Evaluating leakage mechanisms in SiN<i>x</i> dielectric films for process control and development

A thorough understanding of the electron leakage mechanism between niobium superconducting electrode and dielectric film is required for their successful implementation in superconducting electronics. Currently, the leakage of current through dielectric is largely uncharacterized at low temperatures relevant to superconductivity. In this work, a detailed characterization method of processed SiNx dielectric films is presented, based on dc current–voltage hysteresis loops performed in multilayer structures of niobium wires deposited on SiNx. The leakage mechanism and properties of the Nb–SiNx–Nb structures are discussed based on known theoretical models of Mead and the extended Poole–Frenkel model, including the effects of compensation. Furthermore, within-layer and between-layer measurements are also reported, providing information about the bulk and surface contributions to homogeneity and quality of dielectric films. According to this analysis of bulk-limited conduction mechanism, several important physical parameters in the dielectric films can be obtained and exploited for further process improvement and enhancement of device performance.