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 second-harmonic 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.