Electrical Properties of Cr - Al Alloy Thin Films

Abstract

Electrical properties of Cr-Al alloy thin films which were deposited on 96-percent alumina substrates by using resistance-heated evaporation have been investigated. The resistivity of the thin films took a maximum value (2.2 x 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-5</sup> <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\Omeg</tex> *m) at 25 at % Al. The temperature coefficient of resistance (TCR) of the thin films had negative values for Al contents between 6 and about 80 at %, with the maximum negative value occurring at 25 at % Al. The thickness dependences of resistivity and TCR were very small at film thicknesses of 260-2400 A. The thin film containing 25 at % Al had an excellent heat resistance; i.e., changes in TCR and resistivity caused by holding at 773 K for 28.8 ks in a nitrogen atmosphere were less than 20 percent and 100 ppm/K, respectively. X-ray diffraction analysis and observation with transmission electron microscope (TEM) showed that the thin film containing 25 at % Al consisted of microcrystals (about 1000 A in diameter) of bcc-Cr. The crystal structure remained unchanged after the heat treatment at 773 K for 3.6 ks in a nitrogen atmosphere. Cr-Al bulk alloy containing 30 at % Al quenched from 1223 K into iced water also had a negative TCR and high resistivity. From these results, it can he concluded that the electrical characteristics of the thin film is closely related to that of Cr-Al bulk alloy.