http://www.sciam.com/article.c...ng-link-of-electronics
You may dimly recall circuit diagrams from your middle school science class; those little boxes with a battery on one end and a lightbulb on the other. Ring any bells? To an electrical engineer, the battery is a capacitor?a device for storing electric charge?and the lightbulb is a resistor?an obstacle to electric current. Until now, engineers have had only one other basic element to work with?the inductor, which turns current into a magnetic field.
In 1971 researcher Leon Chua of the University of California, Berkeley, noticed a gap in that list. Circuit elements express relationships between pairs of the four electromagnetic quantities of charge, current, voltage and magnetic flux. Missing was a link between charge and flux. Chua dubbed this missing link the memristor and created a crude example to demonstrate its key property: it becomes more or less resistive (less or more conductive) depending on the amount of charge that had flowed through it.
Physicist Stanley Williams of HP Labs says that after a colleague brought Chua's work to his attention, he saw that it would explain a variety of odd behaviors in electronic devices that his group and other nanotech researchers had built over the years. His "brain jolt" came, he says, when he realized that "to make a pure memristor you have to build it so as to isolate this memory function."
So he and his colleagues inserted a layer of titanium dioxide (TiO2) as thin as three nanometers between a pair of platinum layers [see image above]. Part of the TiO2 layer contained a sprinkling of positively charged divots (vacancies) where oxygen atoms would have normally been. They applied an alternating current to the electrode closer to these divots, causing it to swing between a positive and negative charge.
When positively charged, the electrode pushed the charged vacancies and spread them throughout the TiO2, boosting the current flowing to the second electrode. When the voltage reversed, it slashed the current a million-fold, the group reports. When the researchers turned the current off, the vacancies stopped moving, which left the memristor in either its high- or low-resistant state. "Our physics model tells us that the memristive state should last for years," Williams says.
Chua says he didn't expect anyone to make a memristor in his lifetime. "It's amazing," he says. "I had just completely forgotten it." He says the HP memristor has an advantage over other potential nonvolatile memory technologies because the basic manufacturing tools are already in place.
Facebook
Twitter