CAD Analysis of Microstrip Lines Using Micromachining Techniques
High Frequency Electronics
Kamaljeet Singh and Surendra Pal, Deepak Bhatnagar,
The possibility of low cost RF and microwave circuits integrated with digital and analog circuits on the same chip is creating a strong interest in silicon as a microwave circuits. Semiconductor silicon substrates with 1 to 20 Ω-cm resistivity are typically used to manu-facture mixed signal RFICs, and this type of conductive substrate is the well-known cause of signal losses in passive circuits. Commercial foundries employ low resistivity wafers, having higher losses or low Q factor due to leakage in the substrate. To overcome this problem, different topologies have been demonstrated. The commonly employed method is the use of a high resistivity sub-strate (>2kΩ-cm), and circuit realization on this substrate shows performance on par with other dielectric substrates like GaAs . Another method employs the use of polyimide on top of the CMOS substrate to create an interface layer . The third approach employs ground plane patterned between sili-con substrate and the interface layer so that the electric field leakage can be reduced to zero . However all these approaches are either costly or are complex to analyze. The simpler approach is the use of thicker inter-face layer.
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