  To form a conducting layer at the interface between the oxide insulators
LaAlO3 and SrTiO3, the LaAlO3 layer on the SrTiO3 substrate must be at least
four unit-cells-thick. The LaAlO3 SrTiO3 heterointerface thus formed exhibits
various intriguing phenomena such as ferromagnetism and superconductivity. It
has been widely studied for being a low-dimensional ferromagnetic oxide
superconducting system with a strong gate-tunable spin-orbit interaction.
However, its lack of stability and environmental susceptiveness have been an
obstacle to its further experimental investigations and applications. Here, we
demonstrate that capping the bilayer with SrTiO3 relieves this thickness limit,
while enhancing the stability and controllability of the interface. In
addition, the SrTiO3-capped LaAlO3 exhibits unconventional superconductivity;
the critical current dramatically increases under a parallel magnetic field,
and shows a reversed hysteresis contrary to the conventional hysteresis of
magnetoresistance. Its superconducting energy gap of $\Delta \sim 1.31k_BT_c$
also deviates from conventional BCS-type superconductivity. The oxide trilayer
could be a robust platform for studying the extraordinary interplay of
superconductivity and ferromagnetism at the interface electron system between
LaAlO3 and SrTiO3.
