Abstract
Superconducting resonators with high quality factors have been fabricated from aluminum films, suggesting potential applications in quantum computing. Improvement of thin film crystal quality and removal of void and pinhole defects will improve quality factor and functional yield. Epitaxial aluminum films with superb crystallinity, high surface smoothness, and interface sharpness were successfully grown on the c-plane of sapphire using sputter beam epitaxy. This study assesses the effects of varying substrate preparation conditions and growth and prebake temperatures on crystallinity and smoothness. X-ray diffraction and reflectivity measurements yield extensive Laue oscillations and Kiessig thickness fringes for films grown at 200 °C under 15 mTorr Ar, indicating excellent crystallinity and surface smoothness; moreover, an additional substrate preparation procedure which involves (1) a modified substrate cleaning procedure and (2) prebake at 700 °C in 20 mTorr O2 is shown by atomic force microscopy to yield nearly pinhole-free film growth while maintaining epitaxy and high crystal quality. The modified cleaning procedure is environmentally friendly and eliminates the acid etch steps common to conventional sapphire preparation, suggesting potential industrial application both on standard epitaxial and patterned surface sapphire substrates.
Highlights
Superconducting resonators with high quality factors have been fabricated from aluminum films, suggesting potential applications in quantum computing
Much work has been done on superconductivity of aluminum thin films on s apphire[6,7,8,9,10,11,12], and a number of successfully prepared superconducting Josephson tunnel junctions from aluminum are being used as the basis for quantum bit designs[13,14,15,16,17]
Films were fabricated using an ultra-high-vacuum (UHV), off-axis, combinatorial, DC magnetron sputter beam epitaxy system made by AJA International Inc., with beam-shaping shutter control and growth rate tuning via quartz crystal microbalance (QCM)
Summary
Superconducting resonators with high quality factors have been fabricated from aluminum films, suggesting potential applications in quantum computing. Epitaxial aluminum films with superb crystallinity, high surface smoothness, and interface sharpness were successfully grown on the c-plane of sapphire using sputter beam epitaxy. X-ray diffraction and reflectivity measurements yield extensive Laue oscillations and Kiessig thickness fringes for films grown at 200 °C under 15 mTorr Ar, indicating excellent crystallinity and surface smoothness; an additional substrate preparation procedure which involves (1) a modified substrate cleaning procedure and (2) prebake at 700 °C in 20 mTorr O2 is shown by atomic force microscopy to yield nearly pinhole-free film growth while maintaining epitaxy and high crystal quality. Patterning of superconducting resonators typically involves photolithography, ion milling, or chemical wet etch processes on an epitaxial thin film deposited onto a carefully chosen substrate. Surface aluminum oxide can either act as a natural anodization for the film or be exploited for its dielectric properties, as in the case of Al–Al2O3 nanodisks[31,32,33]
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