All MgB$_{2}$ tunnel junction with Al$_{2}$O$_{3}$ tunnel barrier

MgB$_{2}$ tunnel junctions are attractive not only from superconducting electronics application part of view but also from the fundamental physics to understand multi-gap superconductors. All MgB$_{2}$ planar junctions with Al$_{2}$O$_{3}$ tunnel barrier were fabricated in situ in an MBE system by coevaporation of Mg and B for MgB$_{2}$ and plasma oxidized Al for tunnel barrier on Si (111) substrate. The junctions exhibit the current-voltage characteristic for quasiparticle and Josephson tunneling including microwave induced Shapiro steps. From conductance spectrum at 1 K, we clearly observe features that correspond to different $\pi $ and $\sigma $ superconducting energy gaps for the two MgB$_{2}$ electrodes. The observed multi-gap structure will be discussed with the difference of crystallographic orientation of MgB$_{2}$ at the interface between tunnel barrier and both superconducting layers.