On the Accurate Measurement and Calibration of S-Parameters for Millimeter Wavelengths and Beyond

It is well known that, in the millimeter (mm-wave) and sub-mm-wave range, on-wafer S-parameter measurements are often inaccurate and suffer from serious systematic artifacts. In this paper, we confirm that these artifacts are related to spurious wave modes that are excited and propagate in the substrate. These parasitic wave components may be scattered at neighboring structures on the wafer and cause detrimental crosstalk. While these parasitic components deteriorate the measurement itself, an even more serious complication arises from the fact that these modes are already present in the calibration measurement and are unintentionally imported and superposed to the measurement data. In this paper, we present a new type of RF pad with novel screening features and show that these parasitic modes can be efficiently suppressed by the use of proper on-wafer couple structures. Moreover, a novel calibration substrate and method is presented and demonstrated to be capable to remove spurious artifacts from S-parameter measurements up to 450 GHz.