NbNスパッタ薄膜の膜構造と上部臨界磁界

抄録

Superconducting NbN films prepared onto quartz and sapphire substrates by rf sputtering have been investigated on the growth and preferred orientation of grains with B1 structure, and on their upper critical field, H_c2. Fine columnar grains of B1 phase with a preferred orientation in the ‹111› direction perpendicular to the substrate surface are simply formed on quartz. NbN films deposited on the (1102) plane of sapphire have a 1, 500Å thick inital growth layer on which coarse columnar grains grow rapidly with the same preferred orientation as on quartz. The columnar diameter of B1 grains is somewhat affected by substrate temperature, T_d, and increases with T_d up to 600°C. When the T_d exceeds 600°C, films contain B1 grains growing with a (200) preferred orientation. Higher values of H_c2 have been obtained for films deposited on quartz and, especially, the perpendicular critical field, H_c2⊥, appreciably increases with reducing the columnar grain diameter to -150Å. Depositions at higher gas pressures seem to produce a beneficial effect on the growth of small grains which yield an increase in H_c2.