STRAIN SENSITIVITY AND TEMPERATURE INFLUENCE OF NICHROME (80/20 wt.%) THIN FILM FABRICATED BY MAGNETRON SPUTTERING

Abstract

The electromechanical properties of nichrome ( Ni – Cr 80/20 wt.%) used as a common material for application in thin film strain gauges have been studied. The surface topography and chemical composition of Ni – Cr thin films grown on the glass substrate by magnetron sputtering have been analyzed by atomic force microscope (AFM) and energy dispersive spectroscopy (EDS), respectively. The temperature coefficient of resistance (TCR) has been determined by a Nano-volt/Micro ohm meter. The gauge factor (FG) has been determined by the cantilever method. Low stable TCR values (22 ppm to 46 ppm in the 50–150°C temperature range) have been obtained. Resistance stability is achieved by rapid thermal annealing (RTA) at 300°C for 10 min combined with a 24 h thermal annealing (TA) at 150°C. The desired 45 Ω/m sheet resistance and a gauge factor of 2.6 have been attained for 40-nm-thickness films. The films have very small roughness of 2.1~4.4 nm.