Fabrication of three-layer silicon antireflection structures in 200-450  GHz using deep reactive ion etching

We developed broadband antireflection structures for millimeter-wave and submillimeter-wave applications, particularly cryogenic applications. The structures were fabricated on silicon using deep reactive ion etching. Three-layer subwavelength structures were fabricated on both sides of a silicon plate with an area of 20mm². The transmittances of the structures were measured at 28 K. The average transmittance was 97.6% in the frequency range of 200-450 GHz.