Small- and Large-Signal Characterization of RF Substrates down to Cryogenic Temperatures

This work presents for the first time, the RF large-signal characterization of standard, high-resistivity and trap-rich substrates, along with small-signal characterization, down to the temperature of 4.2K. These measurements mark the first instance of such characterization being performed at this temperature, using CPW transmission lines as monitor device of the substrate response. The behavior of effective resistivity, total loss and harmonic levels with temperature, evidence the RF performance enhancement of standard and trap-rich substrates below 50 K, thanks to the substrate dopants freeze-out effect. Meanwhile, high-resistivity substrate performance remains stable across temperature due to the Parasitic Surface Conduction effect.