  Sandwich-type all-MgB2 Josephson tunnel junctions (MgB2/AlOx/MgB2) have been
fabricated for the first time with as-grown MgB2 films formed by molecular beam
epitaxy. The junctions exhibit substantial superconducting current (IcRN
product ~ 0.8 mV at 4.2K), a well-defined superconducting gap (delta = ~2.3
mV), and clear Fraunhofer patterns. The superconducting gap voltage of delta
agrees well with the smaller gap in the multi-gap scenario. The results
demonstrate that MgB2 has great promise for superconducting electronics that
can be operated at T ~ 20 K.
