Influence of annealing and thickness on the electrical properties of invar36 thin film for strain gauge applications

Abstract

Invar36 thin films with various thicknesses from 200 ˚ Ato 1400 ˚ Aare deposited on glass substrates by DC magnetron sputtering technique. After deposition, the samples are annealed in vacuum ambient (10 −5 mbar) upto 500 � C. Electrical properties of as-deposited as well as annealed films are analyzed with resp ect to thickness and annealing temperature. In situ measurement of sheet resistance of films with respect to annealing temperature is carried out by four probe technique. There is a decrease of sheet resistance and resistivity of all films with increasing temperature irr espective of film thickness.The resistivity of the as deposi ted films is around 230 μΩ -cm and decreases with increasing temperature and found as 84 μΩ -cm for 550 ˚ Afilm annealed at 500 � C. Temperature co-efficient of resistance (TCR) of films at different temper ature is measured and is found to be in the range of 10 −4 / � C.Gauge factors of as deposited and annealed at 300 � C and 500 � C films are measured by using four point bending technique and it is found that gauge factor decreases with respect to annealing temperature irr espective of film thickness. The best characteristics among different thickness and annealing temperature are obtained at 500 � C, for the films of thicknesses between 400 ˚ Ato 600 ˚ A.