A Very Low Loss 220–325 GHz Silicon Micromachined Waveguide Technology

This paper reports for the first time on a very low loss silicon micromachined waveguide technology, implemented for the frequency band of 220 – 325 GHz. The waveguide is realized by utilizing a double H-plane split in a three-wafer stack. This ensures very low surface roughness, in particular on the top and bottom surfaces of the waveguide, without the use of any surface roughness reduction processing steps. This is superior to previous micromachined waveguide concepts, including E-plane and single H-plane split waveguides. The measured average surface roughness is 2.14 nm for the top/bottom of the waveguide, and 163.13 nm for the waveguide sidewalls. The measured insertion loss per unit length is 0.02 – 0.07 dB/mm for 220 – 325 GHz, with a gold layer thickness of 1 μm on the top/bottom and 0.3 μm on the sidewalls. This represents, in this frequency band, the lowest loss for any silicon micromachined waveguide published to date and is of the same order as the best metal waveguides.