Fused, fritted glass passivation, using selected diode structures and metallization patterns to help characterize the glass, has been studied. A significant amount of negative charge in the 16 μm thick glass was found which raised the avalanche breakdown voltage of the p + n − device from a calculated 700 to 977V when glass fusion was done in flowing nitrogen. Oxygen fusion placed more negative charge in the glass such that the breakdown voltage in the unmetallized device was raised another 150–1125V. Under fusion conditions that might relate to incomplete organic binder removal (static air organic removal, nitrogen glass fusion) the amount of negative charge in the glass was considerably reduced giving a breakdown voltage of 876V. Thinner glass (6 μm) gave less voltage improvement because of less net negative charge density. The presence of an overlapping field plate on the diode is equivalent to additional negative charge under reverse bias conditions and the fusion ambient becomes unimportant in developing maximum breakdown voltage. This means that a field plate can act effectively over 16 μm thick passivation. Thus, the use of a field plate with the proper choice of design parameters can improve the breakdown voltage in shallow junctions.
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Flowers et al. (1982) studied this question.