On-wafer 4-port measurements from 70 kHz to 220 GHz in a single sweep

After maturing the on-wafer single-sweep 70-kHz-to-220-GHz 2-port measurement for two years, we recently started doing similar measurements with 4 ports. The initial results and challenges will be presented, particularly regarding 4-port calibration. The initial lesson confirmed that, at such high frequencies, a fully automated probe station is a necessity instead of a luxury. Meanwhile, the ultra-broadband measurement from 70 kHz to 220 GHz helps uncover and fix any setup errors such as loose connections or defective components.