[Yr7-10it] Memristors: 'logic, signal routing, AND memory'

[stephen at melbpc.org.au]

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 
the 'memristance.' 

Since they don’t 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 operation’s output signal back onto a memristor, the 
circuit could even reconfigure itself, opening the doors to a variety of 
self-programming circuits.

The HP team’s 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 
CMOS circuits. 

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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Cheers,
Stephen