A multilayer thin film epitaxial passivation of single crystal MgO substrates was developed. YBa2Cu3O7−x films on the buffered MgO substrates demonstrate pure c-axis orientation, absence of in-plane disoriented grains, transition temperature Tc>91 K, and critical current density Jc ∼ 5 MA/cm2 at 77.4 K and were deposited in thicknesses of up to several micrometers without cracks. High-temperature superconductor multilayer flux transformers of 2 μm thickness on the buffered MgO substrates demonstrated improved insulation between the superconducting layers and an increased dynamic range compared to flux transformers on SrTiO3 substrates.