On-Wafer Sub-THz Calibration Using 50µm-Thick GaAs Impedance Standard Substrate

For accurate probing up to sub-THz frequencies, on-wafer calibration is critical. However, most Impedance Standard Substrates (ISSs) used in calibration are made of alumina, even though most MMICs are fabricated on GaAs. This makes it necessary to use 2-tier calibration to de-embed parasitics associated with probe launches, contact pads, etc. To simplify the calibration and to improve its accuracy, we designed and fabricated the world’s first multi-line ISS on 50µm-thick GaAs that includes microstrip and coplanar transmission lines as well as substrate-integrated waveguides. We validated the GaAs ISS by 2-tier calibration involving a commercially available alumina ISS. We shared the GaAs ISS with many on-wafer measurement leaders around the world and received positive feedback so far.