Extraordinary permittivity characterization of 4H SiC at millimeter-wave frequencies

What is it about?

Anisotropic hexagonal materials have two permittivity ε: ordinary permittivity ε_o and extraordinary permittivity ε_e. This work demonstrates techniques for characterizing out-of-plane ε_e of 4H SiC using substrate-integrated waveguides (SIWs) or SIW resonators. Such permittivity characterization techniques can be extended to other frequencies, materials, and orientations.

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Photo by Olav Ahrens Røtne on Unsplash

Photo by Olav Ahrens Røtne on Unsplash

Why is it important?

For millimeter-wave power applications, GaN high-electron mobility transistors (HEMTs) are often grown epitaxially on a high-purity semi-insulating c-axis 4H-SiC substrate. For these anisotropic hexagonal materials, the design and modeling of microstrip and coplanar interconnects require detailed knowledge of both the ordinary permittivity ε_o and the extraordinary permittivity ε_e perpendicular and parallel, respectively, to the c-axis. However, conventional dielectric characterization techniques make it difficult to measure ε_e alone or to separate ε_e from ε_o. As the result, there is little data for ε_e , especially at millimeter-wave frequencies. This work shows simple, accurate, and consistent on-wafer characterization techniques of the extraordinary permittivity. Such permittivity characterization techniques can be extended to other frequencies, materials, and orientations.