Noncontact Electrical Characterization of Printed Resistors Using Microwave Microscopy

This paper presents the noncontact measurement of electrical resistance of a printed resistor using a scanning near-field microwave microscope. The microscope includes a probe that consists of a dielectric resonator coupled to a 200-μm radius, gold-coated tungsten tip that acts as a detecting element. The resonance frequency and quality factor of the probe are sensitive to the proximity of the printed resistor to the tungsten tip. The electrical resistance is obtained through the use of a second-order polynomial equation that relates the quality factor of the microwave probe with its proximity to the resistor. Four-point probe resistance measurement and electromagnetic simulation of the printed resistor confirm the results obtained with the microwave microscope.