A large number of dielectric layer stacks of different combinations of SiC, SiN and SiO2 are studied with respect to their ability to suppress surface-channel currents that give radio-frequency (RF) and microwave losses in coplanar waveguides (CPWs), integrated on high-resistivity silicon (HRS) substrates. Measurements are performed of the Space Charge Layer sheet resistances (SCL-RSH) and the RF losses in CPWs. The lowest, bias-independent losses of 1.6 dB/cm are achieved on thin Low-Pressure Chemical Vapor Deposition (LPCVD)-nitrated Plasma-Enhanced Chemical Vapor Deposition (PECVD) amorphous (α-) SiC layers, for which the surface currents are conducted away from the crystalline HRS into the α-SiC:N. The nitridation appears to have changed the surface of the SiC from an insulating to a highly resistive layer, where the presence of SiC:N compounds suggests a possible n-doping by nitrogen. The α-SiC/SiC:N layer is known to remain stable during high-temperature thermal treatments typically used for dopant activation as indicated previously.
- Coplanar waveguides
- High-resistivity silicon
- Radio-frequency surface losses