Next-generation semiconductors aim to harness the ballistic electron transport capabilities of pure carbon nanotubes, but until now there has been no easy way to integrate the tubes with silicon chips. Now IBM Corp. researchers think they have the solution--coat nanotubes with a ligand that only sticks to high-k dielectrics, then lithographically pattern the wafer with high-k dielectrics wherever transistor channels are wanted. The researchers showed that carbon nanotubes would self-assemble on the lithographically defined channels and that annealling boiled off their ligand coating, leaving behind arrays of carbon nanotube transistors. Normally, when used as the channel for a transistor, carbon nanotubes are many times smaller than the source and drain electrodes--less than 1 nanometer, compared with tens or hundreds of nm. This makes it difficult to fabricate them using traditional lithographic techniques. The process runs on any standard CMOS semiconductor fabrication line. In their proof-of-concept demonstration chip, the IBM researchers fabricated an array of nanotube transistors by patterning 40-nm-deep x 300-nm-wide aluminum lines on a silicon dioxide wafer, placing them where transistor channels were supposed to be. The aluminum was then oxidized to turn it into a high-k dielectric. Next, the chemically treated nanotubes, in an ethanol solution, were applied to the wafer. At this point, the nanotubes stuck only to the high-k dielectric pattern and not to the silicon dioxide substrate. Finally, the IBM team patterned electrodes for the source and drains of the transistors. The resultant demonstration transistors had a 400-nm channel length.
Monday, April 24, 2006
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.
Monday, April 17, 2006
It's the stuff of rock 'n' roll fantasy: a ring that gives its wearer the power to morph the sound of an electric guitar at will. Thanks to the pairing of an automotive airbag accelerometer with a customized version of a popular audio processor, a technology called Hot Hand claims to make that scenario possible. Devised by Analog Devices Inc. spin-off Source Audio LLC (www.sourceaudio.net), Hot Hand puts an ADI accelerometer chip in a ring that guitarists place on a finger of their picking hand. The movements of the ring are tracked by feeding the wired control signals into a box that houses an ADI-customized SigmaDSP--a 56-bit audio processor with 24-bit A/D and D/A converters and a 100-decibel dynamic range. Two foot pedals control on/off and cycling through user-defined presets. Source Audio was founded by two former ADI employees who convinced their former employer to create a customized version of its SigmaDSP for a system-on-chip called the Sound Audio 601 (SA601), to complement the low-power version of an ADI accelerometer chip (the iMEMS ADXL320). The co-founders then recruited former Kurzweil Music Systems Inc. chief scientist to craft the effects. Source Audio's first Hot Hand version applies the SigmaDSP-iMEMS combo to achieve wah-wah and volume effects. Other guitar effects are slated to follow soon.
In an MIT lab, polyelectrolyte coated with anode nanowires eyes next-generation energy: Battery technology has historically lagged far behind semiconductor technology. While chips double their capacity every 18 months or so, batteries are lucky to double capacities in a decade. But now, say materials scientists at the Massachusetts Institute of Technology, bioengineering has broken the bottleneck. Almost half the materials in today's batteries do not contribute to electricity storage, whereas MIT's bioengineered batteries aim to put more than 90 percent of their materials to work storing energy. To do that, the scientists--professors Angela Belcher, Paula Hammond and Yet-Ming Chiang--employ genetically engineered living viruses to assemble thin-film nanowires as the anodes and cathodes of a flexible "battery wrap." At 100 nanometers thick, the next-generation battery wrap can conform to any shape, they said. The battery wrap invented at MIT is based on a genetically engineered derivative of the M13 bacteriophage--a virus parasite that infects a bacterium and reproduces inside it. By altering the genetic dispositions of this well-understood laboratory virus, which cannot infect humans, the materials scientists have been able to persuade the virus to extract cobalt-oxide and gold ions from solution and assemble them into a monolayer of nanowires functioning as a battery anode atop a polyelectrolyte substrate.
