World’s first nanotube computer built

New Carbon-Based Transistors Use Less Energy & Run Faster Than Silicon Chips

Palo Alto (California): A group of Stanford researchers has moved a step closer to answering the question of what happens when silicon, the standard material in today’s microelectronic circuits, reaches its fundamental limits for use in increasingly small transistors. In a paper in the journal Nature on Wednesday, the researchers reported that they had successfully built a working computer — albeit an extremely simple one — entirely from transistors fashioned from carbon nanotubes. The nanotubeshave long held the promise of allowing smaller, faster and lower-powered computing, though they have proved difficult to work with. 
    The computer can right now perform only basic functions at speeds likened to a 1950s computer, but the tiny machine was hailed as a breakthrough in the search for an alternative to silicon transistors. Carbon nanotubes (CNTs) are rolled-up, single-layer sheets of carbon atoms — tens of thousands can fit into the width of a single human hair. They are pliable and have the highest strength-to-weight ratio of any known material. Silicon is a good semiconductor but cannot be reduced to such a thin layer. Experts believe the structure of CNTs may make them better at carrying currents — thus yielding transistors that are faster, more energy efficient and smaller than silicon. 
    “People have been talking about a new era of carbon nanotube electronics moving beyond silicon,” said Stanford professor Subhasish Mitra, who led the research. “But there have been few demonstrations of complete digital systems using this exciting technology. Here is the proof.” 
    The computer is just a few square millimetres in size and able to perform basic counting and number-sorting functions using 178 transistors each holding between 10 and 200 nanotubes. It runs at 1 kilohertz — a processing capacity millions of times weaker than today’s computers. The 178-transistor limit was due to the team using a university chip-making facility rather than an industrial process, meaning the computer could in theory be made much bigger and faster, a statement on the study said. The machine ran a basic operating system that allowed it to multitask and swap between the two processes, it added. 
    Mitra and his team had been able to deal with two inherent shortcomings of CNT transistors: the tubes do not always grow in perfectly straight lines, which means that mispositioned ones can cause a short circuit, while others changed form and couldn’t be switched on and off. The team devised a method to burn up and eliminate the uncontrolled CNTs in a transistor and to bypass mispositioned ones. AGENCIES

BIG BOOST: The new technology raises hopes of future computers that are smaller, faster and more efficient.

Source:::: The Times of India, 27-09-2013, p.17,  http://epaper.timesofindia.com/Default/Client.asp?Daily=TOIM&showST=true&login=default&pub=TOI&Enter=true&Skin=TOINEW&AW=1380269603906