Circuit designers need materials with well-known properties to make predictive circuit models, which is particularly challenging in the millimeter-wave regime. Typical material characterization approaches include on-wafer devices. To get the material properties from these measurements, on-wafer calibrations require a known characteristic impedance. Often, this requirement uses low-loss substrates and a series or shunt load to calculate the capacitance per unit length of the transmission line. This paper investigates three devices with independent analysis procedures to estimate the capacitance per unit length. Although the devices have the same cross section, we observed a significant different in the extracted values and discuss possible mechanisms which may contribute to this difference.
