Robust Microwave Characterization of Inkjet-Printed Coplanar Waveguides on Flexible Substrates

In this paper, we propose a robust algorithm to automate a microwave characterization process, which simultaneously extracts the electrical parameters (conductivity and dielectric constant) of inkjet-printed components on flexible substrates. Initially, the algorithm extracts the propagation constant of printed coplanar waveguide (CPW) standards by the use of a multiline thru-reflect-line calibration. Then, the proposed algorithm utilizes finite-element modeling to dynamically create an interpolated search space by automatic simulation. The algorithm utilizes a least-square optimization routine to minimize the deviation between the model and the measurements. Our technique significantly reduces the computing resources and is able to extract the material parameters using even a nominal ink profile. Characteristic impedances for CPWs are extracted using series resistor measurements from 10 MHz to 20 GHz. It is shown that the proposed characterization methodology is able to detect small changes in material properties induced by changes in fabrication parameters, such as sintering temperature. Ink conductivities of approximately 2.973 × 10
⁷
S/m and a supporting spacer dielectric constant of 1.78 were obtained for the inkjet-printed CPWs on polyethylene terephthalate. In addition, the inkjet-printed CPWs sintered at 170 °C and 220 °C on Kapton had conductivities of 0.187 × 10
⁷
and 0.201 × 10
⁷
S/m, respectively. We demonstrate the advantages of our technique by measuring the material parameters with the conventional approach.