Coaxial Cable-Based Magnetic and Electric Near-Field Probes to Measure On-Chip Components up to 330 GHz

This letter presents miniaturized near-field probes to characterize the electric and magnetic fields in the WR03 waveguide band (220-330 GHz) on-chip. The near-field probes are based on a commercially available coaxial cable, which enables the construction of both open- and short-circuited probes to measure electric and magnetic field components, respectively. Furthermore, it is flexible enough not to damage the wafer under test or the Ground-Signal-Ground (GSG) on-wafer probe contacting the chip. It is shown that the measured near fields enable physical insight into the operation of the chip, which also eases fault detection and the search for error sources. Finally, the electric and magnetic near fields measured above the chip can be used to calculate the far field of the chip antenna. Here, the usually disturbing influence of the on-wafer probe on the measurement can be significantly reduced if only the near field dominated by the antenna, i.e., in close proximity to the chip, is measured. With this technique, both probe radiation and shadowing can be mitigated. Compared with complex and accurate robot solutions necessary to measure the far field in spherical coordinates, the near-field measurement only requires a cartesian sampling along the chip surface.