged oxygen
vacancies, which are dopants in a semiconducting TiO2 film.
A positive bias voltage can push the vacancies away from an electrode and
increase the resistance, whereas a negative bias will attract the
vacancies and decrease the resistance. If left alone, the programmed
state will remain as it is for at least one year.
The researchers hope that this prototype of a hybrid memristor/transistor
circuit will lead to further integrations of memristors with conventional
In addition, the demonstration of a system that can alter its own
programming could lead the way toward a variety of new architectures,
such as adaptive synaptic circuits. Copyright 2009 PhysOrg.com.
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