Algorithm for Efficient Estimation of the Critical Current of the SIS-type Josephson Junctions

Digital algorithms for checking the functionality and measuring critical current of SIS-type Josephson junctions are proposed, taking into account the features of measurements under conditions of fluctuation noise and suitable for implementation in an automatic mode. A piecewise line approximation of the voltage-current characteristic is used following the typical voltage-current characteristic. To obtain the essential statistical information about the random component of the measurement results, the excitation of the Josephson junction by a periodic testing sequence of triangular current pulses was used. For a workable Josephson junction, there is a voltage jump in the vicinity of the critical current for each rising slope of the exciting pulses. The statistics of the threshold crossings on each pulse rising slope of the test pulse sequence are used to estimate the critical current. An efficient estimate of the critical current was obtained by using the maximum likelihood method. The results of statistical modeling confirm the correctness of using this method in the study of superconducting structures. The use of statistical methods makes it possible to improve technical control during serial production of Josephson junctions and debug the appropriate manufacturing technology.