High field measurements with a guarded needle

The electrical degradation of solid dielectrics often originates in the vicinity of defects (impurities, protrusions, or inclusions). The degradation involves a high field region of localized high carrier mobility that leads to the formation of a space charge limited field region in which charge cycles during application of an AC field. This cyclic carrier motion results in hot electrons and ultra-violet (UV) photons produced by carrier recombination, both of which can degrade the dielectric. Carrier mobility-related prebreakdown phenomena can only be studied within microscopic dimensions, as the power dissipation would cause thermal runaway for a macroscopic geometry. The guarded needle apparatus is designed for such measurement, using a sharp metal needle to create local high electrical field, which induces carrier mobility.