Abstract
In high-temperature settings, amorphous alumina thin film insulators offer distinct advantages over crystalline materials, especially including a reduction in pinholes and leakage currents. Nonetheless, the phase stability of amorphous structures is a significant factor in determining their performance as insulators over a broad temperature range. With increasing temperatures, amorphous alumina undergoes a series of crystallization processes, resulting in irreversible alterations such as cracking and delamination due to volume changes between the different Al(2)O(3) polymorphs. In this study, amorphous alumina doped with yttrium and zirconium has been deposited via physical vapor deposition, demonstrating the stability of the amorphous structure up to 1200 °C in ambient air and vacuum. Above 1000 °C, the amorphous films transform into a two-phase system consisting of tetragonal yttria-stabilized zirconia (YSZ) embedded in an amorphous alumina matrix. Compared to undoped alumina, films alloyed with 4.3, 12.2, and 20.7 at. % ZrY exhibited enhanced thermal stability. Samples alloyed with 4-12 at. % ZrY additionally showed stable and reversible resistivity behavior under thermal cycling. Notably, films containing only 4.3 at. % ZrY achieved uncharted resistivity values of (3.33 ± 0.06) × 10(5) and (2.83 ± 0.07) × 10(5) Ω·m at 750 and 850 °C, respectively, representing a substantial enhancement relative to undoped alumina, which exhibited a value of (8.33 ± 0.04) × 10(4) Ω·m at 750 °C.