A protective fabrication method for K₂Cr₃As₃-based quantum device and its interfering Josephson diode effect

The extreme environmental sensitivity of the quasi-one-dimensional unconventional superconductor K₂Cr₃As₃ has long hindered the fabrication of quantum devices and the exploration of its superconducting properties. Here, we develop a protective fabrication procedure compatible with conventional electron-beam lithography (EBL) and use it to construct K₂Cr₃As₃-Al superconducting quantum interference devices (SQUIDs). Critical-current oscillations and a Josephson diode effect (JDE) are observed in these devices. Under microwave irradiation, half-integer Shapiro steps emerge near the SQUID interference minimum, providing evidence for the existence of the secondharmonic component in current phase relation (CPR). Besides, JDE can be further enhanced to nearly 100% by microwave irradiation. Considering the potentially significant kinetic inductance associated with K₂Cr₃As₃, we incorporate finite-inductance effects as an extension of the interfering JDE model with zero inductance, which is further supported by quantitative fitting and overdamped RSJ simulations. These results demonstrate high-quality Josephson coupling at the K₂Cr₃As₃-Al interface and establish a microfabrication route for fragile, air-sensitive superconductors, providing a platform for further device-based studies of K₂Cr₃As₃ and for cryo-electronics applications.