Guarded needle for "charge injection" measurement

The ability to measure resistive current resulting from high-field carrier mobility in dielectrics provides insight into transport phenomena and high-voltage performance. The threshold electric field for the formation of a space-charge limited field region under highly inhomogeneous field conditions has fundamental significance in that above this field, rapid degradation takes place from hot electrons and UV photons generated by carrier recombination. A guarded needle electrode with a tip radius in the range of 5 mum and an electrical guard which extends to within about 35 mum of the tip provides the basis for measuring high-field mobility as the resistive current can be measured independent of the displacement current. The residual displacement current resulting from the fF capacitance from the needle tip to the opposite plane electrode is compensated out of the measurement. In this article, we provide construction details for such a guarded needle. (C) 2002 American Institute of Physics.