ABSTRACT
Since the first electronic computer, ENIAC, was demonstrated in 1946, we human beings have been pursuing faster computers. Basic computer elements executing digital operation have been progressing continuously from the age of vacuum tubes. The basic elements have been changed to transistors, integrated circuits, and then large scale integrated circuits in this half century. During these periods, the operating speed of today’s computers has increased more than one billion times that of ENIAC. Some applications, such as weather forecasting, protein design, and astronomical simulation will never be satisfied by the speed of today’s computers. In the field of telecommunication, we also require very large scale routers with operation speed faster than 10 terra bits per second to deal with the huge amount of information on the Internet. Moreover, modern wireless communications requires wider and wider bandwidths in order to handle higher data rates and increase data capacity. This demands higher sample rate mixed signal circuits and higher clock rate digital signal processing circuits. In order to satisfy the need for higher speeds, researchers have been developing tiny transistors with shorter gate lengths; now they are developing transistors with twenty nanometer gate lengths. Many engineers fear, however, that the switching speed of transistors will saturate in
the near future. Thus, completely new switching elements, such as superconducting devices, single electron transistors, molecular devices, spin transistors, quantum devices and so forth, are now being investigated. Among them, superconducting devices have made remarkable progress.
