Novel fabrication process for all-MgB$_{2}$ Josephson junctions and circuits*

A novel process for fabricating high-quality MgB$_{2}$/MgO/MgB$_{2}$ Josephson junctions and circuits is reported. A 100 nm-thick bottom electrode of MgB$_{2}$ was grown on SiC (0001) substrate by hybrid physical-chemical vapor deposition (HPCVD) and then coated by a 1 $\sim$ 5 nm-thick MgO junction barrier layer and a 20 nm-thick TiO$_{2}$ protection layer. After the bottom MgB$_{2}$ layer was patterned an 80 nm-thick MgO etch-stop layer was then deposited on the sample with a pattern created by photo- or e-beam lithography and lift-off, followed by reactive ion etching in SF$_{6}$ to remove TiO$_{2}$ from the Josephson junction areas. Finally, a 100 nm-thick MgB$_{2}$ serving as both the top electrode and wiring layer was deposited and patterned by photolithography and ion mill. The advantage over previously reported process is that this process combines the MgB$_{2}$ top electrode and the wiring layer, which simplifies fabrication and allows for an additional layer of MgB$_{2}$ to be dedicated to a ground plane in circuits. Characteristics of all-MgB$_{2}$ Josephson junctions fabricated by this process are shown.