Will memristors prove irresistible?

Regardless of whether HP's RRAMs become the killer application, the memristor could turn out to be as important a development as the transistor itself. And as with the transistor, applications may take a while to accumulate.

"The memristor's history is similar to that of the transistor, which was invented 35 years before its first major application," said Wolfgang Porod, an EE professor at Notre Dame University. Created in the 1920s by physicist Julius Edgar Lilienfeld, the device was not developed to its full potential until it came to the attention of Bell Labs researchers William Bradford Shockley, John Bardeen and Walter Houser Brattain, who were awarded the 1956 Nobel Prize for their pioneering work.

The first application, Porod said, was in-ear hearing aids, where "its small size justified its higher cost in those days compared with vacuum tubes." Transistor radios soon followed.

In just the same way, HP sees RRAMs as only the beginning for the memristor. HP Labs foresees its use in neural networks that could learn to adapt by allowing current to flow in either direction, as needed.

"RRAMs are our near-term goal, but our second target for memristors, in the long term, is to transform computing by building adaptive control circuits that learn," said Duncan Stewart, principal investigator for memristors at HP Labs.

Using a crossbar architecture similar to that of the RRAM to harness precise resistance changes in an analog circuit, HP Labs claims that massive memristor arrays with tunable resistance at each crossbar could enable brainlike learning. In the brain, a synapse is strengthened whenever current flows through it, in much the same way as flowing current through a memristor lowers resistance.

"Analog circuits using electronic synapses will require at least five more years of research," Stewart said. HP Labs estimates that commercial applications are about a decade out.