SESSION XV: HIGH-SPEED DIGITAL CIRCUIT TECHNOLOGY

signals crosses the threshold. It has been found that the total number of gates necessary to achieve some finite function can be reduced with the use of threshold logic”2 ,3. However, threshold logic cannot dominate semiconductor devices because its margin is rather narrow. The Josephson device has unique characteristics suitable for solving problems in threshold logic operation. Its transfer curve is ideally step-like; i.e., its input - output separation is near perfect and theputput level does not depend on the input level. The step edge of the threshold current is determined by the junction size. The variation in junction size determines the margin of the threshold gate. The variation has been reduced by employing a cross-type junction with a definite window and by using solid Si in place of porous Si0 as the window material. Thus, sufficient margin for the Josephson threshold gates is provided. TJsing the Josephson threshold logic (JTHL) thus obtained, a multiplier circuit has been made, a typical combinational circuit, as well as a binary counter, representing a typical sequential circuit. The junctions used were 1.5p square and highly reliable NbN was used for the base electrode material.