CAD Analysis of Microstrip Lines Using Micromachining Techniques

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  • Author: 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 [1]. Another method employs the use of polyimide on top of the CMOS substrate to create an interface layer [2]. 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 [3]. However all these approaches are either costly or are complex to analyze. The simpler approach is the use of thicker inter-face layer.