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Technology: Japan claims lead on Josephson chips

Technology: Japan claims lead on Josephson chips

作者:糜封妞  时间:2019-02-26 08:13:00  人气:

By MICHAEL CROSS in TOKYO PLAN to build a computer based on superconducting circuits has been an nounced by NEC, the world’s largest supplier of electronic components. The announcement follows a claimed breakthrough in the construction of microchips containing large numbers of superconducting circuits. These circuits, called Josephson junctions, work at much higher speeds than conventional transistors made from semiconductors, thanks to a phenomenon called the Josephson effect. A Josephson junction consists of two layers of superconducting material separated by a layer of insulator. At a temperature of -269 Degree C, the superconductors can bypass the blocking effect of the insulator and let a current pass through it. But this current is highly sensitive to magnetic fields and switches on and off very quickly when a magnetic field is applied or removed. This property of high-speed switching, which generates virtually no heat, interests designers of computers because the machines are essentially vast bundles of switches. IBM abandoned a project in 1983 to construct a computer based on Josephson junctions to pursue promising developments in conventional semiconductors. NEC’s new device is a memory chip that can store 4000 bits of digital data (the latest semiconductor chips can carry 4 megabits) in a circuit of 25 000 Josephson junctions 6 millimetres square. The superconductors, in four layers each 0.2 micrometres thick, are niobium and aluminium oxide. They work only at the temperature of liquid helium, 4 degrees above absolute zero (-273 Degree C). NEC says that its chip is a breakthrough because, unlike previous circuits built from Josephson junctions, it stores data in a non-volatile form. Other Josephson memory chips, the company says, destroy stored data in the act of ‘reading’ them. The next stage is to build a microprocessor from the circuits, and eventually a complete computer. NEC’s device was one of the fruits of a project organised by the government’s Agency of Industrial Science and Technology (AIST) and private companies. Another partner in the project, Fujitsu, has also built a memory chip capable of storing 4 kilobits of data. This consists of 14 468 Josephson junctions fabricated from a thin film of niobium superconductor. The goal is to build a generation of computers many times faster and more compact than those existing today. Josephson junctions operate 20 to 50 times as fast as circuits made from semiconductors such as silicon or gallium arsenide while consuming only one-thousandth the power. Many engineers believe, however,