The loss mechanisms of silicon coplanar waveguides (CPW) with aluminum metallization are investigated up to 40 GHz. Three main parts contribute to the attenuation of coplanar waveguides (CPWs): the frequency-dependent conductor losses of the metallization, frequency-independent substrate losses, and the specifically investigated bias-dependent interface losses caused by free charges at the Si-SiO2 interface. The minimum losses found in 50-Ω CPWs with 45-μm signal line width were 0.19 db/mm at 10 GHz and 0.33 dB/mm at 40 GHz. High-purity silicon from a float zone (FZ) process was used as substrate. Substrates with lower purity from a Czochralski (CZ) process (resistivity 50-100 Ωcm) resulted in somewhat higher (0.2-0.3 dB/mm) losses for the same CPW geometry.
Published in:
Electron Devices, IEEE Transactions on
(Volume:50
,
Issue:
3
)
Date of Publication: March 2003