A Kelvin probe is a noninvasive vibrating capacitor used to measure the surface potential of a charged dielectric on a conducting (or partially conducting) substrate. Since the Kelvin probe is a noncontact device, the total charge on the dielectric can be measured without depleting/neutralizing any of the charge on the dielectric. A capacitor is formed between the tip of the vibrating probe and the conductive substrate. The dielectric layer and an air gap are located between the electrodes of the capacitor. The method consists of vibrating (dithering) the probe above the dielectric surface, while simultaneously measuring the current through the capacitor as a function of time as the dc-bias voltage is varied.
The mercury probe is used to measure the capacitance vs. voltage (C-V) as well as the current vs. voltage (I-V) characteristics across Hg/dielectric/semiconductor structures. The C-V characteristics allow us to determine the trapped charge within dielectrics and the I-V characteristics allow us to determine the leakage currents through dielectrics.