Tunnel Magnetoresistance Sensors with Magnetostrictive Electrodes: Strain Sensors.

Ali Tavassolizadeh,Eckhard Quandt,Dirk Meyners,Günter Reiss,Tobias Meier,Hendrik Hölscher,Karsten Rott

doi:10.3390/s16111902

Abstract

Magnetostrictive tunnel magnetoresistance (TMR) sensors pose a bright perspective in micro- and nano-scale strain sensing technology. The behavior of TMR sensors under mechanical stress as well as their sensitivity to the applied stress depends on the magnetization configuration of magnetic tunnel junctions (MTJ)s with respect to the stress axis. Here, we propose a configuration resulting in an inverse effect on the tunnel resistance by tensile and compressive stresses. Numerical simulations, based on a modified Stoner–Wohlfarth (SW) model, are performed in order to understand the magnetization reversal of the sense layer and to find out the optimum bias magnetic field required for high strain sensitivity. At a bias field of −3.2 kA/m under a strain, gauge factors of 2294 and −311 are calculated under tensile and compressive stresses, respectively. Modeling results are investigated experimentally on a round junction with a diameter of m using a four-point bending apparatus. The measured field and strain loops exhibit nearly the same trends as the calculated ones. Also, the gauge factors are in the same range. The junction exhibits gauge factors of and −260 for tensile and compressive stresses, respectively, under a −3.2 kA/m bias magnetic field. The agreement of the experimental and modeling results approves the proposed configuration for high sensitivity and ability to detect both tensile and compressive stresses by a single TMR sensor.

Highlights

Research on strain sensing in nano- and microscale has evolved with a perspective on delivering miniaturized, integrated, and high-speed sensing devices
Magnetostrictive tunnel magnetoresistance (TMR) sensors with CoFeB/MgO/CoFeB structures [3,5,6] offer more scalability compared to magnetostrictive giant magnetoresistance sensors [7,8,9,10] and higher gauge factors compared to AlOx -based TMR sensors with amorphous CoFeB [11], crystalline Co50 Fe50 [12] and amorphous (Fe90 Co10 )78 Si12 B10 [13] electrodes
The CoFeB/MgO/CoFeB TMR sensors have been successfully incorporated into membranes for pressure sensing [5,14] and microcantilevers for atomic force microscopy (AFM) [6,15]

Summary

Introduction

Research on strain sensing in nano- and microscale has evolved with a perspective on delivering miniaturized, integrated, and high-speed sensing devices. They are essential for applications that demand high strain sensitivity in small strain scales including force sensors, pressure sensors, and microcantilever technology [1,2]. Profiting from high sensitivity [3], high band-width [4], and miniaturization possibilities, magnetostrictive magnetoresistance (MR) sensors are a promising alternative to piezoresistive and piezoelectric strain sensors. The CoFeB/MgO/CoFeB TMR sensors have been successfully incorporated into membranes for pressure sensing [5,14] and microcantilevers for atomic force microscopy (AFM) [6,15]. Magnetostrictive TMR sensors with CoFeB/MgO/CoFeB structures [3,5,6] offer more scalability compared to magnetostrictive giant magnetoresistance sensors [7,8,9,10] and higher gauge factors compared to AlOx -based TMR sensors with amorphous CoFeB [11], crystalline Co50 Fe50 [12] and amorphous (Fe90 Co10 ) Si12 B10 [13] electrodes.

Methods

Results

Conclusion