Low-Loss Dielectric Ink for Printed Radio Frequency and Microwave Devices

Direct write printing is restricted by the lack of dielectricmaterialsthat can be printed with high resolution and offer dissipation factorsat radio frequency (RF) within the range of commercial RF laminates.Herein, we outline the development of dielectric materials with dielectricloss below 0.006 in X and Ku frequency bands (8.2-18 GHz),the range required for radio frequency and microwave applications.The described materials were designed for printability and processability,specifically a prolonged viscosity below 1000 cps and a robust cureprocedure, which requires minimal heat treatment. In the first stageof this work, nonpolar ring-opening metathesis polymerization (ROMP)is demonstrated at room temperature in an open-air environment witha low-viscosity monomer, 5-vinyl-2-norbornene, using the second-generationGrubbs catalyst (G-II). Differential scanning calorimetry (DSC) wasused to study how the catalyst activity is increased with heatingat various stages in the reaction, which is then used as a strategyto cure the material after printing. The resulting cured poly(5-vinyl-2-norbornene)material is then characterized for dielectric and mechanical performancebefore and after a secondary heat treatment, which mimics processingprocedures to incorporate subsequent printed conductor layers formultilayer applications. After the secondary heat treatment, the materialexhibits a 55.0% reduction in the coefficient of thermal expansion(CTE), an increase in glass-transition temperature (T (g)) from 32.4 to 46.1 & DEG;C, and an increased 25 & DEG;Cstorage modulus from 428 to 1031 MPa while demonstrating a minimalchange in dielectric loss. Lastly, samples of the developed dielectricmaterial are printed with silver overtop to demonstrate how the materialcan be effectively incorporated into fully printed, multilayer RFapplications.