New Wafer-Level High-Frequency Characterization of Coupled Transmission Lines

In this article, a new experimental characterization technique for coupled transmission lines is presented. Three specific experimental test patterns (E-, F-, and G-type structures) that can individually characterize the electromagnetic coupling of two coupled lines are developed and fabricated on the same wafer using a 0.18-μm CMOS process. Since the devised test patterns are two-port networks, well-established two-port network characterization techniques can be exploited. Transmission line model parameters (i.e., propagation constants and characteristic impedances) associated with the three two-port test patterns can be directly determined from the measured S-parameters, followed by circuit model parameters (R, L, C, and G) for two coupled lines. Without rigorous equipment calibration and deembedding parasitic effects, experimental characterizations for two coupled lines using four-port network S-parameter measurements may yield physically ambiguous data above 10 GHz due to the parasitic resonances, whereas the proposed technique can determine stable and accurate network parameters over a broad frequency band. To further support the validity of the proposed technique, they are compared with data using 3-D numerical calculations and low-frequency capacitance measurements.