Additive Manufacturing of RF Metal-Insulator-Metal (MIM) Capacitors on Flexible Substrate

This study aims to demonstrate the fabrication of radio-frequency (RF) metal-insulator-metal (MIM) polyimide capacitors on a flexible Kapton™ (polyimide film) substrate using a purely additive manufacturing technology. The aerosol jet printing technology can effectively replace the use of bulky lumped components in the RF circuits such as filters, matching networks, oscillators, resonators, and mixers. Two capacitor geometries with areas of 0.25, and 0.5625 mm² have been printed. Optical profilometry of the printed metal capacitor plates and the polyimide (insulation) film show that they have average thicknesses of 2.34±0.22 μm and 4.05±0.44 μm, respectively. The measured capacitance for the set of capacitors are 1.746±0.231 pF and 2.513±0.133 pF, which is equivalent to a capacitance tolerance of 10% and 5%, respectively. The S-parameters were measured using the vector network analyzer up to frequency of 50 GHz and a lumped circuit model is extracted and presented through the Smith Chart using Advanced Design System™. Moreover, the results of normalized measured capacitance and conductance as a function of temperature, adhesion, temperature (100°C/ice bath) cycling, and the maximum operating voltage of the capacitor are presented.