Wide If 230-GHz Superconductor-Insulator-Superconductor Mixer

A 230 GHz Superconductor-Insulator-Superconductor (SIS) mixer is designed focusing on a good performance in the IF frequency range of 4–16 GHz over the RF band from 211 to 275 GHz. A transition from a full-height waveguide to a probe is designed using HFSS. The mixer chips containing SIS junctions are designed and optimized to have low total capacitance of circuits to ensure wide IF bandwidth. The chip fabrication was done in Academia Sinica Institute of Astronomy and Astrophysics (ASIAA), where the masks were conducted by TSMC. A lab test was conducted on a superconducting mixer with a cryogenic dewar. The gap voltage in the I-V curve of the mixer is approximately 8 mV, and there is a clear nonlinearity around a current of 110 μA, which matches well with the simulation. The receiver noise temperature is approximately 60 K including optical losses and the noise from the RF input.