A unified model for on-chip CPWs with various types of ground shields

Abstract

Coplanar waveguides (CPW) are promising candidates for high quality passive devices in millimeter-wave frequency bands. In this paper, CPW transmission lines with and without ground shields have been designed and fabricated on 65nm CMOS technology. A physical-based model is proposed to describe the frequency-dependent per-unit-length L, C, R, and G parameters. Started from a standard CPW structure, influences of different kinds of ground shields have been analyzed and included into the general model. The accuracy of the model is confirmed by experimental results.

Identifying and Modeling Resonance-Related Fluctuations on the Experimental Characteristic Impedance for PCB and On-Chip Transmission Lines

“…TLs were fabricated on a CMOS process; their cross section is shown in Figure 3a. These lines present lengths of l = 1380 µm, 2450 µm and 4600 µm and include a metal patterned ground shield separating a distance h = 0.8 µm from the signal trace [14,15]. Moreover, the lines are terminated with ground-signal-ground (GSG) pad arrays, which allow for the measurement of S-parameters using coplanar RF probes with a 150 µm pitch.…”

A unified model and direct extraction methodologies of various CPWs for CMOS mm-wave applications

“…For CPWs, C sg1 characterizes the capacitance between the signal wire and upper ground (Fig.2a) which can be calculated by Y1 formula given in [7]. As part of the EM field is shielded by the below shielding metal while the other part may penetrate to the substrate, a weight factor η is used here to describe the effect of incomplete shielding, namely, (1-η)Y parallel being the admittance of the C-R-C network and ηY parallel being the admittance of the C-L-R path.…”

“…For SCPW, η is a nonlinear function of the metal filling ratio and can be expressed as (f w /(f w +f s )) α , where f w and f s are the width and spacing of shielding metal, α is the fitting parameter [7]. Therefore both the C-R-C network and the C-L-R path are included in the parallel branch extraction of SCPW.…”

“…However, both the measurement and 3-D EM simulation show the per unit capacitance increases with frequency for transmission lines with ground structure which is quite different from the standard CPW [3][4]. A unified model for CPWs has been co-developed by our group [7] and an LC series sub-circuit is proposed to model the phenomenon. The model parameters are extracted by optimization and some empirical formulas are adopted without considering the specific foundry processes.…”