Effect of Substrate Cleanness on Permalloy Thin Films

Abstract

The use of mechanical and chemical cleaning techniques in the production of a clean, random, and smooth microslide glass substrate surface for the vacuum deposition of uniaxial thin Permalloy film elements has been studied. The principal cleaning techniques intensively investigated were: (1) a mild detergent wash followed by a vapor degreasing cycle in isopropyl alcohol; (2) a chalk paste scrub followed by an ultrasonically agitated distilled water rinsing cycle and a forced hot air drying process; and (3) hydrofluoric acid etching followed by a distilled water rinsing cycle and a forced air-drying process. The surface condition of the cleaned microslide glass was assessed with electron micrographs of preshadowed carbon replicas (magnification 88 000×). The micrographs show that the chalk-cleaned glass substrate has the smoothest surface. The variously cleaned substrates were then used for the vacuum deposition of 1700-A 4-mm-diam Permalloy film elements (melt composition 83% nickel, 17% iron). This work was carried out in a 10⁻⁶ mm Hg vacuum system. Twenty-five evaporations were made with a total of 54 elements per evaporation. The Permalloy film elements deposited on the differently cleaned glass substrates were then examined by means of a 1000-cycle hysteresis loop apparatus and the following measurements were made: (1) coercive force H _c ; (2) saturation flux φ _s ; (3) orientation of the anisotropy axis θ (4) magnetoelastic strain coefficient η and (5) anisotropy field H _K . Dispersion measurements of the easy axis were made on a 1000-cycle crossed field hysteresis loop apparatus. Measured in this manner, the chalk-cleaned glass substrates yielded consistently the lower average value of H _C ; i. e., 1.4 oe. The average value of H _K for the three different cleaning techniques was 2.5 oe. Within the total range of values of coercive force and the anisotropy field, the chalk-cleaned and the acid-etched glass substrates yielded the same values; i. e., H _C ±0.2 oe, H _K ±0.3 oe. Measurements of angular dispersion varied from 8° to less than 2° with an average value of less than 3°. The chalk-cleaned substrates yielded the lowest values of angular dispersion.

This work supported by the Department of Defense. (See ASTIA reports on Project Lightning. Second Phase, Fourth Quarterly Progress Report through Third Phase, Fourth Quarterly Progress Report.