Monday, April 24, 2006

"CHIPS: High-k dielectrics turned into spin filters"

Though the International Semiconductor Roadmap predicted that 65-nanometer chips would require high-k dielectrics, some chip makers, Intel Corp. among them, put off switching until the 45-nm node, where researchers widely agree the high-k dielectrics will have to be used. Now, researchers at the University of Utah report, cobalt-doped high-k dielectrics can double as filters for "spintronic" transistors at the 45-nm node and beyond. Ferromagnetic insulators polarize the electrons tunneling through them, en-abling spintronic devices to be built. Researchers worldwide are experimenting with high-k dielectrics of the lanthanoid family, from lanthanum and cerium to gadolinium and dysprosium. Instead of heeding the International Semiconductor Roadmap's forecast that high-k dielectrics would serve as subnanometer insulators for the gates of complementary metal-oxide semiconductor (CMOS) transistors below the 65-nm node, chip makers instead have increased channel strain and enhanced carrier mobilities, thereby avoiding the leakage and reliability challenges involved with scaling down gate oxide thicknesses below 1 nm. But to reach the 45-nm node and beyond, high-k dielectrics are largely seen as essential so that gate oxides can be thinned down to 7 angstroms or less. Now the University of Utah team offers a second incentive to adopt lanthanoid oxides as high-k dielectrics: harnessing the spin of electrons instead of just storing a charge. Today's chips ignore the spin polarization of electrons--usually specified as "up" or "down"--and instead just store randomly polarized charge carriers. Up to the transistor dimensions of today, logic values are represented by the bulk flow of large numbers of electrons, which are randomly polarized. But as devices continue to shrink, the absolute number of electrons they channel will also decrease. By harnessing the spin of those electrons, the researchers argue, the injection and detection of smaller numbers of polarized electrons will enable transistor sizes to shrink further, faster, by using spintronics.