Measured Propagation Characteristics of Finite Ground Coplanar Waveguide on Silicon with a Thick Polyimide Interface Layer

Abstract

Measured propagation characteristicsof Finite Ground Coplanar (FGC) waveguide on silicon substrates with resistivities spanning 3 orders of magnitude (0.1 to 15.5 Ohm cm) and a 20 I.tm thick polyimide interface layer is presented as a function of the FGC geometry. Results show that there is an optimum FGC geometry for minimum loss, and silicon with a resistivity of 0.1 Ohm cm has greater loss than substrates with higher and lower resistivity. Lastly, substrates with a resistivity of 10 Ohm cm or greater have acceptable loss.

Propagation Characteristics of Finite Ground Coplanar Waveguide on Si Substrates With Porous Si and Polyimide Interface Layers

“…To better illustrate the relationship between attenuation and the FGC line dimensions (S+2W), the data from Figure 4 is replotted in Figure 5. In Figure 5, it is seen that there is a minimum attenuation for S+2W=90, or (S+2W)/Hp=4 for aspect ratio normalized to polyimide thickness, which agrees with the design rule presented in [3] that was derived for FGC lines on Si wafers with a polyimide interface layer. Also plotted in Figure 5 is the attenuation of FGC lines on three Si wafers with different resistivities and a 20 µm polyimide interface layer [3].…”

“…In Figure 5, it is seen that there is a minimum attenuation for S+2W=90, or (S+2W)/Hp=4 for aspect ratio normalized to polyimide thickness, which agrees with the design rule presented in [3] that was derived for FGC lines on Si wafers with a polyimide interface layer. Also plotted in Figure 5 is the attenuation of FGC lines on three Si wafers with different resistivities and a 20 µm polyimide interface layer [3]. The lines from [3] have approximately a 50 Ω characteristic impedance and were fabricated and characterized the same as the lines in this paper.…”

“…A second solution that has been proposed is to use polyimide interface layers between the Si and the transmission lines and passive circuit components [2,3] to insulate the electromagnetic fields from the lossy substrate. Finally, a third alternative to decrease circuit losses is to selectively create regions of the substrate that are highly porous.…”

Crosstalk Between Finite Ground Coplanar Waveguides Over Polyimide Layers for 3-D MMICs on Si Substrates

“…To use FGC lines on silicon wafers with resistivities used for CMOS circuits, a thin dielectric layer between the FGC line and silicon is required to minimize electromagnetic-field interaction with the Si substrate. This has enabled measured attenuation levels of around 3 dB/cm at 25 GHz to be reported [16]. Care should be exercised, however, when designing FGC lines on CMOS-type silicon substrates with dielectric overlays, as considerable loss can be attained [14], [16].…”

“…This has enabled measured attenuation levels of around 3 dB/cm at 25 GHz to be reported [16]. Care should be exercised, however, when designing FGC lines on CMOS-type silicon substrates with dielectric overlays, as considerable loss can be attained [14], [16]. Coupling is very small between FGC lines on high-resistivity silicon (HRS) substrate (no dielectric overlay) [17].…”