Measuring Technique and Error Analysis of Complex Permittivity of Polymer Films Based on Contact Method

Contact method is an important method to measure the complex permittivity of polymer films. There are some possible factors affecting its accurate measurement for thin films by direct contact method. To solve the problem, this article analyzes the reasons of errors induced by flatness tolerance and edge effect from the view of a three-electrode structure, and that induced by the state of film surface as well. An equivalent electric circuit model is proposed based on direct contact method and the state of film surfaces. The correction formulas used to measure complex permittivity of films with coarse surface are derived according to the model, and then verified by experimenting different materials. Experimental results show that errors of relative permittivity are under 5% after calculation by the correction formula. In conclusion, the proposed measurement technique is theoretically and practically applicable for the complex permittivity measurement of low-thickness polymer films about 10– $100~\mu \text{m}$ .