Failure Mechanisms in Reverse-Biased Oxide-Passivated Silicon Diodes

THE degradation rate of large area silicon planar diodes under reverse bias in high temperature or gamma radiation ambients has been improved by several process and structural changes. Data is presented that supports the hypothesis that the degradation mechanism is ion migration. Structural changes designed to reduce the electric field strength at the surface yield lower degradation rates. However, one cannot merely reduce the electric field by reducing the impurity density at the surface over the base region because such a high resistivity layer is more sensitive to variation in surface potential. Process changes which minimize the number of local imperfections improve the degradation rate because these imperfections can create local regions of high electric field.