  The macroscopic coherence in superconductors supports dissipationless
supercurrents which could play a central role in emerging quantum technologies.
Accomplishing unequal supercurrents in the forward and backward directions
would enable unprecedented functionalities. This nonreciprocity of critical
supercurrents is called superconducting (SC) diode effect. We demonstrate
strong SC diode effect in conventional SC thin films, such as niobium and
vanadium, employing external magnetic fields as small as 1 Oe. Interfacing the
SC layer with a ferromagnetic semiconductor EuS, we further accomplish
non-volatile SC diode effect reaching a giant efficiency of 65%. By careful
control experiments and theoretical modeling, we demonstrate that the critical
supercurrent nonreciprocity in SC thin films could be easily accomplished with
asymmetrical vortex edge/surface barriers and the universal Meissner screening
current governing the critical currents. Our engineering of the SC diode effect
in simple systems opens door for novel technologies. Meanwhile, we reveal the
ubiquity of Meissner screening effect induced SC diode effect in
superconducting films, which should be eliminated with great care in the search
of exotic superconducting states harboring finite-momentum Cooper pairing.
