Permittivity and Loss Characterization of SUEX Epoxy Films for mmW and THz Applications

We present a systematic characterization of the dielectric permittivity and loss tangent of SUEX dry films for mmW and THz bands. Green and cured SUEX samples of varying thicknesses were studied using two complementary measurement techniques. First, the Nicolson-Ross-Weir technique was used in a two-port T E
₁₀
waveguide environment for 90-140-GHz and 140-220-GHz bands. The samples were also characterized using a transmission-mode time domain THz spectrometer over the 90-GHz-2-THz band. Real part of permittivity and loss tangent were measured to be 3.08 and 0.057, respectively, for the green SUEX sample. Ultraviolet light curing reduces the permittivity and loss tangent down to 2.86 and 0.020, respectively. SUEX films can be easily laminated onto any substrate, eliminating the spin coating and long process optimizations that are required for conventional liquid resists. As such, SUEX is an easy-to-process alternative to commonly used epoxy-based resists, such as SU-8, while exhibiting similar dielectric permittivity and material losses.