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A tunnel diode or Esaki diode is a type of semiconductor that is capable of very fast operation, well into the microwave frequency region, made possible by the use of the quantum mechanical effect called tunneling. It was invented in August 1957 by Leo Esaki when he was with Tokyo Tsushin Kogyo, now known as Sony. In 1973 he received the Nobel Prize in Physics, jointly with Brian Josephson, for discovering the electron tunneling effect used in these diodes. Robert Noyce independently came up with the idea of a tunnel diode while working for William Shockley, but was discouraged from pursuing it. These diodes have a heavily doped p–n junction that is about 10 nm (100 Å) wide. The heavy doping results in a broken bandgap, where conduction band electron states on the n-side are more or less aligned with valence band hole states on the p-side Tunnel diodes were first manufactured by Sony in 1957 followed by General Electric and other companies from about 1960, and are still made in low volume today.〔("Tunnel diodes, the transistor killers" ), ''EE Times'', retrieved 2 October 2009〕 Tunnel diodes are usually made from germanium, but can also be made from gallium arsenide and silicon materials. They are used in frequency converters and detectors.〔Fink, pp. 7–35〕 They have negative differential resistance in part of their operating range, and therefore are also used as oscillators, amplifiers, and in switching circuits using hysteresis. In 1977, the Intelsat V satellite receiver used a microstrip tunnel diode amplifier (TDA) front-end in the 14 to 15.5 GHz frequency band. Such amplifiers were considered state-of-the-art, with better performance at high frequencies than any other transistor-based front end.〔 Mott, R. C. ("Intelsat V 14-GHz tunnel diode noise figure study" ) COMSAT Technical Review, vol. 8, Fall 1978. 〕 The highest frequency room-temperature solid-state oscillators are based on the resonant-tunneling diode (RTD).〔 E. R. Brown, J. R. Söderström, C. D. Parker, L. J. Mahoney, and K. M. Molvar, and T. C. McGill ("Oscillations up to 712 GHz in InAs/AlSb resonant-tunneling diodes" ) 〕 There is another type of tunnel diode called a metal–insulator–metal (MIM) diode, but its present application appears to be limited to research environments due to inherent sensitivities.〔http://scitechstory.com/2010/11/19/the-mim-diode-another-challenger-for-the-electronics-crown/〕 There is also a metal–insulator–insulator–metal MIIM diode which has an additional insulator layer. The additional layer allows "''step tunneling''" for precise diode control.〔(【引用サイトリンク】publisher=OSU College of Engineering )〕 ==Forward bias operation== Under normal forward bias operation, as voltage begins to increase, electrons at first tunnel through the very narrow p–n junction barrier and fill electron states in the conduction band on the n-side which become aligned with empty valence band hole states on the p-side of the p-n junction. As voltage increases further, these states become increasingly misaligned and the current drops. This is called ''negative resistance'' because current decreases with increasing voltage. As voltage increases yet further, the diode begins to operate as a normal diode, where electrons travel by conduction across the p–n junction, and no longer by tunneling through the p–n junction barrier. The most important operating region for a tunnel diode is the negative resistance region. Its graph is different from normal p-n junction diode. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「tunnel diode」の詳細全文を読む スポンサード リンク
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