The Effect of Surface Passivation for Sub-THz Silicon Gradient Refractive Index Lens

Funding Information: ACKNOWLEDGMENT This work was financially supported by the Academy of Finland under grant MilliRAD, number 314541. The authors would like to thank I. Huhtinen for the RF measurements. Publisher Copyright: © 2022 European Microwave Association. This paper describes a study of impact of different passivation methods on performance of gradient refractive index (GRIN) lenses. Three different passivation layers on top of lenses are studied: PolySi, PolySi and PECVD silicon oxide (PolySi+SiO2), and PECVD silicon oxide (SiO2). Antenna gains and radiation patterns of fabricated lenses are measured. The study shows that passivation methods have strong impact on silicon GRIN lenses performance. A model with a low-resistivity layer on top of high-resistivity Si can explain observed effects.