New Electronic Circuits Have Built-In Memory

For nearly 40 years, scientists have speculated that basic electrical circuits have a natural ability to remember things even when the power is switched off. They just couldn't find it.

Now researchers at Hewlett-Packard Co. have proven them right, with a discovery they hope will lead to memory chips that store more data but consume far less power than those found in today's personal computers and other digital devices.

The newly discovered circuit element — called a memristor — could enable cell phones that can go weeks or longer without a charge, PCs that start up instantly, and laptops that retain your session information long after the battery dies.

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It also could challenge flash memory, which is now widely used in portable electronics because of its ability to retain information even when power is off.

Chips incorporating the HP discovery would be faster, suck up less power and take up far less space than today's flash.

"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."

Scientists have suspected since the 1970s that along with the three well-known elements of a basic circuit — the resistor, the capacitor and the inductor — a fourth fundamental building block is possible.

The memristor built by HP Labs researchers and reported Thursday in the scientific journal Nature is made with a layer of titanium dioxide sandwiched 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.

That characteristic gives the memristor an innate ability to remember the amount of charge that has flowed through it long after the power to it is turned off.

That means the circuit itself can be built with a memory function baked in.

Otherwise, data have to be stored in power-hungry transistors configured for storage. That also takes up valuable real estate on microprocessors or requires separate memory chips.

Some outside researchers, however, said more study is required before the memristor upsets the memory business. The HP Labs team said commercial viability is at least "a few years" away.

"These structures are going to be very small. It's obvious to me one could make very dense memory out of them, but how it could compete against other memory like flash remains to be seen," said Porod, who was not involved in the HP research.

Leon Chua, a professor in the electrical engineering and computer sciences department at the University of California, Berkeley, published a paper in 1971 theorizing that it should be possible to build such a structure.

Over the years, researchers observed behavior that seemed to suggest circuits possessed this ability, but they either dismissed it as a fluke or didn't realize the significance of the observation.

Stan Williams, a senior fellow at HP Labs and one of the four researchers on the Nature paper, said his team was able to identify the behavior and build a structure to harness its power because the effect is more apparent — and gets stronger — as the wiring in the circuits gets smaller and smaller.

Chua, who wrote the first paper on the topic when he was a new professor at Berkeley, is now 71 years old and says he's nearing retirement from the university.

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