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Industry has been seeking a thin-film capacitor that can work at high temperature in a harsh environment, where cooling systems are not desired. Up to now, the working temperature of the thin-film capacitor is still limited up to 200 °C. Herein, we design a multilayer structure with layers of paraferroelectric (Ba 0.3 Sr 0.7 TiO 3 , BST) and relaxor ferroelectric (0.85BaTiO 3 −0.15Bi(Mg 0.5 Zr 0.5 )O 3 , BT−BMZ) to realize optimum properties with a flat platform of dielectric constant and high breakdown strength for excellent energy storage performance at high temperature. Through optimizing the multilayer structure, a highly stable relaxor ferroelectric state is obtained for the BST/ BT−BMZ multilayer thin-film capacitor with a total thickness of 230 nm, a period number N = 8, and a layer thickness ratio of BST/ BT−BMZ = 3/7. The optimized multilayer film shows significantly improved energy storage density (up to 30.64 J/cm 3 ) and energy storage efficiency (over 70.93%) in an ultrawide temperature range from room temperature to 250 °C. Moreover, the multilayer system also exhibits excellent thermal stability in such an ultrawide temperature range with a change of 5.15 and 12.75% for the recoverable energy density and energy storage efficiency, respectively. Our results demonstrate that the designed thin-film capacitor is promising for the application in a harsh environment and open a way to tailor a thin-film capacitor toward higher working temperature with enhanced energy storage performance.

BCT/BZT multilayer with excellent energy storage performances with optimistic thermal stability has been fabricated using RF-sputtering system. Not only huge energy storage density of 51.8 J cm−3 with great efficiency of 81.2% at room temperature has been obtained, but also an optimistic thermal stability from RT to 200 °C has been investigated.