Surface trapping parameters of solid dielectrics: Novel measurement method and insulation condition characterization

Charge traps greatly affect the charge transport, trapping and recombination in solid dielectrics such as ceramics and polymers. This paper presents a novel method of measuring the surface trapping parameters such as trapping density and energy level of insulating materials. Based on the isothermal relaxation current (IRC) theory, the trap measurement and calculation formula is deduced and a non-contact measurement setup is specially designed, and electron or hole trap parameters can be determined by choosing negative or positive charging, respectively. Two kinds of materials are selected as the samples, i.e., high temperature vulcanized (HTV) silicone rubber and machinable ceramics (MCs). Experimental results indicate that, with extending duration of aging time, electron and hole trap density both increase, and gradually saturate. SEM and XPS analyses reflect that specimens after aging process appear many physical defects as holes and flaws and chemical defects as strong polar groups, which causes significant influence on surface trap characteristics. It is shown that the glass phase on the surface of MCs greatly influences the existing shallow traps, which in turn degrade the fla-shover characteristics. Removing the glass phase with HF treatment reduces the concentration of shallow traps and stabilizes the flashover voltage. It is considered that charge trap is expected to be as a novel indicator for effective evaluation of aging status and electric withstanding strength of insulating materials.