Conductivity measurement of metal films based on eddy current testing

Currently, most commercial measuring instruments for electrical conductivity are primarily used to measure the conductivity of thick specimens. However, measuring the conductivity of thin films with these instruments can be challenging due to the limitation of skin depth. To address this issue, a conductivity measurement method for metal films has been proposed based on the transformer model of an eddy current sensor. It can be found that the phase of impedance change is related to the thickness and conductivity of the specimen when the thickness of the specimen is less than the skin depth. To validate the method, a finite element model is employed to simulate it, and the relative errors of conductivity measurements are analysed. The experimental results are then compensated using the estimated errors, and the influence of excitation frequency is evaluated. Finally, specimens with different conductivities and thicknesses are prepared to verify the method. The results indicate that the relative errors fall within 7.36% before compensation and within 5.25% after compensation, which demonstrates the feasibility of the proposed method for conductivity measurement of metal films.