An electronic component is provided on a substrate. A thin-film capacitor is attached to the substrate, the thin-film capacitor includes a pyrochlore or perovskite dielectric layer between a plurality of electrode layers, the electrode layers being formed from a conductive thin-film material. A reactive barrier layer is deposited over the thin-film capacitor. The reactive barrier layer includes an oxide having an element with more than one valence state, wherein the element with more than one valence state has a molar ratio of the molar amount of the element that is in its highest valence state to its total molar amount in the barrier of 50% to 100%. Optionally layers of other materials may intervene between the capacitor and reactive barrier layer. The reactive barrier layer may be paraelectric and the electronic component may be a tunable capacitor.