For a coplanar waveguide (CPW) line where the metal conductor is in direct
contact with the HR-Si substrate, the microwave losses are low but are sens
itive to de bias due to de leakage current. With a continuous SiO2 layer in
serted between the CPW metallization and HR-Si substrate, de leakage is eli
minated, but microwave losses increase, An MOS C-V analysis shows that an i
nduced charge layer exists on the substrate surface and is the principle ca
use for increased line losses. If the insulated SiO2 layer beneath the cond
uctor strips of line is made to be noncontinuous, then microwave losses are
decreased from 18 to 3 dB/cm at 30 GHz.