Fabrication of Ta/Ta-oxide/Ta trilayer Josephson junctions

We have been fabricating and studying Ta/Ta-oxide/Ta trilayer superconducting tunnel junctions. The Ta electrodes were deposited on R-plane ( 1 1 ¯ 0 2 ) sapphire substrates at a range of temperatures from room temperature to 720 °C. At deposition temperatures above 400 °C, a body centre cubic structure was obtained. The bottom layer of Ta was epitaxial while the top layer was polycrystalline. In addition, the Ta top layer was found to have a mixture of both body centre cubic ( α ) and tetragonal ( β ) structures. The Ta-oxide layer was formed by thermally oxidizing the base electrode in situ. Different deposition and oxidation parameters were studied to improve the quality of the Ta electrodes and Ta-oxide.