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Proceedings Paper

Magnetic tunnel junction sensors with pTesla sensitivity for biomedical imaging
Author(s): S. Cardoso; L. Gameiro; D. C. Leitao; F. Cardoso; R. Ferreira; E. Paz; P. P. Freitas
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Paper Abstract

Ultrasensitive magnetic field sensors at low frequencies are necessary for several biomedical applications. Suitable devices can be achieved by using large area magnetic tunnel junction sensors combined with permanent magnets to stabilize the magnetic configuration of the free layer and improve linearity. However, further increase in sensitivity and consequently detectivity are achieved by incorporating also soft ferromagnetic flux guides. A detailed study of tunnel junction sensors with variable areas and aspect ratios is presented in this work. In addition, the effect in the sensors transfer curve, namely in their coercivity and sensitivity, as a consequence of the incorporation of permanent magnets and flux guides is also thoroughly discussed. Using sensors with a tunnel magnetoresistance of ~200 %, incorporating both permanent magnets and flux guides sensitivities of 220-260 %/mT were obtained for high aspect ratio sensors, increasing to values larger than ~2000%/mT for large areas and low aspect ratio sensors. Measured noise levels of the final device at 10 Hz yield 3.9×10-17 V2/Hz, leading to an improved lowest detectable field of ~ 94 pT/ Hz0.5.

Paper Details

Date Published: 17 May 2013
PDF: 8 pages
Proc. SPIE 8763, Smart Sensors, Actuators, and MEMS VI, 87631A (17 May 2013); doi: 10.1117/12.2018070
Show Author Affiliations
S. Cardoso, Inesc-MN (Portugal)
Instituto Superior Técnico (Portugal)
L. Gameiro, Inesc-MN (Portugal)
D. C. Leitao, Inesc-MN (Portugal)
F. Cardoso, Inesc-MN (Portugal)
R. Ferreira, International Iberian Nanotechnology Lab. (Portugal)
E. Paz, International Iberian Nanotechnology Lab. (Portugal)
P. P. Freitas, INESC-MN (Portugal)
Instituto Superior Técnico (Portugal)

Published in SPIE Proceedings Vol. 8763:
Smart Sensors, Actuators, and MEMS VI
Ulrich Schmid; José Luis Sánchez de Rojas Aldavero; Monika Leester-Schaedel, Editor(s)

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