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New Properties of Circuits Revealed

May 1, 2008

Researchers at Hewlett-Packard have made a new discovery in circuitry that may enable computers, cell phones and other devices to hold more memory while taking up less energy than modern technology allows.

It had been theorized for almost 40 years, but researchers announced on Wednesday that they finally had proof that basic electrical circuits have four fundamentals, rather than three.

The fourth element, called a memory resistor, or memristor for short, was first considered by Leon Chua of the University of California at Berkeley in the 1970s.

Now, thanks to the research team at Hewlett-Packard led by Stanley Williams, “Ëœmemristance’ can now be added to the list alongside the three other elements — resistors, capacitors and inductors.

The use of memristance could potentially challenge flash memory in portable devices, because it would be a faster, more efficient method. I could also allow the development of cell phones that can go weeks or longer without a charge and PCs that start up instantly.

“It certainly looks promising,” said Wolfgang Porod, professor of electrical engineering at the University of Notre Dame and director of the university’s Center for Nano Science and Technology.

“However, if it’s going to be 100 times better or 1,000 times better (than today’s flash), it’s very hard to say at this point.”

Reporting Thursday in the scientific journal Nature, Williams and his three colleagues said that the memristor built by HP Labs is made with a layer of titanium dioxide placed between two metal electrodes.

The researchers discovered that the amount of resistance it exerts depends on how much electric charge had previously passed through it.

“It’s very different from any other electrical device,” Williams said. “No combination of resistor, capacitor or inductor will give you that property.”

Williams likened the property to water flowing through a garden hose. In a regular circuit, the water flows from more than one direction.

But in a memory resistor, the hose remembers what direction the current is flowing from, and it expands in that direction to improve the flow. If water or current flows from the other direction, the hose shrinks.

“It remembers both the direction and the amount of charge that flows through it. … That is the memory,” Williams said.

Dynamic random access memory, or DRAM, the memory currently found in computers, is lost after the power shuts off, but researchers hope that they will be able to develop a new kind of computer memory that would never need booting up.

“If you turn on your computer it will come up instantly where it was when you turned it off. That is a very interesting potential application, and one that is very realistic,” Williams said.

He added that companies in the market to develop smaller devices will become reliant on memristance.

“It’s essential that people understand this to be able to go further into the world of nanoelectronics,”

“It turns out that memristance, this property, gets more important as the device gets smaller. That is another major reason it took so long to find,” Williams said.

Chua, who wrote the first paper on the topic when he was a new professor at Berkeley, is now 71 years old.

“I never thought I’d live long enough to see this happen,” Chua said. I’m thrilled because it’s almost like vindication. Something I did is not just in my imagination, it’s fundamental.”

Image Caption: Old school – classical resistors are now joined by nanoscopic counterparts.

On the Net:

Hewlett-Packard

Information and Quantum Systems Lab

Nature




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