Resistance Is Not Useless In New Chip Design

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Williams said part of the problem was the math. It was so complex it took years for anyone to work out how to model an actual device.

Later, there were experiments done that showed the kind of behavior expected in a memristor circuit, but it took a number of years before scientists understood what they were seeing, Williams said. HP Labs did experimental work in 2006 that showed the memristor existed, and later worked out how to build them reliably.

To make the memristor, the group at HP used a "plug" of titanium oxide between two electrodes. When the voltage hits the plug, the oxygen atoms move out of position. That movement changes the resistance of the material, and eventually it is high enough that the current can't pass. This is just like opening a switch in an ordinary semiconductor.

When the current is turned off, the oxygen atoms stay in place. Hit the titanium oxide with a current of the opposite polarity, and the oxygen atoms move back near the positions they were in before. The switch in this case is closed.

Williams noted ordinary semiconductor circuits use silicon dioxide, but the bonds between silicon and oxygen atoms are strong. For a memristor to work, some of the atoms have to be knocked out of position by the current.

The plugs are small. Williams said his team got them down to about 3 nanometers, which is less than one percent of the wavelength of visible light. "It's about nine atoms across," Williams said.

Unlike flash memory, the bits are stored in the atoms. In flash memory, the electrons are stored, and as the chips get smaller there are more problems with the electrons tunneling out. This is why flash memory cards can degrade, especially if left in a hot environment (such as a car's dashboard on a summer day). A memory chip made with memristors would not degrade as easily.

Memristor chips could also hold a lot more information. Williams said he thinks chips with at least twice the capacity of flash memory can be achieved.

Along with more information, memristor chips would use less power. Moving electrons around in a flash memory card takes more energy because the distance an electron has to move is longer. Memristor chip circuits are smaller and the atoms don't have to move very far. That cuts down the amount of current needed to operate them.

The down side is degradation with use. Williams noted that the number of switching cycles a memristor can undergo is limited, though given that they will be used for memory it will be less of a problem than it would for a logic circuit. He said the lab has run the memristor circuit through about a billion cycles, but memory isn't used that often.

HP is partnering with Hynix, a Korean semiconductor manufacturer, to build the new chips. Williams said the fabrication of memristors is not very different from ordinary semiconductors, which shortens the time it takes to develop a product.