Shape of things to comeStanford researchers offer revolutionary design for computer chips
Moore’s law stipulates that the number of transistors squeezed onto a computer chip can be doubled about every two years; the law was threteaned by the damaging heat generated by the chips as their transistors become more densely packed; new design solves problem; “What we managed to do is basically get rid of the magnetic field,” says lead researcher
The famous Moore’s law stipulated that the number of transistors squeezed onto a computer chip can be doubled about every two years. It was becoming increasingly apparent that the law was being threatened by a rather prosaic fact: The damaging heat generated by the chips themselves as their transistors become more densely packed. Stanford University researchers have now come up with a new theory of circuit design, recently confirmed by experiments in Germany, which deftly exploits the quirkiness of quantum physics drastically to reduce the heat produced by electricity coursing through the tiny veins of semiconductors. Stanford physics professor Shoucheng Zhang says a new generation of semiconductors, designed around the phenomenon known as the Quantum Spin Hall Effect, could keep Moore’s law in force for decades to come. The theoretical aspect of the effect is intriguing on its own, beyond the benefits for semiconductor design. He and a team at the University of Würzburg published their results in last week’s issue of Science Express, an online version of Science magazine.
Using special semiconductor material made from layers of mercury telluride and cadmium telluride, the experimenters used quantum tricks to align the spin of electrons like a parade of tops spinning together. Now, under these conditions, the current flows only along the edges of the sheet of semiconductor. Interestingly, electrons with identical spins travel in the same direction together, while electrons with the opposite spin move in the opposite direction. Unlike existing semiconductors, this unusual electric current does not generate excessive and destructive heat through dissipation of power or the collision of electrons with impurities in the semiconducting material. Here we come to theoretical significance of the experiment: Zhang says that the electrons’ strange behavior constitutes a new state of matter, joining the three states familiar to high school science students — solids, liquids, gases — as well as more unworldly states such as superconductors, in which electrons flow with no resistance. He describes the quest for new states of matter as the holy grail of condensed matter physics. Note that similar effects have already been demonstrated before, but only at extremely cold temperatures and under the effects of powerful magnetic fields, conditions that do not and cannot exist inside the common computer. “What we managed to do is basically get rid of the magnetic field,” Zhang said.
There are other approaches for the next generation of computer chips, including nanotube technology. Zhang believes that Quantum Spin Hall Effect chips have the advantage because they can be made from materials already familiar to chip makers. In the long run, so-called “spintronics” could see the spin of electrons becoming more important than their electrical charge: Semiconductors would operate on the basis of spin alone, without electrons moving in their usual form of electrical current.
-read more in Markus König et al., “Quantum Spin Hall Insulator State in HgTe Quantum Wells,” Science Express (20 September 2007): 1-5 (sub. req.)
