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An image from an atomic force microscope shows a circuit with 17 memristors lined up in a row. Every memristor shares the same bottom wire (top left to bottom right), and each has its own top wire. The memristors are between the wires.

New Circuit Element
The memristor could be useful for nonvolatile memory

Source: “The missing memristor found”
R. Stanley Williams et al.
Nature
453: 80-83

Results: Researchers at HP Labs have fabricated a memristor, or memory resistor–a fundamental electronic device that had been described theoretically but never produced until now. The amount of charge that flows through the device can be changed by exposing it to an electrical voltage. Applying a positive voltage lowers its resistance, and applying a negative voltage increases it. Furthermore, the change in resistance is proportional to the length of time the voltage is applied: the more the device is charged, the more electricity it conducts. Once set, the resistance stays the same until it’s reset.

Why it matters: Memristors could lead to ­nonvolatile memory chips that store more data than flash ­memory. They could also be used in processors designed to mimic aspects of the human brain. In the brain, learning depends on changes in the strength of connections between neurons. The memristor can be used to set the strength of connections between transistors, achieving a similar effect. Chips using memristors could be useful for face recognition and for controlling robot movement.

Methods: The new memristors consist of two layers of titanium dioxide sandwiched between two electrical contacts. One layer of titanium dioxide is an insulator, blocking the flow of electrons from one contact to the other. The other layer, which has fewer oxygen atoms than titanium dioxide normally does, conducts electricity.

When a voltage is applied, some of the oxygen ions move from the first layer into the oxygen-­deficient layer. That improves the conduc­tivity of the first layer, allowing electrons to pass through the memristor from one contact to the other.

Next steps: Since Hewlett-Packard doesn’t make ­memory chips, the tech­nology will probably be licensed to another company for product development. The HP researchers are working on a prototype that combines transistors and memristors to form a brainlike chip.

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Credit: J. J. Yang, HP Labs

Tagged: Computing, Materials

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