Enhancement of spin valve GMR sensor’s sensitivity with [Ta/NiFe]n on-chip magnetic flux concentrator

Abstract

This study uses an integrated on-chip magnetic flux concentrator to explore the sensitivity enhancement of synthetic antiferromagnetic spin Valve (SV-SAF) sensors. Theoretical simulation on MFC indicates that a high magnetic gain factor up to 50 can be achieved with a lower air gap of $20\mu m$ and thicker, high permeability MFC material. In this report, a laminated film of [Ta/NiFe]${}_n$ of thickness $\sim$ $1\mu m$ was sputter deposited to achieve high permeability and low coercivity films. The magnetic gain factor was estimated by measuring the properties of the transfer curve of a single GMR-SV resistor embedded in the air gap. The results show that the magnetic gain of 25 and 46 were achieved by using 40 and $20\mu m$ air gap respectively. Further studies on Wheatstone bridge configuration reveal that the sensitivity of the spin valve can be improved to 10.7 mV/V/G in an operating field range of $\pm$ 0.5 G. These sensors have potential applications in low-field detection for healthcare applications.