Design and simulation of a coplanar capacitive sensor for non-destructive thin-film dielectric measurement

Abstract

This article presents a different design of coplanar capacitive sensors for application in non-destructive thin film dielectric measurement with high performance and minimal cost. Another difference in this sensor design is that to reduce parasitic components and common noise, the capacitive sensor structure is designed to include a reference capacitor and a sensing capacitor. Using this structure, the dielectric of the thin film can be estimated through the unbalanced capacitance generated between the two signals from the reference capacitor and the sensing capacitor. Two electrode structures were researched, simulated, and the interdigital structure with the highest performance was selected. Simulations were conducted using a Polyethylene (PE) thin film with dielectric varying from 1.375 to 3.19 and a thickness of 40 µm to study the working principle of the sensor. Simulation results show the linearity of the sensor's output capacitance corresponding to different dielectrics. The sensitivity of the sensor is 20.86 fF/1 dielectric unit and 178.96 fF/1 dielectric unit for thin films with thicknesses of 10 µm and 120 µm, respectively. Simulation results demonstrate that this sensor has high potential for application in dielectric measurement of thin films for military and biomedical applications.