The ink-jet printed flexible interdigital capacitors: manufacturing and ageing tests

Correct operation of electronic circuits (including those made with the ink-jet printing technique) requires the electrical parameters of the structures to be constant or to be changeable, but in a predictable way. Due to that, the flexible, ink-jet printed interdigital capacitors (IDSs) were made and then tested in various conditions. We used the conductive silver-based Amepox AX JP-60n ink. As a substrate, we chose the transparent, flexible Melinex OD foil with a thickness of 125 µm. The IDCs were designed and their capacitances were simulated using Comsol Multiphysics Software. Then the test structures were fabricated by the ink-jet printing process using Dimatix DMP 2831 printer. The printed structures were subjected to environmental exposures in a climate chamber to check the influence of temperature and humidity on the tested samples. The IDCs were also subjected to cyclic bending and straightening tests to analyze the outflow of tensile forces on the printed structures, which are exposed to the common factors, that could diminish the quality of the printed and flexible devices. Due to the small capacitance values of the designed and made IDSs, the measurements showed the key importance of the measuring table on which flexible substrates with IDC capacitors were placed for their capacitance value. Performed tests also demonstrated that in most cases, the capacitors are characterized by an increase in capacitance by a few to a dozen or so % after the ageing tests. Obtained results could be a good groundwork for further research, that will include ways of preventing the creation of discontinuities—or minimizing their impact on the printed device performance.