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Technology: Record switch speed for silicon transistors

Technology: Record switch speed for silicon transistors

作者:茅杼沦  时间:2019-02-26 03:06:00  人气:

By JEFF HECHT in BOSTON SILICON TRANSISTORS that can switch at a rate almost twice that of any of their predecessors at room temperature have been made at IBM. The advance is significant, not only because the speed of transistors is crucial to the overall speed of computers, but also because silicon is well understood and easy to manufacture. In contrast, compound semi-conductors, the main competitors to silicon for constructing transistors, are difficult materials to work with. Many researchers believe that any significant improvement in transistor speed can be achieved only by constructing the devices from compound semiconductors, such as gallium arsenide, because electrons can travel through them much more quickly: IBM’s achievement of 75 billion switches per second remains far short of the record for a compound semiconductor transistor at room temperature, 250 billion per second. This record was set by Hughes Research Laboratories in Malibu, California. Two years ago, IBM reported a silicon transistor which switched at 75 billion cycles per second when cooled to the temperature of liquid nitrogen. The new device, which works at room temperature, has a different design, with currents travelling vertically rather than horizontally across its surface, explains Johannes Stork, who developed the transistor at the IBM Watson Research Center in Yorktown Heights, New York. Vertical layers in a transistor can be made thinner than horizontal stripes, so electrons can pass through them more quickly. The new IBM transistor has layers which are 0.05 micrometres thick, compared with 0.1 micrometre stripes in the earlier horizontal IBM transistors. One key development in the new devices is the addition of about 8 per cent germanium to the base of the transistor, which allows electrons to flow through the base more quickly. The base is the switch part of the transistor: changes in the voltage applied to the base switch the current through the transistor, from the emitter to the collector, on and off. The Hughes group used a horizontal structure in their transistor and a more complex compound semiconductor. They deposited layers of aluminium indium arsenide and gallium indium arsenide on a base of indium phosphide. Such compounds are harder to make into useful devices than silicon, but electrons travel through them faster. Hughes researchers believe that they can raise the switching speed to 300 billion cycles a second by shrinking the size of the stripes on their device below their present 0.15 micrometres. Both IBM and Hughes have demonstrated only isolated devices so far. Switching would be much slower if the transistors were connected to other electronic components to form a useful circuit. Although developers believe silicon is a more practical material than compound semiconductors,