Highly sensitive strain sensors based on magnetic tunneling junctions

Abstract

Micrometer-sized highly sensitive strain sensors are presented. The sensors are based on magnetic tunneling junctions (MTJs) incorporating magnetostrictive free layers. The influence of mechanical strain upon the free layer is explained by a model taking into account the total free energy of the sensing layer. Those MTJ devices prepared in situ with magnetostrictive Fe50Co50 layers exhibit a tunneling magnetoresistance (TMR) ratio of 48%. The changes in strain Δε on the order of 0.4 parts per thousand (‰) result in resistance changes of 24%, which in turn leads to gauge factors [(ΔR/R)/Δε] on the order of 600, whereas gauge factors of 2–4 are typical for metal based, and 40–180 for piezoresistive semiconductor strain gauges.

High-performance giant magnetoresistive sensorics on flexible Si membranes

“…The maximum strain applied, estimated by considering purely geometrical factors, was 0.4%, which lies within the range that was estimated in other studies on thicker Si substrates. 26,37 By fitting the experimental data ( Fig. 3(b)) to Eq.…”

“…23 Wafer scale CMOS circuitry on ultra-thin 6 nm Si membranes obtained by controlled spalling technology has been shown to be fully functional at bending radii of 6.3 mm. 24 Bending tests of GMR sensorics prepared on 330-380 lm thick SiO x wafers 25,26 or 250 lm glass slides 27 were carried out to study effects of inverse magnetostriction on the magnetoelectric characteristics 27 and eventually to use those for highly sensitive strain gauges. 25,26 The used thick supports allow bending radii above 100 mm only.…”

“…24 Bending tests of GMR sensorics prepared on 330-380 lm thick SiO x wafers 25,26 or 250 lm glass slides 27 were carried out to study effects of inverse magnetostriction on the magnetoelectric characteristics 27 and eventually to use those for highly sensitive strain gauges. 25,26 The used thick supports allow bending radii above 100 mm only. Due to these large bending radii, it is not possible to assess the applicability of these GMR sensorics for flexible electronics on Si membranes.…”

Magnetostrictive LC Circuit Sensors

“…9) Another advantage of LC circuit strain gauges is that the measurement of frequencies instead of analogous signals is significantly less sensitive to disturbances.…”

“…The resistance in AMR-(anisotropic MR 4) ) but even more the GMR-(giant MR [5][6][7][8] ) or TMR-(tunnel MR 9) ) devices is dependent on the orientation of the magnetic domains. Replacing part of the magnetic material by a magnetostrictive one results in very sensitive strain gauges, especially in the case of TMR junctions.…”