Fabrication of multilayered SU8 structure for terahertz waveguide with ultralow transmission loss

Abstract. A microfabricated hollow air-filled waveguide with two back-to-back bends operating in the WR-3 frequency range of 220 to 325 GHz has been successfully fabricated through a multilayered ultrathick SU8 process and has ultralow transmission loss of 0.028 to 0.03  dB/mm in a performance test. This is the first SU8 constructed hollow waveguide operating at WR-3 frequencies having transmission loss comparable with the state-of-the-art computer numerical control (CNC) machined metal circuits. The multilayered SU8 processing technique has a great advantage of reducing the transmission loss by decreasing the probability of air gaps between SU8 layers. The excellent device performance is also attributed to the precisely controlled layer thickness and ultimately low surface roughness of evaporated silver which only contributes a small part of the microwave signal attenuation.