ＮｂＮスパッタ薄膜の膜構造と上部臨界磁界

Abstract

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, Hc2. 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, 500A 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, Td, and increases with Td up to 600°C. When the Td exceeds 600°C, films contain B1 grains growing with a (200) preferred orientation. Higher values of Hc2 have been obtained for films deposited on quartz and, especially, the perpendicular critical field, Hc2⊥, appreciably increases with reducing the columnar grain diameter to -150A. Depositions at higher gas pressures seem to produce a beneficial effect on the growth of small grains which yield an increase in Hc2.