Non-contact surface resistivity measurement for materials greater than 109 Ω

Abstract

A non-contact surface resistivity probe for materials with resistivity greater than 109 Ω has been developed using surface potential measurement combined with corona charging. The probe is composed of a grid type corona charger and a surface voltmeter located next to the charger. A test material was placed below the probe without contact to the material at a gap of 2 mm. The time variation of the surface potential and the saturation surface potential beneath the charged area are theoretically a function of the surface resistivity; therefore, measurement of the rise time and the saturation potential can be used to predict the surface resistivity in the ranges of lower and higher surface resistivity, respectively. The calibration equation for the probe was determined by solving the circuit equation for a one-dimensional simple circuit model and by extension of the simple model to the actual probe arrangement using experimentally derived constants. The lower surface resistivity, ρsal (from 109 to 8×1013 Ω), can be predicted from ρs = 1.0×1011×Tm1.64 using a 63% rise time, Tm. The higher surface resistivity, ρsah (from 8×1013 to 1016 Ω), can be predicted using the equation ρs = 3.0×1014×Vm1.70 with the converted surface potential, Vm.