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arXiv · 1203.6007

Shadow evaporation of epitaxial Al/Al2O3/Al tunnel junctions on sapphire utilizing an inorganic bilayer mask

Paul B. Welander·Vladimir Bolkhovsky·Terence J. Weir·Mark A. Gouker·William D. Oliver
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Abstract

This letter describes a new inorganic shadow mask that has been employed for the evaporation of all-epitaxial Al/Al2O3/Al superconducting tunnel junctions. Organic resists that are commonly used for shadow masks and other lift-off processes are not compatible with ultra-high vacuum deposition systems, and they can break down at even moderately elevated temperatures. The inorganic mask described herein does not suffer these same shortcomings. It was fabricated from a Ge/Nb bilayer, comprising suspended Nb bridges supported by an undercut Ge sacrificial layer. Utilizing such a bilayer mask on C-plane sapphire, the growth of epitaxial Al tunnel junctions was achieved using molecular beam epitaxy. Crystalline Al2O3 was grown diffusively at 300 C in a molecular oxygen background of 2.0 utorr, while amorphous oxide was grown at room temperature and 25 mtorr. A variety of analysis techniques were employed to evaluate the materials, and tunnel junction current-voltage characteristics were measured at millikelvin temperatures.

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Paul B. Welander, Vladimir Bolkhovsky, Terence J. Weir, Mark A. Gouker, William D. Oliver. 2012-03-27. Shadow evaporation of epitaxial Al/Al2O3/Al tunnel junctions on sapphire utilizing an inorganic bilayer mask. https://arxiv.org/abs/1203.6007

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