Microstrip Design in a Silicon Technology using Closed Form Analytical Expressions

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  • Author: Ain Rehman
This article deals with the design of microstrip lines on a silicon substrate. Silicon is not a preferred microstrip substrate because in the usual case of integrated circuits, it has a low resistivity caus-ing losses at high frequencies. Figure 1 shows a microstrip line that lies on top of a SiO2 layer that in turn lies on a silicon substrate. Since the resistivity of the silicon substrate is usually quite low in standard silicon pro-cesses, the electric field gets virtually shorted near the top of the substrate. However, for usual operating frequencies the magnetic field penetrates the substrate completely [1]. This imbalance causes multiple deleterious effects to take place in this configuration, including increased losses, wave velocity a function of substrate, slow velocity of signal propagation, and others.