All-MgB$_{2}$ sandwich-type Josephson junctions with MgO barrier*

Reproducible all-MgB$_{2}$ Josephson junctions have been made to meet the expectation for superconducting electronics that can work at above 20 K. The sandwich-type junctions were fabricated using MgB$_{2}$ electrodes grown by hybrid physical-chemical vapor deposition and MgO barrier deposited by RF magnetron sputtering. The $I-V$ characteristics show tunneling behavior with a small resistive shunt. The $I_{c}R_{n}$-product is 2.1 and 0.7 mV at 4.2 and 20 K, respectively, with temperature dependence following the theory qualitatively. The junctions exhibit good Fraunhofer pattern and Shapiro steps under applied magnetic field and microwave radiation, respectively. The $J_{c}$ of the junction varies exponentially with the barrier thickness, from 100 to 2$\times $10$^{5}$ A/cm$^{2}$. Transmission electron microscopy reveals both MgB$_{2}$ layers are epitaxially grown with $c$-axis parallel to the SiC (0001) substrate normal. With the same chip $J_{c}$ spead less than 10{\%}, this junction technology has the potential for MgB$_{2}$ circuits.