Inkjet printing RF bandpass filters on liquid crystal polymer substrates

This study investigates inkjet-printed radio frequency bandpass filters on liquid crystal polymer (LCP) substrates. Silver nanoparticle colloidal solution was used as a printing ink. A plasma polymerization technique was used to improve the LCP surface by optimizing the printing contact angle. Silver lines were then inkjet printed on the LCP substrate and cured in an oven to remove excess solvent and material impurities. The lines were printed with varied numbers of passes to study the changes in surface roughness and line width. The silver-film conductivity of the conductive ink was approximately 4 × 10⁶ Siemens/m. The third-order dual-behavior resonators bandpass filter was simulated using software and printed with an inkjet printing system. The minimal insertion loss and maximal return loss were -2.18 and -27.8 dB at 5.4 GHz, respectively. This study describes the optimization of the inkjet printing process and discusses the surface treatment study of the inkjet-printed seed layer and process integration is presented in detail.