The critical current of a Josephson junction is an oscillatory function of the enclosed magnetic flux Φ, because of quantum interference modulated with periodicity h/2e. We calculate these Fraunhofer oscillations in a two-dimensional (2D) ballistic superconductor-normal-metal-superconductor (SNS) junction. For a Fermi circle the amplitude of the oscillations decays as 1/Φ or faster. If the Fermi circle is strongly warped, as it is on a square lattice near the band center, we find that the amplitude decays slower, 1/Φ, when the magnetic length lm=/eB drops below the separation L of the NS interfaces. The crossover to the slow decay of the critical current is accompanied by the appearance of a 2D array of current vortices and antivortices in the normal region, which form a bipartite rectangular lattice with lattice constant ≃lm2/L. The 2D lattice vanishes for a circular Fermi surface, when only the usual single row of Josephson vortices remains.

The breakdown voltage is an important parameter in designing X-ray detectors such as silicon drift detectors (SDDs). In SDDs the complete thickness of the wafer has to be depleted to enable the detection of different energies of X-rays. A high voltage is required to have a fully depleted region while keeping the leakage current low. Multi-guard ring structures are designed to meet both a low leakage current and a high breakdown voltage using deposited PureB layers. To obtain a low leakage current, PureB layers were used. In multi-guard ring structures, parameters such as gap width, number of the rings and overlap of the metal field plate with the oxide have been designed to obtain higher breakdown voltage. Parameters such as gap size, oxide charge, bulk doping concentration and field plate design have an influence on the potential distribution of the guard rings. The designed structure works up to the limit of the measurement systems (1100 V) with very low leakage current in the range of 1.5-3 nA/cm² for the detector.