Josephson parametric amplifiers utilizing aluminum shadow evaporation without a suspended bridge

Low-noise amplication of microwave signals is a key requirement in numerous nanoelectronics experiments, including qubit readout, optomechanics and shot noise spectrometry. Lower system noise temperatures can be reached with superconductive parametric ampliers which, however, have suered from limited bandwidth and/or modest gain. Recently, a solution has been introduced, involving operating a Josephson LC resonator in an impedance-engineered environment. We present our realization of these ampliers, utilizing a bridgeless shadow evaporation technique to achieve junctions with high critical currents, which is required by impedance engineering. The fabrication involves double-layer resist (PMMA/MAA) together with high/low dose e-beam lithography using high voltage (100 kV) to achieve low parasitic undercuts. We have found the process to be both reliable and high-yield, and parametric amplication using these junctions has also been successfully demonstrated.