110 GHz Characterization of Coplanar Waveguides on GaN-on-Si Substrates

We characterize the microwave loss in coplanar waveguides (CPWs) on AlGaN/GaN high-electron mobility transistor (HEMT) buffer layers on high-resistivity silicon (HR-Si) substrates, up to 110 GHz. To our knowledge, this is the first broadband characterization of CPWs on GaN-on-Si. Conventional CPWs on commercially available AlGaN/GaN on HR-Si HEMT layers show a loss as low as 0.8 dB/mm at 110 GHz. Losses are further reduced by etching trenches between the CPW conductors, reaching 0.47 dB/mm at 110 GHz. The work shows that CPWs on GaN-on-Si exhibit performances comparable to those built on semi-insulating InP, demonstrating the suitability of GaN-on-Si technology in millimeter-wave applications.