Monday, April 10, 2006
Since the '60s, microelectromechanical systems have struggled to enter the mainstream. With the success of selected MEMS applications, more players are entering the arena. But few have aimed at a larger market segment than SiTime Corp., whose MEMS-First oscillator lines are meant to be pin-for-pin compatible with quartz crystal oscillators. MEMS first became a high-volume industry with air bag sensors like the iMEMS accelerometers from Analog Devices Inc. and later with the digital-light processing (DLP) chips from Texas Instruments Inc. Most recently, Akustica Inc.'s sensor-silicon MEMS microphone has attracted attention. Now SiTime (Sunnyvale, Calif.) is bidding to become an even higher-volume player, since virtually every electronic device produced today uses a quartz-crystal oscillator as its time base. Gartner Inc. (www.gartner.com) calls the market for analog quartz crystals relatively flat at over $1 billion yearly, with an average selling price of 15 cents on shipments of billions of units per year. Even while still in sampling mode, SiTime has started tapping that vast market by selling more than a million units of its prototypes. Full-volume fabrication of final production units from SiTime, which is fabless, is slated for later in 2006.
Researchers at the Georgia Institute of Technology, in cooperation with the Centre National de la Recherche Scientifique (CNRS) in France, have flattened out carbon nanotubes into monofilms to create a new material they call "epitaxial graphene." The material has low-resistance electrodes, full lithographic compatibility and the ability to control the wave properties of electrons as well as their conventional electronic properties. Carbon nanotubes measure only 1.5 nanometers in diameter. When fabricated as the channel of an otherwise silicon transistor, nanotubes provide an avenue that traverses the semiconductor road map all the way to atomic dimensions. Unfortunately, the vast size difference between 1.5-nm-diameter nanotubes and the 65-nm features of state-of-the-art semiconductors today makes their electrodes overly ohmic, their lithography troublesome and their suceptibility to conventional pitfalls like parasitic capacitance acute. The new material can be integrated with lithographic silicon chip-processing steps, and has so far demonstrated features as small as 80 nm for a conventional field-effect transistor and a quantum interference device that manipulates electrons as waves.
Monday, April 03, 2006
European aerospace researchers have shown the first prototype of a planned "flapless" unmanned air vehicle. Similar to a remote-controlled U.S. Predator drone, the prototype UAV is an early milestone for the five-year Flapless Air Vehicle Integrated Industrial Research (Flaviir) project, which aims to produce a fully autonomous UAV with no moving control surfaces by 2009. The completely smooth, teardrop-shaped black exterior of the envisioned autonomous craft will also be fully shielded against electromagnetic pulse (EP) attacks, whether from lightning strikes or nearby nuclear bombs, planners said. All aircraft today use control surfaces--flaps--to turn, dive and climb. By using using streams of air to control direction in its UAV, the Flaviir effort intends to take computer control one step beyond fly-by-wire aircraft, aiming at com- pletely autonomous operation (see www.flaviir.com). The goal is a low-cost, maintenance-free UAV that will fly at least as well as conventional aircraft.
Analog Devices Inc. has teamed with robotics expert Fred Martin to create a single-board solution for autonomous robots. The Blackfin Handy Board contains all the electronics needed for sensing, processing and actuating robots. The original Handy Board was designed at the Massachusetts Institute of Technology for its Autonomous Robot Design Competition. The HandyBoard's design was published as open source and has become the most popular vehicle to get a robot up and running quickly. The board itself has been widely copied around the world. The Blackfin Handy Board, the first complete redesign of the Handy Board, has also been published as open source. The redesigned board builds in Ethernet and digital video interfaces, a dc stepper motor controller, radio-controlled servo motor controllers and electronic speed controllers, an integrated battery and charger, a 4 x 16-character LCD screen and banks of I/Os for raw analog and digital signals. Analog Devices has also included its two-axis accelerometer and a Xilinx Spartan-3E FPGA. The Blackfin Handy Board comes with Interactive C, National Instruments LabView software, and a software library that includes software operators to manage all board resources.