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Linked magnetron sputtering and pulsed laser deposition UHV chambers for the preparation of epitaxial metal/metal oxide thin film multilayers

A UHV deposition system for the production of epitaxial oxide/metal heterostructures on single crystal ceramic substrates is described. The system has two novel features. The first is the use of linked, dedicated UHV sputtering and pulsed laser deposition chambers for the metal and oxide growth respectively, so as to maintain the cleanliness of the metal surface after deposition. The second is the use of a pulsed oxygen source during oxide growth to minimize damage of the metal layer by oxidation during the growth of the oxide layer. This second issue is illustrated by the growth of magnesium oxide/niobium bilayers on sapphire substrates. The magnesium oxide was grown under varying conditions of oxygen supply. A clean niobium film with no magnesium oxide overlayer showed a resistance ratio of 76. If the magnesium oxide was grown under UHV conditions (no extra oxygen supply) then the resistance ratio of the niobium film was reduced to 26. Growth of the magnesium oxide with synchronous 0.6 ms oxygen pulses (total ambient oxygen exposure 121 Pa s) resulted in a niobium resistance ratio of 18. A similar exposure to oxygen pulses alone (no magnesium oxide layer) reduced the niobium resistance ratio to 1.2. Alternatively the magnesium oxide layer could be grown in an argon ambient, with maintenance of the residual resistance ratio at 60 in 20 Pa of argon.